WO2019244955A1

WO2019244955A1 - Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, method for producing non-aqueous electrolyte secondary battery, and method for use of non-aqueous electrolyte secondary battery

Info

Publication number: WO2019244955A1
Application number: PCT/JP2019/024375
Authority: WO
Inventors: 弘将村松; 眞也大谷; 諒原田; 顕岸本
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2018-06-21
Filing date: 2019-06-19
Publication date: 2019-12-26

Abstract

This non-aqueous electrolyte secondary battery is provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a lithium transition metal composite oxide which has an α-NaFeO2-type crystal structure and is represented by general formula, Li1+αMe1-αO2 (0<α, Me is a transition metal element containing Ni and Mn, or containing Ni, Mn, and Co), and in an X-ray diffraction diagram measured using a CuKα ray, a diffraction peak is observed in the range of 20-22°.

Description

Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, method for producing non-aqueous electrolyte secondary battery , And usage of non-aqueous electrolyte secondary battery

The present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the positive electrode active material, a positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, a method for producing a non-aqueous electrolyte secondary battery, and Regarding how to use it.

Non-aqueous electrolyte secondary batteries represented by lithium secondary batteries have been increasingly used in recent years, and there has been a demand for the development of cathode materials having higher capacities.
Conventionally, as a positive electrode active material for a nonaqueous electrolyte secondary battery, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure has been studied, and a nonaqueous electrolyte secondary battery using LiCoO ₂ has been widely put into practical use. I have. The discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g. As the transition metal (Me) constituting the lithium transition metal composite oxide, Mn, which is abundant as an earth resource, is used, and the molar ratio Li / Me of Li to the transition metal constituting the lithium transition metal composite oxide is approximately 1. In addition, a non-aqueous electrolyte secondary battery using a so-called “LiMeO ₂ type” active material in which the molar ratio Mn / Me of Mn in the transition metal is 0.5 or less has also been put to practical use. For example, the discharge capacity of LiNi _1/2 Mn _1/2 O ₂ or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 150 to 180 mAh / g.

On the other hand, in recent years, among lithium transition metal composite oxides having an α-NaFeO ₂ type crystal structure, the molar ratio Mn / Me of Mn in the transition metal (Me) has been increased, and the molar ratio Li of the transition metal (Me) to Li has been increased. So-called “lithium-rich” active materials having a / Me exceeding 1 are known. The active material, when Li / Me is constant over the size, in the charging process is performed first assembled battery, 4.5V (vs.Li/Li ⁺⁾ or 5.0V (vs.Li/Li ⁺ In the following potential range, there is a characteristic that a region where the change in potential relative to the amount of charged electricity is relatively flat is observed, and charging is performed until the charging process in which the flat region is observed is completed. However, even if the subsequent charging potential is not so noble, it is noted that it has a higher discharge capacity than the “LiMeO ₂ type” active material (see Patent Document 1).

Patent Document 1 discloses an active material for a lithium secondary battery including a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein Li, Co, Ni, and Mn contained in the solid solution are contained. When the composition ratio is Li _{1+ (1/3) x} Co _1-xy Ni _{(1/2) y} Mn _{(2/3) x + (1/2) y} (x + y ≦ 1, 0 ≦ y, 1−x −y = z), expressed by..., And the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane in the X-ray diffraction measurement is I ₍₀₀₃₎ / I ₍₁₀₄ ₎ ₎ > 1, and the potential change appearing with respect to the amount of charge in the positive electrode potential range of more than 4.3 V (vs. Li ^/ Li ⁺ ) to 4.8 V or less (vs. Li ^/ Li ⁺ ) is relatively flat. 4.3 V (vs. L (i / Li ⁺ ) An active material for a lithium secondary battery characterized in that the amount of electricity that can be discharged in a potential region of not more than 177 mAh / g. ”(Claim 3) A battery is described.

The paragraph [0058] states that “The active material for a lithium secondary battery according to the present invention is an active material existing in a region of x> １／, and 2θ = 2θ in an X-ray diffraction diagram using CuKα radiation. A diffraction peak observed in the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type was observed around 20 ° to 30 °, which indicates that Li ⁺ and Mn ⁴⁺ are in an ordered arrangement. It is presumed to be a superlattice line observed in the case of performing. ”In addition, paragraph [0062] describes that“ using the active material for a lithium secondary battery according to the present invention, In order to manufacture a lithium secondary battery capable of taking out a sufficient discharge capacity even if a charging method in which the maximum ultimate potential of the positive electrode is 4.3 V (vs. Li ^/ Li ⁺ ) or less is adopted, The following describes an active material for a lithium secondary battery according to the present invention. It is important to provide a charging step in consideration of the characteristic behavior in the manufacturing process of the lithium secondary battery, that is, to continue the constant current charging using the active material for a lithium secondary battery according to the present invention as a positive electrode. And a region where the potential change is relatively flat is observed over a relatively long period in the range of the positive electrode potential of 4.3 V to 4.8 V. The charging condition adopted here is that the current is 0.1 ItA. , The voltage (positive electrode potential) is 4.5 V (vs. Li ^/ Li ⁺ ) constant-current constant-voltage charging. Even if the charging voltage is set higher, the potential flat region over this relatively long period is x Is hardly observed when a material having a value of 1/3 or less is used, while a region where the potential change is relatively flat is observed with a material having a value of x exceeding 2/3. Also, the conventional Li [Co _1-2x Ni _x This behavior is not observed even with a material of the type Mn _x ] O ₂ (0 ≦ x ≦ 1/2). This behavior is characteristic of the active material for a lithium secondary battery according to the present invention. ” ing.

As an example of the lithium secondary battery, “lithium metal” is used for a negative electrode combined with the positive electrode, and “LiPF ₆ ” is used as an electrolyte in a mixed solvent in which EC / EMC / DMC has a volume ratio of 6: 7: 7. Was subjected to 5 cycles of initial charge and discharge processes at 20 ° C. All voltage control was performed with respect to the positive electrode potential. The charging was performed at a constant current and a constant voltage of 1 ItA and a voltage of 4.5 V. The condition for terminating the charging was a point in time when the current value attenuated to 1/6, and the discharging was a constant current discharging at a current of 0.1 ItA and a termination voltage of 2.0 V. A pause time of 30 minutes was set after charging and discharging in all cycles. "(Paragraphs [0112] to [0114]).

Patent Literature 2 discloses a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte including a non-aqueous solvent. but the general formula _{_{(1) Li 1 + x Mn}} y M z O 2 ( wherein, x, y and z are 0 <x <0.4,0 <y <1,0 <z <1 and x + y + z = 1 Wherein M is at least one metal element and includes at least Ni or Co), wherein the non-aqueous solvent has two or more fluorine atoms directly bonded to a carbonate ring. A nonaqueous electrolyte secondary battery comprising a fluorinated cyclic carbonate. "(Claim 1).

As Example 1 of the secondary battery, the positive electrode active material is “Li _1.2 Mn _0.54 Ni _0.13 Co _0.13 O ₂ ”, the negative electrode contains silicon and carbon, and the nonaqueous electrolyte Is that “LiPF ₆ was dissolved in a non-aqueous solvent in which 4,5-difluoroethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 2: 8 so as to be 1 mol / L”, and the initial charge was performed. The battery was charged with a constant current of 0.5 It until the battery voltage became 4.45 V, and further charged at a constant voltage of 4.45 V until the current value became 0.05 It. The potential of the positive electrode was 4.60 V based on metallic lithium. Thereafter, the battery was discharged at a constant current of 0.5 It until the battery voltage reached 1.50 V "(paragraph [0041]). [0049 ).

Further, a non-aqueous electrolyte secondary battery in which a lithium-rich active material is used for a positive electrode and a compound having an oxalate group bonded to boron is added to a non-aqueous electrolyte is also known.
Patent Literature 3 discloses a lithium ion secondary battery having a positive electrode containing a positive electrode active material that operates at a potential of 4.4 V (vs Li / Li ⁺ ) or more, a negative electrode, and an electrolytic solution containing a nonaqueous solvent. In a battery, the electrolytic solution contains a first lithium salt having a boron atom represented by the following formula (1) and / or formula (2) in an amount of 0.01% by mass or more and 10% by mass or less, And a lithium ion secondary battery containing the second lithium salt having no boron atom in an amount of 1% by mass to 40% by mass .... (claim 1), "The first lithium salt is The lithium ion secondary according to any one of claims 1 to 3, wherein the lithium ion secondary is at least one selected from the group consisting of LiBF ₄ , LiBF ₄ , LiB (C ₂ O ₄ ) ₂ , and LiBF ₂ (C ₂ O ₄ ). Battery "(Claim 4).

In paragraphs [0076] to [0083], as Example 1, the positive electrode active material was “0.5Li ₂ MnO ₃ -0.5LiNi _0.37 Mn _0.37 Co _0.26 O ₂ ”, and the negative electrode active material was graphite. There, the electrolyte "volume of ethylene carbonate and ethyl methyl carbonate ratio of 1: mixed in a mixed solvent of LiPF ₆ salt was contained 1 mol / L solution (...) in 9.8g 2, ... A lithium ion secondary battery that is an “electrolyte solution A” in which 0.2 g of lithium bisoxaborate (hereinafter referred to as “LiBOB”) is described, and paragraphs [0085] to [0087] the, as example 3, create a LiBOB the LiBF _₂ _(C ₂ _O ₂₎ similar lithium ion secondary battery as in example 1 except for using an electrolytic solution C was changed to the electrolytic solution a of example 1 After charging each battery reaching 4.7 V and discharging it to 2.0 V, charging the battery reaching 4.5 V and discharging it to 2.0 V in one cycle was performed. It describes that a battery was evaluated by performing a 50-cycle charge / discharge test as discharge.

Patent Literature 4 discloses a lithium ion battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, in which a positive electrode active material contained in the positive electrode is initially charged and discharged when metal Li is used as a counter electrode. The discharge efficiency is 80% to 90%. The negative electrode active material contained in the negative electrode is composed of a mixed material of a silicon compound and a carbon material, and the negative electrode is doped with lithium for an irreversible capacity in initial charge and discharge. A lithium ion battery, wherein the capacity ratio of the negative electrode to the positive electrode is 0.95 or more and 1 or less in an initial charging electric capacity of the positive electrode and the negative electrode. " “The lithium ion battery according to claim 1, wherein the positive electrode active material is represented by the following chemical formula 1.
[Chemical formula 1] aLi [Li _1/3 Mn _2/3 ] O ₂・ (1-a) Li [Ni _x Co _y Mn _z ] O ₂ (0 ≦ a ≦ 0.3, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) ”(claim 6),“ the non-aqueous electrolytic solution includes a solvent and a supporting salt, and the solvent is at least γ-butyrolactone. The lithium ion battery according to claim 1, wherein the lithium ion battery contains (GBL), and the supporting salt contains at least lithium bis (oxalate) borate (LiBOB). "(Claim 8) Is described.

In paragraphs [0047] to [0054], as Example 1, the positive electrode active material was “(0.2Li ₂ MnO ₃ -0.8LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ”. The negative electrode active material is a composite of “Si, SiO and HC”, and the non-aqueous electrolyte is “1M LiPF ₆ + 0.05M LiBOB EC (ethylene carbonate): GBL (γ-butyrolactone) = 1: 1: 1 (vol%) )), The cut-off voltage of the first charge / discharge is 2.2-4.6 V, the cut-off voltage of the charge / discharge after the second cycle is 2.2-4.3 V, 60 A charge / discharge test was carried out at ℃. "

Patent Literature 5 discloses “In a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a non-aqueous electrolyte having lithium ion conductivity, the positive electrode active material has a layered shape. has the structure represented by the general formula _{_{_{Li 1 + x (Ni a Mn}}} b Co c) O 2 + α (x + a + b + c = 1,0.7 ≦ a + b, 0 <x ≦ 0.1,0 ≦ c / (a + b) <0.35, 0.7.ltoreq.a / b.ltoreq.2.0, -0.1.ltoreq..alpha..ltoreq.0.1), wherein the nonaqueous electrolyte contains an oxalate complex as an anion. Non-aqueous electrolyte secondary battery characterized by containing a salt. "

In paragraphs [0039] to [0058] and in Table 1, as Examples 1 to 8, the positive electrode active materials were Li _1.06 Ni _0.47 Mn _0.47 O ₂ and Li _1.07 Ni _{0. 0.56} Mn _0.37 O ₂ or Li _1.07 Ni _0.42 Co _0.09 Mn _0.42 O ₂ , the negative electrode active material is graphite whose surface is coated with amorphous carbon, The solution was prepared by dissolving LiPF ₆ as a solute to a concentration of 1 M in a solvent in which EC, MEC, and DMC were mixed, adding 1% by weight of VC to the solution, and further adding lithium-bisoxalate borate ( A non-aqueous electrolyte secondary battery, which is an electrolytic solution in which LiBOB) was dissolved to 0.1 M, was prepared. “After the prepared non-aqueous electrolyte secondary battery was charged at a constant current of 1000 mA to 4.2 V, Constant voltage up to 50mA at 2V The battery was charged and discharged to 2.4 V at 330 mA, and the capacity at this time was referred to as a battery discharge capacity ”(paragraph [0045]). Thereafter, it was described that the IV characteristics were measured in a state of charge of SOC 50%. I have.

In Patent Document 6, as Example 22, the positive electrode active material is composed of “80% by mass of lithium manganate (Li _1.1 Mn _1.9 Al _0.1 O ₄ , LMO) and Li _1.15 Ni _0.45 Mn _0.45 Co _0.10 O ₂ (Co-less LNMC) 20% by mass ”(paragraph [0401]), the negative electrode active material was“ artificial graphite powder ”(paragraph [0343]), and the nonaqueous electrolyte Described that “Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed (30:30:40 by volume), then 0.1 mol / L of fully dried LiFSO ₃ and lithium were added. bisoxalato borate _{_{_{(LiB (C 2 O 4)}}} 2, LiBOB) and 0.1 mol / L, and dissolving LiPF ₆ as a percentage of 1 mol / L "(paragraph [ 408]) and those were describes a lithium secondary battery.

The evaluation of the initial discharge capacity of the lithium secondary battery according to Example 22 was as follows: "In a state in which the lithium secondary battery was sandwiched between glass plates in order to increase the adhesion between the electrodes, at 25 ° C., 0.1 C And then discharged to 3.0 V at a constant current of 0.1 C. In the second and third cycles, the battery was charged to 4.2 V at 0.33 C and then charged to 4.2 V. The battery was charged until the current value became 0.05 C at a constant voltage of 0.35 C, discharged to 3.0 V at a constant current of 0.33 C, and the initial discharge capacity was obtained from the discharge process in the third cycle. 0404]), and the high-temperature storage characteristics of the battery were evaluated by measuring the remaining capacity after storage at 75 ° C., the recovery capacity after storage at 75 ° C., and the storage capacity retention rate under constant current charging up to 4.2 V and 4 times. .2V constant voltage charging It has been mounting.

On the other hand, when a battery using a “lithium-excess type” active material as described in Patent Documents 1 to 4 is used through an initial charging process of 4.5 V (vs. Li ^/ Li ⁺ ) or more, “ It is known that the initial coulomb efficiency is low and the high rate discharge performance is inferior to a battery using the “LiMeO ₂ type” active material.
Therefore, acid treatment of a positive electrode active material is known as a technique for improving the initial coulomb efficiency and high-rate discharge performance of a battery using a “lithium-excess type” active material. (Patent Documents 7 to 10)

Patent Document 7, "the general _{_{_{formula: Li 1 + u Ni x Co}}} y Mn z A t O 2 + α (0.1 ≦ u <0.3,0.03 ≦ x ≦ 0.25,0.03 ≦ y ≦ 0 .25, 0.4 ≦ z <0.6, x + y + z + u + t = 1, 0 ≦ α <0.3, 0 ≦ t <0.1, A is a metal having any valence from divalent to hexavalent A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium-excess metal composite oxide composed of secondary particles in which primary particles are aggregated. A mixing step of obtaining a lithium mixture by mixing a lithium compound with secondary particles in which primary particles made of at least one of hydroxides, oxyhydroxides, oxides, and carbonates containing cobalt and manganese are aggregated, The lithium mixture is placed in an oxidizing atmosphere at 800 A baking step of baking at a temperature of about 1050 ° C. to obtain a baking product; and a lithium removal rate of 10 to which a difference in lithium content of the baking product before and after pickling is divided by a lithium content of the baking product before pickling. An acid pickling step in which the pickled slurry is subjected to pickling by controlling the pH of the pickled slurry at 30 ° C. at the end of the pickling at 25 ° C. to 1 to 4 to 1 to 4 and then washed with water; A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a heat treatment step of heat-treating the fired product after the step at a temperature of 200 to 600 ° C. in an oxidizing atmosphere. ” ) Is described.
Then, "The acid used for this pickling is preferably an acid showing a strong acidity with a high dissociation constant, more preferably one of inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid, and one of hydrochloric acid and sulfuric acid. (Paragraph [0073]), "If a strong acid is not used, it is difficult to extract lithium from the crystal structure, and it is not possible to cause dissolution to form fine irregularities on the surface of primary particles. In some cases, the interfacial resistance cannot be reduced. ”(Paragraph [0074]), and the evaluation of the positive electrode active material was performed by preparing a coin-type battery using Li metal for the negative electrode and performing initial charge / discharge. Performed at 0.05 C, 4.8 V charge and 2.5 V discharge, the ratio of discharge capacity to charge capacity was defined as initial charge / discharge efficiency, and charge / discharge at 0.1 C in a voltage range of 2.0 to 4.55 V. Using the discharge capacity at the time of denominator as the denominator, the load efficiency is described as the ratio (%) when the discharge capacity at the time of charge / discharge at 0.1 C of charge and 2 C of discharge is taken as the numerator (paragraph [ 0096] to [0101], [0103]).

Patent Document 8 discloses “a positive electrode active material for a lithium secondary battery including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the lithium transition metal composite oxide contains the transition metal (Me). A diffraction peak of 2θ = 44 ± 1 ° in an X-ray diffraction pattern using a CuKα radiation source, containing Co, Ni and Mn, wherein the molar ratio Mn / Me of Mn in the transition metal is Mn / Me ≧ 0.5. A positive electrode active material for a lithium secondary battery, characterized by having a half width of at least 0.265 ° and containing a P element. ”(Claim 1) The positive electrode active material for a lithium secondary battery according to claim 1, wherein P is contained by heat treatment after the acid treatment. ”(Claim 3).
Then, a lithium secondary battery using the active material according to each example, which was heat-treated after the above-described phosphoric acid treatment, was prepared, and was charged at a constant current and a constant voltage of 0.1 C and a voltage of 4.6 V, and a current of 0.05 C. After performing two cycles of constant current discharge at a final voltage of 2.0 V, a constant current constant voltage charge of a current of 0.2 C and a voltage of 4.3 V and a constant current discharge of a current of 0.5 C and a final voltage of 2.0 V are performed. It describes that the discharge test was performed for 30 cycles, and the discharge capacity at the 30th cycle was recorded as a 0.5C discharge capacity at the 30th cycle (paragraphs [0075] to [0085] and [0123] to [0130]).

Patent Document 9 discloses “a positive electrode active material for a lithium secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ structure, and a transition metal (Me ) Contains Co, Ni and Mn, the molar ratio Li / Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6, and the BJH method Has a pore volume of 0.055 cc / g or more and 0.08 cc / g or less in a pore region in which the pore diameter showing the maximum value of the differential pore volume obtained in the above is up to 60 nm, and has a space at 1000 ° C. (Claim 1), "Precursor preparation for preparing precursor containing Co, Ni and Mn as transition metal elements, showing a single phase belonging to group R3-m" Process, the precursor and L The lithium transition metal composite oxide is produced through a firing step of mixing a salt and heat-treating the mixture at a temperature of 800 ° C. or higher to produce an oxide, and an acid treatment step of treating the oxide with an acid. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6. (claim 9), and the method according to any one of claims 9 to 12, wherein the acid treatment step uses sulfuric acid. Method for producing positive electrode active material for lithium secondary battery "(Claim 13).
Further, as the above-described example, a lithium secondary battery using a lithium transition metal composite oxide, sulfuric acid treatment, and drying was used as a positive electrode, and a lithium secondary battery using metal lithium as a negative electrode. As a process, constant-current constant-voltage charging at a current of 0.1 C and a voltage of 4.6 V, and constant-current discharging at a current of 0.1 C and a final voltage of 2.0 V are performed in two cycles. It is described that constant-current constant-voltage charging of 3 V and constant-current discharging at a current of 1 C and a final voltage of 2.0 V were performed, and the amount of discharged electricity was recorded as a 1 C capacity (paragraphs [0076] to [0087]; [0108] to [0115]).

Patent Document 10 discloses “a positive electrode active material including a lithium transition metal composite oxide having an α-NaFeO ₂ structure, wherein the lithium transition metal composite oxide has a transition metal (Me) containing Co, Ni, and Mn. When the molar ratio of Li and transition metal (Me) (Li / Me) is 1 <Li / Me, and the molar ratio of Mn and transition metal (Me) (Mn / Me) is 0.5 <Mn / Me. And a positive electrode active material for a lithium secondary battery characterized by containing Ce. ”(Claim 1). Examples 1 to 5 describe“ a lithium transition metal composite oxide Li _{1. 18} Co _0.10 Ni _0.17 Mn _0.55 O ₂ ”was charged into a cerium sulfate solution having a pH of 1.6 and heat-treated at 400 ° C. to produce a lithium-transition metal composite oxide containing Ce. Is described ( Paragraphs [0079] to [0082]). Then, a battery was prepared in which the lithium transition metal composite oxide was used as a positive electrode active material and the negative electrode was metallic lithium, subjected to an initial charge / discharge step of 0.1 C, 4.6 V-2.0 V, and charged to a discharge capacity. Using the value (%) divided by the quantity of electricity as the initial efficiency, 30 cycles of constant current constant voltage charging at 0.2 C and 4.45 V and constant current discharging at 0.5 C and 2.0 V are performed, and the first cycle discharge is performed. Table 1 shows the results of evaluating the battery with the ratio (%) of the discharge capacity at the 30th cycle to the capacity as the discharge capacity retention ratio (paragraphs [0090] to [0097]).

Patent Document 11 discloses that “including a step of acid-treating a perlithiated metal oxide and a step of doping the acid-treated perlithiated metal oxide with a metal cation. The perlithiated metal oxide is a method for producing a composite positive electrode active material containing a compound represented by the following chemical formula 4: [Formula 4] xLi ₂ MO _3- (1-x) LiM′O ₂ , M is at least one metal selected from 4-period and 5-period transition metals having an average oxidation number +4, and M ′ is selected from 4-period and 5-period transition metals having an average oxidation number +3. At least one metal, and 0 <x <1 ”(claim 13).
As an example, an acid treatment of adding a substance having a composition of 0.55Li ₂ MnO ₃ -0.45LiNi _0.5 Co _0.2 Mn _0.3 O ₂ to an aqueous HNO ₃ solution and drying the resultant at 80 ° C. Then, the acid-treated substance was put into 500 mL of an aqueous solution of nitrate such as Al and heat-treated at 300 ° C. for 5 hours to obtain an active material doped with a metal cation (paragraphs [0137] to [0147]. ), In the case of the LiNi _0.5 Co _0.2 Mn _0.3 O ₂ active material, there is no change in the charge / discharge curve under the acid treatment conditions, and no Li ion is desorbed by the reaction with the acid solution. Li ₂ MnO ₃ is the discharge curve by substitution of ^{H +} and Li ⁺ ions in acid solution to the acid treatment has changed significantly (paragraph [0159]), a negative electrode as lithium metal, 0.1 the initial charge and discharge The initial efficiency was evaluated by charging and discharging at a constant current of 4.7-2.5 V, and the charging and discharging currents at 0.5 C, 4.6 V constant voltage and constant current were 0.2, 0.33, 1, 2, And that the rate characteristics were evaluated by performing constant current discharge at 3 C and 2.5 V (paragraphs [0165] to [0166]).

Further, by replacing the oxygen site of the “lithium-excess type” active material with F, the initial coulomb efficiency, the rate characteristic, and the cycle life characteristic in the case where the initial charging process exceeding 4.5 V (vs. Li ^/ Li ⁺ ) is performed. And the like (see Patent Documents 12 to 15).

Patent Document 12, a "general formula _{_{_{_{Li (Li a Mn b Ni c}}}} Co d Fe e) O 2-x F x positive electrode active material for non-aqueous electrolyte secondary batteries represented by, in the general formula A, b, c, d, e and x are 0 <a ≦ 0.33, 0 <b ≦ 0.67, 0 ≦ c <1, 0 ≦ d <1, 0 ≦ e <1, 0. A positive electrode active material for a non-aqueous electrolyte secondary battery that satisfies the following formula (1), wherein 1 <x ≦ 1-b.

(Claim 1).
Examples of the active material containing Mn and Ni include “Li _1.2 Ni _0.2 Mn _0.6 O _1.9 F _0.1 ” and “Li _1.2 Ni _0.2 Mn _0.6”. O _1.8 F _0.2 "," _{_{_{_{Li 1.2 Ni 0.2 Mn 0.6 O 1.7}}}} F 0.3 "," _Li 1.2 _Ni 0.2 _Mn 0.6 _{O 1.6} F _0.4 "," _{_{_{_{Li 1.2 Ni 0.4 Mn 0.4 O 1.8}}}} F 0.2 ", as a comparative example," _Li 1.2 _Ni 0.2 _Mn 0.6 _{O 2} ", “Li _1.2 Ni _0.2 Mn _0.6 O _1.95 F _0.05 ” and “Li _1.2 Ni _0.25 Mn _0.55 O _1.9 F _0.1 ” are described, and 4 It was stated that the initial coulomb efficiency was obtained from the initial charge capacity by charging up to .6 V and the initial discharge capacity by discharging up to 2.0 V from the charged state. And are ([0078] from paragraph [0072]).

Patent Document 13 discloses “a lithium-rich lithium metal composite compound containing a layered structure of Li ₂ MnO ₃ , which is doped with a fluoro compound and has a FWHM (half width at half maximum) value in the range of 0.164 ° to 0.185 °. (Claim 1).
As an example, 0.88 moles of a transition metal hydroxide precursor having a molar ratio of Ni: Co: Mn of 2: 2: 6, and 1.18 moles of Li ₂ CO ₃ and LiF in total (LiF is (0.02 to 0.06 mol) of the mixture was fired to obtain a positive electrode active material. The battery characteristics were evaluated by charging and discharging from 2.5 V to 4.6 V to improve the high rate characteristics and the life characteristics. It is described that the evaluation was made (paragraphs [0054] to [0064] and [0073]).

Patent Document 14 discloses that “Li element and at least one transition metal element selected from Ni, Co, and Mn are included (provided that the molar amount of Li element is 1 to the total molar amount of the transition metal element). .2 times more.) A method for producing a positive electrode active material for a lithium ion secondary battery, which comprises contacting a lithium-containing composite oxide with a fluorine gas. "
Then, as an example, a positive electrode active material was obtained by subjecting a lithium-containing composite oxide having a composition “Li (Li _0.2 Ni _0.137 Co _0.125 Mn _0.538 ) O ₂ ” to fluorination treatment (paragraph). [0082] to [0092]), the battery evaluation was that the initial capacity was evaluated by charging and discharging from 4.8 V to 2.5 V, and the cycle characteristics were evaluated by charging and discharging cycles from 4.5 to 2.5 V. (Paragraphs [0101] and [0102]).

Patent Document 15 discloses an electroactive composition containing a crystalline material approximately represented by a composition formula Li _{1 + x} Ni _α Mn _β Co _γ A _δ O _2-z F _z , wherein x is about 0.02 to about 0.19, α is about 0.1 to about 0.4, β is about 0.35 to about 0.869, and γ is about 0.01 to about 0.2. Δ is 0.0 to about 0.1, z is about 0.01 to about 0.2, and A is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce. , Y, Nb, or a combination thereof. "(Claim 1).
Then, as Example 1, a metal carbonate powder containing Ni, Co, and Mn, an appropriate amount of Li ₂ CO ₃ and LiF powder were mixed and fired in two steps to obtain a composition Li _1.2 Ni _0. to obtain a lithium composite oxide of _{_{_{_{175 Co 0.10 Mn 0.525 O 2-}}}} F F F (F = 0.05,0.01,0.02,0.05,0.1 or 0.2) That (paragraphs [0064] to [0069]), as Example 2, an oxide was produced without using LiF, and this oxide was mixed with NH ₄ HF ₂ and heated to produce Li _1.2 Ni. _{_{_{_{0.175 Co 0.10 Mn 0.525 O 2-}}}} F F F, Li 1.167 Ni 0.219 Co 0.125 Mn 0.490 O 2-F F F, Li 1.130 Ni 0.266 Co _0.152 Mn _0.451 O _2- F _FF , Or _{_{_{_{Li 1.090 Ni 0.318 Co 0.182 Mn 0.409}}}} O 2-F F F to obtain lithium composite oxide (paragraph [0070], [0071]), and these lithium composite oxides It describes that a coin cell was manufactured as a positive electrode active material, and a charge / discharge cycle was performed at 2.0 to 4.6 V to obtain data of a specific discharge capacity (paragraphs [0072] to [0078]). .

There is also a prior art in which the crystal structure of the positive electrode active material is specified by measuring a Raman spectrum.
Patent Document 16 discloses that “an anode including an anode current collector and an anode active material disposed on the anode current collector, and a cathode current collector and xLi ₂ MO _3. (1-x) a cathode including a cathode active material having a composition represented by LiCo _y M ′ _(1-y) O ₂ . As Example 1, the cathode active material was “a composition represented by 0.02Li ₂ MnO ₃ .0.98LiNi _0.021 Co _0.979 O ₂ ”, and the Raman spectrum is shown in FIG. (Paragraphs [0026] to [0029]). Other embodiments, "0.04Li _₂ MnO ₃ · 0.96LiCoO _2", composition represented by _{_{_{_{"0.01Li 2 MnO 3 · 0.99LiNi 0.01 Mn}}}} 0.01 Co 0.98 O 2 " Are described (paragraphs [0030] and [0036]).

Patent Literature 17 discloses that “a lithium-based positive electrode active material represented by the following Chemical Formula 1 has a ratio of a peak intensity of A _1g vibration mode having a spinel structure to a peak intensity of A _1g vibration mode having a hexagonal system structure of ₁ in Raman spectrum analysis. : 0.1 to 1: 0.4, the ratio of the peak intensity of peak intensity versus _{E g} oscillation mode of _{a 1 g} oscillation mode of a hexagonal system structure 1: 0.9 to 1: 3.5, A positive electrode active material having a ratio of the peak intensity of the A _1g vibration mode of the spinel structure to the peak intensity of the F _2g vibration mode of 1: 0.2 to 1: 0.4:
[Chemical formula 1]
_{_{_{Li x Co y M 1-y}}} A 2
In the above formula, 0.95 ≦ x ≦ 1.0, 0 ≦ y
≦ 1, and M is selected from the group consisting of Ni, Fe, Pb, Mg, Al, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn and Cr. A is an element selected from the group consisting of O, F, S and P. (Claim 1), since the lithium-based positive electrode active material has only a hexagonal structure before the battery is manufactured, the Raman spectroscopic analysis shows that the peak due to two vibration modes (A _{1g at} 593 cm ⁻¹⁾ is obtained. E _g mode) spectra showing only mode and 484cm ^-1 is obtained, after producing the battery, lithium-based positive active materials are described that will have in addition to the spinel structure of a hexagonal system (Paragraphs [0017] and [0018], FIGS. 1 and 2).

Non-Patent Document 1 discloses NCMs (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li _1.1 Ni _1/3 Co _1/3 Mn _1/3 O ₂ and high energy xLi ₂ MnO _3. (1-x) LiMO ₂ (M = Ni, Co, Mn; x = 0.5) has a peak A _1g near 600 cm ⁻¹ corresponding to the MeO ₆ vibration mode in the Raman spectrum. , O—Me—O vibration mode, a peak E _g peak near 500 cm ⁻¹ , Li ₂ MnO ₃ has a peak such as 612 cm ⁻¹ (A _g1 ), 493 cm ⁻¹ , and xLi ₂ MnO _3. (1-x) LiMO ₂ (x = 0.5) has a peak that Li ₂ MnO ₃ has without LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Especially 496 Shoulder m ^-1 peak and 569cm ^-1 is described that is remarkable. Further, NCMs are before and after charge and discharge, in that it has a peak corresponding to a typical E _g and A _g1, even after charging and discharging, it is described that maintains a laminar LiMO ₂ similar structure before charge and discharge (Page 206, right column, 2 lines, 5 pages, 208 page, left column, 209 pages, right column, “3.2. Ex situ Raman investigation” in full text).

Japanese Patent No. 4877660 JP 2012-104335 A JP 2013-191390 A JP 2016-100054 A JP 2010-050079 JP 2011-187440 A JP 2015-122235 A JP 2016-15298 A International Publication 2015/083330 JP 2016-126935 A JP 2014-170739 A JP 2012-89470 A JP-A-2014-107269 JP 2014-75177 A JP 2012-504316 A JP-T-2016-517615 JP-T-2005-44785

The nonaqueous electrolyte secondary battery is required to ensure safety even if the battery is erroneously charged further beyond the full charge state (SOC 100%) (hereinafter, referred to as “overcharge”). For example, it is defined by "GB / T (China Recommended National Standard)" for automobile batteries. As a method of evaluating the improvement in safety, assuming that the charge control circuit is broken, when a current is forcibly applied beyond the full charge state, a sharp increase in the battery voltage is observed. There is a way to record. If no sharp increase in battery voltage is observed until a higher SOC is reached, the safety is evaluated to be improved.
Here, the SOC is an abbreviation of State of Charge, and represents the state of charge of the battery as a ratio of the remaining capacity at that time to the capacity at the time of full charge, and the full charge state is described as "SOC 100%". .

Patent Literatures 1 to 4 disclose an initial charge / discharge step (hereinafter, also referred to as “overcharge formation”) until a positive electrode potential reaches 4.5 V (vs. Li ^/ Li ⁺ ) or more using a lithium-rich type active material for a positive electrode. Non-aqueous electrolyte secondary battery which is assumed to be manufactured through the above-described method is described. When the non-aqueous electrolyte secondary battery is overcharged, the battery voltage rapidly increases until the SOC reaches a higher level. No delay is shown.
On the other hand,

Patent Literatures

5 and 6 disclose that a lithium-rich type active material having Li / Me of 1 or more is used for a positive electrode, and an initial charge / discharge step is performed at a voltage of 4.2 V (a positive electrode potential is about 4.3 V (vs. Li / Li). ⁺ ), Which is considered to be non-aqueous electrolyte secondary battery. However, the lithium-excess type active materials according to the examples described in

Patent Documents

5 and 6 have a small Li / Me of 1.15 or less. In addition, in Patent Document 1, in the case of a lithium-rich type active material existing in the region of x> 1/3 (Li / Me> 1.25), “2θ = 20 in an X-ray diffraction diagram using CuKα ray” A diffraction peak observed in a monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is observed around ～ 30 ° ”, indicating that Li / Me is much higher than this. In the lithium-rich excess active material described in

Patent Literatures

5 and 6, even when the maximum potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li ^/ Li ⁺ ), 2θ = 20 ° It is highly probable that no diffraction peak is observed in the range of not less than 22 ° and not more than 22 °. Also,

Patent Documents

5 and 6 do not disclose delaying a sudden rise in battery voltage to a higher SOC when the nonaqueous electrolyte secondary battery is overcharged.

As described in Patent Documents 7 to 11, a lithium-rich type active material is used for a positive electrode, and the initial charge / discharge at a positive electrode potential of 4.5 V (Li / Li ⁺ ) or higher (the above-described “overcharge formation”). )), A non-aqueous electrolyte secondary battery is presumed to be used through an acid treatment of a "lithium-rich" active material with hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, or the like. Although it is known that the performance is improved, only the effect of treatment with a strong acid is shown, and the effect of not performing overcharge formation is unknown.

Furthermore, a non-aqueous electrolyte secondary battery containing a lithium-rich type active material in the positive electrode described in Patent Documents 12 to 15 also performs overcharge formation, and when the non-aqueous electrolyte secondary battery is overcharged, There is no indication of delaying the battery voltage spike up to a higher SOC.
The active material described in Patent Literature 16 is not an original lithium-rich active material because of a small Mn content, and the active material described in Patent Literature 17 is not a lithium-rich active material. It is irrelevant to the problem of the non-aqueous electrolyte secondary battery that contains in the positive electrode.

課題 An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC.

One aspect of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material, and has a general formula Li _{1 + α} Me _1-α O ₂ (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co), and contains a lithium transition metal composite oxide, and the active material uses CuKα radiation. This is a non-aqueous electrolyte secondary battery in which a diffraction peak is observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram.

Another aspect of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material, and has a general formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co), and includes a lithium transition metal composite oxide. When charging to 5.0 V (vs. Li ^/ Li ⁺ ) is performed, a positive electrode potential range of 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less is obtained. This is a non-aqueous electrolyte secondary battery in which a region where the change in potential relative to the amount of charged electricity is relatively flat is observed.

According to still another aspect of the present invention, there is provided a method for manufacturing a non-aqueous electrolyte secondary battery according to the above aspect of the present invention, wherein the maximum potential of the positive electrode in the initial charge / discharge step is 4.5 V. (Vs. Li ^/ Li ⁺ ) is a method for producing a non-aqueous electrolyte secondary battery.
In other words, in one aspect or the other aspect of the present invention, the “non-aqueous electrolyte secondary battery” performs the initial charge / discharge step described above, and includes a battery completed to a state that can be shipped in a factory. Say. In the factory, charging and discharging may be performed a plurality of times as necessary.

Yet another aspect of the present invention is a method for using the nonaqueous electrolyte secondary battery according to one aspect or the other aspect of the present invention, wherein a maximum ultimate potential of the positive electrode in a fully charged state (SOC 100%). This is a method for using a non-aqueous electrolyte secondary battery used at a battery voltage of less than 4.5 V (vs. Li ^/ Li ⁺ ).

According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, a method for manufacturing the same, and a method for using the same.

The figure explaining that "a diffraction peak is observed in the range of 20 ° or more and 22 ° or less” in the X-ray diffraction measurement of the lithium-rich type positive electrode active material used for the nonaqueous electrolyte secondary battery. The figure explaining that "the diffraction peak is not observed in the range of 20 degrees or more and 22 degrees or less" in the X-ray diffraction measurement of the lithium-rich type positive electrode active material used for the nonaqueous electrolyte secondary battery. X-ray diffraction diagrams of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention and a positive electrode active material provided in a nonaqueous electrolyte secondary battery according to a conventional example The figure which shows the positive electrode potential change with respect to the amount of charge electricity observed when the positive electrode containing LiMeO type ₂ and a lithium excess type active material is initially charged at the positive charge upper limit potential of 4.6 V (vs. Li ^/ Li ⁺ ). The figure explaining "the area | region where the electric potential change is comparatively flat with respect to the amount of charged electricity" in the nonaqueous electrolyte secondary battery according to the embodiment of the present invention. The figure which shows the electric potential change with respect to the charge electric quantity of a lithium excess type positive electrode active material. shows the _{A 1 g} and _{E g} oscillation mode of the lithium-transition metal composite oxide having an alpha-NaFeO ₂ type crystal structure LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li _1.1 Ni _1/3 Co _1/3 Mn _1/3 O _2.1, xLi ₂ MnO _3. (1-x) LiMO ₂ (M = Ni, Co, Mn; x = 0.5) and Raman spectrum of Li ₂ MnO ₃ before charge and discharge. Raman spectrum before and after charge and discharge of the positive electrode active material according to the example of the present invention 1 is an external perspective view showing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. Schematic diagram of the apparatus used for measuring the press density for calculating the discharge capacity per volume and the amount of charge electricity 1 is a schematic diagram illustrating a power storage device including a plurality of nonaqueous electrolyte secondary batteries according to an embodiment of the present invention. Raman spectra according to examples and reference examples of the present invention 4 is a graph showing the relationship between the Raman peak intensity ratio I ₄₉₀ / I ₆₀₀ and the discharge capacity per volume of the lithium-excess type active materials according to Examples, Reference Examples and Comparative Examples of the present invention.

構成 The configuration, operation and effect of the present invention will be described together with technical ideas. However, the mechanism of action includes an estimation, and its correctness does not limit the present invention. Note that the present invention can be embodied in various other forms without departing from the spirit or main features thereof. Therefore, the embodiments or examples described below are merely examples in all aspects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

A first embodiment of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material. A lithium transition metal composite oxide represented by the formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co); This is a nonaqueous electrolyte secondary battery in which a diffraction peak is observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram using CuKα rays.

Another first embodiment of the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure as an active material. A lithium transition metal composite oxide represented by the general formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co), When the positive electrode potential is charged to reach 5.0 V (vs. Li ^/ Li ⁺ ), the positive electrode potential is 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less. A non-aqueous solution including a positive electrode in which a region in which a change in potential relative to the amount of charged electricity is relatively flat (in a third embodiment described below, referred to as an “overcharge region”) is observed. It is an electrolyte secondary battery.

The nonaqueous electrolyte secondary battery may use, as an active material of the positive electrode, a lithium transition metal composite oxide in which a molar ratio of Mn to transition metal (Me) is 0.4 ≦ Mn / Me. According to this embodiment, the layered structure of the active material can be stabilized.

In the nonaqueous electrolyte secondary battery, a lithium transition metal composite oxide in which a molar ratio of Li to a transition metal (Me) is 1.15 <Li / Me may be used as an active material of the positive electrode.
According to this aspect, it is possible to provide a nonaqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed until a higher SOC is reached.

In the non-aqueous electrolyte secondary battery, a lithium transition metal composite oxide having a molar ratio of Li to transition metal (Me) of Li / Me ≦ 1.35 may be used as an active material of the positive electrode. According to this aspect, the discharge capacity can be improved.

において In the nonaqueous electrolyte secondary battery, the content of the lithium transition metal composite oxide contained in the positive electrode as an active material is preferably more than 80% by mass of the total active material of the positive electrode. According to this aspect, it is possible to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed until a higher SOC is reached. The content of the lithium transition metal composite oxide is more preferably 90% by mass or more of the total active material of the positive electrode, and may be substantially 100% by mass. However, the presence of other small amounts of active material is not excluded unless the effects of the present invention are impaired.

The non-aqueous electrolyte secondary battery is preferably used at a battery voltage at which the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li ^/ Li ⁺ ).

According to the above embodiment, it is possible to provide a non-aqueous electrolyte secondary battery in which a sharp increase in battery voltage is not observed up to a higher SOC.

The non-aqueous electrolyte secondary battery may use, as the non-aqueous electrolyte, a non-aqueous electrolyte containing a fluorinated cyclic carbonate in a non-aqueous solvent. According to such a configuration, in addition to the effect of being able to provide a nonaqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, an increase in AC resistance after storage is suppressed. This has the effect of being able to do so.

The non-aqueous electrolyte may include a compound having an oxalate group bonded to boron.
According to this aspect, in addition to the effect of providing a non-aqueous electrolyte secondary battery in which a sharp increase in battery voltage is not observed up to a higher SOC, the effect of reducing initial AC resistance can be obtained. Is played.

A second embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ type crystal structure And a general formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, and a molar ratio Mn / Me of Mn to Me is Mn / Me. ≧ 0.45), the positive electrode active material has a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and a discharge capacity (a) of 3.0 V (vs. Li ^/ Li ⁺ ). positive electrode for a non-aqueous electrolyte secondary battery, wherein the ratio a / b of the discharge capacity (b) from 2.0 vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ) is 17 ≦ a / b ≦ 25. Active material.

A second embodiment of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the second embodiment, which has an α-NaFeO ₂ type crystal structure, General formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, the molar ratio of Mn to Me Mn / Me is Mn / Me ≧ 0.45 a lithium transition metal composite oxide represented by), with pKa ₁ is treated with 3.1 or more acids, 4.35V (vs.Li/Li ⁺⁾ from 3.0V (vs.Li/Li ⁺⁾ discharge capacity (a) and 3.0V (vs.Li/Li ⁺⁾ from 2.0V (vs.Li/Li ⁺⁾ ratio a / b of the discharge capacity (b) until the 17 ≦ a / b ≦ up 25 is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which produces the positive electrode active material of No. 25.

A third embodiment of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO ₂ type crystal structure Having the general formula Li _{1 + α} Me _1−α O ₂ (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, and the molar ratio Mn / Me of Mn to Me is 0.3. ≦ Mn / Me expressed in <0.55), the maximum value _{I 490} at the maximum value for _{I 600,} 450 cm ^-1 or more 520 cm ^-1 or less in the range of at 650 cm ^-1 or less in the range of 550 cm ^-1 or more in the Raman spectrum Is a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the ratio (I ₄₉₀ / I ₆₀₀ ) is 0.45 or more.
According to the third embodiment of the present invention, there is provided a positive electrode active material having a large amount of charged electricity per volume in the overcharge region and a large discharge capacity per volume.

A third embodiment of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the third embodiment, wherein Ni and Mn, or Ni, Co and Mn are used. A transition metal compound having a molar ratio of Mn to Me of 0.3 ≦ Mn / Me <0.55 is mixed with a Li compound, and the mixture is baked, whereby the molar ratio of Li / Me is 1 <Li. / Me is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, in which a sintering aid is added when producing a lithium transition metal composite oxide.
According to the third other embodiment of the present invention, in particular, a method for producing a positive electrode active material having a large discharge capacity per volume is provided.

Second and third embodiments of the present invention are directed to a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to the second and third embodiments. It is.

A second and third still another embodiment of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery according to the second and third still another embodiment, and includes a positive electrode active material contained in the positive electrode. The substance is a nonaqueous electrolyte secondary battery in which a diffraction peak is observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram using CuKα rays.

A second and third still another embodiment of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery according to the second and third still another embodiment, wherein the positive electrode has a positive electrode potential of 5 when performing charging leading to .0V (vs.Li/Li ^+), to 4.5V (vs.Li/Li ⁺⁾ or 5.0V (vs.Li/Li ⁺⁾ within the following positive electrode potential range, the charge This is a nonaqueous electrolyte secondary battery in which a region in which a change in potential relative to the amount of electricity is relatively flat is observed.
According to the second and third still other embodiments, the non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC because the amount of charge per volume in the overcharge region is large. Is provided.
The above non-aqueous electrolyte secondary battery is preferably used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ).
In this second and third still another embodiment, when used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), a large discharge capacity per volume and a higher SOC are reached. It can be compatible with not observing a sharp rise in battery voltage.

Another embodiment of the first, second and third aspects of the present invention is the method for manufacturing a non-aqueous electrolyte secondary battery described above, wherein the maximum ultimate potential of the positive electrode in the initial charge / discharge step is 4.5 V ( vs. Li ^/ Li ⁺ ).
In the present specification, "initial" charge / discharge refers to one or more times of charging and discharging performed after injecting the nonaqueous electrolyte, and in particular, "initial" charging / discharging refers to Refers to the first charge and discharge performed after injection.
According to this embodiment, when charging is performed so that the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ), it is 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ). In the positive electrode potential range equal to or less than Li ⁺ ), a non-aqueous electrolyte secondary in which a rapid increase in battery voltage is not observed up to a higher SOC by observing a region where the potential change is relatively flat with respect to the charged amount of electricity. A battery is manufactured.

The first, second and third still other embodiments of the present invention relate to a method of using the non-aqueous electrolyte secondary battery, wherein the maximum potential of the positive electrode in a fully charged state (SOC 100%) is 4. This is a method for using a non-aqueous electrolyte secondary battery used at a battery voltage of less than 5 V (vs. Li ^/ Li ⁺ ).

The first embodiment, the first other embodiment, the first still another embodiment (hereinafter, referred to as “first embodiment”) of the present invention, and the second embodiment of the present invention described above. One embodiment, a second other embodiment, and a second still another embodiment (hereinafter, referred to as a “second embodiment”), a third embodiment of the present invention, and a third embodiment. Another embodiment and a third further embodiment (hereinafter, referred to as “third embodiment”) will be described in detail below. Further, the first embodiment, the second embodiment, and the third embodiment are collectively referred to as the present embodiment.
According to the first embodiment, it is possible to provide a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, a method for manufacturing the same, and a method for using the same.
According to the second embodiment, when used at a potential of less than 4.5 V (vs. Li ^/ Li ⁺ ), the positive electrode active material for a non-aqueous electrolyte secondary battery exhibits excellent initial coulomb efficiency and high rate discharge performance. Substance, a method for producing the same, a positive electrode containing the positive electrode active material, a non-aqueous electrolyte secondary battery provided with the positive electrode, and a method for producing the battery. Also, the battery voltage can be increased up to a higher SOC. Non-aqueous electrolyte secondary battery in which no rapid increase in the temperature is observed, a method for manufacturing the battery, and a method for using the battery can be provided.
According to the third embodiment, the amount of charge per volume in the overcharge region is large, and the positive electrode active material for a non-aqueous electrolyte secondary battery having a large discharge capacity per volume, a method for producing the same, and the positive electrode active material And a non-aqueous electrolyte secondary battery provided with the positive electrode, and a method for manufacturing the battery, and a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC. A battery, a method for manufacturing the battery, and a method for using the battery can be provided.

<Composition of lithium transition metal composite oxide>
The lithium transition metal composite oxide contained in the positive electrode of the nonaqueous electrolyte secondary battery according to the present embodiment as an active material has a general formula Li _{1 + α} Me _1−α O ₂ (0 <α, where Me is Ni and Mn, or This is a so-called “lithium-rich” active material represented by a transition metal element containing Ni, Mn and Co). Typically, it can be expressed as Li _{1 + α} (Ni _β Co _γ Mn _δ ) _1−α O ₂ (β + γ + δ = 1).
In the first embodiment, in order to provide a positive electrode active material that can be a nonaqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC, the molar ratio of Li to the transition metal element Me is Li / Me, that is, (1 + α) / (1-α) is preferably larger than 1.15, more preferably 1.2 or more, and further preferably 1.23 or more. In order to make the discharge capacity excellent, Li / Me is preferably 1.35 or less, more preferably 1.3 or less.
In the second embodiment, Li / Me is preferably 1.05 or more in order to prevent a sudden increase in battery voltage from being observed until the SOC exceeds 100% and further to a higher SOC when further charged. , 1.10 or more. In order to suppress a decrease in the discharge capacity, Li / Me is preferably 1.4 or less, more preferably 1.35 or less.
In the third embodiment, Li / Me is preferably equal to or greater than 1.05, and more preferably equal to or greater than 1.1 in that the amount of charge per unit volume in the overcharge region can be increased. Further, it is preferably less than 1.4, more preferably 1.3 or less. Within this range, the discharge capacity per unit volume of the positive electrode active material when manufactured and used in a potential range lower than the overcharge region is improved.
In the first embodiment, the molar ratio Mn / Me of Mn to the transition metal element Me, that is, δ, is preferably 0.4 or more, more preferably 0.45 or more, from the viewpoint of stabilization of the layered structure. . Further, from the viewpoint of charge / discharge capacity, Mn / Me is preferably 0.65 or less, more preferably 0.60 or less.
In the second embodiment, the molar ratio Mn / Me is 0.45 or more from the viewpoint of stabilizing the layered structure. Further, from the viewpoint of charge / discharge capacity, Mn / Me is preferably 0.65 or less, more preferably 0.6 or less.
In the third embodiment, the molar ratio Mn / Me is 0.3 or more and less than 0.55. When it is 0.3 or more, the amount of charged electricity per volume in the overcharge region can be increased. Further, when it is less than 0.55, the discharge capacity per volume in the case of manufacturing and using in a potential range lower than the overcharge region is improved. The molar ratio Mn / Me of Mn is more preferably 0.5 or less, and further preferably 0.45 or less.
In the first and second embodiments, the molar ratio Ni / Me of Ni to the transition metal element Me, that is, β, is set to 0.2 or more in order to improve the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery. Is preferred. Further, it is preferably 0.5 or less, more preferably 0.4 or less.
In the third embodiment, the molar ratio Ni / Me is preferably 0.2 or more, and more preferably 0.3 or more. Also, it is preferably 0.6 or less, more preferably 0.55 or less. Within this range, the polarization in charge / discharge becomes small, so that the discharge capacity when used at a potential lower than 4.5 V (vs. Li ^/ Li ⁺ ) becomes large.
In the present embodiment, the molar ratio Co / Me of Co to the transition metal element Me, that is, γ, is preferably 0.03 or more, more preferably 0.2 or more, from the viewpoint of increasing the conductivity of the active material particles. Is more preferred. Further, in order to reduce material cost, it is preferably set to 0.4 or less, more preferably 0.35 or less, further preferably 0.3 or less, and may be 0.
In addition, the lithium transition metal composite oxide according to the present embodiment is converted into an alkali metal such as Na and K, an alkaline earth metal such as Mg and Ca, and a 3d transition metal such as Fe within a range that does not impair the effects of the present invention. It does not preclude the inclusion of small amounts of other metals, such as the typical transition metals.

<Crystal structure of lithium transition metal composite oxide>
The lithium transition metal composite oxide according to the present embodiment has an α-NaFeO ₂ type crystal structure. The lithium transition metal composite oxide after combining (before charge and discharge of the active material), together with belonging to the space group P3 1 _12, in X-ray diffraction diagram using CuKα ray, 2 [Theta] = 20 ° or 22 ° or less range superlattice peak of _{_{(Li [Li 1/3 Mn 2/3]}} O 2 type peaks seen in monoclinic) is observed. This superlattice peak (hereinafter, referred to as “diffraction peak in the range of 20 ° to 22 °”) is obtained even when charge / discharge is performed in a potential region where the positive electrode potential is less than 4.5 V (vs. Li ^/ Li ⁺ ). Does not disappear (see FIG. 1). However, once charging is performed to a potential at which the overcharge region of 4.5 V (vs. Li / Li ⁺ ) or more ends, the symmetry of the crystal changes with the elimination of Li in the crystal. The diffraction peak in the range of 20 ° to 22 ° disappears, and the lithium transition metal composite oxide is assigned to the space group R3-m (see FIG. 2). Here, P3 ₁ 12 is a crystal structure model obtained by subdividing the atom positions of the 3a, 3b, and 6c sites in R3-m. When order is recognized in the atom arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” is originally described by adding a bar “−” to “3” of “R3m”.

<Diffraction peak in X-ray diffraction diagram of positive electrode active material>
The positive electrode active material of the nonaqueous electrolyte secondary battery according to the present embodiment contains the lithium transition metal composite oxide, and when X-ray diffraction is performed using CuKα radiation, in the X-ray diffraction diagram, 20 ° or more and 22 ° or more. It has a feature that a diffraction peak is observed in the following range.

<How to confirm diffraction peaks>
The positive electrode active material used in the nonaqueous electrolyte secondary battery according to the second and third embodiments, and X-ray diffraction measurement for the positive electrode active material included in the positive electrode included in the nonaqueous electrolyte secondary battery according to the first embodiment, Confirmation that a diffraction peak is observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram using CuKα rays is performed according to the following procedure and conditions. Here, “observed” means that the diffraction angle is in the range of 20 ° to 22 ° with respect to the difference (I ₁₈ ) between the maximum value and the minimum value of the intensity in the range of 17 ° to 19 °. The ratio of the difference (I ₂₁ ) between the maximum value and the minimum value of the intensity, that is, the value of “I ₂₁ / I ₁₈ ” is in the range of 0.001 or more and 0.1 or less.
If the sample to be subjected to the X-ray diffraction measurement is an active material powder (powder before charge / discharge) before producing the positive electrode, the sample is subjected to the measurement as it is. When disassembling a non-aqueous electrolyte secondary battery (hereinafter also referred to as a “battery”) and collecting a sample from a positive electrode taken out of the battery, 10 minutes of the nominal capacity (Ah) of the battery before dismantling the battery. At a current value (A) of 1, the constant current discharge is performed until the battery voltage reaches the lower limit of the voltage specified as the normal use, and the battery is completely discharged. As a result of disassembly, if the battery uses a metal lithium electrode as the negative electrode, the positive electrode is taken out without performing the additional operation described below. If the battery does not use a metal lithium electrode as the negative electrode, as an additional operation, disassemble the battery, take out the positive electrode, and assemble a test battery with the metal lithium electrode as the counter electrode, in order to accurately control the positive electrode potential. At a current value of 10 mA per 1 g of the mixture, constant-current discharge is performed until the voltage becomes 2.0 V (the positive electrode potential becomes 2.0 V (vs. Li ^/ Li ⁺ )), adjusted to a completely discharged state, and then re-disassembled. Then, take out the positive electrode.
The taken-out positive electrode is sufficiently washed with non-aqueous electrolyte attached to the positive electrode using dimethyl carbonate, dried at room temperature for 24 hours, and then a positive electrode mixture is collected from the current collector. The collected positive electrode mixture is lightly crushed in an agate mortar, placed in a sample holder for X-ray diffraction measurement, and used for measurement.
The operations from the disassembly to re-disassembly of the battery, and the washing and drying operations of the positive electrode are performed in an argon atmosphere having a dew point of −60 ° C. or less.

<X-ray diffraction measurement>
In this specification, X-ray diffraction measurement is performed under the following conditions. The source is CuKα, the acceleration voltage is 30 kV, and the acceleration current is 15 mA. The sampling width is 0.01 deg, the scan speed is 1.0 deg / min, the divergence slit width is 0.625 deg, the light receiving slit is open, and the scattering slit width is 8.0 mm.

As shown in Example 1-1 to be described later, after assembling a nonaqueous electrolyte secondary battery using the lithium-rich type active material as a positive electrode and metallic lithium as a negative electrode, the charging upper limit potential is set to 4.25 V (vs. Li / Li). ⁺ ), With a discharge lower limit potential of 2.0 V (vs. Li ^/ Li ⁺ ), a non-aqueous electrolyte secondary battery in a completely discharged state completed by performing charging and discharging twice at a current value equivalent to 0.1 C. When the positive electrode obtained by disassembly is subjected to X-ray diffraction measurement according to the above procedure, a diffraction peak is observed in the range of 20 ° or more and 22 ° or less as in FIG. An X-ray diffraction diagram is obtained.
Further, as shown in Comparative Example 1-2 described later, after assembling a nonaqueous electrolyte secondary battery using the lithium-rich type active material as a positive electrode and metallic lithium as a negative electrode, the charging upper limit potential was set to 4.6 V (vs. Li). / ^Li +), the discharge lower limit voltage as 2.0V (vs.Li/Li ^+), after performing the initial charge and discharge, 4.25 V charging upper limit voltage (vs.Li/Li ^+), the discharge lower limit voltage 2.0 V (vs. Li ^/ Li ⁺ ), obtained by disassembling a completely discharged non-aqueous electrolyte secondary battery completed by performing a second charge / discharge (current value corresponding to 0.1 C) for the second time. When the X-ray diffraction measurement is performed on the positive electrode according to the above-described procedure, an X-ray diffraction diagram in which no peak in the range of 20 ° to 22 ° is observed as in FIG. 2 (partially enlarged view: upper part of FIG. 3) is obtained. That is, as described above, if the battery is charged to a potential of at least 4.5 V (vs. Li ^/ Li ⁺ ), no peak in the range of 20 ° to 22 ° is observed.
In the nonaqueous electrolyte secondary battery according to the first embodiment, even after charging and discharging, a diffraction peak in the range of 20 ° or more and 22 ° or less is observed in the X-ray diffraction diagram of the positive electrode active material measured by the above procedure. Therefore, in the nonaqueous electrolyte secondary battery according to the first embodiment, the maximum ultimate potential of the positive electrode in the fully charged state (SOC 100%) including the initial charge and discharge is 4.5 V (vs. Li ^/ Li ⁺ ). It can be seen that the battery is used at a battery voltage of less than.
Also, in the second and third embodiments, when the upper limit charging potential is changed from 4.25 V (vs. Li / Li ⁺ ) to 4.35 V (vs. Li / Li ⁺ ), Since a diffraction peak in the range of 20 ° or more and 22 ° or less is observed in the X-ray diffraction diagram of the active material, the non-aqueous electrolyte secondary batteries according to the second and third embodiments include the initial charge and discharge, It can be seen that the battery is used at a battery voltage at which the maximum ultimate potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li ^/ Li ⁺ ).
The first charge / discharge condition 2 in which the upper limit charge potential is 4.6 V (vs. Li ^/ Li ⁺ ) and the lower discharge limit potential is 2.0 V (vs. Li ^/ Li ⁺ ) in Examples described later is the third charge / discharge condition. In order to investigate the amount of charge per volume in the overcharge region of the positive electrode active material according to the embodiment, the upper limit charge potential was set to 4.6 V (vs. Li ^/ Li ⁺ ). The nonaqueous electrolyte secondary battery after applying the initial charge / discharge condition 2 in which a diffraction peak in the range of 20 ° to 22 ° is not observed in the X-ray diffraction diagram is the nonaqueous electrolyte secondary battery according to the third embodiment. Absent.

<Change in potential of positive electrode potential>
The nonaqueous electrolyte secondary battery according to this embodiment, in which the diffraction peak in the range of 20 ° to 22 ° is observed in the X-ray diffraction diagram of the positive electrode active material, has a positive electrode potential of 5.0 V (vs. Li). / Li ⁺⁾ when charging was performed leading to 4.5V (vs.Li/Li ⁺⁾ or 5.0V (vs.Li/Li ⁺⁾ within the following positive electrode potential range, the potential relative to the amount of charge A region where the change is relatively flat (hereinafter also referred to as a “region where the potential change is flat”) is observed. In addition, when the charging is performed at least once until the charging process in which the region where the potential change is flat is observed, the charging is performed until the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ). However, the region where the potential change is flat is not observed again.

The principle of the operation mechanism of the present invention will be described with reference to FIG. The solid line in FIG. 4 indicates a nonaqueous electrolyte according to the present embodiment including a positive electrode using a lithium transition metal composite oxide (denoted as “lithium excess type”) as a positive electrode active material and a negative electrode using metallic lithium. The figure shows the change in the positive electrode potential when the secondary battery is assembled and the initial charging is performed with the upper limit charging potential of the positive electrode set to 4.6 V (vs. Li ^/ Li ⁺ ). On the other hand, the broken line has the same configuration except that a positive electrode using a commercially available LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (denoted as “LiMeO ₂ type”) as a positive electrode active material is provided. It shows a change in the positive electrode potential when the same initial charge is performed on the nonaqueous electrolyte secondary battery. In the positive electrode using the lithium-rich type active material, a region where the potential change is flat is observed in the positive electrode potential range of 4.45 V (vs. Li ^/ Li ⁺ ) or more and 4.6 V (vs. Li ^/ Li ⁺ ) or less. Is done. On the other hand, in the positive electrode using the LiMeO _{2 type} active material, the potential change is flat within a positive electrode potential range of 4.45 V (vs. Li ^/ Li ⁺ ) or more and 4.6 V (vs. Li ^/ Li ⁺ ) or less. No area is observed.
Note that the potential range in which a flat region is observed and the capacity at the time of charge and discharge are slightly different depending on the physical properties such as the composition of the positive electrode using the lithium-excess type active material, and thus this diagram is merely an example.

The non-aqueous electrolyte secondary battery according to the present embodiment has a lithium-rich type active material in which a region where the potential change is flat is observed when charging is performed so that the positive electrode potential reaches 5.0 V (vs. Li ^/ Li ⁺ ). Is included in the positive electrode, but in the initial charge / discharge process, the battery is completed without charging until the charging process in which the flat region is observed is completed. It is preferable that the maximum attained potential of the positive electrode in the initial charge / discharge step is less than 4.5 V (vs. Li ^/ Li ⁺ ). Furthermore, the non-aqueous electrolyte secondary battery according to the present embodiment is used under charging conditions in which charging is not performed until the charging process in which the flat region is observed is completed. Therefore, the non-aqueous electrolyte secondary battery according to the present embodiment has not been charged until the charging process in which the flat region is observed is completed from the manufacturing stage to the time of use, and thus the overcharge is not performed. In this case, a region where the potential change is flat with respect to the amount of charged electricity is observed in a positive electrode potential range of 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less. You.
The non-aqueous electrolyte secondary battery according to the present embodiment uses the behavior described above to achieve a higher SOC even when overcharged beyond the SOC of 100%, which is the fully charged state in normal use. A sharp rise in battery voltage (positive electrode potential) can be suppressed.

<Confirmation method of area where potential change is flat>
Here, the following procedure is used to confirm that “a region where the potential change is flat” is observed. A test battery is prepared in which the positive electrode taken out of the nonaqueous electrolyte secondary battery after disassembly is used as a working electrode and metallic lithium as a counter electrode. Since the battery voltage of the test battery and the working electrode potential (positive electrode potential) are almost the same value, the positive electrode potential in the following procedure can be read as the battery voltage of the test battery. After discharging the test battery at a current value of 10 mA per 1 g of the positive electrode mixture to a final potential of the positive electrode of 2.0 V (vs. Li ^/ Li ⁺ ), a rest is performed for 30 minutes. Thereafter, constant current charging is performed at a current value of 10 mA per 1 g of the positive electrode mixture to a final potential of the positive electrode of 5.0 V (vs. Li ^/ Li ⁺ ). Here, when the capacity when reaching 4.45 V (vs. Li / Li ⁺ ) from the start of charging is X (mAh), and the capacity at each potential is Y (mAh), Y / X * 100 is defined as the capacity ratio Z. (%). The dZ / dV curve is obtained by plotting the positive electrode potential on the horizontal axis, dZ / dV with the denominator on the vertical axis as the difference in potential change, and the numerator on the difference in capacitance ratio change.
The solid line in FIG. 5 shows that a non-aqueous electrolyte secondary battery including a positive electrode using a lithium-rich type active material as a positive electrode active material and a negative electrode using metallic lithium was assembled, and 4.6 V (vs. Li / Li) was initially used. ¹² is an example of a dZ / dV curve when charging up to ⁺ ) is performed. As can be seen from the calculation formula, the dZ / dV curve has a large dZ / dV value when the potential change is small with respect to the capacitance ratio change, and a dZ / dV value when the potential change is large with respect to the capacitance ratio change. The value decreases. In the charging process of the lithium-rich type active material, the value of dZ / dV increases in a region where the potential change in a potential region exceeding 4.5 V (vs. Li ^/ Li ⁺ ) is flat. Thereafter, when the region where the potential change is flat ends and the potential starts to rise again, the value of dZ / dV decreases. That is, a peak is observed in the dZ / dV curve. Here, when the maximum value of dZ / dV in the range of 4.5 V (vs. Li ^/ Li ⁺ ) to 5.0 V (vs. Li / Li ⁺ ) is 150 or more, the charge amount is It is determined that a region where the potential change is flat is observed. On the other hand, the broken line is a dZ / dV curve of a battery having the same configuration and performing the same test except that a positive electrode using a commercially available LiMeO ₂ type active material as a positive electrode active material is provided. Corresponding to the fact that the region where the potential change is flat is not observed, the peak as seen in the lithium excess type is not observed. In the present specification, the normal use is a case where the nonaqueous electrolyte secondary battery is used by adopting recommended or specified charge / discharge conditions for the nonaqueous electrolyte secondary battery. When a charger for a non-aqueous electrolyte secondary battery is provided, it refers to a case where the non-aqueous electrolyte secondary battery is used by applying the charger.

<Discharge capacity ratio of positive electrode active material>
The positive electrode active material according to the second embodiment further has a discharge capacity (a) from 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li ^/ Li ⁺ ) and 3.0 V (vs. Li ^/ Li ⁺ ). .Li / Li ⁺⁾ ratio a / b from 2.0V (vs.Li/Li ⁺⁾ to the discharge capacity (b) is 17 ≦ a / b ≦ 25.

The discharge capacity ratio a / b is determined as follows.
When the evaluation target is an active material, N-methylpyrrolidone is used as a dispersion medium, and an active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) are prepared in a 90: 5: 5 application paste. The coating paste is applied to one surface of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate, and a nonaqueous electrolyte secondary battery for evaluation is assembled using lithium metal as a counter electrode. At a current value of 15 mA per 1 g of the positive electrode mixture, constant-current constant-voltage charging is performed with a charging upper limit potential of 4.35 V (vs. Li / Li ⁺ ) and a charge termination condition at a time when the current value attenuates to 1/5. . After providing a break of 10 minutes, a discharge lower limit voltage at the same current value is 2.0V (vs.Li/Li ^+), was treated with constant current discharge, the discharge start 3.0V (vs.Li/Li ⁺ ) And the ratio a / b of the discharge capacity (b) from 3.0 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ).
When the evaluation target is a secondary battery, a constant current discharge is performed at a current value (A) that is 1/10 of the nominal capacity (Ah) of the battery until the battery voltage reaches the lower limit of the specified voltage. To complete discharge. The battery is disassembled in an argon atmosphere having a dew point of −60 ° C. or lower, and a positive electrode plate is obtained. Then, a nonaqueous electrolyte secondary battery using lithium metal as a counter electrode is assembled. The produced battery is discharged at a constant current of 2.0 V (vs. Li ^/ Li ⁺ ) at a current value of 15 mA per 1 g of the positive electrode mixture. Thereafter, constant-current constant-voltage charging is performed with the same current value, a charging upper-limit potential of 4.35 V (vs. Li / Li ⁺ ), and a condition for terminating the charging at a time when the current value attenuates to 1/5. After a pause of 10 minutes, a constant current discharge is performed to 2.0 V (vs. Li ^/ Li ⁺ ) at the same current, and a / b is similarly evaluated.
According to Experimental Example 2 described later, when the discharge capacity ratio a / b satisfies 17 ≦ a / b ≦ 25, a positive electrode active material excellent in initial coulomb efficiency and high-rate discharge performance, and a positive electrode active material containing this positive electrode active material, It was found that the positive electrode for a non-aqueous electrolyte secondary battery according to the second embodiment and the non-aqueous electrolyte secondary battery according to the second embodiment including the positive electrode were obtained.

<Behavior when the non-aqueous electrolyte secondary battery is charged over 4.5 V (vs. Li ^/ Li ⁺ )>
The non-aqueous electrolyte secondary battery according to the second embodiment includes a positive electrode containing the above-described positive electrode active material, and the positive electrode active material has an X-ray diffraction diagram using CuKα rays of 20 ° or more and 22 ° or less. Since a peak in the range is observed, the non-aqueous electrolyte secondary battery according to the second embodiment sets the maximum ultimate potential of the positive electrode in the initial charge / discharge step to less than 4.5 V (vs. Li ^/ Li ⁺ ). It is manufactured by the method for manufacturing a nonaqueous electrolyte secondary battery according to the second embodiment. Further, the non-aqueous electrolyte secondary battery according to the second embodiment does not go through a charging process of 4.5 V (vs. Li ^/ Li ⁺ ) or more during normal use. Therefore, when the charge exceeds 4.5 V (vs. Li ^/ Li ⁺ ) and reaches 5.0 V (vs. Li ^/ Li ⁺ ), the positive electrode is charged to 4.5 V (vs. Li ^/ Li ^+). ) Or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less, a region where the change in potential relative to the amount of charged electricity is relatively flat is observed (see the solid line in FIG. 6). Due to the presence of the flat region, in the nonaqueous electrolyte secondary battery according to the present embodiment, a rapid increase in battery voltage is not observed until a higher SOC is reached.

The solid line in FIG. 6 shows the charge when the charge up to 4.6 V (vs. Li ^/ Li ⁺ ) is initially performed on the nonaqueous electrolyte secondary battery including the positive electrode containing the lithium-rich type active material. An example of a curve is shown. Here, the capacity was converted to SOC based on the capacity from the start of charging until reaching 4.35 V (vs. Li / Li ⁺ ) (SOC 100%). It has a relatively flat charging curve until the positive electrode potential rises sharply when the SOC is around 200%. On the other hand, the dashed line in FIG. 6 indicates that after discharging the non-aqueous electrolyte secondary battery charged to 4.6 V (vs. Li ^/ Li ⁺ ) to 2.0 V (vs. Li ^/ Li ⁺ ), It is a charging curve when the upper limit potential is again set to 4.6 V (vs. Li ^/ Li ⁺ ) and charging is performed. As can be seen from the figure, in a positive electrode that has undergone a charge history of 4.5 V (vs. Li ^/ Li ⁺ ) or more even once, a region where the potential change is flat does not appear.
The confirmation of the region where the potential change is flat is performed based on FIG. 5 as described above.

<Raman spectrum of lithium transition metal composite oxide>
Third embodiment the lithium transition metal composite oxide according to the embodiment, with respect to the maximum value _{I 600} at 550 cm ^-1 or more 650 cm ^-1 or less in the range in the Raman spectrum, the maximum value at 450 cm ^-1 or more 520 cm ^-1 or less in the range the ratio of the _{_{_{I 490 (I 490 / I 600}}} ) is 0.45 or more.
By setting I ₄₉₀ / I ₆₀₀ to 0.45 or more, the amount of charged electricity per volume in the overcharge region is increased, and the discharge capacity per volume is increased.
In the present invention, the significance of specifying I ₄₉₀ / I ₆₀₀ as 0.45 or more is presumed as follows.
The lithium transition metal composite oxide according to this embodiment can be represented as a solid solution of LiMeO ₂ (M = Ni and Mn or including Ni, Co and Mn) and Li ₂ MnO ₃ . LiMeO ₂ and _Li 2 MnO _3, in the Raman spectrum has a peak _{E g} around 490 cm ^-1 corresponding to the peak _{A 1 g} and O-MeO vibration mode near 600 cm ^-1 corresponding to MeO ₆ vibrational mode , the _Li 2 MnO _3, peak _{E g} is known to appear particularly remarkably (refer to non-Patent Document 1). FIG. 7 is a reprint of FIG. 2 of Patent Document 17 illustrating the vibration mode, and FIG. 4 is reprinted.
A large value of I ₄₉₀ / I ₆₀₀ means that the lithium transition metal composite oxide according to the present embodiment has a relatively large amount of Li ₂ MnO ₃ component because the O—Me—O vibration is relatively large. . Since Li ₂ MnO ₃ is a component that contributes to increasing the amount of charged electricity in the overcharge region, the fact that I ₄₉₀ / I ₆₀₀ is 0.45 or more indicates that the battery voltage sharply increases up to a higher SOC. Is not observed.
On the other hand, a small I ₄₉₀ / I ₆₀₀ means that the MeO ₆ oscillation is relatively large, and thus the lithium transition metal composite oxide according to the present embodiment has a relatively large LiMeO ₂ component. LiMeO ₂ has higher density and higher capacity than Li ₂ MnO ₃ . However, in the positive electrode active material containing the lithium transition metal composite oxide according to the third embodiment, when the density is increased by the sintering aid, the ratio of LiMeO ₂ units is considered to be relatively small. It was found that an active material having a ₄₉₀ / I ₆₀₀ of 0.45 or more unexpectedly had a larger discharge capacity per volume than an active material having a ₄₉₀ / I ₆₀₀ of less than 0.45. The reason why I ₄₉₀ / I ₆₀₀ is reduced by the sintering aid is that the valence of the transition metal decreases due to oxygen deficiency in the active material, or the disproportionation during synthesis of the active material (3LiMeO ₂ → LiMn ₂ It is considered that the ratio of LiMeO ₂ units to Li ₂ MnO ₃ units in the active material is increased by eliminating O ₄ + Li ₂ MnO ₃ ). However, for the above reason, in order to increase the discharge capacity per unit volume, I ₄₉₀ / I ₆₀₀ is preferably not too large, and is preferably 0.85 or less.

<Raman spectrum measurement>
The preparation of the sample to be subjected to the Raman spectrum measurement is the same as the preparation of the sample to be subjected to the X-ray diffraction measurement described above. , And the same procedure and conditions except that the lithium transition metal composite oxide particles are taken out and subjected to Raman spectrum measurement as an active material powder (a powder after charge / discharge).
The measurement of the Raman spectrum is performed under the following conditions.
Raman spectroscopy is performed using "LabRAM HR Revolution" manufactured by Horiba, Ltd. The measurement is performed using a 100-fold lens as the objective lens and focusing the laser on the active material powder prepared as described above. At that time, the wavelength 532 nm (YAG laser), and the conditions of the grating 600 g / mm, the exposure time of 30 seconds, the number of integrations twice, measurement at a measurement wavelength 100 cm ^-1 or more 4000 cm ^-1 following conditions. In the spectrum obtained by the measurement, to the maximum value _{I 600} in the range of 550 cm ^-1 or more 650 cm ^-1 or less, the ratio of the maximum value _{I 490} at 450 cm ^-1 or more 520 cm ^-1 or less in the range of _{(I 490} / I ₆₀₀ ).

FIG. 9 is a Raman spectrum of a lithium transition metal composite oxide according to Example 3-2 to be described later, in which a powder before charge / discharge and a powder after charge / discharge were measured by the above procedure. The value of I ₄₉₀ / I ₆₀₀ was 0.57 in the powder before charge / discharge, and the value of I ₄₉₀ / I ₆₀₀ was 0.55 in the powder after charge / discharge. The lithium transition metal composite oxide according to the present embodiment maintains the Raman spectrum shape before and after charging and discharging in a powder state.
Note that FIG. 4 (before charging and discharging), FIG. 5 (after charge and discharge) shows that the Raman spectrum hardly changes.

<Method for producing precursor of lithium transition metal composite oxide>
Next, a method for producing a precursor of the lithium transition metal composite oxide used for producing the positive electrode active material of the nonaqueous electrolyte secondary battery according to the present embodiment will be described.
The lithium transition metal composite oxide according to the present embodiment is basically a raw material containing the metal elements (Li, Ni, Co, and Mn) constituting the active material according to the composition of the target active material (oxide). Can be prepared and calcined.
In producing a composite oxide having a desired composition, a so-called “solid phase method” in which the respective compounds of Li, Ni, Co and Mn are mixed and calcined, or Ni, Co and Mn are present in one particle in advance. A “coprecipitation method” is known in which a coprecipitated precursor is prepared, and a lithium salt is mixed and fired with the precursor. In the synthesis process by the “solid phase method”, particularly, Mn is hard to be uniformly dissolved in Ni and Co, so that it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In the literature, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O _2, etc.) by a solid phase method, but the “coprecipitation method” was selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” was employed in the method for producing the precursor of the lithium transition metal composite oxide according to the present embodiment.

In the method for producing a precursor of the lithium transition metal composite oxide according to the present embodiment, a raw material aqueous solution containing Ni, Co and Mn is dropped, and a compound containing Ni, Co and Mn is coprecipitated in the solution. It is preferred that the precursor be prepared by heating.
In preparing a coprecipitated precursor, Mn among Ni, Co and Mn is easily oxidized, and it is not easy to prepare a coprecipitated precursor in which Ni, Co and Mn are uniformly distributed in a divalent state. , Ni, Co and Mn at the atomic level tend to be insufficient. Therefore, in the present invention, it is preferable to remove dissolved oxygen in order to suppress the oxidation of Mn distributed in the coprecipitated precursor. As a method of removing dissolved oxygen, a method of bubbling a gas containing no oxygen can be used. The gas containing no oxygen (O ₂ ) is not limited, but a nitrogen gas, an argon gas, a carbon dioxide (CO ₂ ) gas, or the like can be used.

The pH in the step of preparing a precursor by coprecipitating a compound containing Ni, Co and Mn in a solution is not limited. In this case, the pH can be adjusted to 9 or more and 12 or less. In order to increase the tap density of the precursor and the composite oxide, it is preferable to control the pH. When the pH is 11.5 or less, the tap density of the composite oxide can be 1.00 g / cm ³ or more, and high-rate discharge performance can be improved. Further, by setting the pH to 11.0 or less, the particle growth can be promoted, so that the stirring continuation time after the completion of the dropwise addition of the raw material aqueous solution can be shortened.

The transition metal compound is a transition metal hydroxide precursor produced by a coprecipitation method in which a raw material compound containing Ni and Mn or a raw material compound containing Ni, Co and Mn is reacted in an aqueous solution having a pH of 10.2 or less. Is more preferred. By setting the pH to 10.2 or less, the particle growth can be promoted, so that the stirring continuation time after the end of the dropwise addition of the raw material aqueous solution can be shortened, and the crystal structure containing αMe (OH) ₂ and βMe (OH) ₂ can be reduced. Can be produced. The precursor having a crystal structure containing αMe (OH) ₂ and βMe (OH) ₂ has a higher tap density than a precursor having a crystal structure of αMe (OH) ₂ single phase or βMe (OH) ₂ single phase. Can be larger. An electrode manufactured using a precursor having a high tap density can increase the press density, and thus can reduce the resistance of the electrode. If the pH is too low, it becomes a precursor of αMe (OH) ₂ single phase, so that the reaction pH preferably exceeds 9.

In the case of producing a hydroxide precursor, an alkali solution containing an alkali metal hydroxide, a complexing agent, and a reducing agent is added to a reaction vessel kept alkaline in addition to a solution containing a transition metal (Me). Thus, it is preferable to coprecipitate the transition metal hydroxide.
As the complexing agent, ammonia, ammonium sulfate, ammonium nitrate and the like can be used, and ammonia is preferable. A precursor having a higher tap density can be produced by a crystallization reaction using a complexing agent.
It is preferred to use a reducing agent together with the complexing agent. As the reducing agent, hydrazine, sodium borohydride and the like can be used, and hydrazine is preferable.
As the alkali metal hydroxide (neutralizing agent), sodium hydroxide, lithium hydroxide or potassium hydroxide can be used.

When the coprecipitated precursor is to be prepared as a coprecipitated carbonate precursor, the pH can be adjusted to 7.5 or more and 11 or less. By setting the pH to 9.4 or less, the tap density of the composite oxide can be 1.25 g / cm ³ or more, and high-rate discharge performance can be improved. Further, by adjusting the pH to 8.0 or less, the particle growth can be promoted, so that the stirring continuation time after completion of the dropwise addition of the raw material aqueous solution can be reduced.

The raw materials of the coprecipitation precursor include nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate and the like as a Ni source, cobalt sulfate, cobalt nitrate, cobalt acetate and the like as a Co source, and a Mn source. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate and the like.

While the raw material aqueous solution of the transition metal compound is supplied dropwise, a mixed alkali solution containing an alkali metal hydroxide (neutralizing agent) such as sodium hydroxide, a complexing agent such as ammonia, and a reducing agent such as hydrazine is used. The method of dropping appropriately is preferable. The concentration of the alkali metal hydroxide to be dropped is preferably 1.0 M or more and 8.0 M or less. The concentration of the complexing agent is preferably at least 0.4M, more preferably at least 0.6M. Further, it is preferably 2.0 M or less, more preferably 1.6 M or less, and even more preferably 1.5 M or less. The concentration of the reducing agent is preferably 0.05 M or more and 1.0 M or less, and more preferably 0.1 or more and 0.5 M or less. The tap density of the hydroxide precursor can be increased by lowering the pH of the reaction vessel and adjusting the concentration of ammonia (complexing agent) to 0.6 M or more.

滴下 The dripping speed of the raw material aqueous solution greatly affects the uniformity of element distribution within one particle of the generated coprecipitated precursor. The preferred dropping rate is affected by the size of the reaction tank, stirring conditions, pH, reaction temperature and the like, but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping speed is more preferably 10 mL / min or less, most preferably 5 mL / min or less.

Further, when a complexing agent such as NH ₃ is present in the reaction tank and a certain convection condition is applied, after the completion of the dropping of the raw material aqueous solution, the stirring is further continued, so that the rotation of the particles and the rotation in the stirring tank are performed. The revolution is promoted, and in this process, the particles gradually grow concentrically spherically while colliding with each other. That is, the coprecipitation precursor undergoes a two-stage reaction of a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction in which the metal complex is generated while the metal complex stays in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle diameter can be obtained by appropriately selecting the time during which stirring is continued after the completion of the dropwise addition of the raw material aqueous solution.

The preferable duration of stirring after completion of the dropwise addition of the raw material aqueous solution is affected by the size of the reaction tank, the stirring conditions, the pH, the reaction temperature, etc., but is preferably 0.5 h or more in order to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery becomes insufficient due to the particle diameter being too large, the length is preferably 15 h or less, more preferably 10 h or less, and most preferably 5 h or less.

Further, it is preferable that the cumulative volume in the particle size distribution of the hydroxide precursor and the lithium transition metal composite oxide in the particle size distribution is D50, which is 50%, of 13 μm or less. For this purpose, for example, when the pH is controlled to 9.1 to 10.2, the stirring duration is preferably 1 h to 3 h.

粒子 When the hydroxide precursor particles are prepared using a sodium compound such as sodium hydroxide as a neutralizing agent, it is preferable to wash and remove sodium ions attached to the particles in a subsequent washing step. For example, when the prepared hydroxide precursor is removed by suction filtration, a condition that the number of times of washing with 500 mL of ion-exchanged water is set to 6 or more can be adopted.

<Production method of lithium transition metal composite oxide>
The method for producing the positive electrode active material of the nonaqueous electrolyte secondary battery according to this embodiment is a method in which the coprecipitated precursor (transition metal compound) produced as described above and a lithium compound are mixed and fired. Is preferred.
In the method for manufacturing a positive electrode active material according to the second embodiment, the lithium transition metal composite oxide contains Ni and Mn, or Ni, Co, and Mn, and the molar ratio of Mn to Me, Mn / Me, is Mn / Me ≧ M. It can be produced by mixing a transition metal compound of 0.45 with a Li compound and firing the mixture.
In the method for producing a positive electrode active material according to the third embodiment, the lithium transition metal composite oxide contains Ni and Mn, or Ni, Co and Mn, and the molar ratio of Mn to Me, Mn / Me, is 0.3 ≦ M. It can be produced by mixing a transition metal compound satisfying Mn / Me <0.55 with a Li compound, followed by firing.
As the Li compound to be mixed with the transition metal compound, lithium hydroxide, lithium nitrate, lithium carbonate, lithium acetate and the like can be used.

When the transition metal compound and the Li compound are mixed and fired, a sintering aid may be used. In the third embodiment, it is preferable to add a sintering aid. As a sintering aid, lithium fluoride (LiF), lithium carbonate (Li ₂ CO ₃ ), sodium fluoride (NaF), sodium chloride (NaCl), lithium sulfate (Li ₂ SO ₄ ), lithium phosphate (Li) It is preferable to use ₃ PO ₄ ), lithium chloride (LiCl), magnesium chloride (MgCl ₂ ) or calcium chloride (CaCl ₂ ). As described above, lithium carbonate is used as a Li compound for producing a lithium transition metal composite oxide, but as in the examples described later, when lithium hydroxide is used as the lithium compound, Lithium carbonate functions as a sintering aid. It is preferable that the addition ratio of these sintering aids is 1 mol% or more and 10 mol% or less based on the total amount of the Li compound. Note that the total amount of the Li compound is preferably charged in excess of about 1 mol% to about 5 mol% in view of the fact that part of the Li compound disappears during firing.

The firing temperature affects the charge / discharge cycle performance of the positive electrode active material.
If the firing temperature is too low, crystallization does not proceed sufficiently, and the charge / discharge cycle performance tends to decrease. In one embodiment of the present invention, the firing temperature is preferably set to 800 ° C. or higher. By setting the temperature to 800 ° C. or higher, active material particles having high crystallinity can be obtained, and charge / discharge cycle performance can be improved.

On the other hand, if the firing temperature is too high, a structural change occurs from the layered α-NaFeO ₂ structure to a rock-salt cubic structure, which is disadvantageous to the movement of lithium ions in the active material during the charge / discharge reaction, and the charge / discharge cycle performance is reduced. descend. In the present invention, the firing temperature is preferably set to 1000 ° C. or lower. By controlling the temperature to 1000 ° C. or lower, active material particles in which the structural change to the rock salt type cubic structure is suppressed can be obtained, and the charge / discharge cycle performance can be improved.
Therefore, when preparing the positive electrode active material containing the lithium transition metal composite oxide according to the present embodiment, the firing temperature is preferably set to 800 ° C. or higher and 1000 ° C. or lower to improve the charge / discharge cycle performance. The temperature is more preferably from 850 ° C to 1000 ° C, and even more preferably from 850 ° C to 950 ° C.

The surface of the primary particles and / or secondary particles of the lithium transition metal composite oxide obtained by firing is coated with a different element in order to obtain a positive electrode active material having a high energy density retention rate and improved Coulomb efficiency. And / or may form a solid solution. An example of the different element is an aluminum compound.
In order to coat the aluminum compound, a method in which the synthesized lithium transition metal composite oxide particles are charged into an aqueous solution of a compound containing aluminum (sulfate, nitrate, acetate, etc.) can be adopted. This aqueous solution is preferably acidic. However, the order of input is not limited to this. For example, a method may be employed in which an aqueous solution of a compound containing aluminum is charged into lithium transition metal composite oxide particles dispersed in water. Further, after or when the lithium transition metal composite oxide is charged into the aqueous solution containing aluminum, a pH adjuster may be charged. The pH adjuster is not limited as long as it is an alkaline solution. Examples of the alkaline solution include a NaOH aqueous solution and a KOH aqueous solution. The pH value adjusted by adding the pH adjuster can be appropriately selected.
The particles to which the aluminum compound has been added are separated by filtration or the like, and the obtained particles are preferably dried at 80 ° C or more and 120 ° C or less. By performing the heat treatment in the inside, lithium transition metal composite oxide particles having an oxide containing aluminum on the particle surface can be obtained.
When the aluminum compound is coated on the surface of the lithium transition metal composite oxide particles, the aluminum compound is preferably contained in an amount of 0.1% by mass or more and 0.7% by mass or less with respect to the lithium transition metal composite oxide. When the content is more preferably 0.2% by mass or more and 0.6% by mass or less, the effect of further improving the energy density maintenance ratio and the effect of improving the Coulomb efficiency are more sufficiently exhibited.

<Acid treatment of positive electrode active material>
In the method for manufacturing a positive electrode active material according to the second embodiment, the positive electrode active material having the discharge capacity ratio a / b of 17 ≦ a / b ≦ 25 is a lithium transition metal composite synthesized by the above method. The oxide can be produced by treating the oxide with an acid having a pKa ₁ of 3.1 or more. Acids having a pKa ₁ of 3.1 or more include boric acid (pKa ₁ = 9.14), citric acid (pKa ₁ = 3.1), tartaric acid (pKa ₁ = 3.2), and malic acid (pKa ₁ = 3.4), acetic acid (pKa ₁ = 4.74) and the like. By pKa ₁ is surface treated with lithium-excess active material used at the right concentrations 3.1 or more acid, under conditions that do not overcharge chemical, the active material and discharge capacity was improved than an equivalent or untreated In addition, the initial coulomb efficiency and the high rate discharge performance can be improved.

Although second detailed mechanism of action of acid treatment in the manufacturing method of the active material in accordance with the embodiment is unknown, acid described above, since the pKa ₁ is 3.1 or more, the lithium ions are hydrogen in the active material It is unlikely to be replaced by ions, and it is unlikely that the molar ratio Li / Me of lithium and the transition metal of the active material will fluctuate significantly. Therefore, the acid treatment with a strong acid such as hydrochloric acid, phosphoric acid, or sulfuric acid having a small pKa ₁ replaces lithium ions with hydrogen ions (Li has been removed), whereby the above molar ratio Li of the active material before and after the treatment is reduced. It is presumed that a mechanism different from the examples described in Table 1 of Patent Literature 7 and Table 1 of Patent Literature 8 in which / Me is reduced or the description in paragraph [0159] of Patent Literature 11 is working.
According to the experimental examples described below, the active material subjected to the acid treatment according to the present embodiment has a voltage of 4.35 V (vs. Li ^/ Li ⁺ ) to 3.0 V (vs. Li / li ⁺⁾ ratio a / b of the discharge capacity up to (a) and 3.0 V (discharge capacity from vs.Li/Li ⁺⁾ to 2.0V (vs.Li/Li ⁺⁾ (b) is reduced (The discharge capacity b was relatively increased), and the specific surface area was moderately increased. Since it is known that the discharge capacity b appears characteristically in the spinel structure, this acid treatment brings about an appropriate spinel-like crystal structure on the surface of the lithium-rich type active material, thereby making it irreversible during the first charge / discharge. It is presumed that the capacity is reduced to improve the initial coulomb efficiency.
In addition, it is speculated that the increase in the BET specific surface area resulted in moderate irregularities on the particle surface, promoting electrolyte penetration and lithium ion diffusion, improving initial coulombic efficiency, and improving high-rate discharge performance. . The BET specific surface area is preferably 6 m ² / g or less.

The specific procedure of the acid treatment is as follows.
5.0 g of the lithium transition metal composite oxide is added to 200 mL of a predetermined acid aqueous solution having a predetermined hydrogen ion concentration, and the temperature of the aqueous solution is maintained at 50 ° C. and stirred at 400 rpm for 2 hours using a stirrer. After stirring, the lithium transition metal composite oxide is filtered using a suction device, washed with ion-exchanged water, and dried at 80 ° C. overnight under normal pressure.

<Negative electrode material>
The negative electrode material of the battery according to the present embodiment is not limited, and a material capable of inserting and extracting lithium ions can be appropriately selected. For example, lithium composite oxides such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , metallic lithium, and lithium alloys (lithium-silicon, lithium-aluminum, lithium -Metallic lithium-containing alloys such as lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys); metals capable of occluding and releasing lithium; metals such as antimony and tin; alloys of these; silicon oxide And metal oxides such as tin oxide, and carbon materials (eg, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, and the like).

<Positive electrode / negative electrode>
The positive electrode active material and the negative electrode material are preferably powders having an average particle size of 100 μm or less. In particular, the powder of the positive electrode active material is preferably 15 μm or less to improve the high output characteristics of the nonaqueous electrolyte secondary battery, and is preferably 10 μm or more to maintain the charge / discharge cycle performance. . In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For the pulverization, for example, a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air jet mill, a sieve, and the like are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. The classification method is not particularly limited, and a sieve, an air classifier, or the like is used as needed in both dry and wet methods.

As described above, the positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail.In addition to the main components, the positive electrode and the negative electrode have a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituent components.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (scale graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon black, acetylene black, Conductive materials such as Ketjen black, carbon whiskers, carbon fibers, metal (copper, nickel, aluminum, silver, gold, etc.) powders, metal fibers, and conductive ceramic materials can be included as one type or a mixture thereof. .

中で Among these, acetylene black is preferred as the conductive agent from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by mass or more and 50% by mass or less, particularly preferably 0.5% by mass or more and 30% by mass or less based on the total mass of the positive electrode or the negative electrode. In particular, it is preferable to use acetylene black after being pulverized into ultrafine particles having a size of 0.1 μm or more and 0.5 μm or less, because the required carbon amount can be reduced. These mixing methods are physical mixing, and ideally, homogeneous mixing. Therefore, it is possible to perform dry or wet mixing using a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, and a planetary ball mill.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene-butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used alone or as a mixture of two or more. The addition amount of the binder is preferably from 1% by mass to 50% by mass, more preferably from 2% by mass to 30% by mass, based on the total mass of the positive electrode or the negative electrode.

The filler is not limited as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by mass or less based on the total mass of the positive electrode or the negative electrode.

The positive electrode and the negative electrode are obtained by mixing the above main components (a positive electrode active material in the positive electrode, a negative electrode material in the negative electrode), and other materials with an organic solvent such as N-methylpyrrolidone, toluene, or water. The mixed solution is applied onto a current collector described in detail below, or pressed and pressed, and heated at a temperature of about 50 ° C. to about 250 ° C. for about 2 hours to form a mixture layer. Is done. For the application method, for example, roller coating such as an applicator roll, screen coating, doctor blade system, spin coating, it is preferable to apply to any thickness and any shape using a bar coater or the like, It is not limited.

電 A current collector foil such as an aluminum foil or a copper foil can be used as the current collector. The current collector of the positive electrode is preferably an aluminum foil, and the current collector of the negative electrode is preferably a copper foil. The thickness of the current collector is preferably 10 μm or more and 30 μm or less. Further, the thickness of the mixture layer is preferably 40 μm or more and 150 μm or less (excluding the thickness of the current collector).

<Non-aqueous electrolyte>
The non-aqueous electrolyte used for the non-aqueous electrolyte secondary battery according to the present embodiment is not limited, and those generally proposed for use in a lithium battery or the like can be used.
Examples of the non-aqueous solvent used for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate or fluorides thereof; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate , Diethyl carbonate, ethyl methyl carbonate, etc., linear carbonates; methyl formate, methyl acetate, methyl butyrate, etc., linear esters; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2- Ethers such as dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide or derivatives thereof alone or two or more of them And the like.

The non-aqueous electrolyte according to the first embodiment preferably contains a fluorinated cyclic carbonate as the non-aqueous solvent. When a nonaqueous electrolyte containing a fluorinated cyclic carbonate is used as the nonaqueous solvent, an increase in AC resistance after storage can be suppressed. Examples of the fluorinated cyclic carbonate include 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate and the like. Above all, it is preferable to use 4-fluoroethylene carbonate (FEC) from the viewpoint that battery swelling due to generation of gas in the battery can be suppressed.
The content of the fluorinated cyclic carbonate is preferably from 3% to 30% by volume in the non-aqueous solvent, more preferably from 5% to 25%.

It is preferable that a compound having an oxalate group bonded to boron is added to the nonaqueous electrolyte according to the first embodiment. A compound having an oxalate group bonded to boron has an effect of reducing initial AC resistance, and can improve output characteristics of a nonaqueous electrolyte secondary battery using a lithium-rich type active material for a positive electrode.

Compounds having an oxalate group bonded to boron include lithium bisoxalate borate (LiBOB), lithium difluoro (oxalato) borate (LiDFOB), and (3-methyl-2,4-pentanedionato) oxalatoborate (MOAB) ) And the like. The chemical structural formulas of the compounds having each oxalate group are shown below.

Lithium bis oxalate borate (LiBOB)

Lithium difluoro (oxalato) borate (LiDFOB)

(3-Methyl-2,4-pentanedionato) oxalatoborate (MOAB)

The lower limit of the addition amount of the compound having an oxalate group bonded to boron is preferably 0.1% by mass or more based on the total mass of the components other than the electrolyte salt constituting the nonaqueous electrolyte for improving the charge / discharge cycle performance. , More preferably 0.2% by mass or more, and the upper limit is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, in order to reduce the possibility of an increase in resistance.

<Method of measuring initial AC resistance>
In this specification, the measurement of the initial AC resistance is performed under the following conditions. The measurement is performed on a non-aqueous electrolyte secondary battery that has been subjected to liquid injection and initial charge / discharge and is in a factory shipping state. Prior to the measurement, the battery is charged and discharged at 25 ° C. with a current of 0.1 C in a predetermined voltage range, and then an open circuit is established and left for 2 hours or more. By the above operation, the non-aqueous electrolyte secondary battery is completely discharged. The resistance between the positive and negative terminals is measured using an impedance meter of a type that applies an alternating current (AC) of 1 kHz, and this is defined as “initial AC resistance (mΩ)”. Non-aqueous electrolyte secondary batteries that have been overcharged or overdischarged shall not be measured.

<Method of measuring AC resistance after storage>
In this specification, the storage test and the measurement of the AC resistance after storage are performed under the following conditions. The non-aqueous electrolyte secondary battery is charged at 25 ° C. to a predetermined voltage at 0.1 C to make the battery fully charged. Then, it is left at 45 ° C for 15 days. Next, after performing a constant current discharge to a predetermined voltage with a current of 0.2 C, the circuit is opened and left for 2 hours or more. By the above operation, the non-aqueous electrolyte secondary battery is completely discharged. The resistance value between the positive and negative terminals is measured at 25 ° C. using an impedance meter of a type that applies an alternating current (AC) of 1 kHz. Non-aqueous electrolyte secondary batteries that have been overcharged or overdischarged shall not be measured.

Additives generally used for non-aqueous electrolytes may be added to the non-aqueous electrolyte as long as the effects of the present invention are not impaired. For example, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenylether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluorobenzene Fluorinated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole and 3,5-difluoroanisole Overcharge inhibitors such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itacone anhydride Negative electrode film forming agents such as cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, propene sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, Dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4′-bis (2,2-dioxo-1,3,2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2 -Dioxo-1,3,2-dioxathiolane, thioanisole, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, triphosphate Trimethylsilyl, may be added tetrakis trimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate and the like alone or in admixture of two or more in a non-aqueous electrolyte.
The amount of these additives in the non-aqueous electrolyte is not particularly limited, but is preferably 0.01% by mass or more, and more preferably 0% by mass or more, based on the entire components other than the electrolyte salt constituting the non-aqueous electrolyte. 0.1% by mass or more, more preferably 0.2% by mass or more, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less. The purpose of adding these is to improve charge / discharge efficiency, suppress increase in resistance, suppress battery swelling, improve charge / discharge cycle performance, and the like.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, and NaBr. , KClO ₄ , KSCN, etc., inorganic ion salts containing one kind of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅₎ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NCLO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, stearyl Organic ionic salts such as lithium sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, and the like can be mentioned, and these ionic compounds can be used alone or in combination of two or more.

Further, by mixing LiPF ₆ or LiBF ₄ with a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. It is more preferable that the low-temperature characteristics can be further improved and self-discharge can be suppressed.

常 Also, a room temperature molten salt or an ionic liquid may be used as the non-aqueous electrolyte.

The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 5 mol / L or less, more preferably 0.5 mol / L in order to reliably obtain a non-aqueous electrolyte secondary battery having high battery characteristics. L and 2.5 mol / L or less.

<Separator>
As the separator used in the nonaqueous electrolyte secondary battery according to the present embodiment, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte secondary battery include, for example, polyolefin resins represented by polyethylene, polypropylene, etc., polyester resins represented by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene fluoride, vinylidene fluoride -Hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer , Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinyl fluoride Den - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. The porosity is preferably 20% by volume or more from the viewpoint of charge and discharge characteristics.

セパレータ Alternatively, the separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride and the like, and a non-aqueous electrolyte. It is preferable to use the non-aqueous electrolyte in a gel state as described above, since it has an effect of preventing liquid leakage.

Further, it is preferable that the separator be used in combination with the above-described porous membrane, nonwoven fabric, or the like and a polymer gel because the liquid retention of the nonaqueous electrolyte is improved. That is, by forming a film coated with a solvent-philic polymer having a thickness of several μm or less on the surface of the polyethylene microporous membrane and the wall surface of the micropore, and holding a non-aqueous electrolyte in the micropores of the film, The conductive polymer gels.

Examples of the above-mentioned solvent-philic polymer include polymers crosslinked with polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a monomer having an isocyanate group, and the like. The monomer can be subjected to a crosslinking reaction by using heating or ultraviolet rays (UV) in combination with a radical initiator, or by using an actinic ray such as an electron beam (EB).

端子 Other components of the battery include a terminal, an insulating plate, a battery case, and the like. These components may be the same as those conventionally used.

<Non-aqueous electrolyte secondary battery>
FIG. 10 shows a nonaqueous electrolyte secondary battery according to this embodiment. FIG. 10 is a perspective view of the inside of the container of the rectangular non-aqueous electrolyte secondary battery as seen through. The non-aqueous electrolyte secondary battery 1 is assembled by injecting a non-aqueous electrolyte (electrolyte solution) into the battery container 3 in which the electrode group 2 is stored. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive terminal 4 via a positive electrode lead 4 ', and the negative electrode is electrically connected to the negative terminal 5 via a negative electrode lead 5'.
The shape of the nonaqueous electrolyte secondary battery according to the embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery.

Non-aqueous electrolyte secondary batteries are generally completed by injecting and sealing an electrolyte, and then being charged and discharged a plurality of times in a factory, before being shipped.
The non-aqueous electrolyte secondary battery according to this embodiment has an initial charge / discharge (production process) of 4.5 (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less in the initial charge / discharge process before shipment from the factory. The battery is shipped without any charging until the charging process in which the region where the potential change is flat is observed within the positive electrode potential range.

The fact that the nonaqueous electrolyte secondary battery according to the present embodiment does not have a history of charging until the charging process in which the flat region is observed is completed means that the positive electrode active material of the battery is the CuKα. In the X-ray diffraction diagram using X-rays, a diffraction peak is observed in a range of 20 ° or more and 22 ° or less, or the battery is charged at a positive electrode potential of 5.0 V (vs. Li ^/ Li ⁺ ). When the test was performed, a region where the potential change was flat with respect to the amount of charged electricity was observed in the positive electrode potential range of 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less. Can be confirmed. The details of these confirmation methods are as described above.
In the third embodiment, since the potential change has a flat region, the amount of charge per unit volume in the overcharge region increases, so that a sharp increase in the battery voltage is observed up to a higher SOC. Not done.

<Calculation method of discharge capacity and charge electricity per volume>
In this specification, the measurement conditions of the press density are as follows. The measurement is performed in the air at room temperature of 20 ° C. or more and 25 ° C. or less. FIG. 11 shows a conceptual diagram of an apparatus used for measuring the press density. A pair of measurement probes 1A and 1B are prepared. The measuring probes 1A and 1B have measuring surfaces 2A and 2B obtained by flattening one end of a stainless steel (SUS304) cylinder having a diameter of 8.0 mm (± 0.05 mm), and the other end thereof is a stainless steel pedestal 3A. , 3B in which the column is fixed vertically. A side body 6 having a through-hole 7 polished and provided with an inner diameter adjusted at the center of an acrylic cylinder so that the stainless steel cylinder can naturally descend slowly in the air by gravity is prepared. The upper and lower surfaces of the side body 6 are polished smoothly.
One of the measurement probes 1A is placed on a horizontal desk such that the measurement surface 2A faces upward, and the column of the measurement probe 1A is inserted into the through hole 7 of the side body 6 so as to cover the side body 6 from above. insert. The other measurement probe 1B is inserted from above the through hole 7 with the measurement surface 2B facing down, and the distance between the measurement surfaces 2A and 2B is set to zero. At this time, the distance between the pedestal 3B of the measurement probe 1B and the pedestal 3A of the measurement probe 1A is measured using calipers.

Next, the measurement probe 1B is pulled out, 0.3 g of the powder of the sample to be measured (positive electrode active material powder) is injected from above the through hole 7 with a spoon, and the measurement probe 1B is again placed with the measurement surface 2B down. It is inserted from above the through hole 7. Using a manual hydraulic press equipped with a pressure gauge, pressure is applied from above the measurement probe 1B until the pressure applied to the active material reaches a value calculated as 40 MPa. After the scale reaches the numerical value, no additional pressurization is performed even if the value indicated by the scale decreases. Thereafter, in this state, the distance between the pedestal 3B of the measurement probe 1B and the pedestal 3A of the measurement probe 1A is measured again by using a caliper. From the difference (cm) from the distance before the sample to be measured, the area of the measurement surface (0.5024 cm ² ), and the amount of the sample to be measured (0.3 g), the density of the sample to be measured in a pressurized state Is calculated, and this is defined as the press density (g / cm ³ ). The pressure applied to the active material is calculated from the relationship between the area of the contact portion with the jig and the area of the measurement surface (the contact area with the powder).
The discharge capacity per unit volume and the charge amount per unit volume are calculated by multiplying the press density of the positive electrode active material powder measured as described above by the discharge capacity per unit mass and the charge amount per unit amount.

非 The nonaqueous electrolyte secondary battery of the present embodiment can also be realized as a power storage device in which a plurality of batteries are assembled. FIG. 12 illustrates an example of a power storage device. 12, power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

The non-aqueous electrolyte secondary battery according to the present embodiment is manufactured without passing through the charging process until the overcharge region ends, and is used without performing charging until the overcharge region ends. It is assumed that it will be. It is preferable that the charging voltage used during the manufacturing process and during the use during the manufacturing be set such that the maximum attainable potential reached by the positive electrode by the charging, that is, the upper charging limit potential is equal to or lower than the potential at which the overcharge region starts. It is preferable that the upper limit charging potential in the initial charge / discharge step and the upper limit charging potential in use are less than 4.5 V (vs. Li ^/ Li ⁺ ). The upper limit charging potential can be, for example, 4.40 V (vs. Li ^/ Li ⁺ ). The charging upper limit voltage may be 4.38V (vs.Li/Li ^+), may be ^{4.36V (vs.Li/Li +), 4.34V (} vs.Li/Li + ) Or 4.32 V (vs. Li / Li ⁺ ).

(Experimental example 1)
(Example 1-1)
<Preparation of lithium transition metal composite oxide>
284 g of nickel sulfate hexahydrate, 303 g of cobalt sulfate heptahydrate, and 443 g of manganese sulfate pentahydrate were weighed and dissolved in 4 L of ion-exchanged water, and the molar ratio of Ni: Co: Mn was 27: A 1.0 M aqueous sulfate solution at 27:46 was prepared.
Next, 2 L of ion-exchanged water was poured into a 5 L reaction vessel, and oxygen contained in the ion-exchanged water was removed by bubbling argon gas for 30 minutes. The temperature of the reaction tank was set to 50 ° C. (± 2 ° C.), and the convection was sufficiently generated in the reaction tank while stirring the inside of the reaction tank at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor. did. The sulfate aqueous solution was dropped into the reaction tank at a rate of 3 mL / min. Here, from the start to the end of the dropping, the pH in the reaction vessel is adjusted by appropriately dropping a mixed alkali aqueous solution composed of 4.0 M sodium hydroxide, 0.5 M ammonia, and 0.2 M hydrazine. Control was performed so that 9.8 (± 0.1) was always maintained, and a part of the reaction solution was discharged by overflow so that the total amount of the reaction solution was always controlled so as not to exceed 2 L. After the completion of the dropwise addition, the stirring in the reaction tank was continued for another 3 hours. After stopping the stirring, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours in an air atmosphere under normal pressure. Then, in order to make the particle size uniform, the mixture was ground for several minutes in an automatic mortar made of agate. Thus, a hydroxide precursor was produced.

To 1.852 g of the hydroxide precursor, 0.971 g of lithium hydroxide monohydrate was added and mixed well using an automatic mortar made of agate. The molar ratio of Li: (Ni, Co, Mn) was 130: A mixed powder was prepared to be 100. Using a pellet molding machine, the mixture was molded at a pressure of 6 MPa to obtain a pellet having a diameter of 25 mm. The amount of the mixed powder used for the pellet molding was determined by converting the mass of the assumed final product to 2 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, and was placed in a box-type electric furnace (model number: AMF20). It was calcined at ℃ for 5 h. The inner dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the electric furnace was turned off, and the alumina boat was allowed to cool naturally while remaining in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the cooling rate thereafter is somewhat slow. After a day and a night, it was confirmed that the temperature of the furnace was 100 ° C. or lower, and then the pellets were taken out and lightly crushed in an agate mortar to make the particle diameter uniform.
Thus, a lithium transition metal composite oxide Li _1.13 Ni _0.235 Co _0.235 Mn _0.40 O ₂ was produced.

<Confirmation of crystal structure>
The lithium transition metal composite oxide was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (manufactured by Rigaku Corporation, model name: MiniFlex II), and it was confirmed that it had an α-NaFeO ₂ type crystal structure.

<Preparation of positive electrode>
N-methylpyrrolidone is used as a dispersion medium, the lithium transition metal composite oxide (hereinafter referred to as “LR”) is used as an active material, and the active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) have a mass ratio of 90: A coating positive electrode paste kneaded and dispersed in a ratio of 5: 5 was prepared. The positive electrode paste for application was applied to one surface of an aluminum foil current collector having a thickness of 20 μm, dried, and then pressed to produce a positive electrode according to Example 1-1.

<Preparation of negative electrode>
A negative electrode was prepared by disposing a metallic lithium foil on a nickel current collector. The amount of metallic lithium was adjusted so that the capacity of the battery when combined with the positive electrode was not limited by the negative electrode.

<Assembly of non-aqueous electrolyte secondary battery>
Using the positive electrode according to Example 1-1, a nonaqueous electrolyte secondary battery was assembled in the following procedure.
LiPF ₆ was dissolved in a mixed solvent of 4-fluoroethylene carbonate (FEC) / propylene carbonate (PC) / ethyl methyl carbonate (EMC) at a volume ratio of 1: 1: 8 to a concentration of 1 mol / L. 0.5% by mass of lithium difluorophosphate (LiDFP) as an additive and 1% by mass of 4,4′-bis (2,2-dioxo-1,3,2-dioxathiolane) (compound A) based on 100% by mass of the solution % Was used as a non-aqueous electrolyte.
A polypropylene microporous membrane surface-modified with polyacrylate was used as a separator. A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) was used for the outer package. The positive electrode according to Example 1-1 and the negative electrode were housed in the package via the separator so that the open ends of the positive terminal and the negative terminal were exposed to the outside, and the metal bonding of the metal-resin composite film was performed. The non-aqueous electrolyte secondary battery is sealed by sealing hermetically sealed portions of the non-aqueous electrolyte except for the portion that becomes the injection hole, and after injecting the non-aqueous electrolyte, sealing the injection hole. Assembled.

<Initial charge / discharge step>
The assembled nonaqueous electrolyte secondary battery was subjected to an initial charge / discharge step at 25 ° C. The charging was performed at a constant current and constant voltage (CCCV) with a current of 0.1 C and a final voltage of 4.25 V. The condition for terminating the charging was a time when the current value attenuated to 1/6. The discharge was a constant current discharge at a current of 0.1 C and a cutoff voltage of 2.0 V. This charge / discharge was performed twice. Here, a resting step of 30 minutes was provided after charging and after discharging, respectively. When the negative electrode material is metallic lithium, the positive electrode potential and the battery voltage have almost the same value, and thus the positive electrode potential in the following procedure can be read as the battery voltage of the test battery. When the counter electrode is graphite, it is known that the potential of the positive electrode is obtained by adding about 0.1 V to the battery voltage in consideration of the potential of the graphite.
Through the above manufacturing steps, a non-aqueous electrolyte secondary battery according to Example 1-1 was completed.

(Comparative Example 1-1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1-1, except that a commercially available LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (hereinafter, referred to as “NCM523”) was used as a positive electrode active material. The battery was assembled and subjected to initial charge and discharge to complete a nonaqueous electrolyte secondary battery according to Comparative Example 1-1.

(Comparative Example 1-2)
A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1-1, and a constant current constant voltage (CCCV) charge having a final voltage of 4.6 V was performed only in the first charge in the initial charge / discharge step. The same initial charge / discharge process as in Example 1-1 was performed to complete a non-aqueous electrolyte secondary battery according to Comparative Example 1-2.

(Example 1-2)
358 g of the lithium transition metal composite oxide Li _1.13 Ni _0.235 Co _0.235 Mn _0.40 O ₂ produced in Example 1-1 was _charged into 200 mL of a 0.1 M aluminum sulfate aqueous solution, and a magnetic stirrer was used. And stirred for 30 seconds at 25 ° C. and 400 rpm. Thereafter, the mixture was separated into a powder and a filtrate by suction filtration. The obtained powder was dried in the air at 80 ° C. for 20 hours. Further, heat treatment was performed in the atmosphere of 400 ° C. for 4 hours using the above-mentioned box-type electric furnace. Thus, a lithium transition metal composite oxide (hereinafter, referred to as “LR-Al”) coated with an aluminum compound was produced. Except that this lithium transition metal composite oxide was used as the positive electrode active material, the assembly and initial charge and discharge of the nonaqueous electrolyte secondary battery were performed in the same manner as in Example 1-1. The water electrolyte secondary battery was completed.

<Confirmation of X-ray diffraction peak of positive electrode active material>
X-ray diffraction measurement was performed under the above-described conditions using the positive electrode mixture collected from the non-aqueous electrolyte secondary battery after the initial charge and discharge according to Example 1-1 and Comparative Example 1-2 under the above-described procedures and conditions. Was. In the positive electrode active material of Example 1-1, a diffraction peak was observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram using CuKα rays (see the lower part of FIG. 3). In the positive electrode active material of No. 2, it was confirmed that no diffraction peak was observed in the range of 20 ° or more and 22 ° or less (see the upper part of FIG. 3).

<Overcharge test>
Using the nonaqueous electrolyte secondary batteries according to Examples and Comparative Examples, constant current (CC) charging was performed at a current value of 10 mA per 1 g of the positive electrode mixture without setting an upper limit of the battery voltage. This charge corresponds to the third charge including the initial charge and discharge. Here, when the capacity at 4.45 V from the start of charging is X (mAh) and the capacity at each voltage is Y (mAh), Y / X * 100 is defined as the capacity ratio Z (%), and the positive electrode potential is The capacitance ratio Z (%) when the voltage soared and reached 5.1 V was recorded as "delay effect". In addition, the maximum value of dZ / dV was determined.

Table 1 shows the delay effect (%) in the overcharge test of the nonaqueous electrolyte secondary batteries according to Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2, and the maximum value of dZ / dV. .

According to Table 1, in the non-aqueous electrolyte secondary battery according to Comparative Example 1-1 including the positive electrode using NCM523, in the overcharge test, the positive electrode potential sharply increased when Z was 135%, and the voltage was increased to 5.1 V. Has been reached and the delay effect is not enough. This is because the positive electrode of the nonaqueous electrolyte secondary battery according to Comparative Example 1-1 had a positive electrode of 4.5 V (vs. Li ^/ Li ⁺ ) or more when charged without setting an upper limit of the voltage in the overcharge test. A region where the potential change is flat with respect to the charged amount of electricity is not observed in the positive electrode potential range of 5.0 V (vs. Li ^/ Li ⁺ ) or less (the maximum value of dZ / dV is less than 150). Related.
Further, the nonaqueous electrolyte secondary battery according to Comparative Example 1-2 was provided with a positive electrode using a lithium-rich type active material, but in the overcharge test, a sharp increase in the positive electrode potential was observed when Z was 130%. Also, the delay effect is not enough. This is because, in the initial charging / discharging step, the charging was performed so that the positive electrode potential reached 4.6 V (vs. Li ^/ Li ⁺ ). The amount of charge of the positive electrode of the nonaqueous electrolyte secondary battery according to Example 1-2 falls within the positive electrode potential range of 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less. Is not observed (a maximum value of dZ / dV is less than 150).
On the other hand, Examples 1-1 and 1-2 according to Examples 1-1 and 1-2 in which a positive electrode using a lithium-rich type active material was provided and the initial charge / discharge step was performed at a potential of less than 4.5 V (vs. Li / Li ⁺ ). In the non-aqueous electrolyte secondary battery, a superior retarding effect is observed as compared with Comparative Examples 1-1 and 1-2. This is because the positive electrode of the nonaqueous electrolyte secondary battery according to Examples 1-1 and 1-2 has a positive electrode of 4.5 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V (vs. Li ^/ Li ⁺ ) or less. This is related to the observation of a region where the potential change is flat with respect to the amount of charge in the potential range (the maximum value of dZ / dV is 150 or more).

Next, a non-aqueous electrolyte battery in which the composition of the non-aqueous electrolyte was changed from that of Example 1-1 or 1-2 was produced.

(Example 1-3)
Same as Example 1-1 except that the solvent of the non-aqueous electrolyte was changed to a mixed solvent of ethylene carbonate (EC) / propylene carbonate (PC) / ethyl methyl carbonate (EMC) in a volume ratio of 25: 5: 70. Then, the non-aqueous electrolyte secondary battery was assembled and initially charged and discharged to complete the non-aqueous electrolyte secondary battery according to Example 1-3.

(Example 1-4)
Example 1-1 The solvent of the nonaqueous electrolyte was changed in the same manner as in Example 1-3, and vinylene carbonate (VC) was further added as an additive in an amount of 0.2% by mass relative to the mass of the nonaqueous electrolyte. In the same manner as in the above, the non-aqueous electrolyte secondary battery was assembled and initially charged and discharged to complete the non-aqueous electrolyte secondary battery according to Example 1-4.

(Example 1-5)
The assembly of the non-aqueous electrolyte secondary battery and the initial charge and discharge were performed in the same manner as in Example 1-1, except that the solvent of the non-aqueous electrolyte was changed to a mixed solvent having a volume ratio of FEC / EMC of 20:80. Thus, a non-aqueous electrolyte secondary battery according to Example 1-5 was completed.

(Example 1-6)
The assembly of the non-aqueous electrolyte secondary battery and the initial charge and discharge were performed in the same manner as in Example 1-1, except that the solvent of the non-aqueous electrolyte was changed to a mixed solvent having a volume ratio of FEC / EMC of 5:95. Thus, a non-aqueous electrolyte secondary battery according to Example 1-6 was completed.

(Examples 1-7, 1-8)
Except that the positive electrode active material was changed to the lithium transition metal composite oxide (LR-Al) coated with the aluminum compound prepared in Example 1-2, the procedure was the same as in Examples 1-3 and 1-4, respectively. The nonaqueous electrolyte secondary battery was assembled and initially charged and discharged to complete the nonaqueous electrolyte secondary batteries according to Examples 1-7 and 1-8.

<Storage test>
The initial AC resistance of the nonaqueous electrolyte secondary batteries according to Examples 1-1 to 1-8 was measured under the above conditions. Thereafter, a storage test was performed under the conditions described above, and the AC resistance after storage was measured. The increase rate (%) of the AC resistance after storage with respect to the initial AC resistance was defined as “the resistance increase rate on the 15th day with respect to the initial state”. Table 2 shows the resistance increase rate (%) of the nonaqueous electrolyte secondary batteries according to Examples 1-1 to 1-8 on the 15th day from the initial stage.

According to Table 2, in Examples 1-1, 1-3 to 1-6 using LR as the positive electrode active material, the non-aqueous electrolytes according to Examples 1-3, 1-4 using the non-aqueous electrolyte containing no FEC were used. Compared with the water electrolyte secondary battery, the non-aqueous electrolyte secondary batteries according to Examples 1-1, 1-5, and 1-6 using the non-aqueous electrolyte containing FEC showed an increase in the AC resistance after storage. It turns out that it is suppressed. Further, in Examples 1-2, 1-7, and 1-8 using LR-Al as the positive electrode active material, examples 1-2-7 and 1-8 using the non-aqueous electrolyte containing no FEC were also used. Compared with the non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery according to Example 1-2 using the non-aqueous electrolyte containing FEC suppresses an increase in the AC resistance after storage. .

Next, an example in which the additive of the non-aqueous electrolyte is changed will be described.
(Example 1-9)
100 mass of a solution obtained by dissolving LiPF ₆ in a mixed solvent of ethylene carbonate (EC) / propylene carbonate (PC) / ethyl methyl carbonate (EMC) in a volume ratio of 25: 5: 70 so as to have a concentration of 1 mol / L. %, And 1.0% by mass of only compound A was used as an additive.
Application using graphite as a negative electrode active material in a mass ratio of graphite: styrene-butadiene rubber (SBR): carboxymethylcellulose (CMC) = 97: 2: 1 (in terms of solid content), and using water as a solvent. A negative electrode paste was prepared, applied to one surface of a 10 μm-thick strip-shaped copper foil current collector, and dried. This was pressurized by a roller press, and then dried under reduced pressure at 100 ° C. for 12 hours to remove water from the electrode plate. Thus, a negative electrode was manufactured.
A non-aqueous electrolyte secondary battery according to Example 1-9 was assembled in the same manner as in Example 1-3 except that the non-aqueous electrolyte and the negative electrode were used. Was completed. When the first and second charges in the initial charge / discharge step are constant current constant voltage (CCCV) charge with a final voltage of 4.25 V, the potential of the graphite negative electrode in the fully charged state is 0.1 V (vs. Li / Li). ⁺ ), And the positive electrode potential has reached about 4.35 V (vs. Li / Li ⁺ ).

(Examples 1-10 to 1-12)
As an additive, the procedure was performed except that LiDFOB was added in 0.2%, 0.5% and 1.0% by mass together with 1.0% by mass of compound A instead of 1.0% by mass of compound A, respectively. In the same manner as in Example 1-9, the nonaqueous electrolyte secondary batteries according to Examples 1-10 to 1-12 were completed.

(Examples 1-13 and 1-14)
Nonaqueous electrolyte secondary batteries according to Examples 1-13 and 1-14 were fabricated in the same manner as in Example 1-11, except that LiDFOB was changed to LiBOB and MOAB, respectively, as additives.

(Comparative Examples 1-3 to 1-6)
In the initial charge / discharge step, the first and second charges were performed at a constant current / constant voltage (CCCV) charge with a final voltage of 4.5 V, respectively, except that the charge was performed in Examples 1-9, 1-11, 1-13, and 1- 1, respectively. In the same manner as in No. 14, non-aqueous electrolyte secondary batteries according to Comparative Examples 1-3 to 1-6 were produced. Note that the potential of the graphite negative electrode in the fully charged state in the initial charge / discharge step is about 0.1 V (vs. Li ^/ Li ⁺ ), and the positive electrode potential reaches about 4.6 V (vs. Li ^/ Li ⁺ ). I have.

The initial AC resistance of the nonaqueous electrolyte secondary batteries according to Examples 1-9 to 1-14 and Comparative Examples 1-3 to 1-6 was measured, and a compound having an oxalate group bonded to boron was included as an additive. In the case where there is no (the non-aqueous electrolyte secondary batteries according to Example 1-9 and Comparative Example 1-3), the rate of increase / decrease of the initial AC resistance of the non-aqueous electrolyte secondary battery containing the additive with respect to the initial AC resistance is referred to as “resistance increase / decrease”. % /% ". The results are shown in Table 3 below. The “addition amount / mass%” in Table 3 is “mass percent of the addition amount of the compound having an oxalate group bonded to boron”.

According to Table 3, Examples 1-9 to 1-14 were manufactured using LR as the positive electrode active material and making the maximum potential of the positive electrode less than 4.5 V (vs. Li ^/ Li ⁺ ) in the initial charge / discharge step. The non-aqueous electrolyte secondary batteries according to Comparative Examples 1-3 to 1-6 which were initially charged and discharged so that the maximum ultimate potential of the positive electrode was 4.5 V (vs. Li ^/ Li ⁺ ) or more. It can be seen that the initial AC resistance is lower than that of the secondary battery. The maximum ultimate potential of the positive electrodes of the nonaqueous electrolyte secondary batteries of Comparative Examples 1-3 to 1-6 is about 4.6 V (vs. Li ^/ Li ⁺ ) as described above. Among the examples, Examples 1-10 to 1-14 in which the non-aqueous electrolyte contains a compound having an oxalate group bonded to boron as an additive, compared to Examples 1-9 not containing the compound. It can be seen that the effect of further reducing the initial AC resistance is exhibited.
The non-aqueous electrolyte secondary batteries according to Comparative Examples 1-3 to 1-6 using the same LR as the positive electrode active material in Examples 1-9 to 1-14 as the positive electrode have the maximum ultimate potential of the positive electrode in the initial charge / discharge step. Is obtained through a process of 4.5 V (vs. Li ^/ Li ⁺ ) or more, and the diffraction peak in the range of 20 ° or more and 22 ° or less of the positive electrode active material is obtained by the method of confirming the diffraction peak according to the above-described procedure. Is confirmed to have disappeared. The non-aqueous electrolyte secondary batteries according to the comparative examples each have a higher initial AC resistance than the non-aqueous electrolyte secondary batteries according to Examples 1-9 to 1-14, and the non-aqueous electrolyte Contains a compound having an oxalate group bonded to boron as an additive, thereby further increasing the initial AC resistance. Therefore, it can be seen that the inclusion of the compound has an adverse effect on the reduction of the initial AC resistance.

(Experimental example 2)
Experimental Example 2 shows an example of the positive electrode active material according to the second embodiment together with a comparative example.
(Example 2-1)
The production of the lithium transition metal composite oxide was performed in the same manner as in Example 1-1, and a lithium transition metal composite oxide Li _1.13 Ni _0.235 Co _0.235 Mn _0.40 O ₂ was produced. .

<Acid treatment of active material>
5.0 g of the above lithium transition metal composite oxide was added to 200 mL of a citric acid aqueous solution having a hydrogen ion concentration of 0.05 M, and the temperature of the aqueous solution was maintained at 50 ° C., and stirred at 400 rpm for 2 hours using a stirrer. After stirring, the positive electrode active material was filtered using a suction device, washed with ion-exchanged water, and then dried at 80 ° C. overnight under normal pressure to acid-treat the lithium transition metal composite oxide. The active material according to -1 was produced. The BET specific surface area was 5.8 m ² / g.

(Examples 2-2, 2-3)
The same procedure as in Example 2-1 was carried out except that the acid treatment of the lithium transition metal composite oxide was performed using a boric acid aqueous solution having a hydrogen ion concentration of 0.05 M or a tartaric acid aqueous solution having a hydrogen ion concentration of 0.05 M instead of citric acid. Active materials according to Examples 2-2 and 2-3 were produced. BET specific surface area were respectively 4.6m ^² /g,5.5m ² / g.

(Reference Example 2-1)
An active material according to Reference Example 2-1 was produced in the same manner as in Example 2-1 except that the lithium transition metal composite oxide was not subjected to an acid treatment. The BET specific surface area was 2.3 m ² / g.

(Reference Examples 2-2 to 2-5)
Reference Example 2 was performed in the same manner as in Example 2-1 except that the acid treatment of the lithium transition metal composite oxide was performed using a sulfuric acid aqueous solution having a hydrogen ion concentration of 0.05 M, 0.03 M, and 0.01 M, respectively. The active materials according to Reference Example 2-5 were prepared in the same manner as in Reference Example 2-4, except that the active materials according to -2 to 2-4 were prepared and the acid treatment time was changed to 10 minutes. The BET specific surface area of Comparative Example 2-2 was 7.4 m ² / g.

(Reference Examples 2-6 to 2-8)
Reference Example 2-6, except that the acid treatment of the lithium transition metal composite oxide was performed using a phosphoric acid aqueous solution having a hydrogen ion concentration of 0.1 M and 0.01 M, respectively. An active material according to Reference Example 2-8 was prepared in the same manner as in Reference Example 2-7, except that the active material according to 2-7 was prepared and the acid treatment time was changed to 10 minutes. The BET specific surface area of Reference Example 2-6 was 5.7 m ² / g.

(Reference Examples 2-9 and 2-10)
Reference Examples 2-9 and 2-2 were prepared in the same manner as in Example 2-1 except that the acid treatment of the lithium transition metal composite oxide was performed using tartaric acid aqueous solutions having hydrogen ion concentrations of 0.1 M and 0.05 M, respectively. An active material according to -10 was produced. BET specific surface area were respectively 7.1m ^² /g,6.5m ² / g.

(Examples 2-4 and 2-5 and Reference Example 2-11)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 40: 5: 55 is prepared, and a mixed powder is prepared such that a molar ratio of Li: (Ni, Co, Mn) is 120: 100. Except that, the active materials according to Examples 2-4, 2-5 and Reference Example 2-11 were produced in the same manner as Examples 2-1 and 2-2 and Reference Example 2-1.

(Example 2-6 and Reference Example 2-12)
Example 2-6 Example 2-6 was repeated in the same manner as in Example 2-4 and Reference Example 2-11, except that the mixed powder was prepared such that the molar ratio of Li: (Ni, Co, Mn) became 130: 100. In addition, an active material according to Reference Example 2-12 was produced.

(Reference Examples 2-13 to 2-15)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 35:25:40 is prepared, and a mixed powder is prepared such that a molar ratio of Li: (Ni, Co, Mn) is 120: 100. Except that, the active materials according to Reference Examples 2-13 to 2-15 were produced in the same manner as in Examples 2-1 and 2-2 and Reference Example 2-1.

(Comparative Examples 2-1 and 2-2)
A mixed powder was prepared from the hydroxide precursor according to Example 2-4 and lithium hydroxide monohydrate so that the molar ratio of Li: (Ni, Co, Mn) was 100: 100. Except for the above, active materials of Comparative Examples 2-1 and 2-2 were produced in the same manner as in Example 2-4 and Reference Example 2-11, respectively.

(Comparative Examples 2-3 to 2-5)
A hydroxide precursor having a molar ratio of Ni: Co: Mn of 33:33:33 is prepared, and the hydroxide precursor and lithium hydroxide monohydrate are combined with Li: (Ni, Co, Comparative Examples 2-3 to 2- in the same manner as in Examples 2-1 and 2-2 and Reference Example 2-1 except that the mixed powder was prepared so that the molar ratio of Mn) was 100: 100. The active material according to No. 5 was produced.

<Confirmation of crystal structure>
The active materials according to Example, Reference Example, and Comparative Example of Experimental Example 2 were subjected to powder X-ray diffraction measurement using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). The active materials according to all Examples, Reference Examples and Comparative Examples had an α-NaFeO ₂ type crystal structure. Further, in the active materials according to Examples and Reference Examples except for Comparative Examples 2-1 to 2-5 ("lithium-rich type" active materials), diffraction peaks are observed in the range of 20 ° to 22 °. It was confirmed.

<Preparation of positive electrode and negative electrode>
A positive electrode was produced in the same manner as in Example 1-1, using the active materials according to the above Examples, Reference Examples, and Comparative Examples. Further, a negative electrode was manufactured in the same manner as in Example 1-1.

<Assembly of non-aqueous electrolyte secondary battery>
Using the positive electrodes according to the above Examples, Reference Examples and Comparative Examples, a non-aqueous electrolyte secondary battery was assembled in the following procedure.
As an electrolytic solution, LiPF ₆ was dissolved in a mixed solvent having a volume ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) of 6: 7: 7 so that the concentration became 1 mol / L. The solution was used. A polypropylene microporous membrane surface-modified with polyacrylate was used as a separator. A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) was used for the outer package. The positive electrode according to each of the above examples, the reference example and the comparative example, and the negative electrode were housed in the exterior body through the separator such that the open ends of the positive electrode terminal and the negative electrode terminal were exposed to the outside, and the metal A non-aqueous electrolyte secondary battery is formed by hermetically sealing the fusion allowance where the inner surfaces of the resin composite film face each other except for a portion serving as a liquid injection hole, and after injecting the electrolytic solution, sealing the liquid injection hole. Was assembled.

<Confirmation of initial coulomb efficiency>
The assembled non-aqueous electrolyte secondary battery was subjected to an initial charge / discharge step at 25 ° C. to confirm initial coulomb efficiency. The charging was performed at a current value of 15 mA (corresponding to 0.1 C) per 1 g of the positive electrode mixture, with constant current and constant voltage charging at an upper limit voltage of 4.35 V, and the condition for terminating the charging was a time when the current value attenuated to 1/5. . The discharge was a constant current discharge with the same current value and a lower limit voltage of 2.85V. Here, a pause process of 10 minutes was provided after charging and after discharging, respectively, the charge capacity and the discharge capacity (0.1 C discharge capacity) were confirmed, and the ratio of the discharge capacity to the charge capacity was defined as the initial coulomb efficiency.

<Measurement of discharge capacity ratio a / b>
Next, the discharge capacity ratio a / b was measured. The charging was performed at a current value of 15 mA (corresponding to 0.1 C) per 1 g of the positive electrode mixture, with constant current and constant voltage charging at an upper limit voltage of 4.35 V. . A pause process of 10 minutes was provided, and the discharge was a constant current discharge with the same current value and a lower limit voltage of 2.0 V. Here, the ratio a / b of the discharge capacity (a) from 4.35 V to 3.0 V and the discharge capacity (b) from 3.0 V to 2.0 V was determined.
In this example, the reference example and the comparative example, in evaluating the above-mentioned discharge capacity ratio a / b, even if the charging and discharging were performed at 0.1 C, the same a was obtained as when the charging and discharging were performed at 0.02 C. After confirming that / b was obtained, the above measurement conditions were set.

<Confirmation of high rate discharge performance>
Furthermore, high rate discharge performance was confirmed. The charging was performed at a constant current and a constant voltage with a current value of 15 mA per 1 g of the positive electrode mixture and an upper limit voltage of 4.35 V. The condition for terminating the charging was a time when the current value attenuated to 1/5. A pause process for 10 minutes was provided, and the discharge was a constant current discharge at a cutoff voltage of 2.85 V at a current of 300 mA (corresponding to 2 C) per gram of the positive electrode mixture. The ratio of the discharge capacity (2C discharge capacity) at this time to the above 0.1C discharge capacity was defined as high-rate discharge performance (2C / 0.1C).

<Confirmation of diffraction peak of positive electrode active material>
Based on the method for confirming the diffraction peak described above, the non-aqueous electrolyte secondary batteries according to Examples and Reference Examples in a completely discharged state were disassembled, the positive electrode mixture was taken out, and X-ray diffraction measurement using CuKα rays was performed. In all Examples and Reference Examples, diffraction peaks were confirmed in the range of 20 ° to 22 ° for the positive electrode active material.

Table 4 shows the measurement results.

From Table 4, it can be seen from the comparison between Examples 2-1 and 2-2 and Reference Example 2-1 that the lithium-rich active material was citric acid (pKa ₁ = 3.1) or boric acid (pKa ₁ = 9). .14), the non-aqueous electrolyte secondary batteries according to Examples 2-1 and 2-2 subjected to charge and discharge at less than 4.5 V using the positive electrode active material obtained in It can be seen that the initial coulomb efficiency and the high-rate discharge performance are improved while maintaining the 0.1 C capacity as compared with the battery according to -1. In the batteries according to Examples 2-1 and 2-2, the ratio a / b of the discharge capacity (a) from 4.35 V to 3.0 V and the discharge capacity (b) from 3.0 V to 2.0 V was 17 The battery according to Reference Example 2-1 had an a / b larger than 25, while the battery was within the range of 25 or less. Note that the active materials of Examples 2-1 and 2-2 had a larger specific surface area than the active material of Reference Example 2-1.

Reference Examples 2-2 to 2-5 show the characteristics of the battery when the acid species was changed to sulfuric acid (pKa ₁ = −3) and the acid treatment was performed at various hydrogen ion concentrations and / or treatment times. The 0.1 C capacity was lower than that of Reference Example 2-1 where no acid treatment was performed, and neither the initial coulomb efficiency nor the high-rate discharge performance was higher than that of Reference Example 2-1. The discharge capacity ratio a / b was smaller than 17 or larger than 25.

In Reference Examples 2-6 to 2-8, the acid species was changed to phosphoric acid (pKa ₁ = 2.12), and the lithium-excess type active material was subjected to acid treatment by changing the hydrogen ion concentration and / or the treatment time, and the positive electrode active 9 shows characteristics of a battery when a substance is used. Again, the 0.1 C capacity was lower than that of Reference Example 2-1 where no acid treatment was performed, and neither the initial coulomb efficiency nor the high-rate discharge performance was higher than that of Reference Example 2-1. The discharge capacity ratio a / b was smaller than 17 or larger than 25.

Example 2-3 and Reference Examples 2-9 and 2-10 are examples relating to a battery having a positive electrode active material treated with tartaric acid (pKa ₁ = 3.2) having a different hydrogen ion concentration.
In Example 2-3, the 0.1 C capacity was substantially the same as that of Reference Example 2-1 without acid treatment, and the initial coulomb efficiency and the high rate discharge performance were improved. In the battery according to -10, the initial coulomb efficiency was improved compared to Example 3-3, but the 0.1 C capacity shown in Reference Example 2-1 could not be maintained, and the high-rate discharge performance was also high in Reference Example 2--3. No improvement from 1 was seen. Further, the discharge capacity ratio a / b was in the range of 17 to 25 in the battery of Example 3-3 having the positive electrode active material treated with tartaric acid having a low hydrogen ion concentration, In the batteries of Reference Examples 2-9 and 2-10 having the positive electrode treated with acid having a high concentration of tartaric acid, the value was smaller than 17. The active material of Example 3-3 had a smaller specific surface area than the active materials of Reference Examples 2-9 and 2-10.
From the above, it can be seen that even when an acid treatment with a pKa ₁ of 3.1 or more is performed, it is necessary to appropriately select the hydrogen ion concentration of the acid solution and satisfy a predetermined discharge capacity ratio a / b.

Examples 2-4 and 2-5 and Reference Example 2-11 are compositions of the lithium-rich type active material according to Examples 2-1 and 2-2 and Reference Example 2-1 (Li / Me = 1.3, Example 2-6 corresponds to an example in which Mn / Me = 0.48) was changed to another composition having a larger Mn composition ratio (Li / Me = 1.2, Mn / Me = 0.55). In Reference Example 2-12, the Li ratio was changed (Li / Me = 1.3, Mn / Me) without changing the Mn / Me of the above composition according to Example 2-4 and Reference Example 2-11. = 0.55) corresponds to an example.
The characteristics of the batteries according to Examples 2-4 and 2-5 were such that the active material had the same composition and the 0.1 C discharge capacity, the initial coulomb efficiency, and the high It can be seen that the discharge capacity ratio a / b is in the range of 17 or more and 25 or less. The characteristics of the battery according to Example 2-6 are also higher than those of Reference Example 2-12 in which the active material has the same composition and the acid treatment is not performed, and the discharge capacity ratio a / b Is in the range of 17 or more and 25 or less. Therefore, it can be seen that even in an active material having a composition range where Mn / Me is larger, the specification of a / b is related to an improvement in battery characteristics.

In Reference Examples 2-13 to 2-15, the composition of the lithium-rich type active material according to Examples 2-1 and 2-2 and Reference Example 2-1 (Li / Me = 1.3, Mn / Me = 0. 48) corresponds to an example in which the composition ratio of Mn is changed to another composition having a smaller composition ratio (Li / Me = 1.2, Mn / Me = 0.40).
The characteristics of the batteries according to Reference Examples 2-13 and 2-14 which were subjected to the acid treatment showed only an improvement in the initial coulomb efficiency as compared with Reference Example 2-15 which was not subjected to the acid treatment. Has not been improved.
Therefore, even when the discharge capacity ratio a / b satisfies 17 or more and 25 or less as in the active material according to Reference Example 2-13, if the Mn / Me is too small, the positive electrode active material according to the second embodiment may be used. It can be seen that the effect on the substance is not exhibited.
Note that the reference example in Experimental Example 2 is not the positive electrode active material according to the second embodiment, but as described above, the non-aqueous electrolyte secondary electrode using the active materials according to all Examples and Reference Examples as the positive electrode. In the battery, since the positive electrode active material has a diffraction peak in the range of 20 ° or more and 22 ° or less, even when the active material according to the above reference example is used for the positive electrode, the active material according to the above example is used as the positive electrode. As in the case of using the non-aqueous electrolyte secondary battery, it is possible to obtain a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed up to a higher SOC.

Comparative Examples 2-1 and 2-2 are not active materials having a lithium-rich composition in which lithium is excessive with respect to the transition metal, but the composition ratio of Mn is increased (Li / Me = 1, Mn /Me=0.55), both of which have a 0.1 C capacity, low high-rate discharge performance, and a discharge capacity ratio a / b outside the range of the present invention.

Comparative Examples 2-3 to 2-5 are examples in which a lithium transition metal composite oxide of Li / Me = 1 and Ni: Co: Me = 33: 33: 33, which has already been put to practical use, was used as the positive electrode active material. is there. Comparative Example 2-4, which was treated with boric acid, had better battery characteristics than Comparative Example 2-5, which was not treated with acid. Comparative Example 2-3, which was treated with citric acid, had a 0.1 C discharge. The capacity and the high-rate discharge performance are reduced, and there is no correlation between each battery characteristic and the discharge capacity ratio a / b.

(Experimental example 3)
Experimental Example 3 shows an example of the positive electrode active material according to the third embodiment together with a comparative example. First, Examples 3-1 to 3-10 and Reference Example 1 in which the transition metal compound having the same composition is used and the production conditions of the lithium transition metal composite oxide are changed will be described.

(Example 3-1)
<Preparation of lithium transition metal composite oxide>
In preparing the lithium transition metal composite oxide, a hydroxide precursor was prepared using a reaction crystallization method. First, 578.3 g of nickel sulfate hexahydrate, 56.2 g of cobalt sulfate heptahydrate, and 385.7 g of manganese sulfate pentahydrate were weighed, and all of them were dissolved in 4 L of ion-exchanged water. A 1.0 M aqueous sulfate solution having a molar ratio of: Mn of 55: 5: 40 was prepared. Next, ₂ L of ion exchange water was poured into a 5 L reaction tank, and N ₂ gas was bubbled for 30 min to remove oxygen contained in the ion exchange water. The temperature of the reaction vessel was set to 50 ° C (± 2 ° C), and the inside of the reaction vessel was stirred at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor, so that convection occurred sufficiently in the reaction layer. did. The sulfate solution was dropped into the reaction tank at a rate of 1.3 mL / min for 50 hours. Here, from the start to the end of the dropping, the pH in the reaction tank is adjusted by appropriately dropping a mixed alkali solution composed of 4.0 M sodium hydroxide, 1.25 M ammonia, and 0.1 M hydrazine. Control was performed so as to always maintain 10.20 (± 0.1), and a part of the reaction solution was discharged by overflow so that the total amount of the reaction solution was always controlled so as not to exceed 2 L. After the completion of the dropwise addition, stirring in the reaction tank was continued for another 1 hour. After stopping the stirring, the mixture was allowed to stand at room temperature for 12 hours or more. Next, using a suction filtration device, the hydroxide precursor particles generated in the reaction tank are separated, and further, sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours in an air atmosphere under normal pressure. Then, in order to make the particle size uniform, the mixture was ground for several minutes in an automatic mortar made of agate. Thus, a hydroxide precursor having a molar ratio of Ni: Co: Mn of 55: 5: 40 was produced.

To 2.264 g of the hydroxide precursor, 1.264 g of lithium hydroxide monohydrate and 0.015 g of lithium fluoride were added and mixed well using an automatic mortar made of agate. Li: (Ni, Co, Mn) ) Was prepared at a molar ratio of 120: 100. The addition ratio of lithium fluoride is 2 mol% with respect to the total amount of the Li compound. Using a pellet molding machine, the mixture was molded at a pressure of 6 MPa to obtain a pellet having a diameter of 25 mm. The amount of the mixed powder subjected to the pellet molding was determined by converting the mass of the assumed final product to 2.5 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), and heated from normal temperature to 900 ° C. in an air atmosphere under normal pressure for 10 hours, 900 It was baked at 4 ° C. for 4 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and the alumina boat was allowed to cool naturally while remaining in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the cooling rate thereafter is slightly slow. After a day and a night, it was confirmed that the temperature of the furnace was 100 ° C. or less, and then the pellets were taken out and crushed for several minutes in an automatic mortar made of agate to make the particle diameter uniform. Thus, the lithium transition metal composite oxide according to Example 3-1 was produced.

(Examples 3-2 to 3-5, Reference Example 1)
The addition ratio of lithium fluoride in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was 5, 8, 10, and 20 mol% with respect to the total amount of the Li compound, respectively. The lithium transition metal composite oxides according to Examples 3-2 to 3-4 and Reference Example 1 were produced in the same manner as in Example 3-1 except for the above.
Further, a lithium transition metal composite oxide according to Example 3-5 was produced in the same manner as in Example 3-1 except that lithium fluoride was not added.

(Example 3-6)
The lithium of Example 3-6 was prepared in the same manner as in Example 3-2, except that a mixed powder of a hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was fired at 950 ° C. A transition metal composite oxide was produced.

(Example 3-7)
Example 3-2 except that the molar ratio of Li: (Ni, Co, Mn) in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was changed to 130: 100. In the same manner as in the above, a lithium transition metal composite oxide according to Example 3-7 was produced.

(Examples 3-8 to 3-10)
The procedure of Example 3-2 was repeated, except that lithium carbonate, sodium fluoride, and sodium chloride were added instead of lithium fluoride to prepare a mixed powder in which 5 mol% was added to the total amount of the lithium compound. Lithium transition metal composite oxides according to Examples 3-8 to 3-10 were produced.

Next, Examples 3-11 to 3-14 and Reference Example 3-2 in which a transition metal compound having another composition is used and the production conditions of the lithium transition metal composite oxide are changed are shown.

(Example 3-11)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 40:15:45, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide of Example 3-11 was produced in the same manner as in Example 3-2, except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Examples 3-12 to 3-14)
In the same manner as in Example 3-11, except that lithium carbonate, sodium fluoride, and sodium chloride were added in place of lithium fluoride, and a mixed powder in which 5 mol% was added to the total amount of the lithium compound was prepared. Then, lithium transition metal composite oxides according to Examples 3-12 to 3-14 were produced.

(Reference Example 3-2)
Reference Example 3 was performed in the same manner as in Example 3-11, except that the addition ratio of lithium fluoride in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was changed to 20 mol%. -2 A lithium transition metal composite oxide was produced.

Further, Examples 3-15 to 3-17, Reference Examples 3-3, 3-4, and Comparative Example 3- in which a transition metal compound having another composition was used and the production conditions of the lithium transition metal composite oxide were changed. 1 to 3-3 are shown.

(Example 3-15)
A lithium transition metal composite oxide according to Example 3-15 was prepared in the same manner as in Example 3-2, except that a hydroxide precursor was prepared by changing the molar ratio of Ni: Mn to 60:40. .

(Example 3-16)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 35:15:50, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. The lithium transition metal composite oxide of Example 3-16 was produced in the same manner as in Example 3-2, except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Example 3-17)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 33:33:33, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride The lithium transition metal composite oxide according to Example 3-17 was produced in the same manner as in Example 3-2, except that the molar ratio of Li: (Ni, Co, Mn) was changed to 110: 100.

(Reference Example 3-3)
The lithium transition metal composite oxidation according to Reference Example 3-3 was performed in the same manner as in Example 3-2, except that a hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 30:15:55. Object was produced.

(Reference Example 3-4)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 30:10:60, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was prepared. A lithium transition metal composite oxide according to Reference Example 3-4 was produced in the same manner as in Example 3-2, except that the molar ratio of Li: (Ni, Co, Mn) was changed to 130: 100.

(Comparative Example 3-1)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 33:33:33, and Li :( in the mixed powder of the hydroxide precursor and lithium hydroxide monohydrate was used. A lithium transition metal composite oxide according to Comparative Example 3-1 was produced in the same manner as in Example 3-5, except that the molar ratio of (Ni, Co, Mn) was changed to 100: 100.

(Comparative Example 3-2)
A hydroxide precursor was prepared by changing the molar ratio of Ni: Co: Mn to 33:33:33, and a mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride The lithium transition metal composite oxide according to Comparative Example 3-2 was produced in the same manner as in Example 3-2, except that the molar ratio of Li: (Ni, Co, Mn) was changed to 100: 100.

(Comparative Example 3-3)
Example 3-2 except that the molar ratio of Li: (Ni, Co, Mn) in the mixed powder of the hydroxide precursor, lithium hydroxide monohydrate, and lithium fluoride was changed to 100: 100. In the same manner as in the above, a lithium transition metal composite oxide according to Comparative Example 3-3 was produced.

<Confirmation of crystal structure of lithium transition metal composite oxide>
It was confirmed that the lithium transition metal composite oxides according to the above Examples and Comparative Examples had an α-NaFeO ₂ type crystal structure by conforming a diffraction pattern with a structural model in X-ray diffraction measurement. In addition, in the active materials according to Examples and Reference Examples except for Comparative Examples 3-1 to 3-3 ("lithium-rich type" active materials), diffraction peaks were observed in a range of 20 ° or more and 22 ° or less. It was confirmed.

<Evaluation of the _{_I} 490 _/ _I _600>
Further, the embodiment described above, the Raman spectra of the lithium-transition metal composite oxide according to the reference examples and comparative examples were measured relative to the maximum value _{I 600} in the range of 550 cm ^-1 or more 650 cm ^-1 or less, 450 cm ^-1 or more 520cm The ratio (I ₄₉₀ / I ₆₀₀ ) of the maximum value I _{490 in} the range of ⁻¹ or less was evaluated. FIG. 13 shows Raman spectra of the lithium transition metal composite oxides according to Examples 3-1 to 3-5.

<Preparation of positive electrode and negative electrode>
A positive electrode was produced in the same manner as in Example 1-1 above, using the lithium transition metal composite oxide according to the above Examples, Reference Examples and Comparative Examples as a positive electrode active material. Note that the test conditions for determining the amount of charge and the discharge capacity of the nonaqueous electrolyte secondary batteries according to all Examples, Reference Examples, and Comparative Examples were the same, so that the active material applied per unit area was not changed. The coating thickness was adjusted.
Further, a negative electrode was manufactured in the same manner as in Example 1-1.

<Assembly of non-aqueous electrolyte secondary battery>
The positive electrodes according to the above Examples, Reference Examples and Comparative Examples were partially cut out and used, and a nonaqueous electrolyte secondary battery was assembled in the same procedure as in Experimental Example 2.

<First charge and discharge process>
The non-aqueous electrolyte secondary battery assembled by the above procedure is completed through an initial charge / discharge step. Here, in the initial charge / discharge process, the first charge / discharge condition 1 is divided into a first group and the first charge / discharge condition 2 is divided into a second group.

(Calculation of discharge capacity per volume)
Using the batteries of the first group, the following initial charge / discharge condition 1 was applied, and the battery was subjected to an initial charge / discharge step. At 25 ° C., charging was performed at a constant current and constant voltage with a current of 0.1 C and a voltage of 4.35 V. The condition for terminating the charging was a point in time when the current value attenuated to 0.02 C. The amount of electricity charged at this time was defined as “the amount of electricity charged when charging at 4.35 V” (mAh / g). The discharge was a constant current discharge at a current of 0.1 C and a cutoff voltage of 2.5 V. This charge / discharge was performed for one cycle. Note that a pause process for 10 minutes was provided after charging.
The discharge capacity per mass at this time was defined as “4.35 V discharge capacity at charge” (mAh / g). On the other hand, the press density of the positive electrode active material powder was measured under the above-mentioned conditions, and the measured press density (g / cm ³ ) was multiplied by “4.35 V discharge capacity at charge” (mAh / g) to obtain a value per volume. Of the battery was calculated (mAh / cm ³ ). Here, “4.35 V discharge capacity at the time of charging” (mAh / cm ³ ) is defined as the charge before the overcharge area is completed and the charge process until the overcharge area is completed. Is an index representing the discharge capacity when used in a lower potential range without performing the above.

<Confirmation of diffraction peak of positive electrode active material>
Based on the method of confirming the diffraction peak described above, disassemble the non-aqueous electrolyte secondary batteries according to Examples and Reference Examples in the completely discharged state after the first charge / discharge step, take out the positive electrode mixture, and use CuKα rays. X-ray diffraction measurement was performed. In all Examples and Reference Examples, diffraction peaks were confirmed in the range of 20 ° to 22 ° for the positive electrode active material.

(Calculation of the amount of charged electricity per volume)
Using the batteries of the second group, the following initial charge / discharge condition 2 was applied and subjected to an initial charge / discharge step. At 25 ° C., the charging was performed at a constant current and a constant voltage with a current of 0.1 C and a voltage of 4.6 V, and the condition for terminating the charging was a time when the current value attenuated to 0.02 C. The discharge was a constant current discharge at a current of 0.1 C and a cutoff voltage of 2.0 V. This charge / discharge was performed for one cycle. Note that a pause process for 10 minutes was provided after charging.
The difference between the charged amount of electricity (mAh / g) at this time and the above-mentioned "charged amount of electricity at 4.35 V charging" (mAh / g) is defined as "the charged amount of electricity between 4.35 V and 4.6 V" (mAh / g). g). By multiplying the above-mentioned press density (g / cm ³ ) by “the amount of charge electricity between 4.35 V and 4.6 V” (mAh / g), the amount of charge electricity per volume “from 4.35 V to 4.6 V” The amount of charge between the batteries "(mAh / cm ³ ) was calculated. Here, “the amount of charge between 4.35 V and 4.6 V” (mAh / cm ³ ) is an index representing the amount of charge in the overcharge region.

Table 5 shows the above results. FIG. 14 shows the relationship between I ₄₉₀ / I ₆₀₀ and the discharge capacity per unit volume, where 1 <Li / Me and Mn / Me <0.55 are indicated by ● (Examples 1-1 to 1). -17 and Reference Examples 3-1 and 3-2), those of 0.55 ≦ Mn / Me are indicated by Δ (Reference Examples 3-3 and 3-4), and those of Li / Me = 1.0 Is indicated by Δ (Comparative Examples 3-1 to 3-3). From FIG. 14, it can be seen that in the composition of 1 <Li / Me and Mn / Me <0.55, there is a correlation between the Raman peak intensity ratio and the discharge capacity per volume. On the other hand, no correlation is observed in the compositions of Li / Me = 1.0 and 0.55 ≦ Mn / Me.

The lithium transition metal composite oxides (positive electrode active materials) according to Examples 3-1 to 3-5 all have the same composition of the transition metal compound (hydroxide precursor) containing Ni, Co, and Mn. Although the / Me ratio is the same, the presence or absence or amount of lithium fluoride as a sintering aid is different. I ₄₉₀ / I ₆₀₀ tended to decrease as the amount of addition increased, but all exceeded 0.45, the discharge capacity per volume at 4.35 V charging exceeded 450 mAh / cm ^3, and It can be seen that the amount of charged electricity per volume exceeds 110 mAh / cm ³ . On the other hand, in Reference Example 3-1 in which the addition amount of lithium fluoride was 20 mol% with respect to the total amount of the lithium compound, I ₄₉₀ / I ₆₀₀ was lower than 0.45 and the volume at the time of charging at 4.35 V was 4. It can be seen that the discharge capacity per unit and the amount of charged electricity per volume in the overcharge region are not sufficiently obtained.

Examples 3-6 and 3-7 correspond to examples in which the firing temperature of the mixed powder in Example 3-2 was changed or the Li / Me ratio was changed. _Both, I 490 _{/ I 600} is greater than 0.45, discharge capacity per volume at 4.35V charging exceeds 450 mAh / cm ^3, charged electricity quantity per volume in the overcharge region of 110 mAh / cm ³ You can see that it exceeds.

Examples 3-8 to 3-10 correspond to examples in which the type of the sintering aid was changed in Example 3-2, and in all cases, I ₄₉₀ / I ₆₀₀ exceeded 0.45 and charged at 4.35 V. It can be seen that the discharge capacity per volume at the time and the amount of charged electricity per volume in the overcharge region are high.
Further, comparing Examples 3-1 to 3-4 and 3-6 to 3-10 with Example 3-5, Examples 3-1 to 3-4 and 3-6 in which a sintering aid was added were added. The positive electrode active materials of Nos. 3 to 10 have a smaller I ₄₉₀ / I ₆₀₀ than that of the positive electrode active material of Example 3-5 to which no sintering aid is added, that is, 0.85 or less. It can be seen that the discharge capacity is high. Therefore, in order to increase the discharge capacity per volume at the time of charging at 4.35 V, it is preferable that I ₄₉₀ / I ₆₀₀ be 0.45 or more and 0.85 or less.

Examples 3-11 to 3-14 and Reference Example 3-2 correspond to examples in which the composition of the lithium transition metal composite oxide was changed from Example 3-2, and Examples 3-12 to 3-14 corresponded to Examples 3-12 to 3-14. This corresponds to an example in which the type of the sintering aid in Example 3-11 is changed. In all of Examples 3-11 to 3-14, I ₄₉₀ / I ₆₀₀ is 0.45 or more, and the discharge capacity per volume at the time of charging at 4.35 V and the amount of electricity charged per volume in the overcharge region. Is high.
Reference Example 3-2 corresponds to an example in which the addition amount of the sintering aid in Example 3-11 was increased. I ₄₉₀ / I ₆₀₀ was lower than 0.45, and the discharge capacity per volume at the time of charging at 4.35 V was 389 mAh / cm ³ , which was not sufficient.

In Examples 3-15 to 3-17, Reference Examples 3-3 and 3-4, and Comparative Examples 3-1 to 3-3, the composition of the lithium transition metal composite oxide was further changed from Example 3-2. It corresponds to an example. From Examples 3-15 to 3-17, if the Mn / Me ratio is 0.33 or more and 0.50 or less, the ratio exceeds 450 mAh / cm ³ under the condition that I ₄₉₀ / I ₆₀₀ becomes 0.45 or more. It can be seen that an active material having a discharge capacity per volume at the time of charging at 4.35 V and a charge amount per volume in an overcharge region exceeding 110 mAh / cm ³ was obtained.
On the other hand, from Reference Examples 3-3 and 3-4, when the Mn / Me ratio is 0.55 or more, even when I ₄₉₀ / I ₆₀₀ is 0.45 or more, sufficient 4.35 V charging is performed. It turns out that the discharge capacity per volume at the time cannot be obtained.
Note that the reference example in Experimental Example 3 is not the positive electrode active material according to the third embodiment, but as described above, the nonaqueous electrolyte secondary electrode using the active materials according to all Examples and Reference Examples as the positive electrode. In the battery, since the positive electrode active material has a diffraction peak in the range of 20 ° or more and 22 ° or less, even when the active material according to the above reference example is used for the positive electrode, the active material according to the above example is used as the positive electrode. As in the case of using a non-aqueous electrolyte secondary battery, a sharp increase in battery voltage is not observed up to a higher SOC.
When the active material according to the present embodiment is used for the positive electrode, the amount of charged electricity per volume in the overcharge region increases, so that a non-aqueous electrolyte secondary battery in which a rapid increase in battery voltage is not observed until a higher SOC is reached. can get.
Comparative Examples 3-1 to 3-3 are active materials in the case of Li / Me = 1, which are not targeted by the present invention. Both I ₄₉₀ / I ₆₀₀ were lower than 0.45, and an active material having sufficient discharge capacity per volume at the time of charging at 4.35 V and sufficient charge quantity per volume in the overcharge region was not obtained.

In the nonaqueous electrolyte secondary battery according to the present invention, even when overcharged, a sudden increase in battery voltage is not observed until a higher SOC is reached.
Further, by including the fluorinated cyclic carbonate in the non-aqueous solvent of the non-aqueous electrolyte, it is possible to suppress an increase in AC resistance after storage.
Further, when the non-aqueous electrolyte contains a compound having an oxalate group bonded to boron, the initial AC resistance can be reduced.
The active material for a non-aqueous electrolyte secondary battery according to the second embodiment exhibits excellent initial Coulomb efficiency and high-rate discharge performance when used in a potential range of less than 4.5 V (vs. Li ^/ Li ⁺ ).
When the positive electrode active material including the lithium transition metal composite oxide according to the third embodiment is used, the charge capacity per volume in the overcharge region is large, and no rapid increase in the battery voltage is observed up to a higher SOC, and In addition, a non-aqueous electrolyte secondary battery having a large discharge capacity per volume can be provided.
Therefore, the non-aqueous electrolyte secondary battery according to the present invention is used for a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and an electric vehicle (HEV), which require high safety, storage performance, efficiency, and high output. It is highly useful as a battery for EV).

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 1A, 1B Measurement probe 2A, 2B Measurement surface 3A, 3B Pedestal 6 Side body 7 Through-hole 20 Power storage unit 30 power storage device

Claims

A positive electrode, a non-aqueous electrolyte secondary battery including a negative electrode and a non-aqueous electrolyte,
The positive electrode, as an active material,
having an α-NaFeO 2 type crystal structure,
A lithium transition metal composite oxide represented by a general formula Li 1 + α Me 1-α O 2 (0 <α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co);
The non-aqueous electrolyte secondary battery, wherein the active material has a diffraction peak observed in a range of 20 ° to 22 ° in an X-ray diffraction diagram using CuKα radiation.
A positive electrode, a non-aqueous electrolyte secondary battery including a negative electrode and a non-aqueous electrolyte,
The positive electrode, as an active material,
having an α-NaFeO 2 type crystal structure,
A lithium transition metal composite oxide represented by a general formula Li 1 + α Me 1-α O 2 (0 <α, Me is a transition metal element containing Ni and Mn, or Ni, Mn and Co);
When the positive electrode is charged to a positive electrode potential of 5.0 V (vs. Li / Li + ), the positive electrode has a voltage of 4.5 V (vs. Li / Li + ) or more and 5.0 V (vs. Li / Li + ) or less. A non-aqueous electrolyte secondary battery in which a region where the potential change is relatively flat with respect to the amount of charged electricity is observed within the positive electrode potential range.
3. The nonaqueous electrolyte secondary according to claim 1, wherein the lithium transition metal composite oxide included in the positive electrode as an active material has a molar ratio of Mn to transition metal (Me) of 0.4 ≦ Mn / Me. 4. battery.
4. The lithium transition metal composite oxide contained in the positive electrode as an active material, wherein the molar ratio of Li to transition metal (Me) is 1.15 <Li / Me. 5. Non-aqueous electrolyte secondary battery.
5. The lithium transition metal composite oxide contained in the positive electrode as an active material, wherein the molar ratio of Li to transition metal (Me) is Li / Me ≦ 1.35. Non-aqueous electrolyte secondary battery.
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the content of the lithium transition metal composite oxide contained in the positive electrode as an active material is more than 80% by mass of the total active material of the positive electrode. .
The non-aqueous solution according to any one of claims 1 to 6, wherein the non-aqueous solution is used at a battery voltage at which the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li / Li + ). Electrolyte secondary battery.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the non-aqueous electrolyte includes a fluorinated cyclic carbonate in a non-aqueous solvent.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein the non-aqueous electrolyte includes a compound having an oxalate group bonded to boron.
A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
The lithium transition metal composite oxide,
having an α-NaFeO 2 type crystal structure,
General formula Li 1 + α Me 1−α O 2 (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, the molar ratio of Mn to Me Mn / Me is Mn / Me ≧ 0.45 ),
The positive electrode active material has a discharge capacity (a) of 4.35 V (vs. Li / Li + ) to 3.0 V (vs. Li / Li + ) and a discharge capacity of 3.0 V (vs. Li / Li + ) of 2 V. The ratio a / b of the discharge capacity (b) up to 0.0 V (vs. Li / Li + ) is 17 ≦ a / b ≦ 25;
Cathode active material for non-aqueous electrolyte secondary batteries.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
having an α-NaFeO 2 type crystal structure,
General formula Li 1 + α Me 1−α O 2 (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, the molar ratio of Mn to Me Mn / Me is Mn / Me ≧ 0.45 a lithium transition metal composite oxide represented by), with pKa 1 is treated with 3.1 or more acids, 4.35V (vs.Li/Li +) from 3.0V (vs.Li/Li +) discharge capacity (a) and 3.0V (vs.Li/Li +) from 2.0V (vs.Li/Li +) ratio a / b of the discharge capacity (b) until the 17 ≦ a / b ≦ up 25. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises producing the positive electrode active material of No. 25.
A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide,
The lithium transition metal composite oxide,
having an α-NaFeO 2 type crystal structure,
General formula Li 1 + α Me 1−α O 2 (0 <α, Me is Ni and Mn, or a transition metal element containing Ni, Mn and Co, and the molar ratio of Mn to Me Mn / Me is 0.3 ≦ Mn / Me. <0.55),
To maximum I 600 at 650 cm -1 or less in the range of 550 cm -1 or more in the Raman spectrum, the ratio of the maximum value I 490 in the range of 450 cm -1 or more 520 cm -1 or less (I 490 / I 600) 0.45 That's it,
Cathode active material for non-aqueous electrolyte secondary batteries.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, comprising Ni and Mn, or Ni, Co and Mn, wherein the molar ratio of Mn to Me, Mn / Me, is 0.3≤. When producing a lithium transition metal composite oxide having a molar ratio Li / Me of 1 <Li / Me by mixing and calcining a Li compound with a transition metal compound satisfying Mn / Me <0.55, A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises adding a sintering aid.
A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 10 or 12.
The positive electrode for a non-aqueous electrolyte secondary battery according to claim 14, wherein the positive electrode active material contained in the positive electrode has a diffraction peak observed in a range of 20 ° or more and 22 ° or less in an X-ray diffraction diagram using CuKα radiation. Non-aqueous electrolyte secondary battery.
The positive electrode for a non-aqueous electrolyte secondary battery according to claim 14, wherein the positive electrode is charged to 4.5 V (vs. Li / Li + ) when the positive electrode potential reaches 5.0 V (vs. Li / Li + ). li +) or higher 5.0V (vs.Li/Li +) following in the positive electrode potential range, the potential change is relatively flat region observed for amount of charge, a non-aqueous electrolyte secondary battery.
17. The non-aqueous electrolyte secondary battery according to claim 15, wherein the non-aqueous electrolyte secondary battery is used at a battery voltage at which the maximum potential of the positive electrode in a fully charged state (SOC 100%) is less than 4.5 V (vs. Li / Li + ).
The method for producing a nonaqueous electrolyte secondary battery according to any one of claims 1 to 9, and 15 to 17, wherein the maximum ultimate potential of the positive electrode in the initial charge / discharge step is 4.5 V (vs. Li / Li). + ) The method for producing a non-aqueous electrolyte secondary battery.
The method for using the nonaqueous electrolyte secondary battery according to any one of claims 1 to 9, and 15 to 17, wherein a maximum ultimate potential of the positive electrode in a fully charged state (SOC 100%) is 4.5 V (vs. A method for using a non-aqueous electrolyte secondary battery, which is used at a battery voltage lower than (Li / Li + ).