JP6068247B2 - Positive electrode material for non-aqueous electrolyte lithium ion secondary battery and non-aqueous electrolyte lithium ion secondary battery using the positive electrode material - Google Patents

Description

  The present invention relates to a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery using a lithium composite oxide as a positive electrode active material, and a non-aqueous electrolyte lithium ion secondary battery using the positive electrode material.

  In recent years, non-aqueous electrolyte lithium ion secondary batteries mounted on portable electronic devices such as mobile phones and laptop computers have been required to have higher capacities by charging at higher voltages, which has led to higher safety. Sex is required.

Japanese Unexamined Patent Application Publication No. 2009-212021 (Patent Document 1) discloses a general composition formula Li _{1 + t} Co _1-xyz Al _x Mg _y M _z O ₂ (where M is Zr, Ti, Cr, Fe, Ge). Represents at least one element selected from the group consisting of Sn, Ce, Hf, Y, Yb, Er, Nb, Mo, Mn, Ni, B, and P, −0.05 ≦ t ≦ 0.1, The lithium-containing cobalt oxide represented by 0.001 ≦ x ≦ 0.015, 0 ≦ y ≦ 1.5x, and 0.15y ≦ z) is used for the positive electrode, so that charging / discharging at high temperature and high voltage is possible. It is described that a non-aqueous electrolyte lithium ion secondary battery having excellent cycle life, high safety, and high capacity is provided.

JP 2009-212021 A

However, a lithium ion battery using a lithium-containing cobalt oxide described in Patent Document 1 as a positive electrode active material is continuously charged at a high voltage of 4.5 V or higher (vs. Li ^/ Li ⁺ ) at a high temperature of 60 ° C. or higher. Then, it turned out that a battery characteristic falls remarkably. This is considered to be due to the fact that elution of Co is promoted by continuous charging at a high voltage, structural destruction of the positive electrode active material occurs, or resistance increases due to Co deposition on the negative electrode surface.

  The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery of the present invention has a general composition formula: Li _{1 + α} Co _1-β-γ Ni _β M _γ O _2-δ (In the formula, M represents at least one element of Al and Mg, and α, β, γ, and δ are 0.01 ≦ α ≦ 0.10, 0.01 ≦ β ≦ 0.05, 0. .001 ≦ γ ≦ 0.02, 0 ≦ δ ≦ 0.01), a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery, The particle surface of the positive electrode material for an electrolyte lithium ion secondary battery is an oxide containing at least one coating element selected from the group consisting of Li, Zr, Ti, Al, Ni, Mn, La, Zn, P and B When the oxide contains Li, the number of atoms of the covering element is 50% or less of the number of Co atoms contained in the positive electrode material for a nonaqueous electrolyte lithium ion secondary battery. Non-aqueous electrolyte lithium ion secondary when not containing 10% or less of Co atoms contained in the pond for a positive electrode material.

  According to the present invention, it is possible to provide a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery that has a large discharge capacity and can be continuously charged at a high voltage at a high temperature.

It is sectional drawing which shows typically the structure of a nonaqueous electrolyte lithium ion secondary battery. It is a table | surface which shows a composition of an Example and a comparative example. It is a table | surface which shows the discharge capacity and continuous charge durable time which were calculated | required with respect to the Example and the comparative example.

The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention is:
General composition formula: Li1 _{+ [alpha]} Co1- [ _{beta]-[gamma]} Ni [ _beta] M [ _{gamma] O2- [delta]} (1)
(In the formula, M represents at least one element of Al and Mg, and 0.01 ≦ α ≦ 0.10, 0.01 ≦ β ≦ 0.05, 0.001 ≦ γ ≦ 0.02, 0. ≦ δ ≦ 0.01).

  By using the positive electrode material satisfying the general composition formula (1), a non-aqueous electrolyte lithium ion secondary battery having a large discharge capacity and capable of continuous charging at a high voltage at a high temperature is obtained.

  In order to produce a positive electrode using the positive electrode material as a positive electrode active material, a positive electrode mixture slurry is prepared by dispersing the positive electrode material in a solvent such as a binder and a conductive additive, and the positive electrode mixture slurry is used as a positive electrode current collector. It is carried out by applying to the surface of the body to form a positive electrode mixture layer.

  The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention is in the form of particles, and the shape thereof is substantially spherical. The average diameter of the particles is preferably 5 μm or more and 20 μm or less. The average diameter can be obtained by measuring the diameter of particles present in a predetermined region with a scanning electron microscope and calculating the average diameter.

The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention needs to reduce the interface with the non-aqueous electrolyte from the viewpoint of suppressing the elution of Co. For this purpose, it is advantageous that the BET specific surface area is small, but if the BET specific surface area of the particles is too small, the density at the time of lamination will be small, so that the battery capacity will be small or the discharge characteristics at high load will be reduced. Problem arises. For this reason, it is preferable that the BET specific surface area S is 0.01 <= S <= 0.5 [m < ² > / g]. The BET specific surface area can be obtained by measuring the surface area using the BET formula, which is a theoretical formula for multimolecular layer adsorption. Specifically, the BET specific surface area was determined using a specific surface area measuring device by a nitrogen adsorption method.

  In the general composition formula (1) representing the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention, α relating to Li is preferably 0.01 ≦ α ≦ 0.10. When α is less than 0.01, the positive electrode active material particles are small, and the particle diameter is less than 5 μm. When the layer of the positive electrode active material is formed using such small particles, the density is small, and thus a sufficient battery capacity cannot be obtained. Moreover, since the surface area becomes large, Co elution is likely to occur. On the other hand, oxygen deficiency occurs when α exceeds 0.10. For this reason, the potential in the low charge state is lowered, and the cycle life is shortened. Furthermore, since there is a lot of lithium on the surface of the positive electrode active material particles, the positive electrode mixture slurry prepared using such a positive electrode active material becomes a gel, and the resistance of the formed positive electrode mixture layer increases, In some cases, gas is generated.

  The range of 0.01 ≦ α ≦ 0.10 means that it is moderately Li-rich. That is, a suitable amount of Co is replaced with Li. In such a state, the transition phenomenon of the structure in which Li is desorbed even at a high voltage is suppressed, and Co elution is prevented. The valence of Co is preferably 2.8 or more and 3.3 or less. The Co valence is calculated from inductively coupled plasma emission spectrometry and iodometric titration, and is obtained by quantifying the atomic ratio of Li and Co and the amount of oxygen.

  In the general composition formula representing the positive electrode material for a nonaqueous electrolyte lithium ion secondary battery according to the present invention, β related to Ni is preferably 0.01 ≦ β ≦ 0.05. The addition of Ni has an effect of suppressing Co elution. Since the change in battery capacity due to some increase or decrease in the amount of Ni added is very small, Ni is preferable as an additive element that suppresses Co elution while maintaining the battery at a high capacity. When β is less than 0.01, the effect of suppressing Co elution is not sufficient. On the other hand, when β exceeds 0.05, a problem occurs in that the potential in a low charge state decreases.

  In the general composition formula (1) representing the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention, γ related to Al and / or Mg is preferably 0.001 ≦ γ ≦ 0.02. . The addition of these elements has the effect of stabilizing the structure of the lithium-containing cobalt oxide, suppressing the elution of Co, and improving the heat resistance. When γ is less than 0.001, these effects are not sufficient. On the other hand, when γ exceeds 0.02, the crystal lattice of lithium cobalt oxide is distorted, and the mobility of Li decreases, It may cause a decrease in battery capacity.

  In addition, when Mg is contained excessively, there is a problem that Mg is eluted with a charge / discharge cycle, leading to a decrease in battery life. Therefore, the amount of Mg added depends on the number of Co atoms contained in the positive electrode material. More preferably, the number of Mg atoms is 0.01 or less. When both Al and Mg are added, the number of Al atoms relative to the number of Co atoms in the positive electrode material is 0.01 or more and 0.02 or less, and the number of Mg atoms is 0.005 or less. More preferred.

  In the general composition formula (1) representing the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention, δ relating to oxygen is preferably 0 ≦ δ ≦ 0.01. The collapse of the crystal structure due to the desorption of oxygen is considered to be one cause of Co elution. If δ is 0.01 or less, oxygen deficiency is sufficiently small.

The lithium-containing cobalt oxide according to the present invention is
General composition formula: Li1 _{+ [alpha]} Co1- [ _{beta]-[gamma]-[eta]} Ni [ _beta] M [ _gamma] M '[ _{eta] O2- [ delta]} (2)
(Wherein M represents at least one element of Al and Mg, and M ′ represents at least one selected from the group consisting of Zr, Mo, V, Ti, Mn, Cr, Fe, Y, W, and B) 0.01 ≦ α ≦ 0.10, 0.01 ≦ β ≦ 0.05, 0.001 ≦ γ ≦ 0.02, 0.001 ≦ η ≦ 0.005, 0 ≦ δ ≦ 0 .01)
It is good also as lithium containing cobalt oxide represented by these.

  In the lithium-containing cobalt oxide represented by the general composition formula (1), a part of Co is a group consisting of Zr, Mo, V, Ti, Mn, Cr, Fe, Y, W, and B. This corresponds to substitution with at least one element selected from

  By using the positive electrode material satisfying the general composition formula (2), it is possible to expect an improvement in the deterioration suppressing effect by the charge / discharge cycle. However, since the battery capacity decreases when the substitution amount is too large, η is preferably 0.001 ≦ η ≦ 0.005. This corresponds to 0.1% or more and 0.5% or less of the number of Co atoms.

  The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention has at least one oxygen atom in the general composition formula (1) or (2) selected from the group consisting of F, S and P. It may be substituted with a seed element. In this case, the effect of suppressing the collapse of the crystal structure due to the desorption of oxygen is further improved. However, since the battery capacity is reduced when the substitution amount is too large, the number of atoms of the substitution element is preferably 2.5% or less of the number of oxygen atoms.

  The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention has at least one selected from the group consisting of Li, Zr, Ti, Al, Ni, Mn, La, Zn, P and B on its surface. You may coat | cover with the oxide containing these elements. In this case, in addition to improving the deterioration suppressing effect due to the charge / discharge cycle, the Co elution suppressing effect is also improved. However, when there is too much quantity of the said covering oxide, resistance will become large and battery capacity will reduce. Therefore, the element contained in the oxide to be coated is preferably 50% or less of the number of Co atoms when Li is included, and 10% or less of the number of Co atoms when Li is not included.

<Preparation of cathode material for non-aqueous electrolyte lithium ion secondary battery>
The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention is obtained by, for example, solidifying a mixture powder in which Li compound, Co compound, Ni compound, Al compound, Mg compound and the like are mixed in an appropriate ratio into a pellet, It can be produced by firing.

LiOH or Li ₂ CO ₃ is preferable as the Li compound, and hydroxides or oxides of these elements are preferable as the Co compound, Ni compound, Al compound, and Mg compound. The firing temperature is preferably 650 to 1200 ° C., and the firing time is preferably 5 to 48 hours. The firing atmosphere is preferably an oxidizing atmosphere such as air or oxygen.

  At least one element selected from the group consisting of Li, Zr, Ti, Al, Ni, Mn, La, Zn, P and B on the surface of the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention For example, the following procedure is used to coat the oxide containing.

  Lithium hydroxide or aqueous ammonia is added to an aqueous solution in which the above elements are dissolved, and a treatment liquid is prepared by dispersing the produced coprecipitate in a solvent. After dispersing the positive electrode material powder for non-aqueous electrolyte lithium ion secondary battery in this treatment liquid, it is dried using a spray dryer or an evaporator to obtain a powder having the surface coated with the above elements. By firing this powder, a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery in which a coating layer is formed is obtained.

  As another method for coating, there is a method in which an alkoxide of a desired element is dissolved in an alcohol solvent and adhered to a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery.

  The firing temperature at the time of coating is preferably 400 to 850 ° C., and the firing time is preferably 5 to 24 hours. The firing atmosphere is preferably an oxidizing atmosphere such as air or oxygen.

  In order to produce a positive electrode using the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery as a positive electrode active material, the positive electrode material is mixed with a binder, a conductive auxiliary agent, etc., and dispersed in a solvent to obtain a positive electrode mixture slurry. The positive electrode mixture slurry is prepared and applied to the surface of the positive electrode current collector to form a positive electrode mixture layer.

  As the binder, any one of a thermoplastic resin and a thermosetting resin may be used as long as it is chemically stable in the nonaqueous electrolyte lithium ion secondary battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or Na + ion thereof Cross-linked product, ethylene-methacrylic acid copolymer or its Na + ion cross-linked product, ethylene-methyl acrylate copolymer or its Na + ion cross-linked product, ethylene-methyl methacrylate copolymer or its Na + ion cross-linked product can be used It is. These may be used alone or in combination of two or more. Among these, PVDF or an acrylic material is preferable in consideration of stability in the nonaqueous electrolyte lithium ion secondary battery, influence on characteristics, and the like.

  The conductive auxiliary agent may be either an inorganic material or an organic material as long as it is chemically stable in the nonaqueous electrolyte lithium ion secondary battery. For example, graphite such as natural graphite or artificial graphite, single- or multi-walled carbon nanotube, graphene, VGCF, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black, thermal black, Carbon fiber, conductive fiber such as metal fiber, metal powder such as aluminum powder, conductive whisker made of carbon fluoride, zinc oxide, potassium titanate, etc., conductive metal oxide such as titanium oxide, organic such as polyphenylene derivatives A conductive material or the like can be used. These may be used alone or in combination of two or more. Among these, graphite having high conductivity and carbon black excellent in liquid absorption are preferable.

  As the form of the conductive auxiliary agent, for example, in the case of a particulate form, it is not limited only to the primary particles, and those having the form of aggregates such as secondary particles (secondary aggregates) and chain structures may be used. it can. In the case of a conductive additive having such an aggregate form, it is easier to handle and the productivity of the positive electrode can be increased.

  The mass of the positive electrode active material in the positive electrode mixture layer is preferably 85 to 99%. When the content ratio of the positive electrode active material is less than 85%, the battery capacity is decreased. Conversely, when the content ratio is greater than 99%, the amount of the conductive auxiliary agent is relatively decreased, and the resistance of the positive electrode is increased.

  The mass of the binder in the positive electrode mixture layer is preferably 0.2 to 6%. Moreover, it is preferable that the mass of the conductive support agent which occupies for a positive mix layer is 0.5 to 9%.

  A positive electrode mixture containing a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention as a positive electrode active material, a binder, a conductive auxiliary agent, and the like is used as N-methyl-2-pyrrolidone (hereinafter referred to as NMP). Disperse to prepare a slurry mixture composition. After this mixture composition is applied to one or both sides of the positive electrode current collector, NMP is evaporated, and a press treatment is performed to form a positive electrode mixture layer on the current collector surface. The press treatment is for adjusting the thickness and density of the positive electrode mixture layer, and can be performed using, for example, a roll press machine or a hydraulic press machine. In this way, the positive electrode is produced. The method for manufacturing the positive electrode is not limited to the above, and other manufacturing methods may be used.

  The material of the positive electrode current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the nonaqueous electrolyte lithium ion secondary battery. For example, in addition to aluminum, aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., aluminum, aluminum alloy, a composite material in which a carbon layer or a titanium layer is formed on the surface of stainless steel, or the like can be used. . Among these materials, aluminum or aluminum alloy is preferable because it is lightweight and has high conductivity. As a material of the positive electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like of the above materials can be used. Further, the surface of the positive electrode current collector can be roughened by surface treatment. Although the thickness of a positive electrode electrical power collector is not specifically limited, 1-500 micrometers is preferable.

  As a method for applying the positive electrode mixture-containing composition to the surface of the current collector, various methods such as spin coating, dipping, and screen printing can be used.

  The nonaqueous electrolyte lithium ion secondary battery according to the present invention has a positive electrode using the positive electrode material for a nonaqueous electrolyte lithium ion secondary battery according to the present invention as a positive electrode active material. There are no particular restrictions on the configuration and structure other than the positive electrode.

In the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention, the transition to CoO ₂ (O1 structure) hardly occurs. For example, for a non-aqueous electrolyte lithium ion secondary battery using a lithium metal for the negative electrode and a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention for the positive electrode, up to 5 V at 0.1 C or less at room temperature In the dQ / dV curve obtained by performing charging and differentiating the charge curve of the positive electrode with voltage, the peak potential due to the phase transition to the O1 structure that appears on the highest potential side is 4.64V. That's it. This indicates that the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to the present invention is not easily transferred to CoO ₂ (O1 structure).

<Synthesis of positive electrode active material>
Li ₂ CO ₃ as the Li compound, Co ₃ O ₄ as the Co compound, Ni (OH) ₂ as the Ni compound, and Al (OH) ₃ as the Al compound are accommodated in a mortar in an appropriate mixing ratio and mixed, and then pelletized And heat-treated at 1000 ° C. for 10 hours in an oxygen atmosphere. The pellets subjected to heat treatment were pulverized in a mortar so that the average diameter of the particles was 15 μm, and the lithium content represented by the general composition formula Li _1.03 Co _0.975 Ni _0.02 Al _0.005 O ₂ Cobalt oxide was synthesized. The composition ratio was measured by ICP (Inductivity Coupled Plasma) method.

<Preparation of positive electrode>
As a positive electrode active material, lithium-containing cobalt oxide powder having the above composition: Li _1.03 Co _0.975 Ni _0.02 Al _0.005 O ₂ is dispersed and mixed in an NMP solution containing PVDF as a binder. A liquid was prepared. The mass of PVDF in the mass of the NMP solution is 10%. The mass ratio of the lithium-containing cobalt oxide having the above composition and the NMP solution was 95: 5. To this mixed solution, 2.5 parts by mass of carbon black as a conductive assistant was added, kneaded in a mortar, and NMP was added to adjust the viscosity to prepare a positive electrode mixture slurry.

  The positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil having a thickness of 15 μm using a baker-type applicator, and then dried at 80 ° C. for 1 hour. An agent layer was formed. The positive electrode current collector on which the positive electrode mixture layer was formed was processed into a disk shape having a diameter of 15 mm, then pressed at a pressure of about 30 MPa, and further dried at 100 ° C. for 20 hours in a vacuum dryer. A positive electrode was produced by such a process.

<Production of negative electrode>
A metal lithium rolled plate having a predetermined thickness was processed into a disk shape having a diameter of 16 mm to produce a negative electrode.

<Non-aqueous electrolyte>
A non-aqueous electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a molar concentration (mol / l) in a solvent in which ethylene carbonate and diethyl carbonate having a volume ratio of 1: 2 are mixed. did.

<Battery assembly>
A flat battery was assembled using the positive electrode, negative electrode, and non-aqueous electrolyte described above. FIG. 1 schematically shows a cross-section of an assembled nonaqueous electrolyte lithium ion secondary battery 1. The assembly was performed as follows.

  After inserting the insulating ring 8 into the side surface of the stainless steel container 13, the negative electrode 4, the separator 3, and the positive electrode 2 were laminated in this order, and the separator 3 was impregnated with the nonaqueous electrolytic solution. As the separator, a polypropylene microporous film was used. An aluminum pressing plate 5 and a leaf spring 6 are sequentially stacked on the positive electrode 2, a stainless steel lid 7 is placed on the insulating packing 9, and tightened with bolts 12 and nuts 11 on the insulating sleeve 10. A flat battery was constructed.

  The positive electrode 2 is electrically connected to the lid 7 via the pressing plate 5 and the leaf spring 6, and the negative electrode 4 is electrically connected to the bolt 12 via the container 13. Thereby, electrical energy can be taken out from the inside of the battery using the lid 7 and the bolt 12 as terminals.

The general composition formula Li _1.03 Co ₀ was used as the positive electrode active material in the same procedure as in Example 1 except that Mg (OH) ₂ was used as the Mg compound instead of Al (OH) ₃ used in Example 1. A lithium-containing cobalt oxide represented by _.95 Ni _0.04 Mg _0.01 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 2 was produced in the same procedure as in Example 1 above.

A lithium-containing cobalt oxide represented by the general composition formula Li _1.06 Co _0.95 Ni _0.04 Al _0.01 O ₂ was synthesized as a positive electrode active material in the same procedure as in Example 1. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 3 was produced in the same procedure as in Example 1.

In addition to the compound used in Example 1, Mg (OH) ₂ was used as the Mg compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.03 Co _0.95 Ni was used as the positive electrode active material. A lithium-containing cobalt oxide represented by _0.035 Al _0.01 Mg _0.005 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 4 was produced in the same procedure as in Example 1.

In the same procedure as in Example 1, a lithium-containing cobalt oxide represented by the general composition formula Li _1.03 Co _0.94 Ni _0.05 Al _0.01 O ₂ was synthesized as a positive electrode active material. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 5 was fabricated in the same procedure as in Example 1 above.

In addition to the compound used in Example 1, ZrO ₂ was used as the Zr compound, and the other procedures were the same as in Example 1 except that the composition as the positive electrode active material: Li _1.06 Co _0.95 Ni _0.04 Al A lithium-containing cobalt oxide represented by _0.005 Zr _0.005 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 6 was produced in the same procedure as in Example 1.

A lithium-containing cobalt oxide represented by the composition: Li _1.10 Co _0.97 Ni _0.02 Al _0.005 Zr _0.005 O ₂ was synthesized as a positive electrode active material in the same procedure as in Example 6. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 7 was fabricated in the same procedure as in Example 1 above.

In addition to the compound used in Example 2, MnCO ₃ was used as the Mn compound, and the other procedures were the same as in Example 2 except that general composition formula Li _1.03 Co _0.95 Ni _0.04 Mg _0.005 A lithium-containing cobalt oxide represented by Mn _0.005 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 8 was fabricated in the same procedure as in Example 1 above.

In addition to the compound used in Example 2, TiO ₂ was used as the Ti compound, and the general composition formula Li _1.03 Co _0.95 Ni _0.04 Mg _0.005 was otherwise obtained in the same procedure as in Example 2. A lithium-containing cobalt oxide represented by Ti _0.005 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 9 was produced in the same procedure as in Example 1 above.

In addition to the compound used in Example 1, MoO ₃ was used as the Mo compound, and the other procedures were the same as in Example 1, and the general composition formula Li _1.03 Co _0.95 Ni _0.04 Al _{0.005 was used.} A lithium-containing cobalt oxide represented by Mo _0.005 O ₂ was synthesized. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 10 was produced in the same procedure as in Example 1 above.

Instead of Al (OH) ₃ used in Example 6, the same procedure as in Example 6 was used except that Mg (OH) ₂ was used as the Mg compound as the Mg compound, and the general composition formula Li ₁ was used as the positive electrode active material. A lithium-containing cobalt oxide represented by _.01 Co _0.98 Ni _0.01 Al _0.005 Zr _0.005 O ₂ was synthesized. Next, ammonia water is dropped into a mixed aqueous solution of LiOH.OH, Al (NO ₃ ) ₃ · 9H ₂ O and Ni (NO ₃ ) ₂ · 6H ₂ O, and the pH of the aqueous solution is in the range of 10-12. And the aqueous solution was filtered. The positive electrode active material was immersed in the filtered aqueous solution and stirred, and a mixed film of LiOH, Ni (OH) ₂ , and Al (OH) ₃ was formed on the surface. The positive electrode active material on which the film was formed was dried at 80 ° C., and further fired at 650 ° C. for 5 hours. In the film formed on the surface of the positive electrode active material by such a process, Li, Ni, and Al are 11% (11 at%), 10% (10 at%), and 1% (atomic ratio with respect to Co, respectively) 1 at%). Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 11 was produced in the same procedure as in Example 1.

A lithium-containing cobalt oxide represented by the general composition formula Li _1.01 Co _0.98 Ni _0.01 Al _0.005 Zr _0.005 O ₂ was synthesized as a positive electrode active material in the same procedure as in Example 6. . Next, aqueous ammonia was added dropwise to a mixed aqueous solution of LiOH.OH and (NH ₄ ) ₂ HPO ₄ to adjust the pH of the aqueous solution to be in the range of 10 to 12, and this aqueous solution was filtered. The positive electrode active material was immersed in the filtered aqueous solution and stirred, and a mixed film of LiOH.OH and (NH ₄ ) ₂ HPO ₄ was formed on the surface. The positive electrode active material on which the film was formed was dried at 80 ° C. and further fired at 400 ° C. for 10 hours. The film formed on the surface of the positive electrode active material by such a process contains 9 at% and 3 at% of Li and P in an atomic ratio with respect to Co, respectively. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 12 was produced in the same procedure as in Example 1.

In the same procedure as in Example 6, a lithium-containing cobalt oxide represented by the general composition formula Li _1.03 Co _0.945 Ni _0.04 Al _0.01 Zr _0.005 O ₂ was synthesized as a positive electrode active material. . Next, Zr (OC ₃ H ₇ ) ₄ was immersed in a 2-propanol solvent and stirred to form a Zr (OC ₃ H ₇ ) ₄ coating on the surface. The positive electrode active material on which the film was formed was dried at 80 ° C. and further fired at 400 ° C. for 10 hours. The film formed on the surface of the positive electrode active material by such a process contains 2 at% Zr in atomic ratio to Co. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 13 was produced in the same procedure as in Example 1.

In the same procedure as in Example 6, a lithium-containing cobalt oxide represented by the general composition formula Li _1.03 Co _0.945 Ni _0.04 Al _0.01 Zr _0.005 O ₂ was synthesized as a positive electrode active material. . Then, it was added dropwise _{Al (NO 3) 3 · 9H} 2 O and _{(NH 4)} ammonia water with stirring a mixed solution of 2 HPO _4, was adjusted to pH of the aqueous solution is in the range of 10 to 12 . The positive electrode active material was immersed in this aqueous solution and stirred, and a mixed film of Al (NO ₃ ) ₃ and (NH ₄ ) ₂ HPO ₄ was formed on the surface. The positive electrode active material on which the film was formed was dried at 80 ° C. and further fired at 400 ° C. for 10 hours. The coating formed on the surface of the positive electrode active material by such a process contains Al and P in an atomic ratio of 1 at% and 1 at%, respectively. Using this positive electrode active material, a non-aqueous electrolyte lithium ion secondary battery according to Example 14 was produced in the same procedure as in Example 1.

  The compositions of the positive electrode active materials of Examples 1 to 14 and the elements covering the surface of the positive electrode active material are listed in FIG.

Comparative example

A lithium-containing cobalt oxide having the composition of the positive electrode active material as shown in Comparative Examples 1 to 4 in FIG. 2 was prepared. The general composition formula of the positive electrode oxide of each comparative example is as follows. Comparative Example 1 is Li _0.098 CoO ₂ , Comparative Example 2 is Li _1.01 Co _0.98 Zr _0.02 O ₂ , Comparative Example 3 is LiCo _0.9 Al _0.1 O ₂ , and Comparative Example 4 is LiCo _0.98 Ni _0.02 O ₂ .

In Comparative Example 4, an Al film was formed on the surface of the produced positive electrode active material by the following procedure. That added dropwise aqueous ammonia with stirring _{Al (NO 3) 3 · 9H} 2 O aqueous solution was adjusted to pH of the aqueous solution is in the range of 10-12. The positive electrode active material was immersed in this aqueous solution to form an Al (NO ₃ ) ₃ coating on the surface. The positive electrode active material on which the film was formed was dried at 80 ° C., and further fired at 650 ° C. for 5 hours. By such a process, Al was formed on the surface of the positive electrode active material.

  Using these positive electrode active materials, a positive electrode was produced in the same procedure as in Example 1, and further, non-aqueous electrolyte lithium ion secondary batteries according to Comparative Examples 1 to 4 were produced in the same procedure as in Example 1. .

<Battery evaluation>
About each nonaqueous electrolyte lithium ion secondary battery of Examples 1-14 and Comparative Examples 1-4, the discharge capacity and the continuous charge durable time were measured in the following way.

<Measurement of discharge capacity>
At room temperature (25 ° C.), charging is performed at a constant current until the battery voltage reaches 4.45 V at a current with a load factor of 0.05 C, and then the current becomes a load factor of 0.005 C at a constant voltage of 4.45 V Charged up to. The battery was left for 1 hour after charging. Next, the battery was discharged at a constant current at a load factor of 0.05 C until the battery voltage reached 3.00 V, and the discharge capacity was measured. The measurement results are shown in FIG.

<Measurement of continuous charge endurance>
After the battery was left in a constant temperature bath at 60 ° C. for 30 minutes, charging was started at a constant current with a load factor of 0.05 C while maintaining the environment at 60 ° C., and the battery was charged until the battery voltage reached 4.5V. After the current value decays, the battery is continuously charged at a constant voltage of 4.5 V until the load factor becomes 0.05 C again, and the time from when charging is started until it reaches 0.05 C again is continued. It was measured as the charge endurance time. The measurement results are shown in FIG.

  The following can be understood from the results shown in FIG. In the nonaqueous electrolyte lithium ion secondary batteries according to Examples 1 to 14, the discharge capacity of 170 mAh / g or more and the continuous charge durability time of 300 hours or more are compatible in constant current discharge from 4.45 V to 3 V. On the other hand, in the non-aqueous electrolyte lithium ion secondary batteries according to Comparative Examples 1 to 4, a discharge capacity of 170 mAh / g or more and a continuous charge durability time of 300 hours or more are not compatible.

  In Comparative Example 1, no transition metal element other than Co is contained in the positive electrode active material. Further, since Li is slightly deficient, the size of the positive electrode active material particles is small and the average diameter is about 3 μm. Although the specific surface area is large, the discharge capacity is high, but it is easy for Co to elute from the surface of the positive electrode active material under high temperature and high voltage, and this is considered to have shortened the continuous charge durability time.

  In Comparative Example 2, Ni is not contained in the positive electrode active material. Further, a transition metal element (at least one element of Al and Mg) corresponding to M in (1) or (2) is not contained in the general composition formula. Furthermore, 2% of the number of Co atoms is replaced by Zr. As a result, the size of the active material particles is small, and the average diameter is about 3 μm. Although the specific surface area of the positive electrode active material is large, it is considered that Zr forms a lithium-containing zirconium oxide, so that the discharge capacity is reduced. In addition, it is considered that the large specific surface area of the positive electrode active material facilitates the elution of Co from the active material surface under high temperature and high voltage, and thus the continuous charge durability time is shortened.

  In Comparative Example 3, the positive electrode active material does not contain Ni. Moreover, Al is excessively contained as a transition metal element corresponding to M in (1) or (2) in the general composition formula. As a result, although the crystal structure is stabilized and the continuous charge endurance time is lengthened, it is considered that the crystal structure is greatly distorted to lower the Li mobility, thereby reducing the discharge capacity.

  In Comparative Example 4, the positive electrode active material does not contain a transition metal element corresponding to M in (1) or (2) in the general composition formula. The surface of the positive electrode active material is coated with an Al oxide so that the number of Al atoms is 20 at% of the number of Co atoms. Both the discharge capacity and the continuous charge endurance time are inferior to those of the examples. In addition, it is thought that the reason why the continuous charge durability time has reached a certain length is that the coating oxide suppresses the contact between the positive electrode active material and the electrolytic solution. However, this oxide coating inhibits the insertion and desorption of Li ions during the battery reaction, so it is considered that the discharge capacity is reduced.

  The details of why the nonaqueous electrolyte lithium ion secondary batteries according to Examples 1 to 14 can provide good results are not clear. However, in the lithium-containing cobalt oxide as the positive electrode active material, the Co element is replaced with an appropriate amount of Ni and an element such as Al or Mg, so that it continuously at a high voltage of 4.5 V or higher at a high temperature of 60 ° C. It is considered that the structural phase transition is suppressed even when charged. In addition to the above-mentioned action, the positive electrode active material whose surface is coated has a synergistic effect of suppressing nucleophilic / electrophilic reaction with the electrolytic solution, and oxygen involved in Co elution. It is considered that the detachment of is reduced.

  As described above, according to the nonaqueous electrolyte lithium ion secondary battery of the present invention, it is possible to provide a nonaqueous electrolyte lithium ion secondary battery having a large discharge capacity and capable of continuous charging at a high voltage at a high temperature. it can. It is excellent in the Co elution suppression effect at the time of charging until the positive electrode potential of the nonaqueous electrolyte lithium ion secondary battery according to the present invention is 4.4 V or higher with respect to lithium. In addition, it can be seen that the capacity at a charge / discharge current value at a practical level is ensured without significantly inhibiting the diffusion of lithium ions.

  Note that the same effect can be obtained by using V, Cr, Fe, Y, W, and B other than Zr, Mn, Ti, and Mo for M ′. Moreover, these elements can also be mixed and used suitably.

  As described above, various embodiments and modifications have been described, but the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte lithium ion secondary battery 2 Positive electrode 3 Separator 4 Negative electrode 5 Holding plate 6 Leaf spring 7 Lid 8 Insulating ring 9 Insulating packing 10 Insulating sleeve 11 Nut 12 Bolt 13 Container

Claims (7)

General composition _{formula: Li 1 + α Co 1-} β-γ Ni β M γ O 2-δ
(In the formula, M represents at least one element of Al and Mg, and α, β, γ, and δ are 0.01 ≦ α ≦ 0.10, 0.01 ≦ β ≦ 0.05, 0. .001 ≦ γ ≦ 0.02, 0 ≦ δ ≦ 0.01)), a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery,
The particle surface of the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery has at least one coating element selected from the group consisting of Li, Zr, Ti, Al, Ni, Mn, La, Zn, P and B. When the oxide contains Li, the number of atoms of the covering element is 50% or less of the number of Co atoms contained in the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery. And when the oxide does not contain Li, it is 10% or less of the number of Co atoms contained in the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery, for a non-aqueous electrolyte lithium ion secondary battery Positive electrode material. The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to claim 1,
Substituting M ′ for Co in the general composition formula,
General composition formula: Li1 _{+ [alpha]} Co1- [ _{beta]-[gamma]-[eta]} Ni [ _beta] M [ _gamma] M '[ _{eta] O2- [ delta].}
(Wherein M ′ represents at least one element selected from the group consisting of Zr, Mo, V, Ti, Mn, Cr, Fe, Y, W, and B, and α, β, γ, δ, and η is 0.01 ≦ α ≦ 0.10, 0.01 ≦ β ≦ 0.05, 0.001 ≦ γ ≦ 0.02, 0 ≦ δ ≦ 0.01, 0.001 ≦ η ≦ 0.005 Is a parameter that satisfies
A positive electrode material for a non-aqueous electrolyte lithium ion secondary battery, characterized by comprising a lithium-containing cobalt oxide represented by: The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery according to claim 1 or 2 ,
The positive electrode material for a non-aqueous electrolyte lithium ion secondary battery is characterized in that the average diameter of the particles of the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery is 5 μm or more and 20 μm or less. In the positive electrode material for nonaqueous electrolyte lithium ion secondary batteries according to any one of claims 1 to 3 ,
The nonaqueous electrolyte lithium ion secondary battery, wherein M contains Mg, and the number of Mg atoms relative to the number of Co atoms contained in the positive electrode material for a nonaqueous electrolyte lithium ion secondary battery is 0.01 or less Positive electrode material. In the positive electrode material for nonaqueous electrolyte lithium ion secondary batteries according to any one of claims 1 to 3 ,
The M includes both Al and Mg, and the number of Al atoms relative to the number of Co atoms contained in the positive electrode material for a non-aqueous electrolyte lithium ion secondary battery is 0.01 or more and 0.02 or less, and the non-aqueous electrolyte A positive electrode material for a non-aqueous electrolyte lithium ion secondary battery, wherein the atomic ratio of Mg to the number of Co atoms contained in the positive electrode material for a lithium ion secondary battery is 0.005 or less. In a non-aqueous electrolyte lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The said positive electrode contains the positive electrode material for nonaqueous electrolyte lithium ion secondary batteries as described in any one of Claim 1 thru | or 5. The nonaqueous electrolyte lithium ion secondary battery characterized by the above-mentioned. The nonaqueous electrolyte lithium ion secondary battery according to claim 6 ,
The peak potential confirmed to be the highest potential of the dQ / dV curve obtained by differentiating the charge curve of the positive electrode with voltage when charged to 5 V at a load factor of 0.1 C or less at room temperature is 4.64 V or more. A non-aqueous electrolyte lithium ion secondary battery, characterized in that:

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