JP5050452B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention provides 1 V vs. 1 The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode containing a substance capable of inserting / extracting lithium ions at a potential of Li / Li ⁺ or higher.

  In recent years, small and lightweight non-aqueous electrolyte secondary batteries have been widely used as power sources for electronic devices such as mobile phones and digital cameras. Generally, lithium transition metal composite oxides are used for the positive electrode of nonaqueous electrolyte secondary batteries, carbon materials are used for the negative electrode, and carbonates containing lithium salts are used for the electrolyte. It has been put to practical use as a feature.

  When a carbon material is used for the negative electrode of a non-aqueous electrolyte secondary battery, it is used by lowering the potential to a potential region where the electrolytic solution undergoes reductive decomposition. SEI (Solid Electrolyte Interface) formed on the negative electrode surface due to the decomposition of the electrolyte suppresses the subsequent decomposition of the electrolytic solution. However, when the potential of the negative electrode becomes high or exposed to a high temperature, SEI dissolves in the electrolytic solution, and decomposition of the electrolytic solution occurs again on the surface of the carbon material.

A technique for charging / discharging in a potential region in which reductive decomposition of an electrolytic solution does not occur using a compound different from a carbon material as a negative electrode active material of a non-aqueous electrolyte secondary battery has been performed for a long time. For example, Patent Document 1 _{discloses a} technique using lithium titanate (Li _4/3 Ti _5/3 O ₄ ), Non-Patent Document 1 _{discloses a} technique using Li _7/3 Ti _5/3 O ₄ , Patent Document 2 Patent Document 3 discloses a technique using titanium oxide (TiO ₂ ), Patent Document 3 discloses a technique using Nb ₂ O ₃ , and Patent Document 4 discloses a technique using Nb ₂ O ₅ .

  Patent Document 5 discloses that in a cell using a positive electrode using a lithium transition metal double oxide as a positive electrode active material and a negative electrode using graphitic carbon as a negative electrode active material, manganese ions are present in the negative electrode. Thus, a technique for suppressing a decrease in capacity and output associated with a charge / discharge cycle is disclosed. In Patent Document 5, manganese ions are reduced on the negative electrode surface by the initial charge and deposited as a transition metal, and the metal manganese exhibits a catalytic action that promotes the decomposition of the nonaqueous electrolytic solution, thereby forming a stable film on the negative electrode surface. By doing so, decomposition of the non-aqueous electrolyte accompanying subsequent charging / discharging is suppressed.

However, as described in Patent Document 6, in the negative electrode using lithium titanate, since the reduction potential is as high as about 1.5 V with respect to Li / Li ⁺ , the film is formed by the decomposition of the nonaqueous electrolytic solution. It is unclear whether it is formed or not, and it is also unclear whether there is a mechanism by which transition metals such as manganese deposited on the negative electrode surface exert a catalytic action.

Further, several techniques for adding a cobalt phosphate compound or cobalt oxide to the negative electrode active material have been disclosed. For example, Patent Document 7 discloses a technique of including cobalt phosphate hydrate in a negative electrode active material in a nonaqueous electrolyte secondary battery using carbon, aluminum, and an aluminum alloy as a negative electrode active material. Patent Document 8 discloses a technique in which an oxide such as Co ₃ O ₄ is dispersed inside a carbon material that is a negative electrode active material.

Furthermore, in Patent Document 9, a carbon material, Li ₄ Ti ₅ O ₁₂ or the like is used as the negative electrode active material, and a manganese compound is included in a part of the surface layer portion, whereby hydrogen generated by the decomposition of water is removed from the manganese compound. (A specific example is only MnO ₂ is described).
JP 07-335261 A JP-A-11-307120 JP 2004-079426 A JP 05-114420 A JP 2005-085545 A JP 2001-210324 A JP 11-191417 A JP 2004-349253 A JP 2001-313077 A J. et al. Jiang, J. et al. Chen and J.H. R. Dahn, J .; Electrochem. Soc. , 151, A2082 (2004)

The negative electrode active material of the non-aqueous electrolyte secondary battery includes 1 V vs. 1 such as lithium titanate, titanium oxide, niobium pentoxide. When using a compound that causes a redox reaction (insertion / desorption of lithium ions) in a potential region of Li / Li ⁺ or higher, compared to the case of using a carbon-based material such as graphite as the negative electrode active material, the charge / discharge cycle Excellent performance.

  However, when lithium titanate, titanium oxide, niobium pentoxide or the like is used as the negative electrode active material of the non-aqueous electrolyte secondary battery and stored at a high temperature of 40 ° C. or higher, there is a problem that the internal resistance of the battery is greatly increased. .

On the other hand, although there are examples in which manganese ions, cobalt phosphate hydrate, and Co ₃ O ₄ are added to a carbon-based material as a negative electrode active material, and examples in which a manganese compound is added to lithium titanate as a negative electrode active material, The effect on internal resistance when the battery was stored at high temperature was unknown.

  In addition, when the negative electrode active material is lithium titanate, titanium oxide, niobium oxide, etc., addition of manganese compounds other than manganese dioxide and cobalt compounds has not been studied, and the effect has not been known.

Therefore, the object of the present invention is 1 V vs. In the non-aqueous electrolyte secondary battery using a material capable of inserting / extracting lithium ions at a potential of Li / Li ⁺ or higher as a negative electrode active material, an increase in internal resistance at high temperature is suppressed and self-discharge is reduced. The object is to provide a non-aqueous electrolyte secondary battery.

The invention of claim 1 is a nonaqueous electrolyte secondary battery comprising a positive electrode active material, a negative electrode active material, and a nonaqueous electrolyte, wherein the compound X is present on the surface of the negative electrode active material, and the negative electrode active material is 1 Vvs. Li / Li ⁺ is a compound capable of inserting / extracting lithium ions at a potential of not less than Li / Li ⁺ , and the compound X includes manganese oxide other than manganese dioxide, manganese phosphate, manganese fluoride, cobalt oxide, cobalt phosphate, fluorine It is at least one selected from the group consisting of cobalt halides.

  The invention of claim 2 is characterized in that, in the non-aqueous electrolyte secondary battery, the ratio of the compound X to the negative electrode active material is 0.1% by mass or less.

According to a third aspect of the present invention, in the nonaqueous electrolyte secondary battery, the negative electrode active material is titanium represented by the general formula Li _x Ti _y O ₄ (1.0 ≦ x ≦ 2.4, 1 ≦ y ≦ 2). It is characterized by being lithium acid lithium.

In the present invention, the negative electrode active material is 1 V vs. Li / Li ⁺ is a compound capable of inserting / extracting lithium ions at a potential of not less than Li / Li ⁺ , and compound X is present on the surface of the negative electrode active material, and the compound X is manganese oxide other than manganese dioxide, manganese phosphate By using at least one selected from the group consisting of manganese fluoride, cobalt oxide, cobalt phosphate, and cobalt fluoride, the increase in internal resistance at high temperatures is suppressed and self-discharge is reduced. A secondary battery can be obtained. The increase in internal resistance is thought to be due to the decomposition reaction of the electrolyte solution on the negative electrode surface. The reason for the reduced self-discharge is presumed to be that the reaction is suppressed.

  The reason is that the compound X present on the surface of the negative electrode active material does not function as a catalyst for the decomposition reaction of the electrolytic solution solvent like manganese on the surface of the carbon material, but a protective component that suppresses the decomposition of the electrolytic solution solvent As a result, even when the battery is stored at a high temperature of 40 ° C. or higher, decomposition of the electrolyte solvent hardly occurs.

  In addition, when the ratio of the compound X to the negative electrode active material is 0.1% by mass or less, the function becomes higher as a protective component that suppresses the decomposition of the electrolyte solution solvent of the compound X, and after high-temperature storage at 40 ° C. or higher. Self-discharge is further reduced, and the increase in the capacity retention rate becomes remarkable.

Furthermore, when the lithium titanate represented by the general formula Li _x Ti _y O ₄ (1.0 ≦ x ≦ 2.4, 1 ≦ y ≦ 2) is used as the negative electrode active material, the charge / discharge cycle performance is better. It becomes.

The present invention provides a nonaqueous electrolyte secondary battery comprising a positive electrode active material, a negative electrode active material, and a nonaqueous electrolyte, wherein the compound X is present on the surface of the negative electrode active material, and the negative electrode active material is 1 Vvs. Li / Li ⁺ is a compound capable of inserting / extracting lithium ions at a potential of not less than Li / Li ⁺ , and the compound X includes manganese oxide other than manganese dioxide, manganese phosphate, manganese fluoride, cobalt oxide, cobalt phosphate, fluorine It is at least one selected from the group consisting of cobalt halides. In the nonaqueous electrolyte secondary battery, the ratio of the compound X to the negative electrode active material is 0.1% by mass or less.

The negative electrode active material used in the present invention is 1 V vs. There is no particular limitation as long as it is a substance that can insert and desorb lithium ions at a potential of Li / Li ⁺ or higher, and various materials can be used as appropriate. For example, lithium titanate, titanium oxide, niobium oxide, and the like can be given.

Among these, lithium titanate is preferable because charge / discharge cycle performance is good. Examples of the lithium titanate, are preferably those represented by the general formula _{Li x Ti y O 4 (1.0} ≦ x ≦ 2.4,1 ≦ y ≦ 2). When x and y deviate from this range in the general formula Li _x Ti _y O ₄ , the stability of the crystal structure of lithium titanate is inferior and the charge / discharge cycle performance deteriorates.

TiO, Ti ₂ O ₃ , anatase TiO ₂ , rutile TiO ₂ or the like can be used as titanium oxide, and NbO, NbO ₂ , Nb ₂ O ₃ , Nb ₂ O ₅ or the like is used as niobium oxide. be able to.

  In the present invention, the compound X functions as a protective component that suppresses the decomposition of the electrolyte solvent on the surface of the negative electrode active material. Therefore, the compound X needs to exist on the surface of the negative electrode active material. Although the compound X should just exist in a part of surface of a negative electrode active material, the whole surface of a negative electrode active material may be covered or it may exist in the inside of a negative electrode active material.

As the compound X existing on the surface of the negative electrode active material, manganese oxide (MnO, Mn ₂ O ₃ , Mn ₂ O ₇ ), manganese phosphate (Mn ₃ (PO ₄ ) ₂ ), manganese fluoride (MnF ₂ , MnF) ₃ ), cobalt oxide (CoO, Co ₂ O ₃ , Co ₃ O ₄ , CoO ₂ ), cobalt phosphate (Co ₃ (PO ₄ ) ₂ ), cobalt fluoride (CoF ₂ , CoF ₃ ), and the like can be used. .

  In the nonaqueous electrolyte secondary battery of the present invention, when the ratio of the compound X to the negative electrode active material exceeds 0.1% by mass, the resistance starts to increase. Therefore, the ratio of compound X to the negative electrode active material is preferably 0.1% by mass or less. Further, since the effect is small when the ratio of the compound X to the negative electrode active material is smaller than 0.01% by mass, the ratio of the compound X to the negative electrode active material is preferably set to 0.01% by mass or more.

There is no restriction | limiting in particular as a positive electrode active material used for the nonaqueous electrolyte secondary battery of this invention, A various material can be used suitably. For example, transition metal compounds such as manganese dioxide and vanadium pentoxide, transition metal chalcogen compounds such as iron sulfide and titanium sulfide, and complex oxides Li _x MO _2−δ of these transition metals and lithium (however, , M represents Co, Ni, or Mn, and 0.4 ≦ x ≦ 1.2 and 0 ≦ δ ≦ 0.5), or these composite oxides may include Al, Mn, Fe, Ni , Co, Cr, Ti, and Zn, or at least one element selected from the group consisting of Zn, or nonmetallic elements such as P and B can be used.

Further, the composite oxide of lithium and nickel, i.e. the positive electrode active material (however represented by _{LiNi p M1 q M2 r O 2} -δ, M1, M2 is Al, Mn, Fe, Ni, Co, Cr, Ti, and It represents at least one element selected from the group consisting of Zn, or a nonmetallic element such as P or B, 0.4 ≦ x ≦ 1.2, 0.8 ≦ p + q + r ≦ 1.2, 0 ≦ δ ≦ Composite oxide of 0.5) or the like can be used.

  Among these, high voltage, high energy density, and excellent cycle performance, lithium-manganese composite oxide, lithium-cobalt composite oxide, lithium-cobalt-nickel composite oxide, lithium-cobalt-nickel-manganese A composite oxide or a composite oxide in which a part of cobalt, nickel, or manganese of these composite oxides is substituted with another element is preferable.

  There is no restriction | limiting in particular as a binder used for a positive electrode, A various material can be used suitably. For example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (FEP), polytetrafluoroethylene (PTFE), fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene- At least one selected from the group consisting of butadiene rubber (SBR), acrylonitrile-butadiene rubber (ABS), fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, or derivatives thereof can be used. .

  There is no restriction | limiting in particular as a electrically conductive agent used for a positive electrode, A various material can be used suitably. For example, Ni, Ti, Al, Fe, or an alloy or carbon material of two or more kinds thereof can be given. Among these, it is preferable to use a carbon material. Examples of the carbon material include amorphous carbon such as natural graphite, artificial graphite, vapor-grown carbon fiber, acetylene black, ketjen black, and needle coke.

  As a solvent used when mixing the positive electrode mixture, a non-aqueous solvent or an aqueous solution can be used. Non-aqueous solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide, methyl ethyl ketone (MEK), cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropyl Examples include amine, ethylene oxide, and tetrahydrofuran (THF). Moreover, you may add a dispersing agent, a thickener, etc. to these.

  There is no restriction | limiting in particular as a binder used for a negative electrode, A various material can be used suitably. For example, in addition to the same binder used for the positive electrode, carboxymethyl cellulose (CMC), carboxy-modified polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polypropylene Alternatively, at least one selected from the group consisting of these derivatives and the like can be used.

  As the solvent used for mixing the negative electrode mixture, the same non-aqueous solvent used for mixing the electrode binder can be used, and a dispersant, a thickener, etc. can be added to these. Good.

  As the current collector substrate of the electrode used in the present invention, iron, copper, nickel, stainless steel (SUS), or aluminum can be used. Examples of the shape include a sheet, a foam, a sintered porous body, and an expanded lattice. Further, a current collector having a hole in an arbitrary shape can be used.

  There is no restriction | limiting in particular as an organic solvent of the electrolyte solution used for this invention, A various material can be used suitably. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane hydrocarbons, etc. Among these, ethers, ketones, esters, lactones, halogenated hydrocarbons, carbonates, and sulfolane hydrocarbons are preferable.

  Further examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 1,2-dichloroethane, γ-butyrolactone, γ-valerolactone, dimethoxyethane, diethoxyethane, methyl formate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, Vinylene carbonate, butylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfo Examples thereof include run, trimethyl phosphate, triethyl phosphate, and phosphazene derivatives, and mixed solvents thereof.

  Especially, it is preferable to use ethylene carbonate, propylene carbonate, (gamma) -butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate individually or in mixture of 2 or more types.

Moreover, there is no restriction | limiting in particular as a solute used for this invention, A various solute can be used suitably. For example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF (CF ₃ ) ₅ , LiPF ₂ (CF ₃ ) ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₅ (CF ₃ ), LiPF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ or the like can be used alone or in admixture of two or more. Of these, LiPF ₆ is preferably used because of its good ion conductivity. Furthermore, the lithium salt concentration is preferably 0.5 to 2.0 mol / dm ³ .

Also included in the electrolyte are carbonates such as vinylene carbonate and butylene carbonate, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, tetraethylammonium It can be used even if it contains at least one selected from the group consisting of a fluoride fluoride complex of fluoride or a derivative thereof, phosphazene and derivatives thereof, an amide group-containing compound, an imino group-containing compound, or a nitrogen-containing compound. Moreover, it can be used even if it contains at least one selected from CO ₂ , NO ₂ , CO, SO _{2 and the} like.

  There is no restriction | limiting in particular as a separator used for this invention, A various material can be used suitably. For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned, and among them, a synthetic resin microporous film is preferable. As the material of the synthetic resin microporous membrane, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polyolefins such as polyethylene, polypropylene, and polybutene are used. Among them, polyethylene and polypropylene microporous membranes, Alternatively, a polyolefin microporous film such as a microporous film obtained by combining these is preferable in terms of thickness, film strength, film resistance, and the like.

  In addition, materials, laminates of multiple microporous membranes with different weight average molecular weights and porosity, and appropriate additives such as various plasticizers, antioxidants, and flame retardants are contained in these microporous membranes You can use what you are doing.

  In addition, the electrolyte can be used in combination with a solid or gel ion conductive electrolyte. When combined, the non-aqueous electrolyte battery includes a positive electrode, a negative electrode and a separator, an organic or inorganic solid electrolyte and the non-aqueous electrolyte, or an organic or inorganic solid electrolyte membrane as the positive electrode, negative electrode and separator. A combination with the non-aqueous electrolyte is mentioned. A porous polymer solid electrolyte membrane can also be used for the ion conductive electrolyte.

Examples of the ion conductive electrolyte include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyethylene glycol and derivatives thereof, LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _0.5-3x R _{0.5 + x} TiO ₃ (R = La, Pr, Nd, Sm), or using thiolysicon typified by Li _4-x Ge _1-x P _x S ₄ it can. Furthermore, oxide glass such as LiI-Li ₂ O—B ₂ O ₅ system, Li ₂ O—SiO ₂ system, or LiI—Li ₂ S—B ₂ S ₃ system, LiI—Li ₂ S—SiS ₂ system, Sulfide glass such as Li ₂ S—SiS ₂ —Li ₃ PO ₄ can be used.

  The shape of the battery of the present invention is not particularly limited, and the present invention is applied to non-aqueous electrolyte secondary batteries of various shapes such as a square, an ellipse, a cylinder, a coin, a button, and a sheet. Is possible.

  Next, a preferred embodiment of the present invention will be described. However, the present invention is not limited to the following examples.

[Examples 1 to 18 and Comparative Examples 1 to 3]
[Example 1]
Manganese dioxide (MnO ₂ ), lithium hydroxide (LiOH) and aluminum oxide (Al ₂ O ₃ ) are mixed, heated in air at 700 ° C. for 10 hours, and positive electrode active material Li _1.1 Mn _1.8 Al _0.1 O ₄ was obtained. A paste was prepared by mixing 92% by mass of this positive electrode active material, 3% by mass of acetylene black as a conductive material, and 5% by mass of an NMP solution (solid content ratio 12% by mass) of PVdF (binder). This paste was applied to an aluminum foil having a thickness of 20 μm and then dried at 80 ° C. Then, after vacuum drying at 150 ° C., the mixture layer was pressed so that the porosity of the mixture layer was 35% to obtain a positive electrode (P1).

Titanium dioxide (TiO ₂ ) and lithium hydroxide (LiOH) were mixed and then heated in air at 600 ° C. for 15 hours to obtain a negative electrode active material Li ₄ Ti ₅ O ₁₂ . A paste was prepared by mixing 87% by mass of this negative electrode active material, 5% by mass of acetylene black as a conductive material, and 8% by mass of an NMP solution (solid content ratio 13% by mass) of PVdF (binder). This paste was applied to a copper foil having a thickness of 10 μm and then dried at 80 ° C. Then, after vacuum drying at 150 ° C., the mixture layer was pressed so that the porosity of the mixture layer was 35% to obtain a lithium titanate negative electrode (N1).

Next, a non-aqueous treatment solution in which Mn (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) were dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 was prepared. . This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

A lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, and a lithium electrode was used as a counter electrode, and a current of 0.5 mA / cm ² was applied at room temperature based on the negative electrode for 15 hours.

After energization, the lithium titanate negative electrode was taken out and washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that manganese oxide (MnO) was generated on the negative electrode surface. In addition, the quantitative analysis of manganese oxide was not performed. As in Example 1, in Examples 2 to 18 below, quantitative analysis of Compound X present on the surface of the negative electrode active material was not performed.

The positive electrode (P1) and the negative electrode (N1) prepared in this way are wound with a polypropylene separator, which is a continuous porous body having a thickness of 2 μm and a porosity of 45%, being stacked therebetween, having a height of 50 mm, a width of 34 mm, and a thickness of The prismatic battery was assembled by inserting into a 5.2 mm container. Finally, a nonaqueous electrolytic solution in which 1.2 mol / dm ³ of LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 is injected into the battery. Thus, the nonaqueous electrolyte secondary battery (A1) of Example 1 having a design capacity of 15 mAh was obtained.

[Example 2]
A non-aqueous treatment liquid was prepared by dissolving Mn (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

The lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A2) of Example 2 was obtained in the same manner as in Example 1.

[Example 3]
A non-aqueous treatment solution was prepared by dissolving Mn (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

The lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that manganese fluoride (MnF ₂ ) was generated on the negative electrode surface. A non-aqueous electrolyte secondary battery (A3) of Example 3 was obtained in the same manner as Example 1 using the negative electrode thus prepared.

[Example 4]
A non-aqueous treatment solution was prepared by dissolving Co (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) in a solvent mixture of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

The lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that cobalt oxide (CoO) was generated on the negative electrode surface. A non-aqueous electrolyte secondary battery (A4) of Example 4 was obtained in the same manner as Example 1 using the negative electrode thus prepared.

[Example 5]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

The lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. A nonaqueous electrolyte secondary battery (A5) of Example 5 was obtained in the same manner as Example 1 using the negative electrode thus prepared.

[Example 6]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

The lithium titanate negative electrode (N1) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that cobalt fluoride (CoF ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A6) of Example 6 was obtained in the same manner as in Example 1.

[Example 7]
A commercially available anatase type titanium dioxide (TiO ₂ ) was used in place of Li ₄ Ti ₅ O _{12 as} the negative electrode active material, and a titanium oxide negative electrode (N2) was obtained in the same manner as the lithium titanate negative electrode (N1).

A non-aqueous treatment liquid was prepared by dissolving Mn (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that manganese oxide (MnO) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A7) of Example 7 was obtained in the same manner as in Example 1.

[Example 8]
A non-aqueous treatment liquid was prepared by dissolving Mn (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. A nonaqueous electrolyte secondary battery (A8) of Example 8 was obtained in the same manner as Example 1 using the negative electrode prepared in this manner.

[Example 9]
A non-aqueous treatment solution was prepared by dissolving Mn (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that manganese fluoride (MnF ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A9) of Example 9 was obtained in the same manner as in Example 1.

[Example 10]
A non-aqueous treatment solution was prepared by dissolving Co (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) in a solvent mixture of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that cobalt oxide (CoO) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A10) of Example 10 was obtained in the same manner as in Example 1.

[Example 11]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A11) of Example 11 was obtained in the same manner as in Example 1.

[Example 12]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

The titanium dioxide negative electrode (N2) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that cobalt fluoride (CoF ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A12) of Example 12 was obtained in the same manner as Example 1.

[Example 13]
A commercially available niobium pentoxide (Nb ₂ O ₅ ) was used instead of Li ₄ Ti ₅ O _{12 as} the negative electrode active material, and a niobium pentoxide negative electrode (N3) was obtained in the same manner as the lithium titanate negative electrode (N1).

A non-aqueous treatment liquid was prepared by dissolving Mn (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that manganese oxide (MnO) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A13) of Example 13 was obtained in the same manner as Example 1.

[Example 14]
A non-aqueous treatment liquid was prepared by dissolving Mn (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A14) of Example 14 was obtained in the same manner as Example 1.

[Example 15]
A non-aqueous treatment solution was prepared by dissolving Mn (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains manganese ions (Mn ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of manganese ions (Mn ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that manganese fluoride (MnF ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A15) of Example 15 was obtained in the same manner as Example 1.

[Example 16]
A non-aqueous treatment solution was prepared by dissolving Co (PF ₆ ) ₂ and lithium carbonate (Li ₂ CO ₃ ) in a solvent mixture of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and carbonate ions (CO ₃ ²⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and oxygen ions (O ²⁻ ) were observed. From this, it was confirmed that cobalt oxide (CoO) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A16) of Example 16 was obtained in the same manner as in Example 1.

[Example 17]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium phosphate (Li ₃ PO ₄ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and phosphate ions (PO ₄ ³⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were observed. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A17) of Example 17 was obtained in the same manner as in Example 1.

[Example 18]
A non-aqueous treatment liquid was prepared by dissolving Co (PF ₆ ) ₂ and lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent of EC and DEC in a volume ratio of 3: 7. This non-aqueous treatment liquid contains cobalt ions (Co ²⁺ ), lithium ions (Li ⁺ ), and hexafluorophosphate ions (PF ₆ ⁻ ).

A niobium pentoxide negative electrode (N3) was immersed in this non-aqueous treatment solution, energized under the same conditions as in Example 1, washed, and then its surface was analyzed by XPS. As a result, peaks of cobalt ions (Co ²⁺ ) and fluorine ions (F ⁻ ) were observed. From this, it was confirmed that cobalt fluoride (CoF ₂ ) was generated on the negative electrode surface. Using the thus prepared negative electrode, a nonaqueous electrolyte secondary battery (A18) of Example 18 was obtained in the same manner as in Example 1.

[Comparative Example 1]
A nonaqueous electrolyte secondary battery (B1) of Comparative Example 1 was obtained in the same manner as in Example 1 except that the lithium titanate negative electrode (N1) was used without being treated with a nonaqueous treatment liquid.

[Comparative Example 2]
A nonaqueous electrolyte secondary battery (B2) of Comparative Example 2 was obtained in the same manner as in Example 1 except that the titanium dioxide negative electrode (N2) was used without being treated with a nonaqueous treatment liquid.

[Comparative Example 3]
A nonaqueous electrolyte secondary battery (B3) of Comparative Example 3 was obtained in the same manner as in Example 1 except that the niobium pentoxide negative electrode (N3) was used without being treated with the nonaqueous treatment liquid.

  Table 1 shows the types of the negative electrode active materials used in the nonaqueous electrolyte secondary batteries (A1 to A18, B1 to B3) of Examples 1 to 18 and Comparative Examples 1 to 3 and the compound X present on the surface of the negative electrode active materials. Summarized.

[Storage test]
The nonaqueous electrolyte secondary batteries (A1 to A18, B1 to B3) of Examples 1 to 18 and Comparative Examples 1 to 3 were charged to 2.65 V at a constant current of 1 CmA at 25 ° C., followed by 2.65 V. After charging at a constant voltage of 3 hours, the battery was discharged to 1.5 V at a constant current of 1 CmA, and the discharge capacity at the first cycle was measured. This was defined as “initial discharge capacity”. Moreover, the internal resistance after discharge was measured by an alternating current method of 1 KHz and was set as “initial internal resistance”.

  Next, after charging under the same charging conditions, it was stored at 80 ° C. for 2 days. Then, after maintaining at 25 ° C. for 5 hours, the battery was discharged to 1.5 V with a constant current of 1 CmA. The discharge capacity at this time was defined as “discharge capacity after storage at 80 ° C.”, and the internal resistance after discharge was measured by an alternating current method of 1 KHz to be “internal resistance after storage at 80 ° C.”. Note that the ratio of “discharge capacity after storage at 80 ° C.” to “initial discharge capacity” is “capacity retention ratio (%)”, and the ratio of “internal resistance after storage at 80 ° C.” to “initial internal resistance” is “internal resistance increase” Ratio ". These measurement results are summarized in Table 2.

From the results of Table 2, manganese oxide and phosphoric acid were formed on the surfaces of lithium titanate (Li ₄ Ti ₅ O ₁₂ ), anatase-type titanium dioxide (TiO ₂ ), and niobium pentoxide (Nb ₂ O ₅ ) as negative electrode active materials. In the case of the nonaqueous electrolyte secondary battery of Examples 1 to 18 in which manganese, manganese fluoride, cobalt oxide, cobalt phosphate, and cobalt fluoride are present, manganese oxide or the like is not present on the surface of the negative electrode active material. Compared to the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 3, the internal resistance increase ratio was small, and the capacity retention ratio was large, indicating that there were few side reactions at high temperatures.

Although the reason for this is not clear, it is considered that a substance such as manganese oxide plays a role of a protective component that reduces decomposition of the electrolytic solution on the surface of the negative electrode active material. Unlike the case where graphite is used as the negative electrode active material in which SEI is formed, this mechanism is different from lithium titanate (Li ₄ Ti ₅ O ₁₂ ), anatase-type titanium dioxide (TiO ₂ ), niobium pentoxide (Nb ₂ O _5). ) Is a characteristic effect when used for the negative electrode.

[Examples 19 to 21]
[Example 19]
Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) used for the negative electrode active material of Example 1 were mixed at a weight ratio of 100: 1, and further machined with a ball mill. The negative electrode active material was mixed. As a result of analyzing the surface of this negative electrode active material by XPS, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were recognized. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using this negative electrode active material, a negative electrode (N4) was produced in the same manner as in the case of the negative electrode (N1), and using this negative electrode (N4), the nonaqueous electrolyte secondary of Example 19 was obtained in the same manner as in Example 1. A battery (A19) was obtained.

[Example 20]
Anatase-type titanium dioxide (TiO ₂ ) and cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) used for the negative electrode active material of Example 7 were mixed at a weight ratio of 100: 1 and further mechanically mixed with a ball mill. Thus, a negative electrode active material was obtained. As a result of analyzing the surface of this negative electrode active material by XPS, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were recognized. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using this negative electrode active material, a negative electrode (N5) was produced in the same manner as in the case of the negative electrode (N2). Using this negative electrode (N5), the nonaqueous electrolyte secondary of Example 20 was obtained in the same manner as in Example 1. A battery (A20) was obtained.

[Example 21]
Niobium pentoxide (Nb ₂ O ₅ ) and cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) used for the negative electrode active material of Example 13 were mixed at a weight ratio of 100: 0.95 and further machined with a ball mill. The negative electrode active material was mixed. As a result of analyzing the surface of this negative electrode active material by XPS, peaks of cobalt ions (Co ²⁺ ) and phosphate ions (PO ₄ ³⁻ ) were recognized. From this, it was confirmed that cobalt phosphate (Co ₃ (PO ₄ ) ₂ ) was generated on the negative electrode surface. Using this negative electrode active material, a negative electrode (N6) was produced in the same manner as in the case of the negative electrode (N3), and using this negative electrode (N6), the nonaqueous electrolyte secondary of Example 21 was obtained in the same manner as in Example 1. A battery (A21) was obtained.

[Storage test]
For the nonaqueous electrolyte secondary batteries (A19 to A21) of Examples 19 to 21, a storage test was performed under the same conditions as in Example 1, and the initial discharge capacity, the discharge capacity after 80 ° C. storage, the capacity retention rate (%), The initial internal resistance, the internal resistance after storage at 80 ° C., and the internal resistance increase ratio were determined. The results are summarized in Table 3.

From the results shown in Table 3, the method in which cobalt phosphate is present on the surface of the negative electrode active material is the same as in Example 5, Example 11, and Example 17, in which the negative electrode is made of cobalt ions (Co ²⁺ ) and lithium ions (Li ⁺ ) And a phosphate ion (PO ₄ ³⁻ ) in a non-aqueous treatment solution, and the anode is energized, and the negative electrode active material and cobalt phosphate are directly mixed by a ball mill as in Examples 19-21. It was found that there was almost no difference between the method and the side reaction at high temperature.

[Examples 22 to 27]
[Example 22]
Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) used for the negative electrode active material of Example 1 were mixed at a weight ratio of 100: 1.9, and further ball mill To obtain a negative electrode active material in which manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) was present on the surface of lithium titanate. As a result of measuring this negative electrode active material by ICP, the ratio of manganese to lithium titanate was 0.2% by mass. A nonaqueous electrolyte secondary battery (A22) of Example 22 was obtained in the same manner as Example 1 except that this negative electrode active material was used.

[Example 23]
A negative electrode active material in which the ratio of manganese to lithium titanate was 0.1% by mass was performed in the same manner as in Example 22 except that lithium titanate and manganese phosphate were mixed at a weight ratio of 100: 0.91. A nonaqueous electrolyte secondary battery (A23) of Example 23 was obtained in the same manner as Example 1 except that this negative electrode active material was produced.

[Example 24]
Except that lithium titanate and manganese phosphate were mixed at a weight ratio of 100: 0.45, a negative electrode active material having a manganese ratio of 0.049% by mass with respect to lithium titanate was obtained in the same manner as in Example 22. A nonaqueous electrolyte secondary battery (A24) of Example 24 was obtained in the same manner as Example 1 except that this negative electrode active material was produced.

[Example 25]
Except that lithium titanate and manganese phosphate were mixed at a weight ratio of 100: 0.33, a negative electrode active material having a manganese ratio of 0.036% by mass with respect to lithium titanate was obtained in the same manner as in Example 22. A nonaqueous electrolyte secondary battery (A25) of Example 25 was obtained in the same manner as Example 1 except that this negative electrode active material was produced.

[Example 26]
A negative electrode active material in which the ratio of manganese to lithium titanate is 0.016% by mass is performed in the same manner as in Example 22 except that lithium titanate and manganese phosphate are mixed at a weight ratio of 100: 0.15. A nonaqueous electrolyte secondary battery (A26) of Example 26 was obtained in the same manner as in Example 1 except that this negative electrode active material was produced.

[Example 27]
A negative electrode active material in which the ratio of manganese to lithium titanate was 0.01% by mass was performed in the same manner as in Example 22 except that lithium titanate and manganese phosphate were mixed at a weight ratio of 100: 0.10. A nonaqueous electrolyte secondary battery (A27) of Example 27 was obtained in the same manner as in Example 1 except that this negative electrode active material was produced.

[Storage test]
For the non-aqueous electrolyte secondary batteries (A22 to A27) of Examples 22 to 27, a storage test was performed under the same conditions as in Example 1, initial discharge capacity, discharge capacity after 80 ° C. storage, capacity retention rate (%), The initial internal resistance, the internal resistance after storage at 80 ° C., and the internal resistance increase ratio were determined. The results are summarized in Table 4. In Table 4, “ratio of Mn” indicates the ratio (mass%) of manganese to lithium titanate in the negative electrode active material. Table 4 also shows the results of Comparative Example 1 for comparison.

From the results of Table 4, the batteries of Examples 22 to 27 in which manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) is present on the surface of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) that is the negative electrode active material ( In the case of A22 to A28), it was found that the capacity retention rate was increased and the self-discharge at high temperature was small compared to the case of the battery (B1) of Comparative Example 1 which did not exist.

  In particular, in the batteries of Examples 23 to 27 (A23 to A27) in which the ratio of manganese to lithium titanate in the negative electrode active material by ICP analysis was 0.1% by mass or less, it was found that the capacity retention ratio was further increased. .

  It was also found that the batteries of Examples 22 to 27 (A22 to A28) had a smaller internal resistance increase ratio than the battery (B1) of Comparative Example 1.

[Examples 28 to 33]
[Example 28]
LiNi _0.5 Mn _1.5 O ₄ was used as the positive electrode active material, and the positive electrode (P2) was produced in the same manner as Li _1.1 Mn _1.8 Al _0.1 O ₄ used in Example 1. did. Further, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) are mixed at a weight ratio of 100: 1.9, and mechanically mixed with a ball mill, A negative electrode active material in which manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) was present on the surface of lithium titanate was obtained. As a result of measuring this negative electrode active material by ICP, the ratio of manganese to lithium titanate was 0.2% by mass. A nonaqueous electrolyte secondary battery (A28) of Example 28 was obtained in the same manner as Example 1 except that this negative electrode active material was used.

[Example 29]
Except that lithium titanate and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) were mixed at a weight ratio of 100: 0.91, the ratio of manganese to lithium titanate was 0.00. A non-aqueous electrolyte secondary battery (A29) of Example 29 was obtained in the same manner as in Example 28 except that a negative electrode active material of 1% by mass was prepared and this negative electrode active material was used.

[Example 30]
Except that lithium titanate and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) were mixed at a weight ratio of 100: 0.45, the ratio of manganese to lithium titanate was 0.00 as in Example 28. A non-aqueous electrolyte secondary battery (A30) of Example 30 was obtained in the same manner as in Example 28 except that a negative electrode active material of 049% by mass was prepared and this negative electrode active material was used.

[Example 31]
Except that lithium titanate and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) were mixed at a weight ratio of 100: 0.33, the ratio of manganese to lithium titanate was 0.00. A non-aqueous electrolyte secondary battery (A31) of Example 31 was obtained in the same manner as in Example 28 except that a negative electrode active material of 036% by mass was prepared and this negative electrode active material was used.

[Example 32]
Except that lithium titanate and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) were mixed at a weight ratio of 100: 0.15, the ratio of manganese to lithium titanate was 0.00. A non-aqueous electrolyte secondary battery (A32) of Example 32 was obtained in the same manner as in Example 28 except that a negative electrode active material of 016% by mass was prepared and this negative electrode active material was used.

[Example 33]
Except that lithium titanate and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) were mixed at a weight ratio of 100: 0.10, the ratio of manganese to lithium titanate was 0.00. A non-aqueous electrolyte secondary battery (A33) of Example 33 was obtained in the same manner as in Example 28 except that a negative electrode active material of 01% by mass was prepared and this negative electrode active material was used.

[Comparative Example 4]
A nonaqueous electrolyte secondary battery (B4) of Comparative Example 4 was obtained in the same manner as in Example 28 except that the lithium titanate negative electrode (N1) was used.

[Storage test]
For the nonaqueous electrolyte secondary batteries (A28 to A33) of Examples 28 to 33 and the nonaqueous electrolyte secondary battery (B4) of Comparative Example 4, a storage test was performed under the same conditions as in Example 1, and the initial discharge capacity, After storage at 80 ° C., the discharge capacity and capacity retention rate (%) were determined. The results are summarized in Table 5. In Table 5, “Mn ratio” represents the ratio (mass%) of manganese to lithium titanate in the negative electrode active material.

From the results of Table 5, the batteries of Examples 28 to 33 in which manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) is present on the surface of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) that is the negative electrode active material ( In the case of A28 to A33), it was found that the capacity retention rate was increased and the self-discharge at high temperature was small as compared with the case of the battery (B4) of Comparative Example 4 which did not exist. In particular, it was found that the capacity retention ratio was higher in the batteries of Examples 29 to 33 (A29 to A33) in which the ratio of manganese to lithium titanate in the negative electrode active material was 0.1% by mass or less.

[Examples 34 to 39]
[Example 34]
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the positive electrode active material, and in the same manner as Li _1.1 Mn _1.8 Al _0.1 O ₄ used in Example 1, the positive electrode ( P3) was prepared. Further, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) are mixed at a weight ratio of 100: 1.9, and mechanically mixed with a ball mill, A negative electrode active material in which manganese phosphate was present on the surface of lithium titanate was obtained. As a result of measuring this negative electrode active material by ICP, the ratio of manganese to lithium titanate was 0.2% by mass. A nonaqueous electrolyte secondary battery (A34) of Example 34 was obtained in the same manner as in Example 1 except that this negative electrode active material was used.

[Example 35]
A negative electrode active material in which the ratio of manganese to lithium titanate is 0.1% by mass is performed in the same manner as in Example 34 except that lithium titanate and manganese phosphate are mixed at a weight ratio of 100: 0.91. A nonaqueous electrolyte secondary battery (A35) of Example 35 was obtained in the same manner as Example 34 except that this negative electrode active material was produced.

[Example 36]
Except that lithium titanate and manganese phosphate were mixed at a weight ratio of 100: 0.45, in the same manner as in Example 34, a negative electrode active material in which the ratio of manganese to lithium titanate was 0.049% by mass A nonaqueous electrolyte secondary battery (A36) of Example 36 was obtained in the same manner as Example 34 except that this negative electrode active material was produced.

[Example 37]
A negative electrode active material in which the ratio of manganese to lithium titanate is 0.036% by mass is performed in the same manner as in Example 34 except that lithium titanate and manganese phosphate are mixed at a weight ratio of 100: 0.33. A nonaqueous electrolyte secondary battery (A37) of Example 37 was obtained in the same manner as Example 34 except that this negative electrode active material was produced.

[Example 38]
A negative electrode active material in which the ratio of manganese to lithium titanate is 0.016% by mass is performed in the same manner as in Example 34 except that lithium titanate and manganese phosphate are mixed at a weight ratio of 100: 0.15. A nonaqueous electrolyte secondary battery (A38) of Example 38 was obtained in the same manner as Example 34 except that this negative electrode active material was produced.

[Example 39]
A negative electrode active material in which the ratio of manganese to lithium titanate is 0.010% by mass is performed in the same manner as in Example 34 except that lithium titanate and manganese phosphate are mixed at a weight ratio of 100: 0.10. A nonaqueous electrolyte secondary battery (A39) of Example 39 was obtained in the same manner as Example 34 except that this negative electrode active material was produced.

[Comparative Example 5]
A nonaqueous electrolyte secondary battery (B5) of Comparative Example 5 was obtained in the same manner as in Example 34 except that the lithium titanate negative electrode (N1) was used.

[Storage test]
For the nonaqueous electrolyte secondary batteries (A34 to A39) of Examples 34 to 39 and the nonaqueous electrolyte secondary battery (B5) of Comparative Example 5, a storage test was performed under the same conditions as in Example 1, and the initial discharge capacity, After storage at 80 ° C., the discharge capacity and capacity retention rate (%) were determined. The results are summarized in Table 6. In Table 6, “Mn ratio” indicates the ratio (mass%) of manganese to lithium titanate in the negative electrode active material.

From the results of Table 6, batteries of Examples 34 to 39 in which manganese phosphate (Mn ₃ (PO ₄ ) ₂ ) is present on the surface of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) that is the negative electrode active material ( In the case of A34 to A39), it was found that the capacity retention rate was increased and the self-discharge at a high temperature was small compared to the case of the battery (B5) of Comparative Example 5 which did not exist. In particular, it was found that in the batteries of Examples 35 to 39 (A35 to A39) in which the ratio of manganese to lithium titanate in the negative electrode active material was 0.1% by mass or less (A35 to A39), the capacity retention ratio was further increased.

Note that the positive electrode active material includes lithium manganate represented by the general formula Li _x Mn _2−xy Al _y O ₄ (0.8 ≦ x ≦ 1.2, y = 0.03), the general formula Li _x Mn. Lithium manganate represented by _2-xy Al _y O ₄ (x = 1.0, 0.01 ≦ y ≦ 0.1), general formula Li _x Mn _2-xy- Ni _y Co _z Nickel / cobalt / lithium manganate represented by O ₂ (0.8 ≦ x ≦ 1.2, y = 0.33, z = 0.33), general formula Li _x Mn _2-xyz When using nickel / cobalt / lithium manganate represented by Ni _y Co _z O ₂ (x = 1.0, 0.16 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.67), and negative electrode using lithium titanate represented in the active material by a general formula _{Li x Ti y O 4 (1.0} ≦ x ≦ 2.4,1 ≦ y ≦ 2) When we obtained the same effect as well.

As described above, the negative electrode active material of the non-aqueous electrolyte secondary battery is 1 Vvs. When a material capable of inserting / extracting lithium ions at a potential of Li / Li ⁺ or higher is used, manganese oxide and phosphoric acid are formed on the surface of the negative electrode active material even when the types of the positive electrode active material and the negative electrode active material are different. When there is at least one selected from the group consisting of manganese, manganese fluoride, cobalt oxide, cobalt phosphate, and cobalt fluoride (= compound X), the increase in internal resistance during high-temperature storage is small, and at high temperatures Thus, it was found that the effect is remarkable when the ratio of the compound X to the negative electrode active material is 0.1% by mass or less.

Claims (4)

In a non-aqueous electrolyte secondary battery including a positive electrode active material, a negative electrode active material, and a non-aqueous electrolyte, compound X is present on the surface of the negative electrode active material, and the negative electrode active material includes lithium titanate, titanium oxide, and oxide. At least one 1 V vs. 1 selected from the group consisting of niobium . The insertion and extraction capable compound of lithium ions Li / Li ⁺ potential greater than said compound X, manganese oxide other than manganese dioxide, manganese phosphate, from the group consisting of manganese fluoride and full Tsu cobalt A non-aqueous electrolyte secondary battery, which is at least one selected. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the compound X to the negative electrode active material is 0.1% by mass or less. In a non-aqueous electrolyte secondary battery including a positive electrode active material, a negative electrode active material, and a non-aqueous electrolyte, compound X is present on the surface of the negative electrode active material, and the negative electrode active material includes lithium titanate, titanium oxide, and oxide. 1 V vs. selected from niobium. Li / Li ⁺ It is a compound capable of inserting / extracting lithium ions at the above potential, and the compound X is cobalt oxide or cobalt phosphate, and the ratio of the compound X to the negative electrode active material is 0.1% by mass or less. There is a nonaqueous electrolyte secondary battery. The negative electrode active material has the general formula Li _x Ti _y O ₄ The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is lithium titanate represented by (1.0 ≦ x ≦ 2.4, 1 ≦ y ≦ 2).