JP5565465B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention generally relates to non-aqueous electrolyte secondary batteries, and more particularly to a non-aqueous electrolyte secondary battery using a lithium titanium composite oxide for a negative electrode.

  With the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and digital cameras, secondary batteries with high energy density and long life are expected as cordless power sources for these electronic devices. In order to meet such demands, secondary batteries have been developed that use an alkali metal ion such as lithium ion as a charge carrier and use an electrochemical reaction associated with charge exchange. Among them, lithium ion secondary batteries having a large energy density are widely used.

  In the above lithium ion secondary battery, lithium-containing transition metal oxides such as lithium cobaltate and lithium manganate are used as the positive electrode active material. In addition, a carbon material capable of inserting and extracting lithium ions is used as the negative electrode active material. Among carbon materials, graphite such as natural graphite and artificial graphite has a discharge voltage as low as 0.2 V with respect to lithium metal, and when graphite is used as a negative electrode active material, a battery having a discharge voltage of 3.6 V is possible. Become. However, when a carbon material is used for the negative electrode, if a short circuit occurs inside the battery, lithium ions may flow from the negative electrode to the positive electrode at once, and the temperature may increase rapidly.

  Then, lithium titanium complex oxides, such as lithium titanate, which does not flow abruptly even if a short circuit occurs inside the battery, have attracted attention. Lithium titanium composite oxide is a material that can occlude and release lithium ions without changing the structure and size of the crystal lattice, and is a promising negative electrode active material for highly reliable non-aqueous electrolyte secondary batteries.

However, the lithium-titanium composite oxide has a high lithium ion insertion / desorption potential of 1.5 V (vs Li / Li ⁺ ), so it is compared with a lithium ion secondary battery using a carbon material for the negative electrode active material. Battery voltage decreases. As a result, there is a problem that the energy density is lowered.

In order to solve this problem, it has been proposed to use a spinel-type lithium manganese nickel composite oxide having a potential flat portion in a region of 4.4 V (vs Li / Li ⁺ ) or higher as a positive electrode active material. In this case, even if a lithium titanium composite oxide having a lithium ion insertion / desorption potential as high as 1.5 V (vs Li / Li ⁺ ) is used as the negative electrode active material, the above-described high potential spinel structure lithium manganese nickel By using the composite oxide as the positive electrode active material, the energy density can be improved.

For example, Japanese Patent Laid-Open No. 2006-66341 (hereinafter referred to as Patent Document 1) has a potential flat portion in a region of 4.4 V (vs Li / Li ⁺ ) or higher as a positive electrode active material of a lithium ion secondary battery. A non-aqueous electrolyte secondary battery using a spinel type lithium-titanium composite oxide as a spinel type lithium manganese nickel composite oxide and a negative electrode active material is disclosed.

When Li (Mn _1.5 Ni _0.45 Mg _0.05 ) O ₄ having a potential flat portion in the vicinity of 4.9 V (vs Li / Li ⁺ ) is used as the positive electrode active material as described in Patent Document 1, the battery The voltage can be 3.35V.

JP 2006-66341 A

However, in a lithium ion secondary battery using Li (Mn _1.5 Ni _0.45 Mg _0.05 ) O ₄ as the positive electrode active material and lithium titanium composite oxide as the negative electrode active material, the voltage change is almost in the entire charging or discharging process. The degree is small, that is, it shows a flat voltage characteristic. For this reason, when using a lithium ion secondary battery that is not fully charged but is rapidly charged so that the charged state is about 80% from a low charged state, it is difficult to detect the charged state of the battery. The problem arises.

  Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that can easily detect a charged state in a non-aqueous electrolyte secondary battery using a lithium titanium composite oxide as a negative electrode active material. is there.

  As a result of intensive studies to solve the problems of the prior art, the present inventor has obtained a spinel structure as a positive electrode active material in a non-aqueous electrolyte secondary battery using a lithium titanium composite oxide as a negative electrode active material. It was found that the voltage change between the initial stage of charging and the end stage of discharging can be increased by using the lithium manganese nickel composite oxide with lithium nickel manganese cobalt composite oxide added. Based on this knowledge, the nonaqueous electrolyte secondary battery according to the present invention has the following characteristics.

  A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode, the negative electrode includes a lithium titanium composite oxide, and the positive electrode is a lithium nickel manganese cobalt composite oxide and a spinel type. And a lithium manganese nickel composite oxide having a structure.

  In the nonaqueous electrolyte secondary battery of the present invention, the lithium nickel manganese cobalt composite oxide preferably has a hexagonal layered rock salt crystal structure belonging to the space group R3m.

The lithium nickel manganese cobalt composite oxide has a ratio of the c-axis lattice constant to the a-axis lattice constant (c / a axis ratio) of 4 in the hexagonal layered rock salt crystal structure belonging to the space group R3m. .96 or less, and the general formula _{Li 1+ α [Ni x Mn y} Co z] O 2 ( wherein, alpha is 0 ≦ α <1.3, x, y and z are x + y + z = 1,0 < x <0.50, 0 <z ≦ 0.15 is satisfied).

  Furthermore, the lattice constant of the a axis is preferably 2.8 angstroms or more.

  Furthermore, the lattice constant of the c axis is preferably 14 angstroms or more.

  According to the present invention, in the nonaqueous electrolyte secondary battery in which the negative electrode includes a lithium titanium composite oxide, the positive electrode includes a lithium nickel manganese cobalt composite oxide and a lithium manganese nickel composite oxide having a spinel structure. The state of charge can be easily detected.

It is a figure which shows the coin-type nonaqueous electrolyte secondary battery as one embodiment of this invention, and the coin-type nonaqueous electrolyte secondary battery produced by the Example and comparative example of this invention. It is a figure which shows the charging / discharging curve of the coin-type nonaqueous electrolyte secondary battery produced in Example 1 of this invention. It is a figure which shows the charging / discharging curve of the coin-type nonaqueous electrolyte secondary battery produced in Example 2 of this invention. It is a figure which shows the charging / discharging curve of the coin-type nonaqueous electrolyte secondary battery produced in Example 3 of this invention. It is a figure which shows the charging / discharging curve of the coin-type nonaqueous electrolyte secondary battery produced in the comparative example 1 of this invention.

  The nonaqueous electrolyte secondary battery of the present invention is a nonaqueous electrolyte secondary battery having a positive electrode and a negative electrode, the negative electrode includes a lithium titanium composite oxide, and the positive electrode has a lithium nickel manganese cobalt composite oxide and a spinel structure. And a lithium manganese nickel composite oxide. As described above, when a positive electrode having a spinel-type lithium manganese nickel composite oxide added with a lithium nickel manganese cobalt composite oxide is used as the positive electrode, the voltage change between the initial charge stage and the final discharge stage can be increased. Thereby, the state of charge can be easily detected.

In the nonaqueous electrolyte secondary battery of the present invention, a lithium manganese nickel composite oxide having a spinel structure used as one of positive electrode materials has a potential when used as a positive electrode, for example, a positive electrode potential in a fully charged state. Is nobler than 4.5 V with respect to the potential of metallic lithium. That is, the lithium manganese nickel composite oxide has an upper limit potential of 4.5 V (vs Li / Li ⁺ ) or more with respect to the potential of metallic lithium. In other words, the lithium manganese nickel composite oxide having a spinel structure has a potential flat portion at 4.5 V (vs Li / Li ⁺ ) or more when used as a positive electrode.

  In the nonaqueous electrolyte secondary battery of the present invention, the lithium nickel manganese cobalt composite oxide preferably has a hexagonal layered rock salt crystal structure belonging to the space group R3m. In this case, a nonaqueous electrolyte secondary battery having good cycle characteristics can be obtained. Note that the lithium nickel manganese cobalt composite oxide has a crystal structure other than the hexagonal layered rock salt type crystal structure belonging to the space group R3m, such as a face-centered cubic crystal structure belonging to the space group Fm3m, etc. Even if it has this, the effect of the above-mentioned this invention can be acquired.

The lithium nickel manganese cobalt composite oxide has a ratio of the c-axis lattice constant to the a-axis lattice constant (c / a axis ratio) of 4 in the hexagonal layered rock salt crystal structure belonging to the space group R3m. .958 or less, and the general formula _{Li 1+ α [Ni x Mn y} Co z] O 2 ( wherein, alpha is 0 ≦ α <1.3, x, y and z are x + y + z = 1,0 < x <0.50, 0 ≦ z ≦ 0.15 is preferably satisfied). In this case, if the c / a axial ratio is 4.958 or less, the lithium-nickel-manganese-cobalt composite oxide is not charged during charging / discharging of the nonaqueous electrolyte secondary battery including the positive electrode including the lithium-nickel-manganese-cobalt composite oxide. Since the expansion and contraction of the lattice can be suppressed, excellent cycle characteristics can be exhibited. In the above general formula, when α is 1.3 or more, the remaining lithium carbonate increases, a large amount of gas is generated during charging and discharging, and the battery expands.

  Furthermore, the lattice constant of the a axis is preferably 2.8 angstroms or more. Furthermore, the lattice constant of the c axis is preferably 14 angstroms or more.

  When the lattice constant of the a axis is less than 2.8 angstroms, the stability of the crystal is low, so that the cycle characteristics deteriorate under high voltage charge / discharge. On the other hand, when the c-axis lattice constant is less than 14 angstroms, the stability of the crystal is low, resulting in poor cycle characteristics under high voltage charge / discharge. When the a-axis lattice constant is 2.8 angstroms or more and the c-axis lattice constant is 14 angstroms or more, some of the 3b-site Li ions and the 3a-site Ni ions cause site exchange. For this reason, even if a large amount of Li ions escape due to overcharge, Ni ions present in the Li layer suppress the expansion and contraction of the lattice. Thereby, the stability of the crystal is improved and excellent cycle characteristics can be exhibited.

The lithium-titanium composite oxide contained in the negative electrode of the present invention preferably has a spinel structure, such as Li ₄ Ti ₅ O ₁₂ having a spinel structure. The lithium titanium composite oxide may contain elements other than lithium, titanium, and oxygen. In addition, an element other than lithium, titanium, and oxygen may be included as a substituted compound in the lithium titanium composite oxide having a spinel structure.

  Next, an example of the manufacturing method of the nonaqueous electrolyte secondary battery of the present invention will be described in detail below.

  First, a positive electrode is formed. For example, a positive electrode active material containing a lithium nickel manganese cobalt composite oxide and a lithium manganese nickel composite oxide having a spinel structure is mixed with a conductive agent and a binder, and an organic solvent or water is added to form a positive electrode active material slurry. The positive electrode active material slurry is coated on the electrode current collector by an arbitrary coating method and dried to form a positive electrode.

  Next, a negative electrode is formed. For example, a negative electrode active material containing a lithium titanium composite oxide is mixed with a conductive agent and a binder, and an organic solvent or water is added to form a negative electrode active material slurry. The negative electrode is formed by coating with a coating method and drying.

  In the present invention, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, and carboxymethyl cellulose can be used.

  Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile, tetrahydrofuran, Nonaqueous solvents such as nitrobenzene and acetone, and protic solvents such as methanol and ethanol can be used. Moreover, the kind of organic solvent, the compounding ratio of the organic compound and the organic solvent, the kind of additive and the addition amount thereof can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

  Next, as shown in FIG. 1, the positive electrode 14 obtained above is impregnated into the electrolyte, so that the positive electrode 14 is infiltrated with the electrolyte, and then the positive electrode current collector at the center of the bottom of the case 11 that also serves as the positive electrode terminal. The positive electrode 14 is placed on the top. Thereafter, the separator 16 impregnated with the electrolyte is laminated on the positive electrode 14, the negative electrode 15 and the current collector plate 17 are sequentially laminated, and the electrolyte is injected into the internal space. Then, a metal spring member 18 is placed on the current collector plate 17, and a gasket 13 is arranged on the periphery, and a sealing plate 12 that also serves as a negative electrode terminal is fixed to the case 11 with a caulking machine or the like to seal the exterior. By doing so, the coin-type non-aqueous electrolyte secondary battery 1 is manufactured.

The electrolyte is interposed between the positive electrode 14 and the negative electrode 15 which is a counter electrode, and transports charge carriers between the two electrodes. As such an electrolyte, an electrolyte having an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at room temperature can be used. For example, an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (C ₂ F ₅ SO ₂ ) ₃ C, or the like can be used.

  As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc. are used. be able to.

Moreover, you may use a solid electrolyte for electrolyte. Examples of the polymer compound used in the solid electrolyte include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and fluoride. Vinylidene fluoride polymers such as vinylidene-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and acrylonitrile-methyl methacrylate copolymer Polymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-ethyl methacrylate copolymer, acrylonitrile-ethyl acrylate copolymer, acrylonitrile-methacrylic acid copolymer, acrylonitrile-a Examples include acrylonitrile polymers such as rilic acid copolymers and acrylonitrile-vinyl acetate copolymers, and also polyethylene oxide, ethylene oxide-propylene oxide copolymers, and polymers of these acrylates and methacrylates. it can. Moreover, you may use what made these polymer compounds contain electrolyte solution and made it gelatinous as electrolyte. Alternatively, only a polymer compound containing an electrolyte salt may be used as an electrolyte as it is. Incidentally, as an _{electrolyte, Li 2 S-P 2 S} 5 _{based, Li 2 S-B 2 S} 3 type, may be used an inorganic solid electrolyte such as sulfide glass represented by Li ₂ S-SiS ₂ system.

  In the above embodiment, the coin-type secondary battery has been described. However, the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Also, the exterior method is not particularly limited, and a metal case, mold resin, aluminum laminate film, or the like may be used.

  Next, examples of the present invention will be specifically described. In addition, the Example shown below is an example and this invention is not limited to the following Example.

  Hereinafter, Examples 1 to 5 and Comparative Examples 1 to 3 of the coin-type nonaqueous electrolyte secondary battery will be described.

  Example 1

  (Preparation of lithium manganese nickel composite oxide)

The production of Li (Mn _1.5 Ni _0.5 ) O ₂ , which is a lithium manganese nickel composite oxide having a spinel structure, was performed as follows. Nickel metal powder having an average particle size of 0.5 μm as a nickel-containing raw material, trimanganese tetraoxide (Mn ₃ O ₄ ) as a manganese-containing raw material, and lithium carbonate (Li ₂ CO ₃ ) as a lithium-containing raw material were prepared. These raw materials were weighed so that the molar ratio was Li / (Mn + Ni) = 0.50 and Mn: Ni = 3.0: 1.0. The weighed raw materials were mixed by a ball mill using water as a solvent to prepare a slurry. The obtained slurry was spray-dried to obtain a dry powder. The obtained dry powder was put in a sheath containing alumina as a main component, and fired at a temperature of 950 ° C. for 20 hours in an oxygen gas atmosphere, thereby producing the above lithium manganese nickel composite oxide.

  (Preparation of lithium nickel manganese cobalt composite oxide)

Next, Li (Ni _0.45 Mn _0.45 Co _0.10 ) O ₂ , which is a lithium nickel manganese cobalt composite oxide having a layered crystal structure, was produced as follows. Nickel metal powder having an average particle size of 0.5 μm as a nickel-containing raw material, manganese trioxide (Mn ₃ O ₄ ) as a manganese-containing raw material, cobalt trioxide (Co ₃ O ₄ ) as a cobalt-containing raw material, and a lithium-containing raw material Lithium carbonate (Li ₂ CO ₃ ) was prepared. These raw materials were weighed so that the molar ratios were Li / (Ni + Mn + Co) = 1.15 and Ni: Mn: Co = 0.45: 0.45: 0.10. The weighed raw materials were mixed by a ball mill using water as a solvent to prepare a slurry. The obtained slurry was spray-dried to obtain a dry powder. The obtained dry powder was put in a sheath containing alumina as a main component, and baked at a temperature of 950 ° C. for 20 hours in an oxygen gas atmosphere, whereby the lithium nickel manganese cobalt acid composite oxide was produced.

  (Preparation of lithium titanium composite oxide)

The production of Li ₄ Ti ₅ O ₁₂ , which is a lithium-titanium composite oxide having a spinel structure, was performed as follows. Lithium carbonate (Li ₂ CO ₃ ) was prepared as a lithium-containing raw material, and titanium oxide (TiO ₂ ) was prepared as a titanium-containing raw material. These raw materials were weighed so that the molar ratio of Li to Ti was Li: Ti = 4: 5. The weighed raw materials were wet mixed using water as a solvent to prepare a slurry. The obtained slurry was spray-dried to obtain a dry powder. The obtained dry powder was fired in the atmosphere at a temperature of 850 ° C. for 1 hour to produce the lithium titanium composite oxide.

  (Preparation of positive electrode)

A spinel type lithium manganese nickel composite oxide and a layered crystal structure lithium nickel manganese cobalt composite oxide prepared above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are 51 in weight ratio. : 34: 7.5: 7.5 was weighed and mixed to prepare a positive electrode mixture. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode slurry. This positive electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a positive electrode sheet. Here, the coating amount of the positive electrode slurry was adjusted so that the weight of the positive electrode mixture excluding the dried aluminum foil was 11.5 mg / cm ² .

  (Preparation of negative electrode)

Next, the spinel-type lithium-titanium composite oxide produced above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are in a weight ratio of 85: 7.5: 7.5. Thus, the negative electrode mixture was prepared by weighing and mixing. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode slurry. The negative electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a negative electrode sheet. Here, the coating amount of the negative electrode slurry was adjusted so that the weight of the negative electrode mixture excluding the dried aluminum foil was 10.8 mg / cm ² .

  (Production and evaluation of batteries)

The positive electrode sheet and the negative electrode sheet prepared as above were punched into a disk having a diameter of 12 mm and a disk having a diameter of 14 mm, respectively, so that a positive electrode 14 and a negative electrode 15 as shown in FIG. 1 were prepared. A current collecting plate 17 was bonded to the negative electrode 15. As the separator 16, a disk-like polyethylene porous film having a diameter of 16 mm was used. As the electrolytic solution, an organic electrolytic solution in which 1 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in 1 liter of the solvent in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was used. In this way, a coin-type non-aqueous electrolyte secondary battery 1 having a diameter of 20 mm and a thickness of 3.2 mm was produced.

  The charge / discharge characteristics were evaluated using the coin-type nonaqueous electrolyte secondary battery 1 produced as described above. The battery was charged and discharged for 10 cycles in a constant temperature bath of 25 ° C. with a current value of 200 μA and a voltage range of 1.5 to 4.0 V.

  (Example 2)

In the production of the positive electrode, the spinel-type lithium manganese nickel composite oxide produced above, the lithium nickel manganese cobalt composite oxide having a layered crystal structure, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder Were weighed to a weight ratio of 76.5: 8.5: 7.5: 7.5 and mixed to produce a positive electrode mixture, and the positive electrode mixture excluding the dried aluminum foil A coin-type non-aqueous electrolyte secondary battery 1 was prepared and evaluated in the same manner as in Example 1 except that the coating amount of the positive electrode slurry was adjusted so that the weight of the battery was 13.3 mg / cm ² .

  (Example 3)

In the production of the positive electrode, the spinel-type lithium manganese nickel composite oxide produced above, the lithium nickel manganese cobalt composite oxide having a layered crystal structure, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder Were weighed to a weight ratio of 80.8: 4.2: 7.5: 7.5 and mixed to produce a positive electrode mixture, and the positive electrode mixture excluding the dried aluminum foil A coin-type non-aqueous electrolyte secondary battery 1 was prepared and evaluated in the same manner as in Example 1 except that the coating amount of the positive electrode slurry was adjusted so that the weight of the battery was 13.7 mg / cm ² .

  Example 4

A coin-type non-aqueous electrolyte secondary battery 1 was prepared in the same manner as in Example 1, except that Li (Ni _0.40 Mn _0.40 Co _0.20 ) O ₂ was used as a lithium nickel manganese cobalt composite oxide having a layered crystal structure. Were fabricated and evaluated.

  (Example 5)

A coin-type non-aqueous electrolyte secondary battery 1 was prepared in the same manner as in Example 1 except that Li (Ni _0.35 Mn _0.35 Co _0.30 ) O ₂ was prepared and used as the lithium nickel manganese cobalt composite oxide having a layered crystal structure. Were fabricated and evaluated.

  (Comparative Example 1)

  (Preparation of positive electrode)

Spinel-type lithium manganese nickel composite oxide produced above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder so that the weight ratio is 85: 7.5: 7.5 A positive electrode mixture was prepared by weighing and mixing. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode slurry. This positive electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a positive electrode sheet. Here, the coating amount of the positive electrode slurry was adjusted so that the weight of the positive electrode mixture excluding the dried aluminum foil was 14.0 mg / cm ² .

  (Preparation of negative electrode)

Next, the spinel-type lithium-titanium composite oxide produced above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are in a weight ratio of 85: 7.5: 7.5. Thus, the negative electrode mixture was prepared by weighing and mixing. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode slurry. The negative electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a negative electrode sheet. Here, the coating amount of the negative electrode slurry was adjusted so that the weight of the negative electrode mixture excluding the dried aluminum foil was 10.8 mg / cm ² .

  Using the positive electrode sheet and the negative electrode sheet prepared above, a coin-type non-aqueous electrolyte secondary battery 1 was prepared and evaluated in the same manner as in Example 1.

  (Comparative Example 2)

  (Preparation of positive electrode)

The lithium nickel manganese cobalt composite oxide having a layered crystal structure produced above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder so that the weight ratio is 85: 7.5: 7.5. Were weighed and mixed to prepare a positive electrode mixture. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode slurry. This positive electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a positive electrode sheet. Here, the coating amount of the positive electrode slurry was adjusted so that the weight of the positive electrode mixture excluding the dried aluminum foil was 10.3 mg / cm ² .

  (Preparation of negative electrode)

Next, the spinel-type lithium-titanium composite oxide produced above, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are in a weight ratio of 85: 7.5: 7.5. Thus, the negative electrode mixture was prepared by weighing and mixing. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode slurry. The negative electrode slurry was uniformly applied onto the surface of an aluminum foil having a thickness of 20 μm, dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a negative electrode sheet. Here, the coating amount of the negative electrode slurry was adjusted so that the weight of the negative electrode mixture excluding the aluminum foil after drying was 10.5 mg / cm ² .

  A coin-type non-aqueous electrolyte secondary battery 1 was produced in the same manner as in Example 1 using the positive electrode sheet and negative electrode sheet produced above. The charge / discharge characteristics of the coin-type non-aqueous electrolyte secondary battery 1 were evaluated by charging and discharging 10 cycles in a constant temperature bath at 25 ° C. with a current value of 200 μm and a voltage range of 1.5 to 3.5V. .

  (Comparative Example 3)

  (Preparation of positive electrode)

  A positive electrode sheet was produced in the same manner as in Example 3.

  (Preparation of negative electrode)

Next, graphite as a negative electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are weighed in a weight ratio of 90: 5: 5 and mixed to prepare a negative electrode mixture. did. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to prepare a negative electrode slurry. This negative electrode slurry was uniformly applied onto the surface of a copper foil having a thickness of 8 μm, dried at a temperature of 120 ° C., and then pressed at a pressure of 1 ton / cm ² to prepare a negative electrode sheet. Here, the coating amount of the negative electrode slurry was adjusted such that the weight of the negative electrode mixture excluding the dried copper foil was 6.1 mg / cm ² .

  A coin-type non-aqueous electrolyte secondary battery 1 was produced in the same manner as in Example 1 using the positive electrode sheet and negative electrode sheet produced above. The charge / discharge characteristics of the coin-type nonaqueous electrolyte secondary battery 1 were evaluated by charging and discharging 10 cycles in a constant temperature bath at 25 ° C. with a current value of 200 μA and a voltage range of 3.0 to 4.7 V. .

  Since the coin-type non-aqueous electrolyte secondary battery 1 of Comparative Example 3 uses a carbon material as the negative electrode, Examples 1 to 3 and Comparative Example 1 using a spinel-type lithium-titanium composite oxide as the negative electrode. Compared with the coin-type non-aqueous electrolyte secondary battery 1 to 2, it is a battery that is easily short-circuited.

  The charge / discharge curves of the coin-type nonaqueous electrolyte secondary battery 1 produced in Examples 1 to 3 and Comparative Example 1 are shown in FIGS.

  Moreover, about the baking powder of lithium nickel manganese cobalt complex oxide of the layered crystal structure produced in said Examples 1-5 and Comparative Examples 2-3, 50 kV, 250 mA, using an X-ray-diffraction apparatus (RINT2500), Powder X-ray diffraction measurement was performed under the conditions of a scanning speed of 10 ° / min and a 0.02 ° step. Table 1 shows the c / a axial ratio, the a-axis length (Å: angstrom), and the c-axis length (オ ン: angstrom) determined from the results of powder X-ray diffraction measurement.

  Furthermore, as an evaluation result of the battery characteristics of the coin-type nonaqueous electrolyte secondary battery 1 produced in the above Examples 1 to 5 and Comparative Examples 1 to 3, “initial discharge capacity” and “capacity maintenance ratio after 10 cycles” Is shown in Table 1. In Table 1, “First-time discharge capacity” in Examples 1 to 3 and Comparative Examples 1 and 2 is the discharge capacity at the first cycle per unit weight of the negative electrode active material, and “First-time discharge capacity” in Comparative Example 3 Is the discharge capacity of the first cycle per unit weight of the positive electrode active material.

  In the battery characteristic evaluation results shown in Table 1, “capacity maintenance ratio after 10 cycles” was calculated by the following formula.

  (Capacity maintenance ratio after 10 cycles) [%] = {(Discharge capacity at 10th cycle) / (Discharge capacity at 1st cycle)} × 100

  As shown in FIGS. 2 to 4, in the coin-type nonaqueous electrolyte secondary battery 1 of Examples 1 to 3, the voltage change between the initial stage of charging and the end stage of discharging can be increased, so that the state of charge or the degree of charge is easily detected. be able to. On the other hand, as shown in FIG. 5, in the coin-type nonaqueous electrolyte secondary battery 1 of Comparative Example 1, since the potential change at the initial stage of charging is flat, it is difficult to detect the state of charge or the degree of charge. is there.

  From the results shown in Table 1, in the coin-type nonaqueous electrolyte secondary batteries 1 of Examples 1 to 3, the c / a axial ratio is 4.958 or less, so the discharge capacity maintenance rate after 10 cycles is high and good. Cycle characteristics can be obtained. On the other hand, in the coin-type nonaqueous electrolyte secondary batteries 1 of Examples 4 to 5, the c / a axial ratio exceeds 4.958. Therefore, compared to Examples 1 to 3, the discharge capacity after 10 cycles The maintenance rate is low, and the capacity reduction accompanying the charge / discharge cycle is large. In addition, in the coin-type non-aqueous electrolyte secondary battery 1 of Comparative Examples 2-3, compared with Examples 1-3, the discharge capacity maintenance rate after 10 cycles is low, and the capacity | capacitance fall accompanying a charging / discharging cycle is large.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

  Since the nonaqueous electrolyte secondary battery of the present invention can easily detect the state of charge or the degree of charge, it is useful as a power source for portable electronic devices such as mobile phones, laptop computers, and digital cameras.

  1: Coin-type non-aqueous electrolyte secondary battery, 11: case, 12: sealing plate, 13: gasket, 14: positive electrode, 15: negative electrode, 16: separator, 17: current collector plate, 18: spring member.

Claims (4)

A non-aqueous electrolyte secondary battery having a positive electrode and a negative electrode,
The negative electrode includes a lithium titanium composite oxide,
The positive electrode is observed contains a lithium-manganese-nickel composite oxide having lithium nickel manganese cobalt composite oxide and spinel structure,
The positive electrode includes a lithium manganese nickel composite oxide having a spinel structure as a main active material,
The non-aqueous electrolyte secondary battery in which the lithium nickel manganese cobalt composite oxide has a hexagonal layered rock salt crystal structure belonging to the space group R3m . In the lithium nickel manganese cobalt composite oxide, the ratio of the c-axis lattice constant to the a-axis lattice constant (c / a axis ratio) in the hexagonal layered rock salt type crystal structure belonging to the space group R3m is 4. 96 or less and the general formula Li _{1 + α} [Ni _x Mn _y Co _z ] O ₂ (where α is 0 ≦ α <1.3, x, y and z are x + y + z = 1, 0 <x <0). The non-aqueous electrolyte secondary battery according to claim 1 , wherein: .50, 0 <z ≦ 0.15 is satisfied. The nonaqueous electrolyte secondary battery according to claim 2 , wherein the a-axis lattice constant is 2.8 angstroms or more. The nonaqueous electrolyte secondary battery according to claim 2 or 3 , wherein the c-axis lattice constant is 14 angstroms or more.

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