JP4713886B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, with the reduction in size and weight of electronic devices such as VTRs, mobile phones, and mobile computers, it has been desired to increase the energy density of secondary batteries that are power sources thereof. For this reason, research on non-aqueous electrolyte secondary batteries using lithium as a negative electrode has been actively conducted.

Incidentally, lithium composite oxides such as LiCoO ₂ and LiNiO ₂ are known as positive electrode active materials for non-aqueous electrolyte secondary batteries. On the other hand, lithium, a lithium alloy, or a compound that occludes and releases lithium is used for the negative electrode. As the non-aqueous electrolyte, a solution obtained by dissolving a lithium salt (electrolyte) in a non-aqueous solvent is often used. Such non-aqueous solvents include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), γ- Butyrolactone (γ-BL), tetrahydrofuran (THF), and 2-methyltetrahydrofuran (2-MeTHF) are known. On the other hand, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , and LiAlCl ₄ are known as lithium salts.

In such a nonaqueous electrolyte secondary battery, it has been proposed to use a mixture of LiCoO ₂ and Li ₂ SnO ₃ as a positive electrode active material for the purpose of suppressing gas generation in a high temperature environment (for example, JP-A-63-121258, etc.).

However, a secondary battery using a mixture of LiCoO ₂ and Li ₂ SnO ₃ as a positive electrode active material has a problem that discharge capacity and discharge rate characteristics are low.

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery with improved discharge capacity and discharge rate characteristics.

According to the present invention, a nonaqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte,
The positive electrode active material contains active material particles A containing a lithium cobalt composite oxide and lithium stannate, and active material particles B containing an oxide represented by the following formula (B), and the positive electrode active material The content of the active material particles A is more than 50% by weight, and the following formulas (1) to (5) are satisfied in the positive electrode active material :
The amount of the lithium stannate when the amount of the lithium cobalt composite oxide is 100 parts by weight is 0.1 to 3 parts by weight.
_{LiNi 1-xy Co x M y} O 2 (B)
1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (1)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (2)
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (3)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, said M contains 1 or more types of elements selected from the group which consists of Mn, B, and Al, and said molar ratio x and y are 0 <x <= 0.5, 0 <= y <= 0. 1, D _C10 , D _C50 , and D _C90 are particle diameters of 10%, 50%, and 90% of the volume cumulative frequency of the active material particles A, respectively, and D _N10 , D _N50 , D _N90 is a particle size in which the volume cumulative frequency of the active material particles B is 10%, 50%, and 90%, respectively.

  As described above in detail, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery with improved discharge capacity and discharge rate characteristics.

  An example of the nonaqueous electrolyte secondary battery according to the present invention will be described.

  The nonaqueous electrolyte secondary battery according to the present invention includes a container, an electrode group that is housed in the container and includes a positive electrode and a negative electrode, and a nonaqueous electrolyte that is held by the electrode group.

  In this secondary battery, a separator may be disposed between the positive electrode and the negative electrode, or a gel or solid nonaqueous electrolyte layer may be used instead of the separator.

  Hereinafter, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte, and the container will be described.

1) Positive electrode The positive electrode includes a current collector and an active material-containing layer supported on one or both surfaces of the current collector.

  The positive electrode active material contains active material particles A containing lithium cobalt composite oxide and lithium stannate, and active material particles B having a composition substantially represented by the following formula (B).

_{LiNi 1-xy Co x M y} O 2 (B)
However, said M contains 1 or more types of elements selected from the group which consists of Mn, B, and Al, and said molar ratio x and y are 0 <x <= 0.5, 0 <= y <= 0. 1.

  The content of the active material particles A in the positive electrode active material is more than 50% by weight. The positive electrode active material satisfies the following formulas (1) to (5).

1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (1)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (2)
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (3)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, D _C10 is a particle size in which the volume cumulative frequency of the active material particles A is 10%, D _C50 is a particle size in which the volume cumulative frequency of the active material particles A is 50%, and D _C90 is the active particle particle A. The volume accumulation frequency of the material particles A is 90%, the DN ₁₀ is the particle diameter of the active material particles B is 10%, and the DN ₅₀ is the volume accumulation frequency of the active material particles B. With a particle size of 50%, the _DN 90 is a particle size in which the volume cumulative frequency of the active material particles B is 90%.

(Active material particles A)
Examples of the active material particles A include a mixture in which lithium stannate is precipitated at a crystal grain boundary of a lithium cobalt composite oxide, a mixture of lithium cobalt composite oxide particles and lithium stannate particles, and a lithium cobalt composite oxide particle. Examples thereof include composite particles in which lithium stannate particles having a particle size of about submicron are bonded to the surface. The particle form of the active material particles A may be single particles or secondary agglomerated particles. The active material particles A may contain a lithium composite oxide containing S such as Li ₂ SO ₄ or a silicon oxide such as SiO.

Examples of the lithium cobalt composite oxide include LiCoO ₂ .

Examples of lithium stannate include Li ₂ SnO ₃ .

  The composition of the active material particles A can be represented by, for example, the following formula (A).

_{Li a Co b M1 c Sn d} O 2 (A)
Where M1 is one or more elements selected from the group consisting of Ni, Mn, B and Al, and the molar ratios a, b and c are 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, 0 <d ≦ 0.05, 0.95 ≦ b + c + d ≦ 1.05 are shown. More preferable ranges of the molar ratios a, b, c, d are 0.97 ≦ a ≦ 1.03, 0.97 ≦ b ≦ 1.03, 0.001 ≦ c ≦ 0.03, 0.001 respectively. ≦ d ≦ 0.03.

  When the amount of the lithium cobalt composite oxide is 100 parts by weight, the amount of lithium stannate is preferably in the range of 0.1 to 3 parts by weight. This is due to the reason described below.

  When the non-aqueous electrolyte secondary battery is repeatedly charged and discharged under a high temperature environment (around 45 ° C.), a decomposition reaction of the non-aqueous electrolyte occurs on the surface of the positive electrode active material. This decomposition product reacts with oxygen supplied from the positive electrode active material to generate carbon dioxide gas, causing a problem that the internal pressure of the secondary battery is increased. Moreover, since a hydrocarbon film is formed on the surface of the positive electrode by the polymerization reaction of the decomposition products, the reaction resistance on the surface of the positive electrode increases. Such a decomposition reaction remarkably occurs when a nonaqueous electrolyte containing γ-butyrolactone is used.

  Lithium stannate has a function of suppressing the decomposition reaction of the nonaqueous electrolyte on the surface of the positive electrode active material. According to the inventors' research, lithium stannate is thought to play a catalytic role in the formation of a good SEI (Solid Electrolyte Interface) on the surface of the positive electrode active material, suppressing gas generation during overcharge. As a result, high temperature cycle characteristics are improved. According to the positive electrode active material containing lithium stannate, it is possible to suppress gas generation and hydrocarbon film formation, which are side reactions, without inhibiting the charge / discharge reaction on the positive electrode surface.

  If the amount of lithium stannate is less than 0.1 parts by weight, the effect of suppressing the side reaction may be insufficient, and excellent high-temperature cycle characteristics may not be obtained. Although the amount of lithium stannate tends to increase the side reaction suppression effect, if the amount of lithium stannate exceeds 3 parts by weight, the charge / discharge capacity per unit weight may be impaired. A more preferable range of the amount of lithium stannate is 0.3 to 2 parts by weight.

The reason why each of (D _C90 / D _C50 ) and (D _C50 / D _C10 ) is limited to the range of 1.4 to 2 is for the reason described below. When (D _C90 / D _C50 ) and (D _C50 / D _C10 ) are 1, it means that the particle size distribution of the active material particles A is monodisperse. When (D _C90 / D _C50 ) and (D _C50 / D _C10 ) are less than 1.4, the active material particles A have a narrow particle size distribution, so that the active material filling amount of the positive electrode is insufficient and a high capacity can be obtained. Disappear.

On the other hand, the active material particles A in which (D _C90 / D _C50 ) exceeds 2 contain a large number of particles having a large particle diameter. Since such an active material particle A has a low lithium diffusion rate, it causes a decrease in large current charge / discharge characteristics.

Further, the active material particle A having (D _C50 / D _C10 ) exceeding 2 contains a large amount of fine particles. Since such active material particles A have high reactivity with the non-aqueous electrolyte, the oxidative decomposition of the non-aqueous electrolyte proceeds in a high-temperature environment, and the charge / discharge cycle life at high temperatures decreases.

A more preferable range of each of (D _C90 / D _C50 ) and (D _C50 / D _C10 ) is 1.5 to 1.9.

The DC ₅₀ of the active material particle A is preferably in the range of 0.2 μm or more and 30 μm or less. This is due to the following reason. If D _C50 is less than 0.2 μm, the crystal growth of the active material particles A is insufficient, and a sufficient discharge capacity may not be obtained. On the other hand, if D _C50 exceeds 30 μm, it is difficult to obtain a uniform positive electrode surface when manufacturing the positive electrode. A more preferable range of D _C50 is 1 μm or more and 15 μm or less.

  The reason why the content of the active material particles A in the positive electrode active material is more than 50% by weight is as follows. When the content of the active material particles A in the positive electrode active material is 50% by weight or less, it is difficult to sufficiently improve the discharge rate characteristics, and the thermal stability of the positive electrode active material is lowered. However, if the content of the active material particles A exceeds 95% by weight, a high discharge capacity may not be obtained. Therefore, the content of the active material particles A is in the range of more than 50% by weight and 95% by weight or less. It is desirable to be inside. A more preferred range is 55 to 90% by weight.

(Active material particles B)
The active material particle B has a composition substantially represented by the following formula (B).

_{LiNi 1-xy Co x M y} O 2 (B)
However, said M contains 1 or more types of elements selected from the group which consists of Mn, B, and Al, and said molar ratio x and y are 0 <x <= 0.5, 0 <= y <= 0. 1.

  The active material particles B may be single particles or secondary agglomerated particles.

The active material particles B are prepared by, for example, mixing (Co _w Ni _1-w ) (OH) ₂ coprecipitated composite hydroxide and LiOH · H ₂ O and firing in air at 850 ° C. The

The active material particles B, high purity _{LiNi 1-xy Co x M y} O 2 be used particles, or Li ₂ CO ₃ and containing an alkaline unreacted materials such as LiOH LiNi _1-xy Co _x it is also possible to use M _y O ₂ particles.

(Molar ratio x of Co)
The reason why the molar ratio x of Co is defined within the above range is as follows. By replacing the nickel component of LiNiO ₂ with a cobalt component, the cycle characteristics and thermal stability of the positive electrode active material are improved. However, the molar ratio x exceeds 0.5, mixed nickel ions _{LiNi 1-xy Co x M y} O 2 is the lithium ion sites become susceptible to disordering. This induces a decrease in discharge capacity and discharge operating voltage or a decrease in large current discharge characteristics. A more preferable range of the molar ratio x is 0.1 ≦ x ≦ 0.25.

(Molar ratio y of element M)
The range of the molar ratio y is preferably 0 ≦ y ≦ 0.1. When y = 0, the nickel site is not replaced by the element M. In the present invention, a sufficient effect can be expected even at y = 0, but it is more preferable to replace the nickel site with the element M in order to further improve the thermal stability. However, the molar ratio y exceeds 0.1, since the irreversible lithium ion is increased in order to maintain the electrical neutrality of _{LiNi 1-xy Co x M y} O 2 itself, the total amount of the lithium ions involved in the charge and discharge Decrease. A more preferable range of the molar ratio y is 0 ≦ y <0.06.

The reason why each of (D _N90 / D _N50 ) and (D _N50 / D _N10 ) is limited to the range of 1.4 to 2 is for the reason described below. When (D _N90 / D _N50 ) and (D _N50 / D _N10 ) are 1, it means that the particle size distribution of the active material particles B is monodisperse. When (D _N90 / D _N50 ) and (D _N50 / D _N10 ) are less than 1.4, the particle size distribution of the active material particles B is narrow, so the active material filling amount of the positive electrode is insufficient and a high capacity can be obtained. Disappear.

On the other hand, the active material particle B having (D _N90 / D _N50 ) exceeding 2 contains a large number of particles having a large particle diameter. Since such an active material particle B has a low lithium diffusion rate, the discharge rate characteristics of the secondary battery are degraded.

In addition, the active material particle B having (D _N50 / D _N10 ) exceeding 2 contains a large amount of fine particles. Since such an active material particle B has high reactivity with respect to the non-aqueous electrolyte, the oxidative decomposition of the non-aqueous electrolyte in a high-temperature environment proceeds, and the charge / discharge cycle life at high temperatures decreases.

A more preferable range of each of (D _N90 / D _N50 ) and (D _N50 / D _N10 ) is 1.5 to 1.9.

The reason for defining (D _N50 / D _C50 ) within the range of 1.5 to 2.5 will be described. When (D _N50 / D _C50 ) is 1, it means that the particle size distribution of the active material particles B and the particle size distribution of the active material particles A almost overlap. When (D _N50 / D _C50 ) is 1 or more and less than 1.5, the particle size distribution of the active material particles B and the particle size distribution of the active material particles A are high, so that the packing density of the positive electrode active material is improved. It becomes difficult. As a result, not only a high discharge capacity cannot be obtained, but also the conductivity of the positive electrode is lowered, making it difficult to improve the discharge rate characteristics. When (D _N50 / D _C50 ) is smaller than 1, since the particle size distribution of the active material particles A is larger than the particle size distribution of the active material particles B, the lithium diffusion rate of the active material particles A is The discharge rate characteristics are deteriorated.

When (D _N50 / D _C50 ) exceeds 2.5, the particle size distribution of the active material particles B is significantly larger than the particle size distribution of the active material particles A. The difference in reactivity of the active material particles A becomes remarkable. As a result, the charge / discharge reaction tends to occur non-uniformly in the positive electrode, so that the charge / discharge cycle life is reduced. In addition, when a paste is prepared using such a positive electrode active material, the dispersibility or coating property of the paste is impaired, so that it is difficult to obtain a positive electrode with stable quality. A more preferable range of (D _N50 / D _C50 ) is 1.6 to 2.4.

  As the positive electrode active material, one type of active material particle A and one type of active material particle B may be used, but two or more types having different compositions may be used as active material particle A, or composition as active material particle B may be used. Two or more different types may be used.

The specific surface area of the positive electrode active material is preferably in the range of 0.5 to ² m ² / g. If the specific surface area is less than 0.5 m ² / g, the filling density of the positive electrode active material may be reduced during electrode production, and a sufficient discharge capacity may not be obtained. Further, the charge / discharge efficiency may be reduced due to the reduction of the reaction area. On the other hand, when the specific surface area exceeds 2 m ² / g, the decomposition reaction of the non-aqueous electrolyte is likely to occur as the reaction area increases, and further, the decomposition reaction of the positive electrode active material is caused by the reaction between the positive electrode active material and the non-aqueous electrolyte. When the battery is abnormal, such as overcharge, the battery is likely to overheat, burst, or ignite.

  The positive electrode is produced, for example, by the method described in (i) to (iii) below.

(i) The positive electrode active material, conductive agent and binder are suspended in an appropriate solvent, and the resulting mixture slurry is applied to a current collector, dried, pressed, and cut into a desired size. By doing so, a positive electrode is obtained. At this time, it is preferable that the coating amount of the slurry per one side of the current collector is in the range of 100 to 300 g / m ² . A more preferable range of the coating amount is 200 to 280 g / m ² .

  (ii) A positive electrode active material, a conductive agent, and a binder are kneaded, and the resulting mixture is formed into a pellet. The resulting pellet is pressure-bonded to a current collector to obtain a positive electrode.

  (iii) A positive electrode active material, a conductive agent, and a binder are kneaded, and the resulting mixture is formed into a sheet shape. Then, the resulting sheet is pressure-bonded to a current collector to obtain a positive electrode.

  Examples of the conductive agent include carbon black such as acetylene black and ketjen black, graphite, and the like.

  Examples of the binder include polyvinylidene fluoride (PVdF), vinylidene fluoride-6-propylene fluoride copolymer, vinylidene fluoride-tetrafluoroethylene-6-propylene terpolymer, and vinylidene fluoride- Pentafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) -vinylidene fluoride terpolymer Tetrafluoroethylene-hexafluoropropylene (FEP) -vinylidene fluoride terpolymer, tetrafluoroethylene-ethylene-vinylidene fluoride terpolymer, chlorotrifluoroethylene-vinylidene fluoride copolymer, chlorotrifluoro Loe Len - ethylene - vinylidene fluoride terpolymer, vinyl fluoride - vinylidene fluoride copolymer, an ethylene - propylene - diene copolymer (EPDM), styrene - can be used butadiene rubber (SBR) and the like.

  The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 10% by weight of the binder.

  As the current collector, for example, an aluminum foil, a stainless steel foil, or a titanium foil can be used. Aluminum foil is most preferable in consideration of tensile strength, electrochemical stability, flexibility during winding, and the like. The thickness of the foil at this time is preferably 10 μm or more and 30 μm or less. In addition to the foil-like current collector, a perforated current collector such as a punched metal or an expanded metal may be used.

The D _C10 , D _C50 and D _C90 of the active material particles A and the D _N10 , D _N50 and D _N90 of the active material particles B are measured, for example, by the method described below.

  First, the secondary battery is disassembled and the positive electrode is taken out. The taken out positive electrode is baked at 400 ° C. in an oxidizing atmosphere such as air to remove the binder contained in the positive electrode. Note that the firing temperature is not limited to 400 ° C., and may be any temperature range in which the binder can be removed and a combustion reaction of the current collector (eg, an aluminum current collector) does not occur.

  Next, the active material-containing layer is peeled off from the current collector, and the active material-containing layer is baked at 600 ° C. in an oxidizing atmosphere such as air, so that the conductive agent is oxidized and burned and discharged as carbon dioxide out of the system. . By this firing, the binder remaining in the active material-containing layer is also removed by oxidative combustion. This firing temperature is not limited to 600 ° C., and the reaction that can remove the conductive agent and the binder by oxidative combustion, and changes the properties of the positive electrode active material, such as a fusion reaction, for example. Any temperature range that does not occur is acceptable.

  After firing, it is confirmed by powder X-ray diffraction measurement that a peak derived from the conductive agent and a peak derived from the binder are not detected.

The powder is analyzed by a microparticle analyzer using microwave induction plasma (for example, a particle analyzer system DP-1000 manufactured by HORIBA, Ltd.), whereby D _C10 , D _C50 and D _{C90 of} the active material particles A D _N10 , D _N50 and D _{N90 of the} material particles B are obtained. This particle analyzer performs measurements based on microwave-induced plasma emission spectrometry, and performs emission analysis by sucking particles on the filter with an aspirator and introducing them one by one into helium microwave plasma. The element is identified from the emission wavelength, the particle diameter is measured from the emission intensity, and the number is measured from the number of times of emission. The usable fine particle analyzer is not limited to the particle analyzer system DP-1000 manufactured by HORIBA, but can be substituted if it has an equivalent performance.

2) Negative electrode The negative electrode includes a current collector and a negative electrode layer carried on one or both surfaces of the current collector.

  The negative electrode layer includes a lithium ion or a compound that occludes / releases lithium atoms as a negative electrode material. Examples of such compounds include conductive polymers (for example, polyacetal, polyacetylene, polypyrrole, etc.), carbon materials such as organic sintered bodies, and the like.

  The characteristics of the carbon material can be adjusted by the type of raw material and the sintering method. Specific examples of the carbon material include a graphite-based carbon material, a carbon material in which a graphite crystal part and an amorphous part are mixed, and a carbon material having a turbulent structure with no regularity in the lamination of crystal layers. it can.

  The said negative electrode is produced by the method demonstrated to the following (I)-(III), for example.

(I) A negative electrode material and a binder are suspended in a suitable solvent, and the resulting mixture slurry is applied to a current collector, dried, pressed, and cut into a desired size. A negative electrode is obtained. At this time, it is preferable that the coating amount of the slurry per one side of the current collector is in the range of 50 to 150 g / m ² .

  (II) The negative electrode material and the binder are kneaded, the resulting mixture is molded into a pellet, and the resulting pellet is pressure-bonded to a current collector to obtain a negative electrode.

  (III) After the negative electrode material and the binder are kneaded and the resulting mixture is formed into a sheet, the negative electrode is obtained by pressure-bonding the obtained sheet to a current collector.

  Examples of the binder include the same ones as described for the positive electrode.

  The mixing ratio of the negative electrode material and the binder is preferably in the range of 80 to 98% by weight of the negative electrode material and 2 to 20% by weight of the binder.

  As the current collector of the negative electrode, for example, a copper foil, a nickel foil or the like can be used. In view of electrochemical stability and flexibility, copper foil is most preferred. The thickness of the foil at this time is preferably 8 μm or more and 20 μm or less. In addition to the foil-like current collector, a perforated current collector such as a punched metal or an expanded metal may be used.

3) Non-aqueous electrolyte As the non-aqueous electrolyte, one having a substantially liquid or gel-like form can be used. The liquid nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent. On the other hand, the gel-like non-aqueous electrolyte contains a liquid non-aqueous electrolyte and a gelling agent that gels the liquid non-aqueous electrolyte. Examples of the gelling agent include a polymer having at least one of acrylic acid and methacrylic acid as a polymerization group in the polyethylene oxide molecule, polymerized to have a large molecular weight or crosslinked, polyacrylonitrile, and the like. .

  Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), Diethoxyethane (DEE), γ-butyrolactone (γ-BL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane, 1,3-dimethoxypropane, vinylene carbonate (VC), etc. Can be mentioned. The kind of non-aqueous solvent to be used can be one kind or two or more kinds.

  Preferred non-aqueous solvents are a non-aqueous solvent a containing EC and γ-BL, a non-aqueous solvent b containing EC, γ-BL and VC, and a non-aqueous solvent c containing EC, γ-BL and PC. Non-aqueous solvent d containing EC, γ-BL, PC and VC. The volume ratio of γ-butyrolactone in each of nonaqueous solvent a to nonaqueous solvent d is preferably 30% by volume or more and 90% by volume or less. By adopting such a configuration, it is possible to suppress gas generation at the time of initial charge and during storage in a charged state.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), bistri Examples include lithium salts such as lithium fluoromethylsulfonylimide [(LiN (CF ₃ SO ₂ ) ₂ ], LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium aluminum tetrachloride (LiAlCl ₄ ), etc. The type can be one type or two or more types, among which lithium tetrafluoroborate (LiBF ₄ ) is preferable because it can suppress gas generation during the initial charge.

  The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 1 to 3 mol / L. More preferably, it is the range of 1-2 mol / L.

4) Separator This separator is formed from a porous sheet.

  For example, a porous film or a non-woven fabric can be used as the porous sheet. The porous sheet is preferably made of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

5) Container The shape of the container may be, for example, a bottomed cylindrical shape, a bottomed rectangular tube shape, a bag shape, or a cup shape.

  The container can be formed of, for example, a resin, a sheet including a resin layer, a metal plate, a metal film, or the like.

  Examples of the resin include polyolefin such as polyethylene and polypropylene, nylon, and the like.

  The resin layer included in the sheet can be formed from, for example, polyethylene, polypropylene, nylon, or the like. As the sheet, it is preferable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer is made of, for example, aluminum, stainless steel, iron, copper, nickel or the like. Among these, aluminum that is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, but may be formed from a combination of two or more types of metals. Of the two protective layers, the protective layer in contact with the outside serves to prevent damage to the metal layer. This external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the internal protective layer plays a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is formed of one type of resin layer or two or more types of resin layers. In addition, a thermoplastic resin can be disposed on the surface of the internal protective layer.

  The metal plate and the metal film can be formed of, for example, iron, stainless steel, or aluminum.

  A thin lithium ion secondary battery which is an example of a non-aqueous secondary battery according to the present invention will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view showing a thin lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 is an enlarged cross-sectional view showing part A of FIG. As shown in FIG. 1, an electrode group 2 is accommodated in the container 1. The electrode group 2 has a structure in which a laminate composed of a positive electrode, a separator, and a negative electrode is wound into a flat shape. As shown in FIG. 2, the laminate includes a separator 3 (from the lower side of the figure), a positive electrode 6 including an active material-containing layer 4, a positive electrode current collector 5, and an active material-containing layer 4, a separator 3, a negative electrode A negative electrode 9 including a layer 7, a negative electrode current collector 8, and a negative electrode layer 7, a separator 3, a positive electrode 6 including a positive electrode current collector 5, an active material containing layer 4, a separator 3, and a negative electrode The negative electrode 9 provided with the layer 7 and the negative electrode current collector 8 is formed by laminating in this order. One end of the strip-like positive electrode lead 10 is connected to the positive electrode current collector 5 of the positive electrode group 2, and the other end is extended from the container 1. On the other hand, one end of the strip-like negative electrode lead 11 is connected to the negative electrode current collector 8 of the negative electrode group 2 and the other end is extended from the container 1.

  In addition, in FIG. 1 and FIG. 2 described above, the electrode group in which the positive electrode and the negative electrode are wound in a flat shape with a separator interposed therebetween is used, but the electrode group by folding the positive electrode and the negative electrode with a separator interposed therebetween, An electrode group in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween may be used.

  Moreover, the example which applied this invention to the square nonaqueous electrolyte secondary battery is shown in FIG.

  As shown in FIG. 3, an electrode group 13 is accommodated in a bottomed rectangular cylindrical container 12 made of metal such as aluminum. In the electrode group 13, a positive electrode 14, a separator 15 and a negative electrode 16 are laminated in this order and wound in a flat shape. A spacer 17 having an opening near the center is disposed above the electrode group 13.

  The nonaqueous electrolyte is held in the electrode group 13. A sealing plate 18 b having an explosion-proof mechanism 18 a and having a circular hole opened near the center is laser welded to the opening of the container 12. The negative electrode terminal 19 is disposed in a circular hole of the sealing plate 18b via a hermetic seal. The negative electrode tab 20 drawn out from the negative electrode 16 is welded to the lower end of the negative electrode terminal 19. On the other hand, a positive electrode tab (not shown) is connected to a container 12 that also serves as a positive electrode terminal.

The positive electrode active material for nonaqueous electrolyte secondary battery according to the present invention described above, the active material particles A containing lithium-cobalt composite oxide and lithium stannate, containing _{LiNi 1-xy Co x M y} O 2 Active material particles B. The content of the active material particles A in the positive electrode active material is more than 50% by weight. Moreover, the said positive electrode active material satisfies the said (1)-(5) Formula.

  According to such a secondary battery, it is possible to improve discharge capacity and discharge rate characteristics while ensuring a practical charge / discharge cycle life.

That is, when the content of the active material particles A in the positive electrode active material is more than 50% by weight, (D _C90 / D _C50 ) of the active material particles A and (D _N90 / D _N50 ) of the active material particles B By making each within the range of 1.4 to 2 and (D _N50 / D _C50 ) within the range of 1.5 to 2.5, the lithium diffusion rate of the positive electrode active material can be improved. The discharge rate characteristics of the secondary battery can be improved. At the same time, since the particle size distribution of the positive electrode active material can have an appropriate width, the packing density of the positive electrode active material can be improved and the discharge capacity can be improved.

Further, by setting (D _C50 / D _C10 ) of the active material particles A and (D _N50 / D _N10 ) of the active material particles B within the range of 1.4 to 2, the positive electrode active material with respect to the nonaqueous electrolyte Since the reactivity can be lowered, the oxidative decomposition of the nonaqueous electrolyte can be suppressed, and a long life can be obtained even at a high temperature such as 45 ° C.

  Therefore, according to the present invention, it is possible to realize a non-aqueous electrolyte secondary battery that simultaneously satisfies the discharge capacity, discharge rate characteristics, active material filling density, and charge / discharge cycle life.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode preferably satisfies the following formula (6).

P ₁ <P ₂ (6)
Where P ₁ is the abundance ratio of the active material particles A on the current collector-side surface (hereinafter referred to as the first surface) of both surfaces of the active material-containing layer, and P ₂ is the first surface. Is the abundance ratio of the active material particles A on the second surface located on the opposite side.

  By satisfying the equation (6), the charge / discharge cycle life at 45 ° C. can be further improved.

  That is, the nonaqueous electrolyte containing ethylene carbonate (EC) and γ-butyrolactone (GBL) can form a protective film derived from EC on the positive electrode surface (second surface). When many active material particles A are present on the surface of the positive electrode, the active material particles A can sufficiently exhibit a function as a catalyst for promoting the protective film formation reaction. E. I. Can be formed. As a result, the reactivity of the positive electrode with respect to GBL can be reduced, so that the charge / discharge cycle life at 45 ° C. can be further improved.

  The positive electrode satisfying the above-described expression (6) is produced, for example, by the method described below.

A positive electrode active material including the active material particles A and the active material particles B, a conductive agent, and a binder containing polyvinylidene fluoride (PVdF) are suspended in a suitable solvent. The obtained mixture slurry is applied to a current collector. Since the active material particles B contain an alkaline unreacted material such as Li ₂ CO ₃ or LiOH, the unreacted material promotes the crosslinking reaction of PVdF. Further, the particle size distribution of the active material particles B is larger than the particle size distribution of the active material particles A. As a result, since the active material particles B are likely to settle in the mixture slurry, the active material particles B are unevenly distributed on the current collector side when the mixture slurry is applied to one or both surfaces of the current collector. After drying the slurry-coated current collector, pressing is performed, and a desired size is obtained by cutting into a desired size.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Preparation of positive electrode>
An active material particle A having a volume cumulative frequency 10% particle size D _C10 of 2 μm, a volume cumulative frequency 50% particle size D _C50 of 3.5 μm, and a volume cumulative frequency 90% particle size D _C90 of 5.8 μm was prepared. The amount of Li ₂ SnO ₃ when the amount of LiCoO ₂ is 100 parts by weight is 1 part by weight. When the powder X-ray diffraction measurement was performed on the active material particles A, a peak derived from LiCoO ₂ and a peak derived from Li ₂ SnO ₃ were detected. The composition formula of the active material particles A was Li _1.023 Co _0.992 Sn _0.005 O ₂ .

On the other hand, as the active material particles B, the volume cumulative frequency 10% particle diameter D _N10 is at 4.1 .mu.m, in 7μm volume cumulative frequency 50% particle diameter D _N50, the volume cumulative frequency 90% particle diameter D _N90 is 11.8μm LiNi _0.8 Co _0.2 O ₂ particles were prepared. The LiNi _0.8 Co _0.2 O ₂ particles contained 0.7% by weight of LiOH.

Table 2 shows (D _N50 / D _N10 ), (D _N90 / D _N50 ), (D _C50 / D _C10 ), (D _C90 / D _C50 ), and (D _N50 / D _C50 ).

  The volume cumulative frequencies of 10%, 50%, and 90% were measured by the method described below. That is, the particle size for each of the nickel-based particles and the cobalt-based particles and the occupied volume of the particles in each particle size interval are measured by a laser diffraction / scattering method. When the volume of the particle size interval is 10% of the total, the particle size is 10% of the volume cumulative frequency, the particle size of 50% is the volume cumulative frequency of 50%, and 90%. The particle diameter is set to a volume cumulative frequency of 90%.

  60 parts by weight of the active material particles A and 40 parts by weight of the active material particles B are mixed, and 3 parts by weight of graphite (trade name: KS6 manufactured by Lonza) is added to 100 parts by weight of the obtained positive electrode active material. Added and mixed with Henschel mixer. A mixture slurry was prepared by dissolving 3 parts by weight of polyvinylidene fluoride in N-methyl-2-pyrrolidone and kneading the resulting solution, the positive electrode active material, and graphite. The mixture slurry was applied to an aluminum foil having a thickness of 15 μm, dried, and then heated and pressed to produce a positive electrode.

<Production of negative electrode>
Graphitized carbon powder was synthesized by graphitizing mesophase pitch-based carbon fibers at 3000 ° C. in an argon gas atmosphere. Subsequently, 100% by weight of the graphitized carbon powder and 5% by weight of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone were mixed to prepare a mixture slurry. This mixture slurry was applied to a copper foil having a thickness of 12 μm, dried, and then heated and pressed to prepare a negative electrode.

  The positive electrode and the microporous film made of polypropylene, in which an aluminum ribbon having a thickness of 100 μm and a length of 70 mm is ultrasonically welded to a predetermined position in advance as a current collecting tab of the positive electrode, and a polyimide protective tape for preventing a short circuit is pasted on the welding site And a negative electrode current collecting tab having a thickness of 100 μm and a length of 70 mm of copper ribbon ultrasonically welded at a predetermined position, and a polyimide protective tape for preventing a short circuit applied to the welded portion. After laminating them in this order, they were wound into a flat shape and heated and pressed at 90 ° C. for 30 seconds to produce an electrode group.

Furthermore, 2 mol / L of LiBF ₄ was dissolved in a mixed solvent of ethylene carbonate and γ-butyrolactone (mixing volume ratio 1: 3) to prepare a nonaqueous electrolytic solution.

  A thin nonaqueous solvent secondary battery (383562 size) shown in FIG. 1 described above is assembled by storing the electrode group and the nonaqueous electrolyte in a container made of an aluminum laminate film in which a power generation element can be stored. It was. All of the injection and sealing steps were performed in a glove box controlled to a dew point of −80 ° C. or lower under an Ar atmosphere.

  The thin non-aqueous solution is the same as described in Example 1 except that the amount of the active material particles A in the positive electrode is 70 parts by weight and the amount of the active material particles B is 30 parts by weight. An electrolyte secondary battery was manufactured.

  The thin non-aqueous solution is the same as described in Example 1 except that the amount of the active material particles A in the positive electrode is 90 parts by weight and the amount of the active material particles B is 10 parts by weight. An electrolyte secondary battery was manufactured.

As the active material particles B, and D _N10 is 4.8 .mu.m, with D _N50 is 6.9 [mu] m, with D _N90 is 10.5 [mu] m, and the LiNi _0.8 Co _0.2 O ₂ particles content of 0.7% by weight LiOH A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that it was used.

As the active material particles B, LiNi _0.8 Co _0.2 O ₂ particles having DN ₁₀ of 3.8 μm, DN ₅₀ of 7.1 μm, DN ₉₀ of 13.8 μm, and a LiOH content of 0.7 wt% are used. Except for this, a thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 above.

The D _C10 of the active material particles A to 2.4 [mu] m, and the D _C50 to 3.4 .mu.m, and except that the D _C90 to 5.1 .mu.m, a thin nonaqueous in a manner similar to that described in Example 1 above An electrolyte secondary battery was manufactured.

The thin non-aqueous solution is the same as described in Example 1 except that the active material particle A has a D _C10 of 1.8 μm, a D _C50 of 3.5 μm, and a D _C90 of 6.6 μm. An electrolyte secondary battery was manufactured.

The D _C10 of the active material particle A is set to 2 μm, the D _{C50 is set} to 3.5 μm, the D _{C90 is set} to 5.8 μm, the D _N10 of the active material particle B is set to 4.6 μm, and the D _{N50 is set} to 8.6 μm. A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that DN 90 was _changed to 13.8 μm.

D _C10 of active material particle A is set to 2 μm, D _{C50 is set} to 3.5 μm, D _{C90 is set} to 5.8 μm, DN ₁₀ of active material particle B is set to 3.2 μm, and D _{N50 is set} to 5.8 μm. A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that DN90 was _9.9 μm.

The D _C10 of the active material particles A to 2.3 .mu.m, a D _C50 to 3.8 .mu.m, and with the D _C90 to 6.5 [mu] m, 2.8 weight content of Li ₂ SnO ₃ in the active material particles A A thin non-aqueous electrolyte secondary battery was _prepared in the same manner as described in Example 1 except that Li _1.027 Co _0.978 Sn _0.015 O ₂ was _added (parts of LiCoO ₂ was 100 parts by weight). Manufactured.

The active material particle A has D _C10 of 2.4 μm, D _C50 of 3.9 μm and D _C90 of 6.2 μm, and the content of Li ₂ SnO ₃ in the active material particle A is 0.2 weight. A thin non-aqueous electrolyte secondary battery was _prepared in the same manner as described in Example 1 except that Li _1.021 Co _0.998 Sn _0.001 O ₂ (parts of LiCoO ₂ was 100 parts by weight) was used. Manufactured.

As active material particles B, LiNi _0.76 Co _0.18 Al _0.06 O ₂ particles having DN ₁₀ of 4.1 μm, DN ₅₀ of 7.0 μm, and DN ₉₀ of 12.0 μm were prepared. The LiNi _0.76 Co _0.18 Al _0.06 O ₂ particles contained 0.5% by weight of LiOH. A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that such active material particles B were used.

As active material particles B, LiNi _0.76 Co _0.18 Mn _0.06 O ₂ particles having DN ₁₀ of 4.1 μm, DN ₅₀ of 7.2 μm, and DN ₉₀ of 11.8 μm were prepared. The LiNi _0.76 Co _0.18 Mn _0.06 O ₂ particles contained 0.2% by weight of LiOH. A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that such active material particles B were used.

<Comparative example 1>
A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that only the active material particles A similar to those described in Example 1 were used as the positive electrode active material. .

<Comparative example 2>
The thin non-aqueous electrolyte secondary is the same as described in Example 1 except that the amount of the active material particles A is 40 parts by weight and the amount of the active material particles B is 60 parts by weight. A battery was manufactured.

<Comparative Example 3>
The D _C10 of the active material particles A to 2.5 [mu] m, and the D _C50 to 3.3 [mu] m, and except that the D _C90 to 4.7 [mu] m, a thin nonaqueous in a manner similar to that described in Example 1 above An electrolyte secondary battery was manufactured.

<Comparative example 4>
The D _C10 of the active material particles A to 1.4 [mu] m, and the D _C50 to 3.8 .mu.m, and except that the D _C90 to 10 [mu] m, a thin nonaqueous electrolyte secondary in a manner similar to that described in Example 1 above A secondary battery was manufactured.

<Comparative Example 5>
D _C10 of active material particle A is 3.1 μm, D _C50 is 5.5 μm, D _C90 is 9 μm, DN ₁₀ of active material particle B is 4.1 μm, DN ₅₀ is 7 μm, and A thin nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that DN90 was _11.8 μm.

<Comparative Example 6>
D _C10 of active material particle A is set to 1.6 μm, D _C50 is set to 2.6 μm, D _{C90 is set} to 4.8 μm, DN ₁₀ of active material particle B is set to 4.1 μm, and D _{N50 is set} to 7 μm. A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that DN90 was _changed to 11.8 μm.

<Comparative Example 7>
A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that only the active material particles B similar to those described in Example 1 were used as the positive electrode active material. .

(Comparative Example 8)
LiCoO ₂ particles having a volume cumulative frequency 10% particle diameter D _C10 of 2.1 μm, a volume cumulative frequency 50% particle diameter D _C50 of 6.2 μm, and a volume cumulative frequency 90% particle diameter D _C90 of 3.7 μm were prepared. .

On the other hand, the volume cumulative frequency 10% particle diameter D _N10 is 4.3 [mu] m, a volume cumulative frequency 50% particle diameter D _N50 is 7.3 .mu.m, the active material particle having a volume cumulative frequency 90% particle diameter D _N90 is 12.8 C Prepared. The active material particles C are particles containing 0.7% by weight of LiOH. The amount of Li ₂ SnO ₃ when the amount of LiNi _0.8 Co _0.2 O ₂ is 100 parts by weight is 12 parts by weight.

The thin nonaqueous electrolyte is the same as that described in Example 1 except that 60 parts by weight of LiCoO ₂ particles and 40 parts by weight of active material particles C are mixed and the obtained positive electrode active material is used. A secondary battery was manufactured.

For the obtained secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 8, the abundance ratio P ₁ of the active material particles A on the surface of the active material containing layer 4 on the current collector 5 side and the active material on the separator 3 side The abundance ratio P ₂ of the active material particles A on the surface of the containing layer 4 (positive electrode surface) was measured.

  Each positive electrode was subjected to SEM observation and EPMA analysis of the cross section in the positive electrode thickness direction. A positive electrode cut out in 2 cm square was embedded in a resin, cured, and cut with a diamond cutter to obtain a cross section. Composition analysis is performed on the surface of the active material containing layer 4 on the current collector 5 side and the surface of the active material containing layer 4 on the separator 3 side, and the presence of the active material particles A and active material particles B in one field of view at a magnification of 500 times The ratio was determined.

The presence ratio P ₂ of the active material particles A on the surface of the active material containing layer 4 on the separator 3 side is larger than the existing ratio P ₁ of the active material particles A on the surface of the active material containing layer 4 on the current collector 5 side. “P ₁ <P ₂ ” is displayed, and the others are shown as “NG” in Table 2 below.

  Moreover, about the obtained secondary battery of Examples 1-13 and Comparative Examples 1-8, the active material density, 0.2C capacity | capacitance, a discharge rate characteristic, energy density, and the cycle life in 45 degreeC by the method demonstrated below. The results are shown in Table 2 below.

<Active material density>
The density per unit volume of the active material (active material density: g / cm ³ ) was calculated from the thickness of the active material-containing layer, and the results are shown in Table 2 below.

<Rated capacity>
The assembled secondary battery was initially charged at a constant current of 140 mA (equivalent to 0.2 CmA) up to 4.2 V at 20 ° C., and after reaching 4.2 V, the battery was initially charged at a constant voltage for a total of 12 hours. The discharge capacity when discharged at a constant current of 140 mA up to 3.0 V was measured to obtain the rated capacity at 0.2 C discharge. The results are shown in Table 2 below.

<Discharge rate characteristics>
After charging at a constant current of 140 mA up to 4.2 V, charge for a total of 12 hours at a constant voltage of 4.2 V, and then discharge at a constant current of 1 CmA (700 mA) up to 3.0 V. It was measured. The 1 C discharge capacity is expressed by setting the 0.2 C discharge capacity to 100%, and the result is shown in the following Table 2 as discharge rate characteristics.

<Energy density>
After charging to 4.2 V at a constant current of 140 mA, charging was further performed at a constant voltage of 4.2 V for a total of 12 hours, and the thickness of the battery at the time of 4.2 V was measured. The average voltage was obtained from the integrated value of the discharge curve up to 3.0 V at 0.2 CmA (140 mA). The volume energy density was determined from the width (35 mm) and length (62 mm) of the battery excluding the positive and negative current collecting tabs, the measured battery thickness, and the average voltage. The results are shown in Table 2.

<Cycle life>
The charge / discharge cycle was repeated under the conditions described below in an environment of 45 ° C. Charging was performed at a constant current of 1 C (700 mA) up to 4.2 V, and after reaching 4.2 V, charging was performed at a constant voltage for a total of 3 hours, and discharging was performed at 1 C up to 3.0 V. The number of cycles at which the discharge capacity reached 80% of the discharge capacity at the first cycle was measured, and the results are shown in Table 2 below as the cycle life.

  As is clear from Tables 1 and 2, the secondary batteries of Examples 1 to 13 can obtain sufficient characteristics in any of active material density, 0.2C capacity, discharge rate characteristics, energy density, and cycle life. I understand that.

  On the other hand, the secondary battery of Comparative Example 1 using only the mixture of lithium stannate and lithium cobalt composite oxide as the positive electrode active material has a lower 0.2 C discharge capacity and energy density than Examples 1-13. It was. The secondary battery of Comparative Example 2 in which the content of the mixture of lithium stannate and lithium cobalt composite oxide is 50% by weight or less has an active material density, a discharge rate characteristic, and a cycle life as compared with Examples 1 to 13. It was low.

In the secondary batteries of Comparative Examples 3 and 4 where (D _C50 / D _C10 ) was out of the range of 1.4 to 2, the active material density and cycle life were lower than those of Examples 1 to 13. In the secondary battery of Comparative Example 5 in which (D _N50 / D _C50 ) is less than 1.5, the active material density, 0.2 C capacity, energy density, and cycle life were lower than those of Examples 1-13. In the secondary battery of Comparative Example 6 in which (D _N50 / D _C50 ) exceeded 2.5, the active material density, discharge rate characteristics, and charge / discharge cycle life were lower than those of Examples 1-13.

  On the other hand, the secondary battery of Comparative Example 7 using only the active material particles B had a lower active material density, discharge rate characteristics, and charge / discharge cycle life as compared with Examples 1-13. In the secondary battery of Comparative Example 8 in which lithium stannate was added to the active material particles B, the 0.2 C capacity and the discharge rate characteristics were lower than those of Examples 1-13.

In the above-described embodiment, an example in which the present invention is applied to a positive electrode active material composed of two types of LiCoO ₂ particles containing Li ₂ SnO ₃ and LiNi _0.8 Co _0.2 O ₂ particles has been described. As long as the discharge capacity and discharge rate characteristics can be improved, three or more kinds of LiCoO ₂ particles containing Li ₂ SnO ₃ and LiNi _0.8 Co _0.2 O ₂ particles mixed with other kinds of particles such as LiMn ₂ O ₄ What consists of particle | grains can be used.

  In the above-described embodiments, examples of applying to a thin non-aqueous electrolyte secondary battery have been described. However, a rectangular non-aqueous electrolyte secondary battery, a cylindrical non-aqueous electrolyte secondary battery, and a coin-type non-aqueous electrolyte secondary battery are described. It can be similarly applied to.

  As described above in detail, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery with improved discharge capacity and discharge rate characteristics.

FIG. 1 is a cross-sectional view showing a thin nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention. FIG. 2 is an enlarged cross-sectional view showing a portion A of FIG. FIG. 3 is a cross-sectional view showing a prismatic nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention.

Claims (8)

A non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte,
The positive electrode active material contains active material particles A containing a lithium cobalt composite oxide and lithium stannate, and active material particles B containing an oxide represented by the following formula (B), and the positive electrode active material The content of the active material particles A is more than 50% by weight, and the following formulas (1) to (5) are satisfied in the positive electrode active material :
The amount of the lithium stannate when the amount of the lithium cobalt composite oxide is 100 parts by weight is 0.1 to 3 parts by weight.
_{LiNi 1-xy Co x M y} O 2 (B)
1.4 ≦ (D _C90 / D _C50 ) ≦ 2 (1)
1.4 ≦ (D _C50 / D _C10 ) ≦ 2 (2)
1.4 ≦ (D _N90 / D _N50 ) ≦ 2 (3)
1.4 ≦ (D _N50 / D _N10 ) ≦ 2 (4)
1.5 ≦ (D _N50 / D _C50 ) ≦ 2.5 (5)
However, said M contains 1 or more types of elements selected from the group which consists of Mn, B, and Al, and said molar ratio x and y are 0 <x <= 0.5, 0 <= y <= 0. 1, D _C10 , D _C50 , and D _C90 are particle diameters of 10%, 50%, and 90% of the volume cumulative frequency of the active material particles A, respectively, and D _N10 , D _N50 , D _N90 is a particle size in which the volume cumulative frequency of the active material particles B is 10%, 50%, and 90%, respectively. The particle size ratio (D _C90 / D _C50 ), the particle size ratio (D _C50 / D _C10 ), the particle size ratio (D _N90 / D _N50 ), and the particle size ratio (D _N50 / D _N10 ) The nonaqueous electrolyte secondary battery according to claim 1, wherein each has a range of 1.5 to 1.9. D _C50 non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the range of 0.2μm~30μm of the active material particles A. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the active material particles A in the positive electrode active material is more than 50 wt% and 95 wt% or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 , wherein the active material particle A has a composition represented by the following formula (A).
_{Li a Co b M1 c Sn d} O 2 (A)
Where M1 is one or more elements selected from the group consisting of Ni, Mn, B and Al, and the molar ratios a, b and c are 0.95 ≦ a ≦ 1.05, 0.95 ≦ b ≦ 1.05, 0 ≦ c ≦ 0.05, 0 <d ≦ 0.05, 0.95 ≦ b + c + d ≦ 1.05 are shown. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the particle size ratio (D _N50 / D _C50 ) is in a range of 1.6 to 2.4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the nonaqueous electrolyte contains γ-butyrolactone. The positive electrode includes an active material-containing layer containing the positive electrode active material, and a current collector on which the active material-containing layer is supported on one side or both sides, and satisfies the following formula (6): The nonaqueous electrolyte secondary battery according to any one of? 7 .
P ₁ <P ₂ (6)
Where P ₁ is the abundance ratio of the active material particles A on the current collector-side surface of both surfaces of the active material-containing layer, and P ₂ is the active material particles A on the remaining surface of the active material-containing layer. Is the abundance ratio.

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