阅读说明：本技术 非水电解质二次电池 (Nonaqueous electrolyte secondary battery ) 是由 前川正宪 石川贵之 长田薰 于 2020-04-15 设计创作，主要内容包括：本发明的目的在于,提供一种高容量的非水电解质二次电池。在作为实施方式的一例的非水电解质二次电池中,正极合剂层包含：含有由通式Li-(a)Ni-(b)Co-((1-b-c))Al-(c)O-(d)(0.9＜a≤1.2、0.88≤b≤0.96、0.04≤c＜0.12、1.9≤d≤2.1)表示的锂过渡金属复合氧化物的正极活性物质、和相对于正极活性物质的质量为0.1～1.0质量％的碳酸锂。锂过渡金属复合氧化物是一次粒子凝聚而成的二次粒子,在一次粒子的表面,存在相对于正极活性物质中的除Li以外的金属元素的总摩尔量为0.05～0.20摩尔％的钨。(The purpose of the present invention is to provide a high-capacity nonaqueous electrolyte secondary battery. In a nonaqueous electrolyte secondary battery as an example of an embodiment, a positive electrode mixture layer includes: containing a compound represented by the formula Li a Ni b Co (1‑b‑c) Al c O d A positive electrode active material of a lithium transition metal composite oxide represented by (0.9 < a.ltoreq.1.2, 0.88 < b.ltoreq.0.96, 0.04 < c.ltoreq.0.12, and 1.9 < d.ltoreq.2.1), and a mass of the positive electrode active material is 0.1 to 1.0 mass% of lithium carbonate. The lithium transition metal composite oxide is a secondary particle formed by aggregating primary particles, and tungsten is present on the surface of the primary particles in an amount of 0.05 to 0.20 mol% relative to the total molar amount of metal elements other than Li in the positive electrode active material.)

1. A nonaqueous electrolyte secondary battery includes: a positive electrode having a positive electrode core and a positive electrode mixture layer provided on the surface of the positive electrode core,

the positive electrode mixture layer includes:

containing a compound represented by the formula Li_aNi_bCo_(1-b-c)Al_cO_dThe positive electrode active material of the lithium transition metal composite oxide is represented by the formula, wherein a is more than 0.9 and less than or equal to 1.2, b is more than or equal to 0.88 and less than or equal to 0.96, c is more than or equal to 0.04 and less than or equal to 0.12, and d is more than or equal to 1.9 and less than or equal to 2.1; and

0.1 to 1.0 mass% of lithium carbonate based on the mass of the positive electrode active material,

the lithium transition metal composite oxide is a secondary particle obtained by aggregating primary particles,

tungsten is present on the surface of the primary particles in an amount of 0.05 to 0.20 mol% relative to the total molar amount of metal elements other than Li in the positive electrode active material.

2. The nonaqueous electrolyte secondary battery according to claim 1,

the lithium transition metal composite oxide is represented by the general formula Li_aNi_bCo_(1-b-c)Al_cO_dThe compound oxide is represented by a is more than 0.9 and less than or equal to 1.2, b is more than or equal to 0.88 and less than or equal to 0.92, c is more than or equal to 0.04 and less than or equal to 0.06, and d is more than or equal to 1.9 and less than or equal to 2.1.

3. The nonaqueous electrolyte secondary battery according to claim 1,

the lithium transition metal composite oxide is represented by the general formula Li_aNi_bCo_(1-b-c)Al_cO_dThe compound oxide is represented by a is more than 0.9 and less than or equal to 1.2, b is more than or equal to 0.91 and less than or equal to 0.92, c is more than or equal to 0.04 and less than or equal to 0.06, and d is more than or equal to 1.9 and less than or equal to 2.1.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3,

in the positive electrode mixture layer, the lithium carbonate is present on the surface of the particles of the positive electrode active material and in the gaps between the positive electrode active materials.

5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4,

the lithium carbonate has a volume-based median particle diameter of 2 μm or more and less than the volume-based median particle diameter of the positive electrode active material.

6. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5,

the content of the binder contained in the positive electrode mixture layer is 0.3 to 0.9 mass% of the total mass of the positive electrode mixture layer.

Technical Field

The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly, to a nonaqueous electrolyte secondary battery including a lithium transition metal composite oxide containing Ni, Co, and Al as a positive electrode active material.

Background

In recent years, as a positive electrode active material for a nonaqueous electrolyte secondary battery that contributes to an increase in battery capacity, a lithium transition metal composite oxide having a high Ni content, which exhibits a high capacity even at a voltage of 4.2V, has been known. For example, patent document 1 discloses a nonaqueous electrolyte secondary battery including a positive electrode containing a lithium transition metal composite oxide and a tungsten compound, the content of Ni of which is more than 90 mol% relative to the total molar amount of metal elements other than Li. Patent document 1 describes a lithium transition metal composite oxide represented by the general formula LiNi_0.91Co_0.06Al_0.03O₂The compound oxide shown.

Further, patent document 2 discloses a lithium secondary battery comprising a lithium secondary battery represented by the general formula Li_xNi_yM_(1-y)O₂(0 < x.ltoreq.1.2, 0.88. ltoreq. y.ltoreq.0.99, M is at least 1 element selected from the group consisting of Al, Co, Fe, Cu, Mg, Ti, Zr, Ce and W), and lithium carbonate.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2015/141179

Patent document 2: international publication No. 2017/145849

Disclosure of Invention

Problems to be solved by the invention

However, lithium transition metal complex oxides with a large Ni content have problems such as unstable crystal structure and easy occurrence of cation shuffling in which Ni ions move to Li ion sites. As one of means for solving these problems, it is generally conceivable to stabilize the crystal structure by increasing the amount of Al added. However, when the amount of Al added is increased, the capacity may be decreased.

The purpose of the present invention is to maintain the crystal structure of a lithium transition metal composite oxide containing Ni, Co and Al as a positive electrode active material in a nonaqueous electrolyte secondary battery and further improve the battery capacity.

Means for solving the problems

A nonaqueous electrolyte secondary battery according to an aspect of the present invention includes: a positive electrode having a positive electrode core and a positive electrode mixture layer provided on the surface of the positive electrode core, wherein the positive electrode mixture layer contains a positive electrode material mixture containing a positive electrode material represented by the general formula Li_aNi_bCo_(1-b-c)Al_cO_dA positive electrode active material of a lithium transition metal composite oxide represented by (0.9 < a.ltoreq.1.2, 0.88. ltoreq.b.ltoreq.0.96, 0.04. ltoreq.c.ltoreq.0.12, 1.9. ltoreq. d.ltoreq.2.1), and lithium carbonate in an amount of 0.1 to 1.0 mass% relative to the mass of the positive electrode active material, wherein the lithium transition metal composite oxide is a secondary particle in which primary particles are aggregated, and tungsten is present on the surface of the primary particle in an amount of 0.05 to 0.20 mol% relative to the total molar amount of metal elements other than Li in the positive electrode active material.

Effects of the invention

According to one aspect of the present invention, a high-capacity nonaqueous electrolyte secondary battery can be provided.

Drawings

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery as an example of the embodiment.

Detailed Description

A lithium transition metal composite oxide containing Ni, Co, and Al and having an Ni content of 88 mol% or more based on the total molar amount of metal elements other than Li has attracted attention as a positive electrode active material having a high capacity, but has a problem that the crystal structure is unstable and cation-mixed discharge is likely to occur. It is known that, when tungsten (W) is present on the particle surface of the lithium transition metal composite oxide, the Li source remaining in the vicinity of the surface reacts with W to form a lithium compound, thereby improving battery performance such as cycle characteristics. On the other hand, if the amount of W added becomes too large, Li ions are extracted from the inside of the particles as well, which causes a decrease in capacity, and therefore it is not easy to achieve both the effect of W addition and high capacity.

The present inventors have found that a crystal structure of a lithium transition metal composite oxide is stabilized and a battery capacity is improved by adding a predetermined amount of lithium carbonate to a positive electrode mixture layer with respect to a positive electrode active material containing the lithium transition metal composite oxide containing Ni, Co, and Al at a specific molar ratio and W present at a predetermined amount on the particle surface of the composite oxide. In addition to stabilization of the crystal structure by the addition of Al, the battery capacity is improved remarkably in a certain composition range by the interaction between W present on the particle surface of the composite oxide and lithium carbonate contained in the positive electrode mixture layer.

Hereinafter, an example of an embodiment of the nonaqueous electrolyte secondary battery according to the present invention will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode assembly 14 is accommodated in a bottomed cylindrical outer can 16 is exemplified, but the outer can is not limited to a cylindrical outer can, and may be, for example, a rectangular outer can, or an outer can composed of a laminate sheet including a metal layer and a resin layer. The electrode assembly may be a wound electrode assembly in which the electrode assembly is formed in a flat shape, or a laminated electrode assembly in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators interposed therebetween.

Fig. 1 is a sectional view of a nonaqueous electrolyte secondary battery 10 as an example of the embodiment. As illustrated in fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), and an outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. The outer can 16 is a bottomed cylindrical metal container having one side opened in the axial direction, and the opening of the outer can 16 is closed by a sealing member 17. For convenience of explanation, the sealing body 17 side of the battery is referred to as "upper" and the bottom side of the outer can 16 is referred to as "lower".

The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. As the nonaqueous solvent, for example, esters, ethers, nitriles, amides, and mixed solvents of 2 or more of these can be used. The nonaqueous solvent may contain a halogen substituent in which at least a part of hydrogen in the solvent is substituted with a halogen atom such as fluorine. The nonaqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like. In the electrolyte salt, for example, LiPF is used₆And the like lithium salts.

The positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14 are each a strip-shaped elongated body, and are wound spirally so as to be stacked alternately in the radial direction of the electrode body 14. In order to prevent precipitation of lithium, negative electrode 12 is formed to have a size one turn larger than that of positive electrode 11. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (short-side direction). The 2 spacers 13 are formed to have a size at least one larger than the positive electrode 11, and are disposed so as to sandwich the positive electrode 11, for example. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

Insulating plates 18 and 19 are disposed above and below the electrode body 14, respectively. In the example shown in fig. 1, the positive electrode lead 20 extends through the through hole of the insulating plate 18 toward the sealing member 17, and the negative electrode lead 21 extends through the outside of the insulating plate 19 toward the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing member 17 by welding or the like, and a cap 27 as a top plate of the sealing member 17 electrically connected to the internal terminal plate 23 serves as a positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

A gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure the sealing property inside the battery. The outer can 16 is formed with a groove 22 that supports the sealing member 17 and has a part of the side surface portion bulging inward. The groove 22 is preferably formed annularly along the circumferential direction of the outer can 16, and supports the sealing member 17 on the upper surface thereof. The sealing member 17 is fixed to the upper portion of the outer can 16 by the groove 22 and the opening end portion of the outer can 16 crimped to the sealing member 17.

Sealing body 17 has a structure in which internal terminal plate 23, lower valve body 24, insulating member 25, upper valve body 26, and cap 27 are stacked in this order from the electrode body 14 side. The members constituting the sealing body 17 have, for example, a disk shape or a ring shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their central portions, and an insulating member 25 is interposed between their peripheral portions. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms so as to push up the upper valve body 26 toward the cap 27 side, and breaks, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 is broken, and the gas is discharged from the opening of the cap 27.

Hereinafter, the positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14, particularly the positive electrode 11, will be described in detail.

[ Positive electrode ]

The positive electrode 11 has a positive electrode core and a positive electrode mixture layer provided on the surface of the positive electrode core. As the positive electrode core, a foil of a metal such as aluminum that is stable in the potential range of the positive electrode 11, a film in which the metal is disposed on the surface layer, or the like can be used. The positive electrode mixture layer preferably contains a positive electrode active material, a binder, and a conductive agent, and is provided on both surfaces of the positive electrode core except for the portion connected to the positive electrode lead 20. The positive electrode 11 can be fabricated by: for example, a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, and the like is applied to the surface of a positive electrode substrate, and after the coating film is dried, the positive electrode mixture slurry is compressed to form positive electrode mixture layers on both surfaces of the positive electrode substrate.

The positive electrode mixture layer contains a positive electrode mixture layer containing Li represented by the general formula_aNi_bCo_(1-b-c)Al_cO_dA positive electrode active material of a lithium transition metal composite oxide represented by (0.9 & lta & lt 1.2, 0.88 & ltb & lt 0.96, 0.04 & ltc & lt 0.12, 1.9 & ltd & lt 2.1), and lithium carbonate in an amount of 0.1 to 1.0 mass% based on the mass of the positive electrode active material. The lithium transition metal composite oxide is a secondary particle in which primary particles are aggregated, and a phase exists on the surface of the primary particleTungsten (W) in an amount of 0.05 to 0.20 mol% based on the total molar amount of metal elements other than Li in the positive electrode active material. The battery capacity is improved remarkably by adding 0.1 to 1.0 mass% of lithium carbonate to the positive electrode active material having 0.05 to 0.20 mol% of W adhered to the particle surface of the composite oxide.

The lithium transition metal composite oxide is more preferably represented by the general formula Li_aNi_bCo_(1-b-c)Al_cO_d(0.9. ltoreq. a.ltoreq.1.2, 0.88. ltoreq. b.ltoreq.0.92, 0.04. ltoreq. c.ltoreq.0.12, 1.9. ltoreq. d.ltoreq.2.1), and particularly preferably a composite oxide represented by the general formula Li_aNi_bCo_(1-b-c)Al_cO_d(a is more than 0.9 and less than or equal to 1.2, b is more than or equal to 0.91 and less than or equal to 0.92, c is more than or equal to 0.04 and less than or equal to 0.06, and d is more than or equal to 1.9 and less than or equal to 2.1).

That is, the content of Ni in the lithium transition metal composite oxide is 88 to 96 mol%, preferably 88 to 92 mol%, and more preferably 91 to 92 mol% with respect to the total molar amount of the metal elements other than Li. The content of Al in the lithium transition metal composite oxide is 4 to 12 mol%, preferably 4 to 6 mol%, based on the total molar amount of the metal elements other than Li. When the Ni content is less than 88 mol%, the crystal structure is inherently stable, and the effect of the present invention is hardly exhibited. On the other hand, if the Ni content exceeds 96 mol%, that is, the a1 content is less than 4 mol%, a stable crystal structure cannot be maintained, and the capacity-improving effect cannot be obtained.

The lithium transition metal composite oxide may contain metal elements other than Li, Ni, Co, and Al, for example, Mn, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Mo, Ba, and the like, within a range that does not impair the object of the present invention.

The positive electrode active material contains a lithium-transition metal composite oxide as a main component, and contains W attached to the surface of primary particles of the composite oxide. Since the lithium transition metal composite oxide is a secondary particle in which primary particles are aggregated, W also adheres to the surface of the secondary particle. W may be present more at the surface than inside the secondary particles. The positive electrode active material has, for example, a structure in which a compound containing W is dispersed at least on the surface of the secondary particles of the lithium transition metal composite oxide.

Examples of the compound containing W include tungsten oxide, lithium tungstate, sodium tungstate, magnesium tungstate, potassium tungstate, silver tungstate, tungsten boride, tungsten carbide, tungsten silicide, tungsten sulfide, tungsten chloride, and the like. Among them, tungsten oxide (WO) is preferable₃). In the compounds containing W, 2 or more compounds may be used in combination.

The content of W in the positive electrode active material is 0.05 to 0.20 mol%, preferably 0.06 to 0.19 mol%, and more preferably 0.07 to 0.18 mol% in terms of W relative to the total molar amount of metal elements other than Li. When the W content is less than 0.05 mol% or exceeds 0.20 mol%, the effect of improving the capacity cannot be obtained. The content of each element in the positive electrode active material was measured by ICP emission spectrometry.

The positive electrode active material can be produced by adding W or a powder of a compound containing W to a powder of a lithium transition metal composite oxide, mixing the mixture, and then performing heat treatment at a temperature of 100 to 300 ℃. By this heat treatment, a positive electrode active material in which W or a compound containing W is attached to the surface of the primary particles of the lithium transition metal composite oxide is obtained. The powders may be mixed in the form of a dispersion or a solution and then subjected to heat treatment.

The volume-based median particle diameter (D50) of the positive electrode active material is, for example, 5 to 30 μm, preferably 10 to 20 μm. The volume-based D50 is a particle size in which the frequency accumulation in the volume-based particle size distribution is 50% from the side where the particle size is small, and is also referred to as a median particle size. D50 can be measured using a laser diffraction particle size distribution measuring apparatus (for example, MICROTRACHRA, manufactured by NIGHT CORPORATION) using water as a dispersion medium.

Lithium carbonate (Li)₂CO₃) As described above, the positive electrode mixture layer is added in an amount of 0.1 to 1.0 mass% with respect to the mass of the positive electrode active material. Lithium carbonate is decomposed to generate carbon dioxide gas when the battery is overcharged, and the current interruption means is activated to prevent overchargeAnd contributes to high capacity through interaction with W. When the lithium carbonate content is less than 0.1% by mass or exceeds 1.0% by mass, the capacity-improving effect cannot be obtained. When the lithium carbonate content exceeds 1.0 mass%, gas is likely to be generated during high-temperature storage. The content of lithium carbonate is preferably 0.1 to 0.8 mass%, more preferably 0.2 to 0.6 mass%, based on the mass of the positive electrode active material.

In the positive electrode mixture layer, lithium carbonate is present on the particle surface of the positive electrode active material (surface of the secondary particles) and in the gaps between the positive electrode active materials, for example. The lithium carbonate is preferably present in the vicinity of the positive electrode active material, and may be attached to the particle surface of the positive electrode active material without via a binder or may be attached to the particle surface via a binder. Preferably, 50 mass% or more of the lithium carbonate contained in the positive electrode mixture layer adheres to the particle surface of the positive electrode active material.

The volume-based D50 of lithium carbonate is not particularly limited, but is preferably 2 μm or more and less than the volume-based D50 of the positive electrode active material. When the particle diameter of lithium carbonate is too small, the number of particles increases, the BET specific surface area increases, and a large amount of binder adheres to lithium carbonate. As a result, the adhesion between the constituent materials of the positive electrode mixture layer and the adhesion between the positive electrode mixture layer and the positive electrode core may not be sufficiently obtained. The volume-based D50 of lithium carbonate is preferably 2 to 12 μm, more preferably 2 to 6 μm.

For example, lithium carbonate is added to the positive electrode mixture slurry together with the positive electrode active material, the binder, and the conductive agent, and the positive electrode mixture slurry is applied to the positive electrode core, thereby being added to the positive electrode mixture layer. Note that, after adding and mixing a lithium carbonate powder to a positive electrode active material powder, a positive electrode mixture slurry may be prepared using the mixed powder.

Examples of the binder included in the positive electrode mixture layer include fluorine resins such as Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), Polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. These resins can be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or salts thereof, polyethylene oxide (PEO), and the like. The content of the binder is not particularly limited, and is preferably 0.3 to 1.5% by mass, and more preferably 0.3 to 0.9% by mass, based on the total mass of the positive electrode material mixture layer.

Examples of the conductive agent contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. The content of the conductive agent is not particularly limited, and is preferably 0.1 to 1.5% by mass, and more preferably 0.3 to 1.2% by mass, based on the total mass of the positive electrode mixture layer.

[ negative electrode ]

The negative electrode 12 has a negative electrode substrate and a negative electrode mixture layer provided on the surface of the negative electrode substrate. For the negative electrode substrate, a foil of a metal such as copper that is stable in the potential range of the negative electrode 12, a film in which the metal is disposed on the surface layer, or the like can be used. The negative electrode mixture layer preferably contains a negative electrode active material and a binder, and is provided on both surfaces of the negative electrode substrate except for a portion to which the negative electrode lead 21 is connected, for example. The anode 12 may be fabricated by: for example, a negative electrode mixture slurry containing a negative electrode active material, a binder, and the like is applied to the surface of a negative electrode substrate, and after the coating is dried, the coating is compressed to form negative electrode mixture layers on both surfaces of the negative electrode substrate.

The negative electrode mixture layer contains, as a negative electrode active material, for example, a carbon-based active material that reversibly stores and releases lithium ions. Suitable carbon-based active materials include natural graphite such as flake graphite, block graphite, and amorphous graphite, and artificial graphite such as block artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). In the negative electrode active material, an Si-based active material composed of at least one of Si and an Si-containing compound may be used, or a carbon-based active material and an Si-based active material may be used in combination.

As the binder contained in the negative electrode mixture layer, as in the case of the positive electrode 11, a fluororesin, PAN, polyimide, an acrylic resin, a polyolefin, or the like may be used, and styrene-butadiene rubber (SBR) is preferably used. Preferably, the negative electrode mixture layer further contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among them, SBR, CMC or a salt thereof, and PAA or a salt thereof are preferably used in combination.

[ spacer ]

As the spacer 13, a porous sheet having ion permeability and insulation properties can be used. Specific examples of the porous sheet include a microporous film, a woven fabric, and a nonwoven fabric. As a material of the spacer 13, polyolefin such as polyethylene and polypropylene, cellulose, and the like are suitable. The spacer 13 may have a single-layer structure or a stacked structure. A heat-resistant layer or the like may be formed on the surface of the spacer.

Examples

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.

< example 1 >

[ Synthesis of Positive electrode active Material ]

To a compound represented by the general formula LiNi_0.91Co_0.03Al_0.06O₂Tungsten oxide is added to the lithium transition metal composite oxide having the layered structure shown (WO)₃) Mixing, and heat treating at 200 deg.C under oxygen atmosphere to obtain particles of lithium transition metal composite oxide with WO attached to the surface₃The positive electrode active material of (1). WO₃The amount of addition of (b) was 0.05 mol% in terms of W relative to the total molar amount of metal elements other than Li in the positive electrode active material.

[ production of Positive electrode ]

A positive electrode mixture slurry was prepared by mixing a positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) at a mass ratio of 100: 1: 0.9, further mixing 0.3 mass% of lithium carbonate with respect to the positive electrode active material, and using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. Next, the positive electrode mixture slurry was applied to both surfaces of a positive electrode core body made of aluminum foil, the coating film was dried and compressed, and then cut into a predetermined electrode size, thereby producing a positive electrode in which positive electrode mixture layers were formed on both surfaces of the positive electrode core body. An exposed portion of the surface of the positive electrode core is provided, and a positive electrode lead is attached to the exposed portion.

[ production of negative electrode ]

The negative electrode active material is prepared by mixing natural graphite with SiO₂Dispersed in phaseWith fine particles of Si in SiO_xThe Si-containing compound is mixed. A negative electrode mixture slurry was prepared by mixing a negative electrode active material, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 95: 3: 2, and using water as a dispersion medium. Next, a negative electrode mixture slurry was applied to both surfaces of a negative electrode substrate made of copper foil, the coating film was dried and compressed, and then cut into a predetermined electrode size, thereby producing a negative electrode in which a negative electrode mixture layer was formed on both surfaces of the negative electrode substrate. An exposed portion where the surface of the negative electrode substrate is exposed is provided, and a negative electrode lead is attached to the exposed portion.

[ preparation of nonaqueous electrolyte solution ]

In a mixed solvent in which Ethylene Carbonate (EC) and Methyl Ethyl Carbonate (MEC) were mixed, LiPF was dissolved at a concentration of 1mol/L₆A nonaqueous electrolytic solution was prepared.

[ production of Battery ]

The positive electrode and the negative electrode were wound in a spiral shape with a polyethylene separator interposed therebetween, and the wound electrode assembly was manufactured by molding the wound electrode assembly in a flat shape. This electrode assembly and the nonaqueous electrolyte solution were contained in a bottomed cylindrical outer can, and a sealing member was attached to an opening of the outer can to prepare a cylindrical nonaqueous electrolyte secondary battery.

< example 2 >

Except that WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were fabricated in the same manner as in example 1, except that the amount of (d) was changed to 0.2 mol%.

< example 3 >

Except using a compound represented by the general formula LiNi_0.91Co_0.05Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the composite oxide shown was a lithium transition metal composite oxide.

< example 4 >

Except that WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3, except that the amount of (d) was changed to 0.2 mol%.

< example 5 >

A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the amount of lithium carbonate added was changed to 0.1 mass% in the preparation of the positive electrode mixture slurry.

< comparative example 1 >

Except that no WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3, except that lithium carbonate was not added to the preparation of the positive electrode mixture slurry.

< comparative example 2 >

Except using a compound represented by the general formula LiNi_0.91Co_0.055Al_0.035O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3, except that the composite oxide shown was a lithium transition metal composite oxide.

< comparative example 3 >

Except that WO was not added in the synthesis of the positive electrode active material₃Except for this, a positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3.

< comparative example 4 >

Except that WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3, except that the amount of (d) was changed to 0.3 mol%.

< comparative example 5 >

A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 3, except that lithium carbonate was not added to prepare the positive electrode mixture slurry.

[ evaluation of Battery Capacity ]

The batteries of examples and comparative examples were charged at 25 ℃ at a constant current of 0.3C until the battery voltage became 4.2V, and then charged at a constant voltage of 4.2V until the current became 0.02C. After charging, the cell was discharged at a constant current of 0.3C until the cell voltage became 2.5V. The discharge capacity at this time was obtained, and the capacity increase/decrease rate (relative value) of each battery was calculated based on the discharge capacity of the battery of comparative example 1. The evaluation results are shown in table 1 together with the structure of the positive electrode mixture layer. The capacity increase/decrease rates of the batteries of examples 6 and 7, which will be described later, were calculated based on the battery of comparative example 6, the capacity increase/decrease rates of the batteries of examples 8 and 9 were calculated based on the battery of comparative example 7, and the capacity increase/decrease rates of the batteries of comparative examples 8 and 9 were calculated based on the battery of comparative example 10.

[ Table 1]

As shown in table 1, it was confirmed that the batteries of the examples all had a high specific capacity as compared with the batteries of the comparative examples. In the case where no W was present on the particle surface of the lithium transition metal composite oxide (comparative example 3) and in the case where no lithium carbonate was present in the positive electrode mixture layer (comparative example 5), the effect of improving the capacity was not obtained. In addition, even when the Al content was 3.5 mol% (comparative example 2) and when the amount of W added was 0.3 mol%, the capacity improvement effect was not obtained. I.e. only in relation to the general formula Li_aNi_bC_o(1-b-c)Al_cO_d(0.9 < a.ltoreq.1.2, 0.88. ltoreq.b.ltoreq.0.96, 0.04. ltoreq.c.ltoreq.0.12, 1.9. ltoreq. d.ltoreq.2.1) and 0.05 to 0.20 mol% of W is adhered to the surface of particles of the lithium transition metal composite oxide, and 0.1 to 1.0 mass% of lithium carbonate is added to the particles, whereby the battery capacity is improved.

< example 6 >

Except using a compound represented by the general formula LiNi_0.88Co_0.08Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the composite oxide shown was a lithium transition metal composite oxide.

< example 7 >

Except using a compound represented by the general formula LiNi_0.88Co_0.08Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 2, except that the composite oxide shown was a lithium transition metal composite oxide.

< comparative example 6 >

Except that no WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 6, except that lithium carbonate was not added to the preparation of the positive electrode mixture slurry.

[ Table 2]

As shown in table 2, it was confirmed that the batteries of examples 6 and 7 had a high specific capacity as compared with the battery of comparative example 6.

< example 8 >

Except using a compound represented by the general formula LiNi_0.92Co_0.04Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the composite oxide shown was a lithium transition metal composite oxide.

< example 9 >

Except using compounds of the formula LiNi_0.92Co_0.04Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 2, except that the composite oxide shown was a lithium transition metal composite oxide.

< comparative example 7 >

Except that no WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 8, except that lithium carbonate was not added to the preparation of the positive electrode mixture slurry.

[ Table 3]

As shown in Table 3, it was confirmed that the batteries of examples 8 and 9 had a high specific capacity as compared with the battery of comparative example 7. From the results shown in tables 1 to 3, it was confirmed that the larger the Ni content, the larger the capacity increase rate. This is considered to be because the greater the Ni content, the more unstable the crystal structure of the lithium transition metal composite oxide is, and the more significant the effect of the present invention is exhibited.

< comparative example 8 >

Except using a compound represented by the general formula LiNi_0.82Co_0.14Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 1, except that the composite oxide shown was a lithium transition metal composite oxide.

< comparative example 9 >

Except using a compound represented by the general formula LiNi_0.82Co_0.14Al_0.04O₂A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in example 2, except that the composite oxide shown was a lithium transition metal composite oxide.

< comparative example 10 >

Except that no WO is added in the synthesis of the positive electrode active material₃A positive electrode and a nonaqueous electrolyte secondary battery were produced in the same manner as in comparative example 8, except that lithium carbonate was not added to the preparation of the positive electrode mixture slurry.

[ Table 4]

As shown in table 4, it was confirmed that the capacity-improving effect could not be obtained when the Ni content was 82 mol%. This is considered to be because, in this case, the crystal structure of the lithium transition metal composite oxide is inherently stable, and it is difficult to exhibit the effects of the present invention.

Description of the reference numerals

10 nonaqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 spacer, 14 electrode body, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 groove part, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket