JP2003203634A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery in which capacity degradation due to charging and discharging cycle is suppressed and capacity degradation due to hot temperature storage is reduced and which, thereby, is excellent in reliability. <P>SOLUTION: This is a lithium ion secondary battery which is constructed of a positive electrode, a negative electrode, and a non-aqueous electrolyte, and of which the positive electrode is made of a positive electrode active material, a conductive assistant, and a binder, and the above positive electrode active material is made of a lithium-contained complex oxide that is expressed by the chemical formula Li<SB>a</SB>(Co<SB>1-x-y</SB>Mg<SB>x</SB>M<SB>y</SB>)<SB>b</SB>O<SB>c</SB>, (wherein, M is at least one kind selected from Ni and Al, and 0≤a≤1.05, 0.03≤x≤0.15, 0≤y≤0.25, 0.85≤b≤1.1, 1.8≤c≤2.1). And the quantity of the conductive assistant contained in the positive electrode is 3.0 parts weight or less for 100 parts weight of the positive electrode active material. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, portable electronic devices for consumer use,
Cordless is rapidly progressing. At present, there is an increasing demand for a small, lightweight battery having a high energy density, which serves as a power source for driving these electronic devices. In particular, since the lithium ion secondary battery has a high voltage and a high energy density, it is expected to grow greatly in the future as a power source for notebook computers, mobile phones, AV equipment and the like. A nickel-cadmium storage battery or a nickel-hydrogen storage battery, which uses an alkaline aqueous solution as an electrolyte, which has been the mainstream until now, is being replaced by a lithium ion secondary battery.

LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiM are used as positive electrode active materials for lithium ion secondary batteries.
Lithium-containing composite oxides such as n ₂ O ₄ have been used. These positive electrode active materials repeat expansion and contraction by charging and discharging. At this time, the crystal structure is broken or the particles are broken, so that the capacity is lowered and the internal resistance is increased with the charge / discharge cycle. For such a problem, it has been reported that the crystal structure is stabilized by substituting a part of cobalt or nickel with another element. For example, there is a report that a part of cobalt in the positive electrode active material is replaced with an element such as magnesium to improve cycle characteristics and safety (see Patent Documents 1 to 3).

[0004]

[Patent Document 1] Japanese Patent No. 3162437

[Patent Document 2] JP-A-5-242891

[Patent Document 3] JP-A-6-168722

[0005]

However, in the prior art as described above, deterioration of cycle characteristics can be suppressed, but, for example, when a battery in a charged state is stored at 85 ° C. for 3 days, It has been confirmed that the amount of gas generated in the battery is relatively large. In particular, in the case of a rectangular thin battery or a battery having an outer packaging material made of a laminated sheet, the strength of the case and the outer packaging material is weak, which may cause an increase in battery thickness and a decrease in capacity due to gas generation. The cause of the increase in gas generation is not certain at present, but the positive electrode active material in which a part of cobalt is replaced with magnesium has high electron conductivity and the surface of the active material is active. It is thought that the property is enhanced and the decomposition of the non-aqueous electrolyte is promoted.

[0006]

The present invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode comprises a positive electrode active material, a conductive agent, and a binder, and the positive electrode active material has the chemical formula Li _{a (Co 1-xy Mg x M} y) b O c (M is at least one selected from Ni and Al, 0 ≦ a ≦ 1.05,
0.03 ≦ x ≦ 0.15, 0 ≦ y ≦ 0.25, 0.85
≦ b ≦ 1.1, 1.8 ≦ c ≦ 2.1), and the amount of the conductive agent contained in the positive electrode is 3 per 100 parts by weight of the positive electrode active material. .0
The present invention relates to a lithium-ion secondary battery that is less than or equal to parts by weight.

The amount of the binder contained in the positive electrode is 1.0 part by weight or more per 100 parts by weight of the positive electrode active material.
It is preferably 0 parts by weight or less. The binder is made of polyvinylidene fluoride, and the polyvinylidene fluoride has a weight average molecular weight of 150,000 or more and 350,000.
The following is preferable. The non-aqueous electrolyte consists of a non-aqueous solvent and a lithium salt soluble in the non-aqueous solvent,
The non-aqueous solvent is γ-butyrolactone and / or γ
It is preferable to include a butyrolactone derivative. It is preferable that the negative electrode includes core particles and a material made of amorphous carbon that covers at least a part of the surface of the core particles, and the core particles are made of graphite. According to the present invention, it is possible to provide a lithium-ion secondary battery that suppresses the capacity decrease due to charge / discharge cycles and also suppresses the capacity decrease during high temperature storage.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the chemical formula Li _a (Co
_1-xy Mg _{x My y} ) _b O _c (M is at least one selected from Ni and Al, 0 ≦ a ≦ 1.05, 0.03 ≦ x
≦ 0.15, 0 ≦ y ≦ 0.25, 0.85 ≦ b ≦ 1.
1. A positive electrode active material composed of a lithium-containing composite oxide represented by the formula 1, 1.8 ≦ c ≦ 2.1) is used. In the crystal of the composite oxide, magnesium is partially substituted for cobalt. Therefore, the crystal structure is stable, and it is difficult for the crystal structure to be broken or the particles to be cracked due to charge / discharge cycles. Therefore, the capacity decrease of the battery is suppressed and the cycle life is improved.

When the content x of magnesium is less than 0.03, the stabilization of the crystal structure of the composite oxide becomes insufficient.
Therefore, when charging and discharging are repeated, the internal resistance increases and the cycle characteristics deteriorate significantly. On the other hand, the content rate x is 0.15
If it exceeds, the charge / discharge capacity of the positive electrode active material decreases. From this, the Mg content x is 0.03 ≦ x ≦ 0.15.
Need to meet.

The complex oxide may contain, as the element M, at least one selected from Ni and Al. The composite oxide containing Ni can be obtained at low cost and has improved heat resistance. In addition, the composite oxide containing Al has improved heat resistance and further improved cycle characteristics. However, if the content y of the element M is larger than 0.25, the following demerits occur. That is, N
When i is excessive, the cycle life characteristics are deteriorated and the gas generation amount at the time of high temperature storage is increased. Further, when Al is excessive, the charge / discharge capacity of the active material decreases, or the tap density of the active material particles decreases and the electrode plate capacity decreases. From this, the content y of M needs to satisfy 0 ≦ y ≦ 0.25.

The positive electrode active material can be obtained, for example, by firing a lithium salt, a magnesium salt, and a cobalt salt at a high temperature in an oxidizing atmosphere. The following materials can be used as a raw material for synthesizing the positive electrode active material. As the lithium salt, lithium carbonate,
Lithium hydroxide, lithium nitrate, lithium sulfate, lithium oxide or the like can be used. As the magnesium salt, magnesium oxide, basic magnesium carbonate, magnesium chloride, magnesium fluoride, magnesium nitrate, magnesium sulfate, magnesium acetate, magnesium oxalate, magnesium sulfide, or magnesium hydroxide can be used. As the cobalt salt, cobalt oxide,
Cobalt hydroxide or the like can be used.

By mixing the positive electrode active material with a conductive agent, a binder, a dispersion medium, etc., a paste-like positive electrode mixture can be obtained. As the conductive agent, an electron conductive material that does not easily undergo a chemical change in the battery can be used without particular limitation, but a carbon material is particularly preferable. For example, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, natural graphite powder such as scaly graphite, artificial graphite powder, and conductive carbon fiber can be used. These may be used alone or in combination of two or more.

The positive electrode used in the present invention is a positive electrode active material 100.
It contains 3 parts by weight or less of the conductive agent per part by weight. By setting the amount of the conductive agent to 3 parts by weight or less, the decomposition of the non-aqueous electrolyte on the surface of the conductive agent under high temperature storage can be reduced, and the decrease in capacity after high temperature storage is suppressed. Further, the conductive agent has a relatively large specific surface area, but by setting the amount of the conductive agent to 3 parts by weight or less, the amount of the binder coating the conductive agent can be reduced. Therefore, even if the amount of the binder is 4 parts by weight or less per 100 parts by weight of the positive electrode active material, sufficient electrode plate strength can be obtained. By thus reducing the amount of the insulating binder, the load characteristics of the battery are improved, and the synergistic effect of further improving the cycle characteristics can be obtained. However, if the amount of the binder is less than 1 part by weight per 100 parts by weight of the positive electrode active material, it becomes difficult to obtain sufficient electrode plate strength.

As the binder, either a thermoplastic resin or a thermosetting resin may be used, or these may be used in combination. Among these, polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PT
FE) is preferable, and PVdF is particularly preferable. Above all, when PVdF having a molecular weight of 150,000 or more is used,
The binding strength is improved and sufficient electrode plate strength can be obtained even with an extremely small amount. In this case, the amount of the insulating binder can be further reduced, so that the load characteristics of the battery are further improved and the cycle characteristics are further improved, which is a synergistic effect. On the other hand, when the molecular weight of PVdF is 350,000 or more, conversely, the load characteristics tend to deteriorate and the cycle characteristics tend to deteriorate. The dispersion medium is an aqueous dispersion medium or N-methyl-2-
An organic dispersion medium such as pyrrolidone can be used.

For the lithium ion secondary battery, it is preferable to use a non-aqueous electrolyte composed of a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate,
Cyclic carbonates such as butylene carbonate and vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, aliphatic carboxylic acids such as methyl formate, methyl acetate, methyl propionate and ethyl propionate Esters, γ-butyrolactone, γ-valerolactone, γ-butyrolactone derivatives such as α-methyl-γ-butyrolactone, chain ethers such as 1,2-dimethoxyethane, cyclic ethers such as tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimeto Xymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propanesartone, anisole, An aprotic organic solvent such as dimethyl sulfoxide or N-methyl-2-pyrrolidone can be used. These may be used alone, but it is preferable to use two or more kinds in combination.

The non-aqueous solvent preferably contains γ-butyrolactone and / or γ-butyrolactone derivative. When the above-mentioned positive electrode active material is used, the amount of gas generated during high-temperature storage tends to increase in a non-aqueous electrolyte containing a cyclic carbonate and a chain carbonate that are commonly used. Therefore, the positive electrode active material described above,
Compatibility with a non-aqueous electrolyte containing a cyclic carbonate and a chain carbonate cannot be said to be good. On the other hand, in the case of a non-aqueous electrolyte containing γ-butyrolactone or a γ-butyrolactone derivative, the amount of gas generated during high-temperature storage can be suppressed to a small amount even when the above-mentioned positive electrode active material is used. It is considered that this is because γ-butyrolactone or a γ-butyrolactone derivative forms a film on the surface of the positive electrode and suppresses the reaction of generating gas.

The above-mentioned effect is obtained by γ-butyrolactone and / or
Alternatively, it can be obtained when the content of the γ-butyrolactone derivative in the non-aqueous solvent is 0.5% by weight or more. When the content is less than 0.5% by weight, the film formation on the surface of the positive electrode under high temperature storage becomes insufficient and the above effect cannot be obtained. However, if the content exceeds 80% by weight,
The ionic conductivity of the non-aqueous electrolyte is lowered and the rate characteristics of the battery are lowered. Particularly preferred solvent in the present invention is γ-
Butyrolactone 0.5-70% by volume, vinylene carbonate 0.5-4% by volume, cyclic carbonate 10-4
It is a mixed solvent with 0% by volume, and may further contain 0 to 85% by volume of chain carbonate.

The lithium salt which can be dissolved in a non-aqueous solvent includes
For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiA
lCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiC
F ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ ,
LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl
₁₀ , lower aliphatic lithium carboxylate, LiCl, LiB
r, LiI, lithium chloroborane and the like can be mentioned. These may be used alone or in combination of two or more. Further, it is preferable to use at least LiPF ₆ . The concentration of the lithium salt in the non-aqueous electrolyte is not particularly limited, but it is preferably 0.2 to 2 mol / liter, and particularly preferably 0.5 to 1.5 mol / liter.

The negative electrode material used in the present invention is a compound capable of inserting and extracting lithium ions, such as a lithium alloy, a carbon material, an inorganic oxide, an inorganic chalcogenide, a nitride, a metal complex and an organic polymer compound. Good. These may be used alone or in combination of two or more. Among these negative electrode materials, a carbon material is particularly preferable. For example, a combination of lithium and a carbon material, lithium and an inorganic oxide, a combination of lithium and a carbon material and an inorganic oxide, and the like can be given. These negative electrode materials are preferable in that they give high capacity, high discharge potential, high safety, high cycle characteristics, and the like.

As the lithium alloy, Li--Al,
Li-Al-Mn, Li-Al-Mg, Li-Al-S
n, Li-Al-In, Li-Al-Cd, Li-Al
-Te, Li-Ga, Li-Cd, Li-In, Li-
Pb, Li-Bi, Li-Mg, etc. are mentioned. In this case, the lithium content is preferably 10% by weight or more.

Examples of the carbon material include coke, pyrolytic carbons, natural graphite, artificial graphite, mesocarbon microbeads, graphitized mesophase microspheres, vapor grown carbon, glassy carbons, polyacrylonitrile, pitch, cellulose or Examples thereof include carbon fibers made of vapor grown carbon, amorphous carbon, and fired bodies of organic substances. These may be used alone or in combination of two or more.
In addition to carbon, carbon materials include O, B, P, N, S, and S.
It may contain a different element or compound such as iC or B ₄ C.
The content of the different element or compound is preferably 0 to 10% by weight.

Examples of the inorganic oxide include titanium oxide, tungsten oxide, molybdenum oxide, niobium oxide, vanadium oxide, iron oxide and the like. Further, as the inorganic chalcogenide, for example,
Examples thereof include iron sulfide, molybdenum sulfide, titanium sulfide and the like.
Examples of the organic polymer compound include polymer compounds such as polythiophene and polyacetylene. Examples of the nitride include cobalt nitride, copper nitride, nickel nitride, iron nitride, manganese nitride and the like.

As the carbon material, a material composed of graphite core particles and amorphous carbon covering at least a part of the surface of the core particles (hereinafter referred to as material X) is particularly preferable. When the material X is used, when magnesium is eluted from the positive electrode, magnesium can be incorporated into the amorphous carbon on the surface, so that magnesium is inserted between the graphite layers,
It is possible to prevent the negative electrode characteristics from deteriorating. Therefore, it is possible to obtain the effect of further improving the capacity reduction after storage at high temperature. The average particle size of the material X is preferably 3 to 20 μm.

By mixing the above negative electrode material with a binder, a dispersion medium, etc., a paste-like negative electrode mixture can be obtained. As the binder and the dispersion medium, the same ones as those used in the production of the positive electrode can be used. The positive electrode can be obtained by applying a positive electrode mixture on a core material made of metal foil, rolling, and drying. The negative electrode can be obtained by applying a negative electrode mixture on a core material made of metal foil or the like, rolling and drying. When the positive electrode and the negative electrode are sheet-shaped, it is preferable to provide the electrode mixture layer on both surfaces of the core material. The electrode mixture layer on one surface may be composed of a plurality of layers. In addition to the electrode mixture layer, a protective layer containing no active material,
It may have an undercoat layer provided on the core material, an intermediate layer provided between the electrode mixture layers, and the like.

The present invention will now be described based on embodiments with reference to the drawings. FIG. 1 shows the structure of the prismatic lithium ion secondary battery produced in the example. Although a prismatic battery was manufactured here, the shape of the battery of the present invention is not limited to this. The present invention can be applied to, for example, a cylindrical battery, a coin battery, a button battery, a sheet battery, a laminated battery, a flat battery, and a large battery used in an electric vehicle or the like.

[0026]

EXAMPLES Example 1 (i) Preparation of Positive Electrode Active Material An aqueous solution containing cobalt sulfate at a concentration of 0.95 mol / liter and magnesium sulfate at a concentration of 0.05 mol / liter was continuously supplied to a reaction tank. The pH of water is 1
A precursor of the active material was synthesized while dripping sodium hydroxide into the reaction tank so as to be 0 to 13. As a result, Co
_A hydroxide consisting of _0.95 Mg _0.05 (OH) ₂ was obtained.

This precursor and lithium carbonate are mixed at a molar ratio of lithium, cobalt and magnesium of 1: 0.9.
The mixture was mixed at 5: 0.05, and the mixture was calcined at 600 ° C. for 10 hours and pulverized. Next, the pulverized fired product was fired again at 900 ° C. for 10 hours, pulverized and classified to obtain a positive electrode active material represented by the chemical formula Li (Co _0.95 Mg _0.05 ) O ₂ .

(Ii) Preparation of Positive Electrode To 100 parts by weight of the obtained positive electrode active material, 1.5 parts by weight of acetylene black was mixed as a conductive agent, and polyvinylidene fluoride (PVdF) having a molecular weight of 300,000 was used as a binder. 2 parts by weight of N-methyl-2-pyrrolidone solution was added as a resin component, and the mixture was stirred and mixed to obtain a paste-like positive electrode mixture. The positive electrode mixture was applied to both surfaces of a core material of aluminum foil having a thickness of 15 μm, dried, rolled, and cut into predetermined dimensions to obtain a positive electrode.

(Iii) Preparation of Negative Electrode 100 parts by weight of scaly graphite having an average particle size of 20 μm was mixed with 1 part by weight of an aqueous solution of carboxymethyl cellulose as a thickener, and styrene-butadiene rubber was used as a binder. Was added and stirred and mixed to obtain a paste-like negative electrode mixture. The negative electrode mixture was applied to both sides of a core material of a copper foil having a thickness of 10 μm, dried, rolled, and cut into a predetermined size to obtain a negative electrode.

(Iv) Assembly of Battery A positive electrode and a negative electrode thus prepared were wound in a flat spiral shape with a separator made of microporous polyethylene having a thickness of 20 μm interposed therebetween to form an electrode plate group 1. The positive electrode lead 2 and the negative electrode lead 3 were welded to the positive electrode and the negative electrode, respectively. An insulating ring made of polyethylene resin was attached to the upper part of the electrode plate group 1 and housed in an aluminum battery case 4 as shown in FIG.
The insulating ring is not shown in FIG. Positive electrode lead 2
The other end was spot-welded to the aluminum sealing plate 5. The other end of the negative electrode lead 3 was spot-welded to the lower portion of the nickel negative electrode terminal 6 in the center of the sealing plate 5. The open end of the battery case 4 and the sealing plate 5 were laser-welded, and a predetermined amount of non-aqueous electrolyte was injected from the injection port. Finally, the inlet was closed with an aluminum sealing plug 7 and welded to the sealing plate 5 with a laser.

As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / liter in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3 was used. The battery thus manufactured was designated as Battery 1A of the present invention.

Example 2 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
In the same manner as in Example 1 except that the amount was 3.0 parts by weight,
A battery 2A of the present invention was produced.

Example 3 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
A battery 3A of the present invention was produced in the same manner as in Example 1 except that the amount was 0.05 part by weight.

Example 4 The amount of acetylene black, which is the conductive agent for the positive electrode, was 0 per 100 parts by weight of the positive electrode active material.
A battery 4A of the present invention was produced in the same manner as in Example 1 except that the weight part was used. That is, the positive electrode of the battery 4A is
Does not contain conductive agent.

Example 5 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
In the same manner as in Example 1 except that the amount was 0.1 part by weight,
Battery 5A of the present invention was produced.

Example 6 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
In the same manner as in Example 1 except that 0.5 part by weight was used,
Battery 6A of the present invention was produced.

Example 7 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
In the same manner as in Example 1 except that the amount was 1.0 part by weight,
Battery 7A of the present invention was produced.

Example 8 In accordance with Example 1, a hydroxide composed of Co _0.97 Mg _0.03 (OH) ₂ was synthesized as a precursor. The molar ratio of this precursor to lithium carbonate was 1: 0.97: lithium, cobalt and magnesium.
The same operation as in Example 1 was carried out except that the mixture was mixed so as to obtain 0.03, and the chemical formula was Li (Co _0.97 Mg _0.03 ) O.
A positive electrode active material represented by ₂ was obtained. Next, a battery 8A of the present invention was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Example 9 According to Example 1, a hydroxide composed of Co _0.85 Mg _0.15 (OH) ₂ was synthesized as a precursor. The molar ratio of lithium, cobalt and magnesium of the precursor and lithium carbonate was 1: 0.85:
The same operation as in Example 1 was carried out except that the mixture was mixed to give 0.15, and the chemical formula Li (Co _0.85 Mg _0.15 ) O was obtained.
A positive electrode active material represented by ₂ was obtained. Next, a battery 9A of the present invention was produced in the same manner as in Example 1 except that this positive electrode active material was used.

<Example 10> According to Example 1, a hydroxide composed of Co _0.90 Mg _0.10 (OH) ₂ was synthesized as a precursor. The molar ratio of this precursor and lithium carbonate was 1: 0.9: lithium, cobalt and magnesium.
The same operation as in Example 1 was carried out except that the mixture was mixed so as to have a ratio of 0.1, and the chemical formula Li (Co _0.90 Mg _0.10 ) O ₂
A positive electrode active material represented by Next, a battery 10A of the present invention was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Example 11 The procedure of Example 1 was repeated, except that the amount of PVdF having a molecular weight of 300,000, which was the binder for the positive electrode, was 4 parts by weight per 100 parts by weight of the positive electrode active material. Battery 11A was produced.

Example 12 The procedure of Example 1 was repeated, except that the amount of PVdF having a molecular weight of 300,000 as a binder for the positive electrode was 1 part by weight per 100 parts by weight of the positive electrode active material. Battery 12A was produced.

Example 13 PVd as a binder for the positive electrode
A battery 13A of the present invention was produced in the same manner as in Example 1 except that the molecular weight of F was 350,000.

Example 14 PVd as a binder for the positive electrode
A battery 14A of the present invention was produced in the same manner as in Example 1 except that the molecular weight of F was set to 150,000.

Example 15 Ethylene carbonate, ethylmethyl carbonate, γ-butyrolactone and vinylene carbonate were added in a volume ratio of 20: 77.5: 0.5:
LiPF ₆ was dissolved in the mixed solvent mixed in 2 at a concentration of 1.0 mol / liter. A battery 15A of the present invention was produced in the same manner as in Example 1 except that the thus obtained non-aqueous electrolyte was used.

Example 16 L was added to a mixed solvent prepared by mixing ethylene carbonate, ethylmethyl carbonate, γ-butyrolactone and vinylene carbonate at a volume ratio of 20: 48: 30: 2 at a concentration of 1.0 mol / liter.
The iPF ₆ was dissolved. The battery 1 of the present invention was prepared in the same manner as in Example 1 except that the thus obtained non-aqueous electrolyte was used.
6A was produced.

Example 17 In a mixed solvent prepared by mixing ethylene carbonate, ethylmethyl carbonate, γ-butyrolactone and vinylene carbonate at a volume ratio of 20: 8: 70: 2, Li was added at a concentration of 1.0 mol / liter.
The PF ₆ was dissolved. The battery 17 of the present invention was prepared in the same manner as in Example 1 except that the non-aqueous electrolyte thus obtained was used.
A was produced.

Example 18 Flake graphite having an average particle size of 20 μm was mixed with petroleum pitch and fired at 800 ° C. to coat at least a part of the surface of the flake graphite with amorphous carbon. Carbon material thus obtained (average particle size 22 μm)
A battery 18A of the present invention was produced in the same manner as in Example 1 except that was used instead of flake graphite.

Example 19 Cobalt sulfate was contained in a concentration of 0.90 mol / liter, magnesium sulfate was contained in a concentration of 0.05 mol / liter, and 0.05 mol / liter was contained.
An aqueous solution containing nickel sulfate at a concentration of 1 liter was prepared. Using this aqueous solution, a hydroxide composed of Co _0.90 Mg _0.05 Ni _0.05 (OH) ₂ as a precursor was synthesized according to Example 1. This precursor and lithium carbonate were mixed in the same manner as in Example 1 except that the molar ratio of lithium, cobalt, magnesium, and nickel was 1: 0.90: 0.05: 0.05. The operation was performed to obtain a positive electrode active material represented by the chemical formula Li (Co _0.90 Mg _0.05 Ni _0.05 ) O ₂ . Next, a battery 19A of the present invention was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Example 20 Precursor according to Example 1
As Co_0.85Mg_0.05Ni_0.10(OH)₂Consisting of water
The oxide was synthesized. This precursor and lithium carbonate are
Molar ratio of thium to cobalt to magnesium to nickel
But mixed so that it becomes 1: 0.85: 0.05: 0.10.
The same operation as in Example 1 was carried out except that
Formula Li (Co _0.85Mg_0.05Ni_0.10) O₂Positive represented by
A polar active material was obtained. Then, using this positive electrode active material
A battery 20A of the present invention was manufactured in the same manner as in Example 1 except for the above.
Made

Example 21 According to Example 1, the precursor
As Co_0.80Mg_0.05Ni_0.15(OH)₂Consisting of water
The oxide was synthesized. This precursor and lithium carbonate are
Molar ratio of thium to cobalt to magnesium to nickel
But mixed so that it becomes 1: 0.80: 0.05: 0.15.
The same operation as in Example 1 was carried out except that
Formula Li (Co _0.80Mg_0.05Ni_0.15) O₂Positive represented by
A polar active material was obtained. Then, using this positive electrode active material
A battery 21A of the present invention was manufactured in the same manner as in Example 1 except for the above.
Made

Example 22 According to Example 1, the precursor
As Co_0.70Mg_0.05Ni_0.25(OH)₂Consisting of water
The oxide was synthesized. This precursor and lithium carbonate are
Molar ratio of thium to cobalt to magnesium to nickel
But mixed so that it becomes 1: 0.70: 0.05: 0.25.
The same operation as in Example 1 was carried out except that
Formula Li (Co _0.70Mg_0.05Ni_0.25) O₂Positive represented by
A polar active material was obtained. Then, using this positive electrode active material
A battery 22A of the present invention was manufactured in the same manner as in Example 1 except for the above.
Made

Example 23 An aqueous solution containing cobalt sulfate at a concentration of 0.85 mol / liter, magnesium sulfate at a concentration of 0.05 mol / liter, and aluminum sulfate at a concentration of 0.1 mol / liter was prepared. . Using this aqueous solution, a hydroxide composed of Co _0.85 Mg _0.05 Al _0.1 (OH) ₂ as a precursor was synthesized according to Example 1. Similar to Example 1 except that the precursor and lithium carbonate were mixed so that the molar ratio of lithium, cobalt, magnesium, and aluminum was 1: 0.85: 0.05: 0.1. performing operations to obtain a positive electrode active material represented by the chemical formula _{Li (Co 0.85 Mg 0.05 Al 0.} 1) O 2. Next, a battery 23A of the present invention was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Example 24 According to the same manner as in Example 1, a hydroxide composed of Co _0.70 Mg _0.05 Al _0.25 (OH) ₂ was synthesized as a precursor. This precursor and lithium carbonate were mixed in the same manner as in Example 1 except that the molar ratio of lithium, cobalt, magnesium and aluminum was 1: 0.70: 0.05: 0.25. Do the operation,
A positive electrode active material represented by the chemical formula Li (Co _0.70 Mg _0.05 Al _0.25 ) O ₂ was obtained. Then, the battery 24A of the present invention was manufactured in the same manner as in Example 1 except that this positive electrode active material was used.
Was produced.

Comparative Example 1 According to Example 1, a hydroxide composed of Co _0.98 Mg _0.02 (OH) ₂ was synthesized as a precursor. The molar ratio of this precursor and lithium carbonate was 1: 0.98: lithium, cobalt and magnesium.
The same operation as in Example 1 was carried out except that the mixture was mixed so as to obtain 0.02, and the chemical formula Li (Co _0.98 Mg _0.02 ) O was obtained.
A positive electrode active material represented by ₂ was obtained. Next, a battery 1B of a comparative example was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Comparative Example 2 In accordance with Example 1, a hydroxide composed of Co _0.80 Mg _0.20 (OH) ₂ was synthesized as a precursor. The molar ratio of lithium, cobalt and magnesium of the precursor and lithium carbonate was 1: 0.80:
The same operation as in Example 1 was carried out except that the mixture was mixed to give 0.20, and the chemical formula Li (Co _0.80 Mg _0.20 ) O was obtained.
A positive electrode active material represented by ₂ was obtained. Next, a battery 2B of a comparative example was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Comparative Example 3 A battery 3B of Comparative Example was produced in the same manner as in Example 1 except that the positive electrode active material represented by the chemical formula LiCoO ₂ containing no magnesium was used.

Comparative Example 4 The amount of acetylene black, which is the conductive agent for the positive electrode, was changed to 100 parts by weight of the positive electrode active material.
In the same manner as in Example 1 except that the amount was 4.0 parts by weight,
A battery 4B as a comparative example was produced.

Example 25 This example was prepared in the same manner as in Example 1 except that the amount of PVdF having a molecular weight of 300,000 as a binder for the positive electrode was changed to 0.5 part by weight per 100 parts by weight of the positive electrode active material. Battery 25A of the invention was made.

Example 26 The present invention was carried out in the same manner as in Example 1 except that the amount of PVdF having a molecular weight of 300,000 as a binder for the positive electrode was changed to 5 parts by weight per 100 parts by weight of the positive electrode active material. Battery 26A was produced.

Example 27 PVd as a positive electrode binder
A battery 27A of the present invention was produced in the same manner as in Example 1 except that the molecular weight of F was set to 400000.

Example 28 PVd as a binder for the positive electrode
A battery 28A of the present invention was produced in the same manner as in Example 1 except that the molecular weight of F was 100000.

Comparative Example 5 According to Example 1, a hydroxide composed of Co _0.65 Mg _0.05 Ni _0.3 (OH) ₂ was synthesized as a precursor. This precursor and lithium carbonate, the molar ratio of lithium, cobalt, magnesium and nickel,
The same operation as in Example 1 was carried out except that the mixture was mixed at a ratio of 1: 0.65: 0.05: 0.3 to obtain the chemical formula Li.
A positive electrode active material represented by (Co _0.65 Mg _0.05 Ni _0.3 ) O ₂ was obtained. Next, a battery 5B of a comparative example was produced in the same manner as in Example 1 except that this positive electrode active material was used.

Comparative Example 6 According to Example 1, the precursor
Then Co_0.65Mg_0.05Al_0.3(OH)₂Hydroxylation consisting of
The thing was synthesized. This precursor and lithium carbonate
Molar ratio of cobalt to magnesium to aluminum
Mixed so that the ratio becomes 1: 0.65: 0.05: 0.3
The same operation as in Example 1 was performed except that
Li (Co _0.65Mg_0.05Al_0.3) O₂Positive electrode activity represented by
The substance was obtained. Then, using this positive electrode active material
A battery 6B of a comparative example was prepared in the same manner as in Example 1 except for the above.
It was

[Evaluation of Battery] The batteries prepared in Examples 1 to 28 and Comparative Examples 1 to 6 were compared in charge / discharge cycle characteristics and high temperature storage characteristics. (I) Charge / Discharge Cycle Characteristics After charging the battery at a constant voltage for 2 hours under the conditions of a charge voltage of 4.20 V and a maximum charge current of 700 mAh, a discharge current of 700 m
The cycle of constant current discharge of the battery under the conditions of Ah and the final discharge voltage of 3.0 V was repeated in an environment of 20 ° C. 1
The ratio of the discharge capacity at the 300th cycle when the discharge capacity at the cycle was 100 is shown in Tables 1 and 2 as the capacity retention rate A.

(Ii) High temperature storage characteristics A battery was charged at a constant voltage for 2 hours under the conditions of a charging voltage of 4.20 V and a maximum charging current of 700 mAh, and then a discharging current of 700 m
Under the conditions of Ah and the end-of-discharge voltage of 3.0 V, the battery is discharged at a constant current for 2 cycles under the environment of 20 ° C.
The charge / discharge capacity at the cycle was confirmed. Then, the charged battery was stored at 85 ° C. for 3 days. Then, the battery after storage was charged and discharged again at 20 ° C. for 2 cycles under the same conditions as above, and the capacity retention rate B after storage at high temperature was obtained. The ratio of the discharge capacity at the second cycle after high temperature storage when the discharge capacity before storage is 100 is shown in Tables 1 and 2 as capacity retention rate B.

[0067]

[Table 1]

[0068]

[Table 2]

In Tables 1 and 2, comparing the battery characteristics of Examples 1 to 10 with the battery characteristics of Comparative Examples 1 to 4, magnesium-added positive electrode active materials were used, and the amount of conductive agent was changed to the positive electrode active materials. On the other hand, it can be seen that both the cycle characteristics and the high temperature storage characteristics are improved by using the positive electrode whose content is 3% by weight or less.

Battery 1B of Comparative Example 1 in which the amount of magnesium added was too small could obtain only the same cycle characteristics (capacity maintenance ratio A) as Battery 3B of Comparative Example 3 in which magnesium was not added. Further, the battery 2B of Comparative Example 2 in which the amount of magnesium added was too large had a low initial capacity, and the capacity retention rate B during high temperature storage was as low as 69%.

The amount of the conductive agent is 3% by weight based on the positive electrode active material.
The characteristics are excellent in the following cases, and 4% by weight of Comparative Example 4
Battery 4B had a low high temperature storage property of 68%. From the comparison between the batteries of Examples 1, 11, and 12 and the batteries of Examples 25, 26, by setting the amount of the binder contained in the positive electrode to 1 to 4% by weight with respect to the positive electrode active material, It can be seen that both cycle characteristics and high temperature storage characteristics are improved.

Battery 2 of Example 25 containing too little binder
In 5A, the electrode plate strength tended to be weak and the cycle characteristics were 80%. In addition, Example 2 in which the amount of the binder is too large
The battery 26A of No. 6 tended to have a low load characteristic, and the cycle characteristic was 79%. From the comparison between the battery characteristics of Examples 1, 13 and 14 and the battery characteristics of Comparative Examples 7 and 8, the PVdF molecular weight of the binder contained in the positive electrode was determined to be 15,000.
It can be seen that by setting it to 0 to 350,000, both cycle characteristics and high temperature storage characteristics are improved.

Battery 27A of Example 27, in which the binder had an excessively large molecular weight, tended to have low load characteristics and low cycle characteristics. The battery 28A of Example 28 having a too low molecular weight had a tendency that the electrode plate strength was weak and the cycle characteristics were low. The battery 15A of the present invention comprises a non-aqueous solvent such as ethylene carbonate, ethyl methyl carbonate and γ-.
Volume ratio of butyrolactone and vinylene carbonate is 2
Since the mixed solvent mixed at 0: 77.5: 0.5: 2 is used, the capacity retention rate A after repeated charge and discharge is slightly inferior to the battery 1A, but the capacity retention rate after high temperature storage B was good. It is considered that this is because the generation of gas during storage could be reduced.

In addition, the battery 17A of the present invention uses ethylene carbonate, ethyl methyl carbonate, γ
Since the mixed solvent in which butyrolactone and vinylene carbonate are mixed at a volume ratio of 20: 8: 70: 2 is used, the capacity retention rate A after repeated charge and discharge is further reduced, but the capacity retention rate after high temperature storage is reduced. B was very good. From the above, it was found that when the non-aqueous solvent contained γ-butyrolactone, an effect of improving the capacity retention rate at the time of high temperature storage was obtained.

The battery 18A of the present invention uses scaly graphite having a surface coated with amorphous carbon for the negative electrode, and therefore is stored at a higher temperature than the battery 1A of the present invention using mere scaly graphite. The characteristics were excellent. It is considered that by covering the surface of the graphite, the activity of the surface of the graphite was suppressed and the storage characteristics were improved.

In the batteries 19A to 22A of the present invention, since the positive electrode active material containing nickel was used, the cost of raw materials could be reduced. It was also found that the characteristics are the same as those of the battery 1A of Example 1 in which nickel was not added to the positive electrode active material, and the battery could be sufficiently used. From the comparison with the battery 5B of Comparative Example 5, the addition amount of nickel was cobalt,
10 to 25 based on the total amount of magnesium and nickel
It can be said that the mol% is the optimum range.

Since the batteries 23A and 24A of the present invention use the positive electrode active material to which aluminum is added, the capacity of the active material itself is lowered, and the battery capacity of the battery 23A is the same as that of Example 1.
5% lower than that. However, on the other hand, the capacity retention rate A and the capacity retention rate B were both improved. However, as in the battery 6B of Comparative Example 6, 30 mol% of aluminum was added to the total amount of cobalt, magnesium and aluminum.
When added, the battery capacity decreased by 15% and sufficient characteristics could not be obtained. Therefore, the amount of aluminum added is
It can be said that the optimum range is 25 mol% or less with respect to the total amount of cobalt, magnesium and aluminum.

[0078]

According to the present invention, the capacity decrease due to the charge / discharge cycle of the lithium ion secondary battery is suppressed, and the capacity decrease due to the high temperature storage is also reduced. Therefore, according to the present invention, a highly reliable lithium ion secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view in which a part of a prismatic battery according to an embodiment of the present invention is cut away.

[Explanation of symbols]

1 plate group 2 Positive lead 3 Negative electrode lead 4 battery case 5 Seal plate 6 Negative electrode terminal 7 plug

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yutaka Kawaken             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Ryoichi Tanaka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Hideya Asano             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H029 AJ03 AJ04 AJ05 AK03 AL01                       AL02 AL04 AL06 AL07 AL08                       AL12 AL19 AM02 AM03 AM04                       AM05 AM07 BJ04 BJ14 DJ08                       DJ09 DJ18 EJ04 EJ12 EJ14                       HJ01 HJ02 HJ11                 5H050 AA07 AA08 AA10 BA17 CA08                       CB01 CB02 CB05 CB07 CB08                       CB09 CB12 DA02 DA03 DA09                       DA10 DA11 DA18 EA10 EA24                       EA28 FA20 GA22 HA01 HA02                       HA11

Claims (5)

[Claims] 1. A positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode active material, a conductive agent, and a binder, and the positive electrode active material has the chemical formula Li _a (Co _1-xy Mg _x M _y )
_b O _c (M is at least 1 selected from Ni and Al)
Seed, 0 ≦ a ≦ 1.05, 0.03 ≦ x ≦ 0.15, 0 ≦
y ≦ 0.25, 0.85 ≦ b ≦ 1.1, 1.8 ≦ c ≦
A lithium ion secondary battery comprising the lithium-containing composite oxide represented by 2.1), wherein the amount of the conductive agent contained in the positive electrode is 3.0 parts by weight or less per 100 parts by weight of the positive electrode active material. 2. The amount of the binder contained in the positive electrode is
The lithium ion secondary battery according to claim 1, wherein the amount is 1.0 part by weight or more and 4.0 parts by weight or less per 100 parts by weight of the positive electrode active material. 3. The binder comprises polyvinylidene fluoride, and the polyvinylidene fluoride has a weight average molecular weight of 150,000 or more and 350,000 or less.
The lithium-ion secondary battery described. 4. The non-aqueous electrolyte comprises a non-aqueous solvent and a lithium salt soluble in the non-aqueous solvent, and the non-aqueous solvent contains γ-butyrolactone and / or γ-butyrolactone derivative. Lithium-ion secondary battery. 5. The lithium ion secondary according to claim 1, wherein the negative electrode contains core particles and a material made of amorphous carbon that covers at least a part of the surface of the core particles, and the core particles are made of graphite. battery.