JP2000195553A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

[PROBLEMS] To improve the cycle life characteristics of a non-aqueous electrolyte secondary battery at a high temperature using a composite oxide containing lithium and manganese as a positive electrode active material. At least one of a positive electrode and a negative electrode contains at least one additive selected from the group consisting of a chelating agent, a polyimide resin, a chelating resin, an ion exchanger, and azoles and derivatives thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Organic electrolyte secondary batteries typified by lithium secondary batteries have a high energy density and are therefore used in portable devices such as VTR-integrated cameras, notebook computers and mobile phones. Note that a lithium secondary battery using metal lithium or a lithium alloy for the negative electrode has problems such as that dendritic lithium precipitates on the negative electrode during charging, causing an internal short circuit with the positive electrode. Then, a composite oxide of lithium and a transition metal, such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ), is used as a positive electrode active material, and a carbon material is used. A non-aqueous electrolyte secondary battery has been developed in which is used as an active material for a negative electrode.

[0003] Among the above-mentioned various positive electrode active materials, composite oxides using manganese have recently attracted particular attention because of their large resources, excellent cost performance, and high safety. However, the chemical formula Li _x Mn _y O ₂ (x is 0.4 ≦ x ≦ 1.
35, y has a problem that the charge / discharge cycle life is short when the composite oxide represented by 0.65 ≦ y ≦ 1) is used as the positive electrode active material. In particular, when used at a high temperature of 50 ° C. or more, manganese was eluted from the positive electrode, and the problem that the cycle life was shortened was recognized.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent life characteristics at high temperatures.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, in the first invention, a chemical formula Li _x Mny _y O ₂ (x is 0.4 ≦ x ≦
1.35, y is 0.65 ≦ y ≦ 1) A positive electrode using a composite oxide capable of occluding and releasing lithium ions as an active material, and a negative electrode using a carbon powder capable of occluding and releasing lithium ions as an active material. In a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte in which a lithium salt is dissolved, at least one of the positive electrode and the negative electrode includes a chelating agent, a polyimide resin, a chelating resin, an ion exchanger, and azoles and derivatives thereof. Characterized in that it contains at least one additive selected from the group of

In the second invention, the additive is added in an amount of 0.01 to 10% by volume based on the active material of the positive electrode or the negative electrode.
Characterized in that it is contained at a ratio of

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a non-aqueous electrolyte secondary battery using a positive electrode and a negative electrode capable of inserting and extracting lithium ions according to the present invention will be specifically described.

[0008] 1. Additive to positive electrode or negative electrode In the present invention, at least one of the above positive electrode or negative electrode, a chelating agent, a polyimide resin, a chelate resin, an ion exchanger and at least one selected from the group of azoles and derivatives thereof. It is characterized by containing. As the chelating agent, most can be used as long as they form a chelating compound with manganese ions. That is, ethylenediaminetetraacetic acid, 1,2-dihydroxyanthraquinone-3-yl-methylamino-N,
N'-diacetate, 5,5'-dibromopyrogallol sulfophthalein, 1- (1-hydroxy-2-naphthylazo) -6-nitro-2-naphthol-4-sulfonic acid sodium salt, cyclo-tris- [7 -(1-Azo-8-hydroxynaphthalene-
3,6-disulfonic acid)] 6 sodium salt, 4-methylambelliferone-8-methyleneiminodiacetic acid, 3-sulfo-
2,6-dichloro-3 ', 3''-dimethyl-4'-fuchsone-
5 ', 5''-dicarboxylic acid trisodium salt, 3,3'-bis [N, N-di (carboxymethyl) aminomethyl] timolsulfonephthalein, sodium salt, 7- (1-naphthylazo)- 8-hydroxyquinoline-5-sulfonic acid sodium salt, 4- (2-pyridylazo) resorcinol, pyrocatecholsulfonephthalein, 3,3'-bis [N, N-di (carboxymethyl) aminomethyl] -ortho-cresol Sulfonephthalein, disodium salt, and the like are possible.

The polyimide resin can form a chelate compound with a manganese ion and can be used if it is insoluble in a non-aqueous electrolyte. That is, it is generally represented by the structural formula (1), for example, 4,4′-oxydi-p-phenylenepyromellitimide / 4,4′-methylene-bisbenzenepyromellitimide copolymer ( Structural formula (2)) and poly 4,4'-oxydi-p-phenylene pyromellitimide (structural formula (3)).

[0010]

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[0011]

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[0012]

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The chelate resin can form a chelate compound with a manganese ion, and can be used if it is insoluble in a non-aqueous electrolyte. That is, a polymer substrate such as a styrene-based, acrylic-based, or phenol-based material having a functional group such as an iminodiacetic acid group, a polyamine group, a thiol group, a dithiocarbamic acid group, an aminomethylphosphonic acid group, or an oxime group is used. be able to.

The ion exchanger can form a chelate compound with a manganese ion and can be used as long as it is insoluble in a non-aqueous electrolyte. A cation exchange type or amphoteric ion exchange type organic or inorganic exchanger can be used. . As the organic ion exchanger, there is one in which an acidic hydroxyl group, a carboxyl group, a sulfone group, or the like is covalently bonded to a base synthetic resin such as polystyrene cross-linked with divinylbenzene. Examples of the inorganic exchanger include acid clay, synthetic zeolite, palm chit, and zirconium tungstate.

The azoles are a 5-atom heterocyclic ring having two or more hetero atoms in the ring, and at least one of the hetero atoms is a nitrogen atom. As two hetero atoms, imidazole, oxazole,
There are thiazole, selenazole, pyrazole, isoxazole, isothiazole and the like. Examples of three heteroatoms include 1,2,3-triazole, 1,2,5-triazole, 1,2,4-triazole, 1,3,4-triazole, and 1,2,3-oxadiazine. Azole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1, There are 2,5-thiadiazole, 1,3,4-thiadiazole and the like. In the case of four heteroatoms,
1,2,3,4-tetrazole, 1,2,3,4-oxatriazole, 1,2,3,4-thiatriazole, 1,2,3,5-
Tetrazole, 1,2,3,5-oxatriazole, 1,
2,3,5-thiatriazole and the like.

2. Preparation of positive electrode LiMn ₂ O _{4 having} an average particle size of 10 μm, carbon powder having an average particle size of 3 μm, and polyvinylidene fluoride as a binder (trade name: KF
# 112, manufactured by Kureha Chemical Industry Co., Ltd .; hereinafter, abbreviated as PVDF) at a weight ratio of 86: 8.6: 5.4 in a solvent, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP). Make a slurry. The above-mentioned chelating agent, polyimide resin, chelating resin, ion exchanger, azoles and the like were added to the slurry and used after sufficiently kneading. This slurry is applied to both surfaces of an aluminum foil (positive electrode current collector 1) having a thickness of 20 μm by a roll-to-roll method, dried, and then pressed to be integrated. After that, the width is 54mm and the length is
It was cut into 450 mm to produce a strip-shaped positive electrode. In addition, as the positive electrode active material, a chemical formula Li _x Mn _y O ₂ (x is 0.4 ≦ x ≦ 1.35, y
Can be a complex oxide containing lithium and manganese represented by 0.65 ≦ y ≦ 1). For example, LiMnO ₂ , LiMn ₂ O
_{4, Li 2 Mn 4 O 9} , Li 4 Mn 5 O 12, Li 2 MnO 3, Li 7 Mn 5 O 12, Li 5 Mn 4
O _{9 and the} like can be used. Also, Li, Al, V, Cr, Fe, C
It is at least one metal selected from the group consisting of o, Ni, Mo, W, Zn, B and Mg, and may be a lithium manganese composite oxide in which the manganese site or the lithium site is substituted.

3. Preparation of negative electrode Amorphous carbon with an average particle size of 20 μm capable of occluding and releasing lithium ions, PVDF as a binder mixed at a weight ratio of 92: 8, and a suitable amount of NMP serving as a dispersing solvent added thereto, followed by sufficient addition And disperse into a slurry. This slurry is applied to both surfaces of a copper foil (negative electrode current collector 3) having a thickness of 10 μm by a roll-to-roll method, dried, and then pressed to be integrated. Then, the negative electrode was produced by cutting it into a strip having a width of 56 mm and a length of 500 mm. In addition, as the negative electrode active material, a carbon material such as graphite, activated carbon, carbon fiber, carbon black, mesocarbon microbeads, which can be doped with and dedoped with lithium ions, can also be used.

4. Preparation of Electrolyte The non-aqueous electrolyte according to the present invention is a non-aqueous electrolyte in which an electrolyte is dissolved in a non-aqueous solvent. Non-aqueous electrolyte used in the present invention,
Ethylene carbonate (EC) and dimethyl carbonate
1 mol / l of LiPF ₆ as an electrolyte dissolved in a mixed solvent with (DMC) (EC: DMC = 1: 2, but shown by volume ratio). In addition to the above-mentioned solvents, cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, and the like are generally used. That is, as the cyclic carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc., and as the chain carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, etc. Esters include γ-butyrolactone, γ-butyrolactone
Valerolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone and the like are generally used. As the chain ester, methyl formate, ethyl formate,
Methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, methyl valerate and the like, as cyclic ethers, 1,4-dioxane, 1,3-dioxolane,
Tetrahydrofuran, 2-methyltetrahydrofuran,
3-Methyl-1,3-dioxolan, 2-methyl-1,3-dioxolan and the like are generally used. As the chain ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether and the like are generally used. As the non-aqueous electrolyte, two or more of the various non-aqueous solvents described above can be used in combination.

On the other hand, LiBF ₄ , LiClO ₄ , LiA
sF ₆ , LiOSo ₂ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) _{3 and the} like are also commonly used. And these electrolytes are 2
A combination of more than one kind can be used. In addition, these electrolytes are those that dissociate in a non-aqueous electrolyte to generate Li ions, and are usually 0.5 to 2 mol / l, preferably
It is contained in the non-aqueous electrolyte in the range of 0.7 to 1.5 mol / l.

[5] Battery assembly and test The prepared strip-shaped positive electrode and negative electrode were assembled to a thickness of 25 μm and a width of 5 μm.
An electrode group is formed by spirally winding the film through a separator 5 made of an 8 mm polyethylene porous film. This electrode group is inserted into the battery can 6, and the terminal of the negative electrode current collector 3 is welded to the bottom of the battery can 6. 5 ml of the above-mentioned mixed electrolytic solution is placed in the battery can 6.
Injected. After welding one of the positive electrode tab terminals 8 to the positive electrode current collector 1, the other of the positive electrode tab terminals 8 is welded to the positive electrode cap 7. Then, the positive electrode cap 7 is attached to the insulating gasket 9.
Was placed over the battery can 6, and this portion was caulked and hermetically sealed to form a cylindrical battery having a diameter of 18 mm and a height of 65 mm. Here, in the positive electrode cap 7, a current cutoff mechanism (pressure switch) that operates according to an increase in battery internal pressure and a safety valve that operates at a pressure higher than this pressure are incorporated. The fabricated organic electrolyte secondary battery has an ambient temperature of 25 ° C and 4.2V
After charging at a constant voltage (limited current of 300 mA) for 10 hours, the battery was discharged at a constant current of 1 CmA to a final voltage of 2.7 V to check the initial discharge capacity. Then, in a 50 ° C constant temperature bath,
A life test was repeated in which discharge at 1 CmA (discharge end voltage 2.7 V) and charging at a current value of 0.5 CmA (charge end voltage 4.2 V, 4 hours) were repeated. The life was defined as the time when the capacity was reduced to 80% or less of the initial discharge capacity, and the number of cycles is shown in Table 1.

[0021]

EXAMPLES The present invention is described below with reference to examples, but the present invention is not limited to these examples.

Example 1 As a chelating agent for the positive electrode,
A non-aqueous electrolyte secondary battery to which (2-pyridylazo) resorcinol was added was tested. Incidentally, 4- (2-pyridylazo) resorcinol was added to a 1% by volume based on the LiMn ₂ O _4.

(Example 2) As a polyimide resin, a 4,4'-oxydi-p-phenylenepyromellitimide / 4,4'-methylene-bisbenzenepyromellitimide copolymer having an average particle size of 8 μm was used as a polyimide resin. The non-aqueous electrolyte secondary battery to which the structural formula (2) was added was tested. The amount of the polyimide resin added is 2% by volume based on LiMn ₂ O ₄ .

[0024]

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Example 3 A non-aqueous electrolyte secondary battery in which a polyalkylene polyamine type chelate resin (trade name: Diaion CR-20, manufactured by Mitsubishi Chemical Corporation) having an average particle size of 20 μm was added to a positive electrode was tested. The addition amount of the chelating resin is
It is 0.5% by volume with respect to LiMn ₂ O ₄ .

Example 4 A non-aqueous electrolyte secondary battery in which an antimony-based inorganic ion exchanger (trade name: IXE-300, manufactured by Toa Gosei) was added to the positive electrode was tested. The amount of the inorganic ion exchanger added was 3% by volume based on LiMn ₂ O ₄ .

Example 5 A non-aqueous electrolyte secondary battery in which an azole, 5-amino-3-mercapto-1,2,3-triazole, was added to the positive electrode was tested. The amount of the inorganic ion exchanger added was 1% by volume based on LiMn ₂ O ₄ .

Example 6 A non-aqueous electrolyte secondary battery in which a polyimide resin poly 4,4'-oxydi-p-phenylene pyromellitimide (structural formula (3)) was added to a negative electrode was tested.
The amount of the inorganic ion exchanger added was 1% by volume based on LiMn ₂ O ₄ .

[0029]

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Comparative Example 1 A non-aqueous electrolyte secondary battery in which no additive was added to the positive electrode and the negative electrode was tested. Table 1 shows the life test results. The non-aqueous electrolyte secondary batteries of the present invention (Examples 1 to 6) have a longer life and are superior to the battery of (Comparative Example 1). Since the nonaqueous electrolyte secondary battery according to the present invention can trap manganese ions eluted from the positive electrode active material, it can suppress the precipitation of manganese on the negative electrode and greatly improve the life cycle. It is considered possible.

[0031]

[Table 1]

(Examples 7 to 10) 4- (2-pyridylazo) resorcinol was added to the positive electrode as a chelating agent in an amount of 0.1 to 1%.
The added non-aqueous electrolyte secondary batteries containing 005, 0.01, 10, and 15% by volume were tested, and the results are shown in Table 2. 4-
When the content of (2-pyridylazo) resorcinol increases, the life cycle tends to be longer, but the initial discharge capacity decreases. Therefore, it is understood that the content of the chelating agent is preferably 0.01 to 10% by volume. In this example, the case of 4- (2-pyridylazo) resorcinol as a chelating agent was shown, but similar results were obtained for other polyimide resins, chelating resins, ion exchangers, azoles and the like.

[0033]

[Table 2]

The shape of the non-aqueous electrolyte secondary battery according to the present invention is not limited to a cylindrical shape, but may be a coin shape or a square shape.

[0035]

As described above, a nonaqueous electrolyte secondary battery using a composite oxide containing lithium and manganese as a positive electrode active material has a chelating agent, a polyimide resin, and a chelating resin on at least one of the positive electrode and the negative electrode. By containing at least one selected from the group consisting of ion exchangers and azoles and their derivatives, the cycle life at high temperatures can be greatly improved, which is excellent.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cylindrical lithium ion secondary battery embodying the present invention.

[Explanation of symbols]

1: positive electrode current collector, 2: positive electrode active material, 3: negative electrode current collector,
4: negative electrode active material, 5: separator, 6: battery can,
7: positive electrode cap, 8: positive electrode tab terminal, 9: gasket.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Kiyotaka Mashimo 4-3-1, Higashicho, Hitachi City, Ibaraki Prefecture F-term in the Ibaraki Research Laboratory, Hitachi Chemical Co., Ltd. 5H029 AJ00 AJ05 AK03 AL06 AM01 AM02 AM03 AM04 AM05 AM07 BJ02 BJ03 BJ14 DJ08 EJ11 EJ12 HJ02 HJ07

Claims (2)

[Claims] 1. A chemical formula Li _x Mn _y O _{2 (x} is 0.4 ≦ x ≦ 1.35, y is 0.6
5 ≦ y ≦ 1) a positive electrode using a composite oxide capable of storing and releasing lithium ions as an active material, a negative electrode using a carbon powder capable of storing and releasing lithium ions as an active material, and a lithium salt In a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte in which is dissolved, at least one of the positive electrode and the negative electrode, a chelating agent, a polyimide resin, a chelate resin, an ion exchanger and a group of azoles and derivatives thereof. A non-aqueous electrolyte secondary battery comprising at least one type of additive. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the additive is contained at a ratio of 0.01 to 10% by volume based on the active material of the positive electrode or the negative electrode.