JPH08213048A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte secondary battery which is excellent in cycle characteristics in toughness, adhesion to metal, nonaqueous electrolyte resistance or the like by specifying binder resin in a nonaqueous electrolyte secondary battery. CONSTITUTION: A nonaqueous electrolyte secondary battery is provided with a negative electrode having a negative electrode mixed layer containing at least carbon material as a negative electrode active material carrier and binder resin, a positive electrode containing positive electrode active material and binder resin and nonaqueous electrolyte. In this case, in the nonaqueous electrolyte secondary battery, the binder resin is polyamide imide resin on which logarithmic viscosity is not less than 0.3dl/g, and the content of a binder in a negative electrode mix is 5wt.% to 20wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode having a negative electrode mixture layer made of a carbon material and a binder resin, a positive electrode, and a non-aqueous electrolyte, and particularly to a binder resin.

[0002]

2. Description of the Related Art With the recent remarkable progress of electronic technology, electronic devices are becoming smaller and lighter, and accordingly, batteries are required to be smaller and lighter and have high energy density. Conventionally, as a general-purpose secondary battery,
Aqueous solution batteries such as lead batteries and nickel-cadmium batteries were the mainstream. Although these batteries have excellent cycle characteristics, they were not sufficiently satisfactory in terms of battery weight and energy density.

In recent years, as a secondary battery replacing a lead battery or a nickel-cadmium battery, a non-aqueous electrolyte secondary battery using lithium or a lithium alloy as a negative electrode has been actively researched and developed. This battery has the features of high energy density, low self-discharge, and light weight. However, with this battery, as the charge and discharge cycle progresses,
In the negative electrode, there is a high possibility that lithium will grow into a dendrite-like crystal during charging, and this crystal will reach the positive electrode to cause an internal short circuit, which has been a major obstacle to practical use.

On the other hand, according to the non-aqueous electrolyte secondary battery using the carbon material as the negative electrode active material carrier in the negative electrode,
Lithium previously supported on the carbon material of the negative electrode by a chemical or physical method, and lithium contained in the crystal structure of the positive electrode active material and lithium dissolved in the electrolytic solution, respectively, between the carbon layers in the negative electrode during charging and discharging. Doped and dedoped from the carbon layer. Therefore, even if the charge / discharge cycle progresses, dendrite-like crystals are not deposited on the negative electrode during charging, an internal short circuit hardly occurs, and good charge / discharge cycle characteristics are exhibited. Further, since it has a high energy density and is lightweight, it is being developed for practical use.

Applications of such non-aqueous electrolyte secondary batteries include video cameras and laptop personal computers. Since such electronic devices consume a relatively large amount of current, it is necessary for the battery to withstand a heavy load. Therefore, as a battery structure, a spiral wound electrode body structure formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode in the length direction via a strip-shaped separator is effective.
According to the battery having the spirally wound electrode structure, a large electrode area can be obtained, so that the battery can withstand use under heavy load.

In such a wound electrode body, it is desirable to make the electrode thin in order to increase the electrode area and charge the active material or the active material carrier as much as possible in a limited space. Therefore, as a method of manufacturing the strip-shaped electrode, a method of applying a paste containing a binder and an active material to a current collector and drying it is desirable. According to this method, the thickness of the electrode mixture layer in the strip-shaped electrode can be set to about several microns to several hundreds of microns. Conventionally, meshed meshed punched metal and punched metal with many holes were often used as electrode current collectors, but these electrode current collectors are used for thinning electrodes to obtain heavy load characteristics. Is not suitable for. Therefore, it is preferable that a metal foil is used as the electrode current collector and that the metal foil is as thin as possible.

[0007]

However, since the surface of such a metal foil is flat, the negative electrode mixture layer formed by applying the negative electrode mixture paste to the metal foil as the negative electrode current collector and drying it. However, there are problems such as peeling and cracking during the manufacture and use of the battery. In particular, it is easy to peel off when producing a wound electrode body. An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the negative electrode mixture layer in the negative electrode does not crack or peel.

[0008]

In order to achieve the above-mentioned object, the present invention provides a negative electrode having a negative electrode mixture layer containing at least a carbon material as a negative electrode active material end itself and a binder resin, and a positive electrode active material. In a non-aqueous electrolyte secondary battery comprising a positive electrode containing a binder resin and a non-aqueous electrolyte, the binder resin is a polyamide-imide resin having a logarithmic viscosity of 0.3 dl / g or more, and the binder resin in the negative electrode mixture. Content of 5% by weight or more and 20% by weight
The present invention relates to a non-aqueous electrolyte secondary battery characterized by the following.

The polyamide-imide resin of the present invention is preferably one synthesized from trimellitic anhydride and diphenylmethane diisocyanate. Further, a polyfunctional epoxy resin is added to the polyamide-imide resin in an amount of 3% by weight or more and 50% by weight.
Those blended in the following ranges are more preferable.

Polyamideimide resin is a resin suitable as a binder for forming the negative electrode mixture layer because it has high mechanical strength, heat resistance, adhesion to metal, and chemical resistance. The polyamide-imide resin used in the present invention is obtained by reacting an acid component and an amine component. In the present invention, trimellitic anhydride is used as the acid component. Further, in order to impart solubility in a solvent, polymerizability, etc., in addition to trimellitic anhydride, aliphatic dicarboxylic acid, aromatic dicarboxylic acid, tricarboxylic acid and its anhydride, tetracarboxylic acid and its dianhydride, etc. Can be further used as the acid component.

As the aliphatic dicarboxylic acid, oxalic acid,
Malonic acid, succinic acid, glutaric acid, adipic acid, vimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, cyclohexanedicarboxylic acid and the like are preferable, and adipic acid and sebacine are preferable. It is an acid.

As the aromatic dicarboxylic acid, isophthalic acid, 5-tert-butyl-1,3-benzenedicarboxylic acid, terephthalic acid, diphenylmethane-4,4'dicarboxylic acid, diphenylmethane-2,4-dicarboxylic acid,
Diphenylmethane-3,4-dicarboxylic acid, diphenylmethane-3,3'-dicarboxylic acid, 1,2-diphenylethane-4,4'dicarboxylic acid, diphenylethane-
2,4-dicarboxylic acid, diphenylethane-3,4-dicarboxylic acid, diphenylethane-3,3'-dicarboxylic acid, 2,2'-bis- (4-carboxyphenyl) propane, 2- (2-carboxyphenyl) ) -2- (4-carboxyphenyl) propane, 2- (3-carboxyphenyl) -2- (4-carboxyphenyl) propane,
Diphenyl ether-4,4'-dicarboxylic acid, diphenyl ether-2,4-dicarboxylic acid, diphenyl ether-3,4-dicarboxylic acid, diphenyl ether-
3,3'-dicarboxylic acid, diphenyl sulfone 4,4 '
Dicarboxylic acid, diphenylsulfone-2,4-dicarboxylic acid, diphenylsulfone-3,4-dicarboxylic acid, diphenylsulfone-3,3'dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, benzophenone-3
3'-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, naphthalenedicarboxylic acid, bis-[(4-carboxy) phthalimide] -4,4'-diphenyl ether,
Bis-[(4-carboxy) phthalimide] -α, α '
-Meta-xylene etc. are mentioned, Preferably it is isophthalic acid and terephthalic acid.

As the tricarboxylic acid, butane-1,
Examples thereof include 2,4-tricarboxylic acid and naphthalene 1,2,4-tricarboxylic acid, and anhydrides thereof.

As the tetracarboxylic acid, butane-1,
2,3,4-tetracarboxylic acid, pyromellitic acid, benzophenone 3,3 ', 4,4'-tetracarboxylic acid, diphenyl ether-3,3', 4,4'-tetracarboxylic acid, diphenyl ether-3,3 '4,4'-Tetracarboxylic acid, biphenyl-3,3', 4,4'tetracarboxylic acid, naphthalene-2,3,6,7-tetracarboxylic acid, naphthalene-1,2,4,5- Examples thereof include tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid, and dianhydrides thereof. Pyromellitic dianhydride is preferred.

Other acid anhydrides include ethylene glycol bis-anhydro trimellitate, propylene glycol bis-anhydro trimellitate, neopentyl glycol bis-anhydro trimellitate, polyethylene glycol bis-anhydro trimellitate and polypropylene glycol bis. Also included are alkylene glycol bis-anhydro trimellitates such as anhydro trimellitate. These acid components may be used alone or as a mixture of two or more kinds together with trimellitic anhydride.

On the other hand, examples of the amine component include diamine and diisocyanate. In the present invention, 4,4'diaminodiphenylmethane or diphenylmethane diisocyanate as an isocyanate component corresponding thereto is an essential component.

It is also possible to replace part of the amine component with other diamines or diisocyanates. Specifically, m-phenylenediamine, p-phenylenediamine, oxydianiline, methylenediamine, hexafluoroisopropylidene diamine, diamino m-xylylene, diamino-p-xylylene, 1,4-naphthalenediamine, 1,5 naphthalene. Diamine, 2,6-naphthalenediamine, 2,7-naphthalenediamine, 2,2'-
Bis- (4-aminophenyl) propane, 2,2′-bis- (4-aminophenyl) hexafluoropropane,
4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 3,3 'diaminodiphenyl sulfone, 3,3' diaminodiphenyl ether,
3,4-diaminobiphenyl, 4,4'diaminobenzophenone, 3,4-diaminodiphenyl ether, isopropylidenedianiline, 3,3'diaminobenzophenone, o-tolidine, 2,4-tolylenediamine, 1,
3-bis- (3-aminophenoxy) benzene, 1,4
-Bis- (4-aminophenoxy) benzene, 1,3-
Bis- (4-aminophenoxy) benzene, 2,2-bis- [4- (4-aminophenoxy) phenyl] propane, bis- [4- (4-aminophenoxy) phenyl]
Sulfone, bis- [4- (3-aminophenoxy) phenyl] sulfone, 4,4'-bis- (4-aminophenoxy) biphenyl, 2,2'-bis- [4- (4-aminophenoxy) phenyl] Hexafluoropropane,
4,4'-diaminodiphenyl sulfide, 3,3'-
Examples thereof include aromatic diamines such as diaminodiphenyl sulfide, aliphatic diamines such as ethylenediamine, propylenediamine, tetramethylenediamine, hexamethylenediamine, and alicyclic diamines such as dicyclohexyl-4,4′-diamine and isophoronediamine. Also,
The isocyanate which replaced the amino group of the said diamine with -N = C = O group is also mentioned. The above amine components may be used alone or in combination of two or more 4,4′-diaminodiphenylmethane or diphenylmethane-4,
You may use together with 4'- diisocyanate. The above-mentioned acid component and amine component are usually mixed in equimolar amounts, but one component may be increased or decreased as needed.

The polyamide-imide resin used in the present invention is produced by a usual method such as a diisocyanate method or an acid chloride method, but the diisocyanate method is preferable from the viewpoint of polymerizability and cost.

As the solvent used for the polymerization of the polyamide-imide resin, amide solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide and dimethylimidazolidinone, dimethylsulfoxide,
Sulfur solvents such as sulfolane, nitro solvents such as nitromethane and nitroethane, ether solvents such as diglyme and tetrahydrofuran, ketone solvents such as cyclohexanone and methyl ethyl ketone, nitrile solvents such as acetonitrile and propionitrile, and γ-butyrolactone. And a solvent having a relatively high dielectric constant such as tetramethylurea. These may be used alone or as a mixed solvent, and a solvent having a relatively low dielectric constant such as xylene or toluene may be mixed and used.

The reaction temperature is usually 50 to 200 ° C.,
It is preferably 70 to 180 ° C. Further, in order to accelerate the reaction, a tertiary amine such as t-butylamine, a metal compound such as an alkali metal, an alkaline earth metal, cobalt, tin or zinc, or a catalyst such as a metalloid compound may be added.

The polyamideimide resin thus obtained has a logarithmic viscosity of 0.3 dl / g or more, preferably 0.4 dl / g from the viewpoint of toughness and flexibility as a negative electrode mixture layer.
g or more is required. When the logarithmic viscosity is less than 0.3 dl / g, cracks occur when the negative electrode current collector is used.

In order to further improve the toughness, flexibility, resistance to non-aqueous electrolyte solution and adhesion to metal foil of the negative electrode mixture layer of the present invention, a polyfunctional epoxy resin may be blended as one component of the binder. it can. Polyfunctional epoxy resin is not particularly limited, aliphatic polyfunctional epoxy resin such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol pentaglycidyl ether,
Cyclohexanediol diglycidyl ether, alicyclic polyfunctional epoxy resin such as hydrogenated bisphenol A diglycidyl ether, aromatic such as bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, bisphenol F diglycidyl ether, phenol novolac polyglycidyl ether Examples include polyfunctional epoxy resins.

The amount of the polyfunctional epoxy resin used is 3% by weight or more and 50% by weight or less, preferably 5% by weight or more and 30% by weight or less of the binder in the negative electrode mixture layer. When the amount of the polyfunctional epoxy resin used is less than 3% by weight, the effects of improving toughness, flexibility, non-aqueous electrolyte resistance and adhesion to metal foil are not exhibited, and when it exceeds 50% by weight, polyamideimide The compatibility with the resin decreases, the negative electrode mixture layer becomes rather brittle, and cracks easily occur.

The compounding ratio of the carbon material and the binder resin in the negative electrode mixture layer of the present invention is 95: 5 to 80:20 by weight. If the carbon material exceeds 95% by weight, the negative electrode material mixture layer may be cracked when the current collector is wound, or may be easily peeled from the metal foil. Further, if the carbon material is less than 80% by weight, the charge / discharge cycle characteristics will deteriorate.

Examples of the carbon material used for the negative electrode active material-supporting material of the present invention include cokes such as pitch coke and needle coke, polymers, carbon fibers and graphite materials. Such a carbon material can be produced, for example, by carbonizing an organic material by firing at about 700 to 1500 ° C. A polymer such as petroleum pitch or furan resin is used as a raw material of a carbon material, and when carbonized, by adding a phosphorus compound or a boron compound, a carbon material having a large doping amount with respect to lithium can be obtained. preferable.

On the other hand, as the positive electrode active material in the positive electrode,
Transition metal oxides such as manganese dioxide and vanadium pentoxide, transition metal chalcogenides such as iron sulfide and titanium sulfide, or complex compounds of these with lithium such as the general formula LiMO ₂ (where M is Co or Ni It is possible to use a composite metal oxide represented by at least one kind). Particularly, since high voltage and high energy density are obtained and the cycle characteristics are excellent, LiCoO ₂ ,
A lithium-cobalt composite oxide such as LiCo0.8Ni0.2O ₂ or a lithium-cobalt-nickel composite oxide is preferable. Further, as the non-aqueous electrolyte, a non-aqueous electrolytic solution in which an electrolyte such as a lithium salt is dissolved in a non-aqueous organic solvent can be used.

Here, the organic solvent is not particularly limited, but for example, ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, 1,
2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,
3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like can be used alone or in admixture of two or more. The electrolyte dissolved in the organic solvent is also LiClO ₄ , LiAsF ₆ ,
LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , Li
Cl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li
Any of the known ones such as can be used. The non-aqueous electrolyte may be solid, and examples thereof include polymer solid electrolyte.

[0028]

EFFECTS OF THE INVENTION Polyamide-imide resin forms a film that is tough, has excellent flexibility, has excellent dispersibility of carbon materials, and has excellent adhesion to metal foils and excellent resistance to non-aqueous electrolytes. It is suitable as a binder resin for the negative electrode mixture layer of a water electrolyte secondary battery, and if it is mixed with an epoxy resin, a more excellent binder is obtained.

[0029]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Experimental Example 1 Synthesis of Polyamideimide Resin In a reaction vessel, 192 g of trimellitic anhydride and 250 g of 4,4'-diisocyanate of diphenylmethane were charged together with 531 g of N-methyl-2pyrrolidone, and the mixture was heated to 180 ° C. and reacted for 5 hours. Then, while cooling, 295 g of xylene was added to obtain a polymer solution having a solid content concentration of 30%.
A solution of 0.5 g of this dry polymer dissolved in 100 ml of N-methyl-2-pyrrolidone had a logarithmic viscosity of 0.68 dl / g measured by an Ubbelohde viscometer at 25 ° C.

Experimental Example 2 Preparation of Carbon Material After oxygen-crosslinking was carried out by introducing 10 to 20% by weight of a functional group containing oxygen into petroleum pitch, the oxygen-crosslinked precursor was subjected to 1000 in a stream of an inert gas. By firing at ℃, a carbonaceous material having properties close to glassy carbon was obtained.

Experimental Example 3; Preparation of Negative Electrode Current Collector 75 to 97 parts by weight of the carbonaceous material prepared in Experimental Example 2 and 88.3 to 10 parts by weight of the polyamide-imide solution prepared in Experimental Example 1 were mixed to obtain N. The paste was diluted with methyl 2 pyrrolidone to a solid content concentration of 50% by weight, dispersed with a three-roll mill, and kneaded to apply a paste having a dry film thickness of 80 μ on both surfaces of a 10 μ copper foil, and dried. After that, it was pressed with a hot roll at 200 ° C. and slit into a strip having a width of 41 mm and a length of 280 mm.

Experimental Example 4; Preparation of Positive Electrode 90 parts by weight of lithium cobalt oxide (LiCoO ₂ ) and 5 parts by weight of graphite, 16.7 parts by weight of the polyamideimide resin solution synthesized in Experimental Example 1, N-methyl-2pyrrolidone 8
8.3 parts by weight are mixed, dispersed and kneaded with a three-roll mill, and the paste is applied to both sides of a 20 μ aluminum foil so that the dry film thickness is 80 μ, dried, and then pressed with a hot roll at 200 ° C. It was slit into a width of 39 mm and a length of 230 mm.

Experimental Example 5: Preparation of Battery The negative electrode current collector prepared in Experimental Example 3 with nickel lead attached and the positive electrode current collector prepared in Experimental Example 4 with aluminum lead attached. A four-layer laminate was prepared by alternately laminating a porous polypropylene film having a thickness of 25 μm and a width of 44 mm. A wound electrode body was prepared in which the negative electrode current collector was placed inside the laminated body in the length direction. The spirally wound electrode body was housed in a nickel-plated iron battery can, and insulators were arranged above and below the electrode body. The battery can was mixed with an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane. A non-aqueous electrolyte solution in which LiPF ₄ was dissolved at a concentration of 1 mol / l was injected.

Experimental Example 6; Charge / Discharge Cycle Test For the battery prepared in Experimental Example 5, the charging upper limit voltage was 4.
After setting the voltage to 1 V and performing constant current charging at 500 mA for 2 hours, a charging / discharging cycle of discharging to a final voltage of 2.75 V with a constant load of 18Ω was repeated. A value obtained by dividing the discharge capacity at 100 cycles by the capacity at 10 cycles (initial value) of the charge / discharge cycle was defined as the capacity retention rate.

Examples 1 to 3 In producing the negative electrode current collector in Experimental Example 3, the carbonaceous material and the polyamide-imide solution were mixed at a solid content ratio of 95:
5, 90:10, 80:20 weight ratio, Experimental Example 3,
A non-aqueous electrolyte secondary battery was prepared according to Nos. 4 and 5. The characteristics are shown in Table 1.

Examples 4 to 6 In preparing the negative electrode current collector in Experimental Example 3, a carbonaceous material, a polyamide-imide resin, and an epoxy resin (Yukaka Shell Co .;
The mixing ratio of Epicoat 154) is 95: 4 in terms of solid content ratio.
5: 0.5, 95: 3.5: 1.5, 95: 2.5:
A non-aqueous electrolyte secondary battery was prepared according to Experimental Examples 3, 4, and 5 with a weight ratio of 2.5. The characteristics are shown in Table 1.

Comparative Example 1 When a negative electrode current collector was prepared in Experimental Example 3, the carbon material and the polyamide-imide resin were mixed at a solid content ratio of 97: 3.
A negative electrode current collector was prepared as a weight ratio, and an electrode body was tried to be prepared according to Experimental Examples 4 and 5, but cracking and peeling occurred on the negative electrode current collector during the winding operation, making it unusable.

Comparative Example 2 When a negative electrode current collector was prepared in Experimental Example 3, the carbonaceous material and the polyamide-imide resin were mixed at a solid content ratio of 75: 2.
A negative electrode current collector was prepared in a weight ratio of 5 to prepare non-aqueous electrolyte secondary batteries according to Experimental Examples 4 and 5. The characteristics are shown in Table 1.

Comparative Example 3 When a negative electrode current collector was prepared in Experimental Example 3, the carbonaceous material, the polyamide-imide resin, and the Epicoat 154 were mixed at a solid content ratio of 95: 2: 3 by weight. The compatibility between the resin and Epicoat 154 was poor, the carbonaceous material was not dispersed, and the copper foil could not be applied uniformly.

Comparative Example 4 A polyamideimide resin was synthesized under the same conditions as in Experimental Example 1 by charging 288 g of trimellitic anhydride, 250 g of diphenylmethane diisocyanate and 531 g of N-methyl-2pyrrolidone in a reaction vessel. The logarithmic viscosity of the obtained polyamide-imide was 0.25 dl / g. Using this polyamideimide resin, an attempt was made to make a non-aqueous electrolyte secondary battery by the same method as in Example 1, but during the winding operation, the negative electrode current collector became cracked and peeled off, making it unusable. It was

[0042]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Yamaguchi 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd.

Claims (3)

[Claims] 1. A non-aqueous solution comprising a negative electrode including a negative electrode mixture layer containing at least a carbon material as a negative electrode active material supporting material and a binder resin, a positive electrode including a positive electrode active material and a binder resin, and a non-aqueous electrolyte. In the electrolyte secondary battery, the binder resin is a polyamide-imide resin having an inherent viscosity of 0.3 dl / g or more, and the content of the binder resin in the negative electrode mixture is 5% by weight or more and 20% by weight.
The following are non-aqueous electrolyte secondary batteries. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the binder resin is a polyamideimide resin synthesized from trimellitic anhydride and diphenylmethane 4,4′diisocyanate. 3. The binder resin is a polyamide-imide resin mixed with a polyfunctional epoxy compound, and the content of the polyfunctional epoxy resin in the binder resin is 3% by weight or more and 50% by weight or less. The non-aqueous electrolyte secondary battery according to claim 1 or 2.