JP2000200608A - Nonaqueous-electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous-electrolyte secondary battery excellent in adhesiveness of an active material to metallic foil, having little reduction in capacitance owing to a binder having large flexibility, relieved of breakage, etc., of electrodes if a spirally wound electrode is employed, and excellent in safety. SOLUTION: In a nonaqueous-electrolyte secondary battery having a positive electrode and negative electrode with a separator impregnated with a nonaqueous electrolytic solution interposed between them, the positive electrode and negative electrode are each made up of a conductive substrate and a coating film formed thereon and containing an electrode active material and a binder, and this nonaqueous-electrolyte secondary battery is characterized in that the binder is a urethane resin that contains aromatic imide groups and soft segments capable of forming a single polymer having a glass-transition point of 30 deg.C or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte using a resin containing an aromatic imide group and a soft segment capable of forming a polymer having a glass transition point of 30 ° C. or lower as a binder for an electrode coating film. Related to secondary batteries.

[0002]

2. Description of the Related Art In recent years, with the spread of portable electronic devices such as portable video cameras and portable personal computers, there is a strong demand for small, lightweight, and high energy density batteries as mobile power supplies.

As a battery to be suspended, research and development of a non-aqueous electrolyte secondary battery using lithium or a lithium alloy for a negative electrode have been actively conducted. This secondary battery has excellent features of high energy density, low self-discharge, and light weight. However, such a secondary battery uses a nonaqueous electrolyte secondary battery using such lithium or lithium alloy as a negative electrode. The next battery is
At the time of charging, lithium grows in a dendrite crystal at the negative electrode, and with the progress of the charge / discharge cycle, this dendrite-like crystal reaches the positive electrode and has the disadvantage of causing an internal short circuit. It was a major obstacle.

Therefore, in order to solve such a problem, a negative electrode in which lithium, which is a negative electrode active material, is supported on a carbon material, which is a negative electrode active material carrier, by a chemical or physical method, A non-aqueous electrolyte secondary battery using a composite oxide of lithium as a positive electrode active material as a positive electrode has attracted attention.

In such a non-aqueous electrolyte secondary battery, lithium supported on the carbon material of the negative electrode, lithium contained in the crystal structure of the lithium composite oxide of the positive electrode, and lithium contained in the electrolyte Each of the lithium dissolved in the negative electrode is doped between the carbon layers of the carbon material of the negative electrode during charging, and is undoped from the carbon layer during discharging. No crystal-like precipitation is observed, an internal short circuit hardly occurs, and relatively good charge / discharge characteristics are exhibited. further,
It has the advantages of high energy density and light weight.

On the other hand, since many portable electronic devices consume relatively large current, the mobile power supply of such devices needs to withstand heavy loads. Therefore, as the battery structure, a spiral electrode structure in which the positive electrode and the negative electrode are formed in a belt shape and wound in the length direction thereof through a belt-shaped separator is used. preferable.

[0007] By adopting such an electrode structure, the electrode area can be increased and a limited space can be filled with as much active material as possible, so that a heavy load can be used. In order to take such a structure, it is preferable that the positive electrode and the negative electrode have flexibility and are in the form of a thin film.

As a non-aqueous electrolyte secondary battery having a flexible and thin-film electrode, for example, Japanese Patent Application Laid-Open No. 7-122
No. 303 discloses that a negative electrode is formed by providing a carbon material on a metal foil with a fluorine-containing polyimide as a binder, and a composite oxide of lithium is polyvinylidene fluoride as a binder.
(Hereinafter referred to as PVdF) discloses a non-aqueous electrolyte secondary battery having a positive electrode provided on a metal foil.

However, polyimide has a strong adhesiveness between the substance and the metal foil, and the above-mentioned problem of capacity reduction hardly occurs. However, polyimide has a high rigidity, so that if a spiral wound electrode body structure is employed, cracks and the like occur in the electrodes, which causes a problem that the characteristics of the nonaqueous electrolyte secondary battery are deteriorated.

Further, when a fluororesin is used as a binder, the adhesiveness between the active material and the metal foil is weak, and when charge and discharge are repeated several hundred times or more, the carbon material or the composite oxide becomes a metal. The capacity is reduced due to peeling off from the foil or cracking on the electrode surface.
As described in Japanese Patent No. 3031, a fluorine-based resin is decomposed and hydrogen fluoride is generated with an increase in battery temperature,
There is a problem in that it may react with lithium ions in the battery and cause damage or rupture of the battery.

[0011]

SUMMARY OF THE INVENTION In view of the above problems of the conventional non-aqueous secondary battery, an object of the present invention is to provide a binder having excellent adhesiveness between an active material and a metal foil and having high flexibility. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery which has a small reduction in capacity, has no electrode cracking even when a spiral wound electrode structure is adopted, and is excellent in safety.

[0012]

In order to achieve the above object, according to the present invention, there is provided a non-aqueous electrolyte in which a positive electrode and a negative electrode are arranged via a separator impregnated with a non-aqueous electrolyte. In the secondary battery, the positive electrode and the negative electrode are each formed of a conductive substrate and a coating film formed thereon, which contains an electrode active material and a binder, wherein the binder is an aromatic imide group. And a soft segment capable of forming a polymer having a glass transition point of 30 ° C. or lower.

Further, the present invention according to claim 2 is characterized in that the urethane resin comprises (A) a dihydroxy compound represented by the following formula (1) or (2) and (B) a hydroxy group at both terminals. A non-aqueous electrolyte secondary battery comprising a polymer having a number average molecular weight of 300 to 10,000 and a glass transition temperature of 30 ° C. or lower, and (C) a polyfunctional isocyanate. .

Embedded image (R1 and R2 are, independently of each other, residues obtained by removing an amino group and a hydroxy group from a hydroxy compound having one amino group having a molecular weight of 47 to 300.)

Embedded image (R3 is one selected from hydrogen, a hydrocarbon group and a substituted hydrocarbon group, and R4 and R5 are each independently selected from a hydroxy compound having one amino group having a molecular weight of 47 to 300 and an amino group. It is a residue excluding a hydroxy group.)

In the present invention, as the aromatic imide group, one represented by the general formula [A1] is usually used.

Embedded image (X1 and X2 each independently represent hydrogen, an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a substituted aliphatic hydrocarbon group, a substituted aromatic hydrocarbon group, an amide group, an imide group, a carbonyl group, an ether group, X1 is at least one selected from a thiol group, a sulfonyl group and a sulfone group.
And X2, X2 and X3, and X3 and X4 may be bonded and cyclized. However, when X2 and X3 are bonded to form an imide ring, X1 and X2 and X3 and X4 are not cyclized. )

Of these, preferred aromatic imide groups are those represented by the general formula [A2] or [A3].

Embedded image

Embedded image (Y is selected from hydrogen, aliphatic hydrocarbon group, aromatic hydrocarbon group, substituted aliphatic hydrocarbon group, substituted aromatic hydrocarbon group, carbonyl group, ether group, thiol group, sulfonyl group and sulfone group One kind)

In the urethane resin binder used in the present invention, the aromatic imide group is rigid,
It contains a soft segment capable of forming a homopolymer having a glass transition point of 30 ° C. or lower in order to impart flexibility. The aromatic imide group is contained in the main chain and / or the side chain of the binder resin.

Soft segments capable of forming a polymer having a glass transition point of 30 ° C. or lower include those having an aliphatic polyester, polylactone, aliphatic polycarbonate, polysiloxane, polyether, polyolefin, polybutadiene, polyisoprene, or polychloroprene structure. Is preferred. These may be used alone or in combination of two or more.

The resin used as the binder of the non-aqueous electrolyte secondary battery of the present invention has a flexural modulus of 10,000 kgf / c.
Desirably, it is less than m2. Above this, the effect of softening the electrodes is reduced.

The urethane resin binder used in the present invention comprises (A) a dihydroxy compound represented by the general formula (1) or (2), and (B)
Has a hydroxy group at both ends, number average molecular weight 300 ~
It is preferable that the polymer comprises a polymer having a glass transition temperature of 30 ° C. or lower at 10,000 and (C) a polyfunctional isocyanate.

Embedded image (R1 and R2 are, independently of each other, residues obtained by removing an amino group and a hydroxy group from a hydroxy compound having one amino group having a molecular weight of 47 to 300)

Embedded image (R3 is one selected from hydrogen, a hydrocarbon group and a substituted hydrocarbon group, and R4 and R5 are each independently
It is a residue obtained by removing an amino group and a hydroxy group from a hydroxy compound having one amino group having a molecular weight of 47 to 300. )

The dihydroxy compound represented by the general formula (1) or (2) can be produced by a known method. For example, an aromatic tetracarboxylic acid or a reactive derivative of the aromatic tetracarboxylic acid such as an anhydride, an acid chloride, or an alkyl ester thereof, and a molecular weight of 47 to 3
The compound can be prepared by reacting the compound with a hydroxy compound having one primary amino group. The above formula General formula (1)
When the molecular weight of the hydroxy compound having one amino group used for producing the dihydroxy compound represented by the formula (1) exceeds 300, the heat resistance of the obtained polyurethane decreases.

Examples of the aromatic tetracarboxylic acid or its anhydride include pyromellitic acid, 3,3 ′, 4,
4′-biphenyltetracarboxylic acid, 3,3 ′, 4
4'-benzophenonetetracarboxylic acid, 3,3 ',
4,4′-diphenylmethanetetracarboxylic acid, 3,
3 ', 4,4'-diphenylpropanetetracarboxylic acid, 3,3', 4,4'-diphenylethertetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7- Naphthalenetetracarboxylic acid,
1,2,5,6-naphthalenetetracarboxylic acid, 3,
4,9,10-perylenetetracarboxylic acid and anhydrides thereof.

The acid chlorides and alkyl esters of the aromatic tetracarboxylic acids include pyromellitic acid tetrachloride, pyromellitic acid tetramethyl ester,
Pyromellitic acid dimethyl ester dichloride. Above all, pyromellitic anhydride, 3,3 ', 4
4'-benzophenonetetracarboxylic anhydride, 3,
Preferred are 3 ', 4,4'-diphenylpropanetetracarboxylic anhydride and 3,3', 4,4'-diphenylethertetracarboxylic anhydride. These may be used alone or in combination of two or more.

The above amino group having a molecular weight of 47 to 300 is
As the hydroxy compound having the same, amino methanol,
2-aminoethanol, 3-aminopropanol, 4-
Aminobutanol, 5-aminopentanol, 3-amino-2,2-dimethyl-1-propanol, 6-aminohexanol, 6-amino-2-methyl-2-heptanol, 4-aminocyclohexanol, 3-aminophenol , 4-aminophenol, 4-aminocresol, 3-aminobenzyl alcohol, 4-aminophenethyl alcohol and the like. Among them, aminomethanol, 2-aminoethanol, 3-aminopropanol,
4-aminobutanol, 5-aminopentanol, 6-
Aminohexanol and 4-aminophenol are preferred. These may be used alone or in combination of two or more.

The reaction for obtaining the dihydroxy compound represented by the general formula (1) or (2) is performed by a known method. For example, the above-mentioned aromatic tetracarboxylic acid or a reactive derivative thereof, preferably, an amino group of 2 molar equivalents or more with respect to the aromatic tetracarboxylic dianhydride is added to 1
A hydroxy compound having the same is added, and under an inert gas atmosphere at 100 to 300 ° C., preferably under normal pressure, 120 to 25 ° C.
It is performed by heating at 0 ° C. This reaction can be performed without a solvent, but various inert solvents may be used. As this solvent, toluene, xylene, dimethylsulfoxide, sulfolane, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, diphenylsulfone, N, N'-dimethylimidazolidinone and the like are suitably used.

The solvent does not necessarily dissolve the aromatic tetracarboxylic acid and its reactive derivative, and the reaction proceeds sufficiently even in a suspended state or a slurry state. The reaction time is usually 1 to 24 hours, preferably 2 to 18 hours at the above temperature.

After completion of the reaction, the reaction mixture is cooled, filtered and washed to obtain the desired product. The operation of the washing solution is appropriately selected depending on the divalent hydroxy compound and the solvent used. The component (B) in the present invention is a polymer having hydroxy groups at both ends, a number average molecular weight of 300 to 10,000, and a glass transition temperature of 30 ° C or lower.

The component (B) includes polyester, polylactone, polycarbonate, polysiloxane, polyether, polyolefin having hydroxyl groups at both ends,
Polybutadiene, polyisoprene, polychloroprene and the like are preferably used. These may be used alone or in combination of two or more.

The above-mentioned polyester has a dicarboxylic acid and a diol as main components. As the dicarboxylic acid, an aliphatic dicarboxylic acid is preferable, and for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, and sebacic acid are suitably used. These may be used alone or in combination of two or more. Glycol is preferably used as the diol, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol , Neopentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, cyclopentane-1,2-diol, cyclohexane -1,2-diol, cyclohexane-1,3-
Examples thereof include diol, cyclohexane-1,4-diol, cyclohexane-1,4-dimethanol, diethylene glycol, triethylene glycol, and the like. These may be used alone or in combination of two or more.

The polylactone is obtained by ring-opening polymerization of lactone to form an aliphatic chain. The lactone is preferably one having 4 or more carbon atoms in the ring, more preferably a 5- to 8-membered ring, such as ε-caprolactone, δ-valerolactone, γ-butyrolactone, and the like. They may be used alone or in combination of two or more.

The polycarbonate is preferably a polyalkylene carbonate, such as polyethylene carbonate,
Examples thereof include polypropylene carbonate, polytetramethylene carbonate, polyhexamethylene carbonate, and the like, and copolymers thereof. These may be used alone or in combination of two or more.

Examples of the polysiloxane include polydimethylsiloxane, polydiethylsiloxane, polydiphenylsiloxane, polymethylphenylsiloxane and the like, and copolymers thereof. These may be used alone or in combination of two or more.

The polyether is preferably a polyalkylene oxide. For example, homopolymers and copolymers such as polyethylene oxide, polypropylene oxide, polytetramethylene oxide, and polyhexamethylene oxide, and chain extension of these polyethers by carbonate bonds. These may be used alone or in combination of two or more.

The polyolefin preferably has a hydroxy group at both ends and contains at least one of the following components a), b) and c) as components.

Embedded image When the number average molecular weight of the component (B) is too small, the ability to impart flexibility to the resulting polyurethane decreases,
If it is too large, the reactivity is reduced, and the physical properties such as the mechanical strength of the obtained polyurethane are reduced.
000, preferably 400-5,000. More preferably, it is 500 to 2,500. (B)
The glass transition temperature (hereinafter, abbreviated as Tg) of the component is preferably 30 ° C or lower, more preferably -170 ° C to 0 ° C. Tg
If it is higher than 30 ° C., the bending elastic modulus of the formed resin increases, and the flexibility of the electrode decreases.

In the resin used as a binder of the non-aqueous electrolyte secondary battery of the present invention, a polyfunctional isocyanate is used as the component (C). As the polyfunctional isocyanate used as (C), any of an aromatic polyfunctional isocyanate and an aliphatic polyfunctional isocyanate can be used.

As the polyfunctional isocyanate, diisocyanate is mainly used. Examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, and tetramethyl xylene diisocyanate.

Examples of the aliphatic diisocyanate include 1,2-ethylene diisocyanate, 1,3-propylene diisocyanate, 1,4-butane diisocyanate, 1,6-hexamethylene diisocyanate,
4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), lysine diisocyanate, 1,3-di (isocyanatomethyl) cyclohexane, 1,4-di (isocyanatomethyl ) Cyclohexane, trimethylhexamethylene diisocyanate and the like. Further, those obtained by reacting the above-mentioned diisocyanate with an active hydrogen compound to protect the isocyanate group can also be used.

Examples of the active hydrogen compound include alcohols having 10 or less carbon atoms, phenols such as phenol and cresol, lactams such as ε-caprolactam, oximes, dialkyl malonate, alkyl acetylacetate and acetylacetone. Methylene compounds. The resin used as a binder for the non-aqueous electrolyte secondary battery of the present invention includes, as a chain extender, aromatic diols and fats other than the dihydroxy compound represented by the general formula (1) or (2). Aromatic glycols, aromatic diamines, aliphatic diamines and the like may be contained as constituents.

Examples of the aromatic diol include hydroquinone, resorcin, chlorohydroquinone, bromohydroquinone, methylhydroquinone, phenylhydroquinone, methoxyhydroquinone, phenoxyhydronone, 4,4 '.
-Dihydroxybiphenyl, 4,4'-dihydroxydiphenylether, 4,4'-dihydroxydiphenylsulfide, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxybenzophenone, 4,
4′-dihydroxydiphenylmethane, bisphenol A, 1,1-di (4-hydroxyphenyl) cyclohexane, 1,2-bis (4-hydroxyphenoxy) ethane, 1,4-dihydroxynaphthalene, 2,6-dihydroxynaphthalene and the like can give. These may be used alone or in combination of two or more.

Examples of the aliphatic glycol include ethylene glycol, 1,2-propylene glycol,
1,3-propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8- Octanediol, 1,9-nonanediol, 1,10-decanediol, cyclopentane-1,2-diol, cyclohexane-1,2-diol, cyclohexane-1,3-diol, cyclohexane-1,4-diol, Examples thereof include cyclohexane-1,4-dimethanol, diethylene glycol, and triethylene glycol. These may be used alone or in combination of two or more.

As the aromatic diamine, for example,
4-diaminobenzene, 4,4'-bisaniline, 4,
4'-Diaminodiphenylmethane, 3,3'-dichloro-4,4'-diaminodiphenylmethane and the like are used. Examples of the aliphatic diamine include ethylene diamine, 1,2-propylene diamine, 1,3-propylene diamine, 1,4-butylenediamine, 1,5-pentamethylene diamine, 1,6-hexamethylene diamine, and 1,7. -Heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine,
1,10-decamethylenediamine and the like. The above aromatic diol, aliphatic glycol, aromatic diamine and aliphatic diamine may be used alone or in combination of two or more.

When the above aromatic diol, aliphatic glycol, aromatic diamine and aliphatic diamine are used,
These compounds are combined with the above general formula (1) or general formula (2)
The aromatic diol, aliphatic glycol, aromatic diamine and aliphatic diamine are preferably used in a total amount of less than 95 mol%, more preferably less than 90 mol%, based on the total number of moles of the dihydroxy compound represented by the formula (1). More preferably, it is more preferably used in an amount of less than 80 mol%. When the aromatic diol, the aliphatic glycol, the aromatic diamine and the aliphatic diamine are used in a total amount of 95 mol% or more, the heat resistance of the obtained polyurethane and the compression set at a high temperature are reduced.

The resin used as the binder in the non-aqueous electrolyte secondary battery of the present invention may contain a small amount of a trifunctional or higher functional isocyanate compound or a trifunctional or higher functional chain extender. The amount of trifunctional or higher functional isocyanate compound is 3 mol% or less based on 100 mol% of diisocyanate compound.
5 mol% or less with respect to 00 mol%. When the amount of either the trifunctional or higher functional isocyanate compound or the trifunctional or higher functional chain extender exceeds these amounts, the obtained resin is cross-linked to disperse the active material and the binder in the electrode coating solution. Decrease.

The trifunctional or higher functional isocyanate compound includes a cyclic trimer of the above diisocyanate compound,
Triphenylmethane-4,4 ′, 4 ″ -triisocyanate, carbodiimide-modified diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, and the like are used. As the above-mentioned trifunctional or higher functional chain extender, trimethylolpropane, glycerin, hydroxyhydroquinone, pentaerythritol and the like are used.

In the resin used as a binder of the non-aqueous electrolyte secondary battery of the present invention, the components (A), (B) and (C) are used as constituents in a molar ratio of (C) /
(B) is 0.97 to 6.0, preferably 0.97
~ 3.1 and the molar ratio of (C) / [(A) +
(B)] is set to 0.9 to 1.1. When a bifunctional chain extender other than the component (A) is used, the total number of moles of the component (A) and the difunctional chain extender other than the component (A) and the mole number of the component (B) is used. The reaction is performed such that the molar ratio of the component (C) is 0.9 to 1.1. When a trifunctional or higher functional chain extender is used, 1 mol of the trifunctional or higher functional chain extender is used as 1 mol (the number of functional groups of the trifunctional or higher functional chain extender / 2).
The above molar ratio is calculated as mole.

When a trifunctional or higher functional isocyanate is used, one mole of the trifunctional or higher functional isocyanate is converted into (the number of functional groups of the trifunctional or higher functional chain extender / 2) mol, and this value and the component (C) component are converted. The above molar ratio is calculated using the sum with the number of moles. When the molar ratio of (C) / (B) is less than 0.97, the adhesiveness between the binder and the active material is reduced. When the molar ratio is more than 6.0, the flexural modulus is increased, and the flexibility of the electrode is reduced. descend.
When the molar ratio of (C) / [(A) + (B)] is less than 0.9, the molecular weight of the resin used as the binder of the non-aqueous electrolyte secondary battery of the present invention is not sufficiently large, and When the ratio exceeds 1.1, gelation occurs during polymerization, and the dispersibility of the active material and the binder in the electrode coating solution decreases.

The urethane resin as a binder in the present invention desirably has an intrinsic viscosity of 0.3 dl / g to 6.0 dl / g measured in N, N'-dimethylformamide at 30 ° C. More preferably, it is 0.5 to 4.0 dl / g. When the intrinsic viscosity is less than 0.3 dl / g, the viscosity of the electrode coating solution is reduced, and sedimentation of the active material occurs. The heat resistance and mechanical properties of the obtained thermoplastic polyurethane decrease, and if it exceeds 6.0 dl / g, the viscosity of the coating solution for electrodes becomes high and coating becomes difficult.

The method for producing the urethane resin is not particularly limited, and includes, for example, a stirring blade, a raw material inlet, a gas blowing port, and a pressure reducing port, and an inner wall made of a metal such as glass or stainless steel. The reaction can be performed using a reaction vessel, extruder, kneader, or the like that can control the temperature within a range.

A dihydroxy compound represented by the general formula (1) or (2) as the component (A) or a chain extender other than these, a polymer of the component (B),
As a method for reacting the diisocyanate compound or the trifunctional or higher isocyanate compound as the component (C), a conventionally known method can be used. In particular, after the component (B) and the component (C) and the trifunctional or higher isocyanate compound are reacted in the first step to synthesize a prepolymer of both terminal isocyanates, the component (A) is added in the second step, A method in which the prepolymer and the component (A) are reacted is preferably a method in which the obtained thermoplastic urethane resin has improved blockability and a high molecular weight product is obtained.

In the above method, the reaction temperature in the first stage is suitably from 50 ° C. to 200 ° C. Preferably 70 ° C
190 ° C. When the temperature is lower than 50 ° C., the reaction hardly proceeds. When the temperature is higher than 200 ° C., the isocyanate partially evaporates or decomposes, so that a polymer having sufficient strength cannot be obtained. As the reaction solvent, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, diphenylsulfone, N, N'-dimethylimidazoline, tetrahydrofuran and the like are preferably used, but the reaction proceeds without any problem even in the absence of a solvent. . The reaction time is preferably from 2 minutes to 2 hours. If the time is less than 2 minutes, the reaction does not proceed sufficiently. If the time exceeds 2 hours, the product causes a side reaction.

In the above method, the reaction temperature in the second step is from 100 ° C. to 280 ° C., preferably from 100 ° C. to 2 ° C.
30 ° C. When the temperature is lower than 100 ° C., the reaction becomes slow. When the temperature is higher than 280 ° C., the produced polymer is partially decomposed and a polymer having sufficient strength cannot be obtained.
The component (A) is preferably added by dissolving the component (A) in a polar solvent in advance. As the polar solvent, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, diphenylsulfone, N, N'-dimethylimidazoline, tetrahydrofuran and the like are preferably used. In the method of adding the polar solvent solution of the component (A), the reaction proceeds favorably in a temperature range of 100 ° C to 190 ° C.

The reaction time is preferably from 10 minutes to 6 hours. 1
If the time is less than 0 minutes, the reaction does not proceed sufficiently, and if it is 6 hours or more, the product is decomposed. Preferably, 20 minutes to 4.5 hours are suitable.

The chain extender may be added at the first stage, may be added at the same time as the component (A) at the second stage, or may be added at the final stage of the reaction. The addition of the chain extender increases the molecular weight of the polymer and increases the viscosity of the reaction system. Therefore, in order to uniformly and efficiently react the component (A), it is preferable to add the component at the final stage of the reaction. The above reaction is preferably carried out in an inert gas such as dry nitrogen, argon and xenon. This is effective for suppressing decomposition of the product and deactivation of the isocyanate group.

Further, a catalyst can be used in the above reaction. Preferred catalysts are diacyl stannous, tetraacyl stannic, dibutyltin oxide, dibutyltin dilaurate, dimethyltin malate, tin dioctanoate, tin tetraacetate, stannas octoate, triethylenediamine, diethylenediamine, triethylamine, metal naphthenate. Octylic acid metal salts, triisobutylaluminum, tetrabutyltitanate, calcium acetate, germanium dioxide, and antimony trioxide. Two or more of these catalysts may be used in combination.

The above binder is mixed with a positive electrode active material or a negative electrode active material to prepare a positive electrode coating solution or a negative electrode coating solution. The method of mixing is not particularly limited, and a planetary stirring device, a planetary mixer, a disper, a sand mill, a ball mill, a kneader, and the like can be used. The positive or negative electrode can be obtained by applying the obtained positive electrode coating solution or negative electrode coating solution on a conductive substrate to form an electrode coating film.

A metal foil is used as the conductive substrate. The material of the metal foil is not particularly limited, and examples thereof include gold, silver, copper, nickel, stainless steel, aluminum, and titanium. Among them, stainless steel, aluminum, titanium and the like are preferable for the positive electrode, and copper is preferable for the negative electrode. The thickness of the metal foil used as the conductive substrate is preferably several μm to several hundred μm.

The coating solution for the negative electrode is formed from a mixture of a crystalline or low-crystalline carbon material and a binder. The crystalline or low-crystalline carbon material is used as a negative electrode active material.

As the crystalline carbon material, those having a plane spacing of (002) plane in X-ray diffraction of 3.7 ° or more are preferable. When the plane spacing is less than 3.7 °, the doping amount of lithium decreases, and the current capacity per unit weight of carbon decreases.

As the crystalline carbon material, for example,
Coke such as pitch coke and needle coke; carbon fiber, artificial graphite, natural graphite and the like.
The crystalline carbon material is, for example, 700 to 3,000.
It is obtained by firing and carbonizing an organic material at a temperature of ° C.

Examples of the organic material include a furan resin consisting of a homopolymer of furfuryl alcohol or furfural; a furan resin consisting of a copolymer of furfuryl alcohol and furfural; and acrylic resins such as cellulose, phenolic resins and polyacrylonitrile;
Examples thereof include vinyl halide resins such as vinyl chloride resins, polyamide imide resins, polyamide resins, and organic polymer compounds such as polyacetylene and polyparaphenylene.
Among them, a furan resin composed of a homopolymer of furfuryl alcohol or furfural and a furan resin composed of a copolymer of furfuryl alcohol and furfural are preferably used.

The organic material has a ratio of hydrogen atom to carbon atom (hydrogen atom / carbon atom) of 0.6 to 0.5.
By using a petroleum pitch of No. 8 and subjecting it to oxygen crosslinking to introduce a functional group containing oxygen, a precursor having an oxygen content of 10 to 20% by weight can be used. A crystalline carbon material obtained by baking this precursor is also suitably used as the negative electrode active material.

Further, as the organic material, for example, two or more monocyclic hydrocarbon compounds having three or more ring members such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, pyrylene, pentaphene, and pentacene can be used. Condensed condensed cyclic hydrocarbon compounds and derivatives thereof; three- or more-membered heteromonocyclic compounds such as indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and Condensed heterocyclic compounds formed by condensing at least two or more heterocyclic monocyclic compounds having at least two or three or more membered rings with one or more monocyclic hydrocarbon compounds having at least three membered rings, and derivatives thereof, etc. May be used.

Examples of the low crystalline carbon material include a graphitizable carbon material and a non-graphitizable carbon material. The graphitizable carbon material is obtained, for example, by using tar pitch obtained from petroleum or coal as a raw material and subjecting the raw material to heat treatment at 500 to 1,000 ° C. The non-graphitizable carbon material is obtained by, for example, firing and carbonizing an organic compound such as a phenol resin, and preferably has a turbostratic structure in which carbon net surfaces are randomly stacked.
This is because graphitization does not proceed even if the heat treatment temperature is increased, and the interlayer distance is considerably wider than natural graphite.

The above-mentioned crystalline or low-crystalline carbon material and the above-mentioned binder are dispersed in an organic solvent to form a slurry, which is then coated on a metal foil and dried to form an electrode coating film. Thereby, a negative electrode for a secondary battery is obtained. The organic solvent used here is not particularly limited, and for example, N-methylpyrrolidone, N, N-dimethylformamide, N,
N-dimethylacetamide and the like.

The amount of the binder in the negative electrode is preferably 0.5 to 20 parts by weight, more preferably 0.7 to 10 parts by weight, based on 100 parts by weight of the carbon material. When the amount is less than 0.5 part by weight, it is difficult to apply the carbon material to the metal foil, and when the amount exceeds 20 parts by weight, the capacity as a secondary battery is reduced.

When the above-mentioned active material is a positive electrode, the general formula L
iMO2 (wherein, M represents at least one selected from the group consisting of Co, Ni, Mn and V), Lix
MyMn2-y O4 (where M is Cr, Co, Ni, M
n represents at least one selected from the group consisting of n. 0
<X ≦ 1, 0 <y ≦ 2) or a composite oxide represented by LiVO5 is used.

The composite oxide represented by LiMO 2 is not particularly limited, and examples thereof include a lithium-cobalt composite oxide, a lithium-nickel composite oxide, a lithium-cobalt-nickel composite oxide, and a lithium-manganese composite oxide. And a lithium-vanadium composite oxide. The composite oxide represented by Lix My Mn2-y O4 is not particularly limited, and examples thereof include lithium-manganese-chromium composite oxide, lithium-manganese-cobalt composite oxide, and lithium-manganese-nickel composite oxide. No. These may be used alone or in combination of two or more. When two or more of the above lithium oxides are used in combination, they may be used in the form of a mixture or may be used as a solid solution.

In the present invention, lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium
Cobalt / nickel composite oxide and lithium / manganese composite oxide are preferably used. These composite oxides may be mixed with an electron conductive auxiliary such as graphite, carbon black, and acetylene black.

A slurry prepared by dispersing the above-mentioned composite oxide and the above-mentioned binder in an organic solvent or the like is coated on a metal foil and dried to form a coating film for an electrode. To obtain a positive electrode.

The compounding amount of the binder in the positive electrode is preferably 0.5 to 20 parts by weight, more preferably 0.7 to 10 parts by weight, based on 100 parts by weight of the composite oxide. If the compounding amount is less than 0.5 part by weight, it becomes difficult to apply the composite oxide to a metal foil, and if it exceeds 20 parts by weight, the capacity as a secondary battery decreases.

The method for applying the above-mentioned coating liquid to the above-mentioned current collector is not particularly limited, and may be a doctor blade, a knife coater,
Applicator, comma coater, gravure coater,
Roll coaters, lip coaters, etc. can be used. When the electrode coating film is formed by lamination, these coating methods are appropriately combined, for example, a simultaneous multilayer coating method (wet-on-wet), a sequential multilayer coating method (wet-on-dry), and the like. May be adopted.

The drying method is not particularly limited, and hot air, infrared rays, far infrared rays and the like can be used. The temperature is preferably 30 to 200C, more preferably 50 to 180C, and 80 to 16C.
0 ° C. is more preferred. Further, drying under reduced pressure can be further performed as necessary. Further, a method of performing a strong pressure press using a roll press machine after forming the electrode coating film may be employed.

The shapes of the negative electrode and the positive electrode are not particularly limited, and may be any shape such as a sheet shape, a square shape, and a cylindrical shape. In the nonaqueous electrolyte secondary battery of the present invention, the negative and positive electrodes are arranged so as to face each other via a separator impregnated with an electrolytic solution.

The separator is preferably made of a material which is excellent in electrolyte impregnation and liquid retention. Such a material is not particularly limited, and is, for example, a nonwoven fabric of a polyolefin resin; a thickness of 10 to 50 μm, and an aperture ratio of 30 to 70.
%, A microporous polypropylene film, a microporous polyethylene film, etc., and a multilayer film of the above materials.

As the electrolytic solution, a solution obtained by dissolving an electrolyte in an organic solvent is used. The organic solvent is not particularly limited, but, for example, carbonates, sulfolane, chlorinated hydrocarbons, ethers, esters, ketones, lactones, nitriles and the like are used. Specifically, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane,
1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-
1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like, which may be used alone,
Two or more kinds may be used in combination.

The electrolyte is not particularly limited. For example, LiClO 4, LiPF 6, LiBF 4, LiB
Ph4 (wherein Ph represents a phenyl group), LiCl,
LiBr, MeSO3 Li (where Me represents a methyl group), CF3 SO3, etc., may be used alone or in combination of two or more.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode and the negative electrode are formed from an electrode coating solution containing a binder and a conductive substrate, and the binder has an aromatic imide group. In addition to containing the resin, the resin has a low flexural modulus, so it has excellent adhesiveness between the active material and the binder, and the electrode has flexibility, so that the capacity decreases due to peeling of the coating film containing the active material. Even if a spiral wound electrode body structure is adopted, the electrode is free from cracks and the like, and safety is excellent.

[0077]

EXAMPLES (Examples) Hereinafter, the present invention will be described based on examples. Physical properties were measured by the following methods. [Tg] Differential scanning calorimeter (DSC-22 manufactured by Seiko Denshi)
0C) and the temperature was increased at a rate of 5 ° C./min. [Number average molecular weight] The number average molecular weight in terms of polystyrene was determined by gel filtration chromatography. [Intrinsic viscosity] Using an Ubbelohde viscometer, N, 30 ° C
Measured in N'-dimethylformamide. [Flexural modulus] Measured according to JIS K7171. The size of the test piece was a standard test piece and was prepared by press molding.

[Synthesis Example 1] <Synthesis of N, N'-di (2-hydroxyethyl) pyromellitic diimide> Pyromellitic dianhydride 218 g
(1 mol) and 134 g of 2-aminoethanol (2.2
Mol) was charged into a 1-liter glass flask equipped with a stirring blade, a raw material inlet, a gas inlet, and a reflux tower and capable of controlling the temperature from room temperature to 300 ° C., and stirred in a slurry state under a nitrogen atmosphere. Then, the mixture was heated at 175 ° C. for 2 hours while refluxing the generated steam. After cooling to room temperature, the obtained solid was recrystallized from N, N'-dimethylformamide (hereinafter abbreviated as DMF), and the obtained crystal was washed with a small amount of DMF, then with water, and then at 100 ° C. After drying under reduced pressure, red crystals were obtained. The melting point of the crystal was 281 ° C., the yield was 93%, and the proton nuclear magnetic resonance spectrum characteristic absorption value (at room temperature in deuterated dimethyl sulfoxide) was as follows. Methylene group 3.7 ppm Hydroxy group 4.83 ppm Phenylene group 8.2 ppm

[Synthesis Example 2] <Synthesis of urethane resin binder (1)> 400 g of a polyolefin having a hydroxyl group at both ends and having a number average molecular weight of about 2,000 (manufactured by Mitsubishi Chemical; polytail HA, Tg = -126 ° C.)
(0.2 mol) and 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as MDI) 100 g (0.4
mol) was stirred from room temperature to 300 ° C. in a 10 liter capacity equipped with a stirring blade, a raw material inlet, a gas inlet, and a reflux tower.
And the reaction was carried out at 180 ° C. for 20 minutes under a dry nitrogen atmosphere.

Thereafter, 60.8 g of the above N, N'-di (2-hydroxyethyl) pyromellitic diimide (0.
2 mol) of N-methylpyrrolidone
(Hereinafter referred to as NMP) together with the reaction system.
For 1.5 hours. A viscous fluid was obtained as the reaction proceeded. Further, NMP was added to adjust the solid content to 10% by weight. When the solid content was recovered and the intrinsic viscosity was measured, it was 2.1 dl / g, and the flexural modulus was 1100.
kgf / cm2.

[Synthesis Example 3] <Synthesis of Urethane Resin Binder (2)> 100 g of a polyolefin having a hydroxyl group at both ends and having a number average molecular weight of about 2,000 (manufactured by Mitsubishi Chemical; polytail HA, Tg = -126 ° C.)
(0.05 mol), 50 g (0.2 mol) of MDI, 45.6 g (0.15 mol) of N, N'-di (2-hydroxyethyl) pyromellitic diimide, and 0.5 liter of NMP As in the case of 2, the solid content was finally adjusted to 10% by weight. The solid content was recovered and the intrinsic viscosity was measured to be 3.3 dl / g, and the flexural modulus was 8
000 kgf / cm2.

Example 1 Natural graphite (“L” manufactured by Nippon Graphite Co., Ltd.)
B-CG ", a negative electrode active material) powder (95 parts by weight), the binder (1) solution (50 parts by weight), and NMP (210 parts by weight) were mixed and dispersed to form a slurry-like negative electrode coating solution. I got This negative electrode coating solution was applied to a copper foil having a thickness of 15 μm, and then dried at 140 ° C. in an air circulation oven to produce a negative electrode.

Separately, 0.5 mol of carbon lithium and 1 mol of carbon cobalt were mixed and calcined in air at 900 ° C. for 5 hours to obtain LiCoO 2. Li obtained
90 parts by weight of CoO2 and 5 parts by weight of graphite as a conductive agent were mixed and dispersed in 45 parts by weight of the binder solution and 50 parts by weight of NMP to obtain a slurry-like coating solution for a positive electrode. The coating solution for a positive electrode was applied to a copper foil having a thickness of 15 μm, and then dried at 140 ° C. in an air-circulating oven to prepare a positive electrode.

The above-mentioned negative electrode and positive electrode were arranged via a microporous propylene film separator, and a nonaqueous electrolytic solution (1 mol of LiPF6 per 1 liter of an equal mixture of ethylene carbonate and dimethyl carbonate) was used. ) To prepare a test battery.

Example 2 In obtaining a coating liquid for a negative electrode,
Natural graphite ("LB-CG", manufactured by Nippon Graphite Co., Ltd., negative electrode active material)
92 parts by weight of the powder, 80 parts by weight of the binder solution, and NMP
A test battery was prepared in the same manner as in Example 1, except that 30 parts by weight were mixed and dispersed.

Example 3 In obtaining a coating solution for a negative electrode,
Natural graphite ("LB-CG", manufactured by Nippon Graphite Co., Ltd., negative electrode active material)
Of the above binder (2) and 90 parts by weight of NMP were mixed and dispersed.
A test battery was produced in the same manner as in Example 1.

(Comparative Example 1) Polyimide ("95V1001" manufactured by Sony Chemical Co., Ltd.) was used alone as the binder for the positive and negative electrodes instead of the above-mentioned binder.
A test battery was produced in the same manner as in Example 1.

The performance of the test battery obtained above was evaluated with respect to the following items, and the results are shown in Table 1.

(1) Capacity maintenance rate (%) After charging the test battery at a constant voltage of 4.2 V for 5 hours, 1 m
The charge / discharge cycle was repeated with one cycle of discharging at a constant current of A / cm2 at a final voltage of 2.75 V. The discharge capacity at the 10th cycle and the discharge capacity at the 200th cycle were measured. And the ratio of the 100th cycle (200 cycles / 10 cycles) was expressed in percentage. (2) Adhesiveness of coating film The metal foil on which the electrode was prepared was placed on a stainless steel flat plate (I) having a semicircular groove with a radius of 0.5 mm, and the end from above had a radius of 0.3 mm. The flat plate (II) made of stainless steel rounded into a semicircle was pressed and bent so that the end thereof was fitted into the groove of the flat plate (I). Then, take out the metal foil, observe the adhesion state of the lowermost coating film in the bent and deformed part with a scanning microscope, and if it adheres without peeling, o, peeling is recognized even a little Was determined to be ×.

[0090]

[Table 1]

[0091]

The non-aqueous electrolyte secondary battery of the present invention has the above-mentioned constitution, and the binder contains an aromatic imide group and a soft segment capable of forming a polymer having a glass transition point of 30 ° C. or lower. In general, an aromatic polyimide portion having high rigidity is made of a resin having a low flexural modulus in combination with the characteristics of the soft segment, and has an active material and a conductive property inherent to an aromatic imide group. Since the electrode can exhibit excellent adhesiveness to the conductive substrate, the electrode has flexibility, a decrease in capacity due to peeling of the coating film containing the active material is small, and a spiral wound electrode structure is used. Even if it is taken, there is no breakage of the electrode and the like, and the safety is excellent. That is, the non-aqueous electrolyte secondary battery of the present invention is excellent in charge / discharge cycle characteristics, discharge capacity and charge / discharge characteristics, and also excellent in adhesion to a conductive substrate. Yes, it maintains a high capacity even after several hundred charge / discharge cycles. In addition, since the binder does not contain fluorine, rupture of the battery due to generation of hydrogen fluoride and the like are avoided,
Therefore, it can be suitably used for portable video cameras, portable personal computers, portable telephones, transceivers, cameras, headphone stereos, portable televisions and the like.

Continuation of the front page F term (reference) 5H003 AA04 AA06 BB01 BB05 BB11 BD01 5H029 AJ05 AJ11 AK03 AK18 AL06 AL07 AM02 AM03 AM04 AM05 AM07 DJ08 EJ12 HJ02

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a positive electrode and a negative electrode are arranged via a separator impregnated with a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are formed on a conductive substrate and on the conductive substrate. A urethane containing an aromatic imide group and a soft segment capable of forming a polymer having a glass transition point of 30 ° C. or lower, the coating comprising an electrode active material and a binder. A non-aqueous electrolyte secondary battery characterized by being a resin. 2. The urethane resin comprises: (A) a dihydroxy compound represented by the general formula (1) or (2); and (B) a hydroxyl group at both ends, and a number average molecular weight of 300 to A non-aqueous electrolyte secondary battery comprising a polymer having a glass transition temperature of 30 ° C. or lower at 10,000 and (C) a polyfunctional isocyanate. Embedded image (R1 and R2 are, independently of each other, residues obtained by removing an amino group and a hydroxy group from a hydroxy compound having one amino group having a molecular weight of 47 to 300). (R3 is one selected from hydrogen, a hydrocarbon group and a substituted hydrocarbon group, and R4 and R5 are each independently
It is a residue obtained by removing an amino group and a hydroxy group from a hydroxy compound having one amino group having a molecular weight of 47 to 300. )