JPH1197029A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve charge and discharge characteristics and the capacity maintaining ratio in long repeat use by improving the capacity through a process of making a lowermost layer film to be brought in contact with a conductive base body contains binder made of polyamide elastomer and an electron transmitting auxiliary material. SOLUTION: It is desirable that polyamide elastomer has the melting point of 140 deg.C or more, the crystal fusing heat value of 3 mj/mg or more, and the limiting viscosity (Ubbelohde's viscometer, ortho-chlorophenol solution, 30 deg.C) of 0.35 to 2 dL/g. Moreover, it is desirable that the elastomer is polyester amide formed by reacting either dicarboxylic acid to be expressed by the following formula I or diol to be expressed by the formula II and polyamide having the reduced viscosity (1 g/dL 98% sulfuric acid, 20 deg.C) of 0.5 to 7 dL/g. The formula I: HOOC-R<1> -COOH (R<1> is an alkylene group having the carbon numbers of 2 to 8), the formula II: HO-R<2> -OH (R<2> is an alkylene group having the carbon numbers of 2 to 6).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery having a high capacity and excellent charge / discharge characteristics.

[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, demand for batteries as a portable power supply has been rapidly increasing. Also, there is a very high demand for such batteries to be reduced in size, weight, and energy density.

[0003] A primary battery such as an alkaline manganese battery is used only as a single discharge as a mobile power source, and is disadvantageous in terms of cost and waste disposal. In addition, as a secondary battery that can be repeatedly charged and discharged,
Water-based batteries such as lead batteries and nickel-cadmium batteries are the mainstream, but these water-based batteries have excellent charge / discharge characteristics, but are not suitable for portable electronic devices in terms of battery weight and energy density. It cannot be said that the power supply has sufficiently satisfactory characteristics.

[0004] Therefore, as a secondary battery, research and development of a non-aqueous electrolyte secondary battery using lithium or a lithium alloy for a negative electrode has been actively conducted. This battery has excellent features of high energy density, low self-discharge, and light weight.

However, in such a nonaqueous electrolyte secondary battery using lithium or a lithium alloy for the negative electrode, lithium grows in a dendrite-like crystal at the negative electrode at the time of charging. There is a drawback that dendrite-like crystals reach the positive electrode and cause an internal short circuit, which has been a major obstacle to practical use.

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

In such a non-aqueous electrolyte secondary battery, a composite oxide crystal of lithium, which is previously supported on the carbon material of the negative electrode or supported on the carbon material when acting as a negative electrode, and lithium of the positive electrode, is used. Lithium contained in the structure and lithium dissolved in the electrolytic solution are doped into the carbon layer of the carbon material of the negative electrode during charging, and undoped from the carbon layer during discharging. For this reason, even when the charge / discharge cycle proceeds, no precipitation of dendrite-like crystals at the negative electrode is observed during charging, an internal short circuit hardly occurs, and relatively good charge / discharge characteristics are exhibited. It also has a high energy density and is lightweight.

[0008] Many portable electronic devices such as portable video cameras and portable personal computers consume relatively large current. Therefore, such a portable power supply for portable electronic devices needs to withstand heavy loads. Therefore, as the battery structure, a positive electrode and a negative electrode are formed in a strip shape, and a spiral wound electrode body structure formed by winding in the length direction through a strip separator is used. preferable. According to such a structure, the electrode area can be increased and the limited space can be filled with as much active material as possible, so that it can withstand use under heavy load. In order to take such a structure, the positive electrode and the negative electrode need to be flexible and have a thin film shape.

According to this method, an active material-containing slurry obtained by mixing a binder, an active material, an active material carrier and the like is applied to an electrode current collector such as a metal foil and then dried to form an electrode current collector. An active material-containing layer was formed. As such a binder, for example, polyvinylidene fluoride (Japanese Patent Laid-Open No. 4-249)
860), and a three-dimensional cross-linked body having polyglycerin as a main chain (Japanese Patent Application Laid-Open No. 4-308655).

However, in these non-aqueous electrolyte secondary batteries, when the charge and discharge are repeated several hundred times or more, the active material-containing layer repeatedly expands and contracts due to charge and discharge. Cracks are generated on the surface, so that the capacity is reduced, so that long-term repeated use has been difficult. In order to solve this problem, in order to enhance the adhesion between the active material-containing layer and a metal foil as a conductive substrate, JP-A-5-6766 discloses that the surface roughness of the metal foil is determined by the center line average roughness. It has been proposed to roughen the surface to an Ra of 0.15 μm or more. This is to prevent the active material-containing layer from dropping off or peeling off from the metal foil by roughening the surface of the metal foil and increasing the contact surface between the active material-containing layer and the metal foil. It is.

However, in this method, it is difficult to fill the paint to the bottom of the concave portion on the surface of the roughened metal foil. Therefore, the effect is obtained even though the surface is roughened and the surface area of the metal foil is increased. I couldn't. When the surface of the metal foil having a total thickness of about 20 μm or less is roughened to a center line average roughness Ra of 0.15 μm or more, the depth of the irregularities on the metal foil surface becomes approximately 10% of the total thickness of the metal foil. If the battery is charged and discharged several hundred times or more, mechanical fatigue accumulates on the metal foil as the conductive substrate, causing cracks and breaks, thereby deteriorating the capacity of the battery. was there.

[0012]

SUMMARY OF THE INVENTION Therefore, Japanese Patent Application Laid-Open No. Hei 8-3
No. 29928 discloses that the above-mentioned active material-containing layer is composed of a multilayer film composed of two or more layers, and the lowermost layer film in contact with the conductive substrate is formed of a binder, an electron conductive material having a particle diameter larger than the average thickness of the binder and the average thickness. A method of forming a film containing an auxiliary material has been proposed. However, even in this method, the adhesiveness between the conductive substrate and the active material-containing layer is not yet sufficient in order to follow the expansion and contraction of the active material-containing layer and to apply the flexibility required to form a spiral wound electrode body structure. Not enough.

The present invention solves the above problems and suppresses the separation of the active material-containing layer from the conductive substrate and the occurrence of cracks and breaks in the conductive substrate during charging and discharging, thereby achieving high capacity and high charging and discharging characteristics. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery which is excellent in durability and has a high capacity retention ratio even in long-term repeated use.

[0014]

The non-aqueous electrolyte secondary battery of the present invention has an electrode having a conductive substrate on which a coating containing a substance capable of doping and undoping lithium ions and a binder is formed. In the nonaqueous electrolyte secondary battery in which the coating film is composed of at least two multilayer films, the lowermost film in contact with the conductive substrate contains a binder made of a polyamide elastomer and an electron conduction aid. It is a thing.

The conductive substrate used in the present invention is not particularly limited. For example, gold, silver, copper, nickel,
And metal foils such as stainless steel, aluminum, and titanium. For the positive electrode, stainless steel, aluminum, titanium and the like are preferable, and for the negative electrode, copper and the like are preferable.
The metal foil having a thickness of several μm to several hundred μm is preferably used.

The electrode used in the present invention forms a coating containing a substance capable of doping and undoping lithium ions and a binder, and the coating comprises a multilayer film of at least two layers.

In the present invention, it is sufficient that either the positive electrode or the negative electrode has the above configuration, but in order to make the electrode more durable, both the positive electrode and the negative electrode have the above configuration. Is preferred.

As the material capable of doping and undoping lithium ions (hereinafter referred to as "active material"), those used in ordinary lithium secondary batteries can be used. LiMO ₂ (where M is
Co, Ni, represents at least one selected from the group consisting of Mn and _{V), Li x M y Mn} 2-y O 4 ( wherein,
M is, Co, represents at least one selected from the group consisting of Ni and Mn), the composite oxide is used which is represented by _{Li x V y Mn 2-y} O 5.

The composite oxide represented by LiMO ₂ is not particularly limited, and examples thereof include lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium-cobalt-nickel composite oxide, and lithium-manganese composite oxide. And lithium-vanadium composite oxide. These are used alone or as a mixture or a solid solution.

[0020] is not particularly restricted but includes composite oxide represented by the _{Li x M y Mn 2-y} O 4, for example, lithium
Manganese / chromium composite oxide, lithium / manganese / cobalt composite oxide, lithium / manganese / nickel composite oxide, and the like can be given. These are used alone or as a mixture or a solid solution.

Of these, lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium-cobalt-nickel composite oxide, and lithium-manganese composite oxide are preferably used.

Further, a conductive agent such as graphite or black carbon may be used in combination with these composite oxides.

As the negative electrode active material, lithium and its alloys, and crystalline or low-crystalline carbon materials are used.

The crystalline carbon material preferably has a (002) plane spacing of at least 3.7 angstroms in X-ray diffraction. If it is less than 3.7 angstroms, the doping amount of lithium is small, and the current capacity per unit weight of carbon is small. The crystalline carbon material is not particularly limited, and examples thereof include coke such as pitch coke and needle coke; carbon fiber, artificial graphite, and natural graphite.

The crystalline carbon material is, for example, 700 to
It can be produced by carbonizing an organic material by a method such as firing at a temperature of about 3000 ° C. The organic material is not particularly limited, for example, furan resin composed of a homopolymer of furfuryl alcohol or furfural, furan resin composed of a copolymer of furfuryl alcohol and furfural, cellulose, phenol resin, acrylic resin such as polyacrylonitrile, poly Examples thereof include a halogenated vinyl resin such as vinyl chloride, a polyamideimide resin, a polyamide resin, and an organic polymer compound such as polyacetylene and polyparaphenylene. Of these, a furan resin composed of a furfuryl alcohol or furfural homopolymer and a furan resin composed of a copolymer of furfuryl alcohol and furfural are preferably used.

Further, as the organic material, petroleum pitch having a hydrogen atom / carbon atom ratio of 0.6 to 0.8 is used,
By subjecting this to oxygen crosslinking for introducing a functional group containing oxygen, a precursor having an oxygen content of 10 to 20% by weight is obtained, and then a crystalline carbon material obtained by firing this precursor is also used. It is preferably used.

Further, as the organic material, for example, two or more monocyclic hydrocarbon compounds having three or more members such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, pyrylene, pentaphene and pentacene are 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 A fused heterocyclic compound, which is obtained by condensing at least two or more heterocyclic monocyclic compounds having three or more rings with one or more monocyclic hydrocarbon compounds having three or more rings, and derivatives thereof; It can also 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 by performing a heat treatment at 500 to 1000 ° C. using tar pitch obtained from petroleum or coal as a raw material. Also,
The non-graphitizable material is obtained by firing and carbonizing an organic compound such as a phenol resin, and 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.

In the present invention, among the multilayer films, the lowermost film in contact with the conductive substrate contains a binder made of a polyamide elastomer and an electron conduction aid.

The above-mentioned polyamide elastomer is a kind of thermoplastic elastomer, and is a block copolymer composed of polyamide as a hard segment responsible for physical crosslinking and polyether and aliphatic polyester as a soft segment responsible for elastomer properties. And usually has a polyamide content of 5 to 90% by weight.

As the polyamide-based elastomer,
There is no particular limitation, and commercially available products can be used. Examples of the commercially available products include NOVAMID PAE (manufactured by Mitsubishi Chemical Corporation), PAE (manufactured by Ube Industries, Ltd.), and DAIAMID P
AE (manufactured by Daicel Huls), Pebax (manufactured by Toray Industries, Inc.), and Gleek A (manufactured by Dainippon Ink Co., Ltd.).

The polyamide elastomer has a melting point of 140 ° C. or more, a heat of crystal fusion of 3 mJ / mg or more, and an intrinsic viscosity (Ubelude viscometer, orthochlorophenol solution, 30 ° C.) of 0.35 to 2 dL / d. g is preferable. When the melting point is 140 ° C. or less,
This is because the degree of swelling with respect to the electrolytic solution becomes too high and battery performance tends to decrease. Although the upper limit of the melting point is not particularly limited, it is usually lower than 220 ° C. which is the melting point of the polyamide used for producing the polyamide elastomer.

The polyamide is not particularly limited.
For example, aliphatic nylons such as 4-nylon, 6-nylon, 6,6-nylon, 11-nylon, 12-nylon, 6,10-nylon and 6,12-nylon; aromatics such as isophthalic acid and terephthalic acid Carboxylic acid, metaxylenediamine, 2,2-bis (paraaminocyclohexyl) propane, 4,4'-diaminodicyclohexylmethane, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, etc. And a polycondensate with an aromatic, alicyclic or side-chain substituted aliphatic diamine. Preferably, 6-nylon, 6,
6-nylon, 12-nylon, etc., whose melting points are about 240 ° C., 265 ° C., and 180 ° C., respectively.

The heat of melting of the crystal is preferably 3 mJ / mg or more, and usually 70 mJ, since the heat resistance of the crystal is lowered if it is too low, and the battery performance, especially the initial capacity, tends to be lowered due to too high a degree of swelling. / Mg or less.

If the intrinsic viscosity is too low, the resistance of the polyamide elastomer to the electrolytic solution will be low, and if charge and discharge are repeated many times, it will be difficult to follow the swelling / shrinking of the active material. If it is too high, the positive electrode active material and the binder described below are dispersed in an organic solvent, and the solubility in an organic solvent such as N-methylpyrrolidone used when coating and drying is reduced. Since the workability is reduced, it is preferably from 0.35 to 2 dL / g, more preferably from 0.4 to 1.9 dL / g in (Ubelude viscometer, orthochlorophenol solution, 30 ° C.).

In the present invention, the polyamide elastomer includes at least one of dicarboxylic acids represented by the following general formula (1), at least one diol represented by the following general formula (2), and , Reduced viscosity (1 g / dL 98% sulfuric acid solution, 20 ° C.)
It is preferably a polyesteramide obtained by reacting a polyamide of 7 dL / g. HOOC-R ¹ -COOH (1) (wherein, R ¹ represents an alkylene group having 2 to 8 carbon atoms) HO-R ² -OH (2) (wherein, R ² represents 2 to 6 carbon atoms) Represents an alkylene group)

The dicarboxylic acid represented by the above general formula (1) is not particularly restricted but includes, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,
Suberic acid, azelaic acid, sebacic acid and the like can be mentioned.

In the present invention, in addition to the dicarboxylic acid represented by the above general formula (1), other various dicarboxylic acids are appropriately used as a dicarboxylic acid component as long as the physical properties of the obtained binder are not impaired. can do.

The diol represented by the above general formula (2) is not particularly restricted but includes, for example, ethylene glycol,
Examples thereof include 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, and 1,6-hexanediol. Above all,
Branched diols such as 1,2-propanediol and neopentyl glycol are preferred because they improve the flexibility of the resulting binder.

In the present invention, in addition to the diol represented by the general formula (2), glycol and polyalkylene oxide are appropriately used as a diol component as long as the physical properties of the obtained binder are not impaired. be able to.
The glycol is not particularly limited.
7-heptanediol, 1,8-octanediol,
1,9-nonanediol, 1,10-decanediol,
Cyclopentane-1,2-diol, cyclohexane-
Examples thereof include 1,2-diol, cyclohexane-1,3-diol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol. The polyalkylene oxide is not particularly limited, and includes, for example, polyethylene oxide, polypropylene oxide, polytetramethylene oxide, polyhexamethylene oxide and the like.

In the present invention, in addition to the above-mentioned dicarboxylic acids and diols, a trifunctional or higher functional carboxylic acid or a trifunctional or higher functional polyol may be appropriately used in combination as long as the physical properties of the obtained binder are not impaired. it can. Examples of the trifunctional or higher carboxylic acid include trimellitic acid and benzenetetracarboxylic acid. Examples of the above trifunctional or higher polyol include trimethylolpropane and pentaerythritol. These three
It is preferable that the carboxylic acid or polyol having a functionality of 2 or more is not more than 2 parts by weight based on 100 parts by weight of the total amount of dicarboxylic acid and diol.

The polyamide has an amide bond in the main chain of the polymer and can be dissolved in dicarboxylic acids and diols, which are constituents of polyester, and can be heated and melted. The reduced viscosity of the polyamide is
0.5 to 7.0 dL / g (1 g / dL 98% sulfuric acid solution,
20 ° C.). If it is less than 0.5 dL / g, the mechanical strength of the obtained polyester amide at a high temperature is insufficient, and if it exceeds 7.0 dL / g, the solubility is reduced and the synthesis becomes difficult.

The above polyamide has a molecular weight of about 1000 to 6
0000 is preferred. More preferably 200
0 to 50,000.

The polyamide is not particularly limited.
For example, aliphatic nylons such as 4-nylon, 6-nylon, 6,6-nylon, 11-nylon, 12-nylon, 6,10-nylon, 6,12-nylon and the like; isophthalic acid, terephthalic acid, meta-xylylene diene Amine, 2,
2-bis (paraaminocyclohexyl) propane, 4,
4'-diaminodicyclohexylmethane, 2,2,4-
Examples thereof include polyamides obtained by polycondensation of aromatic, alicyclic, and side-chain substituted aliphatic monomers such as trimethylhexamethylenediamine and 2,4,4-trimethylhexamethylenediamine.

The content of the polyamide in the polyester amide is preferably from 5 to 90% by weight. When the amount is less than 5% by weight, the mechanical strength of the obtained binder is insufficient, and when it exceeds 90% by weight, the content of the hard segment increases, so that the binder becomes hard and obtains a binder having good rubber elasticity. Can not. More preferably, it is 7 to 75% by weight.

The polyester amide can be synthesized by any method, for example, by polymerizing a dicarboxylic acid and a diol in the presence of a polyamide. The above polymerization usually comprises a two-stage reaction of an esterification reaction and a polycondensation reaction.

As the first step, the esterification reaction proceeds. The esterification reaction needs to be performed in the state of a transparent and homogeneous solution by dissolving the polyamide in a polyester component. In a heterogeneous state, the reaction does not proceed efficiently. The melting temperature is preferably from 150 to 230C. 1
If it is lower than 50 ° C., it is difficult to dissolve, and if it is higher than 230 ° C., a decomposition reaction may occur.

As a second step, the polycondensation reaction proceeds. The polycondensation reaction is preferably performed under reduced pressure, preferably at 10 mmHg or less, at 180 to 260 ° C. 18
When the temperature is lower than 0 ° C., the reaction rate is low and the polymerization viscosity is high, so that efficient polymerization becomes difficult, and 260 ° C.
If it exceeds 300, decomposition reaction and coloring will occur.

In the polycondensation reaction, it is preferable to charge 1.2 to 3 moles of the diol per 1 mole of the dicarboxylic acid. For 1 mole of the dicarboxylic acid,
When the amount of the diol is less than 1.2 mol, the esterification reaction does not proceed efficiently. When the amount of the diol exceeds 3 mol, it is disadvantageous in terms of cost because an excess diol component is used. Since the cleavage reaction of the polyamide is likely to occur, the blocking property is reduced, and the heat resistance is reduced.

In the above polycondensation reaction, a catalyst generally used in the production of polyester may be used. The catalyst is not particularly limited, for example, lithium, sodium, potassium, cesium, magnesium, calcium,
Barium, strontium, zinc, aluminum, titanium, cobalt, germanium, tungsten, tin, lead,
Metals such as antimony, arsenic, cerium, boron, cadmium, manganese, and zirconium; and organic metal compounds, organic acid salts, metal alkoxides, and metal oxides thereof. These may be used alone or in combination of two or more. Among them, calcium acetate, stannous diacyl, stannic tetraacyl, dibutyltin oxide,
Dibutyltin dilaurate, dimethyltin malate, tin dioctanoate, tin tetraacetate, triisobutylaluminum, tetrabutyltitanate, tetrapropoxytitanate, titanium (oxy) acetylacetate,
Germanium dioxide, tungstic acid, antimony trioxide and the like are preferably used.

In the present invention, the above-mentioned polyamide-based elastomer may be mixed with other thermoplastic resin, rubber component and the like to be used as a mixed binder. The thermoplastic resin is not particularly limited, for example, polyolefin,
Modified polyolefin, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyamide, polycarbonate, polysulfone, polyester, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PT
FE), a fluororesin such as a tetrafluoroethylene-hexafluoropropylene copolymer and a vinylidene fluoride-hexafluoropropylene copolymer.

The rubber component is not particularly restricted but includes, for example, natural rubber, styrene-butadiene copolymer (SB
R), hydrogenated SBR, polybutadiene, polyisoprene,
Acrylonitrile-butadiene copolymer, ethylene-propylene copolymer (EPR), ethylene-propylene-
Diene terpolymer (EPDM), polychloroprene,
Butyl rubber, acrylic rubber, silicone rubber, urethane rubber, olefin-based thermoplastic elastomer, styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), hydrogenated SBS,
Examples include styrene-based thermoplastic elastomers such as hydrogenated SIS, PVC-based thermoplastic elastomers, ester-based thermoplastic elastomers, amide-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers.

In the present invention, the electron conduction aid contained in the lowermost layer film is not particularly limited, and may be a metal powder or fiber such as aluminum, nickel or copper, or a carbon powder or carbon fiber generally used for a battery. Powdered or fibrous materials having good electrical conductivity can be used. Further, those in which these particles are connected in a chain can also be used.

The lowermost layer film is prepared by adding a solvent to the polyamide-based elastomer, the electron-conducting auxiliary material and, if necessary, adding a solvent thereto and mixing the slurry,
The slurry is formed by applying and drying the slurry on a conductive substrate. This lowermost layer film can be used to form a coating film for any of the positive electrode and the negative electrode, but the types and composition ratios of materials such as an electron conduction aid and a binder may be the same for both the positive electrode and the negative electrode. And may be different.

In the present invention, the binder used for the coating film other than the lowermost layer in the multilayer film is not particularly limited, and the above-mentioned thermoplastic resin or rubber component which can be mixed with the above-mentioned polyamide elastomer can be used. .

In order to produce a positive electrode in the present invention, first, a lowermost layer film is formed on a conductive substrate as described above, and the positive electrode active material and a binder are dispersed in an organic solvent. The slurry is applied on the lowermost film,
dry.

The organic solvent is not particularly restricted but includes, for example, N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide. Further, a method such as performing a strong pressure press using a roll press machine after forming the coating film can be adopted.

The mixing ratio of the positive electrode active material and the binder was 100 parts by weight of the positive electrode active material and 1 part of the binder.
-20 parts by weight are preferred. If the amount is less than 1 part by weight, it is difficult to apply the positive electrode active material on the lowermost film, and if it exceeds 20 parts by weight, the capacity of the secondary battery is reduced.

To produce a negative electrode in the present invention, first, a lowermost layer film is formed on a conductive substrate as described above,
The negative electrode active material and the binder are dispersed in an organic solvent to form a slurry, and the slurry is applied to the lowermost layer film and dried. As the organic solvent, the same organic solvent as used in the case of the positive electrode is used. Further, a method such as performing a strong pressure press using a roll press machine after forming the coating film can be adopted.

The mixing ratio of the negative electrode active material and the binder is 1 to 100 parts by weight of the negative electrode active material.
20 parts by weight are preferred. If the amount is less than 1 part by weight, it is difficult to apply the negative electrode active material on the lowermost film. If the amount exceeds 20 parts by weight, the capacity of the secondary battery is reduced.

As a method of applying the slurry when forming the coating film, any coating method such as an extrusion coater, a reverse roller, a doctor blade, etc. may be employed. By appropriately combining these coating methods, for example, a simultaneous multilayer coating method (wet /
On-wet method) and sequential multilayer coating method (wet /
A lamination method such as an on-dry method may be employed.
In addition, since the lowermost layer film does not directly aim at the electrochemical reaction, there is no need to provide a void serving as an ion passage.
It can be highly filled, thereby further increasing the adhesive strength with the conductive substrate surface. As a method for filling the lowermost layer film as described above, for example, the solvent content of the paint for forming the lowermost layer film is reduced, and the lowermost layer film is coated and dried to form the lowermost layer film. In the case of the method, a method such as performing a strong pressure press using a roll press machine after forming the lowermost layer film can be adopted.

The positive electrode and the negative electrode may have a sheet shape, a square shape, a cylindrical shape, or the like, and may be used as the electrodes of the secondary battery of the present invention. In this case, the positive electrode is opposed to the negative electrode via the separator.

For the separator, a material having excellent liquid retention properties is used. Such a material is not particularly limited, and may be, for example, a nonwoven fabric of a polyolefin resin,
A microporous polypropylene film or a microporous polyethylene film having a numerical aperture of 0 to 50 μm and an opening ratio of 30 to 70%, or a multilayer film thereof can be used. These may be used via an electrolytic solution, but are preferably used after being impregnated with the electrolytic solution.

As the electrolytic solution, a solution obtained by dissolving an electrolyte in an organic solvent is used. The organic solvent is not particularly limited, for example, carbonates, sulfolane,
Examples include chlorinated hydrocarbons, ethers, esters, ketones, lactones, nitriles, and the like. Specific examples include, for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, Examples include methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like. These may be used alone or in combination of two or more.

The electrolyte is not particularly limited, and may be, for example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiBP
h ₄ , LiCl, LiBr, MeSO ₃ Li, CF ₃ S
O ₃ Li, LiAsF ₆ , Li (CF ₃ SO) ₂ N, L
iC ₄ F ₉ SO _{3 and the} like. In the formula, Ph represents a phenyl group, and Me represents a methyl group.

(Function) The lithium secondary battery of the present invention has an electrode in which a coating containing a substance capable of doping and undoping lithium ions and a binder is formed on a conductive substrate. In a non-aqueous electrolyte secondary battery composed of a multilayer film of at least two layers, the lowermost layer film in contact with the conductive substrate contains a binder made of a polyamide elastomer and an electron conduction aid, The polyamide-based elastomer has excellent adhesiveness to a metal foil as a conductive substrate or a coating film containing an active material and a binder, and also has excellent solvent resistance to an electrolytic solution of a secondary battery. In addition, since the polyamide-based elastomer has a low elastic modulus and excellent flexibility, the resulting electrode has flexibility and can be freely set in shape.

For this reason, a secondary battery using an electrode using the above-mentioned polyamide-based elastomer as a binder for the lowermost layer film in contact with the conductive substrate has a lower layer film in contact with the conductive substrate which is flexible and has an adhesive property. Because it is excellent in properties, even when charging and discharging are repeated, it easily follows the expansion and contraction of the active material and is relaxed by the lowermost film, so that the negative electrode active material,
The positive electrode active material does not peel off from the metal foil,
Since there is no crack on the electrode surface, the capacity retention rate is increased even after long-term repeated use. Furthermore, a spiral wound electrode structure can be easily obtained, and a limited space can be filled with as much active material as possible, so that a secondary battery with high energy density and high capacity can be manufactured. Becomes

[0068]

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

Example 1 (1) Preparation of Positive Electrode Preparation of Polyamide Elastomer 146 parts by weight of adipic acid, 108 parts by weight of butylene glycol, 125 parts by weight of neopentyl glycol [butylene glycol / neopentyl glycol = 50/50 (mole) Ratio), adipic acid component / diol component at preparation = 1
/2.4 (molar ratio)], 6-nylon (manufactured by Toyobo Co., Ltd .;
Part number “T850”, reduced viscosity in 98% sulfuric acid at 20 ° C. 3.5 dL / g) 120 parts by weight, 0.25 part by weight of tetrabutyl titanate as a catalyst, 1,3,5 as a stabilizer
-Trimethyl-2,4,6-tris (3,5-di-t-
Butyl-4-hydroxybenzyl) benzene (0.4 parts by weight) and tris (2,4-di-t-butylphenyl) phosphite (0.4 parts by weight) were added, and the reaction system was heated to 200 ° C. under nitrogen.
The temperature rose. After 10 minutes, the nylon dissolved and became a clear solution. The mixture was kept at this temperature for further 4 hours to carry out an esterification reaction. The progress of the esterification reaction was confirmed by measuring the amount of distilled water. After the progress of the esterification reaction, the temperature was raised to 240 ° C. in 20 minutes, and the pressure was reduced. The polymerization system reached a reduced pressure of 1 mmHg or less in 10 minutes. As a result of performing a polycondensation reaction in this state for 1 hour, 327 parts by weight of a transparent polyamide elastomer (hereinafter, referred to as “binder B1”) was obtained.

Preparation of Lowermost Layer Film A 10% by weight solution of the obtained binder B1 in N-methylpyrrolidone (hereinafter abbreviated as NMP) was prepared.
10 parts by weight of copper powder having an average particle size of 3 μm was added to parts by weight, and the mixture was stirred and mixed to prepare a coating liquid for the lowermost layer film. This coating solution was applied to an aluminum foil of 1 cm × 5 cm × 15 μm using an applicator having a clearance of 15 μm and dried to prepare a lowermost layer film.

Production of Positive Electrode 0.5 mol of carbon lithium and 1 mol of carbon cobalt were mixed and calcined in air at 900 ° C. for 5 hours,
LiCoO ₂ was obtained. 95 parts by weight of the obtained LiCoO ₂ , 5 parts by weight of graphite as a conductive agent, and polyvinylidene fluoride as a binder (KF-13 manufactured by Kureha Chemical Co., Ltd.)
00) 5 parts by weight were dispersed in 100 parts by weight of N-methylpyrrolidone to obtain a slurry coating solution. This coating liquid was applied to the above-mentioned aluminum foil provided with the lowermost layer film and dried to prepare a positive electrode. Similarly, a positive electrode was formed on the back surface of the aluminum foil.

(2) Preparation of Negative Electrode Preparation of Lowermost Layer Film A 10% by weight NMP solution of the same binder B1 as used for preparing the lowermost layer film of the positive electrode was prepared, and an average was prepared based on 100 parts by weight of this solution. A coating liquid for the lowermost layer film was prepared by adding 10 parts by weight of aluminum powder having a particle diameter of 3 μm and stirring and mixing. This coating solution was applied to a copper foil of 1 cm × 5 cm × 15 μm using an applicator having a clearance of 15 μm and dried to prepare a lowermost layer film.

Preparation of Negative Electrode A petroleum pitch as a starting material is provided with one functional group containing oxygen.
After oxygen cross-linking to introduce 0 to 20% by weight, this oxygen cross-linked precursor is cooled to 1000 ° C. in an inert gas stream.
Then, a carbon material was obtained. As a result of performing X-ray diffraction measurement on the obtained carbon material, (002)
The face-to-face spacing was 3.76 Å. This carbon material was pulverized to obtain a carbon material powder having an average particle diameter of 10 μm.

100 parts by weight of the obtained powder of the carbon material and 5 parts by weight of polyvinylidene fluoride (KF-1100 manufactured by Kureha Chemical Co., Ltd.) as a binder were dispersed in 100 parts by weight of NMP, and a slurry-like coating solution was prepared. did. This coating liquid was applied to the above-mentioned copper foil provided with the lowermost layer film using an applicator having a clearance of 300 μm, and dried to prepare a negative electrode. Similarly, a negative electrode was formed on the back surface of the copper foil.

(3) Preparation of Battery A test battery was prepared using the positive electrode and the negative electrode.
At this time, a non-aqueous electrolyte obtained by dissolving LiPF ₆ of a lithium salt at a ratio of 1/1 (molar ratio) in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in an equal amount was used as the electrolyte. A microporous propylene film was used as a separator.

(Example 2) Preparation of polyamide elastomer 6-nylon (manufactured by Toyobo Co .; product number "T850") instead of 6-nylon (manufactured by Unitika; product number "A105")
0 ", reduced viscosity at 98C in 98% sulfuric acid, 6.2 dL /
g) A transparent polyamide elastomer (hereinafter referred to as “binder B2”) 604 in the same manner as in Example 1 except that 400 parts by weight and the polycondensation reaction were performed for 2 hours.
Parts by weight were obtained. A test battery was produced in the same manner as in Example 1 using the obtained binder B2.

Example 3 Preparation of Polyamide Elastomer 6-Nylon (manufactured by Toyobo Co .; product number "T850") instead of 6-nylon (manufactured by Unitika Ltd .; product number "A105")
0 ", reduced viscosity at 98C in 98% sulfuric acid, 6.2 dL /
g) A transparent polyamide elastomer (hereinafter referred to as “binder B”) was prepared in the same manner as in Example 1 except that 31 parts by weight was used.
3 "). The obtained binder B3
And a test battery was produced in the same manner as in Example 1.

Example 4 Preparation of Polyamide Elastomer 161 parts by weight of adipic acid, 119 parts by weight of butylene glycol, 137 parts by weight of neopentyl glycol [butylene glycol / neopentyl glycol = 50/50 (molar ratio), Acid component / diol component = 1
/2.4 (molar ratio)], 6-nylon (manufactured by Toyobo Co., Ltd .;
Part number "T850", reduced viscosity in 98% sulfuric acid at 20 ° C, 3.5 dL / g) 76 parts by weight, pentaerythritol 0.75 parts by weight, tetrabutyl titanate 0.6 parts by weight as a catalyst, 3,5-trimethyl-
0.4 parts by weight of 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 0.1 part of tris (2,4-di-t-butylphenyl) phosphite.
4 parts by weight were added, and the reaction system was heated to 200 ° C. under nitrogen. After 10 minutes, the nylon dissolved and became a clear solution. The mixture was kept at this temperature for further 4 hours to carry out an esterification reaction. The progress of the esterification reaction was confirmed by measuring the amount of distilled water. After the progress of the esterification reaction, the temperature was raised to 240 ° C. in 20 minutes, and the pressure was reduced. The polymerization system reached a reduced pressure of 1 mmHg or less in 10 minutes. In this state, a polycondensation reaction was performed for 1 hour to obtain 304 parts by weight of a transparent polyamide elastomer (hereinafter, referred to as “binder B4”).

Preparation of Lowermost Layer Film A 10% by weight NMP solution of the obtained binder B4 was prepared.
To 100 parts by weight of this solution, 150 parts by weight of conductive carbon (manufactured by Nippon Graphite Co., Ltd., product number "KEX") was added and stirred and mixed to prepare a coating solution for the lowermost layer film. This coating solution was applied to an 1c using an applicator having a clearance of 15 μm.
An aluminum foil of mx 5 cm x 15 µm was applied and dried to form a lowermost layer film.

Production of Positive Electrode A positive electrode was produced in the same manner as in Example 1 using the obtained lowermost film.

(2) Preparation of Negative Electrode Preparation of Lowermost Layer Film A 10% by weight NMP solution of the same binder B4 as used for preparing the lowermost layer film of the positive electrode was prepared. Carbon (manufactured by Nippon Graphite Co .; product number "KE
X ") A coating liquid for the lowermost layer film was prepared by adding 150 parts by weight and stirring and mixing. This coating solution was applied to a 1 cm × 5 cm ×
A 15 μm copper foil was applied and dried to produce a lowermost layer film.

Production of Negative Electrode A negative electrode was produced in the same manner as in Example 1 using the obtained lowermost film.

(3) Production of Battery A test battery was produced in the same manner as in Example 1 using the above positive electrode and negative electrode.

Example 5 Preparation of Polyamide Elastomer 146 parts by weight of adipic acid, 136 parts by weight of ethylene glycol (adipic acid component / diol component at preparation = 1/1)
2.2 (molar ratio)], 76 parts by weight of 6-nylon (manufactured by Toyobo Co., Ltd .; product number “T850”, reduced viscosity in 98% sulfuric acid at 20 ° C. 3.5 dL / g), 0.75 parts by weight of pentaerythritol Parts, 0.6 parts by weight of tetrabutyl titanate as a catalyst, 1,3,5-trimethyl- as a stabilizer
0.4 parts by weight of 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 0.1 part of tris (2,4-di-t-butylphenyl) phosphite.
4 parts by weight were added, and the reaction system was heated to 200 ° C. under nitrogen. After 10 minutes, the nylon dissolved and became a clear solution. The mixture was kept at this temperature for 1 hour to carry out an esterification reaction. The progress of the esterification reaction was confirmed by measuring the amount of distilled water. After the progress of the esterification reaction, the temperature was raised to 240 ° C. in 20 minutes, and the pressure was reduced. The polymerization system reached a reduced pressure of 1 mmHg or less in 15 minutes. As a result of a polycondensation reaction for 30 minutes in this state, 208 parts by weight of a transparent polyamide elastomer (hereinafter, referred to as “binder B5”) was obtained. A test battery was produced in the same manner as in Example 1 using the obtained binder B5.

Example 6 Preparation of Polyamide Elastomer A transparent polyamide elastomer (hereinafter, referred to as “Example 6”) was prepared in the same manner as in Example 1 except that 9 parts by weight of 6-nylon (manufactured by Toyobo Co., Ltd., product number “T850”) was used. "Binder B6")
217 parts by weight were obtained. A test battery was produced in the same manner as in Example 1 using the obtained binder B6.

Evaluation of Polyamide Elastomer Polyamide Elastomer Obtained (Binders B1 to B5)
Was evaluated by the following method.

1. Intrinsic viscosity [η] Using an Ubbelohde viscosity tube, 3
It was measured at 0 ° C. 2. Polyamide content Calculated from the weight of the polyamide at the time of charging with respect to the weight of the produced polyesteramide. 3. Melting Point and Heat of Crystal Melting Using a differential scanning calorimeter (DSC), the temperature was raised from room temperature to 240 ° C., then lowered at −20 ° C./min to −100 ° C., and measured again at a heating rate measuring rate of 10 ° C./min. The melting point and the heat of crystal fusion were determined.

The above results are summarized in Table 1.

[0089]

[Table 1]

Comparative Example 1 Polyvinylidene fluoride (KF-130 manufactured by Kureha Chemical Co., Ltd.) was used as a binder for the lowermost film.
0, described as “PVDF” in the table), except that a test battery was prepared in the same manner as in Example 1.

(Comparative Example 2) 6-nylon (manufactured by Unitika Ltd .; product number "A1050") as a binder used for the lowermost layer film
A test battery was prepared in the same manner as in Example 1 except that を was used.

With respect to the discharge capacity, the capacity retention rate, and the adhesion of the coating films of the batteries prepared in Examples 1 to 6 and Comparative Examples 1 and 2,
It was evaluated by the following method.

1. Discharge capacity (Ah / kg) After charging the produced battery at a constant voltage of 4.2 V for 5 hours, a final voltage of 1.0 mA / cm ^{2 at} a constant current of 2.
Discharged at 75V. By repeating this charge / discharge cycle, 1
The discharge capacity at the 0th cycle was measured.

2. Capacity maintenance rate (%) After charging the obtained battery at a constant voltage of 4.2 V for 5 hours, a final voltage of 2.75 V at a constant current of 1.0 mA / cm ^2.
Was discharged. This charge / discharge cycle was repeated, the discharge capacity at the 10th cycle and the discharge capacity at the 200th cycle were measured, and the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the 10th cycle was defined as the capacity retention ratio.

3. Adhesiveness of coating film Each of the positive electrode and the negative electrode for which an electrode was prepared was applied with a radius of 0.
A stainless steel flat plate 1 having a semi-circular groove of 5 mm dug thereon is placed on the flat stainless steel plate 1, and a stainless steel flat plate 2 whose end is rounded into a semicircle with a radius of 0.3 mm is placed on the end of the flat plate 2. Was pressed so as to fit into the groove of the flat plate 1. After that, each electrode is taken out, and the bonding state of the interface between the bent portion of the metal foil and the lowermost film (in the table, described as “metal foil”) and the interface between the film containing the active material and the lowermost film ( In the table: "Film containing active material") was observed with a scanning electron microscope. The one that was adhered was rated as ○, and the one that was peeled was rated X.

Table 2 summarizes the above results.

[0097]

[Table 2]

[0098]

Since the secondary battery of the present invention has the above-described configuration, it has a high capacity and excellent charge / discharge characteristics.
In addition, because of its excellent adhesion to the conductive substrate, it can be used repeatedly over a long period of time, and has a high capacity retention rate even over several hundred charge / discharge cycles. PCs, mobile phones, transceivers,
It can be suitably used as a power source for moving electronic devices such as cameras, headphone stereos, and portable televisions.

Claims (3)

[Claims] 1. An electrode comprising a conductive substrate on which a coating containing a substance capable of doping / undoping lithium ions and a binder is formed, wherein the coating comprises a multilayer film of at least two layers. A non-aqueous electrolyte secondary battery, wherein the lowermost film in contact with the conductive substrate contains a binder made of a polyamide elastomer and an electron conduction aid. 2. A polyamide elastomer having a melting point of 140 ° C. or more and a heat of crystal fusion of 3 mJ / m 2.
g or more, and the intrinsic viscosity (Ubellude viscometer, orthochlorophenol solution, 30 ° C.) is 0.35 to 2 dL / g.
The non-aqueous electrolyte secondary battery according to claim 1, wherein 3. A polyamide elastomer comprising at least one of dicarboxylic acids represented by the following general formula (1), at least one diol represented by the following general formula (2), and a reduced viscosity ( 1g / dL
(98% sulfuric acid solution, 20 ° C.) is a polyesteramide obtained by reacting a polyamide having a content of 0.5 to 7 dL / g, wherein the content of the polyamide in the polyesteramide is:
The non-aqueous electrolyte secondary battery according to claim 1, wherein the content is 5 to 90% by weight. HOOC-R ¹ -COOH (1) (wherein, R ¹ represents an alkylene group having 2 to 8 carbon atoms) HO-R ² -OH (2) (wherein, R ² represents 2 to 6 carbon atoms) Represents an alkylene group)