JP3356021B2 - Non-aqueous electrolyte secondary battery binder and battery electrode mixture using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a binder for a non-aqueous electrolyte secondary battery and a battery electrode mixture using the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for small and portable electric and electronic devices such as audio tape recorders, camera-integrated video tape recorders, notebook computers, and mobile phones. Along with this, compact, lightweight, high-performance secondary batteries that can be used repeatedly are required, and various new batteries such as nickel-metal hydride batteries and lithium-ion batteries are commercialized in addition to conventional lead batteries and nickel-cadmium batteries. ing. Of these, nickel-hydrogen secondary batteries using an alkaline electrolyte have problems that the voltage is low, the energy density cannot be increased, and the self-discharge is large. On the other hand, lithium ion secondary batteries using non-aqueous electrolytes have high voltage, high energy density, low self-discharge,
It has the advantage of being ultra-lightweight and is a secondary battery that is expected to grow significantly in the future.

A key point in improving the energy density of the lithium ion secondary battery is an electrode manufacturing technique. For this electrode, for example, when producing a negative electrode using a carbonaceous material such as coke or carbon as a negative electrode active material, the carbonaceous material is powdered and dispersed in a solvent together with a binder to prepare a negative electrode mixture. After coating on the current collector, the solvent is removed by drying and rolling is performed. Note that in this specification, a carbonaceous material that merely stores and releases lithium ions is also referred to as an active material. Similarly, for the positive electrode, for example, a lithium-containing oxide is used as a positive electrode active material, which is powdered, dispersed in a solvent together with a conductive agent and a binder to prepare a positive electrode mixture, and applied to a positive electrode current collector.
It is produced by removing the solvent by drying and rolling. Conventionally, polyvinylidene fluoride has been often used as a binder for this lithium ion secondary battery. For example, Japanese Patent Application Laid-Open No. Hei 4-249589 discloses that a positive electrode mixture prepared by mixing a lithium-containing oxide such as LiCoO ₂ as a positive electrode active material and graphite as a conductive agent with polyvinylidene fluoride is dispersed in N-methylpyrrolidone. The slurry was applied to a positive electrode current collector of aluminum foil, and a negative electrode mixture prepared by mixing a carbonaceous material as the negative electrode active material and polyvinylidene fluoride was dispersed in N-methylpyrrolidone to form a slurry. There is disclosed a technique in which the resultant is coated on a copper foil as a negative electrode current collector, dried, and then compression-molded by a roller press to process the electrode sheet. However, the solvent of polyvinylidene fluoride is limited to a special organic solvent having a high boiling point such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, which is expensive and expensive. And so on. Further, polyvinylidene fluoride easily swells in an organic solvent of a non-aqueous electrolyte such as propylene carbonate, ethylene carbonate, diethyl carbonate, or a mixture thereof used in a lithium ion secondary battery. Therefore, as the charge and discharge are repeated, the adhesiveness to the metal foil as the current collector becomes poor, and as a result, the internal resistance of the battery increases and the battery performance deteriorates. Furthermore, the electrode sheet using the polyvinylidene fluoride binder is poor in flexibility, at the time of the step of folding the electrode sheet at 180 degrees in the production of a square battery, and at the time of the step of rolling the electrode sheet into a small size at the production of a cylindrical battery, The problem that the electrode mixture is separated from the electrode sheet is likely to occur, and the production yield is reduced. Also, JP-A-4-953
No. 63 discloses a vinylidene fluoride-hexafluoropropylene copolymer and a vinylidene fluoride-3 for the purpose of imparting a binding property against expansion and contraction of a positive electrode active material during charge and discharge in a nonaqueous electrolyte secondary battery. A material having rubber elasticity, which is mainly composed of a fluorinated ethylene copolymer called a fluorinated ethylene copolymer, is described as a binder. But,
Such copolymers have poorer crystallinity than polyvinylidene fluoride, and therefore easily swell in an organic solvent of a non-aqueous electrolyte more than polyvinylidene fluoride, and are eluted depending on the type of the electrolyte and a binder. Will no longer fulfill its role. As a similar binder, Japanese Patent Publication No. 8-4007 discloses a binder comprising a fluorine-based polymer copolymer mainly composed of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene instead of polyvinylidene fluoride. It is described that it is used for.
The composition range of the copolymer described in the claims is a molar fraction of 0.3 to 0.9 for vinylidene fluoride, 0.03 to 0.5 for hexafluoropropylene, and 0 to 0 for tetrafluoroethylene. .5, the sum of the mole fractions of these three monomers is 0.80-1. Also in this patent, polyvinylidene fluoride has a strong polarity such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, methylsulfoxide and the like described above, and has a high boiling point, and because it is soluble only in toxic special solvents. When an electrode is manufactured by applying and forming an active material using the solvent, it takes too much time to dry the high-boiling solvent, and because of its toxicity, it is necessary to prepare a closed facility, an exhaust facility, and the like. It is pointed out that it has the above problem. In this publication, in order to solve the above problems, low-cost, low-boiling general-purpose resins such as ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, and ethers such as dioxane and tetrahydrofuran. The above-mentioned copolymer which is soluble in an organic solvent or a mixture thereof is used as a binder. However, this copolymer is basically the same as the above-mentioned vinylidene fluoride-hexafluoropropylene binary copolymer and vinylidene fluoride-3 fluoroethylene chloride binary copolymer, and the organic solvent of the non-aqueous electrolyte is basically the same. On the other hand, since the swelling property is large, the electrode mixture may peel off from the current collector and the active material may fall off during long-term use of the battery, which may cause a problem such as a decrease in battery performance.

Further, Japanese Patent Application Laid-Open No. 7-147156 discloses that an electrode in which a mixed layer of an insoluble and infusible substrate having a polyacene skeleton structure and a specific binder is adhered in a metal foil form as an electrode is used to improve the battery capacity. Then, the binder has an atomic ratio of fluorine atom / carbon atom of 1.5.
Less than 0.75 or more. However, specifically disclosed is only polyvinylidene fluoride, and for example, the ethylene-tetrafluoroethylene copolymer and the propylene-tetrafluoroethylene copolymer described in the publication are both insoluble in organic solvents. In view of the fact that it is preferable to obtain a homogeneous electrode, it is considered that the complete dissolution of the fluorinated polymer is unsuitable as a binder and is considered unrealistic.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer which is more flexible than polyvinylidene fluoride and can be used not only in conventional solvents such as N-methylpyrrolidone, dimethylacetamide and dimethylformamide, but also in acetone and methyl ethyl ketone. It is soluble in low-boiling organic solvents, and, in addition, propylene carbonate, ethylene carbonate, diethyl carbonate,
An object of the present invention is to provide a binder for a non-aqueous electrolyte secondary battery having a low swelling property with respect to an organic solvent of a non-aqueous electrolyte such as dimethoxyethane or a mixture thereof and a battery electrode mixture using the binder. .

[0006]

According to the study of the present inventors, a copolymer mainly composed of vinylidene fluoride and tetrafluoroethylene is used as a binder for a non-aqueous electrolyte secondary battery. As a result, it has been found that the production process can be simplified and the production cost can be reduced, and that the battery performance can be improved because the swelling property with respect to the non-aqueous electrolyte is reduced.

That is, according to the present invention, a positive electrode mixture comprising a positive electrode active material, a conductive agent and a binder is held by a positive electrode current collector and / or a negative electrode mixture comprising a negative electrode active material and a binder. In a binder used for a non-aqueous electrolyte secondary battery including a negative electrode held by a negative electrode current collector and a non-aqueous electrolyte, the binder is 50 to 80 mol% of vinylidene fluoride.
A ternary or higher copolymer comprising 17% by mole to less than 50% by mole of tetrafluoroethylene and less than 3% by mole of a monomer copolymerizable therewith;
Lolidone, tetrahydrofuran, methyl ethyl ketone
Room temperature up to 10% by weight of these solvents in water and acetone.
The present invention relates to a binder for a non-aqueous electrolyte secondary battery comprising a copolymer soluble at 0 ° C.

[0008] In the present invention, polytetrafluoroethylene is not used as a binder.

The copolymer preferably has a large molecular weight from the viewpoint of improving cycle characteristics. For example, in the case of a copolymer having three or more components, the number average molecular weight is 150,000 to 500,000.
00 is preferred.

[0010] The binder of the present invention is particularly useful when a lithium-containing oxide is used as a positive electrode active material.

[0011] The present invention also relates to a battery electrode mixture containing the above-mentioned binder.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The binder of the present invention has a copolymerization ratio of vinylidene fluoride of 50 to 80 mol%, preferably 60 to 80 mol%.
Vinylidene fluoride is 80 mol% - characterized by comprising the terpolymer of tetrafluoroethylene.

Specifically, vinylidene fluoride 50 to 80
Mol%, preferably 60 to 80 mol% , tetrafluoroethylene 17 mol% or more and less than 50 mol%, preferably 1 mol%
7 mol% or more and less than 40 mol% and less than 3 mol% of monomers copolymerizable therewith, preferably less than 2.8 mol%,
More preferably, a binder comprising a tertiary or higher copolymer composed of less than 2.5 mol% is exemplified.

The vinylidene fluoride copolymer used in the present invention can be polymerized by a known polymerization method, and among them, a radical copolymerization method is preferred. That is, the polymerization method is not particularly limited as long as it proceeds radically, but is started by, for example, an organic or inorganic radical polymerization initiator, heat, light, or ionizing radiation. The form of polymerization is also solution polymerization, bulk polymerization,
Suspension polymerization, emulsion polymerization and the like can be used.

When the amount of vinylidene fluoride is less than 50 mol%, it becomes difficult to dissolve the organic solvent in general. on the other hand,
When the content is more than 80 mol%, the swelling property of the electrolyte such as propylene carbonate, ethylene carbonate and diethylene carbonate becomes large. As a result, the battery using them as a binder for long-term use or under high temperature During continuous use, the mixture is separated from the current collector and the active material is dropped, and the battery performance is reduced. Further 80 mol%
If the amount is larger, the solubility in general-purpose low-boiling organic solvents deteriorates, and special high-boiling organic solvents such as N-methylpyrrolidone and dimethylformamide must be used. , Making it impossible to increase production efficiency. In addition, since the obtained copolymer material is hard and has poor flexibility, there is a limit to a small winding and folding process of the electrode sheet, which also hinders an increase in battery performance.

The molecular weight of the ternary or higher copolymer Ru used in the present invention, relatively low molecular weight in order to improve cycle characteristics
The number average molecular weight in GPC (gel permeation chromatography) measurement is 1 in terms of polystyrene.
Those of 50,000 to 500,000 are preferred.

The adhesiveness between the binder and the current collector is sufficient with a copolymer of vinylidene fluoride and tetrafluoroethylene, but further impairs the excellent non-aqueous electrolyte swellability of the copolymer. Adhesion can be further improved by copolymerizing monomers that can be copolymerized with them to a lesser extent.
However, the amount of addition is preferably less than 3 mol%, and when more than 3 mol% is added, the crystallinity of the copolymer of vinylidene fluoride and tetrafluoroethylene is generally significantly reduced, and as a result, the swellability of the non-aqueous electrolyte tends to deteriorate. There is. Monomers copolymerizable with vinylidene fluoride and tetrafluoroethylene include unsaturated dibasic acid monoesters such as those described in JP-A-6-172452, such as maleic acid monomethyl ester and citraconic acid monomethyl ester , citraconic acid monoethyl ester and vinylene carbonate, also as described in _{JP-a-7-201316, -SO 3 M, -OSO 3} M, -COO
M, -OPO ₃ M (M is an alkali metal represents a) -NHR ¹ a or an amine polar ^{group, -NR 2 R 3 (R 1} , R 2,
And R ³ is having a hydrophilic polar group such as an alkyl group), for example, _{CH 2 = CH-CH 2 -Y} , CH 2 =
_{C (CH 3) -CH 2 -Y} , CH 2 = CH-CH 2 -O-C
^{_{O-CH (CH 2 COOR 4}} ) -Y, CH 2 = CH-CH 2
—O—CH ₂ —CH (OH) —CH ₂ —Y, CH ₂ ＣC
_{(CH 3) -CO-O-} CH 2 -CH 2 -CH 2 -Y, CH
_{2 = CH-CO-O-} CH 2 -CH 2 -Y, CH 2 = CH-
_{CO-NH-C (CH 3} ) 2 -CH 2 -Y (Y is a hydrophilic polar group and R ⁴ represents an alkyl group) and other, such as maleic anhydride or maleic acid. Further, C
H ₂ ＣＨCH—CH ₂ —O— (CH ₂ ) _n —OH (3 ≦ n ≦
8),

[0018]

Embedded image

[0019] _{CH 2 = CH-CH 2 -O-} (CH 2 -CH 2
—O) _n —H (1 ≦ n ≦ 14), CH ₂ ＣＨCH—CH ₂ —
O— (CH ₂ —CH (CH ₃ ) —O) _n —H (1 ≦ n ≦ 1
4) and carboxylated and / or — (CF ₂ ) _n —CF ₃ (3 ≦ n
Allyl ether and ester monomers substituted with ≦ 8), such as CH ₂ ＣＨCH—CH ₂ —O—CO—C ₂ H _{4
-COOH, CH 2 = CH-CH} 2 -O-CO-C 5 H 10
—COOH, CH ₂ ＣＨCH—CH ₂ —OC ₂ H ₄ — (CF
_{2) n CF 3, CH 2} = CH-CH 2 -CO-O-C 2 H 4 -
_{(CF 2) n CF 3,} CH 2 = C (CH 3) -CO-O-C
H ₂ —CF _{3 and the} like can also be used as copolymerizable monomers. By the way, besides the compounds containing polar groups as described above, a collection of aluminum or copper metal foil is provided by slightly lowering the crystallinity of a copolymer of vinylidene fluoride and tetrafluoroethylene to give the material flexibility. It can be inferred from previous research that the adhesiveness with the electric body can be improved. Thus, unsaturated hydrocarbon monomers such as ethylene and propylene (CH ₂ ＣＨCH
R and R are a hydrogen atom, an alkyl group or a halogen such as Cl), a fluorine-based monomer such as ethylene trifluoride chloride, hexafluoropropylene, hexafluoroisobutene, or CF ₂ ＣＦCF—O—C _n F _{2n + 1} ( n is an integer of 1 or _{more), CH 2 = CF-C} n F 2n + 1 (n is an integer of 1 or more),
_{CH 2 = CF- (CF 2 CF} 2) n H (n is an integer of 1 or more), further _{CF 2 = CF-O- (CF} 2 CF (CF 3)
_{O) m -C n F 2n +} 1 (m, n is an integer of 1 or more) can be used. In addition, equation (1):

[0020]

Embedded image

(Where Y is —CH ₂ OH, —COOH,
A carboxylate, a carboxyester group or an epoxy group, X and X ¹ are the same or different and each is a hydrogen atom or a fluorine atom, and R _f is a divalent fluorinated alkylene group having 1 to 40 carbon atoms or 1 to 40 carbon atoms. Represents a divalent fluorinated alkylene group having an ether bond), and a fluorine-containing ethylenic monomer having at least one functional group represented by the following formula: By copolymerizing one or more of these monomers, the adhesion to the current collector is further improved, and the electrode active material does not peel off from the current collector even after repeated charging and discharging. And good charge / discharge cycle characteristics.

The copolymer mainly composed of vinylidene fluoride and tetrafluoroethylene (hereinafter, also referred to as “vinylidene fluoride-tetrafluoroethylene copolymer”) used for the binder for the battery of the present invention is a polyolefin. Although it is soluble in nitrogen-containing organic solvents such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide, which are solvents of vinylidene chloride, it is also soluble in commonly used low-boiling general-purpose organic solvents. The degree of swelling is small relative to the organic electrolyte. Therefore, a flexible electrode mixture and electrode sheet can be provided by using the copolymer.

General-purpose organic solvents having a low boiling point include ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; tetrahydrofuran;
Ether solvents such as dioxane; and mixed solvents thereof.

When the copolymer is used as a binder, it is common to disperse and mix an electrode material such as an electrode active material in a solution in which the copolymer is dissolved in a solvent. In addition, for example, after mixing the copolymer powder and the electrode active material powder first, an organic solvent may be added to prepare a mixture. Further, the powder of the copolymer and the electrode active material is heated and melted, and extruded with an extruder to prepare a thin film mixture, and the conductive adhesive or the general-purpose organic solvent is coated on the current collector. To form an electrode sheet. Further, a solution of the copolymer may be applied to a preformed electrode active material. Thus, the method of applying the binder is not particularly limited.

As one of the methods for improving the adhesiveness between a current collector containing a binder comprising a copolymer and a current collector, a mixture paint applied on the current collector is used in the binder. There is a method of performing a drying treatment at a temperature higher than the melting point of the copolymer. However, in the case of the conventional binder polyvinylidene fluoride, Japanese Patent Laid-Open No.
Japanese Patent No. 249859 discloses a relatively high temperature (170 to 180).
℃ or more. The general melting point of polyvinylidene fluoride is 1
It is described that when the mixture paint is dried at around 75 ° C.), the material of polyvinylidene fluoride changes, and as a result, the capacity retention of the charge / discharge cycle characteristics deteriorates.
In the copolymer used in the present invention, such a problem does not occur due to the heating and drying treatment, the intended improvement in adhesiveness is recognized, and the battery performance is stable.

[0026] As the binder of the present invention, further prior to improve the adhesion Symbol ternary or higher copolymer in polymethacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyamide, polyamideimide, resins such as polycarbonate May be included,
The content of these resins in the binder is about 20% by volume.
It is preferred that:

The non-aqueous electrolyte secondary battery to which the binder of the present invention is applied is a positive electrode comprising a positive electrode mixture comprising a positive electrode active material, a conductive agent and a binder held on a positive electrode current collector. A negative electrode in which a negative electrode mixture comprising a negative electrode active material and a binder is held on a negative electrode current collector; and a non-aqueous electrolyte.

The present invention also relates to a battery electrode mixture comprising the above binder and another electrode material. Other electrode materials include the following positive electrode active materials, negative electrode active materials, and conductive agents.

The positive electrode active material used in the present invention includes:
Transition metal oxides such as manganese dioxide and vanadium pentoxide; transition metal chalcogenides such as iron sulfide and titanium sulfide; and composite oxides containing lithium can be used. In particular, since a high voltage and a high energy density are obtained and the charge / discharge cycle characteristics are excellent, the formula L
i _X A _1-Y M _Y O ₂ (A is at least one transition metal element selected from the group consisting of Mn, Co, and Ni; M is B;
Mg, Ca, Sr, Ba, Ti, V, Cr, Mn, F
e, Co, Ni, Cu, Al, In, Nb, Mo, W,
A lithium-containing oxide represented by at least one element selected from the group consisting of Y and Rh, 0.05 ≦ X ≦ 1.1, 0 ≦ Y ≦ 0.5) is preferable. Specific examples include lithium cobaltate (LiCoO _2), lithium nickel oxide (LiNiO _2), lithium manganate (LiMn ₂ O ₄₎ is desirable.

On the other hand, as the negative electrode active material, a carbonaceous material that can be doped / dedoped with lithium or the like is used. For example, a conductive polymer such as polyacene or polypyrrole, coke, polymer charcoal, carbon fiber, etc. Because of the high energy density per unit, pyrolytic carbons, cokes (such as petroleum coke, pitch coke, and coal coke), carbon black (such as acetylene black), glassy carbon, and organic polymer material fired bodies (organic polymer The material is preferably fired at a temperature of 500 ° C. or higher in an inert gas stream or in a vacuum).

Examples of the conductive agent include carbon blacks such as acetylene black and Ketjen black, and carbon materials such as graphite.

The binder of the present invention is used as a binder in a positive electrode mixture and / or a negative electrode mixture, and its compounding ratio is 0.1 to 20% by weight, preferably 1 to 10% by weight of the electrode mixture. %. The remainder is the electrode material.

The positive electrode current collector to which the electrode mixture is adhered is, for example, aluminum foil, and the negative electrode current collector is, for example, copper foil.

The non-aqueous electrolyte is not particularly limited. Examples of the organic solvent include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like. One or more known solvents such as dimethyl carbonate and diethyl carbonate can be used. Any conventionally known electrolyte can be used,
LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , L
iCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li,
Cesium carbonate or the like can be used. Furthermore, in order to further improve the adhesiveness with the current collector, for example, an acrylic resin such as polymethacrylate and polymethyl methacrylate, a polyimide, a polyamide, and a polyamideimide resin are further included in the battery electrode mixture of the present invention. You may use together.

The binder of the present invention can be used as a binder for a non-aqueous electrolyte secondary battery not only for a lithium ion secondary battery using the above-described liquid electrolyte but also for a separator holding an electrolyte or an electrolyte. It is also useful for a polymer electrolyte lithium secondary battery as a polymer electrolyte (so-called polymer gel electrolyte) that also plays a role of.

[0036]

EXAMPLES Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. In addition, as a binder for non-aqueous electrolyte secondary batteries
50-80 mol% of usable vinylidene fluoride and tetra
Binary composed of 20 to 50 mol% of fluoroethylene
The copolymer is also described in Examples, but is a reference example. two
Examples (reference) relating to the copolymer are Examples 1 to 3.
You.

Examples 1 to 9 Binary copolymers of vinylidene fluoride and tetrafluoroethylene shown in Table 1 and terpolymers obtained by copolymerizing other copolymerizable monomers to improve adhesion. The polymer was produced by a conventional method. Table 1 shows their compositions, molecular weights and their solubility in organic solvents. In addition, as Comparative Examples 1 to 4, Table 1
The results for the copolymer and polyvinylidene fluoride (VP825 manufactured by Daikin Industries, Ltd.) are also shown.

The solubility of the organic solvent in each solvent was from room temperature to 50 ° C. for 10% by weight of the copolymer shown in Table 1.
Table 1
In the table, ○ indicates soluble and × indicates insoluble.

[0039]

[Table 1]

Example 10 10 g of the copolymer powder of Examples 1 to 9 was filled in a mold having a diameter of 12 cm, and was pressed at 230 ° C. and a gauge pressure of 15 with a 50-ton press.
The sheet was pressed at kg / cm ² for 15 minutes to obtain a sheet having a thickness of about 0.5 mm. Similarly, the polyvinylidene fluoride of Comparative Example 3 was press-molded into a sheet. Strips having a width of 0.5 cm and a length of 3 cm were cut out from these sheets and subjected to dynamic viscoelasticity measurement (Rheometrics).
s), measurement frequency: 3.5 Hz, 25 ° C.). Table 2 shows the results.

[0041]

[Table 2]

Example 11 The copolymer molded sheets of Examples 1 to 9 produced in Example 10 were cut into strips having a width of 1 cm and a length of 5 cm, and were cut out using a hydrometer (DENSI METER manufactured by Toyo Seiki Co., Ltd.). The volume was measured. Next, they were immersed in a mixed solution of propylene carbonate and ethylene carbonate (1: 1 by volume) and a mixed solution of ethylene carbonate and diethyl carbonate (1: 1 by volume) heated to 85 ° C., respectively.
The volume change rate after 72 hours (the ratio of the volume increased by immersion) was measured. For comparison, the polyvinylidene fluoride and the copolymer powder of Comparative Examples 3 and 4 were used in Example 10.
And a strip sheet cut into the same shape from a molded sheet obtained in the same manner as described above, and a terpolymer fluorovinyl rubber (vinylidene fluoride (VdF) -tetrafluoroethylene (TFE) -hexafluoropropylene (HFP)) Vinylidene / tetrafluoroethylene / hexafluoropropylene = 60/20/20, mol%) was formed into a sheet in the same manner as in Example 10, and a strip sheet cut into the same shape was measured in the same manner. Table 3 shows the results.

[0043]

[Table 3]

Example 12 (Preparation of negative electrode) Carbon black 60 was used as a negative electrode active material.
Parts by weight, as a binder, Example 1 (binary), Examples 4 to
5 parts by weight of each of the copolymers 6 and 9 (ternary) or the polyvinylidene fluoride of Comparative Example 3 and N-
35 parts by weight of methylpyrrolidone, methylethylketone, or tetrahydrofuran were mixed using a ball mill for 10 hours to prepare a negative electrode mixture. This mixture is dried on both sides of a 10 μm thick copper foil serving as a negative electrode current collector to a thickness of 10 μm.
It was applied so as to have a thickness of 0 μm, finally dried at 120 ° C., and then subjected to a rolling treatment to produce a strip-shaped negative electrode.

(Preparation of Positive Electrode) LiCo as a positive electrode active material
60 parts by weight of O ₂ , 5 parts by weight of acetylene black as a conductive agent, and Examples 1 (binary) and Examples 4 to 4 as binders
5 parts by weight of each of the copolymers 6 and 9 (ternary) or the polyvinylidene fluoride of Comparative Example 3 and N-
30 parts by weight of methylpyrrolidone, methylethylketone, or tetrahydrofuran were mixed using a ball mill for 10 hours to prepare a positive electrode mixture. This mixture was applied to both sides of a 20 μm-thick aluminum foil serving as a positive electrode current collector so that the thickness after drying became 100 μm.
After drying at ℃, rolling treatment was performed to produce a belt-shaped positive electrode.

(Preparation of Battery) A battery was prepared using the band-shaped negative electrode and the band-shaped positive electrode prepared as described above according to the method described in JP-A-7-201316.

That is, the strip-shaped positive electrode and the strip-shaped negative electrode are laminated via a polypropylene film having a thickness of 25 μm as a separator, and this is wound many times to obtain an outer shape 1
An 8 mm spiral electrode body was produced. The spiral electrode body was housed in a nickel-plated iron battery can, and insulating plates were placed above and below the spiral electrode body. Then, the aluminum positive electrode lead was led out of the positive electrode current collector and welded to the battery lid, and the nickel negative electrode lead was led out of the negative electrode current collector and welded to the battery can.

A non-aqueous electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1 in a battery can containing the spiral electrode body. The liquid was injected.
Then, a safety valve device having a current interruption mechanism, the battery lid is fixed to the battery can by caulking through an insulating sealing gasket whose surface is coated with asphalt, and a cylindrical non-aqueous electrolyte having a diameter of 18 mm and a height of 65 mm is removed. The secondary batteries used were produced (shown as batteries A to P in Table 4).

The thus prepared non-aqueous electrolyte secondary battery was charged for 2.5 hours at room temperature under the conditions of a maximum charging voltage of 4.2 V and a charging current of 1 A, and then 6.2.
A charge / discharge cycle such as discharging with a constant resistance of Ω was repeatedly performed, a change in discharge capacity was observed, and the number of cycles at which the discharge capacity decreased to 50% of the initial capacity (50% capacity cycle number) was examined. Table 4 shows the results.

[0050]

[Table 4]

As can be seen from the results shown in Table 4, the batteries A to M using the vinylidene fluoride-tetrafluoroethylene-based copolymer were 50 times larger than the batteries N to P using the polyvinylidene fluoride as the binder. % Capacity cycle number, and exhibit good charge / discharge cycle characteristics. In addition, the reason that the cycle characteristics of the battery M are particularly good is that the aluminum foil, the copper foil, which is a current collector, It is considered that the adhesiveness with the mixture was further improved.

Thus, the use of a vinylidene fluoride-tetrafluoroethylene copolymer, particularly a copolymer having a relatively large number average molecular weight, as a binder can improve the charge / discharge cycle characteristics of a battery. Is effective.

Example 13 (Preparation of Negative Electrode) A belt-like material was prepared in the same manner as in Example 12, except that N-methylpyrrolidone was used as the solvent for the binder and the drying temperature of the mixture was 190 ° C. A negative electrode was manufactured.

(Preparation of positive electrode) A belt-shaped positive electrode was prepared in the same manner as in Example 12, except that N-methylpyrrolidone was used as a solvent for the binder and the drying temperature of the mixture was 190 ° C. did.

(Preparation of Battery) A secondary battery using a non-aqueous electrolyte was prepared in the same manner as in Example 12 using the band-shaped negative electrode and band-shaped positive electrode thus prepared (shown as batteries Q to U in Table 5). A test (50% capacity cycle number) was conducted in the same manner as in Example 12. Table 5 shows the results.

[0056]

[Table 5]

As can be seen from the results in Table 5, the batteries Q to T using the vinylidene fluoride-tetrafluoroethylene-based copolymer had a 50% capacity compared to the battery U using the polyvinylidene fluoride as the binder. It has a large number of cycles and exhibits good charge / discharge cycle characteristics.

This indicates that the use of a vinylidene fluoride-tetrafluoroethylene copolymer as a binder is effective in improving the charge / discharge cycle characteristics of a battery.

[0059]

According to the present invention, it is more flexible than the conventional polyvinylidene fluoride, and is not limited to conventional solvents such as N-methylpyrrolidone, dimethylacetamide and dimethylformamide, but also has low flexibility such as acetone and methyl ethyl ketone. Binder for non-aqueous electrolyte secondary batteries that is soluble in general-purpose organic solvents having a boiling point and has less swelling in organic solvents of non-aqueous electrolyte than conventional fluorine-based binary or terpolymer. And a battery electrode mixture. As a result, in battery manufacturing, manufacturing costs can be reduced by simplifying manufacturing equipment and improving yield, and the battery performance can be reduced by 50%.
It is possible to provide a battery having a large% capacity cycle number and exhibiting good charge / discharge cycle characteristics.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadashi Ino 1-1 Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works (72) Inventor Kenji Ichikawa 1-1-1, Nishiichitsuya, Settsu-shi, Osaka Daiki (56) References JP-A-9-199133 (JP, A) JP-A-10-134819 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/62 H01M 10/40

Claims (5)

(57) [Claims] 1. A positive electrode comprising a positive electrode active material, a conductive agent and a binder held by a positive electrode current collector and / or a negative electrode mixture comprising a negative electrode active material and a binder comprising a negative electrode current collector In a binder used for a nonaqueous electrolyte secondary battery comprising a negative electrode held by a body and a nonaqueous electrolyte, the binder does not contain polytetrafluoroethylene, and vinylidene fluoride 50 to 50% 80 mol% and tetrafluoroethylene 1
A ternary or higher copolymer composed of 7 mol% or more and less than 50 mol% and less than 3 mol% of a monomer copolymerizable therewith, comprising N-methylpyrrolidone, tetrahydrofuran
, Methyl ethyl ketone and acetone
A binder for a non-aqueous electrolyte secondary battery, comprising a copolymer that can be dissolved at room temperature to 50 ° C. up to 10% by weight of the copolymer . 2. The copolymer has a number average molecular weight of 150,
Non-aqueous electrolyte binder for secondary battery according to claim 1 wherein the 000～500,000. 3. A non-aqueous electrolyte binder for secondary battery according to claim 1 or 2, wherein the positive electrode active material a lithium-containing oxide. 4. A mixture for batteries comprising a non-aqueous electrolyte secondary battery binder according to any one of claims 1-3. 5. A non-aqueous electrolyte secondary battery comprising the battery mixture according to claim 4 .