WO2004049475A1

WO2004049475A1 - Binder composition for electrode of nonaqueous electrolyte battery, and electrode mixture, electrode and battery using same

Info

Publication number: WO2004049475A1
Application number: PCT/JP2003/014903
Authority: WO
Inventors: Mitsuyasu Sakuma; Nobuo Ahiko; Tomoaki Kawakami; Takumi Katsurao
Original assignee: Kureha Chemical Industry Company, Limited
Priority date: 2002-11-22
Filing date: 2003-11-21
Publication date: 2004-06-10
Also published as: TW200410439A; JPWO2004049475A1; KR20050085095A; CN100365853C; AU2003284631A1; TWI330902B; CN1714465A; JP4851092B2

Abstract

A composition comprising at least a functional group-containing vinylidene fluoride polymer and a polar polymer having a hydroxyl group and/or a carbonyl group in the molecule is used as a binder for an electrode (a positive or negative electrode) active material. Consequently, a nonaqueous electrolyte battery can have improved performance stability and improved safety at the time of internal short-circuiting while maintaining a necessary large capacity.

Description

Non-aqueous electrolyte battery electrode binder composition and electrode mixture using the same,

Electrodes and batteries Technical field

The present invention relates to an electrode binder used in the production of a nonaqueous electrolyte battery, particularly a lithium ion battery, an electrode mixture using the same, an electrode, and a nonaqueous electrolyte battery using the same. Light

Background art

In recent years, the development of electronic technology has been remarkable, and various devices have been reduced in size and weight. Along with the downsizing and weight reduction of electronic devices, demands for downsizing and weight reduction of batteries serving as power sources have become very large. Non-aqueous rechargeable batteries using lithium as batteries that can obtain more energy with a small volume and weight are used as power sources for small electronic devices mainly used in homes such as mobile phones, personal computers, and video camcorders. Has been used.

The electrode structure for a lithium-ion battery is used in a state where an active material and a conductive agent are held on a current collector by a binder. A lithium composite oxide is used as a positive electrode active material, a carbon-based material is used as a negative electrode active material, and a carbon-based material is used as a negative electrode active material. A vinylidene fluoride polymer is mainly used as a binder for binding the active materials.

Japanese Patent Application Laid-Open No. 11-329443 exemplifies a mixture of a vinylidene fluoride-based polymer and a cellulose-based polymer having no functional group. It was not considered at all.

However, the market demand for smaller and lighter equipment and longer battery life has imposed higher capacity on lithium-ion batteries, and the capacity inside the battery has been reduced by clogging the electrodes, etc. On the other hand, if a short circuit occurs inside the battery, an excessive current will flow locally, causing a sudden rise in the temperature of the battery, causing a dangerous condition such as explosion, smoke or ignition of the battery. There is a problem that the property increases. Disclosure of the invention

Therefore, the main problem of the present invention is to maintain the required high capacity of a non-aqueous electrolyte battery while improving its performance stability and safety in the event of an internal short circuit. An object of the present invention is to provide a binder composition for an electrode, and an electrode and a non-aqueous electrolyte battery using the same.

The present invention solves the above-mentioned problems, and according to a first aspect, a positive electrode and / or a negative electrode of a nonaqueous electrolyte battery including a positive electrode capable of inserting and extracting lithium and a negative electrode. A binder composition used as a binder of the above, comprising at least a functional group-containing vinylidene fluoride polymer and a polar polymer having a hydroxyl group and / or a carbonyl group in the molecule. It is intended to provide a binder composition for a non-aqueous electrolyte battery electrode characterized by the following.

In another aspect, the present invention provides an electrode mixture containing the binder composition and an electrode active material, an electrode having a layer of the electrode mixture on a current collector, and at least one of a positive electrode and a negative electrode. The present invention provides a non-aqueous electrolyte battery including:

It is not clear why the binder composition described above can improve the performance stability and safety in the event of an internal short circuit while maintaining the required high capacity of a non-aqueous electrolyte battery, but it is not clear why. The carboxyl group ゃ glycidyl group in the vinylidene fluoride polymer and the hydroxyl group and carbonyl group of the polar polymer form a hydrogen bond with the hydroxyl group on the surface of the current collector and the surface of the electrode active material, and the adhesiveness as a binder A lithium ion selective permeable film is formed on the surface of the electrode active material to block the permeation of the non-aqueous electrolyte, and is synthesized by the reaction between the electrolyte and lithium ions during charging and discharging on the surface of the electrode active material. The generation of lithium compounds is suppressed, so even if the temperature inside the charged battery rises due to a short circuit, etc., there are few thermally unstable lithium compounds and the decomposition heat generation is suppressed. In addition, it is thought to have the function of suppressing the direct reaction between lithium ions in the active material and the electrolyte. In addition, the temperature rise in a nail penetration test, which was performed to predict the temperature rise during an internal short circuit described later, and the adhesive strength of the binder show an inverse correlation, indicating that the safety during an internal short circuit It is understood that the adhesiveness of the binder also plays an important role in improving (decreasing the temperature rise). In other words, it can be understood that the (a) selective permeability of lithium ion and the (mouth) improvement in adhesive strength of the binder synergistically contribute to the improvement of safety in the event of an internal short circuit. Preferred embodiment

Examples of the functional group-containing vinylidene fluoride-based polymer of the present invention include vinylidene fluoride monomer alone or other monomers copolymerizable with a vinylidene fluoride monomer, for example, carbonization of ethylene or propylene. Hydrogen-based monomer, or butyl fluoride, trifluoroethyl Fluorine-containing monomers other than fusidylvinylidene, such as triethylene, tetraphthanol, ethylene, hexafolenoleethylene, hexafluoropropylene, and fluoroanolequinolebininoleether (Preferably 20% by weight or less of the total amount with the vinylidene fluoride monomer), and 0.1 to 3 parts by weight of a monomer having a functional group is added to 100 parts by weight of the mixture. Copolymers are preferably used. Monomers having a functional group include those having a carboxyl group and those having a glycidyl group. Examples of the carboxyl group-containing monomer include unsaturated monobasic acids such as acrylic acid and crotonic acid, unsaturated dibasic acids such as maleic acid and citraconic acid, and monomethyl maleate which is a monoalkyl ester thereof. Esters, monoethyl maleate, monomethyl citraconic acid, monoethyl citraconic ester and the like. Examples of the glycidyl group-containing monomer include acrylidicidyl ether, methacrylic glycidyl ether, glycidinole crotonate, and dalicidyl acetyl acetate. A functional group-containing vinylidene fluoride polymer obtained by copolymerizing at least one or more of these is preferably used. These functional group-containing vinylidene fluoride polymers can be obtained by known methods such as suspension polymerization, emulsion polymerization, and solution polymerization. As a method for introducing a functional group, a vinylidene fluoride-based polymer may be dehydrofluorinated with a heated base or the like, and then treated with an organic acid or an oxidizing agent to obtain a polymer containing a functional group.

As disclosed in JP-A-9-189023, the molecular weight of a functional group-containing vinylidene fluoride polymer is determined by measuring the intrinsic viscosity (4 g of resin in 1 liter of N, N —The logarithmic viscosity at 30 ° C. of a solution dissolved in dimethylformamide) is 0.8 to 20 dl / g, preferably 1.0 to 20 dl Zg, and more preferably 1.0 to 1 dl / g. 5 dl / g, more preferably 1.2 to 15 dl Zg is suitably used. If the intrinsic viscosity of the vinylidene fluoride polymer is less than the above range, the viscosity of the electrode mixture becomes low and coating becomes difficult, and if it exceeds the above range, dissolution in an organic solvent becomes difficult and Absent.

The polar polymer used in the present invention includes a polymer having a hydroxyl group and a polymer having a carboxy group. Examples of the polymer having a hydroxyl group include an ethylene vinylinoleanol copolymer, a senorelose polymer, and a vinylol phenol polymer. Examples of the polymer having a carboxy group include a polyacrylic acid-based polymer, more specifically, polyacrylic acid, a polyacrylic acid cross-linked polymer, and metal salts thereof. Examples of the polar polymer include polybutylpyrrolidone Is also preferably used.

If necessary, in addition to a functional group-containing vinylidene fluoride-based polymer, a polar polymer having a hydroxyl group or a hydroxyl group, a homopolymer of vinylidene fluoride, vinylidene fluoride and fusidani vinyl, A copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride such as trifluoroethylene, chlorofluoroethylene, tetrafluoroethylene, and hexafluoropropylene can be added.

In the present invention, the mixing ratio between the functional group-containing vinylidene fluoride copolymer and the polar polymer is 10 to 99% by weight, preferably, the functional group-containing vinylidene fluoride copolymer. 20-95 weight. / ₀ , the polar polymer is 1 to 90% by weight, preferably 5 to 80% by weight. If the mixing ratio of the polar polymer is less than the above range, the state of coating on the surface of the active material is insufficient and the contact area between the surface of the active material and the electrolytic solution is increased, resulting in poor battery safety. Further, the adhesiveness between the polymer electrode and the current collector and the binding property between the electrode active materials are reduced, and there is a concern that the discharge capacity during repeated charge and discharge is reduced.

On the other hand, if the mixing ratio of the polar polymer is larger than the above range, the film formed on the electrode surface becomes too thick, the lithium ion permeability at the interface between the active material and the electrolyte is inferior, and the internal resistance increases. There is a concern that the charge / discharge capacity may decrease.

The binder composition of the present invention is usually prepared by dissolving a functional group-containing vinylidene fluoride polymer and a polar polymer constituting the binder composition in a solvent, and further dissolving the positive electrode or negative electrode active material and, if necessary, An auxiliary agent such as a conductive auxiliary agent to be added is dispersed to form a slurry-like electrode mixture, which is used for manufacturing an electrode. The solvent is preferably a polar organic solvent, such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, Hexamethylphosphamide, triethyl phosphate, acetone and the like. These organic solvents can be used alone or in combination of two or more.

In the present invention, the active material of the lithium ion secondary battery for other, in the case of the positive electrode, the general formula L i MY ₂ (M is C o, N i, F e , Mn, C r, transition metals V, etc. At least one of the following: Y is a chalcogen element such as 0 or S); in the case of a negative electrode, natural graphite, artificial graphite, coke, activated carbon, phenolic resin, pitch, etc. powdery carbonaceous material, a metal oxide-based _{G e 0, G e 0 2} , SO, S n0 2, P b O, P b 0 2 or the like or a mixed metal oxide thereof, S i, S i S For example, a key compound such as n and a silicon compound are used. The binder composition is used in an amount of 0.1 to 30 parts by weight, and especially 0 to 30 parts by weight, based on 100 parts by weight of the electrode (positive electrode or negative electrode) active material and the conductive additive (these are collectively referred to as “powder electrode material”). It is preferable to use 5 to 20 parts by weight.

When the binder composition is used by dissolving it in an organic solvent in advance, the solvent may be used alone or as a mixture of two or more, and the binder composition may be used in an amount of 0.1 to 30 parts by weight, particularly 100 parts by weight of the solvent. It is preferable to use it at a ratio of 1 to 20 parts by weight.

As a device used for mixing the mixture comprising the binder composition, the powdered electrode material, and the organic solvent, a homogenizer, a multiaxial planetary dispersion / mixing / kneading machine or an emulsifier can be used, but is not limited thereto. It is not done.

The mixture slurry prepared by the above method is uniformly dispersed and mixed with the powdered electrode material and the binder composition, and is applied to the current collector with good applicability. The coating method may be a known method, and among them, the doctor blade method is preferably used. The mixture on the current collector is solvent-dried at, for example, 50 to 170 ° C., and if necessary, subjected to a pressing step to form an electrode structure for a non-aqueous secondary battery or the like.

The binder composition and the electrode mixture of the present invention are used for forming at least one of a positive electrode and a negative electrode, and if any one of them is preferably used for forming a negative electrode. This is because the powdered electrode material constituting the negative electrode requires a binder having higher adhesiveness, and the binder composition of the present invention is particularly suitable.

【Example】

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

(Production of functional group-containing bilidene fluoride copolymer A)

In a 2-liter autoclave, ion-exchanged water (175 g), methylcellulose (0.4 g), vinylidene fluoride monomer (VDF) (398 g), maleic acid monomethyl ester (MMM) (2) g, 2.5 g of isopropyl peroxydicarbonate and 5 g of ethyl acetate were subjected to suspension polymerization at 28 ° C. for 27 hours.

After the polymerization is completed, the polymer slurry is dehydrated, washed with water, dehydrated, and then dried at 80 ° C for 20 hours. The functional group-containing hydrofluoric acid of the present invention having a yield of 89% and an inherent viscosity of 1.1 d 1 A vinylidene fluoride polymer A was obtained.

(Production of functional group-containing vinylidene fluoride polymer B)

In a 2-liter autoclave, ion-exchanged water (175 g), methylcellulose (0.4 g), vinylidene fluoride monomer (VDF) 400 g, 2-methyldaricidinolemethacrylate (2M-GMA) 3 g, isopropyl peroxydicarbonate 2.5 _g and 5 _g of ethyl acetate were charged, and suspension polymerization was performed at 28 ° C. for 25 hours. After the polymerization, the polymer slurry is dehydrated and washed with water.After dehydration, the polymer slurry is dried at 80 ° C for 20 hours to obtain a functional group-containing vinylidene fluoride having a yield of 90% and an inherent viscosity of 2.4 d 1. Polymer B was obtained.

(Production of vinylidene fluoride polymer C)

In a 2-liter autoclave, ion-exchanged water (175 g), methylcellulose (0.4 g), vinylidene fluoride monomer (VDF) (400 g), isopropyl peroxydicarbonate (2.5 g), Each amount of 5 g of ethyl acetate was charged, and suspension polymerization was performed at 26 ° C for 20 hours.

After the polymerization is completed, the polymer slurry is dehydrated, washed with water, dehydrated, and dried at 80 ° C for 20 hours. A vinylidene fluoride polymer having a yield of 91% and an inherent viscosity of 1.1 d 1 / g is obtained. C (polyvinylidene fluoride) was obtained.

(Preparation of positive electrode)

N-methyl-2-pyrrolidone (NMP) was added to 94 parts by weight of lithium cobaltate ("Cellseed C-5", manufactured by Nippon Chemical Industry), 3 parts by weight of vinylidene fluoride polymer C, and 3 parts by weight of carbon black. 43 parts by weight were added and mixed to prepare a positive electrode mixture. The obtained mixture was uniformly applied on a 10 / m-thick aluminum foil so that the film thickness after drying was about 100 μηι, and dried at 130 ° C for 25 minutes. A positive electrode structure (active material amount: 29 1 g / m ² ) was obtained.

(Preparation of negative electrode)

1 part by weight of functional group-containing vinylidene fluoride polymer A, 1 part by weight of ethylene vinyl alcohol copolymer (EVOH, “Eval EP-G156B” made of Kuraray clay, ethylene mole content 47%) A negative electrode mixture composition A of the present invention was prepared by mixing 88 parts by weight of spherical natural graphite powder (produced in China) with an average particle diameter of 30 μm and 67 parts by weight of NMP. The resulting mixture was applied evenly on a copper foil with a thickness of 8 / zm to a thickness of about 100 / xm after drying, and dried at 130 ° C for 25 minutes. A negative electrode structure A (the amount of the active material: 163 g / m ² ) was obtained.

(Method of measuring peel strength of electrode mixture layer in electrode structure)

The negative electrode structure applied to the current collector and dried was used as a sample, and the peel strength of the electrode mixture layer from the current collector was measured by a 180 ° peel test in accordance with JIS K 6854.

(Measurement of peel strength) When the peel strength of the negative electrode structure A was measured, it was 3.8 g iZmm.

(Production of battery)

Positive electrode structure cut out to 48 mm x 48 mm and fitted with charge and discharge leads, and negative electrode structure A cut out to 5 Omm x 50 mm and fitted with charge and discharge leads To overlap through a 52 mm x 52 mm polyethylene separator with a thickness of 20 m, and the lead part comes out to an aluminum laminate bag with dimensions of 80 mm x 80 mm and polyethylene on the outside embedded manner, ethylene carbonate methyl E chill carbonate / Jimechiruka one Boneto (9Z 1 3 1 6 volume ratio), the L i PF ₆ after the electrolytic solution 1 g was added containing with 1 M concentration in a mixed solvent, Arumiramine one DOO The battery bag was sealed to obtain Battery A of the present invention.

(Charge and discharge)

Battery A was charged to 4.2 V with a constant current of 0.2 mA, then discharged to 3.0 V with a constant current of 0.2 mA, and then 4.37 V with a constant current of 1 mA. Charged up to. The charge capacity (integral value of the charge current value) of the battery in the second charge was 133 mAh.

(Nail penetration test)

In the room where the room temperature was maintained at 23 ° C, the above charged battery A was allowed to stand on a wooden plate with the negative electrode facing up, and a nail with a diameter of 1 mm was stabbed and penetrated. The rise in battery surface temperature was measured using an infrared thermograph (“TVS-100” manufactured by Avionics). The maximum temperature rise of battery A after nail penetration was 3 ° C.

The procedure of Example 1 was repeated except that polyacrylic acid (PAA) (“AQUPEC HV—501”, manufactured by Sumitomo Seika) was used instead of EVOH in the fabrication of the negative electrode. Got B.

The peel strength of negative electrode structure B was 1. O g f Zmm Battery B had a charge capacity of 135 mAh, and the maximum temperature rise in the nail penetration test was 3.5 ° C.

The procedure of Example 1 was repeated except that the functional group-containing vinylidene fluoride polymer B was used in place of the functional group-containing vinylidene fluoride polymer A in the preparation of the negative electrode. Got C.

The peel strength of negative electrode structure C was 4.3 gf / mm, the charge capacity of battery C was 13 OmAh, and the maximum temperature rise in the nail penetration test was 3 ° C.

<Example 4> The same procedure as in Example 1 was carried out, except that hydroxethyl cellulose (HEC) (“HEC Daicel EP850”, manufactured by Daicel Chemical Industries) was used instead of EVOH in the preparation of the negative electrode. Battery D was obtained.

The peel strength of negative electrode structure D was 0.9 gf / mm, the charge capacity of battery D was 133 mAh, and the maximum temperature rise in the nail penetration test was 3 ° C.

The procedure of Example 1 was repeated, except that polyparabule fuenoren (PPVP) (“Markalinker I-S-2PJ”, Maruzen Petrochemical Co., Ltd.) was used instead of EVOH in the preparation of the negative electrode. Structure H and battery H were obtained.

The peel strength of the negative electrode structure H was 5.4 g f Zmm, the charging capacity of the battery H was 134 mAh, and the maximum temperature rise in the nail penetration test was 4 ° C.

The procedure of Example 1 was repeated, except that the amount of the functional group-containing vinylidene fluoride polymer A was increased from 11 g to 12 g in the preparation of the negative electrode, and EV0H was not used. Battery E was obtained.

The peel strength of the negative electrode structure E was 0.9 gf / mm, the charge capacity of the battery E was 133 mAh, and the maximum temperature rise in the nail penetration test was 12 ° C.

The same procedure as in Example 3 was carried out except that the amount of the functional group-containing vinylidene fluoride polymer B was increased from 11 g to 12 g in the preparation of the negative electrode, and EVOH was not used. Battery F was obtained.

The peel strength of the negative electrode structure F was 3.1 g f / mm, the charge capacity of the battery F was 124 mAh, and the maximum temperature rise in the nail penetration test was 6.5 ° C.

Comparative Example 3> '

A negative electrode structure G and a battery G were obtained in the same manner as in Example 1, except that a vinylidene fluoride polymer C was used in place of the functional group-containing vinylidene fluoride polymer A in the preparation of the negative electrode. The peel strength of the negative electrode structure G was 0.1 μg f / mm, the charge capacity of the battery G was 134 mAh, and the maximum temperature rise in the nail penetration test was 6 ° C.

A negative electrode structure G and a battery G were obtained in the same manner as in Comparative Example 1, except that the functional group-containing vinylidene fluoride polymer A was used in place of the functional group-containing vinylidene fluoride polymer A in the preparation of the negative electrode. Peel strength of negative electrode structure H is 0.7 f / mm Battery H has a charge capacity of 13 mAh The maximum temperature rise in the nail penetration test was 9 ° C.

The summary and evaluation results of the binder composition used in the above Examples and Comparative Examples are shown in Table 1 below.

[table 1 ]

Industrial applicability

As can be seen from the results in Table 1 above, in a nonaqueous electrolyte battery including a positive electrode capable of inserting and extracting lithium and a negative electrode, the binder for the positive electrode Z or the negative electrode was a functional group-containing vinylidene fluoride polymer. By using a binder polymer composition for a non-aqueous electrolyte battery electrode, which is a polar polymer, it is possible to obtain an electrode having excellent adhesiveness and a battery having excellent safety.

Claims

The scope of the claims

1. A binder composition used as a binder for a positive electrode and / or a negative electrode of a nonaqueous electrolyte battery provided with a positive electrode and a negative electrode capable of inserting and extracting lithium, and at least a functional group-containing fluorine. A binder composition for a non-aqueous electrolyte battery electrode, comprising a vinylidene fluoride polymer and a polar polymer containing a hydroxyl group and / or a carbonyl group in a molecule.

2. The binder composition according to claim 1, wherein the negative electrode is made of a carbon material.

3. The binder composition for a non-aqueous electrolyte battery electrode according to claim 1, wherein the functional group of the functional group-containing vinylidene fluoride polymer is at least one of a carboxyl group and a glycidyl group.

4. A polar polymer containing a hydroxyl group or a carboxyl group in the molecule. Ethylene bulcohol copolymer, senorelose polymer, polyacrylic acid polymer, polybutylpyrrolidone and burphenol. 4. The pinda composition according to any one of claims 1 to 3, wherein the composition comprises at least one kind of a polymer.

5. An electrode mixture for a non-aqueous electrolyte liquid battery comprising the binder composition according to any one of claims 1 to 4 and an electrode active material.

6. An electrode for a non-aqueous electrolyte battery having an electrode mixture layer comprising the electrode mixture according to claim 5 on a current collector.

7. A non-aqueous electrolyte battery comprising the electrode according to claim 6 as at least one of a positive electrode and a negative electrode.