JP4851092B2 - Non-aqueous electrolyte battery electrode binder composition and use thereof - Google Patents

Description

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

  In recent years, the development of electronic technology has been remarkable, and various devices have been reduced in size and weight. Along with the reduction in size and weight of electronic devices, there is an increasing demand for reduction in size and weight of batteries that serve as power sources. Non-aqueous secondary batteries using lithium are used as power sources for small electronic devices mainly used in homes such as mobile phones, personal computers, video camcorders, etc., as batteries that can obtain greater energy with less volume and weight. Has been.

  An 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 as a positive electrode active material, a carbon-based material as a negative electrode active material, A vinylidene fluoride polymer is mainly used as a binder for binding these active materials.

  JP-A-11-329443 (Patent Document 1) exemplifies a mixture of a vinylidene fluoride polymer having no functional group and a cellulose polymer. However, the binding property is not sufficient, and the safety is also improved. It was not considered at all.

However, market demands for smaller and lighter devices and longer battery duration have imposed higher capacities for lithium-ion batteries, and capacity has been increased by packing electrodes inside the batteries compared to conventional batteries. On the other hand, if a short circuit occurs inside the battery, an excessive current flows locally, leading to a rapid temperature rise of the battery, increasing the risk of causing dangerous conditions such as battery rupture, smoke, and fire. There was a problem to do.
JP-A-11-329443

  Therefore, the main problem of the present invention is to provide a binder composition for an electrode of a nonaqueous electrolyte battery that has improved performance stability and safety during internal short circuit while maintaining the necessary high capacity of the nonaqueous electrolyte battery. And an electrode and a nonaqueous electrolyte battery using the same.

The present invention solves the above-mentioned problems, and in its first aspect, binding of a positive electrode and / or a negative electrode of a nonaqueous electrolyte battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium a binder composition for use as agents, at least (i) carboxy group or a functional group-containing vinylidene fluoride polymer from 20 to 95 wt% having a glycidyl group and (ii) an ethylene-vinyl alcohol copolymer, cellulose A functional polymer containing vinylidene fluoride comprising 5 to 80 % by mass of a polar polymer selected from the group consisting of a polymer, a vinylphenol polymer, polyacrylic acid, a polyacrylic acid crosslinked polymer, and polyvinylpyrrolidone Both the polymer (a) and the polar polymer (b) are dissolved in a polar organic solvent to form a solution. It is to provide an electrolytic solution battery electrode solution type binder composition.

  In another aspect, the present invention includes an electrode mixture including the binder composition and an electrode active material, an electrode having a layer of the electrode mixture on a current collector, and the electrode as at least one of a positive electrode and a negative electrode. A non-aqueous electrolyte battery is provided.

  The reason why the above-mentioned binder composition can improve the performance stability and safety at the time of internal short circuit while maintaining the necessary high capacity of the non-aqueous electrolyte battery is not necessarily clear, but the functional group-containing vinylidene fluoride While the carboxyl group and glycidyl group in the 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 or the surface of the electrode active material to improve adhesiveness, A lithium ion selective permeable film that blocks the permeation of the non-aqueous electrolyte solution is formed on the surface of the electrode active material, and the lithium compound synthesized by the reaction between the electrolyte solution and the lithium ion during charge / discharge on the surface of the electrode active material. Since the generation is suppressed, there are few thermally unstable lithium compounds even when the temperature inside the charged battery rises due to a short circuit etc. It is believed that inhibit also act directly reaction of lithium ions and the electrolyte solution in the material. In addition, since the temperature rise in the nail penetration test conducted to predict the temperature rise at the time of internal short circuit, which will be described later, and the adhesive strength of the binder show an inverse correlation, improvement of safety at the time of internal short circuit It is understood that the adhesive property of the binder also contributes to (decrease in temperature rise). That is, it is understood that (b) selective permeability of lithium ions and (b) improvement in adhesive strength possessed by the binder synergistically contribute to safety improvement during internal short circuit.

As the functional group-containing vinylidene fluoride polymer of the present invention, the vinylidene fluoride monomer alone or other monomers copolymerizable with the vinylidene fluoride monomer, for example, hydrocarbons such as ethylene and propylene Monomers or fluorine-containing monomers other than vinylidene fluoride such as vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, and fluoroalkyl vinyl ether (preferably fluorine monomers) The copolymer obtained by adding a monomer having a functional group of 0.1 to 3 parts by mass to 100 parts by mass of a mixture of 20 % by mass or less of the total amount with the vinylidene chloride monomer) Preferably used. Monomers having a functional group include those having a carboxyl group and those having a glycidyl group. Examples of the monomer containing a carboxyl group include unsaturated-basic acids such as acrylic acid and crotonic acid, unsaturated dibasic acids such as maleic acid and citraconic acid, or monomethyl maleate which is a monoalkyl ester thereof. Examples include esters, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester. Examples of the monomer containing a glycidyl group include allyl glycidyl ether, methallyl glycidyl ether, crotonic acid glycidyl ester, and allyl acetic acid glycidyl ester. Of these, a functional group-containing vinylidene fluoride polymer obtained by copolymerizing at least one of them 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 disclosed in JP-A-9-289023, the molecular weight of the functional group-containing vinylidene fluoride polymer has an inherent viscosity (4 g of resin dissolved in 1 liter of N, N-dimethylformamide). 0.8 to 20 dl / g, preferably 1.0 to 20 dl / g, more preferably 1.0 to 15 dl / g, and still more preferably 1.2 to 15 dl / g. What is g is used suitably. If the inherent 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.

  The polar polymer used in the present invention includes a polymer having a hydroxyl group and a polymer having a carbonyl group. As the polymer having a hydroxyl group, an ethylene vinyl alcohol copolymer, a cellulose polymer, or a vinyl phenol polymer is used. In addition, as the polymer having a carbonyl group, a polyacrylic acid polymer, more specifically, polyacrylic acid or a polyacrylic acid crosslinked polymer is used. Polyvinyl pyrrolidone is also preferably used as the polar polymer.

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

In the present invention, the mixing ratio of the functional group-containing vinylidene fluoride copolymer and the polar polymer is such that the functional group-containing vinylidene fluoride copolymer is 20 to 95 % by mass and the polar polymer is 5 %. -80 mass% . When the mixing ratio of the polar polymer is less than the above range, the covering state of the active material surface is insufficient, the contact area between the active material surface and the electrolytic solution is widened, and the battery safety is inferior. Furthermore, the adhesiveness between the polymer electrode and the current collector and the binding property between the electrode active materials are lowered, and there is a concern that the discharge capacity may be lowered due to repeated charge and discharge.

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

  The binder composition of the present invention is usually prepared by dissolving the functional group-containing vinylidene fluoride polymer and polar polymer constituting the binder composition in a solvent, and further adding a positive electrode or negative electrode active material and as necessary. An auxiliary agent such as a conductive auxiliary agent 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 monodimethyl sulfoxide, hexamethylphosphoamide, triethyl. Examples include phosphate and acetone. These organic solvents can be used alone or in combination of two or more.

In the present invention, as an active material for lithium ion secondary electricity and the like, in the case of a positive electrode, a general formula LiMY ₂ (M is at least one kind of transition metal such as Co, Ni, Fe, Mn, Cr, V: Y is In the case of a composite metal chalcogen compound represented by (chalcogen elements such as O and S), and a negative electrode, powdery carbonaceous material such as natural graphite, artificial graphite, coke, activated carbon, phenolic resin or pitch carbonized material, Metal oxide-based GeO, GeO ₂ , SO, SnO ₂ , PbO, PbO ₂ or the like, or composite metal oxides thereof, silicon and silicon compounds such as Si, SiSn, or the like are used.

The binder composition is 0.1 to 30 parts by weight , particularly 0.5 to 100 parts by weight of an electrode (positive electrode or negative electrode) active material and a conductive additive (these are collectively referred to as “powder electrode material”). It is preferable to use it at a ratio of ˜20 parts by mass .

Further, when used in dissolving in advance the binder composition in an organic solvent, the solvent, alone or in combination, per 100 parts by weight of solvent, binder composition 0.1 to 30 parts by weight, in particular 1 It is preferable to use it at a ratio of ˜20 parts by mass .

  As an apparatus used for mixing a binder composition, a powder electrode material, and a mixture composed of an organic solvent, a homogenizer, a multi-axis planetary dispersion / mixing / kneading machine, or an emulsifier can be used, but is not limited thereto. It is not something.

  In the mixture slurry prepared by the above method, the powder electrode material and the binder composition are uniformly dispersed and mixed, and are applied to the current collector with good coating properties. The application method may be a known method, among which the doctor blade method is preferably used. The mixture on the current collector is solvent-dried at, for example, 50 to 170 ° C., and an electrode structure for non-aqueous secondary electricity and the like is formed through a pressing process as necessary.

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

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

(Production of functional group-containing vinylidene fluoride copolymer A)
In an autoclave with an internal volume of 2 liters, 1075 g of ion exchange water, 0.4 g of methyl cellulose, 398 g of vinylidene fluoride monomer (VDF), 2 g of maleic acid monomethyl ester (MMM), 2.5 g of diisopropyl peroxydicarbonate, 5 g of ethyl acetate The suspension polymerization was carried out at 28 ° C. for 27 hours.

  After completion of the polymerization, the polymer slurry is dehydrated, washed with water, dehydrated, dried at 80 ° C. for 20 hours, and the yield is 89% and the inherent viscosity of the present invention is 1.1 dl / g. Combined A was obtained.

(Production of functional group-containing vinylidene fluoride polymer B)
In an autoclave with an internal volume of 2 liters, 1075 g of ion exchange water, 0.4 g of methyl cellulose, 400 g of vinylidene fluoride monomer (VDF), 3 g of 2-methylglycidyl methacrylate (2M-GMA), 2.5 g of diisopropyl peroxydicarbonate, A volume of 5 g of ethyl acetate was charged, and suspension polymerization was performed at 28 ° C. for 25 hours.

  After completion of the polymerization, the polymer slurry is dehydrated, washed with water, dehydrated, and dried at 80 ° C. for 20 hours to obtain a functional group-containing vinylidene fluoride polymer B having a yield of 90% and an inherent viscosity of 2.4 dl / g. It was.

(Production of vinylidene fluoride polymer C)
In an autoclave with an internal volume of 2 liters, 1075 g of ion-exchanged water, 0.4 g of methyl cellulose, 400 g of vinylidene fluoride monomer (VDF), 2.5 g of diisopropyl peroxydicarbonate, and 5 g of ethyl acetate were charged at 26 ° C. Suspension polymerization was performed for 20 hours.

  After completion of the polymerization, the polymer slurry was dehydrated, washed with water, dehydrated, dried at 80 ° C. for 20 hours, and the yield was 91% and the inherent viscosity was 1.1 dl / g. Vinylidene fluoride polymer C (polyvinylidene fluoride) Got.

<Example 1>
(Preparation of positive electrode)
Lithium cobaltate ( "Cellseed C-5", Nippon Chemical Industrial Co., Ltd.) 94 parts by weight, vinylidene fluoride polymer C3 parts by weight of carbon black 3 parts by N- methyl-2-pyrrolidone (NMP) 43 parts by weight additives And mixed to prepare a positive electrode mixture. The obtained mixture was uniformly applied on an aluminum foil having a thickness of 10 μm so that the film thickness after drying was about 100 μm, and dried at 130 ° C. for 25 minutes to obtain a positive electrode structure (active material amount: 291 g). / M ² ).

(Preparation of negative electrode)
Functional group-containing vinylidene fluoride polymer A11 parts by weight of ethylene-vinyl alcohol copolymer (EVOH, manufactured by Kuraray Co., Ltd., "EVAL EP-G156B" molar ethylene content of 47%) relative to 1 part by weight, spherical natural an average particle size of 30μm A negative electrode mixture composition A of the present invention was prepared by mixing 88 parts by mass of graphite powder (produced in China) and 67 parts by mass of NMP. The obtained mixture was uniformly applied onto a copper foil having a thickness of 8 μm so that the film thickness after drying was about 100 μm, dried at 130 ° C. for 25 minutes, and negative electrode structure A (active material amount: 163 g / m ² ) was obtained.

(Method for measuring peel strength of electrode mixture layer in electrode structure)
Using the negative electrode structure coated and dried on the current collector as a sample, the peel strength of the electrode mixture layer from the current collector was measured by a 180 ° peel test in accordance with JIS K6854.

(Measurement of peel strength)
The peel strength of the negative electrode structure A was measured and found to be 3.8 gf / mm.

(Production of battery)
The positive electrode structure cut out to 48 mm × 48 mm and attached with the charge / discharge lead portion and the negative electrode structure A cut out into 50 mm × 50 mm and attached with the charge / discharge lead portion were attached to 52 mm so that the electrode surfaces face each other. X52mm and 20μm thick polyethylene separators, and 80mm x 80mm in size and assembled into an aluminum laminated bag with polyethylene outside so that the lead part is outside, ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate (9/13/16 volume ratio) After adding 1 g of an electrolytic solution containing LiPF ₆ at a concentration of 1 M in the mixed solvent, the aluminum laminate bag was sealed to obtain a battery A of the present invention.

(Charge / discharge)
The battery A was charged to 4.2 V with a constant current of 0.2 mA, discharged to 3.0 V with a steady flow of 0.2 mA, and further charged to 4.37 V with a constant current of 1 mA. The charging capacity (integrated value of the charging current value) of the battery in the second charging was 133 mAh.

(Nail penetration test)
The charged battery A is left in a room where the room temperature is kept at 23 ° C. so that the negative electrode is on top of a wooden board, and then a nail with a diameter of 1 mm is pierced and penetrated, and an infrared thermography ( The rise of the battery surface temperature was measured with "TVS-100" manufactured by Avionics.

  The maximum temperature rise after nail penetration of battery A was 3 ° C.

<Example 2>
A negative electrode structure B and a battery B were obtained in the same manner as in Example 1, except that polyacrylic acid (PAA) (“AQUPEC HV-501”, manufactured by Sumitomo Seika) was used instead of EVOH in the production of the negative electrode. It was.

  The peel strength of the negative electrode structure B was 1.0 gf / mm, the charge capacity of the battery B was 135 mAh, and the maximum temperature increase in the nail penetration test was 3.5 ° C.

<Example 3>
A negative electrode structure C and a battery C were obtained in the same manner as in Example 1 except that the functional group-containing vinylidene fluoride polymer B was used instead of the functional group-containing vinylidene fluoride polymer A in the production of the negative electrode. It was.

  The peel strength of the negative electrode structure C was 4.3 gf / mm, the charge capacity of the battery C was 130 mAh, and the maximum temperature increase in the nail penetration test was 3 ° C.

<Example 4>
A negative electrode structure D and a battery D were obtained in the same manner as in Example 1 except that hydroxyethyl cellulose (HEC) (“HEC Daicel EP850”, manufactured by Daicel Chemical Industries) was used instead of EVOH in the production of the negative electrode.

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

<Example 5>
Except for using polyparavinylphenol (PPVP) (“Marcalinker S-2P”, Maruzen Petrochemical Co., Ltd.) instead of EVOH in the production of the negative electrode, the same procedure as in Example 1 was carried out. Battery H was obtained.

  The peel strength of the negative electrode structure H was 5.4 gf / mm, the charge capacity of the battery H was 134 mAh, and the maximum temperature increase in the nail penetration test was 4 ° C.

<Comparative Example 1>
The negative electrode structure E and battery E were prepared in the same manner as in Example 1 except that the functional group-containing vinylidene fluoride polymer A was increased from 11 parts by mass to 12 parts by mass and EV0H was not used. Got.

  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 increase in the nail penetration test was 12 ° C.

<Comparative example 2>
The negative electrode structure F and the battery F were prepared in the same manner as in Example 3 except that the functional group-containing vinylidene fluoride polymer B was increased from 11 parts by mass to 12 parts by mass and EVOH was not used. Got.

  The peel strength of the negative electrode structure F was 3.1 gf / mm, the charge capacity of the battery F was 124 mAh, and the maximum temperature increase 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 the vinylidene fluoride polymer C was used in place of the functional group-containing vinylidene fluoride polymer A in preparation of the negative electrode.

  The peel strength of the negative electrode structure G was 0.7 gf / mm, the charge capacity of the battery G was 134 mAh, and the maximum temperature increase in the nail penetration test was 6 ° C.

<Comparative example 4>
A negative electrode structure G and a battery G were obtained in the same manner as in Comparative Example 1 except that the vinylidene fluoride polymer C was used in place of the functional group-containing vinylidene fluoride polymer A in preparation of the negative electrode.

  The peel strength of the negative electrode structure H was 0.7 gf / mm, the charge capacity of the battery H was 132 mAh, and the maximum temperature increase in the nail penetration test was 9 ° C.

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

  As can be seen from the results in Table 1, in the nonaqueous electrolyte battery including a positive electrode and a negative electrode capable of inserting and extracting lithium, the positive electrode / or negative electrode binder is a functional group-containing vinylidene fluoride polymer. It can be seen that by using a binder composition for a nonaqueous electrolyte battery electrode that is a polar polymer, an electrode having excellent adhesion and a battery having excellent safety can be obtained.

Claims (5)

A positive electrode and / or the binder composition used as a binder of the negative electrode of the nonaqueous electrolyte battery and a capable of absorbing and desorbing positive and negative electrodes of lithium, at least (i) carboxy group or a glycidyl group 20-95 % by mass of a functional group-containing vinylidene fluoride-based polymer having styrene and (b) an ethylene vinyl alcohol copolymer, a cellulose polymer, a vinyl phenol polymer, polyacrylic acid, a polyacrylic acid crosslinked polymer, and polyvinyl It consists of 5 to 80 % by mass of a polar polymer selected from the group consisting of pyrrolidone, and both the functional group-containing vinylidene fluoride polymer (a) and the polar polymer (b) are dissolved in a polar organic solvent. Then, the solution type binder composition for nonaqueous electrolyte battery electrodes characterized by forming a solution. The binder composition according to claim 1, wherein the negative electrode is made of a carbon material. The electrode mixture for nonaqueous electrolyte battery electrodes containing the binder composition of Claim 1 or 2 , and an electrode active material. The electrode for nonaqueous electrolyte batteries which has the electrode mixture layer which consists of an electrode mixture of Claim 3 on a collector. A nonaqueous electrolyte battery comprising the electrode according to claim 4 as at least one of a positive electrode and a negative electrode.