JP2013020752A - Binder for battery electrode, composition for battery electrode, electrode for battery and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for battery electrode which ensure excellent adhesion to a collector even in small amount.SOLUTION: The binder for battery electrode is a polymer having 80-99.99 mol% of vinylcyanide unit and 0.01-20 mol% of phosphate group-containing unit, in which the insolubles for N-methylpyrrolidone is 50 mass% or less. The composition for battery electrode contains the inventive water soluble binder. The electrode for battery includes a collector and a mixture layer provided on the collector, where the mixture layer contains the composition for battery electrode and the electrode active material, and the second battery includes the electrode for battery.

Description

 The present invention relates to a battery electrode binder, a battery electrode composition, a battery electrode, and a secondary battery.

 Secondary batteries are used as storage batteries for low-power consumer devices such as notebook computers and mobile phones, and hybrid vehicles and electric vehicles. As the secondary battery, a lithium ion secondary battery (hereinafter sometimes simply referred to as a battery) is frequently used. Generally, as a battery electrode, a battery electrode including a current collector and a mixture layer provided on the current collector and holding an electrode active material and a conductive additive by a binder is used.

As the battery electrode binder, for example, a fluorine polymer such as polyvinylidene fluoride (PVDF) is used for the positive electrode. When this PVDF is used as a battery electrode binder, since the binding force is insufficient, it is difficult to improve battery performance such as battery capacity, rate characteristics and cycle characteristics. For example, increasing the amount of conductive aid is effective in improving the rate characteristics that are affected by the ease of electron movement. In order to increase the amount of the conductive additive in a limited space in the battery, it is necessary to reduce the amount of the binder. If the amount of the binder is simply reduced, the adhesion with the electrode active material is impaired, and the mixture layer is peeled off from the current collector or the electrode active material is missing from the mixture layer due to repeated charge and discharge. Thus, there is a problem that the battery performance is lowered.

To solve this problem, polar groups such as carboxyl groups and hydroxyl groups are introduced into polyacrylonitrile-based (hereinafter sometimes referred to as PAN-based) resins having electrochemical stability substantially equivalent to that of PVDF. A method for improving the adhesion of the binder to the electric body has been proposed (for example, Patent Document 1).
In addition, for example, a method has been proposed in which a phosphoric acid group is introduced as a polar group into an acrylic resin to improve adhesion to a current collector (see Patent Document 2).

JP 2005-327630 A International Publication No. 2006/101182 Pamphlet

However, in the technique of Patent Document 1, when the amount of the binder is reduced, it cannot be said that the adhesion between the current collector and the mixture layer is sufficient.
Further, in the technique of Patent Document 2, since a crosslinking component that can be insoluble in N-methyl-2-pyrrolidone (NMP) used as a solvent is contained in the composition for battery electrodes, The adhesiveness of the agent layer was not sufficient. In addition, if the cross-linking component is not included, the mixture layer is excessively swollen with respect to the electrolytic solution, the adhesion is lowered, or the battery electrode binder is dissolved in the electrolytic solution to reduce the battery life. There was concern.
Therefore, the present invention is directed to a battery electrode binder that is excellent in adhesion to a current collector even in a small amount.

 The binder for battery electrodes of the present invention is a polymer having 80 to 99.99 mol% of vinyl cyanide units and 0.01 to 20 mol% of phosphoric acid group-containing units, and has an insoluble content of 50 to N-methylpyrrolidone. It is characterized by being a polymer of mass% or less.

 The battery electrode composition of the present invention comprises the battery electrode binder of the present invention.

 The battery electrode of the present invention comprises a current collector and a mixture layer provided on the current collector, and the mixture layer comprises the battery electrode composition of the present invention and an electrode active material. It is characterized by containing.

 The secondary battery of the present invention includes the battery electrode of the present invention.

  According to the battery electrode binder of the present invention, the adhesiveness to the current collector can be improved even with a small amount.

(Binder for battery electrode)
The binder for battery electrodes of the present invention is a polymer having vinyl cyanide units and phosphate group-containing units.

The vinyl cyanide unit means a structural unit derived from a vinyl cyanide monomer.
Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-cyanoacrylate, dicyanovinylidene, and fumaronitrile. Among them, acrylonitrile is preferable because it is easily polymerized and can be obtained at low cost.
These vinyl cyanide monomers can be used individually by 1 type or in combination of 2 or more types.

  When the total of all the structural units constituting the polymer is 100 mol%, the content of vinyl cyanide units in the polymer is 80 to 99.99 mol%, preferably 95 to 99 mol%. . If the content of the vinyl cyanide unit is not less than the above lower limit value, it easily dissolves in the solvent to increase the adhesion to the current collector, and if it is not more than the above upper limit value, the adhesion to the current collector is enhanced.

The phosphate group-containing unit is a structural unit derived from a phosphate group-containing monomer.
The phosphate group-containing monomer is a vinyl monomer having a phosphate group, and preferably a (meth) acrylate and an allyl compound having a phosphate group.

Examples of the (meth) acrylate having a phosphoric acid group include 2- (meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxyethyl acid phosphate monoethanolamine salt, and diphenyl ((meth) acryloyloxyethyl). Phosphate, (meth) acryloyloxypropyl acid phosphate, 3-chloro-2-acid phosphooxypropyl (meth) acrylate, acid phosphooxypolyoxyethylene glycol mono (meth) acrylate, acid phosphooxypolyoxypropylene glycol ( And (meth) acrylate. In addition to these monofunctional phosphate group-containing monomers, bifunctional phosphate group-containing monomers may be used as long as the adhesion to the current collector is not lowered.
Examples of the allyl compound having a phosphoric acid group include allyl alcohol acid phosphate.
Among these phosphoric acid group-containing monomers, 2-methacryloyloxyethyl acid phosphate is preferable because of excellent adhesion to the current collector and handling properties during electrode production.
2-Methacryloyloxyethyl acid phosphate is industrially available as light ester P1-M (trade name, manufactured by Kyoeisha Chemical Co., Ltd.).
Phosphoric acid group-containing monomers can be used singly or in appropriate combination of two or more.

 When the total of all the structural units constituting the polymer is 100 mol%, the content of the phosphoric acid group-containing unit in the polymer is 0.01 to 20 mol%, preferably 1 to 10 mol%. It is. If the content rate of a phosphoric acid group containing unit is more than the said lower limit, the adhesiveness with respect to a collector will increase, and if it is below the said upper limit, it melt | dissolves easily in a solvent and the adhesiveness with respect to an electrical power collector will increase.

The binder for battery electrodes may have a structural unit (arbitrary structural unit) other than the vinyl cyanide unit and the phosphate group-containing unit as necessary. By having an arbitrary structural unit, mechanical properties such as rigidity and bending strength of the mixture layer are enhanced.
Examples of the monomer (arbitrary monomer) that is the source of the arbitrary structural unit include (meth) ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and the like. Acrylate; Vinyl halide monomers such as vinyl chloride, vinyl bromide and vinylidene chloride; Carboxyl group-containing monomers such as (meth) acrylic acid, itaconic acid and crotonic acid and salts thereof; styrene, α-methylstyrene, etc. Aromatic vinyl monomers; maleimides such as maleimide and phenylmaleimide; sulfones such as (meth) allylsulfonic acid, (meth) allyloxybenzenesulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid Acid group-containing vinyl monomers and their salts; (meth) acrylamide, vinyl acetate, etc. And the like.
Arbitrary monomers can be used individually by 1 type or in combination of 2 or more types as appropriate.

When the total of all the structural units constituting the polymer is 100 mol%, the content of the arbitrary structural unit in the polymer is preferably 0 to 19.99 mol%. At this time, the content of vinyl cyanide units in the polymer is 80 to 99.99 mol%, and the content of phosphoric acid group-containing units is 0.01 to 20 mol%.
Moreover, as for the content rate of the arbitrary structural unit in a polymer, 0-4 mol% is more preferable. At this time, the content of vinyl cyanide units in the polymer is 95 to 99 mol%, and the content of phosphate group-containing units is 1 to 5 mol%.

As will be described later, the battery electrode binder is dispersed in a solvent containing NMP and applied to the current collector. Since the phosphate group-containing monomer has bifunctionality in its production process, it tends to be a component insoluble in NMP (NMP insoluble matter) in the polymer. The increase in the insoluble content of NMP affects the slurry characteristics of the mixture layer, the contact state between the electrode active material and the electrode active material, and the contact state between the electrode active material and the current collector.
For this reason, the binder for battery electrodes has an NMP insoluble content of 50% by mass or less, preferably 10% by mass or less, in terms of performance and quality control. When the NMP insoluble content exceeds the above upper limit, the adhesion with the electrode active material or the current collector becomes insufficient.
The NMP insoluble content can be adjusted by increasing or decreasing the amounts of the polymerization initiator and the chain transfer agent when the battery electrode binder is produced. When there are few polymerization initiators or chain transfer agents, the molecular weight tends to increase and the insoluble matter tends to increase.
As for the molecular weight of the binder for battery electrodes, the weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) using N, N-dimethylformamide (DMF) as a solvent is preferably 5 to 300,000.

<Method for producing battery electrode binder>
The battery electrode binder can be produced by a known polymerization method. For example, a vinyl cyanide monomer, a phosphate group-containing monomer, and an optional monomer as required are added to a solvent, and a polymerization temperature of 0 to It is produced by maintaining at 90 ° C., preferably 50 to 60 ° C., for a polymerization time of 1 to 10 hours, preferably 2 to 4 hours.
In the polymerization, since the vinyl cyanide monomer has a large polymerization exotherm, it is preferable to proceed the polymerization while dropping in a solvent.
Examples of the polymerization method include bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization and the like. Among them, the suspension is easy to produce and the post-treatment process (recovery and purification) is easy. Polymerization is preferred.

Suspension polymerization is a method in which a vinyl cyanide monomer, a phosphate group-containing monomer, a polymerization initiator and, if necessary, an optional monomer are dispersed in water and maintained at an arbitrary temperature.
As the polymerization initiator used for suspension polymerization, a water-soluble polymerization initiator is preferable because of excellent polymerization initiation efficiency and the like.
Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; water-soluble peroxides such as hydrogen peroxide; 2,2′-azobis (2-methylpropionamidine) And water-soluble azo compounds such as dihydrochloride. Of these, persulfate is preferable because of easy polymerization.
An oxidizing agent such as persulfate is a redox initiator in combination with a reducing agent such as sodium hydrogen sulfite, ammonium hydrogen sulfite, sodium thiosulfate, hydrosulfite, and a polymerization accelerator such as sulfuric acid, iron sulfate, copper sulfate. Can be used as

In the suspension polymerization, a chain transfer agent can be used for the purpose of adjusting the molecular weight.
Examples of the chain transfer agent include mercaptan compounds, thioglycols, carbon tetrachloride, α-methylstyrene dimers, and hypophosphites. Among these, mercaptan compounds are preferable.

In the suspension polymerization, a solvent other than water can be added in order to adjust the particle diameter of the obtained battery electrode binder.
Examples of solvents other than water include amides such as NMP, N, N-dimethylacetamide, and N, N-dimethylformamide; N, N-dimethylethyleneurea, N, N-dimethylpropyleneurea, tetramethylurea, and the like. Ureas; lactones such as γ-butyrolactone and γ-caprolactone; carbonates such as propylene carbonate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; methyl acetate, ethyl acetate, n-butyl acetate, butyl cellosolve acetate, Esters such as butyl carbitol acetate, ethyl cellosolve acetate and ethyl carbitol acetate; Grimes such as diglyme, triglyme and tetraglyme; Hydrocarbons such as toluene, xylene and cyclohexane; Examples thereof include sulfoxides such as til sulfoxide; sulfones such as sulfolane; alcohols such as methanol, isopropanol and n-butanol.
These solvent can be used individually by 1 type or in combination of 2 or more types.

When the battery electrode binder is produced by emulsion polymerization, a surfactant can be used.
Examples of the surfactant include anionic surfactants such as dodecyl sulfate and dodecyl benzene sulfonate; nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene alkyl ester; alkyltrimethylammonium salt and alkyl Examples thereof include cationic surfactants such as amines.
These surfactants can be used individually by 1 type or in combination of 2 or more types as appropriate.

(Battery electrode composition)
The composition for battery electrodes of the present invention contains a binder for battery electrodes.
The form of the battery electrode composition is not particularly limited, and examples thereof include a powder form or a solution form in which a battery electrode binder is dissolved in a solvent such as NMP.

 50-100 mass% is preferable and, as for content of the binder for battery electrodes in a powdery composition for battery electrodes, 80-100 mass% is more preferable. There exists a possibility that the effect of this invention may become difficult to be exhibited as it is less than the said lower limit.

 0.5-10 mass% is preferable and, as for content of the binder for battery electrodes in a solution-form composition for battery electrodes, 0.5-2 mass% is more preferable. If it is less than the above lower limit value, the effect of the present invention may not be exhibited.

 The composition for battery electrodes may contain arbitrary components, such as binders (arbitrary binder) other than the binder for battery electrodes of this invention, and a viscosity modifier as needed.

Optional binders include polymers such as styrene-butadiene rubber, poly (meth) acrylonitrile, ethylene-vinyl alcohol copolymer, vinyl acetate polymer; fluoropolymers such as polyvinylidene fluoride, tetrafluoroethylene, pentafluoropropylene, etc. Can be mentioned. By containing these optional binders, the battery performance of the battery electrode composition can be further improved.
As for content of the arbitrary binder in the composition for battery electrodes, 0-50 mass parts is preferable with respect to 100 mass parts of binders for battery electrodes, for example.

Examples of the viscosity modifier include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and ammonium salts thereof; poly (meth) acrylates such as sodium poly (meth) acrylate; polyvinyl alcohol, polyethylene oxide , Polyvinylpyrrolidone, copolymer of acrylic acid or acrylate and vinyl alcohol, maleic anhydride, maleic acid or copolymer of fumaric acid and vinyl alcohol, modified polyvinyl alcohol, modified polyacrylic acid, polyethylene glycol, polycarboxylic acid Among them, the additive is preferably electrochemically stable because it remains on the electrode. By containing these viscosity modifiers, it can be easily applied when a battery electrode is produced.
As for content of the viscosity modifier in the composition for battery electrodes, 0-20 mass parts is preferable with respect to 100 mass parts of binders for battery electrodes, for example.

<Method for producing battery electrode composition>
Examples of the method for producing a battery electrode composition include a method of powder-mixing a powdered battery electrode binder and optionally a powdery optional component, a powdered battery electrode binder, and a necessary method Depending on the above, there may be mentioned a method of dispersing a powdery optional component in a solvent such as NMP.

(Battery electrode)
The battery electrode includes a current collector and a mixture layer provided on the current collector.
The mixture layer contains the battery electrode composition and the electrode active material, and is, for example, a layer formed on at least one surface of the plate-shaped current collector.

 The thickness of the mixture layer can be appropriately determined according to the type of the electrode active material. When the electrode active material is lithium metal oxide, the thickness of the mixture layer is, for example, preferably 70 to 110 μm, and more preferably 90 to 110 μm. When the electrode active material is graphite, the thickness of the mixture layer is preferably, for example, 30 to 70 μm, and more preferably 50 to 70 μm.

 As for content of the composition for battery electrodes in a mixture layer, content of the binder for battery electrodes in a mixture layer becomes like this. Preferably it is 0.5-10 mass%, More preferably, it is 0.5-4 mass%. More preferably, the amount is 0.5 to 2% by mass. If it is more than the said lower limit, the adhesiveness of a mixture layer and a collector will improve more. If it is below the said upper limit, since the binder for battery electrodes of this invention is excellent in adhesiveness, peeling of a mixture layer and a collector can be prevented favorably.

In the case of a lithium ion secondary battery, the positive electrode active material (positive electrode active material) has a higher potential (relative to metallic lithium) than the negative electrode active material (negative electrode active material) and absorbs lithium ions during charge and discharge. A removable material is used. For example, a lithium-containing metal composite oxide containing at least one metal selected from iron, cobalt, nickel, manganese and vanadium and lithium, polyaniline, polythiophene, polyacetylene and derivatives thereof, polyparaphenylene and derivatives thereof, Examples thereof include conductive polymers such as polyarylene vinylene and derivatives thereof such as polypyrrole and derivatives thereof, polythienylene and derivatives thereof, polypyridinediyl and derivatives thereof, polyisothianaphthenylene and derivatives thereof. As the conductive polymer, a polymer of an aniline derivative that is soluble in an organic solvent is preferable. A positive electrode active material can be used individually by 1 type or in combination of 2 or more types as appropriate.
Examples of the negative electrode active material include carbon materials such as graphite, amorphous carbon, carbon fiber, coke, and activated carbon; and composites of the carbon materials with metals such as silicon, tin, and silver, or oxides thereof. It is done. A negative electrode active material can be used individually by 1 type or in combination of 2 or more types as appropriate.
In the lithium ion secondary battery, it is preferable to use a lithium-containing metal composite oxide as the positive electrode active material and graphite as the negative electrode active material. By setting it as such a combination, the voltage of a lithium ion secondary battery can be raised, for example to 4V or more.

 Although content of the electrode active material in a mixture layer is not specifically limited, 80-99.5 mass% is preferable, 90-99 mass% is more preferable, 95-99 mass% is further more preferable. If it is more than the said lower limit, the function as a mixture layer will fully be exhibited. If it is below the said upper limit, the adhesiveness of a mixture layer and a collector can be improved more.

The positive electrode mixture layer may contain a conductive additive. Battery performance can be further improved by containing a conductive additive.
Examples of the conductive assistant include graphite, carbon black, and acetylene black. These conductive assistants can be used singly or in appropriate combination of two or more.

 Although content of the conductive support agent in a mixture layer is not specifically limited, 1-10 mass% is preferable and 4-6 mass% is more preferable. If it is more than the said lower limit, the function as a mixture layer will be improved more. If it is below the said upper limit, the adhesiveness of a mixture layer and a collector can be improved more.

The current collector may be a substance having conductivity, and examples thereof include metals such as aluminum, copper, and nickel.
The shape of the current collector can be determined according to the shape of the target battery, and examples thereof include a thin film shape, a net shape, and a fiber shape. Among these, a thin film shape is preferable.
Although the thickness of a collector is not specifically limited, 5-30 micrometers is preferable and 8-25 micrometers is more preferable.

<Method for producing battery electrode>
A conventionally well-known method can be used as a manufacturing method of the battery electrode. For example, a battery electrode composition and an electrode active material are dispersed in a solvent to prepare a slurry (in particular, an electrode slurry) (slurry preparation process), and this electrode slurry is applied to a current collector (application) Step), the solvent is removed (solvent removal step), and a solid layer holding the electrode active material with the battery electrode binder is obtained.

In the slurry preparation step, the battery electrode composition, the electrode active material, and, if necessary, a conductive additive or additive are dispersed in a solvent.
The solvent may be any solvent that can uniformly dissolve or disperse the battery electrode composition. For example, NMP, NMP and an ester solvent (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) Examples thereof include a mixed solution or a mixed solution of NMP and a glyme-based solvent (diglyme, triglyme, tetraglyme, etc.). Moreover, you may use water together.
These solvent can be used individually by 1 type or in combination of 2 or more types.

 The content of the solvent in the electrode slurry may be the minimum necessary amount that can maintain the dissolved or dispersed state of the battery electrode composition at room temperature. In addition, the content of the solvent in the electrode slurry is determined in consideration of the viscosity that can be easily applied to the current collector in the application step.

 The coating process is not limited as long as the electrode slurry can be applied to the current collector with an arbitrary thickness. For example, the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, and the brush coating method. And the like.

 The solvent removal step only needs to be able to remove the solvent, and examples thereof include a method of heating to the boiling point of the solvent or higher, a method of evaporating the solvent under reduced pressure conditions, and the like.

 After the solvent removal step, the mixture layer may be rolled as necessary (rolling step). By providing a rolling process, the area of the mixture layer can be expanded and adjusted to an arbitrary thickness.

(Secondary battery)
The secondary battery of the present invention comprises the above-described battery electrode of the present invention. In the secondary battery, for example, a wound product obtained by laminating and winding a positive electrode for a battery and a negative electrode for a battery via a separator made of a polyethylene microporous film or the like is housed in a battery container together with an electrolytic solution. And the like.

The electrolytic solution is obtained by dissolving an electrolyte in an organic solvent.
Examples of the organic solvent for the electrolytic solution include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; lactones such as γ-butyrolactone; trimethoxymethane, 1,2-dimethoxy Ethers such as ethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; acetonitrile, Nitrogens such as nitromethane and NMP; esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, and phosphate triester; diglyme, trigly , Glymes such as tetraglyme; ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone; sulfones such as sulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone, 4- Examples include sultone such as butane sultone and naphtha sultone. These organic solvents can be used individually by 1 type or in combination of 2 or more types as appropriate.

As the electrolyte, for _{example, LiClO 4, LiBF 4, LiI} , LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) 4, LiCH _{3 SO 3, LiC 4 F 9} SO 3, Li (CF 3 SO 2) 2 N, Li [(CO 2) 2] 2 B and the like.
As an electrolytic solution of the lithium ion secondary battery, a solution in which LiPF ₆ is dissolved in carbonates is preferable.

≪Method for manufacturing secondary battery≫
An example of a method for manufacturing a secondary battery will be described.
First, a positive electrode for a battery and a negative electrode for a battery are wound through a separator to form a wound body. The obtained wound body is inserted into a battery can, and a tab terminal previously welded to a negative electrode current collector is welded to the bottom of the battery can. Next, an electrolyte is injected into the battery can, and a tab terminal that has been previously welded to the positive electrode current collector is welded to the battery lid, and the lid is placed on top of the battery can via an insulating gasket. Then, the portion where the lid and the battery can are in contact is caulked and sealed to obtain a secondary battery.

As described above, the battery electrode binder of the present invention has 80 to 99.99 mol% of vinyl cyanide units and 0.01 to 20 mol% of phosphoric acid group-containing units, so that the adhesiveness to the current collector is improved. Enhanced. In addition, since the insoluble content in N-methylpyrrolidone is 50% by mass or less, even with a small amount, the adhesion between the electrode active material and the electrode active material and the adhesion between the electrode active material and the current collector are improved. it can.
For this reason, it is useful as a battery electrode binder for a secondary battery that requires higher battery performance and longer life.

  EXAMPLES Hereinafter, although an Example is shown and demonstrated about this invention, this invention is not limited to an Example. Unless otherwise specified, “%” in each example represents “mass%”.

Example 1
Distilled water 870 g was charged into a 2 liter separable flask equipped with a stirrer, a thermometer, a cooling pipe and a nitrogen gas introduction pipe, and was bubbled for 15 minutes using nitrogen gas under an air flow rate of 100 mL / min. The temperature was raised to 55 ° C. with stirring, and then the nitrogen gas aeration was switched to overflow.
Next, 0.72 g of ammonium persulfate, 2.16 g of 50% ammonium sulfite, 0.0135 g of 0.1% iron sulfate and 30 g of distilled water were added as polymerization initiators.
64.1 g of acrylonitrile and light ester P1-M (trade name, manufactured by Kyoeisha Chemical Co., Ltd., 2-methacryloyloxyethyl acid phosphate: bis (2-methacryloyloxyethyl) acid phosphate = 80 as a phosphate group-containing monomer 20 (mass ratio) 2.5 g was added and mixed, and this was bubbled with nitrogen gas for 15 minutes. After bubbling, the solution was added dropwise into the separab flask over 30 minutes. After completion of the dropwise addition, polymerization was carried out by maintaining at the same temperature for 2 hours.
After polymerization, stirring was stopped and the mixture was cooled with water. The reaction solution was filtered by suction and washed with 10 L of hot water at 55 ° C. Subsequently, it dried at 65 degreeC for 24 hours, and the binder for battery electrodes was obtained. The yield was 15% by mass. Mw by the GPC measurement (solvent: DMF) of the obtained binder for battery electrodes was 143,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Example 2)
Addition amount of acrylonitrile is 60.0 g, addition amount of light ester P1-M is 6.66 g, addition amount of ammonium persulfate is 1.44 g, addition amount of 50% ammonium sulfite is 4.32 g, 0.1% iron sulfate A battery electrode binder was obtained in the same manner as in Example 1 except that the amount of the aqueous solution added was changed to 0.0270 g. Mw of the obtained battery electrode binder measured by GPC (solvent: DMF) was 130,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Example 3)
Addition amount of acrylonitrile 54.88 g, addition amount of light ester P1-M 11.72 g, addition amount of ammonium persulfate 2.88 g, addition amount of 50% ammonium sulfite 8.64 g, 0.1% iron sulfate A battery electrode binder was obtained in the same manner as in Example 1 except that the amount of the aqueous solution added was 0.054 g. Mw of the obtained battery electrode binder measured by GPC (solvent: DMF) was 141,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

Example 4
50.1 g of acrylonitrile, 15.62 g of light ester P1-M, 4.32 g of ammonium persulfate, 12.96 g of 50% ammonium sulfite, 0.1% iron sulfate A battery electrode binder was obtained in the same manner as in Example 1 except that the amount of the aqueous solution added was 0.081 g. Mw by the GPC measurement (solvent: DMF) of the obtained binder for battery electrodes was 120,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Example 5)
Addition amount of acrylonitrile is 50.1 g, addition amount of light ester P1-M is 15.62 g, addition amount of ammonium persulfate is 2.88 g, addition amount of 50% ammonium sulfite is 8.64 g, 0.1% iron sulfate A battery electrode binder was obtained in the same manner as in Example 1 except that the amount of the aqueous solution added was 0.054 g. Mw of the obtained binder for battery electrodes by GPC measurement (solvent: DMF) was 101,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Comparative Example 1)
Implemented except that 2.80 g of 2-methacryloyloxyethyl succinate (trade name: Light Ester HO-MS, manufactured by Kyoeisha Chemical Co., Ltd.), which is a carboxyl group-containing monomer, was used instead of Light Ester P1-M. A battery electrode binder was obtained in the same manner as in Example 1. Mw by GPC measurement (solvent: DMF) of the obtained battery electrode binder was 202,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Comparative Example 2)
Except for using 3.4 g of 2-methacryloyloxyethyl hexahydrophthalic acid (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Ester HO-HH), which is a carboxyl group-containing monomer, instead of Light Ester P1-M In the same manner as in Example 1, a battery electrode binder was obtained. Mw of the obtained battery electrode binder measured by GPC (solvent: DMF) was 26,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Comparative Example 3)
The same as in Example 1 except that 3.4 g of 2-hydroxyethyl methacrylate (Mitsubishi Rayon Co., Ltd., trade name: Acryester HO), which is a hydroxyl group-containing monomer, was used instead of the light ester P1-M. Thus, a battery electrode binder was obtained. Mw by the GPC measurement (solvent: DMF) of the obtained battery electrode binder was 187,000.
About the obtained binder for battery electrodes, the content rate of each structural unit, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.

(Comparative Example 4)
100 g of distilled water, 15 g of n-butyl acrylate, 15 g of ethyl acrylate, 1.33 g of acrylonitrile, 1 g of light ester P1-M, 1 g of glycidyl methacrylate, 1 g of sodium dodecylbenzenesulfonate, and 2,2′-azobisisobutyronitrile. 23 g of the mixture was emulsified.
The above-mentioned emulsion was put into a 1 L separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen gas introduction pipe.
After bubbling with nitrogen gas at a flow rate of 100 mL / min for 15 minutes, it was switched to overflow and polymerization was carried out by maintaining at 65 ° C. for 3 hours.
After the polymerization, 90 g of NMP (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 10 g of the solid content, and water was evaporated under reduced pressure to obtain a battery electrode binder as a slurry (solvent: NMP). About the obtained binder for battery electrodes, NMP insoluble matter, peel strength, and flexibility were evaluated, and the results are shown in Table 1.
In addition, since the binder for battery electrodes of this example was insoluble in deuterated dimethyl sulfoxide, the content rate of each structural unit could not be measured. For this reason, Table 1 shows the charged composition.

(Comparative Example 5)
Polyvinylidene fluoride (Kureha Co., Ltd., PVDF # 1000) was used as the battery electrode binder. The battery electrode binder was evaluated for NMP insoluble content, peel strength, and flexibility, and the results are shown in Table 1.

(Evaluation method)
<Content of each structural unit>
<< Content of each structural unit in Examples 1 to 5 >>
The amount of phosphoric acid in the battery electrode binders of Examples 1 to 5 was determined by ICP emission analysis shown below. From the obtained amount of phosphoric acid, the phosphoric acid ratio (mol%) in the battery electrode binder of each example was calculated, and this was used as the content of the phosphoric acid group-containing unit. Moreover, the content rate of the phosphoric acid group containing unit was reduced from 100 mol%, and the content rate of the vinyl cyanide unit was computed.

[ICP emission analysis]
0.05 g of a sample was weighed into a microwave decomposition tube, 15 mL of concentrated nitric acid was added, the lid was capped, and the sample was set in a microwave device, and decomposed under the following conditions. Subsequently, after cooling, the residual pressure was released, the lid was opened, and it was visually confirmed that the contents were decomposed. Thereafter, the solution was transferred to a glass measuring flask using a funnel, and the volume was adjusted to 50 mL with pure water and the washing solution. Furthermore, after diluting 10 times with pure water, phosphorus was quantified by ICP emission spectrometry. As an apparatus, an ICP emission analyzer IRIS-AP manufactured by Thermo Fisher Scientific Co., Ltd. was used.

[Microwave decomposition conditions]
・ Step1
Temperature: 120 ° C., pressure: 100 PSI, time: 5 minutes, Power: 600 W-30%
・ Step2
Temperature: 150 ° C., pressure: 150 PSI, time: 5 minutes, Power: 600 W-35%
・ Step3
Temperature: 180 ° C., Pressure: 180 PSI, Time: 5 minutes, Power: 30% -40%

≪Content of each structural unit in Comparative Examples 1 to 3≫
The composition of the binder for battery electrodes of Comparative Examples 1 to 3 was determined by the following method.
After the sample was dissolved in deuterated dimethyl sulfoxide, the solution was filtered. It measured by < ¹ > H-NMR (the JEOL Co., Ltd. make, JNM GSX-270) using the filtered solution, and computed the composition from the integrated value.

<NMP insoluble matter>
The NMP insoluble content of the battery electrode binder in each example was determined by the following method.
After 0.2 g of a sample was immersed in 20 mL of NMP at 60 ° C. for 72 hours, it was filtered through an 80 mesh polyethylene mesh.
20 mL of NMP was applied to the solid content on the mesh to dry the solid content on the mesh. The mass of the dried product was measured and expressed as a percentage with respect to the mass (0.2 g) of the sample before immersion.

<Peel strength>
The battery electrode binder of each example was put into a separable flask, NMP (manufactured by Wako Pure Chemical Industries, Ltd.) was added and dissolved so that the concentration of the battery electrode binder was 10%, and a binder solution was prepared. .

After dispersing 2 parts of PAN-based carbon fiber (CF) having a diameter of 7 μm and a chop length of 3 mm and 1 part of fibrous polyvinyl alcohol (manufactured by Unitika Ltd.) having a chop length of 3 mm in water, the basis weight is 10 to 15 g / m ^2. Then, the paper was made with a paper machine and dried to obtain a paper-like CF.
The obtained paper-like CF was impregnated with 15% ferrite J-325 / methanol solution (manufactured by DIC Corporation, trade name: Ferrite J-325) and dried. Thereafter, the dried product was hot-pressed at 180 ° C. and 100 kg / cm ² . The hot-pressed product was fired at 1500 ° C. in a nitrogen atmosphere to prepare a CF sheet.

A copper foil (300 mm × 200 mm × 20 μm) was used as a current collector, this copper foil was fixed to a glass plate, and a binder solution was applied on the copper foil at a thickness of 130 μm.
After applying the binder liquid, a CF sheet (50 mm × 100 mm) was placed and blended well with the binder liquid. After drying at 100 ° C. for 1 hour, the glass plate was removed from the copper foil, and a test sheet in which the copper foil and the CF sheet were bonded together with a battery electrode binder was obtained.

 The obtained test sheet was cut into a strip having a width of 10 mm, and the test sheet was then polycarbonate sheet (50 mm × 100 mm × 1 mm) with a double-sided tape having a width of 25 mm (trade name: # 570, manufactured by Sekisui Chemical Co., Ltd.). Pasted on. At this time, the CF sheet was brought into contact with the polycarbonate plate. Next, the test sheet and the polycarbonate plate were pressure-bonded with a rubber roller, and this was used as a test piece.

A polycarbonate plate as a test piece is fixed to a tensile and compression tester (manufactured by Imada Manufacturing Co., Ltd., trade name: SV-201 type), and the copper foil is peeled off at 10 mm / min in the 180 ° direction under the condition of about 25 ° C. Then, the stress at that time was measured.
When the copper foil was peeled off, the entire area of the CF sheet was peeled off from the copper foil and remained on the double-sided tape was taken as the measurement range, and the lowest stress in the measurement range was taken as the measurement value.
This measurement was performed three times, and the average value of the measured values was taken as the peel strength. It can be said that the larger this value is, the stronger the battery electrode binder is in close contact with the current collector.

<Flexibility>
The binder solution prepared in “<Peel Strength>” was applied to a glass plate and dried to prepare a film having a thickness of 50 μm. This film was cut into a strip of 10 mm × 50 mm to obtain a test piece.
Under an environment of about 25 ° C., the test piece was folded in half near the center in the longitudinal direction (25 mm from the end), and a load of 500 g was applied on the fold for 1 minute. Thereafter, the folds were widened, and the presence or absence of cracks or cracks was confirmed. This test was performed on 10 test pieces and classified into the following evaluation criteria to evaluate flexibility. The occurrence of cracks or cracks in the test piece was confirmed visually.

≪Evaluation criteria≫
A: The number of test pieces in which cracks or cracks occurred was 0 to 4 points.
(Triangle | delta): The number of the test piece which the crack or the crack generate | occur | produced was 5-8 points.
X: The number of test pieces in which cracks or cracks occurred was 9 to 10 points.

 As shown in Table 1, in each of Examples 1 to 5 to which the present invention was applied, the peel strength was 12.1 N / cm or more, and the flexibility was “◯”. Among them, Example 1 having an NMP insoluble content of less than 1% by mass and a vinyl cyanide unit content of 99.2 mol% was particularly excellent in peel strength. This is presumed to be due to the large amount of dissolved component in the binder solution, and when applied to the current collector and dried, the contact area increases and the adhesion between the battery electrode binder and the current collector is improved. Is done.

On the other hand, Comparative Examples 1 to 3 having a carboxyl group-containing unit instead of a phosphate group-containing unit have a low peel strength of 3.8 to 4.5 N / cm, although the flexibility is “◯”. Met.
Moreover, the comparative example 4 whose NMP insoluble content exceeds 50 mass% was 8.5 N / cm in peeling strength, and was inferior to peeling strength compared with Examples 1-5.
In Comparative Example 5 using PVDF, the peel strength was extremely low and the flexibility was “x”.
From these results, it was found that the battery electrode binder of the present invention can improve the battery performance by reducing the peeling between the mixture layer and the current collector and the loss of the electrode active material even with a small amount. Furthermore, it has been found that the occurrence of cracks and the like during winding and bending of the battery electrode can be prevented.

Claims (4)

 A binder for battery electrodes, which is a polymer having 80 to 99.99 mol% of vinyl cyanide units and 0.01 to 20 mol% of phosphoric acid group-containing units and having an insoluble content with respect to N-methylpyrrolidone of 50% by mass or less.  The composition for battery electrodes containing the binder for battery electrodes of Claim 1.  A battery electrode comprising: a current collector; and a mixture layer provided on the current collector, wherein the mixture layer includes the battery electrode composition according to claim 2 and an electrode active material.   A secondary battery comprising the battery electrode according to claim 3.