JP2019029177A - Resin composition for power storage device electrode - Google Patents

Abstract

To provide a resin composition for a power storage device electrode, which has excellent ion permeability while ensuring a good binding property to the electrode.SOLUTION: In an embodiment, the present disclosure relates to a resin composition for a power storage device electrode, which comprises polymer particles. The polymer particles have ion permeability, and the rate of change in elasticity [(post-treatment elastic modulus)/(pre-treatment elastic modulus)] of the polymer particles before and after a treatment with a liquid electrolyte is 30% or less.SELECTED DRAWING: None

Description

  The present disclosure relates to a resin composition for an electricity storage device electrode.

  Due to the recent spread of smartphones, zero emission regulations in the automobile market, and the expansion of the use of natural energy, demand for power storage devices is increasing. For this reason, it is desired that the power storage device be small, light, and have a large capacity. In automobiles and the like, there is a growing demand for higher output and higher energy density. Under such demands, development of power storage devices such as lithium ion secondary batteries, alkaline ion secondary batteries, electric double layer capacitors, and lithium ion capacitors has been promoted.

  Such an electricity storage device generally includes an electrode in which a composite material layer containing an active material or the like is applied on a metal foil, and an electrical storage device electrode resin (binder) for preventing the composite material layer from peeling off. Is added to the composite layer, but the binder itself is a material that is insulative and poor in ion permeability, which is an obstacle to the capacity and input / output characteristics of the battery. In particular, it is known that the ion conductivity is greatly impaired at a low temperature or a consolidated electrode plate, which causes deterioration in durability and capacity reduction.

  In order to solve such problems, binders that can improve battery characteristics have been proposed (for example, Patent Documents 1, 2, and 3).

  Patent Document 1 includes 0.01 to 30% by mass of a carboxyl group-containing monomer (a-1) and 20 to 60% by mass of acrylonitrile (a-2), with the remainder being copolymerizable. The binder for lithium secondary battery electrodes containing resin obtained by copolymerizing the monomer mixture which consists of (a-3) is disclosed.

  In Patent Literature 2, (a) 1 to 80 parts by weight of (meth) acrylic acid ester monomer and (b) 1 to 20 parts by weight of unsaturated carboxylic acid monomer per 100 parts by weight of binder resin. And (c) a binder comprising resin particles obtained by polymerization of 0.001 to 40 parts by weight of a vinyl monomer.

  Patent Document 3 discloses an electrode binder using two types of polymers having different elastic moduli.

JP 2013-4229 A Special table 2008-537841 gazette JP 2009-224239 A

However, conventional electricity storage device electrode resins (binders) as proposed in Patent Documents 1 to 3 have high solubility in the electrolyte solution or poor affinity with the electrolyte solution. An electrode using a resin for an electricity storage device electrode does not have the capability of allowing alkali ions contained in the electrolyte to permeate the inside of the resin, and it is difficult to obtain a sufficient effect to reduce the ionic resistance of the battery. It was. That is, the battery characteristics of an electrode using a conventional resin for an electricity storage device electrode were not sufficient.
The reason why the battery characteristics of an electrode using a conventional resin for an electricity storage device electrode (binder) is not sufficient is considered to be ionic resistance. And in order to improve the battery characteristic of an electrode, the resin for electrical storage device electrodes which has a new characteristic is calculated | required.

  This indication provides the resin composition for electrical storage device electrodes which shows the outstanding ion permeability, ensuring the favorable binding property to an electrode.

  The present disclosure is a resin composition for an electricity storage device electrode including polymer particles, the polymer particles having ion permeability, and an elastic change rate of the polymer particles before and after treatment with an electrolytic solution [(elastic modulus after treatment). ) / (Elastic modulus before treatment)] is related to a resin composition for an electricity storage device electrode, which is 30% or less.

  According to the present disclosure, it is possible to provide an effect that it is possible to provide a resin composition for an electricity storage device electrode having excellent ion permeability while ensuring good binding to an electrode.

  In the present disclosure, the binder for the electricity storage device electrode has ion permeability, and the elastic change rate before and after the treatment with the electrolytic solution [(elastic modulus after treatment) / (elastic modulus before treatment)] is within a predetermined range. It is based on the knowledge that by including certain polymer particles, excellent ion permeability can be imparted while ensuring good binding properties as a binder.

  That is, in one aspect, the present disclosure is a resin composition for an electricity storage device electrode including polymer particles, the polymer particles having ion permeability, and an elastic change rate before and after treatment of the polymer particles with an electrolytic solution. [(Elastic modulus after treatment) / (Elastic modulus before treatment)] relates to a resin composition for an electricity storage device electrode (hereinafter also referred to as “resin composition according to the present disclosure”) of 30% or less. According to the present disclosure, it is possible to provide a resin composition having excellent ion permeability while ensuring good binding to an electrode.

The details of the mechanism of the effect of the present disclosure are not clear, but the following is presumed.
The resin composition according to the present disclosure has polymer particles having a predetermined rate of change in elasticity, so that it has a good binding property as a binder and greatly reduces the elasticity to ensure an ion flow path between the electrodes. Therefore, it is considered that inhibition of ion movement is suppressed even in a scene where mobility such as charge transfer is reduced, such as at low temperatures.
However, these are estimations, and the present disclosure is not limited to these mechanisms.

  Hereinafter, the resin composition according to the present disclosure will be specifically described.

[Polymer particles]
The resin composition according to the present disclosure includes polymer particles having ion permeability (hereinafter also referred to as “polymer particles of the present disclosure”). The ion permeability can be evaluated by, for example, a measurement method using an inductively coupled plasma mass spectrometer (ICP-MS), and specifically can be evaluated by the method described in the examples.

  The polymer particles of the present disclosure have an elastic change rate before and after treatment with an electrolytic solution [(elastic modulus after treatment) / (elastic modulus before treatment)] of 30% or less from the viewpoint of ion permeability at low temperatures, 10% or less is preferable, 3% or less is more preferable, and from the viewpoint of binder stability, 0.01% or more is preferable and 0.05% or more is preferable. The elastic modulus and elastic change rate can be measured, for example, by the method described in the examples. As a method for adjusting the elastic modulus, for example, when the polymer is an acrylate polymer, the amount of the monomer having many lower alkyl groups is increased, and the molar ratio of acrylate ester or acrylamide is increased.

In the present disclosure, the electrolytic solution is an electrolytic solution used for an electricity storage device. For example, the solubility parameter sp is 8.0 (cal / cm ³ ) ^1/2 or more and 11.5 (cal / cm ³ ) ^1/2 or less. The electrolyte solution is mentioned. As the electrolytic solution, a solution in which an electrolyte is dissolved in an organic solvent or ionic liquids can be usually used.
Examples of the organic solvent include esters. Specifically, cyclic carbonates such as ethylene carbonate (EC, sp: 11.0) and propylene carbonate (PC, sp: 10.19); dimethyl carbonate ( Chain carbonates such as DMC, sp: 8.51), ethyl methyl carbonate (EMC, sp: 8.52), diethyl carbonate (DEC, sp: 8.53); ethyl propionate (sp: 8.72) 1 type, 2 types, or 3 or more types of combinations chosen from chain | strand-shaped carboxylic acid ester; cyclic lactones etc. are mentioned. In particular, from the viewpoint of stability against oxidation / reduction, a mixed solvent of a cyclic carbonate and a chain carbonate is preferable. Specific examples of the mixed solvent include, for example, a mixed solvent (sp: 10.12) containing EC and DEC at a volume ratio of 1/1, and a mixed solvent (sp: containing EC and DEC at a volume ratio of 3/7). : 9.61), mixed solvent containing EC and MEC at a volume ratio of 3/7 (sp: 9.50), mixed solvent containing PC and DEC at a volume ratio of 2/8 (sp: 9.18) ), A mixed solvent containing EC, DEC and DMC at a volume ratio 1/1/1 (sp: 9.58), and a mixed solvent containing EC, DEC and EMC at a volume ratio 1/1/1 (sp : 9.65) and the like.
The electrolyte refers to an ionic compound having a function of conducting electricity by dissolving in an organic solvent. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ CO ₂ , LiCl, LiBr, and LiSCN alone or in combination. Can be used in combination. Of these, LiPF ₆ and LiBF ₄ are preferably used.
Other ionic liquids include, for example, bis (fluorosulfonyl) amide (FSA), alkyl salts of bis (trifluoromethanesulfonyl) amide (TFSA); N-methylpropylpyrrolidinium (P13); diethylmethylmethoxyethylammonium (DEME); triglyme (G3) and the like.

  The polymer particles of the present disclosure preferably have a low solubility because they are stably present in the electrolytic solution. The solubility of the polymer particles of the present disclosure in the electrolyte solution is preferably less than 3% by mass, more preferably 1.5% by mass or less, still more preferably 1% by mass or less, from the viewpoint of stability in the electrolyte solution. More preferably less than%. The solubility can be measured, for example, by the method described in the examples.

The solubility parameter sp of the polymer particles of the present disclosure is preferably 9.0 (cal / cm ³ ) ^1/2 or more, and 9.3 (cal / cm ³ ) ^1/2 or more from the viewpoint of affinity with the electrolytic solution. Is more preferably 9.5 (cal / cm ³ ) ^1/2 or more, and from the same viewpoint, 11.0 (cal / cm ³ ) ^1/2 or less is preferable, and 10.7 (cal / cm ³ ) is more preferable. cm ³ ) ^1/2 or less is more preferable, and 10.5 (cal / cm ³ ) ^1/2 or less is still more preferable. In the present disclosure, the solubility parameter sp is the Fedors method [R. F. Fedors. Polym. Eng. Sci., 14, 147 (1974)]. When the polymer particles of the present disclosure have a solubility parameter within the above range, the affinity between the resin composition according to the present disclosure and the electrolytic solution is good, and the electrolytic solution can be smoothly permeated. For example, when the polymer is an acrylate polymer, the solubility parameter sp can be adjusted by considering the ratio of the hydrophilic functional group to the hydrophobic functional group of the raw material used for the monomer and the strength of the polarity.

In the present disclosure, the solubility parameter difference Δsp between the polymer particles and the electrolytic solution is preferably 1.0 (cal / cm ³ ) ^1/2 or less from the viewpoint of affinity with the electrolytic solution, and 0.9 (cal / cm cm ³ ) ^1/2 or less is more preferable, 0.8 (cal / cm ³ ) ^1/2 or less is more preferable, and 0.7 (cal / cm ³ ) ^1/2 or less is still more preferable. By making the value of Δsp within a certain range, the electrolyte solution can be easily transmitted.

  The glass transition temperature (Tg) of the polymer particles of the present disclosure is preferably within a certain range from the viewpoints of binding properties and ion permeability. The Tg of the polymer particles of the present disclosure is preferably not more than a certain value from the viewpoint of binding properties with the electrode without inhibiting the permeability of the electrolytic solution, specifically, preferably 60 ° C. or less, and 30 More preferably, it is not higher than ° C. The Tg of the polymer particles of the present disclosure is preferably a certain value or more from the viewpoint of stability in the electrolytic solution, specifically, −50 ° C. or more is preferable, and −30 ° C. or more is more preferable. This is considered to be due to the difference in Tg of the polymer particles themselves, which influences the flow and binding force of the electrolytic solution by the change in the shape of the binder due to the temperature in the electrolytic solution. The adjustment of Tg can be performed by appropriately selecting the monomer composition ratio and molecular weight with reference to Tg in various known homopolymers. A glass transition temperature (Tg) can be measured by the method as described in an Example, for example.

  Examples of the polymer particles of the present disclosure include monofunctional (meth) acrylate, monofunctional (meth) acrylamide, monofunctional monomer having an acidic group, styrenic monofunctional monomer, and monofunctional monomer having a nitrogen-containing heterocyclic ring. Examples thereof include a polymer containing a structural unit derived from at least one selected monofunctional monomer. In the present disclosure, the monofunctional monomer refers to a monomer having one unsaturated bond. The monofunctional monomer may be used alone or in combination of two or more. In the present disclosure, (meth) acrylate means methacrylate or acrylate.

  As monofunctional (meth) acrylate, ester (meth) acrylate is mentioned, for example, Specifically, alkyl ester (meth) acrylate, cycloalkyl group containing ester (meth) acrylate, aromatic group containing ester (meth) Examples thereof include one or a combination of two or more selected from acrylate, hydroxyl group-containing ester (meth) acrylate, and nitrogen atom-containing ester (meth) acrylate.

  Examples of the alkyl ester (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, normal propyl (meth) acrylate, isopropyl (meth) acrylate, normal butyl (meth) acrylate, isobutyl (meth) acrylate, secondary Butyl (meth) acrylate, tertiary butyl (meth) acrylate, normal pentyl (meth) acrylate, normal hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl ( Examples thereof include (meth) acrylate, isostearyl (meth) acrylate, and behenyl (meth) acrylate.

  Examples of the cycloalkyl group-containing ester (meth) acrylate include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclobentanyl (meth) acrylate, and the like.

  Examples of the aromatic group-containing ester (meth) acrylate include benzyl (meth) acrylate and the like.

  Examples of the hydroxyl group-containing ester (meth) acrylate include hydroxyalkyl (meth) acrylate, alkoxy polyalkylene glycol (meth) acrylate, polyalkylene glycol (meth) acrylate, and the like.

  Examples of the nitrogen atom-containing ester (meth) acrylate include amino group-containing ester (meth) acrylate, specifically, N, N′-dimethylaminoethyl (meth) acrylate and N, N′-diethylaminoethyl. (Meth) acrylate etc. are mentioned.

  Examples of the monofunctional (meth) acrylamide include (meth) acrylamide, N, N′-dimethylacrylamide, N-isopropylacrylamide and the like.

  Examples of the monofunctional monomer having an acidic group include a monofunctional monomer containing one or more acidic groups selected from a carboxylic acid group, a phosphoric acid group, a sulfuric acid group, and a sulfonic acid group. Examples of the monofunctional monomer having a carboxylic acid group include (meth) acrylic acid and unsaturated dibasic acid. Examples of the monofunctional monomer having a sulfonic acid group include styrene sulfonic acid and sodium styrene sulfonate.

  Examples of the styrenic monofunctional monomer include styrene.

  Examples of the monofunctional monomer having a nitrogen-containing heterocyclic ring include vinyl pyridine and vinyl pyrrolidone.

As one embodiment of the polymer particles of the present disclosure, a structural unit derived from a monofunctional (meth) acrylate (hereinafter also referred to as “monomer (A)”) from the viewpoint of ease of synthesis, binding property, and ion permeability. A polymer containing (hereinafter also referred to as “structural unit (A)”) is preferably exemplified.
As other embodiments of the polymer particles of the present disclosure, from the same viewpoint, a monofunctional monomer having a structural unit (A) derived from a monomer (A) of a monofunctional (meth) acrylate and an acidic group (hereinafter referred to as “monomer”). A polymer containing a structural unit derived from “B)” (hereinafter also referred to as “structural unit (B)”) is preferable. Each of the monomers (A) and (B) may be used alone or in combination of two or more.

  As the monofunctional (meth) acrylate of the monomer (A), ester (meth) acrylate is preferable among the above-described monofunctional (meth) acrylates from the viewpoint of ease of synthesis, binding property and ion permeability, and carbon 1 type or combination of 2 or more types selected from alkyl ester (meth) acrylates having a number of 1 to 8 or less, hydroxyalkyl (meth) acrylates, alkoxy polyalkylene glycol (meth) acrylates, and polyalkylene glycol (meth) acrylates. preferable.

  The content of the structural unit (A) in all the structural units of the polymer particles of the present disclosure is preferably 70% by mass or more, more preferably 75% by mass or more from the viewpoints of ease of synthesis, binding properties, and ion permeability. Preferably, 80% by mass or more is more preferable, 85% by mass or more is more preferable, and from the same viewpoint, 100% by mass or less is preferable, 99% by mass or less is more preferable, and 97% by mass or less is more preferable. When the structural unit (A) is composed of structural units derived from a plurality of types of monomers (A), the content of the structural unit (A) refers to the total amount thereof.

  The monofunctional monomer having an acidic group of the monomer (B) is a monofunctional monomer having a carboxylic acid group among the above-described monofunctional monomers having an acidic group, from the viewpoint of ease of synthesis, binding property and ion permeability. Monomers are preferred. Examples of the monofunctional monomer having a carboxylic acid group include (meth) acrylic acid; unsaturated dibasic acids such as maleic acid, itaconic acid and salts thereof; and the like. From the viewpoint of ion permeability, (meth) acrylic acid is preferred. Examples of (meth) acrylic acid include one or a combination of two or more selected from acrylic acid, methacrylic acid, and salts thereof. The salt is preferably at least one selected from ammonium salts, sodium salts, lithium salts and potassium salts from the viewpoint of ease of synthesis, binding and ion permeability, and at least one of lithium salts and sodium salts is more preferable. preferable. When monomer (B) is a salt of (meth) acrylic acid, neutralized at least one monomer of acrylic acid and methacrylic acid with alkali (ammonia, sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.) Alternatively, it may be neutralized after becoming a structural unit of a polymer obtained by polymerizing at least one of the monomers. From the viewpoint of controlling the polymerization reaction, it is preferably neutralized after becoming a polymer structural unit after polymerization.

  The content of the structural unit (B) in all the structural units of the polymer particles of the present disclosure is preferably 0% by mass or more and more preferably 1% by mass or more from the viewpoints of ease of synthesis, binding properties, and ion permeability. Preferably, from the same viewpoint, 10 mass% or less is preferable, 8 mass% or less is preferable, 7 mass% or less is more preferable, and 5 mass% or less is still more preferable. When the structural unit (B) is composed of structural units derived from a plurality of types of monomers (B), the content of the structural unit (B) refers to the total amount thereof.

  The mass ratio (A / B) of the structural unit (A) to the structural unit (B) in the polymer particles of the present disclosure is preferably 5 or more from the viewpoint of ease of synthesis, binding properties, and ion permeability. The above is more preferable, 15 or more is more preferable, and from the same viewpoint, 100 or less is preferable, 70 or less is more preferable, and 50 or less is more preferable.

  From the viewpoint of ease of synthesis, the total content of the structural units (A) and (B) in all the structural units of the polymer particles of the present disclosure is preferably more than 80% by mass, more preferably 90% by mass or more, and 100 More preferred is mass%.

  The polymer particle of this indication may contain other structural units other than the structural unit derived from monofunctional monomers, such as a monomer (A) and a monomer (B), in the range which does not impair the effect of this indication. Examples of the other structural unit include a structural unit derived from a monomer copolymerizable with the above-mentioned monofunctional monomer (hereinafter also referred to as “monomer (C)”) (hereinafter also referred to as “structural unit (C)”). . A monomer (C) may be used individually by 1 type, and may be used together 2 or more types.

  Examples of the monomer (C) include polyfunctional monomers, and specific examples include crosslinkable monomers having two or more vinyl groups. Examples of the crosslinkable monomer having two or more vinyl groups include polyfunctional (meth) acrylates and aromatic divinyl compounds. In the present disclosure, the polyfunctional monomer refers to a monomer having two or more unsaturated bonds. When the polymer particle of this indication further contains the structural unit (C) derived from a polyfunctional monomer (C), the expansion | swelling by liquid absorption can be suppressed. In addition, a battery manufactured using polymer particles containing the structural unit (C) derived from the polyfunctional monomer (C) can further suppress the internal resistance of the battery, and is particularly suitable for a high-capacity battery.

Examples of the polyfunctional (meth) acrylate monomer (C) include compounds represented by the following formula (I).

In the formula (I), R ¹⁰ is preferably a hydrogen atom or a methyl group from the viewpoint of ease of synthesis and suppression of liquid absorption expansion. X is preferably —O— or —NH— from the viewpoint of suppression of liquid absorption expansion. n is preferably an integer of 1 or more and 20 or less from the viewpoint of suppression of liquid absorption expansion.

  Specific examples of the compound represented by the above formula (I) include, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, decaethylene glycol di (meth) acrylate. And at least one selected from pentadecaethylene glycol di (meth) acrylate.

  Examples of other polyfunctional (meth) acrylate monomers (C) include 1,3-butylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, and 1,6-hexanediol di ( (Meth) acrylate, glycerin di (meth) acrylate, allyl (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, diethylene glycol di (meth) acrylate phthalate, caprolactone-modified dipentaerythritol hexa ( Less selected from (meth) acrylate, caprolactone-modified hydroxypivalate ester neopentyl glycol di (meth) acrylate, polyester (meth) acrylate, and urethane (meth) acrylate Also it includes one or.

  Examples of the monomer (C) of the aromatic divinyl compound include at least one selected from divinylbenzene, divinylnaphthalene, and derivatives thereof.

  When the polymer particle of the present disclosure contains a structural unit derived from the polyfunctional monomer (C), the content of the structural unit (C) in the polymer particle of the present disclosure is the structural unit (A) from the viewpoint of suppressing liquid absorption and expansion. And 0.001 mol% or more, preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and more preferably 1 mol% from the same viewpoint with respect to the total number of moles of (B). The following is preferable, 0.9 mol% or less is more preferable, and 0.8 mol% or less is still more preferable. When a structural unit (C) consists of a structural unit derived from 2 or more types of monomers (C), content of a structural unit (C) says those total content.

[Method for producing polymer particles]
The polymer particle of this indication can be manufactured by polymerizing a monomer (A) and a monomer (B) and a monomer (C) as needed, for example. That is, this indication is related with a manufacturing method of polymer particles including a polymerization process which polymerizes monomer (A) and a monomer mixture containing monomer (B) and monomer (C) as needed in one mode. Examples of the polymerization method include known polymerization methods such as an emulsion polymerization method, a solution polymerization method, a suspension polymerization method, and a bulk polymerization method, and the emulsion polymerization method is preferred from the viewpoint of ease of production of the polymer.

  In the present disclosure, the content of the structural unit (A) in all the structural units of the polymer particles can be regarded as a ratio of the usage amount of the monomer (A) to the total amount of the monomer used for polymerization. The content of the structural unit (B) in all the structural units of the polymer particles can be regarded as a ratio of the amount of the monomer (B) used relative to the total amount of monomers used for polymerization. The ratio (A / B) of the content of the structural unit (A) to the structural unit (B) is regarded as the ratio of the usage amount of the monomer (A) to the usage amount of the monomer (B) in the total amount of monomers used for polymerization. Can do. The total content of the structural unit (A) and the structural unit (B) in all the structural units of the polymer particles is regarded as a ratio of the total usage amount of the monomer (A) and the monomer (B) to the total amount of monomers used for polymerization. Can do. The content of the structural unit (C) in the polymer particles can be regarded as a ratio of the amount of the monomer (C) used to the total number of moles of the monomers (A) and (B) used for the polymerization.

  Examples of the emulsion polymerization method include a known method using an emulsifier and a method substantially using no emulsifier (so-called soap-free emulsion polymerization method), and the soap-free emulsion polymerization method is preferable from the viewpoint of battery characteristics. Examples of the polymer particles of the present disclosure include polymer particles obtained by emulsion polymerization, preferably soap-free emulsion polymerization, of a monomer mixture containing the monomer (A).

  When an emulsifier is used in the polymerization step, the emulsifier is preferably a water-soluble emulsifier from the viewpoint of ease of synthesis. As a water-soluble emulsifier, an anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant, a polymer surfactant, and a reactive surfactant are used from the viewpoint of easy synthesis. And at least one surfactant selected from the group consisting of: a reactive surfactant is preferred from the viewpoints of binding properties and ion permeability. A reactive surfactant refers to a surfactant that is incorporated into a polymer during polymerization. One type of surfactant may be used, or two or more types may be used in combination.

  Examples of the anionic surfactant include polyoxyalkylene alkyl ether sulfate, polyoxyalkyl ether sulfate, polyoxyalkylene alkylphenyl ether sulfate, polyoxyalkylene carboxylic acid sulfate, alkyl allyl poly Examples thereof include sulfate salts such as ether sulfates, sulfonate salts, and phosphate ester salts.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides such as monolaurate of glycerol, polyoxyethyleneoxypropylene Examples include copolymers, condensation products of ethylene oxide and fatty acid amines, amides or acids.

  Examples of the cationic surfactant include alkyl pyridinyl chloride and alkyl ammonium chloride.

  Examples of amphoteric surfactants include lauryl betaine, stearyl betaine, and lauryl dimethylamine oxide.

  Polymeric surfactants include modified starch, modified cellulose, polyvinyl alcohol, sodium poly (meth) acrylate, potassium poly (meth) acrylate, ammonium poly (meth) acrylate, polyhydroxyethyl (meth) acrylate, poly Examples thereof include hydroxypropyl (meth) acrylate, a copolymer of two or more polymerizable monomers which are constituent units of these polymers, or a copolymer with other monomers.

  The amount of the emulsifier used in the emulsion polymerization is preferably 0.05% by mass or less with respect to the total amount of monomers from the viewpoints of binding properties and ion permeability.

  In the polymerization step, a polymerization initiator can be used. As the polymerization initiator, a water-soluble polymerization initiator is preferable from the viewpoint of polymerization stability. Examples of the water-soluble polymerization initiator include ammonium persulfate and potassium persulfate. Although the usage-amount of the polymerization initiator in the said superposition | polymerization process can be set suitably, 0.01 mass% or more and 2 mass% or less are preferable with respect to the monomer whole quantity.

  In the polymerization step, water such as ion exchange water can be used as a solvent. Although the usage-amount of the water in the said superposition | polymerization process can be set suitably, it is 40 mass parts or more and 1500 mass parts or less (6.25-71.4 mass% in polymerization solid content) with respect to 100 mass parts of monomer whole quantity, for example. be able to.

  What is necessary is just to set suitably as polymerization conditions according to the kind of polymerization initiator, monomer, solvent, etc. to be used. For example, the polymerization reaction can be performed in a temperature range of 60 to 100 ° C. in a nitrogen atmosphere, and the polymerization time can be set to 0.5 to 20 hours, for example.

  The arrangement of each structural unit constituting the polymer particle in the present disclosure may be random, block, or graft. The composition analysis of the polymer can be performed by, for example, NMR spectrum, UV-vis spectrum, IR spectrum, affinity chromatography and the like.

  The form of the polymer particles of the present disclosure may be a powder or a polymer particle dispersion in which polymer particles are dispersed in water.

  The average particle size of the polymer particles of the present disclosure is preferably 0.1 μm or more, more preferably 0.2 μm or more, and more preferably 1 μm or less, from the viewpoints of battery characteristics, binding properties, and ion permeability, and 0.9 μm or less. The following is more preferable, 0.8 μm or less is further preferable, and less than 0.7 μm is still more preferable.

  The polymer particles of the present disclosure preferably have a property of absorbing the electrolyte from the viewpoint of battery characteristics. That is, the liquid absorption amount of the polymer particles of the present disclosure with respect to the electrolytic solution (hereinafter also referred to as “electrolytic solution absorption amount”) is preferably 130% or more, more preferably 200% or more, and 300% from the viewpoint of battery characteristics. The above is more preferable, 500% or more is more preferable, and from the same viewpoint, it is preferably 10,000% or less, more preferably 8000% or less, and still more preferably 5000% or less. In the present disclosure, the electrolyte solution absorption amount can be measured by the method described in Examples. When the electrolyte solution absorption amount of the polymer particles of the present disclosure is equal to or greater than a predetermined value, the resin composition according to the present disclosure may be a portion where it is difficult to pass the electrolyte solution by filling the resin composition in the electrode plate. It is considered that alkali ions permeate through the resin together with the electrolytic solution or are retained inside, thereby facilitating the entry and exit of ions on the surface of the active material. And when the electrode produced using the resin composition which concerns on this indication is used for an electrical storage device, it will be connected with the improvement of a battery characteristic.

  From the viewpoint of battery characteristics, the content of the polymer particles in the resin composition according to the present disclosure is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and 70% by mass. The following is preferable, 65 mass% or less is more preferable, and 60 mass% or less is still more preferable.

[Aqueous medium]
The resin composition according to the present disclosure may further contain an aqueous medium. Examples of the aqueous medium include ion exchange water. When the resin composition according to the present disclosure contains an aqueous medium, examples of the form of the resin composition according to the present disclosure include a polymer particle dispersion in which the polymer particles are dispersed in an aqueous medium. As the polymer particle dispersion, for example, a mixed liquid containing polymer particles obtained by the emulsion polymerization method described above can be used as it is. The content of the aqueous medium in the resin composition according to the present disclosure can be the remainder of the polymer particles and other optional components described below.

[Other optional ingredients]
The resin composition according to the present disclosure may contain other optional components in addition to the polymer particles and the aqueous medium as long as the effects of the present disclosure are not impaired. Examples of other optional components include at least one selected from a surfactant, a thickener, an antifoaming agent, and a neutralizing agent.

  Examples of the surfactant include known surfactants. For example, surfactants that can be used as the above-described emulsifier may be used. In the resin composition according to the present disclosure, the content of the surfactant is preferably 0.5% by mass or less and preferably 0.2% by mass or less with respect to the total solid content of the resin composition from the viewpoint of battery characteristics. More preferably, 0.1% by mass or less is further preferable, and substantially 0% by mass is even more preferable. That is, it is preferable that the resin composition according to the present disclosure does not substantially contain a surfactant from the viewpoints of binding properties, ion permeability, and battery characteristics. In the present disclosure, the surfactant content in the resin composition includes the surfactant derived from the emulsifier used in the emulsion polymerization.

[Method for Producing Resin Composition]
The resin composition which concerns on this indication can be manufactured by mix | blending the polymer particle mentioned above and the aqueous medium and arbitrary component mentioned above as needed by a well-known method. That is, this indication is related with the manufacturing method (henceforth "the manufacturing method concerning this indication") of a resin composition including the compounding process which mixes at least polymer particles. The said mixing | blending can be performed using well-known mixing apparatuses, such as a stirrer, a disper, a homomixer, for example. The amount of each component in the blending step can be the same as the content of each component in the resin composition described above.

  The production method according to the present disclosure can include a polymerization step of polymerizing a monomer mixture containing at least monomer A to obtain polymer particles. In the polymerization step of the production method according to the present disclosure, the polymerization method, the type of each component that can be used for the polymerization, and the amount of use thereof can be the same as those in the polymerization step of the polymer particle production method described above.

  The resin composition according to the present disclosure can be used as, for example, an electricity storage device electrode material, an electricity storage device electrode binder, and the like. The resin composition according to the present disclosure may be, for example, a positive electrode binder or a negative electrode binder. A negative electrode binder is preferred. Examples of the electricity storage device include a secondary battery and a capacitor. The resin composition according to the present disclosure is suitably used, for example, as a material for a lithium ion secondary battery.

[Electrode for power storage devices]
The resin composition according to the present disclosure can be used for producing a composite material layer of an electrode for an electricity storage device (positive electrode and / or negative electrode). That is, in one aspect, the present disclosure is an electrode for an electrical storage device including a current collector and a composite material layer formed on the current collector, wherein the composite material layer includes the active material and the present disclosure. The present invention relates to an electrode for an electricity storage device (hereinafter, also referred to as “electrode according to the present disclosure”) including the resin composition.

  The composite material layer is obtained, for example, by preparing a slurry containing an active material, the resin composition according to the present disclosure, and a solvent, applying the slurry to a current collector, and drying and removing the solvent in the slurry. . As an active material, it can select suitably according to the kind etc. of an electrical storage device. For example, when the electrode according to the present disclosure is a negative electrode for a lithium ion secondary battery, examples of the active material include a carbon material, a silicon material, a titanium material, and a tin material. When the electrode according to the present disclosure is a positive electrode for a lithium ion secondary battery, examples of the active material include metal oxides, metal phosphates, and sulfur materials. As a solvent, what is necessary is just a solvent which can disperse | distribute the resin composition which concerns on this indication, For example, water, N-methylpyrrolidone (NMP), etc. are mentioned. The current collector can be selected from conductive materials, and examples thereof include metal foils such as copper foil, nickel foil, aluminum foil, and stainless steel foil.

  Hereinafter, although an example explains this indication, this indication is not limited to this.

1. Preparation of polymer particle dispersion (Examples 1 to 4 and Comparative Example 1)
The following raw materials were used for the preparation of the polymer particle dispersions of Examples 1 to 4 and Comparative Example 1 shown in Table 1. Abbreviations of raw materials used in Table 1 and the following examples are as follows.

<Monomer (A)>
MMA: Methyl methacrylate (Wako Pure Chemical Industries)
EA: Ethyl acrylate (manufactured by Wako Pure Chemical Industries)
BA: Butyl acrylate (Wako Pure Chemical Industries)
2-EHA: 2-ethylhexyl acrylate <monomer (B)>
AA: Acrylic acid (Wako Pure Chemical Industries)
<Monomer (C)>
EGDMA: Ethylene glycol dimethacrylate (manufactured by Wako Pure Chemical Industries)
<Polymerization initiator>
APS: ammonium persulfate KPS: potassium persulfate <neutralized salt>
Na: Sodium Li: Lithium NH ₄ : Ammonium <Emulsifier>
Sodium dodecylbenzenesulfonate

[Polymer particle dispersion of Example 1]
194 g of EA as monomer (A), 6 g of AA as monomer (B), 0.20 g of EGDMA as monomer (C) [0.1 mol% with respect to the total number of moles of monomers (A) and (B)], and ions 340 g of exchanged water was placed in a glass 4-neck separable flask having an internal volume of 1 L, and stirred for a certain time (0.5 hours) under a nitrogen atmosphere. And after heating up the reaction solution in a flask to about 70 degreeC, the polymerization initiator solution which melt | dissolved 1g of APS in 10g of ion-exchange water is added in a flask, The reaction solution in a flask is 70-75 degreeC vicinity. By maintaining for 6 hours, polymerization and aging were performed to obtain a polymer particle dispersion. Thereafter, the polymer particle dispersion in the flask is cooled to room temperature, neutralized by adding 29.14 g of 1N LiOH aqueous solution, and then aggregates are removed using a 200 mesh filter cloth, and the concentration is 30 to 35% by mass. The polymer particle dispersion of Example 1 was obtained by concentrating to a degree. Table 1 shows the amount and type of each component used in the preparation of the polymer particle dispersion of Example 1.

[Polymer particle dispersion of Example 2]
Example 1 The same manner as in Example 1 except that the amount of monomer (C) used was changed to 1.0 g [0.5 mol% based on the total number of moles of monomers (A) and (B)]. 2 polymer particle dispersion was obtained. Table 1 shows the amount and type of each component used in the preparation of the polymer particle dispersion of Example 2.

[Polymer particle dispersion of Example 3]
A polymer particle dispersion of Example 3 was obtained in the same manner as in Example 1 except that the monomer (C) was not used. Table 1 shows the amount and type of each component used in the preparation of the polymer particle dispersion of Example 3.

[Polymer particle dispersion of Example 4]
Other than changing the type and blending amount of the monomer (A) to MMA 60 g and BA 120 g, changing the type and blending amount of the monomer (B) to 20 g AA, and not using the monomer (C) In the same manner as in Example 1, a polymer particle dispersion of Example 4 was obtained. Table 1 shows the amount and type of each component used in the preparation of the polymer particle dispersion of Example 4.

[Polymer particle dispersion of Comparative Example 1]
69 g of 2-EHA as the monomer (A), 3.75 g of AA as the monomer (B), 2.25 g of EGDMA as the monomer (C) [2.66 mol% based on the total number of moles of the monomers (A) and (B) , 183 g of ion-exchanged water and 1.5 g of an emulsifier (sodium dodecylbenzenesulfonate) were placed in a glass 4-neck separable flask having an internal volume of 1 L and stirred for a certain time (0.5 hours) under a nitrogen atmosphere. . And after heating up the reaction solution in a flask to about 70 degreeC, the polymerization initiator solution which melt | dissolved 0.23 g of KPS in 10 g of ion-exchange water is added in a flask, and the reaction solution in a flask is 60-65 degreeC. Polymerization and aging were carried out by holding in the vicinity for 6 hours to obtain a polymer particle dispersion. Thereafter, the polymer particle dispersion in the flask is cooled to room temperature and adjusted to pH 6 by adding 10% aqueous ammonia, and then aggregates are removed using a 200 mesh filter cloth so that the concentration is about 30 to 35% by mass. The polymer particle dispersion of Comparative Example 1 was obtained. Table 1 shows the amount and type of each component used in the preparation of the polymer particle dispersion of Comparative Example 1.

2. About physical properties of polymer particles The elastic modulus, elastic change rate, solubility, glass transition temperature, average particle diameter, and liquid absorption amount of each polymer particle of Examples 1 to 4 and Comparative Example 1 were determined as follows. The results are shown in Table 2. Further, Table 2 collectively shows sp of each polymer particle and Δsp of each polymer particle and EC / DEC (volume ratio 1/1).

[Elastic modulus and elastic change rate]
1 g of a polymer obtained by drying the polymer particle dispersion on a flat plate (hereinafter referred to as polymer particle film) was immersed in 100 g of an electrolytic solution and allowed to stand at room temperature (25 ° C.) for 72 hours. An EC / DEC mixed solvent (volume ratio 1/1) was used as the electrolytic solution. After the immersion, the polymer particle film was taken out and the excess electrolyte was wiped off, and then cut into 1 cm square. Using an Anton Paar rheometer "MCR302", the measurement was performed at 25 ° C, jig PP08, normal force 1N, frequency 2Hz, strain 0.01-1000%, angular velocity 0.01 (1 / s) The storage elastic modulus was used for calculating the elastic change rate. The polymer particle film before immersion in the electrolyte was also measured under the same conditions.
Elastic change rate (%) = Storage elastic modulus of the film after immersion / Storage elastic modulus of the film before immersion × 100

[solubility]
The solubility was calculated using an existing measurement table specific to the substance. In the case of a mixture, the proportion was calculated by proportional distribution. As the electrolytic solution, an EC / DEC mixed solvent (volume ratio 1/1) and an EC / DEC mixed solvent (volume ratio 3/7) were used.

[Glass transition temperature (Tg)]
According to the Fox formula [TGFox, Bull. Am. Physics Soc., Vol. 1, No. 3, page 123 (1956)], the glass transition temperature Tg is obtained from the Tgn of the homopolymer of each monomer constituting the polymer, It calculated | required by calculation from the following formula (I).
1 / Tg = Σ (Wn / Tgn) (I)
In formula (I), Tgn represents Tg represented by the absolute temperature of the homopolymer of each monomer component, and Wn represents the mass fraction of each monomer component.

[Average particle diameter of polymer particles]
The average particle diameter of the polymer particles is measured by diluting with a dispersion medium (water) at room temperature until reaching a predetermined light intensity range of the apparatus using a laser diffraction particle size measuring instrument (LA-920 manufactured by Horiba Seisakusho). did.

[Liquid absorption]
1 g of a polymer particle film obtained by drying the polymer particle dispersion was immersed in 300 g of an electrolytic solution and allowed to stand at room temperature (25 ° C.) for 72 hours. The precipitate was filtered with a membrane filter, the weight was measured, and the liquid absorption was calculated according to the following formula. An EC / DEC mixed solvent (volume ratio 1/1) was used as the electrolytic solution.
Absorbed amount (%) = [weight of precipitate that has absorbed electrolyte (g) −polymer weight before immersion (g)] / weight of polymer before immersion (g) × 100

3. Evaluation of ion permeability [Evaluation using inductively coupled plasma mass spectrometer (ICP-MS)]
First, an EC / DEC mixed solvent (volume ratio 1/1) I containing no lithium (Li) salt and a lithium-containing solvent II in which lithium perchlorate is dissolved in an EC / DEC mixed solvent (volume ratio 1/1). (1 mol / L: LiClO ₄ ) was prepared. Next, the polymer particle dispersion is poured into a tray equipped with a Teflon (registered trademark) sheet in an amount such that the thickness after drying becomes 0.7 mm, and is dried at 105 ° C. for 24 hours to obtain a polymer film (thickness). Thickness: 0.7 mm). Then, the EC / DEC mixed solvent I was brought into contact with one surface of the polymer film and the lithium-containing solvent II was brought into contact with the other surface, and shaken for 8 hours. Thereafter, the presence or absence of Li in the EC / DEC mixed solvent I was confirmed by inductively coupled plasma mass spectrometry ICP-MS. The results are shown in Table 2. When Li is detected, it is determined that there is ion permeability, and in Table 2, “A” is written. When Li is not detected, it is determined that there is no ion permeability, and is expressed as “B” in Table 2.

[Evaluation by AC impedance method]
<Preparation of measurement electrode>
94.8 parts by weight of graphite (manufactured by Hitachi Chemical Co., "SMG") as the negative electrode active material, 1.7 parts by mass of acetylene black (manufactured by Denka Co., "HS-100") as the conductive additive, carboxymethylcellulose as the thickener A slurry prepared by mixing 1.5 parts by mass of sodium (manufactured by Wako Pure Chemical Industries, Ltd.), 2 parts by mass of a binder, and 122 parts by mass of water was applied onto a 20 μm thick copper foil, dried and pressed to a thickness of 27 μm. After forming the negative electrode active material layer, it was punched out to a size of 18 mmΦ to obtain a measurement electrode.
<Assembly of measurement cell>
The measurement electrode was set on the working electrode of a three-electrode cell (“TSB-1” manufactured by Toyo Technica), and metal Li was set on the reference electrode and the auxiliary electrode. Then, a LiPF ₆ solution having a concentration of 1 M [solvent: EC / EMC mixed solvent (volume ratio: 3/7), manufactured by Kishida Chemical Co., Ltd.] was injected as a nonaqueous electrolytic solution to obtain a measurement cell.
<Measurement of AC impedance>
Using a potentio galvanostat “SI 1287” manufactured by Solartron, the reference electrode was charged at a constant current (0.45 mA) at 25 ° C. until the voltage reached 0.1V. Then, after cooling a cell to -10 degreeC, the alternating current impedance method (10 mV, frequency 0.05Hz-100KHz) was measured using the impedance gain analyzer (FRA) "1260A" by Solartron. The resistance value was calculated from the arc width of the obtained Cole-Cole plot. The measurement results are shown in Table 2. It can be determined that the smaller the resistance value, the better the ion permeability.

  As shown in Table 2, the elastic change rate of the polymer particles of Examples 1 to 4 was significantly reduced as compared with Comparative Example 1. In Comparative Example 1, it was found that the elastic modulus before infiltration of the electrolytic solution was close to that of Examples 1 to 4, but the elastic modulus after infiltration remained high.

3. Production and evaluation of electrodes (Examples 5 to 6)
[Production of negative electrode]
Negative electrode pastes of Examples 5 to 6 were prepared with the compositions shown in Table 3, and negative electrodes were prepared using the respective negative electrode pastes as follows. The materials used for the negative electrode paste are as follows.
Resin Composition: Polymer Particle Dispersion Negative Electrode Active Material of Examples 1 and 2 and Comparative Example 1: Graphite, Showa Denko, “AF-C”
Negative electrode conductive material: Carbon fiber, Showa Denko, "VGCF-H"
Negative electrode thickener: carboxymethylcellulose sodium (CMC), manufactured by Daicel, “# 2200”

  First, after mixing 288 g of the negative electrode active material, 3 g of the negative electrode conductive material, and 3 g of the negative electrode thickener, the amount of distilled water necessary for the final solid content concentration to be 50 to 55% by mass is gradually added and a disper is used. And kneaded. Then, 6 g of the resin composition as a polymer solid content was added to the kneaded product, and further kneaded with a disper. Then, defoaming was performed with a stirring defoaming machine ("Shintaro Awatori" manufactured by Sinky), coarse particles were removed with a 150 mesh filter cloth, and negative electrode pastes of Examples 5 to 6 were obtained. Here, the solid content concentration (% by mass) of the negative electrode paste is the total amount (% by mass) of the solid content of the negative electrode active material, the negative electrode conductive material, the negative electrode thickener and the resin composition contained in the negative electrode paste. ). The solid content concentrations of the negative electrode paste and the resin composition were calculated by drying at 105 ° C. for 24 hours and measuring the weight loss. The viscosity of the negative electrode paste was measured using a B-type viscometer (temperature 25 ° C., rotation speed 6 rpm, rotor No. 3).

Next, the negative electrode pastes of Examples 5 to 6 were each coated on a copper foil as a current collector with a bar coater after adjusting the thickness so as to be 80 g / m ² after drying. The coating film was dried at 80 ° C. for 5 minutes using a blow dryer, and further dried at 150 ° C. for 10 minutes. Thereafter, the electrode density was adjusted to 1.3 to 1.4 g / cm ³ by a roll press and left in a dry room for more than one night to prepare a negative electrode having a negative electrode mixture layer.

[Evaluation of binding property of negative electrode]
After punching out the negative electrode to 45 mm x 45 mm, aligning the corners and making a valley fold into a triangle, crease it with a finger, and open it again when the coating film (negative electrode mixture layer) does not peel off, A B is shown. The results are shown in Table 3.

  As shown in Table 3, the negative electrodes of Examples 5 to 6 using the resin composition of Example 1 or 2 having excellent lithium ion permeation amount and lithium ion retention amount had good binding properties.

  As described above, the resin composition of the present disclosure having excellent ion permeability while ensuring good binding to an electrode is useful in lithium ion batteries, lithium ion capacitors and other power storage devices. is there.

Claims (6)

A resin composition for an electricity storage device electrode comprising polymer particles,
The polymer particles have ion permeability,
A resin composition for an electrical storage device electrode, wherein an elastic change rate [(elastic modulus after treatment) / (elastic modulus before treatment)] of the polymer particles before and after treatment with an electrolytic solution is 30% or less.   The said polymer particle is a resin composition for electrical storage device electrodes of Claim 1 containing the structural unit derived from ester (meth) acrylate.   The resin composition for an electricity storage device electrode according to claim 1, which contains substantially no surfactant. Further containing an aqueous medium,
The resin composition for an electricity storage device electrode according to any one of claims 1 to 3, wherein the resin composition is a polymer particle dispersion in which the polymer particles are dispersed in the aqueous medium.   The resin composition for an electrical storage device electrode according to any one of claims 1 to 4, which is a binder for a positive electrode.   The resin composition for an electricity storage device electrode according to any one of claims 1 to 4, which is a binder for a negative electrode.