JP2014241197A - Composite for producing protective film, protective film, manufacture method of the same, and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film that is excellent in electrolyte permeability and liquid retention and can suppress an increase in internal resistance of an electricity storage device, a method for producing the protective film, a composition for producing the protective film, and the protective film An electricity storage device is provided.
A composition according to the present invention is a composition for producing a protective film disposed between a positive electrode and a negative electrode of an electricity storage device, comprising water-insoluble polymer particles (A2) and an aqueous medium. And the spinnability is 60 to 85%.
[Selection] Figure 1

Description

  The present invention relates to a composition for producing a protective film disposed between a positive electrode and a negative electrode of an electricity storage device, a protective film produced using the composition, a production method thereof, and an electricity storage comprising the protective film Regarding devices.

  In recent years, a power storage device having a high voltage and a high energy density has been required as a power source for driving electronic equipment. In particular, lithium ion batteries and lithium ion capacitors are expected as power storage devices having high voltage and high energy density.

  The power storage device having such a high voltage and high energy density is required to be further downsized. In order to achieve miniaturization of an electricity storage device, it is essential not only to make a power generation element such as a positive electrode and a negative electrode thin, but also to make a thin film such as a separator that separates the positive electrode and the negative electrode. However, when the interval between the positive electrode and the negative electrode is reduced due to the miniaturization of the electricity storage device, there may be a problem that a short circuit is likely to occur.

  In particular, in an electricity storage device using metal ions such as lithium ions, dendrites due to metal ions are likely to occur on the electrode surface by repeated charge and discharge. Since such dendrites usually precipitate as needle-like crystals, they tend to grow through the separator, which is a porous film. When the dendrite grows through the separator and reaches the surface of the counter electrode, the electricity storage device is short-circuited and loses the charge / discharge function. As the separator becomes thinner and the distance between the positive electrode and the negative electrode becomes narrower, the risk of such a phenomenon increases, and the reliability decreases accordingly.

  In order to avoid such a phenomenon, for example, in Patent Document 1 and Patent Document 2, battery characteristics are improved by forming a porous layer including a resin binder containing polyamide, polyimide, and polyamideimide on a porous separator substrate. Improvement techniques are being studied. On the other hand, Patent Document 3 discusses a technique for improving battery characteristics by forming a porous protective film containing a binder containing a fluorine resin and a rubber resin on at least one surface of a positive electrode and a negative electrode. ing. In Patent Document 4, a battery is formed by forming a porous layer containing a copolymer containing a (meth) acrylonitrile monomer unit and a (meth) acrylate monomer unit on a porous separator substrate. Techniques for improving the characteristics are being studied.

International Publication No. 2009/041395 JP 2009-87562 A JP 2009-54455 A International Publication No. 2010/074202

However, according to the materials described in the above-mentioned patent documents, although a protective film is formed on the surface of the separator or the electrode, a short circuit caused by dendrite generated along with charge / discharge can be suppressed. As a result, the permeability and liquid retention of the electrolyte solution are reduced, which prevents lithium ions from adsorbing and desorbing to the active material. As a result, there is a problem that the internal resistance of the electricity storage device increases and the charge / discharge characteristics are deteriorated.

  Furthermore, the protective film formed on the separator or the electrode surface by a material as described in the above-mentioned patent document has low adhesion to the electrode, and therefore, the spacing between the electrodes tends to be non-uniform. As a result, there has been a problem that the electrode reaction accompanying charge / discharge proceeds non-uniformly within the electrode surface, and the charge / discharge characteristics deteriorate.

  Thus, in the prior art, there is no known protective film material that is excellent in electrolyte permeability and liquid retention and that can suppress an increase in internal resistance of the electricity storage device. In particular, when a binder made of an organic polymer is applied as a protective film on the surface facing the positive electrode, a high degree of oxidation resistance that can withstand the oxidation of the positive electrode reaction is required.

  Therefore, some aspects of the present invention provide a protective film capable of suppressing the increase in internal resistance of the electricity storage device and its manufacturing method, while being excellent in electrolyte permeability and liquid retention by solving the above-described problems, The present invention provides a composition for producing the protective film and an electricity storage device provided with the protective film.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of the composition according to the present invention is:
A composition for producing a protective film disposed between a positive electrode and a negative electrode of an electricity storage device,
Water-insoluble polymer particles (A2) and an aqueous medium,
The spinnability is 60 to 85%.

[Application Example 2]
In the composition of Application Example 1,
The water-insoluble polymer particles (A2) may be particles having pores.

[Application Example 3]
In the composition of Application Example 1 or Application Example 2,
The water-insoluble polymer particles (A2) can have a repeating unit derived from a compound having two or more polymerizable unsaturated groups.

[Application Example 4]
In the composition of Application Example 3,
The compound having two or more polymerizable unsaturated groups may be at least one selected from the group consisting of polyfunctional (meth) acrylic acid esters and aromatic polyfunctional vinyl compounds.

[Application Example 5]
In the composition of any one of Application Examples 1 to 4,
Furthermore, a water-soluble polymer (A1) can be contained.

[Application Example 6]
In the composition of Application Example 5,
The water-soluble polymer (A1) can be contained in an amount of 0.1 to 15 parts by mass with respect to 100 parts by mass of the water-insoluble polymer particles (A2).

[Application Example 7]
In the composition of any one of Application Examples 1 to 6,
The water-insoluble polymer particles (A2) may have an average particle diameter (Da2) of 100 nm to 3000 nm.

[Application Example 8]
In the composition of any one of Application Examples 1 to 7,
The insoluble content of the water-insoluble polymer particles (A2) in toluene is 90% or more, and the 10% weight loss temperature when heated at 20 ° C./min in thermogravimetric analysis under an air atmosphere is 320 ° C. or more. Can be.

[Application Example 9]
By the method using the composition of any one of Application Examples 1 to 8, a protective film disposed between the positive electrode and the negative electrode of the electricity storage device can be manufactured.

[Application Example 10]
One embodiment of the protective film according to the present invention is manufactured by the method of Application Example 9.

[Application Example 11]
One embodiment of the electricity storage device according to the present invention includes a positive electrode, a negative electrode, a protective film of Application Example 10 disposed between the positive electrode and the negative electrode, and an electrolytic solution.

  A protective film produced using a composition for producing a protective film disposed between the positive electrode and the negative electrode of the electricity storage device according to the present invention (hereinafter also referred to as “composition for protective film”) is provided. According to the electricity storage device, it is possible to suppress an increase in internal resistance while being excellent in electrolyte permeability and liquid retention. That is, the power storage device according to the present invention has excellent charge / discharge characteristics because the degree of increase in the internal resistance of the power storage device is small even after repeated charge / discharge or overcharge. In addition, since the said protective film is arrange | positioned between a positive electrode and a negative electrode, it can also suppress the short circuit resulting from the dendride which generate | occur | produces with charging / discharging.

  Since the composition for a protective film according to the present invention is further excellent in oxidation resistance, it can be particularly suitably used for forming a protective film opposite to the positive electrode of the electricity storage device.

It is the schematic diagram which showed the cross section of the electrical storage device which concerns on 1st Embodiment. It is the schematic diagram which showed the cross section of the electrical storage device which concerns on 2nd Embodiment. It is the schematic diagram which showed the cross section of the electrical storage device which concerns on 3rd Embodiment. 6 is a TGA chart of water-insoluble polymer particles (A2) obtained in Synthesis Example 4.

  Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited to only the embodiments described below, and includes various modifications that are implemented without departing from the scope of the present invention.

1. Composition for Protective Film The composition for protective film according to the present embodiment is a composition for producing a protective film disposed between a positive electrode and a negative electrode of an electricity storage device, and is a water-insoluble polymer particle (A2), an aqueous medium,
And the spinnability is 60 to 85%. In addition, the composition for protective films which concerns on this Embodiment has the function to bind | conclude water-insoluble polymer particles (A2), and the water-soluble polymer which can adjust spinnability arbitrarily ( It is preferable to contain A1). Hereinafter, each component contained in the composition for protective films which concerns on this Embodiment is demonstrated in detail. “(Meth) acrylic acid” in the following description is a concept including both acrylic acid and methacrylic acid. Similar terms such as “(meth) acrylonitrile” should be understood similarly.

1.1. Water-soluble polymer (A1)
The protective film composition according to this embodiment preferably contains a water-soluble polymer (A1). Since this water-soluble polymer (A1) is water-soluble, it exists in a dissolved state in an aqueous medium. The water-soluble polymer (A1) functions as a binder that binds the water-insoluble polymer particles (A2) to be described later. In addition, a separator and an electrode, a protective film and a separator, or a protective film and an electrode It is thought that it functions also as a binder which adhere | attaches each.

  Moreover, by dissolving the water-soluble polymer (A1) in an aqueous medium, the spinnability of the protective film composition can be arbitrarily adjusted within a range of 60 to 85%. Thereby, the leveling property of the composition for protective films improves, and the thickness uniformity of a protective film becomes favorable. The spinnability will be described in detail later. Furthermore, by dissolving the water-soluble polymer (A1) in an aqueous medium, the dispersion stability of the water-insoluble polymer particles (A2) described later can be improved, and a homogeneous protective film can be produced. The composition for protective films which can be obtained is obtained.

  Examples of the water-soluble polymer (A1) include cellulose compounds such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and hydroxyethylcellulose; ammonium salts or alkali metal salts of the above cellulose compounds; poly (meth) acrylic acid, modified Polycarboxylic acids such as poly (meth) acrylic acid; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol-based (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; Mention may be made of water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as acrylic acid, maleic acid and fumaric acid and vinyl esters. Among these, polycarboxylic acid-based polymers such as polycarboxylic acids and alkali metal salts of polycarboxylic acids are preferable, and poly (meth) acrylic acid-based polymers are more preferable. These water-soluble polymers (A1) may be used alone or in combination of two or more.

  When the water-soluble polymer (A1) is a polycarboxylic acid-based polymer, it is derived from (a) an ethylenically unsaturated carboxylic acid ester with respect to 100% by mass of all repeating units of the water-soluble polymer (A1). It is preferable to contain 50 to 95% by mass of repeating units and 5 to 50% by mass of repeating units derived from (b) an ethylenically unsaturated carboxylate. Hereinafter, the repeating unit contained in the water-soluble polymer (A1), the mode of the water-soluble polymer (A1), the production method, and the like will be described in detail.

1.1.1. (A) Repeating unit derived from ethylenically unsaturated carboxylic acid ester (a) Repeating unit derived from ethylenically unsaturated carboxylic acid ester (hereinafter also simply referred to as “repeating unit (a)”) is ethylenically unsaturated. It has a structure in which a carbon-carbon double bond of a saturated carboxylic acid ester is a single bond. Examples of the ethylenically unsaturated carboxylic acid ester include compounds represented by the following general formula (1).

^{CHR 1 = CR 2 -C (=} O) -OR 3 ··· (1)
(In the formula, R ¹ and R ² each independently represents a hydrogen atom or a methyl group. R ³ represents an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or an alkyl group having 1 to 10 carbon atoms. Represents a hydroxyalkyl group.)

In the general formula (1), specific examples of R ³ include alkyl groups having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group and a 2-ethylhexyl group; a cyclopentyl group and a cyclohexyl group. A cycloalkyl group having 3 to 10 carbon atoms such as a group; a hydroxyalkyl group having 1 to 10 carbon atoms such as a hydroxyethyl group, a hydroxypropyl group, and a hydroxybutyl group.

Among these, from the viewpoint of the binding property of the water-insoluble polymer particles (A2) described later and the stability at the time of emulsion polymerization, those having high hydrophobicity are preferable, that is, an alkyl group having 1 to 10 carbon atoms. A cycloalkyl group having 3 to 10 carbon atoms is preferred. In view of solubility in water, more preferably, it is an alkyl group having 1 to 8 carbon atoms or a cycloalkyl group having 3 to 8 carbon atoms, and more preferably an alkyl group having 1 to 6 carbon atoms. It is. It is preferable that R ³ in the general formula (1) is an alkyl group because the glass transition temperature (Tg) of the obtained water-soluble polymer (A1) is lowered. R ³ is particularly preferably an alkyl group having 1 to 4 carbon atoms, and most preferably an alkyl group having 1 to 2 carbon atoms. When the alkyl group has 1 to 4 carbon atoms, the copolymer with the ethylenically unsaturated carboxylate monomer is easily dissolved in water. These ethylenically unsaturated carboxylic acid ester monomers may be used alone or in combination of two or more.

  Specific examples of such ethylenically unsaturated carboxylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, (meth ) N-butyl acrylate, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, N-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, cyclohexyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylic (Meth) acrylic acid esters such as hydroxybutyl acid; methyl crotonic acid, ethyl crotonic acid, crotonic acid -Propyl, i-propyl crotonate, n-butyl crotonate, i-butyl crotonate, n-amyl crotonate, i-amyl crotonate, hexyl crotonate, 2-ethylhexyl crotonate, n-octyl crotonate, croton And crotonic acid esters such as acid nonyl, decyl crotonate, cyclohexyl crotonate, hydroxymethyl crotonate, hydroxyethyl crotonate, and hydroxybutyl crotonate.

  The content of the repeating unit (a) in the water-soluble polymer (A1) is preferably 50 to 95% by mass with respect to 100% by mass of the total amount of repeating units of the water-soluble polymer (A1). More preferably, it is -80 mass%, It is especially preferable that it is 50-70 mass%. A water-soluble polymer (A1) can be easily manufactured by emulsion polymerization because the content rate of a repeating unit (a) exists in the said range. On the other hand, when the content ratio of the repeating unit (a) exceeds the above range, there is a possibility that the solubility in water is insufficient and a uniform solution may not be obtained, and when the content ratio of the repeating unit (a) is less than the above range, emulsification is performed. Production by polymerization may be difficult.

1.1.2. (B) Repeating unit derived from ethylenically unsaturated carboxylate (b) Repeating unit derived from ethylenically unsaturated carboxylate (hereinafter also referred to simply as “repeat unit (b)”) is an ethylenically unsaturated carboxylate. It represents a structure in which a carbon-carbon double bond of a saturated carboxylate is a single bond. By having the repeating unit (b) in the water-soluble polymer (A1), a “water-soluble” function can be expressed.

  Examples of the ethylenically unsaturated carboxylate include, for example, an ethylenically unsaturated monocarboxylate having 3 to 10 carbon atoms such as alkali metal salts such as (meth) acrylic acid, crotonic acid and isocrotonic acid; itaconic acid and maleic acid And ethylenically unsaturated dicarboxylates having 4 to 10 carbon atoms such as alkali metal salts such as fumaric acid, citraconic acid, mesaconic acid and glutaconic acid. Among these, C3-C6 ethylenically unsaturated monocarboxylates, such as acrylic acid and methacrylic acid, are preferable.

  Examples of the alkali metal forming the alkali metal salt include lithium, sodium, potassium, and the like, preferably lithium. By using such an alkali metal salt of an ethylenically unsaturated carboxylic acid as a monomer, a protective film produced using the protective film composition containing the water-soluble polymer (A1) is used as an electrolyte. In contrast, swelling can be suppressed. As these ethylenically unsaturated carboxylate, 1 type may be used and 2 or more types may be used.

  As long as the ethylenically unsaturated carboxylate can synthesize a water-soluble polymer (A1) by a polymerization method described later, the carboxyl group may not form a salt, and a part thereof It may be in the form of a carboxyl group (—COOH). In the case where a part of the ethylenically unsaturated carboxylate is a carboxyl group, when the total of the carboxylate group and carboxyl group of the ethylenically unsaturated carboxylate is 100 mol%, the carboxyl What is in the form of a group is preferably 50 mol% or less, more preferably 40 mol% or less, and particularly preferably 30 mol% or less.

  The content ratio of the repeating unit (b) in the water-soluble polymer (A1) is preferably 5 to 50% by mass with respect to 100% by mass of the total amount of repeating units of the water-soluble polymer (A1). More preferably, it is -48 mass%, and it is especially preferable that it is 31-45 mass%. When the content ratio of the repeating unit (b) is in the above range, the water-soluble polymer (A1) can be easily produced by emulsion polymerization, and water of the produced water-soluble polymer (A1) can be obtained. It becomes possible to express the solubility in. On the other hand, when the content ratio of the repeating unit (b) is less than the above range, there is a fear that the solubility in water is insufficient and a uniform solution may not be obtained, and when the repeating unit (b) exceeds the above range, production by emulsion polymerization May become difficult.

1.1.3. (C) Repeating unit derived from other polymerizable monomer When the water-soluble polymer (A1) is a polycarboxylic acid polymer, as long as it contains the repeating unit (a) and the repeating unit (b). , (C) may contain a repeating unit derived from another polymerizable monomer (hereinafter also simply referred to as “repeating unit (c)”). Examples of such monomers include styrene monomers such as styrene, α-methylstyrene, and ethyl vinyl benzene; (meth) acrylamides such as (meth) acrylic acid amide and N, N-dimethyl (meth) acrylamide. Monofunctional monomers; polyfunctional allylic monomers such as vinyl acetate and diallyl phthalate; and polyfunctional acrylates such as 1,6-hexanediol diacrylate.

Further, a (meth) acrylic ester or vinyl compound having a polyalkylene oxide group having a hydrophobic group such as an alkyl group having 5 to 30 carbon atoms which may be halogenated at the terminal can also be used. In this case, by having a hydrophobic group at the end of the alkylene oxide, the viscosity of the composition can be changed by the association of the hydrophobic group. The hydrophobic group at the end of the alkylene oxide is preferably an alkyl group having 5 to 30 carbon atoms, and more preferably an alkyl group having 15 to 20 carbon atoms. Among these polymerizable monomers, among these, (meth) acrylic ester having a polyalkylene oxide group having a hydrophobic group such as an alkyl group having 5 to 30 carbon atoms which may be halogenated at the end, A vinyl compound is preferred. As these other polymerizable monomers, one type may be used, or two or more types may be used.

  When the water-soluble polymer (A1) contains the repeating unit (c), the content is 20% by mass or less with respect to 100% by mass of the total amount of the repeating units of the water-soluble polymer (A1). Is preferably 10% by mass or less, and more preferably 5% by mass or less.

  The ratio of the repeating unit in the water-soluble polymer (A1) is [repeating unit (a) / repeating unit (b) / when the total amount of repeating units of the water-soluble polymer (A1) is 100% by mass. Repeating unit (c)] = 50 to 95% by mass / 5 to 50% by mass / 0 to 20% by mass is preferable.

  Since the repeating unit (a) and the repeating unit (c) are repeating units other than the carboxylic acid component of the repeating unit (b) for exhibiting water solubility, they are not particularly limited. However, the water-soluble polymer (A1) preferably contains a repeating unit derived from an ethylenically unsaturated carboxylic acid ester which is the repeating unit (a) as a main component for the following reasons, and the repeating unit (c). It is preferable that the content rate of the repeating unit derived from the other monomer which is is 0-20 mass%.

That is, when the repeating unit (a) is a repeating unit derived from the ethylenically unsaturated carboxylic acid ester represented by the general formula (1), the ethylenically unsaturated carboxylic acid ester is an ester structure moiety, That is, it is a monomer having a structural portion represented by —C (═O) —OR ³ in the general formula (1), and is a hydrophobic monomer but contains a polar group. For this reason, it tends to become the core of the emulsion droplets during emulsion polymerization, while it tends to be uniformly dissolved in water when neutralized with an alkali metal salt after polymerization. Therefore, as a main component other than the repeating unit (b), a repeating unit derived from the ethylenically unsaturated carboxylic acid ester (repeating unit (a)) is a main component, and the content ratio is 50 to 95% by mass. preferable. Since the water-soluble polymer (A1) contains the hydrophobic part and the polar part in a well-balanced manner as described above, it can also function as a dispersant for the water-insoluble polymer particles (A2) described later. It can be used suitably for producing a stable composition for a protective film.

1.1.4. Manufacturing method of water-soluble polymer (A1) A water-soluble polymer (A1) can be manufactured by polymerizing each monomer component derived from the repeating unit mentioned above. The method for polymerizing the monomer component is not particularly limited, and examples thereof include emulsion polymerization, reverse phase suspension polymerization, suspension polymerization, solution polymerization, aqueous solution polymerization, and bulk polymerization. Among these polymerization methods, the emulsion polymerization method is preferable.

  The above-mentioned emulsion polymerization method is a method in which polymerization proceeds in a micelle, so that a high molecular weight copolymer can be easily polymerized at a high concentration, and the viscosity of the polymerization solution is also low. A water-soluble polymer (A1) having a weight average molecular weight of 500,000 or more is prepared as an aqueous dispersion by an emulsion polymerization method, and is easily manufactured by neutralizing with an alkali metal salt and solubilizing (homogenizing). It can be done and has advantages in terms of production costs.

  The emulsion polymerization can be performed using an emulsifier. The emulsifier is not particularly limited. For example, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants, and radical polymerizable compounds in the structure of these surfactants. Examples thereof include a reactive surfactant having an unsaturated group.

  In particular, reactive surfactants can incorporate surfactants into the polymer structure by virtue of their polymerizable unsaturated groups, and reduce the surfactant components that are present free in aqueous solutions when made into aqueous solutions. Is preferable. These emulsifiers may be used alone or in combination of two or more.

  Examples of the reactive surfactant include Latemul PD (manufactured by Kao Corporation), Adekaria Soap SR (manufactured by ADEKA Corporation), Aqualon HS, Aqualon KH (above, Daiichi Kogyo Seiyaku Co., Ltd.), Eleminol RS (Manufactured by Sanyo Chemical Industries, Ltd.). Thus, it is also one of preferred embodiments of the present invention that the water-soluble polymer (A1) is obtained using a reactive surfactant during emulsion polymerization.

  A polymerization initiator can be used for the polymerization of the monomer components. As the polymerization initiator, those usually used as a polymerization initiator can be used, and are not particularly limited as long as they generate radical molecules by heat. When emulsion polymerization is performed as a polymerization method, a water-soluble initiator is preferably used. Examples of the polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyano). Water-soluble azo compounds such as pentanoic acid; thermal decomposition initiators such as hydrogen peroxide; hydrogen peroxide and ascorbic acid, t-butyl hydroperoxide and rongalite, potassium persulfate and metal salts, ammonium persulfate and sodium bisulfite And the like, and the like. These polymerization initiators can be used alone or in combination of two or more.

  The amount of the polymerization initiator used is preferably 0.05 to 2 parts by mass and preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the total amount of monomer components used for the polymerization reaction. Is more preferable.

  In the emulsion polymerization, a chain transfer agent may be used to adjust the molecular weight. Examples include halogenated substituted alkanes, alkyl mercaptans, thioesters, alcohols and the like, but are not particularly limited thereto. These chain transfer agents may be used alone or in combination of two or more. The chain transfer agent is preferably used in an amount of 0 to 1 part by mass with respect to 100 parts by mass of the total amount of monomer components used for the polymerization reaction.

  Although there is no limitation in particular about the polymerization temperature in the said emulsion polymerization, Preferably it is 20-100 degreeC, More preferably, it is 50-90 degreeC. The polymerization time is not particularly limited, but is preferably 1 to 10 hours in consideration of productivity. When emulsion polymerization is performed, a hydrophilic solvent, an additive, or the like can be added within a range that does not adversely affect the resulting copolymer.

  The method for adding each monomer component to the emulsion polymerization reaction system is not particularly limited, and a batch polymerization method, a monomer component dropping method, a pre-emulsion method, a power feed method, a seed method, a multistage addition method, or the like is used. be able to.

  The nonvolatile content of the emulsion obtained after the emulsion polymerization reaction is preferably 20 to 60%. When the non-volatile content is in the range of 20 to 60%, it becomes easy to maintain the fluidity and dispersion stability of the obtained emulsion. Moreover, it is preferable also from the point of the production efficiency of the target polymer. On the other hand, if the non-volatile content exceeds the above range, the viscosity of the emulsion is too high, so that dispersion stability may not be maintained and aggregation may occur. It may take a long time, and the production efficiency deteriorates in terms of the production amount of the target polymer.

  The average particle size of the emulsion is not particularly limited, but is preferably 10 nm to 1 μm, and more preferably 30 to 500 nm. When the particle diameter of the emulsion is within this range, the possibility that the viscosity becomes too high or the dispersion stability cannot be maintained and aggregation is reduced can be reduced. On the other hand, when the particle diameter of the emulsion is less than the above range, the viscosity of the emulsion may be too high, or the dispersion stability may not be maintained, and aggregation may occur, and if it exceeds the above range, the dispersion stability of the polymer particles may be increased. It becomes difficult to keep. The average particle size of the emulsion can be measured by a particle size distribution measuring apparatus using a dynamic light scattering method as a measurement principle.

  The water-soluble polymer (A1) is preferably obtained by neutralizing polymer particles (water dispersion) obtained by the above method with an alkali metal salt. The alkali metal salt is a salt of lithium, sodium, potassium or the like. In order to neutralize with these metal salts, an aqueous solution of lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium carbonate or the like can be used, preferably water. Lithium oxide, lithium hydrogen carbonate, lithium carbonate. By neutralizing with these metal salts, it becomes a uniform aqueous solution and becomes a transparent solution in appearance. Neutralization is preferably 50% or more of the theoretical carboxylic acid content, more preferably 65% or more. Further, the pH after neutralization is preferably 6 or more, and more preferably 7 or more and 9 or less.

  Thus, it is also one of preferred embodiments of the present invention that the water-soluble polymer (A1) is obtained by neutralizing a polymer synthesized by emulsion polymerization with an alkali metal salt. is there.

  Here, the “transparent solution” means a solution having a total light transmittance of 90 to 100% of an aqueous solution containing 2% by mass of a nonvolatile content obtained by neutralizing an emulsion polymerized polymer with an alkali metal salt. That is, the water-soluble polymer (A1) has a total light transmittance of 90 to 100% in an aqueous solution adjusted to a nonvolatile content of 2% by mass. The total light transmittance is preferably 95% or more, and more preferably 97% or more. Moreover, the water-soluble polymer (A1) preferably has a haze of an aqueous solution adjusted to 2% by mass of non-volatile content of 3% or less, and more preferably 1% or less. The total light transmittance and haze can be measured using a haze meter (product name “NDH5000”, manufactured by Nippon Denshoku Industries Co., Ltd.). Moreover, said pH can be performed by measuring the value in 25 degreeC using glass electrode type hydrogen ion meter F-21 (product name, Horiba, Ltd. make).

1.1.5. Physical properties of water-soluble polymer (A1) The water-soluble polymer (A1) preferably has a weight average molecular weight of 50,000 or more. When the weight average molecular weight of the water-soluble polymer (A1) is 50,000 or more, the spinnability of the composition for a protective film according to the present embodiment can be set to an optimum range for coating a protective film, A homogeneous protective film can be produced. A weight average molecular weight can be measured by the measurement by the gel permeation chromatography method (GPC method) currently performed in the Example mentioned later.

  The water-soluble polymer (A1) preferably has a 2% by weight aqueous solution viscosity of 50 to 20,000 mPa · s, more preferably 100 to 10,000 mPa · s, and 150 to 5, 000 mPa · s is particularly preferable. The viscosity can be measured using a B-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) at 25 ± 1 ° C. and 30 rpm.

1.2. Water-insoluble polymer particles (A2)
The composition for a protective film according to the present embodiment contains water-insoluble polymer particles (A2). Hereinafter, the monomer constituting the repeating unit contained in the water-insoluble polymer particles (A2), the physical properties of the water-insoluble polymer particles (A2), the mode, the production method, and the like will be described in detail.

1.2.1. Monomer 1.2.1.1. Compound having two or more polymerizable unsaturated groups The water-insoluble polymer particles (A2) preferably contain a repeating unit derived from a compound having two or more polymerizable unsaturated groups. The content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups is 5 parts by mass when the total amount of the repeating units of the water-insoluble polymer particles (A2) is 100 parts by mass. Preferably, the amount is 10 parts by mass or more.

  When the content ratio of the repeating unit derived from the compound having two or more polymerizable unsaturated groups is within the above range, the heat resistance and solvent resistance of the protective film produced from the protective film composition according to the present embodiment It is preferable because the function of preventing a short circuit due to dendrite is improved. Furthermore, the composition for a protective film according to the present embodiment can improve the toughness of the protective film formed by containing such water-insoluble polymer particles (A2).

  Although it does not restrict | limit especially as a compound which has two or more polymerizable unsaturated groups, For example, a polyfunctional (meth) acrylic acid ester, an aromatic polyfunctional vinyl compound, etc. are mentioned.

  Examples of the polyfunctional (meth) acrylic acid ester include a compound represented by the following general formula (2), a (poly) (meth) acrylic acid ester of a polyhydric alcohol, and the like.

（上記一般式（２）中、Ｒ^４は水素原子またはメチル基であり、Ｒ^５は重合性の炭素―炭素不飽和結合、エポキシ基およびヒドロキシアルキル基よりなる群から選ばれる少なくとも１種の官能基を有する、炭素数１〜１８の有機基である。）

(In the general formula (2), R ⁴ is a hydrogen atom or a methyl group, and R ⁵ is at least one functional group selected from the group consisting of a polymerizable carbon-carbon unsaturated bond, an epoxy group, and a hydroxyalkyl group. It is a C1-C18 organic group having a group.)

Preferable specific examples of R ^{5 in} the general formula (2) include, for example, vinyl group, isopropenyl group, allyl group, (meth) acryloyl group, epoxy group, glycidyl group, hydroxyalkyl group and the like.

  In the present invention, “polyfunctional (meth) acrylic acid ester” means (meth) acrylic acid ester having two or more (meth) acryloyl groups, one (meth) acryloyl group, and further polymerizable. (Meth) acrylic acid ester having at least one functional group selected from the group consisting of a carbon-carbon unsaturated bond, an epoxy group, and a hydroxyl group.

Polyfunctional (meth) acrylic acid esters include ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, hexa ( Examples thereof include dipentaerythritol (meth) acrylate, glycidyl (meth) acrylate, 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, allyl (meth) acrylate, and the like. It can be one or more selected. Among these, at least one selected from the group consisting of ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate and allyl (meth) acrylate is preferable. Particularly preferred is ethylene glycol acrylate. The polyfunctional (meth) acrylic acid ester exemplified above may be used alone or in combination of two or more.

  As the aromatic polyfunctional vinyl compound, for example, a compound represented by the following general formula (3) can be preferably used.

（上記一般式（３）中、複数存在するＲ^６はそれぞれ独立に、重合性の炭素―炭素不飽和結合を有する有機基であり、複数存在するＲ^７はそれぞれ独立に、水素原子または炭素数１〜１８の炭化水素基である。ｎは２〜６の整数であり、ｍは０〜４の整数である。）

(In the general formula (3), a plurality of R ⁶ are each independently an organic group having a polymerizable carbon-carbon unsaturated bond, and a plurality of R ⁷ are each independently a hydrogen atom or a carbon number. A hydrocarbon group of 1 to 18. n is an integer of 2 to 6, and m is an integer of 0 to 4.)

Examples of R ⁶ in the general formula (3) include a vinylene group having 2 to 12 carbon atoms, an allyl group, a vinyl group, and an isopropenyl group, and among these, a vinylene group having 1 to 12 carbon atoms. It is preferable that Examples of R ⁷ in the general formula (3) include a hydrogen atom, a methyl group, and an ethyl group.

  Examples of the aromatic polyfunctional vinyl compound include aromatic divinyl compounds such as divinylbenzene and diisopropenylbenzene, but are not limited thereto. Of these, divinylbenzene is preferred. The aromatic polyfunctional vinyl compounds exemplified above may be used alone or in combination of two or more.

  As the compound having two or more polymerizable unsaturated groups, at least one selected from the group consisting of the polyfunctional (meth) acrylic acid ester and the aromatic polyfunctional vinyl compound described above can be preferably used. Among these, aromatic divinyl compounds are more preferable, and divinylbenzene is particularly preferable. When the water-soluble polymer (A1) has a repeating unit derived from a compound having two or more polymerizable unsaturated groups, the water-insoluble polymer particles (A2) are polymerized in the same manner as the water-soluble polymer (A1). It is preferable to have a repeating unit derived from a compound having two or more polymerizable unsaturated groups.

  When the water-insoluble polymer particles (A2) contain a repeating unit derived from divinylbenzene, the content ratio of divinylbenzene is preferably 20 to 100% by mass, more preferably 50 to 100% by mass with respect to the total monomers. %, Particularly preferably 80 to 100% by mass. When the content ratio of divinylbenzene is within the above range, the obtained water-insoluble polymer particles (A2) are more excellent in heat resistance and electrolytic solution resistance.

1.2.1.2. Monomer having fluorine atom The water-insoluble polymer particles (A2) preferably contain a repeating unit derived from a monomer having a fluorine atom. Examples of the monomer having a fluorine atom include an olefin compound having a fluorine atom and a (meth) acrylic acid ester having a fluorine atom. Examples of the olefin compound having a fluorine atom include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, ethylene trifluoride chloride, and perfluoroalkyl vinyl ether. As the (meth) acrylic acid ester having a fluorine atom, for example, a compound represented by the following general formula (4), (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like.

（上記一般式（４）中、Ｒ^８は水素原子またはメチル基であり、Ｒ^９はフッ素原子を含有する炭素数１〜１８の炭化水素基である。）

(In the general formula (4), R ⁸ is a hydrogen atom or a methyl group, and R ⁹ is a C 1-18 hydrocarbon group containing a fluorine atom.)

Examples of R ⁹ in the general formula (4) include a fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated aryl group having 6 to 16 carbon atoms, and a fluorinated aralkyl group having 7 to 18 carbon atoms. Among these, a fluorinated alkyl group having 1 to 12 carbon atoms is preferable. Preferable specific examples of R ^{9 in} the general formula (4) include, for example, 2,2,2-trifluoroethyl group, 2,2,3,3,3-pentafluoropropyl group, 1,1,1, 3,3,3-hexafluoropropan-2-yl group, β- (perfluorooctyl) ethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,4,4,4- Hexafluorobutyl group, 1H, 1H, 5H-octafluoropentyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H, 1H, 11H-perfluoroundecyl group, perfluorooctyl group, etc. Can do. Of these, the monomer having a fluorine atom is preferably an olefin compound having a fluorine atom, more preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene. preferable. The monomer having a fluorine atom may be used alone or in combination of two or more.

1.2.1.3. Unsaturated carboxylic acid The water-insoluble polymer particles (A2) preferably contain a repeating unit derived from an unsaturated carboxylic acid. Examples of the unsaturated carboxylic acid include monocarboxylic acids or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these are used. can do. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid and methacrylic acid, and acrylic acid is more preferable.

  The content ratio of the repeating unit derived from the unsaturated carboxylic acid in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 0 to 10 parts by mass.

1.2.1.4. Conjugated diene compound The water-insoluble polymer particles (A2) may further contain a repeating unit derived from a conjugated diene compound. Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like. , One or more selected from these. Among these, 1,3-butadiene is particularly preferable.

1.2.1.5. Other unsaturated monomers The water-insoluble polymer particles (A2) further contain repeating units derived from other unsaturated monomers copolymerizable therewith in addition to the above-mentioned repeating units. May be.

  As such an unsaturated monomer, for example, an unsaturated carboxylic acid ester (excluding those corresponding to the compound having two or more polymerizable unsaturated groups and the monomer having a fluorine atom), Examples include α, β-unsaturated nitrile compounds, aromatic vinyl compounds (excluding those corresponding to the compounds having two or more polymerizable unsaturated groups) and other monomers.

  As the unsaturated carboxylic acid ester, a (meth) acrylic acid ester can be preferably used, and examples thereof include an alkyl ester of (meth) acrylic acid and a cycloalkyl ester of (meth) acrylic acid. The alkyl ester of (meth) acrylic acid is preferably an alkyl ester of (meth) acrylic acid having an alkyl group having 1 to 10 carbon atoms, such as methyl (meth) acrylate, ethyl (meth) acrylate, (meth N-propyl acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i- (meth) acrylate Examples include amyl, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, and decyl (meth) acrylate. Examples of the cycloalkyl ester of (meth) acrylic acid include cyclohexyl (meth) acrylate. The unsaturated carboxylic acid ester exemplified above may be used alone or in combination of two or more. Among these, it is preferable that it is an alkyl ester of (meth) acrylic acid, and is selected from methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate and 2-ethylhexyl acrylate. It is more preferable to use one or more.

  Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, and one or more selected from these may be used. it can. Among these, at least one selected from the group consisting of acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.

  Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, ethylvinylbenzene, and the like. Can do. Among the above, the aromatic vinyl compound is particularly preferably styrene.

  Examples of the other monomers include alkyl amides of unsaturated carboxylic acids such as (meth) acrylamide and N-methylol acrylamide; unsaturated carboxylic acids such as aminoethyl acrylamide, dimethylaminomethyl methacrylamide and methylaminopropyl methacrylamide. An aminoalkylamide etc. can be mentioned and 1 or more types selected from these can be used.

  The content ratio of the repeating unit derived from the unsaturated carboxylic acid ester in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 1 to 85 parts by mass, and more preferably 10 to 80 parts by mass. .

  The content ratio of the repeating unit derived from the α, β-unsaturated nitrile compound in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 5 to 85 parts by mass, and 10 to 80 parts by mass. Is more preferable.

  The content ratio of the repeating unit derived from the aromatic vinyl compound in 100 parts by mass of the water-insoluble polymer particles (A2) is preferably 1 to 90 parts by mass, and more preferably 5 to 85 parts by mass.

1.2.2. Physical properties of water-insoluble polymer particles (A2) 1.2.2.1. Average particle size (Da2)
The average particle diameter (Da2) of the water-insoluble polymer particles (A2) is preferably in the range of 100 to 3000 nm, and more preferably in the range of 100 to 1500 nm. In addition, it is preferable that the average particle diameter (Da2) of the water-insoluble polymer particles (A2) is larger than the average pore diameter of the separator that is a porous film. Thereby, the damage to a separator can be reduced and it can prevent that a water-insoluble polymer particle (A2) is clogged with the microporous of a separator.

  The average particle diameter (Da2) of the water-insoluble polymer particles (A2) is a particle size distribution measured using a particle size distribution measuring apparatus based on the light scattering method, and the particles are accumulated from small particles. This is the value of the particle diameter (D50) at which the cumulative frequency of the number of particles is 50%. Examples of such a particle size distribution measuring apparatus include Coulter LS230, LS100, LS13320 (above, manufactured by Beckman Coulter. Inc), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.), and the like. These particle size distribution measuring devices are not intended to evaluate only the primary particles of the water-insoluble polymer particles (A2), but may also be evaluated as secondary particles formed by aggregation of the primary particles. it can. Therefore, the particle size distribution measured by these particle size distribution measuring devices can be used as an indicator of the dispersion state of the water-insoluble polymer particles (A2) contained in the composition.

1.2.2.2. Toluene-insoluble content The toluene-insoluble content of the water-insoluble polymer particles (A2) is preferably 90% or more, more preferably 95% or more, and most preferably 100%, that is, not dissolved. It is presumed that the toluene insoluble content is approximately proportional to the amount of insoluble content in the electrolytic solution used in the electricity storage device. For this reason, if the toluene insoluble content is in the above range, it is possible to suppress the elution of the polymer into the electrolyte even when a power storage device is manufactured and charging / discharging is repeated over a long period of time. It can be inferred that it is favorable because the change can be suppressed.

The toluene insoluble content can be calculated as follows. 100 g of an aqueous dispersion containing water-insoluble polymer particles (A2) is weighed into a Teflon (registered trademark) petri dish and dried at 120 ° C. for 1 hour. The obtained solid is pulverized in an agate mortar to obtain a powder. 1 g of the obtained powder is immersed in 400 mL of toluene and shaken at 50 ° C. for 3 hours. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate insoluble components, and the weight (Y (g)) of the residue obtained by evaporating and removing the dissolved toluene was measured. The toluene insoluble matter is obtained by 1).
Toluene insoluble content (%) = ((1-Y) / 1) × 100 (5)

1.2.2.3. The temperature at which weight loss of 10 wt% in an air atmosphere _{(T 10)}
The temperature (T ₁₀ ) at which the water-insoluble polymer particles (A2) are reduced by 10% by weight in an air atmosphere is preferably 320 ° C. or higher, and more preferably 350 ° C. or higher. The temperature (T ₁₀ ) at which the water-insoluble polymer particles (A2) are reduced by 10% by weight in an air atmosphere is presumed to correlate with the chemical stability against oxidation at high temperature and high voltage inside the battery. Therefore, if the temperature (T ₁₀ ) at which the water-insoluble polymer particles (A2) are reduced by 10% by weight in the air atmosphere is within the above temperature range, the stability against oxidation at high temperature and high voltage inside the battery is improved. As a result, the decomposition rate of the polymer particles is less likely to occur, so that the remaining capacity ratio is improved.

The temperature (T ₁₀ ) at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in an air atmosphere can be measured as follows. 100 g of an aqueous dispersion containing water-insoluble polymer particles (A2) is weighed into a Teflon (registered trademark) petri dish and dried at 120 ° C. for 1 hour. The obtained solid is pulverized in an agate mortar to obtain a powder. The powder is subjected to thermogravimetric analysis with a thermal analyzer (for example, model “DTG-60A” manufactured by Shimadzu Corporation). As a result, the temperature at which the weight of the water-insoluble polymer particles (A2) is reduced by 10% by weight in the air atmosphere when heated at a heating rate of 20 ° C./min in an air atmosphere is defined as (T ₁₀ ).

1.2.3. Aspect of water-insoluble polymer particles (A2) When water-insoluble polymer particles (A2) are measured by differential scanning calorimetry (DSC) in accordance with JIS K7121, water-insoluble polymer particles (A2) are in the range of −50 ° C. to + 300 ° C. The endothermic peak is not observed in the conductive polymer particles (A2). This indicates that the water-insoluble polymer particles (A2) are crosslinked with a compound having two or more polymerizable unsaturated groups. Thereby, heat resistance and intensity | strength can be provided to the protective film obtained from the composition for protective films.

  The water-insoluble polymer particles (A2) are preferably particles having one or more pores therein. When the water-insoluble polymer particles (A2) have one or more pores therein, the permeability and liquid retention of the electrolyte solution of the obtained protective film are improved, and good charge / discharge characteristics are exhibited. Can do. The particle structure may be, for example, a hollow structure having pores inside the particle, or a core-shell type structure having a plurality of pores from the surface of the particle to the inside (core). Also good.

  When the water-insoluble polymer particles (A2) have one or more pores therein, the volume porosity is preferably 1% to 80%, more preferably 2% to 70%. It is particularly preferably 5% to 60%. When the volumetric porosity is in this range, it is possible to achieve both the permeability and liquid retention of the electrolytic solution of the protective film obtained and the improvement of toughness.

The volume porosity of the water-insoluble polymer particles (A2) was observed with an electron microscope (Hitachi High-Technologies Corporation, Hitachi transmission electron microscope H-7650) for the water-insoluble polymer particles (A2). The average particle diameter and particle inner diameter of 100 particles extracted randomly were measured and calculated by the following formula (6).
Volume porosity (%) = (particle inner diameter) ³ / (average particle diameter) ³ × 100 (6)

1.2.4. Method for Producing Water-Insoluble Polymer Particles (A2) As long as the water-insoluble polymer particles (A2) contained in the protective film composition according to the present embodiment have the above-described configuration, The synthesis method is not particularly limited, but specifically, it is preferable to use methods such as emulsion polymerization, seeding emulsion polymerization, suspension polymerization, seeding suspension polymerization, and solution precipitation polymerization. Among these, emulsion polymerization and seeding emulsion polymerization are preferable. Of these, seeding emulsion polymerization is particularly preferred because the particle size distribution can be easily controlled uniformly.

  When the water-insoluble polymer particles (A2) have a hollow structure, the methods described in JP-A-2002-30113, JP-A-2009-120784, and JP-A-62-127336 are used. In the case of the core-shell type, it can be manufactured according to the method described in JP-A-4-98201.

1.3. Aqueous medium The composition for a protective film according to the present embodiment further contains an aqueous medium. The aqueous medium is preferably a medium containing water. This aqueous medium can contain a small amount of non-aqueous medium in addition to water. Examples of such non-aqueous media include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these are used. can do. The content ratio of such a non-aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, based on the entire aqueous medium. Most preferably, the aqueous medium is composed only of water without containing a non-aqueous medium.

  The composition for a protective film according to the present embodiment uses an aqueous medium as a medium, and preferably contains no non-aqueous medium other than water, so that the degree of adverse effects on the environment is low, and safety for handling workers. Also gets higher.

1.4. Other components The composition for protective films which concerns on this Embodiment can contain other components, such as surfactant, as needed.

1.4.1. Surfactant The composition for a protective film according to the present embodiment can contain a surfactant from the viewpoint of improving its dispersibility and dispersion stability. Examples of the surfactant include an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a fluorosurfactant.

  Examples of the anionic surfactant include sulfates of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, sulfates of polyethylene glycol alkyl ethers, etc .; examples of the nonionic surfactants include polyethylene glycol Examples thereof include alkyl esters, alkyl ethers of polyethylene glycol, alkyl phenyl ethers of polyethylene glycol, and the like.

  As the amphoteric surfactant, for example, the anion portion is composed of a carboxylate salt, a sulfate ester salt, a sulfonate salt or a phosphate ester salt, and the cation portion is composed of an amine salt, a quaternary ammonium salt or the like. Things can be mentioned. Specific examples of such amphoteric surfactants include betaine compounds such as lauryl betaine and stearyl betaine; surface activity of amino acid types such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, octyldi (aminoethyl) glycine, and the like. An agent can be mentioned.

  Examples of the fluorosurfactant include fluorobutyl sulfonate, phosphoric acid ester having a fluoroalkyl group, carboxylate having a fluoroalkyl group, and a fluoroalkylethylene oxide adduct. Examples of such commercially available fluorosurfactants include F-top EF301, EF303, EF352 (above, manufactured by Tochem Products Co., Ltd.); Megafac F171, F172, F173 (above, manufactured by DIC Corporation); FC430, FC431 (above, manufactured by Sumitomo 3M Limited); Asahi Guard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfinol E1004, KH-10, KH-20, KH-30, KH-40 (above, manufactured by Asahi Glass Co., Ltd.); Footents 250, 251, 222F, FTX-218 (above, manufactured by Neos Co., Ltd.), and the like. As an emulsifier, the 1 type (s) or 2 or more types selected from the above can be used.

1.5. Manufacturing method of composition for protective film The composition for protective film which concerns on this Embodiment is 0.1-2000 water-soluble polymer (A1) with respect to 100 mass parts of water-insoluble polymer particles (A2). It is preferably contained in a proportion of parts by mass, more preferably contained in a proportion of 3 to 1500 parts by mass, and 5 to 1000.
It is particularly preferable that it is contained at a ratio of parts by mass. In addition, the above-mentioned content ratio forms a protective film having a function as an adhesive layer interposed between the positive electrode or the negative electrode and the separator when forming a protective film on one surface of the positive electrode or the negative electrode or the surface of the separator. The preferred range differs depending on the case.

  When the protective film composition according to the present embodiment is used for a protective film formed on one surface of a positive electrode or a negative electrode or the surface of a separator, the water-insoluble polymer particles (A2) are used in 100 parts by mass. The water-soluble polymer (A1) contained in the protective film composition is preferably contained in a proportion of 0.1 to 15 parts by mass, and contained in a proportion of 3 to 12 parts by mass. It is more preferable that it is contained at a ratio of 5 to 10 parts by mass. When the content ratio of the water-insoluble polymer particles (A2) and the water-soluble polymer (A1) contained in the protective film composition is within the above range, the toughness of the formed protective film and the permeation of lithium ions As a result, the rate of increase in resistance of the obtained electricity storage device can be further reduced.

  Moreover, when using the composition for protective films which concerns on this Embodiment as an object for protective films which have a function as an adhesive layer, it is for above-mentioned protective films with respect to 100 mass parts of water-insoluble polymer particles (A2). The water-soluble polymer (A1) contained in the composition is preferably contained in a proportion of 1 to 2000 parts by mass, more preferably 5 to 1500 parts by mass. It is especially preferable that it is contained at a ratio of ˜1000 parts by mass. The adhesion between the water-insoluble polymer particles (A2) and the water-soluble polymer (A1) contained in the composition for the protective film within the above range, the adhesion of the protective film to the electrode formed; The balance of lithium ion permeability is improved, and as a result, the rate of increase in resistance of the obtained electricity storage device can be further reduced.

  The composition for a protective film according to the present embodiment is a mixture of the water-soluble polymer (A1), the water-insoluble polymer particles (A2), and other components used as necessary. To be prepared. As means for mixing them, for example, a known mixing apparatus such as a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer can be used.

  The mixing and stirring for producing the protective film composition according to the present embodiment includes a mixer capable of stirring to such an extent that the aggregate of the water-insoluble polymer particles (A2) does not remain in the protective film composition; It is necessary to select sufficient dispersion conditions as necessary. The degree of dispersion is preferably mixed and dispersed so that aggregates larger than at least 20 μm are eliminated. The degree of dispersion can be measured with a grain gauge.

  The composition for the protective film of the electricity storage device as described above is composed of the water-insoluble polymer particles (A2), the water-insoluble polymer particles (A2) -electrodes, and the water-insoluble polymer particles (A2)- An electrode including a protective film having excellent adhesion between separators can be formed, and an electricity storage device including such an electrode has a sufficiently low resistance increase rate.

The protective film composition according to the present embodiment is characterized in that its spinnability is 60 to 85%. The spinnability is more preferably 62 to 80%. If the spinnability is less than the above range, the leveling property may be insufficient when the protective film composition is applied, and thus it may be difficult to obtain a uniform thickness of the protective film. When such a protective film having a non-uniform thickness is used, an in-plane distribution of charge / discharge reaction occurs, making it difficult to achieve stable battery performance. On the other hand, if the spinnability exceeds the above range, dripping is likely to occur when the protective film composition is applied, and it is difficult to obtain a protective film having a stable quality. Therefore, if the spinnability is within the above range, the occurrence of these problems can be suppressed, and it becomes easy to manufacture an electricity storage device that achieves both good electrical characteristics and adhesion. Note that the composition for a protective film according to the present embodiment may provide a spinnability in the above range by simply dispersing the water-insoluble polymer particles (A2) in an aqueous medium. It can be easily adjusted by further adding the polymer (A1).

“Spinning” in the present invention is a physical property measured as follows.
First, a Zaan cup (made by Dazai Equipment Co., Ltd., Zaan Bisco City Cup No. 5) having an opening with a diameter of 5.2 mm at the bottom is prepared. With this opening closed, 40 g of the protective film composition is poured into the Zahn cup. Thereafter, when the opening is opened, the protective film composition flows out from the opening. Here, when the opening is opened as T ₀ , when the spinning of the protective film composition is finished as T _A , and when the outflow of the protective film composition is finished as T _B , The “threadability” in the calligraphy can be obtained from the following formula (7).
Spinnability (%) = ((T _A −T ₀ ) / (T _B −T ₀ )) × 100 (7)

2. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the drawings. An electricity storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, a protective film disposed between the positive electrode and the negative electrode, and an electrolytic solution, and the protective film includes the above-described protective film composition. It is produced using an object. Hereinafter, first to third embodiments will be described with reference to the drawings.

2.1. First Embodiment FIG. 1 is a schematic view showing a cross section of an electricity storage device according to a first embodiment. As shown in FIG. 1, the electricity storage device 1 includes a positive electrode 10 in which a positive electrode active material layer 14 is formed on the surface of a positive electrode current collector 12 and a negative electrode 20 in which a negative electrode active material layer 24 is formed on the surface of a negative electrode current collector 22. And a protective film 30 provided between the positive electrode 10 and the negative electrode 20, and an electrolyte solution 40 that fills between the positive electrode 10 and the negative electrode 20. In the electricity storage device 1, no separator is provided between the positive electrode 10 and the negative electrode 20. This is because if the positive electrode 10 and the negative electrode 20 are completely fixed with a solid electrolyte or the like, the positive electrode 10 and the negative electrode 20 do not come into contact with each other to cause a short circuit.

  The positive electrode 10 shown in FIG. 1 is formed so that the positive electrode active material layer 14 is not provided on one surface along the longitudinal direction and the positive electrode current collector 12 is exposed. A layer 14 may be provided. Similarly, the negative electrode 20 shown in FIG. 1 is formed so that the negative electrode active material layer 22 is not provided on one surface along the longitudinal direction and the negative electrode current collector 22 is exposed, A negative electrode active material layer 24 may be provided.

  As the positive electrode current collector 12, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used according to the type of the target power storage device. For example, when forming the positive electrode of a lithium ion secondary battery, it is preferable to use aluminum among the above as the positive electrode current collector 12. In such a case, the thickness of the positive electrode current collector 12 is preferably 5 to 30 μm, and more preferably 8 to 25 μm.

  The positive electrode active material layer 14 includes one or more positive electrode active materials of a positive electrode material that can be doped / dedoped with lithium, and is configured to include a conductivity-imparting agent such as graphite as necessary. . In addition, as a binder, a thickener used for dispersion of a fluorine-containing polymer such as polyvinylidene fluoride or polyfluorinated acrylate or a positive electrode active material, or a styrene butadiene rubber (SBR) or (meth) acrylate copolymer A polymer composition containing a coalescence may be used.

The positive electrode active material is not particularly limited as long as it is a positive electrode material that can be doped / undoped with lithium and contains a sufficient amount of lithium. Specifically, a composite metal composed of lithium and a transition metal represented by the general formula LiMO ₂ (wherein M contains at least one of Co, Ni, Mn, Fe, Al, V, and Ti). It is preferable to use an oxide or an intercalation compound containing lithium. In addition, Li _a MX _b (M is one selected from transition metals, X is selected from S, Se, PO ₄ and 0 <a, b is an integer) can also be used. In particular, when a lithium composite oxide represented by Li _x M _I O ₂ or Li _y M _{II 2} O ₄ is used as the positive electrode active material, a high voltage can be generated and the energy density can be increased, which is preferable. . In these composition formulas, M _I represents one or more transition metal elements, preferably at least one of cobalt (Co) and nickel (Ni). M _II represents one or more transition metal elements, and is preferably manganese (Mn). The values of x and y vary depending on the charge / discharge state of the battery, and are usually in the range of 0.05 to 1.10. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiNi _z Co _1-z O ₂ (where 0 <z <1), LiMn ₂ O _{4, and the} like.

  As the negative electrode current collector 22, for example, a metal foil, an etching metal foil, an expanded metal, or the like can be used. Specific examples of these materials include metals such as aluminum, copper, nickel, tantalum, stainless steel, and titanium, and can be appropriately selected and used according to the type of the target power storage device. Of the above, copper is preferably used as the negative electrode current collector 22. In such a case, the thickness of the current collector is preferably 5 to 30 μm, and more preferably 8 to 25 μm.

  The negative electrode active material layer 24 is configured to include any one or two or more negative electrode materials that can be doped / undoped with lithium as a negative electrode active material, and if necessary, a binder similar to the positive electrode It is comprised including.

  As the negative electrode active material, for example, a carbon material, a crystalline or amorphous metal oxide, or the like can be suitably used. Examples of carbon materials include non-graphitizable carbon materials such as coke and glassy carbon, and graphites of highly crystalline carbon materials having a developed crystal structure. Specifically, pyrolytic carbons, cokes ( Pitch coke, needle coke, petroleum coke, etc.), graphite, glassy carbons, polymer compound fired bodies (phenol resins, furan resins, etc. fired and carbonized at an appropriate temperature), carbon fibers, activated carbon, etc. Can be mentioned. As crystalline or amorphous metal oxides, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn) ), Lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or platinum (Pt) ) As a constituent element. In particular, those containing silicon (Si) or tin (Sn) as constituent elements can be suitably used.

Note that the above-described active material layer is preferably subjected to press working. Examples of means for performing the press working include a roll press machine, a high-pressure super press machine, a soft calendar, and a 1-ton press machine. The conditions for the press working are appropriately set according to the type of processing machine used and the desired thickness and density of the active material layer. In the case of a lithium ion secondary battery positive electrode, the thickness is preferably 40 to 100 μm and the density is preferably 2.0 to 5.0 g / cm ³ . In the case of a lithium ion secondary battery negative electrode, the thickness is preferably 40 to 100 μm and the density is preferably 1.3 to 1.9 g / cm ³ .

The protective film 30 is disposed between the positive electrode 10 and the negative electrode 20. 1, the protective film 30 is disposed between the positive electrode 10 and the negative electrode 20 so as to be in contact with the positive electrode active material layer 14, but is disposed so as to be in contact with the negative electrode active material layer 24. May be. The protective film 30 may be disposed as a self-supporting film between the positive electrode 10 and the negative electrode 20 without being in contact with the positive electrode 10 or the negative electrode 20. Thereby, even if it is a case where dendrites precipitate by repeating charging / discharging, since it is guarded by the protective film 30, a short circuit does not occur. Therefore, the function as an electricity storage device can be maintained.

  The protective film 30 can be formed, for example, by applying the above-described protective film composition on the surface of the positive electrode 10 (or the negative electrode 20) and drying it. For example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method or the like is applied as a method for applying the protective film composition to the surface of the positive electrode 10 (or the negative electrode 20). Can do. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.

  Although the film thickness of the protective film 30 is not specifically limited, It is preferable that it is the range of 0.5-4 micrometers, and it is more preferable that it is the range of 0.5-3 micrometers. When the thickness of the protective film 30 is within the above range, the permeability of the electrolytic solution into the electrode and the liquid retaining property are improved, and an increase in the internal resistance of the electrode can be suppressed.

  The electrolytic solution 40 is appropriately selected and used according to the type of the target power storage device. As the electrolytic solution 40, a solution in which an appropriate electrolyte is dissolved in a solvent is used.

When manufacturing a lithium ion secondary battery, a lithium compound is used as an electrolyte. Specifically, for example _{LiClO 4, LiBF 4, LiI,} LiPF 6, LiCF 3 SO 3, 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) can be cited ₂ N or the like. The electrolyte concentration in this case is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

  The type and concentration of the electrolyte in the case of manufacturing a lithium ion capacitor are the same as in the case of the lithium ion secondary battery.

  In any of the above cases, examples of the solvent used in 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; trimethoxy Silane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, ether such as 2-methyltetrahydrofuran; Sulfoxide such as dimethyl sulfoxide; 1,3-dioxolane, 4-methyl-1,3-dioxolane, etc. Oxolane derivatives; nitrogen-containing compounds such as acetonitrile and nitromethane; esters such as methyl formate, methyl acetate, butyl acetate, methyl propionate, ethyl propionate, and phosphate triester Glyme compounds such as diglyme, triglyme and tetraglyme; ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone; sulfone compounds such as sulfolane; oxazolidinone derivatives such as 2-methyl-2-oxazolidinone; 1,3-propane sultone; Examples include sultone compounds such as 1,4-butane sultone, 2,4-butane sultone, and 1,8-naphtha sultone.

2.2. Second Embodiment FIG. 2 is a schematic view showing a cross section of an electricity storage device according to a second embodiment. As shown in FIG. 2, the electricity storage device 2 includes a positive electrode 110 in which a positive electrode active material layer 114 is formed on the surface of a positive electrode current collector 112 and a negative electrode 120 in which a negative electrode active material layer 124 is formed on the surface of a negative electrode current collector 122. A protective film 130 provided between the positive electrode 110 and the negative electrode 120, an electrolyte solution 140 that fills between the positive electrode 110 and the negative electrode 120, and a separator 150 provided between the positive electrode 110 and the negative electrode 120. It is provided.

  The electricity storage device 2 is different from the electricity storage device 1 described above in that the protective film 130 is disposed so as to be sandwiched between the positive electrode 110 and the separator 150. 2, the protective film 130 is sandwiched between the positive electrode 110 and the separator 150, but the protective film 130 is sandwiched between the negative electrode 120 and the separator 150. It may be arranged so that. By adopting such a configuration, even when dendrite is deposited by repeated charge and discharge, the protective film 130 guards and no short circuit occurs. Therefore, the function as an electricity storage device can be maintained.

  The protective film 130 can be formed by, for example, applying a composition for forming a protective film, which will be described later, to the surface of the separator 150, bonding the positive electrode 110 (or the negative electrode 120), and then drying. As a method for applying the protective film forming composition to the surface of the separator 150, for example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, or the like can be applied. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.

  Any separator 150 may be used as long as it is electrically stable, chemically stable with respect to the positive electrode active material, the negative electrode active material, or the solvent, and has no electrical conductivity. . For example, a polymer nonwoven fabric, a porous film, glass or ceramic fibers in a paper shape can be used, and a plurality of these may be laminated. In particular, a porous polyolefin film is preferably used, and a composite of this with a heat-resistant material made of polyimide, glass, ceramic fibers or the like may be used.

  The other configuration of the power storage device 2 according to the second embodiment is the same as that of the power storage device 1 according to the first embodiment described with reference to FIG.

2.3. Third Embodiment FIG. 3 is a schematic view showing a cross section of an electricity storage device according to a third embodiment. As shown in FIG. 3, the electricity storage device 3 includes a positive electrode 210 in which a positive electrode active material layer 214 is formed on the surface of a positive electrode current collector 212, and a negative electrode 220 in which a negative electrode active material layer 224 is formed on the surface of a negative electrode current collector 222. An electrolyte 240 filling between the positive electrode 210 and the negative electrode 220, a separator 250 provided between the positive electrode 210 and the negative electrode 220, and a protective film 230 formed so as to cover the surface of the separator 250. It is provided.

  The electricity storage device 3 is different from the electricity storage device 1 and the electricity storage device 2 described above in that the protective film 230 is formed so as to cover the surface of the separator 250. By adopting such a configuration, even when dendrites are deposited by repeated charge and discharge, the protective film 230 guards the short circuit. Therefore, the function as an electricity storage device can be maintained.

The protective film 230 can be formed, for example, by applying the above-described protective film composition to the surface of the separator 250 and drying it. Examples of the method for applying the protective film composition to the surface of the separator 250 include a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, and a die coating method. The drying treatment of the coating film is preferably performed in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably for a processing time of 1 to 120 minutes, more preferably 5 to 60 minutes.

  Regarding other configurations of the power storage device 3 according to the third embodiment, the power storage device 1 according to the first embodiment described with reference to FIG. 1 and the power storage according to the second embodiment described with reference to FIG. Since it is the same as the device 2, the description thereof is omitted.

2.4. Manufacturing Method As a manufacturing method of the above-described power storage device, for example, two electrodes (two of a positive electrode and a negative electrode or two of a capacitor electrode) are overlapped via a separator as necessary, and this is used as a battery. Examples of the method include a method of winding, folding, etc. in a battery container according to the shape, injecting an electrolyte into the battery container, and sealing. The shape of the battery can be an appropriate shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.

2.5. Applications The power storage device as described above is suitable as a secondary battery or a capacitor mounted on an automobile such as an electric vehicle, a hybrid car, or a truck, and a secondary battery used for an AV device, an OA device, a communication device, or the like. It is also suitable as a capacitor.

3. EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. “Part” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.

3.1. Synthesis of water-soluble polymer (A1) 3.1.1. Synthesis example 1
In a four-necked separable flask equipped with a stirrer, thermometer, cooler, nitrogen inlet tube, and dropping funnel, ion-exchanged water (115 parts by mass), polyoxyethylene dodecyl ether sulfonate ammonium salt (1.5 parts by mass) ). While stirring at an internal temperature of 68 ° C., nitrogen was gently flowed to completely replace the inside of the reaction vessel with nitrogen.

  Next, sulfonate (1.5 parts by mass) of polyoxyethylene dodecyl ether was dissolved in ion-exchanged water (92 parts by mass). As a monomer component of the polymer, a mixture of ethyl acrylate (65 parts by mass) and methacrylic acid (35 parts by mass) was added to prepare a pre-emulsion. 5% of the pre-emulsion containing the monomer component was put into a reaction vessel and stirred, and then sodium bisulfite (0.017 part by mass) was added. Separately, ammonium persulfate (0.23 parts by mass) was dissolved in ion-exchanged water (23 parts by mass) to prepare a polymerization initiator aqueous solution. 5% of this polymerization initiator aqueous solution was put into the reaction vessel, and initial polymerization was performed for 20 minutes. The temperature in the reaction vessel was kept at 72 ° C., and the remaining pre-emulsion and initiator aqueous solution were uniformly added dropwise over 2 hours. After completion of the dropping, the dropping tank was washed with ion-exchanged water (8 parts by mass) and then charged into the reaction vessel. The internal temperature was kept at 72 ° C. and stirring was continued for 1 hour, followed by cooling to complete the reaction to obtain an emulsion having a solid content of 30%.

  5% lithium hydroxide / monohydrate aqueous solution (10.2 parts by mass) and ion-exchanged water (133.2 parts by mass) were added to the emulsion (10 parts by mass / solid content 3 parts by mass) and stirred. Further, by concentration under reduced pressure, an aqueous solution S1 containing 40% of the water-soluble polymer (A1) was obtained. The weight average molecular weight of the water-soluble polymer (A1) thus obtained was determined using “HLC-8010” gel permeation chromatography manufactured by Tosoh Corporation. (Mw) = 1,000,000.

3.1.2. Synthesis example 2
As the monomer component of the polymer, instead of ethyl acrylate (65 parts by mass) and methacrylic acid (35 parts by mass), ethyl acrylate (55 parts by mass), methacrylic acid (40 parts by mass), and ethylene oxide of octadecyl alcohol An emulsion was obtained in the same manner as in Synthesis Example 1 except that 30 mol adduct methacrylic acid ester (5 parts by mass) was used. 5% lithium hydroxide / monohydrate aqueous solution (11.7 parts by mass) and ion-exchanged water (132.3 parts by mass) were added to the obtained emulsion (10 parts by mass / solid content 3 parts by mass) and stirred. Further, by concentration under reduced pressure, an aqueous solution S2 containing 40% of the water-soluble polymer (A1) was obtained. The weight average molecular weight of the water-soluble polymer (A1) thus obtained was determined using “HLC-8010” gel permeation chromatography manufactured by Tosoh Corporation. (Mw) = 720,000.

3.1.3. Synthesis example 3
Instead of the sulfonic acid ammonium salt of polyoxyethylene dodecyl ether used as an emulsifier, a sulfonic acid ammonium salt of polyoxyethylene-1- (allyloxymethyl) alkyl ether was used in the same manner as in Synthesis Example 1, An emulsion was obtained. 5% lithium hydroxide / monohydrate aqueous solution (10.2 parts by mass) and ion-exchanged water (133.2 parts by mass) were added to the emulsion (10 parts by mass / solid content 3 parts by mass) and stirred. Further, by concentration under reduced pressure, an aqueous solution S3 containing 40% of the water-soluble polymer (A1) was obtained. The weight average molecular weight of the water-soluble polymer (A1) thus obtained was determined using “HLC-8010” gel permeation chromatography manufactured by Tosoh Corporation. (Mw) = 910,000.

3.2. Synthesis of water-insoluble polymer particles (A2) 3.2.1. Synthesis example 4
100 parts by mass of styrene, 10 parts by mass of t-dodecyl mercaptan, 0.8 parts by mass of sodium dodecylbenzenesulfonate, 0.4 parts by mass of potassium persulfate, and 200 parts by mass of water were placed in a 2 L flask and stirred. Then, the temperature was raised to 80 ° C. in a nitrogen gas atmosphere, and polymerization was performed for 6 hours. As a result, an aqueous dispersion containing polymer particles having a polymerization yield of 98% and an average particle size of 170 nm and a standard deviation of the particle size of 0.02 μm was obtained. The polymer particles had a toluene dissolved content of 98%, and the molecular weight measured by gel permeation chromatography was weight average molecular weight (Mw) = 5,000 and number average molecular weight (Mn) = 3,100.

  After sufficiently substituting the inside of the reaction vessel with nitrogen, 5 parts by mass of polymer particles (in terms of solid content) and 1.0 part by mass of sodium lauryl sulfate were obtained. Then, 0.5 parts by mass of potassium persulfate, 400 parts by mass of water, 45 parts by mass of styrene, and 50 parts by mass of divinylbenzene were mixed and stirred at 30 ° C. for 10 minutes to allow the polymer particles to absorb the monomer. Then, it heated up at 70 degreeC and reacted for 3 hours. Then, after cooling, the reaction was stopped, the pH was adjusted to 7 with a 2.5N aqueous sodium hydroxide solution, and an aqueous dispersion L1 containing 20% of water-insoluble polymer particles (A2) was obtained.

  The particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000”, manufactured by Otsuka Electronics Co., Ltd.) using the dynamic light scattering method as a measurement principle, and water-insoluble polymer particles (A2) are obtained from the particle size distribution. The average particle size (Da2) was determined to be 380 nm.

  100 g of the water dispersion of the water-insoluble polymer particles (A2) was weighed in a petri dish and dried at 120 ° C. for 1 hour. The obtained solid was pulverized in an agate mortar to obtain a powder.

1 g of the obtained powder (powder composed of water-insoluble polymer particles (A2)) was immersed in 400 mL of toluene and shaken at 50 ° C. for 3 hours. Next, the toluene phase was filtered through a 300-mesh wire mesh to separate insoluble components, and the weight of the residue (Y (g)) obtained by evaporating and removing the dissolved toluene was measured from the following formula ( When the toluene insoluble content was determined by 5), the toluene insoluble content of the water-insoluble polymer particles (A2) was 99%.
Toluene insoluble content (%) = ((1-Y) / 1) × 100 (5)

  When the obtained powder (powder composed of water-insoluble polymer particles (A2)) was measured by a differential scanning calorimeter (manufactured by NETZSCH, DSC204F1 Phoenix), the melting temperature Tm and the glass transition temperature Tg were observed. Was not.

Further, the obtained powder (powder composed of water-insoluble polymer particles (A2)) was subjected to thermogravimetric analysis with a thermal analyzer (manufactured by Shimadzu Corporation, model “DTG-60A”). . A TGA chart is shown in FIG. The temperature at which the water-insoluble polymer particles (A2) lose 10% by weight when heated at a heating rate of 20 ° C./min in an air atmosphere (hereinafter, this reduction start temperature is expressed as “T ₁₀ ”). It was 379 ° C.

3.2.2. Synthesis Examples 5-14
In Synthesis Example 4 above, an aqueous dispersion containing water-insoluble polymer particles (A2) having the composition shown in Table 1 was prepared except that the composition and the amount of emulsifier were appropriately changed, and the solid content concentration of the aqueous dispersion was prepared. According to the above, water was removed under reduced pressure or added to obtain water dispersions L2 to L11 having a solid content concentration of 20%. About the obtained water-insoluble polymer particle (A2), as a result of the toluene insoluble content measurement performed in the same manner as in Synthesis Example 4, the results of DSC measurement (glass transition temperature Tg, melting temperature Tm) and TG measurement The results (weight loss starting temperature T ₁₀ ) are also shown in Table 1.

3.2.3. Synthesis Example 15
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 109.5 parts by mass of water, 0.2 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 part by mass of octyl glycol as a molecular weight regulator and polymerization As an initiator, 0.5 part by mass of sodium persulfate was added. Next, 20% of a monomer mixture obtained by mixing 20 parts by mass of methacrylic acid and 80 parts by mass of methyl methacrylate was charged into a pressure resistant reactor. Thereafter, the temperature is raised to 75 ° C. while stirring, and a polymerization reaction is carried out for 1 hour after reaching 75 ° C., and then the remaining monomer mixture is continuously put into a pressure-resistant reaction vessel over 2 hours while maintaining the temperature at 75 ° C. Added. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles (A2a) having a solid content of 40% and an average particle diameter of 200 nm.

  186 parts by mass of water is put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 10 parts by mass of the polymer particles (A2a) having a particle size of 200 nm are solidified. Sodium persulfate 0.5 part by mass was added as an agent, and the temperature was raised to 80 ° C. with stirring. Next, a monomer mixture obtained by mixing 30 parts by weight of methacrylic acid, 69.5 parts by weight of methyl methacrylate and 0.5 parts by weight of divinylbenzene was kept in a pressure-resistant reaction vessel at a temperature of 80 ° C. and continuously 3 with stirring. I put it in over time. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles (A2b) having a solid content of 31% and an average particle diameter of 400 nm.

350 parts by mass of water is put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 15 parts by mass of the polymer particles (A2b) having a particle diameter of 400 nm as described above are started. As an agent, 0.4 part by mass of sodium persulfate was added, and the temperature was raised to 80 ° C. while stirring. Next, a monomer mixture obtained by mixing 50 parts by mass of styrene, 25 parts by mass of divinylbenzene, and 25 parts by mass of ethylvinylbenzene was continuously added to the pressure resistant reactor over 4 hours while stirring. While the monomer mixture was charged, the temperature of the pressure resistant reactor was maintained at 80 ° C. After the completion of the continuous addition of the monomer mixture, 5 parts by mass of 25% ammonium water was placed in a pressure-resistant reaction vessel maintained at 80 ° C. and aged for 3 hours to obtain 2 water-insoluble polymer particles (A2).
An aqueous dispersion L12 containing 0% was obtained.

As a result of measuring the insoluble content of toluene in the same manner as in Synthesis Example 4 with respect to the obtained water-insoluble polymer particles (A2), the results of DSC measurement (glass transition temperature Tg, melting temperature Tm) and the results of TG measurement (Weight reduction start temperature T ₁₀ ) is also shown in Table 1.

  In addition, using the obtained water dispersion L12 as a sample, the particle size distribution is measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle, The average particle diameter (Da2) of the water-insoluble polymer particles (A2) was determined from the particle size distribution and found to be 1000 nm.

  In order to analyze the structure of the particles in more detail, an aqueous dispersion containing 20% water-insoluble polymer particles (A2) containing 20% is dried and solidified, and adjusted to a pH 10 that is 20 times the solid content. The water-soluble component was completely removed by washing 3 times with the aqueous ammonia and further 4 times with ion-exchanged water, and dried and solidified again to obtain a powder of water-insoluble polymer particles (A2). When this powder was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation), a hollow polymer having an average particle diameter of 1,000 particles and a particle inner diameter of 600 nm was observed. The particles had a volume porosity of 22%.

3.2.4. Synthesis Example 16
In the synthesis example 15, the polymer particles (A2b) were replaced with 15 parts by mass of solids, 50 parts by mass of styrene, 25 parts by mass of divinylbenzene, and 25 parts by mass of ethylvinylbenzene. Water containing 20% water-insoluble polymer particles (A2) in the same manner as in Synthesis Example 15 except that 50 parts by mass, 77 parts by mass of styrene, 22 parts by mass of divinylbenzene, and 1 part by mass of acrylic acid were used. Dispersion L13 was obtained.

As a result of measuring the insoluble content of toluene in the same manner as in Synthesis Example 4 with respect to the obtained water-insoluble polymer particles (A2), the results of DSC measurement (glass transition temperature Tg, melting temperature Tm) and the results of TG measurement (Weight reduction start temperature T ₁₀ ) is also shown in Table 1.

  In addition, using the obtained water dispersion L13 as a sample, the particle size distribution was measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle. When the average particle diameter (Da2) of the water-insoluble polymer particles (A2) was determined from the particle size distribution, it was 810 nm.

  Further, in the same manner as in Synthesis Example 15, the detailed particle structure of the obtained water-insoluble polymer particles (A2) was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation). As a result, 100 observed particles were hollow polymer particles having an average particle diameter of 810 nm and a particle inner diameter of 700 nm, and the volume porosity was 65%.

3.2.5. Synthesis Example 17
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 99 parts by mass of styrene, 1 part by mass of methacrylic acid and 8 parts by mass of t-dodecyl mercaptan, 0.4 parts by mass of sodium lauryl sulfate in 200 parts by mass of water And an aqueous solution in which 1.0 part by mass of potassium persulfate was dissolved and polymerized at 70 ° C. for 8 hours with stirring to obtain an aqueous dispersion of polymer particles having an average particle diameter of 250 nm.

Next, 10 parts by mass of the polymer particles, 0.1 part by mass of polyoxyethylene nonylphenyl ether, 0.3 part by mass of sodium lauryl sulfate and 0.5 part by mass of potassium persulfate are added to 900 parts by mass of water. Distributed. A mixture of 60 parts by weight of methyl methacrylate, 30 parts by weight of divinylbenzene, 10 parts by weight of styrene and 20 parts by weight of toluene was added thereto and stirred at 30 ° C. for 1 hour, followed by stirring at 70 ° C. for 5 hours and cooling. When the steam strip treatment was performed, an aqueous dispersion L14 containing hollow water-insoluble polymer particles (A2) was obtained.

  The obtained water-insoluble polymer particles (A2) were measured for toluene insolubles in the same manner as in Synthesis Example 4, DSC measurement results (glass transition temperature Tg, melting temperature Tm), and TG measurement results (weight loss). The starting temperature T10) is also shown in Table 1.

  In addition, using the obtained water dispersion L14 as a sample, the particle size distribution was measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle, When the average particle diameter (Da2) of the water-insoluble polymer particles (A2) was determined from the particle size distribution, it was 490 nm.

  Further, in the same manner as in Synthesis Example 15, the detailed particle structure of the obtained water-insoluble polymer particles (A2) was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation). As a result, 100 observed particles were hollow polymer particles having an average particle diameter of 490 nm and a particle inner diameter of 350 nm, and the volume porosity was 36%.

3.2.6. Synthesis Example 18
In Synthesis Example 17, instead of 60 parts by mass of methyl methacrylate, 30 parts by mass of divinylbenzene, 10 parts by mass of styrene and 20 parts by mass of toluene, 60 parts by mass of methyl methacrylate, 40 parts by mass of allyl methacrylate and 15 parts by mass of toluene A water dispersion L15 containing water-insoluble polymer particles (A2) was obtained in the same manner as in Synthesis Example 17 except that was used.

The obtained water-insoluble polymer particles (A2) were measured for toluene insolubles in the same manner as in Synthesis Example 4, DSC measurement results (glass transition temperature Tg, melting temperature Tm), and TG measurement results (weight loss). The starting temperature T ₁₀ ) is also shown in Table 1.

  In addition, using the obtained water dispersion L15 as a sample, the particle size distribution was measured using a particle size distribution measuring apparatus (model “FPAR-1000” manufactured by Otsuka Electronics Co., Ltd.) having a dynamic light scattering method as a measurement principle. When the average particle diameter (Da2) of the water-insoluble polymer particles (A2) was determined from the particle size distribution, it was 420 nm.

  Further, in the same manner as in Synthesis Example 15, the detailed particle structure of the obtained water-insoluble polymer particles (A2) was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation). As a result, the 100 observed particles were hollow polymer particles having an average particle diameter of 420 nm and a particle inner diameter of 220 nm, and the volume porosity was 14%.

3.2.7. Synthesis Example 19
In a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 109.5 parts by mass of water, 0.2 part by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 part by mass of octyl glycol as a molecular weight regulator and polymerization As an initiator, 0.5 part by mass of sodium persulfate was added. Next, 20% of a monomer mixture obtained by mixing 15 parts by mass of methacrylic acid and 85 parts by mass of methyl methacrylate was charged into a pressure resistant reactor. Thereafter, the temperature is raised to 75 ° C. while stirring, and a polymerization reaction is carried out for 1 hour after reaching 75 ° C., and then the remaining monomer mixture is continuously put into a pressure-resistant reaction vessel over 2 hours while maintaining the temperature at 75 ° C. Added. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles having a solid content of 40% and an average particle size of 200 nm.

Into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, 186 parts by mass of water is charged, and 10 parts by mass of the polymer particles having a particle diameter of 200 nm as described above are added as a polymerization initiator. Sodium sulphate (0.5 parts by mass) was added and the temperature was raised to 80 ° C. with stirring. Next, a monomer mixture obtained by mixing 30 parts by weight of methacrylic acid, 69.5 parts by weight of methyl methacrylate and 0.5 parts by weight of divinylbenzene was kept in a pressure-resistant reaction vessel at a temperature of 80 ° C. and continuously 3 with stirring. I put it in over time. Thereafter, aging was further performed for 2 hours to obtain an aqueous dispersion of polymer particles having a solid content of 31% and an average particle diameter of 400 nm.

  350 parts by mass of water was put into a pressure-resistant reaction vessel having a capacity of 2 liters equipped with a stirrer and a temperature controller, and 20 parts by mass of the polymer particles having a particle diameter of 400 nm as a polymerization initiator were added thereto as a polymerization initiator. 0.4 parts by mass of sodium sulfate was added, and the temperature was raised to 80 ° C. while stirring. Next, a monomer mixture obtained by mixing 90 parts by mass of styrene, 9 parts by mass of divinylbenzene, and 1 part by mass of acrylic acid was continuously added to the pressure resistant reactor over 4 hours while stirring. While the monomer mixture was charged, the temperature of the pressure resistant reactor was maintained at 80 ° C. After the completion of continuous addition of the monomer mixture, 5 parts by mass of 25% ammonium water is placed in a pressure-resistant reaction vessel maintained at 80 ° C., and aged for 3 hours to contain 20% of water-insoluble polymer particles (A2). Dispersion L16 was obtained.

The obtained water-insoluble polymer particles (A2) were measured for toluene insolubles in the same manner as in Synthesis Example 4, DSC measurement results (glass transition temperature Tg, melting temperature Tm), and TG measurement results (weight loss). The starting temperature T ₁₀ ) is also shown in Table 1.

  In addition, using the obtained water dispersion L16 as a sample, the particle size distribution is measured using a particle size distribution measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., “FPAR-1000”) based on the dynamic light scattering method, The average particle diameter (Da2) of the water-insoluble polymer particles (A2) was determined from the particle size distribution and found to be 1000 nm.

  Further, in the same manner as in Synthesis Example 15, the detailed particle structure of the obtained water-insoluble polymer particles (A2) was observed using a Hitachi transmission electron microscope H-7650 (manufactured by Hitachi High-Technologies Corporation). As a result, 100 observed particles were hollow polymer particles having an average particle diameter of 1000 nm and a particle inner diameter of 800 nm, and the volume porosity was 51%.

3.2.8. List of water-insoluble polymer particles (A2) The monomer composition of the water-insoluble polymer particles (A2) obtained above and the measurement results of the respective physical property values are summarized in Table 1 below.

Abbreviations of each component in Table 1 mean the following compounds, respectively.
<Compound having two or more polymerizable unsaturated groups>
AMA: Allyl methacrylate EDMA: Ethylene glycol dimethacrylate DVB: Divinylbenzene <Unsaturated carboxylic acid ester>
・ MMA: Methyl methacrylate <Aromatic vinyl compound>
-ST: Styrene-EVB: Ethyl vinyl benzene <Unsaturated carboxylic acid>
AA: acrylic acid <nitrile compound>
-AN: Acrylonitrile In addition, the notation of "-" in Table 1 shows that the applicable component was not used.

3.3. Example 1
3.3.1. Preparation of composition for protective film The aqueous solution S1 and the aqueous dispersion L1 are mixed so that the water-soluble polymer (A1) is 10 parts by mass with respect to 100 parts by mass of the water-insoluble polymer particles (A2). Further, ion exchange water is added so that the spinnability becomes 70%. K. Mixing and dispersing treatment was carried out using Fillmix (R) 56-50 (manufactured by PRIMIX Co., Ltd.) to prepare a protective film composition.

3.3.2. Measurement of Spinnability of Protective Film Composition The spinnability of the obtained protective film composition was measured as follows.
First, a Zaan cup (made by Dazai Equipment Co., Ltd., Zaan Biscocity Cup No. 5) having an opening with a diameter of 5.2 mm at the bottom of the container was prepared. With the opening of the Zahn cup closed, 40 g of the protective film composition prepared above was poured. When the opening was opened, the protective film composition flowed out. At this time, the moment of opening the opening time is T _0, a time continued to flow out so as to draw the yarn in the protective film composition flows out was determined visually, the time was T _A. Moreover, to continue the measurement from no longer attracted yarn was measured time T _B to the protective film composition can not flow out. The measured values T ₀ , T _A and T _B were substituted into the following formula (7) to determine the spinnability.
Spinnability (%) = ((T _A −T ₀ ) / (T _B −T ₀ )) × 100 (7)
Table 2 also shows the measurement results of the spinnability.

3.3.3. Production of positive electrode <Preparation of positive electrode active material>
Commercially available lithium iron phosphate (LiFePO ₄ ) was pulverized in an agate mortar and classified using a sieve to prepare active material particles having a particle diameter (D50 value) of 0.5 μm.

<Preparation of slurry for positive electrode>
A biaxial planetary mixer (trade name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation), 4 parts by mass of polyvinylidene fluoride (PVDF) (in terms of solid content), 100 parts by mass of the above active material particles, and acetylene black 5 Part by mass and 68 parts by mass of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 1 hour. Further, 32 parts by mass of NMP was added and stirred for 1 hour to obtain a paste. The resulting paste was stirred at 200 rpm for 2 minutes, 1,800 rpm for 5 minutes, and further under vacuum (5.0 ×) using a stirring defoaming machine (trade name “Awatori Nertaro” manufactured by Shinky Co., Ltd.). The slurry for positive electrode was prepared by stirring and mixing at 1,800 rpm for 1.5 minutes at 10 ³ Pa).

<Preparation of electrode for positive electrode>
The positive electrode slurry was uniformly applied to the surface of a current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 100 μm, and dried at 120 ° C. for 20 minutes. Then, the positive electrode with the positive electrode active material layer formed on the surface of the current collector was obtained by pressing with a roll press so that the density of the film (active material layer) was 2.0 g / cm ³ .

3.3.4. Production of protective film (production of positive electrode with protective film)
After applying the protective film composition obtained above on the surface of the positive electrode active material layer of the positive electrode obtained above using a die coating method, it is dried at 120 ° C. for 5 minutes to protect the surface of the positive electrode active material layer. A film was formed. The protective film had a thickness of 3 μm.

3.3.5. Production of negative electrode <Preparation of slurry for negative electrode>
A biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Corporation), 4 parts by mass of polyvinylidene fluoride (PVDF) (in terms of solid content), and 100 parts by mass of graphite as a negative electrode active material (solid) Minute conversion), 80 parts by mass of N-methylpyrrolidone (NMP) was added, and the mixture was stirred at 60 rpm for 1 hour. Then, after adding 20 parts by mass of NMP, using a stirring defoaming machine (product name “Awatori Netaro” manufactured by Shinky Co., Ltd.) for 2 minutes at 200 rpm, then for 5 minutes at 1,800 rpm, further vacuum Below, the slurry for negative electrodes was prepared by stirring and mixing for 1.5 minutes at 1,800 rpm.

<Preparation of electrode for negative electrode>
The negative electrode slurry was uniformly applied to the surface of a current collector made of copper foil by a doctor blade method so that the film thickness after drying was 150 μm, and dried at 120 ° C. for 20 minutes. Then, the negative electrode in which the negative electrode active material layer was formed on the surface of the current collector was obtained by pressing using a roll press machine so that the film density was 1.5 g / cm ³ .

3.3.6. Assembly of Lithium Ion Battery Cell A bipolar coin cell (Hosen Co., Ltd.) obtained by punching and molding the negative electrode produced above to a diameter of 16.16 mm in an Ar-substituted glove box with a dew point of −80 ° C. or lower. And product name “HS flat cell”). Next, a separator made of a polypropylene porous membrane punched into a diameter of 24 mm (trade name “Celguard # 2400” manufactured by Celgard Co., Ltd.) was placed, and after injecting 500 μL of an electrolyte solution so that air did not enter, The positive electrode with a protective film manufactured in the above is punched and molded to a diameter of 15.95 mm and placed so that the separator and the protective film formed on the positive electrode face each other, and the outer body of the bipolar coin cell is closed with a screw. The lithium ion battery cell (electric storage device) was assembled by sealing. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

3.3.7. Evaluation of Charging / Discharging Rate Characteristics The electricity storage device manufactured above was charged at a constant current (0.2 C) at room temperature, and when the voltage reached 4.2 V, the constant voltage (4.2 V) was continued. The charging was continued at, and when the current value reached 0.01 C, the charging was completed (cut off), and the charging capacity at 0.2 C was measured. Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 0.2 C was measured.

Next, charging is started at a constant current (3C) for the same cell, and when the voltage reaches 4.2V, charging is continued at a constant voltage (4.2V). The charging capacity at 3C was measured with the time point of becoming the completion of charging (cut-off). Next, discharge was started at a constant current (3C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 3C was measured.

  Using the measured values above, calculate the charge rate (%) by calculating the ratio (percent%) of the charge capacity at 3C to the charge capacity at 0.2C at 3C versus the discharge capacity at 0.2C. The discharge rate (%) was calculated by calculating the discharge capacity ratio (percentage%). In Tables 2 to 3, when both the charge rate and the discharge rate are 80% or more, it is judged that the charge / discharge rate characteristics are good, and “◯”. When either or both of the charge rate and the discharge rate were less than 80%, the charge / discharge rate characteristics were judged to be poor and indicated as “x”. The results are also shown in Table 2.

  In the measurement conditions, “1C” indicates a current value at which discharge is completed in one hour after constant current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and 10 C is a current value at which discharge is completed over 0.1 hours.

3.4. Examples 2-10, Comparative Examples 1-5
A composition for a protective film was prepared in the same manner as in Example 1 except that the proportions shown in Table 2 were used. Moreover, the electrical storage device was manufactured similarly to Example 1 using the obtained composition for protective films, and was evaluated. The evaluation results are also shown in Table 2. Evaluation of content ratio, spinnability, charge / discharge rate characteristics of water-soluble polymer (A1) and water-insoluble polymer particles (A2) in the protective film compositions according to Examples 1 to 10 and Comparative Examples 1 to 5 The results are summarized in Table 2 below.

  In addition, the notation of “-” in Table 2 indicates that the corresponding component was not used.

3.5. Example 11
3.5.1. Production of Positive Electrode and Negative Electrode A positive electrode and a negative electrode were produced in the same manner as in Example 1.

3.5.2. Production of protective film (production of separator with protective film)
A protective film composition obtained in the above “3.3.1. Preparation of protective film composition” on both sides of a separator made of a polypropylene porous film (manufactured by Celgard, trade name “Celguard # 2400”). Was applied using a dip coating method and then dried at 80 ° C. for 10 minutes to form protective films on both sides of the separator. The thickness of the protective film obtained was 2 μm on one side (total of 4 μm on both the front and back sides).

3.5.3. Assembly of Lithium Ion Battery Cell A bipolar coin cell (Hosen Co., Ltd.) obtained by punching and molding the negative electrode produced above to a diameter of 16.16 mm in an Ar-substituted glove box with a dew point of −80 ° C. or lower. And product name “HS flat cell”). Next, the separator with the protective film prepared in “3.5.2. Preparation of protective film (manufacture of separator with protective film)” punched to a diameter of 24 mm is placed, and electrolysis is performed so that air does not enter. After injecting 500 μL of the liquid, the positive electrode manufactured above was punched and molded to a diameter of 15.95 mm, and the outer body of the two-pole coin cell was closed with a screw and sealed, so that a lithium ion battery cell (Electric storage device) was assembled. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

3.5.4. Adhesiveness between protective film and electrode From the negative electrode, separator with protective film, and positive electrode produced above, test pieces each having a width of 2 cm and a length of 5 cm were cut out, and the negative electrode active material layer and the positive electrode active material layer were each provided with a protective film. A negative electrode / a separator with a protective film / a positive electrode was laminated so as to face the separator. The obtained laminate was impregnated with a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio) and sandwiched between polyester films (Toray Industries, Lumirror S10, 250 μm thickness), 80 ° C. × 5 minutes, 0 Heated and pressurized at 1 MPa. Then, before the solvent dried, the negative electrode and the positive electrode were peeled off from the separator with a protective film, and evaluated as follows. The evaluation results are also shown in FIG.
A: When both the negative electrode and the positive electrode are peeled off and there is resistance, and a part or all of the active material layer is adhered and transferred to the protective film. ○: When both the negative electrode and the positive electrode are peeled off, there is resistance, but the active material layer X is not transferred to the protective film ×: When either the negative electrode or the positive electrode is removed, there is no resistance, and it has already been removed

3.5.5. Evaluation of charge / discharge rate characteristics The charge / discharge rate characteristics were evaluated in the same manner as in Example 1. The evaluation results are also shown in FIG.

3.6. Examples 12-20, Comparative Examples 6-10
A protective film composition was prepared in the same manner as in Example 11 except that the proportions shown in Table 3 were used. Moreover, the electrical storage device was manufactured similarly to Example 11 using the obtained composition for protective films, and was evaluated. The evaluation results are also shown in Table 3. Content ratio of water-soluble polymer (A1) and water-insoluble polymer particles (A2) in the compositions for protective films according to Examples 11 to 20 and Comparative Examples 6 to 10, spinnability, protective film / electrode adhesion The evaluation results of the charge / discharge rate characteristics are summarized in Table 3 below.

  In addition, the notation of “-” in Table 3 indicates that the corresponding component was not used.

3.7. Evaluation Results As is apparent from Table 2 above, an electricity storage device (lithium ion battery) comprising a positive electrode with a protective film produced from the composition for a protective film according to the present invention shown in Examples 1 to 10 was charged / discharged. The rate characteristics were excellent. On the other hand, in Comparative Examples 1-5, the electrical storage device which shows a favorable charging / discharging rate characteristic was not obtained.

  As is clear from Table 3 above, an electricity storage device (lithium ion battery) comprising a separator having a protective film on both sides made from the composition for a protective film according to the present invention shown in Examples 11 to 20 is a rechargeable battery. It was confirmed that the discharge rate characteristics were excellent and the adhesion between the protective film and the electrode was good. On the other hand, in Comparative Examples 6-10, the electrical storage device which shows a favorable charging / discharging characteristic was not obtained. Further, in Comparative Examples 6 and 10, since the protective film had poor binding force, the protective film dropped off when the battery was produced, and the battery having the protective film could not be produced.

  The present invention is not limited to the above embodiment, and various modifications can be made. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). The present invention also includes a configuration in which a non-essential part of the configuration described in the above embodiment is replaced with another configuration. Furthermore, the present invention includes a configuration that achieves the same effects as the configuration described in the above embodiment or a configuration that can achieve the same object. Furthermore, the present invention includes a configuration obtained by adding a known technique to the configuration described in the above embodiment.

  1, 2, 3 ... Electric storage device 10, 110, 210 ... Positive electrode, 12, 112, 212 ... Positive electrode current collector, 14, 114, 214 ... Positive electrode active material layer, 20, 120, 220 ... Negative electrode, 22, 122 222, negative electrode current collector, 24, 124, 224 ... negative electrode active material layer, 30, 130, 230 ... protective film, 40, 140, 240 ... electrolyte, 150, 250 ... separator

Claims (11)

Water-insoluble polymer particles (A2) and an aqueous medium,
The composition for producing the protective film arrange | positioned between the positive electrode and negative electrode of an electrical storage device whose spinnability is 60 to 85%.   The composition according to claim 1, wherein the water-insoluble polymer particles (A2) are particles having pores.   The composition according to claim 1 or 2, wherein the water-insoluble polymer particles (A2) have a repeating unit derived from a compound having two or more polymerizable unsaturated groups.   The composition according to claim 3, wherein the compound having two or more polymerizable unsaturated groups is at least one selected from the group consisting of polyfunctional (meth) acrylic acid esters and aromatic polyfunctional vinyl compounds. .   Furthermore, the composition as described in any one of Claims 1 thru | or 4 containing a water-soluble polymer (A1).   The composition of Claim 5 which contains the said water-soluble polymer (A1) 0.1-15 mass parts with respect to 100 mass parts of the said water-insoluble polymer particles (A2).   The composition according to any one of claims 1 to 6, wherein an average particle diameter (Da2) of the water-insoluble polymer particles (A2) is 100 nm or more and 3000 nm or less.   The insoluble content of the water-insoluble polymer particles (A2) in toluene is 90% or more, and the 10% weight loss temperature when heated at 20 ° C./min in thermogravimetric analysis under an air atmosphere is 320 ° C. or more. The composition according to any one of claims 1 to 7, wherein   The method to produce the protective film arrange | positioned between the positive electrode and negative electrode of an electrical storage device using the composition as described in any one of Claims 1 thru | or 8.   A protective film produced by the method of claim 9.   An electricity storage device comprising: a positive electrode; a negative electrode; the protective film according to claim 10 disposed between the positive electrode and the negative electrode; and an electrolytic solution.

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