JP7220216B2 - Composition for power storage device, slurry for power storage device electrode, power storage device electrode, and power storage device - Google Patents

Description

The present invention comprises an electricity storage device composition, an electricity storage device electrode slurry containing the composition and an active material, an electricity storage device electrode formed by coating and drying the slurry on a current collector, and the electrode. related to a power storage device.

2. Description of the Related Art In recent years, power storage devices with high voltage and high energy density have been required as power sources for driving electronic devices. Lithium ion batteries, lithium ion capacitors, and the like are expected as such power storage devices.

Electrodes used in such electricity storage devices are produced by applying a composition (electrode slurry) containing an active material and a polymer functioning as a binder to the surface of a current collector and drying the composition. Properties required for the polymer used as a binder include bonding ability between active materials, adhesion ability between the active material and current collector, abrasion resistance in the electrode winding process, and subsequent cutting. Powder-off resistance, etc., in which fine powder of the active material does not fall off from the applied and dried composition coating film (hereinafter also referred to as "active material layer").

It has been empirically found that the bonding ability between the active materials, the adhesion ability between the active material and the current collector, and the resistance to falling powder are approximately proportional to each other. Therefore, in the present specification, the term "adhesion" may be used to collectively refer to these.

By the way, recently, from the viewpoint of meeting the demands for higher output and higher energy density of electric storage devices, studies are underway to use materials having a large lithium storage capacity as active materials. For example, as disclosed in Patent Document 1, a method of utilizing a silicon material having a maximum theoretical lithium storage capacity of about 4,200 mAh/g as an active material is considered promising.

However, an active material using such a material having a large lithium absorption capacity undergoes a large volume change due to absorption and release of lithium. For this reason, when conventionally used electrode binders are applied to such a material with a large lithium storage capacity, the active material peels off due to the inability to maintain adhesion, which is noticeable during charging and discharging. capacity decrease occurs.

Techniques for improving the adhesiveness of the binder for electrodes include techniques for controlling the surface acid amount of particulate binder particles (see Patent Documents 2 and 3), and binders having epoxy groups or hydroxy groups. Techniques for improving characteristics have been proposed (see Patent Documents 4 and 5). Also, a technique has been proposed (see Patent Document 6) in which an active material is bound by a rigid molecular structure of polyimide to suppress the volume change of the active material. A technique using a water-soluble polymer such as polyacrylic acid has also been proposed (see Patent Document 7).

Japanese Patent Application Laid-Open No. 2004-185810 WO2011/096463 WO2013/191080 JP 2010-205722 A Japanese Unexamined Patent Application Publication No. 2010-3703 JP 2011-204592 A WO2015/098050

However, the electrode binders disclosed in Patent Documents 1 to 7 above have a large lithium absorption capacity, and a new active material typified by a silicon material that has a large volume change accompanying lithium absorption and release. It could not be said that the adhesiveness was sufficient for the conversion. When such an electrode binder is used, the electrode deteriorates due to, for example, falling off of the active material due to repeated charging and discharging.

Accordingly, some aspects of the present invention provide a composition for an electricity storage device which is excellent in flexibility and adhesion and which can produce an electricity storage device electrode exhibiting good charge/discharge durability characteristics. Moreover, some aspects of the present invention provide a slurry for an electricity storage device electrode containing the composition. In addition, some aspects of the present invention provide an electricity storage device electrode that exhibits excellent flexibility and adhesion as well as good charge/discharge durability. Furthermore, some aspects of the present invention provide an electricity storage device with excellent charge/discharge durability characteristics.

The present invention has been made to solve at least part of the above problems, and can be implemented as any of the following aspects.

One aspect of the composition for an electricity storage device according to the present invention is
containing polymer particles (A) and a liquid medium (B),
The polymer particles (A) have a number average particle diameter of 50 nm or more and 500 nm or less,
When the total number of repeating units contained in the polymer particles (A) is 100 parts by mass, the polymer particles (A) are
1 to 50 parts by mass of repeating units (a1) derived from a conjugated diene compound;
5 to 90 parts by mass of repeating units (a2) derived from an unsaturated carboxylic acid;
(Meth) containing 5 to 90 parts by mass of repeating units (a3) derived from acrylamide,
The total amount of the repeating unit (a2) and the repeating unit (a3) is 50 parts by mass or more.

In one aspect of the power storage device composition,
The pH can be 6-11.

In any aspect of the power storage device composition,
The viscosity at pH 9 of the 5% by mass aqueous dispersion of the polymer particles (A) may be 500 to 150,000 mPa·s.

In any aspect of the power storage device composition,
The liquid medium (B) can be water.

One aspect of the electricity storage device electrode slurry according to the present invention is
It contains the power storage device composition according to any one of the above aspects and an active material.

In one aspect of the electricity storage device electrode slurry,
A silicon material can be contained as the active material.

In any aspect of the electricity storage device electrode slurry,
It may further contain at least one polymer selected from the group consisting of styrene-butadiene copolymers, acrylic polymers and fluorine-based polymers.

In any aspect of the electricity storage device electrode slurry,
A thickening agent may also be included.

One aspect of the electricity storage device electrode according to the present invention is
A current collector, and an active material layer formed by coating and drying the slurry for a power storage device electrode according to any one of the aspects above on the surface of the current collector.

One aspect of the electricity storage device according to the present invention is
The electricity storage device electrode of the above aspect is provided.

According to the electric storage device composition of the present invention, flexibility and adhesion can be improved, so that an electric storage device electrode exhibiting good charge-discharge durability can be produced. The power storage device composition according to the present invention exhibits the above effect particularly when the power storage device electrode contains a material having a large lithium storage capacity as an active material, such as a carbon material such as graphite or a silicon material. That is, since a material having a large lithium storage capacity can be used as the active material, the battery performance is also improved.

Preferred embodiments of the present invention will be described in detail below. It should be understood that the present invention is not limited only to the embodiments described below, but includes various modifications implemented within the scope of the present invention. In the present specification, "(meth)acrylic acid" is a concept encompassing both "acrylic acid" and "methacrylic acid". Similarly, "-(meth)acrylate" is a concept that includes both "-acrylate" and "-methacrylate". Similarly, "(meth)acrylamide" is a concept that includes both "acrylamide" and "methacrylamide."

In the present specification, a numerical range described using "to" means that the numerical values described before and after "to" are included as lower and upper limits.

1. Power Storage Device Composition The power storage device composition according to the present embodiment contains polymer particles (A) and a liquid medium (B). The composition for an electricity storage device according to the present embodiment is used for producing an electricity storage device electrode (active material layer) with improved bonding ability between active materials, adhesion ability between an active material and a current collector, and powder falling resistance. It can be used as a material, and can also be used as a material for forming a protective film for suppressing short circuits caused by dendrites that occur during charging and discharging. Hereinafter, each component contained in the composition for an electricity storage device according to this embodiment will be described in detail.

1.1. Polymer particles (A)
The composition for an electricity storage device according to this embodiment contains polymer particles (A). The polymer particles (A) contain repeating units (a1) derived from a conjugated diene compound (hereinafter simply referred to as "repeating units (a1)”.) 1 to 50 parts by mass, a repeating unit (a2) derived from an unsaturated carboxylic acid (hereinafter also simply referred to as “repeating unit (a2)”.) 5 to 90 parts by mass, ( 5 to 90 parts by mass of a repeating unit (a3) derived from meth)acrylamide (hereinafter also simply referred to as "repeating unit (a3)"), and the repeating unit (a2) and the repeating unit (a3) is 50 parts by mass or more. Moreover, the polymer particles (A) may contain, in addition to the repeating units, repeating units derived from other monomers copolymerizable therewith. Other monomers include, for example, unsaturated carboxylic acid esters having a hydroxyl group, unsaturated carboxylic acid esters (excluding the unsaturated carboxylic acid esters having a hydroxyl group), α,β-unsaturated nitrile compounds, A cationic monomer, an aromatic vinyl compound, a compound having a sulfonic acid group, and the like are included.

The polymer particles (A) contained in the electricity storage device composition according to the present embodiment are preferably in the form of latex dispersed in the liquid medium (B). When the polymer particles (A) are in the form of latex dispersed in the liquid medium (B), the slurry for the electricity storage device electrode prepared by mixing with the active material (hereinafter also simply referred to as "slurry") is stabilized. It is preferable because the properties are improved and the coatability of the slurry to the current collector is improved.

Hereinafter, each repeating unit constituting the polymer particles (A), physical properties of the polymer particles (A), and the production method will be described in this order.

1.1.1. Each Repeating Unit Constituting the Polymer Particle (A) <Repeating Unit (a1) Derived from Conjugated Diene Compound>
The content of the repeating unit (a1) derived from the conjugated diene compound is 1 to 50 parts by mass when the total of repeating units contained in the polymer particles (A) is 100 parts by mass. The lower limit of the content of the repeating unit (a1) is preferably 2 parts by mass, more preferably 3 parts by mass. The upper limit of the content of the repeating unit (a1) is preferably 48 parts by mass, more preferably 45 parts by mass. By containing the repeating unit (a1) in the above range, the dispersibility of the active material and filler is improved, and a uniform active material layer and protective film can be formed. It exhibits excellent charge-discharge characteristics. In addition, stretchability can be imparted to the polymer particles (A) covering the surface of the active material, and the stretchability of the polymer particles (A) can improve adhesion, so that good charge-discharge durability can be achieved. show.

Conjugated diene compounds include, but are not limited to, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and the like. It can be one or more selected from among these. Among these, 1,3-butadiene is particularly preferred.

<Repeating unit (a2) derived from unsaturated carboxylic acid>
The content of the repeating units (a2) derived from unsaturated carboxylic acid is 5 to 90 parts by mass when the total of repeating units contained in the polymer particles (A) is 100 parts by mass. The lower limit of the content of the repeating unit (a2) is preferably 7 parts by mass, more preferably 10 parts by mass. The upper limit of the content of the repeating unit (a2) is preferably 85 parts by mass, more preferably 80 parts by mass. By containing the repeating unit (a2) within the above range, the dispersibility of the active material and filler is improved. Furthermore, by improving the affinity with the silicon material as the active material and suppressing the swelling of the silicon material, good charge/discharge durability is exhibited.

The unsaturated carboxylic acid is not particularly limited, but includes mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and is one or more selected from these. be able to.

<Repeating unit (a3) derived from (meth)acrylamide>
The content of the repeating units (a3) derived from (meth)acrylamide is 5 to 90 parts by mass when the total of repeating units contained in the polymer particles (A) is 100 parts by mass. The lower limit of the content of the repeating unit (a3) is preferably 7 parts by mass, more preferably 10 parts by mass. The upper limit of the content of the repeating unit (a3) is preferably 85 parts by mass, more preferably 80 parts by mass. When the content of the repeating unit (a3) is within the above range, the glass transition temperature (Tg) of the polymer particles (A) is favorable. As a result, the dispersibility of the active material and filler is improved. In addition, the flexibility of the resulting active material layer is moderate, and the adhesion between the current collector and the active material layer is improved. Furthermore, since the bonding ability between a carbon material such as graphite and an active material containing a silicon material can be enhanced, the resulting active material layer has better flexibility and adhesion to the current collector. .

(Meth)acrylamide is not particularly limited, but acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide amide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolmethacrylamide, N-methylolacrylamide, diacetoneacrylamide, maleic acid amide, acrylamide tert-butylsulfonic acid and the like. . These (meth)acrylamides may be used singly or in combination of two or more.

When the total amount of the repeating units contained in the polymer particles (A) is 100 parts by mass, the total amount of the repeating units (a2) and the repeating units (a3) is 50 parts by mass or more, and 55 parts by mass. It is preferably 60 parts by mass or more, more preferably 60 parts by mass or more. When the total amount of the repeating unit (a2) and the repeating unit (a3) is within the above range, the dispersibility of the active material and filler is improved, and flexibility and adhesion are improved, resulting in good charge-discharge durability. indicates

<Other repeating units>
The polymer particles (A) may contain, in addition to the repeating units (a1) to (a3), repeating units derived from other monomers copolymerizable therewith. Examples of such repeating units include a repeating unit (a4) derived from an unsaturated carboxylic acid ester having a hydroxyl group (hereinafter also simply referred to as "repeating unit (a4)"), an unsaturated carboxylic acid ester (wherein the hydroxyl group (excluding unsaturated carboxylic acid esters having a repeating unit (a5) (hereinafter also simply referred to as “repeating unit (a5)”), a repeating unit (a6) derived from an α,β-unsaturated nitrile compound ) (hereinafter also simply referred to as “repeating unit (a6)”), repeating unit (a7) derived from an aromatic vinyl compound (hereinafter also simply referred to as “repeating unit (a7)”), and having a sulfonic acid group A repeating unit (a8) derived from a compound (hereinafter also simply referred to as “repeating unit (a8)”), a repeating unit derived from a cationic monomer, and the like can be mentioned.

Specific examples of unsaturated carboxylic acid esters having a hydroxyl group include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate and the like. Among these, 2-hydroxyethyl (meth)acrylate and glycerin mono(meth)acrylate are preferred. In addition, these monomers can be used individually by 1 type or in combination of 2 or more types.

The unsaturated carboxylic acid ester is not particularly limited, but (meth)acrylic acid ester is preferable. Specific examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, and n-(meth)acrylate. -butyl, iso-butyl (meth)acrylate, n-amyl (meth)acrylate, iso-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, (meth)acrylic acid 2 - Ethylhexyl, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tri(meth)acrylic acid trimethylolpropane, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, etc., and at least one selected from these can. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is preferred, and methyl (meth)acrylate is particularly preferred. preferable.

Specific examples of the α,β-unsaturated nitrile compound include, but are not particularly limited to, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and are selected from these. It can be one or more. Among these, one or more selected from acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.

Specific examples of the aromatic vinyl compound include, but are not limited to, styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one selected from among these. Can be more than seed. Among these, styrene is particularly preferred.

Specific examples of compounds having a sulfonic acid group include, but are not limited to, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2- Compounds having a sulfonic acid group such as acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof may also be used. .

The cationic monomer is not particularly limited, but is at least one monomer selected from the group consisting of secondary amines (salts), tertiary amines (salts) and quaternary ammonium salts. is preferred. Specific examples of these cationic monomers are not particularly limited, but 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt, 2-(meth)acrylate (Diethylamino)ethyl, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-(meth)acrylate [(3,5-Dimethylpyrazolyl)carbonylamino]ethyl, 2-(0-[1'-methylpropylideneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)acrylate (meth)acrylate Ethyl, methacryloylcholine chloride, tris(2-acryloyloxyethyl)isocyanurate, 2-vinylpyridine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride water hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichlormide, N-allylbenzylamine, N-allylaniline, 2,4- Diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-heptene- 4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride and the like. These monomers may be used individually by 1 type, and may use 2 or more types together.

The polymer particles (A) are composed of the repeating units (a5), the repeating units (a6) and the repeating units (a7) when the total number of repeating units contained in the polymer particles (A) is 100 parts by mass. ) and the repeating unit (a2) is preferably 5 to 50 parts by mass. When the polymer particles (A) contain the repeating units in the above ratio, the dispersibility of the active material and filler is improved, and the flexibility and adhesion are further improved, thereby exhibiting good charge/discharge durability.

When the total number of repeating units contained in the polymer particles (A) is 100 parts by mass, the polymer particles (A) have the repeating units (a2), the repeating units (a3), and the repeating units (a4). ) and the repeating unit (a8) is preferably 50 to 95 parts by mass, more preferably 52 to 92 parts by mass, and particularly preferably 55 to 90 parts by mass. When the polymer particles (A) contain the repeating units in the above ratio, the dispersibility of the active material and filler is improved, and the flexibility and adhesion are further improved, thereby exhibiting good charge/discharge durability.

When the total number of repeating units contained in the polymer particles (A) is 100 parts by mass, the polymer particles (A) have the repeating units (a1), the repeating units (a5), and the repeating units (a6). ) and the repeating unit (a7) is preferably 50 parts by mass or less, more preferably 5 to 48 parts by mass, and particularly preferably 8 to 45 parts by mass. When the polymer particles (A) contain the repeating units in the above ratio, the dispersibility of the active material and filler is improved, and the flexibility and adhesion are further improved, thereby exhibiting good charge/discharge durability.

1.1.2. Physical properties of polymer particles (A) <number average particle size>
The number average particle size of the polymer particles (A) is 50 to 500 nm, preferably 60 to 450 nm, more preferably 70 to 400 nm. When the number average particle diameter of the polymer particles (A) is within the above range, the polymer particles (A) are likely to be adsorbed on the surface of the active material. You can follow and move. As a result, it is possible to suppress the migration of only one of the two particles independently, so that the deterioration of the electrical characteristics can be reduced.

The number average particle size of the polymer particles (A) can be calculated from the average value of 50 particle sizes obtained from an image of the polymer particles (A) observed with a transmission electron microscope (TEM). Examples of transmission electron microscopes include "H-7650" manufactured by Hitachi High-Technologies Corporation.

<Glass transition temperature>
The polymer particles (A) preferably have only one endothermic peak in the temperature range of 60° C. to 160° C. when measured by differential scanning calorimetry (DSC) according to JIS K7121. The endothermic peak temperature (that is, the glass transition temperature (Tg)) is more preferably in the range of 70°C to 150°C. When the polymer particles (A) have only one endothermic peak in the DSC analysis and the peak temperature is within the above range, the polymer particles (A) exhibit good adhesion and adhere to the active material layer. It is preferable because it can impart better flexibility and adhesiveness to the material.

1.1.3. Method for producing polymer particles (A) The method for producing polymer particles (A) is not particularly limited, but for example, emulsification performed in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, or the like. It can be based on a polymerization method. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, compounds described in Japanese Patent No. 5999399 and the like can be used.

The emulsion polymerization method for synthesizing the polymer particles (A) may be a one-stage polymerization or a multi-stage polymerization of two or more stages, preferably a multi-stage polymerization of two or more stages.

When polymer particles (A) are synthesized by one-step polymerization, the mixture of the above monomers is preferably subjected to polymerization at 40 to 80° C. in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator and the like. can be by emulsion polymerization for 4 to 18 hours.

When the polymer particles (A) are synthesized by two-stage polymerization, it is preferable to set the polymerization in each stage as follows.

The ratio of the monomers used in the first-stage polymerization is the total mass of monomers (the sum of the mass of the monomers used in the first-stage polymerization and the mass of the monomers used in the second-stage polymerization). On the other hand, it is preferably in the range of 5 to 60% by mass, more preferably in the range of 5 to 55% by mass. By carrying out the first-stage polymerization at such a proportion of the monomers used, it is possible to obtain particles of the polymer particles (A) that are excellent in dispersion stability and are less likely to form aggregates, and at the same time, the composition for an electricity storage device can be obtained. It is preferable because the increase in viscosity over time is also suppressed.

The types and proportions of the monomers used in the first-stage polymerization may be the same as or different from the types and proportions of the monomers used in the second-stage polymerization.

From the viewpoint of dispersibility of the polymer particles (A) to be obtained, the polymerization conditions at each stage are preferably as follows.
- First-stage polymerization; preferably temperature of 40 to 80°C; polymerization time of preferably 2 to 36 hours; polymerization conversion rate of preferably 50% by mass or more, more preferably 60% by mass or more.
- Second stage polymerization; preferably temperature of 40 to 80°C; polymerization time of preferably 2 to 10 hours.

By setting the total solid concentration in the emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed in a state in which the obtained polymer has good dispersion stability. The total solid content concentration is preferably 45% by mass or less, more preferably 40% by mass or less.

Regardless of whether the synthesis of the polymer particles (A) is performed as a one-step polymerization or a two-step polymerization method, the pH is adjusted to 6 by adding a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed. To about 11, preferably from 7 to 11, more preferably from 7 to 10. The neutralizing agent used here is not particularly limited, but examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia and the like. By setting the pH within the above range, the stability of the polymer particles (A) is improved. By concentrating the polymerization mixture after the neutralization treatment, the solid content concentration can be increased while maintaining good stability of the polymer particles (A).

1.2. Liquid medium (B)
The composition for an electricity storage device according to this embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, more preferably water. The aqueous medium can contain a non-aqueous medium other than water. Examples of the non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. can be done. By using an aqueous medium as the liquid medium (B), the composition for an electricity storage device according to the present embodiment has a lower degree of adverse effects on the environment and a higher level of safety for workers handling it.

The content of the non-aqueous medium contained in the aqueous medium is preferably 10 parts by mass or less, more preferably 5 parts by mass or less per 100 parts by mass of the aqueous medium. preferable. Here, the term "substantially does not contain" means that a non-aqueous medium is not intentionally added as a liquid medium, and the non-aqueous medium that is inevitably mixed when preparing the composition for an electricity storage device. may contain

1.3. Other Additives The composition for an electricity storage device according to the present embodiment can contain additives other than the components described above, if necessary. Examples of such additives include polymers other than the polymer particles (A), preservatives, thickeners, and the like.

<Polymer other than polymer particles (A)>
The composition for an electricity storage device according to this embodiment may contain a polymer other than the polymer particles (A). Examples of such polymers include, but are not limited to, SBR (styrene-butadiene rubber) polymers, acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as structural units, PVDF (polyvinylidene fluoride), and the like. Fluorinated polymers and the like are included. These polymers may be used singly or in combination of two or more. By containing a polymer other than the polymer particles (A), flexibility and adhesion may be further improved.

The content ratio of the polymer particles (A) in the electricity storage device composition according to the present embodiment is the polymer particles (A), the polymer other than the polymer particles (A) optionally contained, and the thickener It is preferably 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, and particularly preferably 25 to 75 parts by mass, based on the total of 100 parts by mass.

<Preservative>
The composition for an electricity storage device according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, fungi, etc. and the generation of foreign matter when the composition for an electricity storage device is stored. Specific examples of antiseptics include compounds described in Japanese Patent No. 5477610 and the like.

<Thickener>
The composition for an electricity storage device according to this embodiment may contain a thickener. By containing a thickener, it may be possible to further improve the applicability and the charge/discharge characteristics of the obtained electricity storage device.

Specific examples of thickeners include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; the cellulose compound or the ammonium salt or alkali metal salt of the poly(meth)acrylic acid; polyvinyl polyvinyl alcohol-based (co)polymers such as alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; Water-soluble polymers such as saponified products can be mentioned. Among these, alkali metal salts of carboxymethylcellulose, alkali metal salts of poly(meth)acrylic acid, and the like are preferable.

Examples of commercially available thickeners include alkali metal salts of carboxymethylcellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (manufactured by Daicel Corporation).

When the power storage device composition according to the present embodiment contains a thickener, the content of the thickener is 5 parts by mass or less with respect to 100 parts by mass of the total solid content of the power storage device composition. is preferred, and 0.1 to 3 parts by mass is more preferred.

1.4. Method for producing a composition for an electricity storage device The composition for an electricity storage device according to the present embodiment is produced by performing multistage polymerization of two or more stages in the presence of, for example, a known emulsifier (surfactant), chain transfer agent, polymerization initiator, or the like. It can be produced by emulsion polymerization. Specifically, the composition for an electricity storage device is a polymer obtained by polymerizing a repeating unit group containing a repeating unit (a1) derived from a conjugated diene compound and a repeating unit (a2) derived from an unsaturated carboxylic acid. A first step of obtaining particles, and in the presence of the polymer particles, polymerizing a repeating unit group containing a repeating unit (a2) derived from an unsaturated carboxylic acid and a repeating unit (a3) derived from (meth)acrylamide. and a second step, wherein the total amount of the repeating unit (a2) and the repeating unit (a3) is 50 parts by mass or more when the total of all repeating units is 100 parts by mass. can do.

The electrical storage device composition obtained by the production method described above is preferably in the form of latex dispersed in the liquid medium (B). When the power storage device composition is in the form of latex dispersed in the liquid medium (B), the stability of the power storage device electrode slurry prepared by mixing with the active material is improved, and the slurry is applied to the current collector. It is preferable because the coatability of is improved.

Specific examples of emulsifiers include sulfuric acid ester salts of higher alcohols, alkylbenzenesulfonates, alkyldiphenylether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, and naphthalenesulfonic acid/formalin condensation. anionic surfactants such as nonionic surfactants, sulfate ester salts of nonionic surfactants; nonionic surfactants such as polyethylene glycol alkyl esters, polyethylene glycol alkylphenyl ethers, polyethylene glycol alkyl ethers; perfluorobutyl sulfone Fluorinated surfactants such as acid salts, perfluoroalkyl group-containing phosphates, perfluoroalkyl group-containing carboxylates, perfluoroalkyl ethylene oxide adducts, etc., and one or more selected from these can be used.

Specific examples of chain transfer agents include alkylmercaptans such as n-hexylmercaptan, n-octylmercaptan, tert-octylmercaptan, n-dodecylmercaptan, tert-dodecylmercaptan and n-stearylmercaptan; dimethylxanthogen disulfide; xanthogen compounds such as diisopropyl xanthogen disulfide; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram monosulfide; 2,6-di-tert-butyl-4-methylphenol, styrenated phenol, etc. phenol compounds; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane and carbon tetrabromide; vinyl ether compounds such as α-benzyloxystyrene, α-benzyloxyacrylonitrile and α-benzyloxyacrylamide In addition, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate, α-methylstyrene dimer, etc. can be mentioned, and one or more selected from these. can be used.

Specific examples of polymerization initiators include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate and ammonium persulfate; cumene hydroperoxide, benzoyl peroxide, tert-butyl hydroperoxide, acetyl Oil-soluble polymerization initiators such as peroxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, azobisisobutyronitrile, 1,1'-azobis(cyclohexanecarbonitrile), etc. can be appropriately selected and used. Among these, it is particularly preferable to use potassium persulfate, sodium persulfate, cumene hydroperoxide or tert-butyl hydroperoxide. It is also preferred to use a redox initiator that combines an oxidizing agent and a reducing agent, such as the above persulfate and sodium bisulfite. The proportion of the polymerization initiator to be used is not particularly limited, but is appropriately set in consideration of the monomer composition, the pH of the polymerization reaction system, the combination of other additives, and the like.

As described above, the composition for an electricity storage device according to the present embodiment can be produced by multistage emulsion polymerization of two or more stages, but it is preferable to carry out multistage polymerization of two or more stages.

When the composition for an electricity storage device is produced by two-stage polymerization, it is preferable to set the polymerization in each stage as follows.

The ratio of the monomers used in the first-stage polymerization is the total mass of monomers (the sum of the mass of the monomers used in the first-stage polymerization and the mass of the monomers used in the second-stage polymerization). On the other hand, it is preferably in the range of 5 to 60% by mass, more preferably in the range of 5 to 55% by mass. By carrying out the first-stage polymerization at such a proportion of the monomers used, it is possible to obtain polymer particles that are excellent in dispersion stability and are less likely to form aggregates, and the viscosity of the electrical storage device composition increases over time. is also suppressed, which is preferable.

The types and proportions of the monomers used in the first-stage polymerization may be the same as or different from the types and proportions of the monomers used in the second-stage polymerization.

From the viewpoint of the dispersibility of the composition for an electricity storage device obtained, the polymerization conditions at each stage are preferably as follows.
- First-stage polymerization; preferably temperature of 40 to 80°C; polymerization time of preferably 2 to 36 hours; polymerization conversion rate of preferably 50% by mass or more, more preferably 60% by mass or more.
- Second stage polymerization; preferably temperature of 40 to 80°C; polymerization time of preferably 2 to 10 hours.

By setting the total solid concentration in the emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed in a state in which the obtained polymer has good dispersion stability. The total solid content concentration is preferably 45% by mass or less, more preferably 40% by mass or less.

In the production of the composition for electric storage devices, the pH can be adjusted to about 6 to 11, preferably 7 to 11, more preferably 7 to 10 by adding a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed. preferable. The neutralizing agent used here is not particularly limited, but examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia and the like. By adjusting the pH within the above range, the stability of the electrical storage device composition is improved. Further, by concentrating the polymerization mixture after the neutralization treatment, the solid content concentration can be increased while maintaining good stability of the composition for an electricity storage device.

The composition for an electricity storage device thus obtained can also be pulverized by removing the liquid medium (B). As means for removing the liquid medium (B) in this case, there is a method of drying and removing the liquid medium (B) using a high viscosity concentrator or a hot air dryer.

<Repeating unit (a1) derived from conjugated diene compound>
In the first step, the content of the repeating unit (a1) derived from the conjugated diene compound is 1 to 50 parts by mass when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. is preferably The lower limit of the content of the repeating unit (a1) is more preferably 2 parts by mass, particularly preferably 3 parts by mass. The upper limit of the content of the repeating unit (a1) is more preferably 48 parts by mass, particularly preferably 45 parts by mass.

In the second step, the content of the repeating unit (a1) derived from the conjugated diene compound is 0 to 10 parts by mass when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. is preferably The upper limit of the content of the repeating unit (a1) is more preferably 5 parts by mass.

By containing the repeating unit (a1) in the above range, the dispersibility of the active material and filler is improved, and a uniform active material layer and protective film can be formed. It exhibits excellent charge-discharge characteristics. In addition, stretchability can be imparted to the composition for an electricity storage device that coats the surface of the active material, and the composition for an electricity storage device expands and contracts to improve adhesion, thereby exhibiting good charge/discharge durability.

Conjugated diene compounds include, but are not limited to, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and the like. It can be one or more selected from among these. Among these, 1,3-butadiene is particularly preferred.

<Repeating unit (a2) derived from unsaturated carboxylic acid>
In the first step, the content of the repeating unit (a2) derived from an unsaturated carboxylic acid is 1 to 10 parts by mass when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. It is preferable that it is a part. The lower limit of the content of the repeating unit (a2) is more preferably 2 parts by mass, particularly preferably 3 parts by mass.

In the second step, the content of repeating units (a2) derived from an unsaturated carboxylic acid is 4 to 90 parts by mass when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. It is preferable that it is a part. The lower limit of the content of the repeating unit (a2) is more preferably 7 parts by mass, particularly preferably 10 parts by mass. The upper limit of the content of the repeating unit (a2) is more preferably 85 parts by mass, particularly preferably 80 parts by mass.

By containing the repeating unit (a2) within the above range, the dispersibility of the active material and filler is improved. Furthermore, by improving the affinity with the silicon material as the active material and suppressing the swelling of the silicon material, good charge/discharge durability is exhibited.

The unsaturated carboxylic acid is not particularly limited, but includes mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and is one or more selected from these. be able to.

<Repeating unit (a3) derived from (meth)acrylamide>
In the second step, the content of repeating units (a3) derived from (meth)acrylamide is 5 to 90 parts by mass when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. It is preferable that it is a part. The lower limit of the content of the repeating unit (a3) is more preferably 7 parts by mass, particularly preferably 10 parts by mass. The upper limit of the content of the repeating unit (a3) is more preferably 85 parts by mass, particularly preferably 80 parts by mass.

When the content of the repeating unit (a3) is within the above range, the glass transition temperature (Tg) of the composition for an electricity storage device is favorable. As a result, the dispersibility of the active material and filler is improved. In addition, the flexibility of the resulting active material layer is moderate, and the adhesion between the current collector and the active material layer is improved. Furthermore, since the bonding ability between a carbon material such as graphite and an active material containing a silicon material can be enhanced, the resulting active material layer has better flexibility and adhesion to the current collector. .

(Meth)acrylamide is not particularly limited, but acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide amide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolmethacrylamide, N-methylolacrylamide, diacetoneacrylamide, maleic acid amide, acrylamide tert-butylsulfonic acid and the like. . These (meth)acrylamides may be used singly or in combination of two or more.

When the total amount of all repeating units contained in the electricity storage device composition is 100 parts by mass, the total amount of the repeating unit (a2) and the repeating unit (a3) is 50 parts by mass or more, and 55 parts by mass. It is preferably 60 parts by mass or more, more preferably 60 parts by mass or more. When the total amount of the repeating unit (a2) and the repeating unit (a3) is within the above range, the dispersibility of the active material and filler is improved, and flexibility and adhesion are improved, resulting in good charge-discharge durability. indicates

<Other repeating units>
In the first step and/or the second step of the above method for producing a composition for an electricity storage device, the repeating unit group includes, in addition to the repeating units (a1), (a2), and (a3), these and It may contain repeating units derived from other copolymerizable monomers. Examples of such repeating units include a repeating unit (a4) derived from an unsaturated carboxylic acid ester having a hydroxyl group, and a repeating unit derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group). units (a5), repeating units (a6) derived from an α,β-unsaturated nitrile compound, repeating units (a7) derived from an aromatic vinyl compound, repeating units (a8) derived from a compound having a sulfonic acid group, Examples thereof include repeating units derived from cationic monomers.

Specific examples of unsaturated carboxylic acid esters having a hydroxyl group include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate and the like. Among these, 2-hydroxyethyl (meth)acrylate and glycerin mono(meth)acrylate are preferred. In addition, these monomers can be used individually by 1 type or in combination of 2 or more types.

The unsaturated carboxylic acid ester is not particularly limited, but (meth)acrylic acid ester is preferable. Specific examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, and n-(meth)acrylate. -butyl, i-butyl (meth)acrylate, n-amyl (meth)acrylate, iso-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, (meth)acrylic acid 2 - Ethylhexyl, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tri(meth)acrylic acid trimethylolpropane, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, etc., and at least one selected from these can. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is preferred, and methyl (meth)acrylate is particularly preferred. preferable.

Specific examples of the α,β-unsaturated nitrile compound include, but are not particularly limited to, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and are selected from these. It can be one or more. Among these, one or more selected from acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.

Specific examples of the aromatic vinyl compound include, but are not limited to, styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one selected from among these. Can be more than seed. Among these, styrene is particularly preferred.

Specific examples of compounds having a sulfonic acid group include, but are not limited to, vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2- Compounds having a sulfonic acid group such as acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof may also be used. .

The cationic monomer is not particularly limited, but is at least one monomer selected from the group consisting of secondary amines (salts), tertiary amines (salts) and quaternary ammonium salts. is preferred. Specific examples of these cationic monomers are not particularly limited, but 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt, 2-(meth)acrylate (Diethylamino)ethyl, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-(meth)acrylate [(3,5-Dimethylpyrazolyl)carbonylamino]ethyl, 2-(0-[1'-methylpropylideneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)acrylate (meth)acrylate Ethyl, methacryloylcholine chloride, tris(2-acryloyloxyethyl)isocyanurate, 2-vinylpyridine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride water hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichlormide, N-allylbenzylamine, N-allylaniline, 2,4- Diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-heptene- 4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride and the like. These monomers may be used individually by 1 type, and may use 2 or more types together.

1 selected from the group consisting of the repeating unit (a5), the repeating unit (a6) and the repeating unit (a7) when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass The total amount of the seed or more and the repeating unit (a2) is preferably 5 to 50 parts by mass or more. By containing such a repeating unit in the above ratio, the dispersibility of the active material and the filler is improved, and the flexibility and adhesion are further improved, so that good charge/discharge durability is exhibited.

The repeating unit (a2), the repeating unit (a3), the repeating unit (a4), and the repeating unit (a8) when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. is preferably 50 to 95 parts by mass, more preferably 52 to 92 parts by mass, and particularly preferably 55 to 90 parts by mass. By containing such a repeating unit in the above ratio, the dispersibility of the active material and the filler is improved, and the flexibility and adhesion are further improved, so that good charge/discharge durability is exhibited.

The repeating unit (a1), the repeating unit (a5), the repeating unit (a6), and the repeating unit (a7) when the total of all repeating units contained in the electricity storage device composition is 100 parts by mass. is preferably 50 parts by mass or less, more preferably 5 to 48 parts by mass, and particularly preferably 8 to 45 parts by mass. By containing such a repeating unit in the above ratio, the dispersibility of the active material and the filler is improved, and the flexibility and adhesion are further improved, so that good charge/discharge durability is exhibited.

1.5. Physical Properties of Electricity Storage Device Composition 1.5.1. pH
The pH of the power storage device composition according to the present embodiment is preferably 6 to 11, more preferably 7 to 11, and particularly preferably 7 to 10.5. If the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling and liquid dripping, and it is easy to produce an electricity storage device electrode that has both good electrical properties and adhesion. Become.

"pH" as used herein refers to a physical property measured as follows. It is a value measured in accordance with JIS Z8802:2011 at 25° C. with a pH meter using a glass electrode calibrated with a neutral phosphate standard solution and a borate standard solution as pH standard solutions. Examples of such a pH meter include "HM-7J" manufactured by Toa DKK Co., Ltd. and "D-51" manufactured by Horiba, Ltd.

Although it is not denied that the pH of the electrical storage device composition is affected by the composition of the monomers constituting the polymer particles (A), it should be added that it is not determined solely by the composition of the monomers. . That is, it is generally known that the pH of the composition for an electricity storage device changes depending on the polymerization conditions and the like even if the monomer composition is the same. do not have.

For example, even if the monomer composition is the same, when all the unsaturated carboxylic acid is charged from the beginning to the polymerization reaction solution and then other monomers are added sequentially, and when the monomers other than the unsaturated carboxylic acid are added is added to the polymerization reaction solution and the unsaturated carboxylic acid is added at the end, the amount of carboxyl groups derived from the unsaturated carboxylic acid exposed on the surface of the obtained polymer is different. Thus, it is considered that the pH of the composition for an electricity storage device is greatly changed by simply changing the order of adding the monomers in the polymerization method.

1.5.2. Viscosity The viscosity of the 5% by mass aqueous dispersion of the polymer particles (A) at pH 9 is preferably 500 to 150,000 mPa s, more preferably 1,000 to 150,000 mPa s. ,000 to 150,000 mPa·s is particularly preferred. It is preferable that the viscosity at pH 9 is equal to or higher than the lower limit, because the dispersibility of the active material and the filler is improved, and a homogeneous slurry can be prepared. It is preferable that the viscosity at pH 9 is equal to or less than the above upper limit, because the dispersibility of the polymer particles (A) itself is improved.

The viscosity of the 5% by mass aqueous dispersion of polymer particles (A) is a value measured according to JIS Z 8803 at a temperature of 25.0° C. using a Brookfield viscometer. As the B-type viscometer, for example, "RB-80L" or "TVB-10" manufactured by Toki Sangyo Co., Ltd. can be used.

1.5.3. Number Average Particle Size The number average particle size of the power storage device composition according to the present embodiment is preferably 50 to 500 nm, more preferably 60 to 450 nm, and particularly preferably 70 to 400 nm. When the number average particle size of the power storage device composition is within the above range, the power storage device composition tends to be adsorbed on the surface of the active material, so that the power storage device composition moves along with the movement of the active material. be able to. As a result, it is possible to suppress the migration of only one of the two particles independently, so that the deterioration of the electrical characteristics can be reduced.

The number average particle diameter of the composition for an electricity storage device can be calculated from the average value of 50 particle diameters obtained from an image of the composition for an electricity storage device observed with a transmission electron microscope (TEM). Examples of transmission electron microscopes include "H-7650" manufactured by Hitachi High-Technologies Corporation.

1.5.4. Glass transition temperature The power storage device composition according to the present embodiment has only one endothermic peak in the temperature range of 60 ° C. to 160 ° C. when measured by differential scanning calorimetry (DSC) in accordance with JIS K7121. is preferably The endothermic peak temperature (that is, the glass transition temperature (Tg)) is more preferably in the range of 70°C to 150°C. When the power storage device composition has only one endothermic peak in the DSC analysis and the peak temperature is within the above range, the power storage device composition exhibits good adhesion to the active material layer. It is preferable because it can impart better flexibility and adhesiveness.

2. Power Storage Device Slurry The power storage device slurry according to the present embodiment contains the power storage device composition described above. As described above, the composition for an electricity storage device according to the present embodiment can be used as a material for forming a protective film for suppressing short circuits caused by dendrites that occur during charging and discharging. It can also be used as a material for producing an electricity storage device electrode (active material layer) with improved bonding ability between active materials, adhesion ability between an active material and a current collector, and resistance to falling powder. Therefore, an electricity storage device slurry for forming a protective film (hereinafter also referred to as "protective film forming slurry") and an electricity storage device slurry for forming an active material layer of an electricity storage device electrode (hereinafter referred to as "electricity storage (also referred to as “slurry for device electrodes”).

2.1. Slurry for forming a protective film The term "slurry for forming a protective film" as used herein refers to a slurry that is applied to the surface of an electrode or a separator or both, and then dried to form a protective film on the surface of an electrode or a separator or both. Refers to the dispersion used to form the The protective film-forming slurry according to the present embodiment may be composed only of the composition for an electricity storage device described above, and may further contain an inorganic filler. Hereinafter, each component contained in the protective film forming slurry according to the present embodiment will be described in detail. In addition, since it is as above-mentioned about the composition for electrical storage devices, description is abbreviate|omitted.

2.1.1. Inorganic Filler The slurry for forming a protective film according to the present embodiment can improve the toughness of the formed protective film by containing an inorganic filler. At least one particle selected from the group consisting of silica, titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), and magnesium oxide (magnesia) is preferably used as the inorganic filler. Among these, titanium oxide and aluminum oxide are preferable from the viewpoint of further improving the toughness of the protective film. As titanium oxide, rutile-type titanium oxide is more preferable.

The average particle size of the inorganic filler is preferably 1 μm or less, more preferably in the range of 0.1 to 0.8 μm. The average particle size of the inorganic filler is preferably larger than the average pore size of the separator, which is a porous membrane. This can reduce damage to the separator and prevent the inorganic filler from clogging the micropores of the separator.

The protective film-forming slurry according to the present embodiment preferably contains 0.1 to 20 parts by mass of the above-described power storage device composition in terms of solid content with respect to 100 parts by mass of the inorganic filler. It is more preferable to contain up to 10 parts by mass. When the content of the electricity storage device composition is within the above range, the resulting protective film has a good balance between toughness and lithium ion permeability, and as a result, the resulting electricity storage device has a lower rate of increase in resistance. can do.

2.1.2. Liquid Medium For the protective film-forming slurry according to the present embodiment, the material described in “1.2. Liquid Medium (B)” of the composition for an electric storage device can be used as necessary. The amount of the liquid medium to be added can be adjusted as necessary so as to obtain the optimum viscosity of the slurry according to the coating method and the like.

2.1.3. Other Components The protective film-forming slurry according to the present embodiment can use appropriate amounts of the materials described in “1.3. Other Additives” of the composition for an electric storage device described above, if necessary.

2.2. Slurry for Electricity Storage Device Electrode The “slurry for electricity storage device electrode” in this specification is used to form an active material layer on the surface of the current collector by applying the slurry to the surface of the current collector and then drying it. It refers to a dispersion liquid that can be used. The electricity storage device electrode slurry according to the present embodiment contains the above-described electricity storage device composition and an active material.

In general, a slurry for electricity storage device electrodes often contains a binder component such as an SBR-based copolymer and a thickener such as carboxymethyl cellulose in order to improve adhesion. On the other hand, the slurry for an electricity storage device electrode according to the present embodiment can improve flexibility and adhesiveness even with the polymer particles (A) described above. Of course, the electricity storage device electrode slurry according to the present embodiment may contain a polymer other than the polymer particles (A) and a thickener in order to further improve adhesion.

Hereinafter, components contained in the slurry for electricity storage device electrodes according to the present embodiment will be described.

2.2.1. Polymer particles (A)
The composition, properties, and production method of the polymer particles (A) are as described above, and thus the description is omitted.

The content of the polymer particles (A) in the electricity storage device electrode slurry according to the present embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, with respect to 100 parts by mass of the active material. is more preferable, and 1.5 to 6 parts by mass is particularly preferable. When the content of the polymer particles (A) is within the above range, the dispersibility of the active material in the slurry will be good, and the slurry will have excellent coatability. The same applies to the case where the electricity storage device electrode slurry according to the present embodiment contains a polymer or a thickener other than the polymer particles (A).

2.2.2. Active material Examples of active materials used in the electricity storage device electrode slurry according to the present embodiment include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, and aluminum compounds. is mentioned. Specific examples of these include compounds described in Japanese Patent No. 5999399 and the like.

In addition, the active material layer may contain active materials exemplified below. For example _, a _conductive polymer such as _polyacene ; represents an oxygen atom, and X, Y and Z are numbers in the ranges of 1.10>X>0.05, 4.00>Y>0.85 and 5.00>Z>1.5, respectively.) and composite metal oxides represented by and other metal oxides.

The electricity storage device electrode slurry according to the present embodiment can be used for producing both positive and negative electricity storage device electrodes, and is preferably used for both the positive electrode and the negative electrode.

When lithium iron phosphate is used as the positive electrode active material, there is a problem that the charge/discharge characteristics are insufficient and the adhesion is poor. Lithium iron phosphate has a fine primary particle size and is known to be a secondary aggregate. It is considered that one of the factors is that it causes peeling from the current collector and that the conductive network inside the active material layer is easily broken.

However, in the electricity storage device electrode produced using the electricity storage device electrode slurry according to the present embodiment, even when lithium iron phosphate is used, the above-described problems do not occur, and good electrical characteristics are exhibited. be able to. The reason for this is that the polymer particles (A) can strongly bind lithium iron phosphate and at the same time maintain the state in which lithium iron phosphate is strongly bound even during charging and discharging. This is probably because it is possible.

On the other hand, when a negative electrode is produced, it is preferable to use one containing a silicon material among the active materials exemplified above. Since the silicon material has a larger lithium absorption amount per unit weight than other active materials, the inclusion of the silicon material as the negative electrode active material can increase the power storage capacity of the resulting power storage device. As a result, the output and energy density of the electricity storage device can be increased.

Further, the negative electrode active material is more preferably a mixture of a silicon material and a carbon material. Since the volume change of the carbon material is small during charging and discharging, the use of a mixture of the silicon material and the carbon material as the negative electrode active material can alleviate the influence of the volume change of the silicon material, and the active material layer and the aggregate can be reduced. It is possible to further improve the ability to adhere to the electric body.

When silicon (Si) is used as an active material, silicon has a high capacity, but causes a large volume change when absorbing lithium. For this reason, repeated expansion and contraction of the silicon material causes pulverization, peeling from the current collector, and separation between the active materials, which tends to break the conductive network inside the active material layer. As a result, the cycle characteristics are extremely degraded in a short period of time.

However, in the electricity storage device electrode produced using the electricity storage device electrode slurry according to the present embodiment, even when a silicon material is used, the above-described problems do not occur, and good electrical characteristics can be exhibited. can. The reason for this is that the polymer particles (A) can firmly bind the silicon material, and at the same time, the polymer particles (A) expand and contract even if the silicon material expands in volume due to the absorption of lithium. It is considered that this is because the state in which the silicon material is firmly bound can be maintained.

The content of the silicon material in 100% by mass of the active material is preferably 1% by mass or more, more preferably 1 to 50% by mass, further preferably 5 to 45% by mass, and 10% by mass. It is particularly preferable to set the content to 40% by mass. When the content of the silicon material in 100% by mass of the active material is within the above range, an electricity storage device having an excellent balance between improvement in output and energy density of the electricity storage device and charge/discharge durability characteristics can be obtained.

The shape of the active material is preferably granular. The average particle size of the active material is preferably 0.1 to 100 μm, more preferably 1 to 20 μm. Here, the average particle size of the active material is the volume-average particle size calculated from the particle size distribution obtained by measuring the particle size distribution using a particle size distribution analyzer based on the principle of laser diffraction. Examples of such a laser diffraction particle size distribution analyzer include HORIBA LA-300 series and HORIBA LA-920 series (manufactured by HORIBA, Ltd.).

2.2.3. Other Components In addition to the components described above, other components may be added to the electricity storage device electrode slurry according to the present embodiment, if necessary. Such components include, for example, polymers other than the polymer particles (A), thickeners, conductivity-imparting agents, liquid mediums (excluding those brought in from the electricity storage device composition), pH adjusters, Corrosion inhibitors and the like. The polymer and the thickening agent other than the polymer particles (A) can be selected from the compounds exemplified in the above "1.3. Other additives" and used for the same purpose and content ratio. can. Examples of the conductivity imparting agent include compounds described in Japanese Patent No. 5999399 and the like.

<Liquid medium>
The liquid medium that can be additionally added to the electricity storage device electrode slurry according to the present embodiment may be the same as or different from the liquid medium (B) contained in the electricity storage device composition. It is preferable to select and use from among the liquid media exemplified in "1.2. Liquid Medium (B)" above.

The usage ratio of the liquid medium (including the amount brought in from the electricity storage device composition) in the electricity storage device electrode slurry according to the present embodiment is the solid content concentration in the slurry (total mass of components other than the liquid medium in the slurry refers to the proportion of the total mass of the slurry.The same shall apply hereinafter.) is preferably 30 to 70% by mass, more preferably 40 to 60% by mass.

<pH adjuster/corrosion inhibitor>
The electricity storage device electrode slurry according to the present embodiment can contain a pH adjuster or a corrosion inhibitor for the purpose of suppressing corrosion of the current collector depending on the type of active material.

Examples of pH adjusters include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, and potassium hydroxide. Sulfuric acid, ammonium sulfate, sodium hydroxide, potassium hydroxide are preferred. Moreover, it can be used by selecting from among the compounds described in the production method of the polymer particles (A).

Corrosion inhibitors include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, molybdic acid. ammonium, sodium molybdate, potassium molybdate, etc., and among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

2.2.4. Method for Preparing Electricity Storage Device Electrode Slurry The electricity storage device electrode slurry according to the present embodiment can be produced by any method as long as it contains the above-described electricity storage device composition and active material. However, it can be produced, for example, by the method described in Japanese Patent No. 5999399 or the like.

3. Electricity Storage Device Electrode The electricity storage device electrode according to the present embodiment includes a current collector and an active material layer formed by coating and drying the above-described electricity storage device electrode slurry on the surface of the current collector. is. Such an electricity storage device electrode is produced by applying the above electricity storage device electrode slurry to the surface of a current collector such as a metal foil to form a coating film, and then drying the coating film to form an active material layer. can be manufactured. The electricity storage device electrode thus produced has an active material layer containing the polymer particles (A) and the active material, and optional components added as necessary, bound on the current collector. Therefore, it has excellent flexibility and adhesion, and exhibits good charge-discharge durability.

The current collector is not particularly limited as long as it is made of a conductive material.

There is no particular limitation on the method of applying the slurry for the electricity storage device electrode to the current collector, and for example, the method described in Japanese Patent No. 5999399 can be used. The electricity storage device electrode manufactured in this way has excellent flexibility and adhesion, and exhibits good charge/discharge durability.

In the electricity storage device electrode according to the present embodiment, when a silicon material is used as the active material, the content of silicon element in 100 parts by mass of the active material layer is preferably 2 to 30 parts by mass, and 2 to 20 parts by mass. more preferably 3 to 10 parts by mass. When the content of the silicon element in the active material layer is within the above range, the electric storage capacity of the electric storage device manufactured using it is improved, and in addition, an active material layer having a uniform distribution of the silicon element can be obtained. .

In the present invention, the content of silicon element in the active material layer can be measured by the method described in Japanese Patent No. 5999399, for example.

4. Electricity Storage Device The electricity storage device according to the present embodiment includes the electricity storage device electrode described above, further contains an electrolytic solution, and can be manufactured by a conventional method using parts such as a separator. As a specific manufacturing method, for example, the negative electrode and the positive electrode are superimposed with a separator interposed therebetween, and this is placed in a battery container by winding or folding according to the shape of the battery, and the electrolyte is injected into the battery container. A method of sealing by pressing can be exemplified. The shape of the battery can be an appropriate shape such as a coin shape, a cylindrical shape, a square shape, a laminate shape, or the like.

The electrolyte may be in the form of a liquid or a gel, and may be selected from known electrolytes used in electricity storage devices that effectively exhibit the functions of a battery, depending on the type of active material. The electrolytic solution can be a solution of an electrolyte dissolved in a suitable solvent. Examples of these electrolytes and solvents include compounds described in Japanese Patent No. 5999399 and the like.

5. Examples Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. "Parts" and "%" in Examples and Comparative Examples are based on mass unless otherwise specified.

5.1. Example 1
5.1.1. Preparation and Evaluation of Electricity Storage Device Composition (1) Preparation of Electricity Storage Device Composition An electricity storage device composition containing polymer particles (A1) was obtained by two-stage polymerization as shown below. First, in the first-stage polymerization, a reactor was charged with 220 parts by mass of water, 22 parts by mass of a monomer mixture consisting of 8 parts by mass of 1,3-butadiene, 12 parts by mass of styrene, and 2 parts by mass of acrylic acid, and chain transfer 0.1 parts by mass of t-dodecyl mercaptan as an agent, 1 part by mass of sodium alkyldiphenyl ether disulfonate as an emulsifier, and 0.2 parts by mass of potassium persulfate as a polymerization initiator were charged and polymerized at 60° C. for 18 hours while stirring. Then, the reaction was terminated at a polymerization addition rate of 96%. Subsequently, in the second-stage polymerization, 180 parts by mass of water, 18 parts by mass of acrylic acid, 60 parts by mass of acrylamide, and 0.2 parts by mass of potassium persulfate as a polymerization initiator were added to the reactor. After continuing the polymerization reaction at 80° C. for 2 hours, the reaction was terminated. The polymerization addition rate at this time was 98%. Unreacted monomers are removed from the dispersion of the polymer particles (A1) thus obtained, and after concentration, a 10% aqueous sodium hydroxide solution and water are added to obtain 20 mass of the polymer particles (A1). % of pH 9.0 was obtained.

(2) Measurement of number-average particle size One drop of latex obtained by diluting the power storage device composition obtained above to 0.1 wt% was dropped onto the collodion support film with a pipette, and 0.02 wt% of osmium tetroxide was added. One drop of the solution was dropped on the collodion support film with a pipette and air-dried for 12 hours to prepare a sample. The sample prepared in this way was observed using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corporation, model number "H-7650") at a magnification of 10K (magnification), and an image was obtained using the HITACHI EMIP program. Analysis was performed, and the number average particle diameter of 50 randomly selected polymer particles (A1) was calculated to be 100 nm.

(3) Measurement of pH The pH of the electrical storage device composition obtained above was measured at 25°C using a pH meter (manufactured by HORIBA, Ltd.), and was confirmed to be pH 9.0.

(4) Measurement of Viscosity The viscosity of the electric storage device composition obtained above was measured using a Brookfield viscometer at 25° C. and found to be 10,000 mPa·s.

(5) Measurement of Tg The composition for an electricity storage device obtained above was measured using a differential scanning calorimeter (manufactured by NETZSCH, DSC204F1 Phoenix) in accordance with JIS K7121, and the endothermic peak of the polymer (A1) was measured. was observed once at 100°C.

5.1.2. Preparation and evaluation of slurry for electricity storage device electrodes (1) Synthesis of silicon material (active material) A mixture of pulverized silicon dioxide powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was heated to 1100 to 1600. In an electric furnace adjusted to the range of ° C., heat treatment is performed for 10 hours under a nitrogen stream (0.5 NL / min), and oxidation represented by the composition formula SiO _x (x = 0.5 to 1.1) A powder of silicon (average particle size 8 μm) was obtained. 300 g of this silicon oxide powder was placed in a batch heating furnace, and the temperature was raised from room temperature (25° C.) to 1100° C. at a temperature elevation rate of 300° C./h while maintaining a reduced pressure of 100 Pa absolute pressure with a vacuum pump. . Then, while maintaining the pressure in the heating furnace at 2000 Pa and introducing methane gas at a flow rate of 0.5 NL/min, heat treatment (graphite coating treatment) was performed at 1100° C. for 5 hours. After completion of the graphite coating treatment, the powder was cooled to room temperature at a rate of 50° C./h to obtain about 330 g of graphite-coated silicon oxide powder. This graphite-coated silicon oxide is a conductive powder (active material) in which the surface of silicon oxide is coated with graphite, and has an average particle size of 10.5 μm. The ratio of the graphite film was 2% by mass.

(2) Preparation of slurry for electricity storage device electrode 4 parts by mass of polymer (A1) (solid content conversion value, above (Added as a composition for an electricity storage device obtained in ), artificial graphite (manufactured by Hitachi Chemical Co., Ltd., trade name “MAG”), which is highly crystalline graphite as a negative electrode active material, 76 parts by mass (solid content conversion value), 19 parts by mass of the graphite-coated silicon oxide powder obtained above (solid content conversion value) and 1 part by mass of carbon (acetylene black manufactured by Denka Co., Ltd.) as a conductivity imparting agent were added, and the mixture was rotated at 60 rpm to 1 part. Stirring was performed for a period of time to obtain a paste. After adding water to the obtained paste and adjusting the solid content concentration to 48% by mass, a stirring and defoaming machine (manufactured by Thinky Co., Ltd., trade name "Awatori Mixer") was used at 200 rpm for 2 minutes. , 1800 rpm for 5 minutes, and further under reduced pressure (about 2.5×10 ⁴ Pa) under reduced pressure (approximately 2.5×10 4 Pa), by stirring and mixing at 1800 rpm for 1.5 minutes to obtain a power storage device electrode slurry containing 20% by mass of Si in the negative electrode active material ( C/Si (20%)) was prepared.

5.1.3. Production and Evaluation of Electricity Storage Device (1) Production of Electricity Storage Device Electrode (Negative Electrode) On the surface of a current collector made of a copper foil having a thickness of 20 μm, the slurry for an electricity storage device electrode (C/Si (20%)) obtained above was applied. was uniformly applied by a doctor blade method so that the film thickness after drying was 80 μm, dried at 60° C. for 10 minutes, and then dried at 120° C. for 10 minutes. After that, a power storage device electrode (negative electrode) was obtained by pressing with a roll press so that the density of the active material layer was 1.5 g/cm ³ .

(2) Evaluation of Adhesion Strength of Negative Electrode Coating Layer On the surface of the electrode sheet obtained above, 10 cuts were made vertically and horizontally at intervals of 2 mm from the active material layer to the current collector using a knife. I made a grid of cuts. An adhesive tape with a width of 18 mm (manufactured by Nichiban Co., Ltd., trade name “CELLOTAPE” (registered trademark) defined in JIS Z1522) was attached to this cut and immediately peeled off, and the degree of detachment of the active material was visually evaluated. Evaluation criteria are as follows. Table 1 shows the evaluation results.
(Evaluation criteria)
- 5 points: 0 pieces of the active material layer fell off.
- 4 points: 1 to 5 active material layers fell off.
3 points: 6 to 20 active material layers fell off.
2 points: 21 to 40 active material layers fell off.
- 1 point: 41 or more active material layers fell off.

(3) Production of counter electrode (positive electrode) A binder for electrochemical device electrodes (manufactured by Kureha Co., Ltd., product name “KF”) is added to a biaxial planetary mixer (manufactured by Primix Co., Ltd., product name “TK Hibismix 2P-03”). Polymer #1120", hereinafter abbreviated as "PVDF") 4.0 parts by mass (solid content conversion value), conductive aid (manufactured by Denka Co., Ltd., trade name "Denka Black 50% pressed product") 3.0 parts by mass Then, 100 parts by mass of LiCoO ₂ (manufactured by Hayashi Kasei Co., Ltd.) having an average particle size of 5 μm as a positive electrode active material (solid content conversion value) and 36 parts by mass of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 2 hours. rice field. After adding NMP to the obtained paste and adjusting the solid content concentration to 65% by mass, a stirring and defoaming machine (manufactured by Thinky Co., Ltd., trade name "Awatori Mixer") was used at 200 rpm for 2 minutes. , 1,800 rpm for 5 minutes, and further under reduced pressure (about 2.5×10 ⁴ Pa) at 1,800 rpm for 1.5 minutes to prepare a positive electrode slurry. This 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 solvent removal was 80 μm, and the solvent was removed by heating at 120° C. for 20 minutes. . Thereafter, a counter electrode (positive electrode) was obtained by pressing with a roll press so that the density of the active material layer was 3.0 g/cm ³ .

(4) Lithium-ion battery cell assembly In a glove box filled with Ar so that the dew point is -80°C or lower, the negative electrode produced above was punched into a diameter of 15.95 mm and molded into a two-electrode coin cell (Takara Izumi Co., Ltd., trade name "HS Flat Cell"). Next, a separator made of a polypropylene porous film punched to a diameter of 24 mm (manufactured by Celgard Co., Ltd., trade name “Celgard #2400”) was placed, and 500 μL of an electrolytic solution was injected so as not to enter air. A lithium-ion battery cell (electrical storage device) was assembled by placing a punched positive electrode having a diameter of 16.16 mm and sealing the outer body of the bipolar coin cell with screws. 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).

(5) Evaluation of charge-discharge cycle characteristics For the electricity storage device manufactured above, charging was started at a constant current (1.0 C) in a constant temperature bath adjusted to 25 ° C., and the voltage reached 4.2 V. After that, charging was continued at a constant voltage (4.2 V), and charging was completed (cutoff) when the current value reached 0.01C. After that, discharge was started at a constant current (1.0 C), and the discharge was completed (cutoff) when the voltage reached 3.0 V, and the discharge capacity in the first cycle was calculated. In this way, charging and discharging were repeated 100 times. The capacity retention rate was calculated by the following formula and evaluated according to the following criteria. Table 1 shows the evaluation results.
Capacity retention (%) = (discharge capacity at 100th cycle)/(discharge capacity at 1st cycle)
(Evaluation criteria)
- 5 points: Capacity retention is 95% or more.
・4 points: Capacity retention rate is 90% or more and less than 95%.
- 3 points: Capacity retention is 85% or more and less than 90%.
2 points: Capacity retention rate is 80% or more and less than 85%.
- 1 point: Capacity retention is 75% or more and less than 80%.
- 0 point: Capacity retention rate is less than 75%.

In the measurement conditions, "1 C" indicates a current value at which discharge is completed in 1 hour when a cell having a certain electric capacity is discharged at a constant current. For example, "0.1 C" means a current value at which discharge is completed in 10 hours, and "10 C" means a current value at which discharge is completed in 0.1 hour.

5.2. Examples 2-26, Comparative Examples 1-10
Preparation and evaluation of power storage device composition (1) Preparation of power storage device composition” above, the type and amount of each monomer are described in Table 1 or Table 2 below, respectively. A composition for an electric storage device containing 20% by mass of the polymer component was obtained in the same manner as above, except that the above was carried out. In this specification, the polymer particles (A) obtained in Example 1 are referred to as "polymer particles (A1)", and similarly, the polymer particles (A) obtained in Example 5 are referred to as "polymer particles (A1)". The polymer particles (A) obtained in Example 19 are referred to as "polymer particles (A5)", and the polymer particles (A19) are referred to as "polymer particles (A19)". Further, the polymer particles obtained in Comparative Example 1 are referred to as "polymer particles (B1)", and similarly, the polymer particles obtained in Comparative Example 9 are referred to as "polymer particles (B9)" and the like. do.

Furthermore, in the same manner as in Example 1 above except that the composition for an electricity storage device prepared above was used, an electricity storage device electrode slurry was prepared, an electricity storage device electrode and an electricity storage device were produced, respectively, and an electricity storage device electrode and an electricity storage device were prepared. was evaluated similarly.

5.3. Example 32
In the same manner as in Example 5, a composition for an electricity storage device having a pH of 9.0 and containing 20% by mass of polymer particles (A5) was obtained. Next, in a biaxial planetary mixer (manufactured by Primix Co., Ltd., trade name "TK Hibismix 2P-03"), 1 mass of a thickener (trade name "CMC2200", manufactured by Daicel Co., Ltd.) is added as a pre-added component. part (solid content conversion value, added as an aqueous solution having a concentration of 2% by mass), 1 part by mass of the polymer particles (A5) (solid content conversion value, containing 20% by mass of the polymer particles (A5) obtained above 76 parts by mass of artificial graphite (manufactured by Hitachi Chemical Co., Ltd., trade name “MAG”), which is highly crystalline graphite as a negative electrode active material (added as a composition for an electricity storage device with a pH of 9.0) (solid content conversion value) , 19 parts by mass of the graphite-coated silicon oxide powder obtained above (solid content conversion value) and 1 part by mass of carbon (Acetylene Black manufactured by Denka Co., Ltd.) as a conductivity imparting agent were added, and the mixture was spun at 60 rpm for 1 hour. Stirring was performed for hours. Next, SBR (trade name “TRD105A”, manufactured by JSR Corporation) was added as a post-addition component in an amount corresponding to 2 parts by mass (solid content conversion value), and the mixture was further stirred for 1 hour to obtain a paste. After adding water to the obtained paste and adjusting the solid content concentration to 48% by mass, a stirring and defoaming machine (manufactured by Thinky Co., Ltd., trade name "Awatori Mixer") was used at 200 rpm for 2 minutes. , 1800 rpm for 5 minutes, and further under reduced pressure (about 2.5×10 ⁴ Pa) under reduced pressure (approximately 2.5×10 4 Pa), by stirring and mixing at 1800 rpm for 1.5 minutes to obtain a power storage device electrode slurry containing 20% by mass of Si in the negative electrode active material ( C/Si (20%)) was prepared.

An electricity storage device electrode and an electricity storage device were produced in the same manner as in Example 1 except that the electricity storage device electrode slurry prepared above was used, and evaluated in the same manner as in Example 1 above.

5.4. Examples 27-31, 33, Comparative Examples 11-17
A power storage device electrode slurry was prepared in the same manner as in Example 32 except that the composition of the power storage device electrode slurry was changed as shown in Table 3 below, and power storage device electrodes and power storage devices were produced. 32 was evaluated in the same manner.

5.5. Evaluation Results Tables 1 to 3 below summarize the compositions, physical properties, and evaluation results of the polymers used in Examples 1 to 33 and Comparative Examples 1 to 17.

The abbreviations of the monomers in Tables 1 to 3 represent the following compounds, respectively.
<Conjugated diene compound>
・ BD: 1,3-butadiene <unsaturated carboxylic acid>
・ TA: itaconic acid ・ AA: acrylic acid ・ MAA: methacrylic acid <(meth)acrylamide>
・AAM: acrylamide ・MAM: methacrylamide <unsaturated carboxylic acid ester having a hydroxyl group>
・HEMA: 2-hydroxyethyl methacrylate ・HEA: 2-hydroxyethyl acrylate <unsaturated carboxylic acid ester>
・MMA: methyl methacrylate ・EDMA: ethylene glycol dimethacrylate ・2EHA: 2-ethylhexyl acrylate <α, β-unsaturated nitrile compound>
・AN: acrylonitrile <aromatic vinyl compound>
・ST: styrene ・DVB: divinylbenzene <compound having a sulfonic acid group>
・NASS: sodium styrene sulfonate

In Comparative Example 3 and Comparative Example 4 in Table 2 above, "-" in the number average particle size column indicates that the polymer dissolved in water and did not develop a particle shape, so the particle size was Indicates that the measurement was not possible.

As is clear from the above Tables 1 and 2, the electricity storage device electrode slurries prepared using the electricity storage device compositions according to the present invention shown in Examples 1 to 26 were obtained in Comparative Examples 1 to 10. It was found that active materials that undergo a large volume change during charging and discharging can be preferably bound to each other, and that the adhesion between the active material layer and the current collector can be maintained satisfactorily. As a result, despite repeated charging and discharging and repeated expansion and contraction of the volume of the active material, an electricity storage device electrode that can suppress the peeling of the active material layer and can continue to maintain good charge and discharge characteristics. Got. It was also found that an electricity storage device (lithium ion secondary battery) provided with these electricity storage device electrodes has good charge/discharge rate characteristics. The reason for this is that the electricity storage device electrodes according to Examples 1 to 26 shown in Tables 1 and 2 above reduce the film thickness change of the active material layer due to charge and discharge compared to Comparative Examples 1 to 10. It is presumed that this is because the conductive network inside the active material layer can be maintained.

Further, as is clear from the results in Table 3 above, the electricity storage device electrode slurries prepared using the electricity storage device compositions according to the present invention shown in Examples 27 to 33 were obtained in Comparative Examples 11 to 17. Compared to , even if a thickener or other polymer is used in combination, active materials with large volume changes due to charging and discharging can be suitably bound to each other, and the active material layer and the current collector adhere to each other. It was found that the properties can be maintained well.

The present invention is not limited to the above embodiments, and various modifications are possible. The present invention includes configurations substantially the same as the configurations described in the embodiments (for example, configurations with the same function, method and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential portions of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention also includes a configuration that achieves the same effects or achieves the same purpose as the configurations described in the above embodiments. Furthermore, the present invention also includes configurations obtained by adding known techniques to the configurations described in the above embodiments.

Claims (10)

containing polymer particles (A) and a liquid medium (B),
The polymer particles (A) have a number average particle diameter of 50 nm or more and 500 nm or less,
When the total number of repeating units contained in the polymer particles (A) is 100 parts by mass, the polymer particles (A) are
1 to 50 parts by mass of repeating units (a1) derived from a conjugated diene compound;
5 to 90 parts by mass of repeating units (a2) derived from an unsaturated carboxylic acid;
(Meth) containing 5 to 90 parts by mass of repeating units (a3) derived from acrylamide,
A composition for an electricity storage device, wherein the total amount of the repeating unit (a2) and the repeating unit (a3) is 50 parts by mass or more. The composition for an electricity storage device according to claim 1, which has a pH of 6 to 11. 3. The composition for an electricity storage device according to claim 1, wherein a 5% by mass aqueous dispersion of the polymer particles (A) has a viscosity at pH 9 of 500 to 150,000 mPa·s. The composition for an electricity storage device according to any one of claims 1 to 3, wherein the liquid medium (B) is water. An electricity storage device electrode slurry containing the electricity storage device composition according to claim 1 and an active material. 6. The electricity storage device electrode slurry according to claim 5, containing a silicon material as said active material. 7. The electricity storage device electrode slurry according to claim 5, further comprising at least one polymer selected from the group consisting of styrene-butadiene copolymers, acrylic polymers and fluoropolymers. The slurry for an electricity storage device electrode according to any one of claims 5 to 7, further comprising a thickener. An electricity storage device comprising: a current collector; and an active material layer formed by coating and drying the slurry for an electricity storage device electrode according to any one of claims 5 to 8 on the surface of the current collector. device electrode. An electricity storage device comprising the electricity storage device electrode according to claim 9 .