JP6828782B1 - Composition for power storage device, slurry for power storage device electrode, power storage device electrode, and power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for a power storage device capable of producing a power storage device electrode having excellent flexibility and adhesion and exhibiting good charge / discharge durability characteristics. A composition for a power storage device according to the present invention contains a polymer (A) and a liquid medium (B), and the total of repeating units contained in the polymer (A) is 100 mass by mass. When the parts are taken as parts, the polymer (A) has 5 to 90 parts by mass of the repeating unit (a1) represented by the following structural formula (1) and 5 to 90 parts by mass of the repeating unit (a2) derived from the unsaturated carboxylic acid. It contains 90 parts by mass and 5 to 90 parts by mass of a repeating unit (a3) derived from (meth) acrylamide, and the solubility of the polymer (A) in water at 25 ° C. and 1 atm is 100 g of water. On the other hand, it is 1 g or more. [Selection diagram] None

Description

The present invention includes a composition for a power storage device, a slurry for a power storage device electrode containing the composition and an active material, a power storage device electrode formed by applying and drying the slurry to a current collector, and the electrode. Regarding storage devices.

In recent years, a power storage device having a high voltage and a high energy density has been required as a power source for driving an electronic device. As such a power storage device, a lithium ion battery, a lithium ion capacitor, and the like are expected.

An electrode used in such a power storage device is usually manufactured by applying a composition (slurry for an electrode) containing an active material and a polymer functioning as a binder to the surface of a current collector and drying it. To. The properties required for the polymer used as a binder include the ability to bond the active materials to each other, the ability to adhere the active material to the current collector, the abrasion resistance in the process of winding the electrodes, and the subsequent cutting. Examples include powder drop resistance in which fine powder of the active material does not fall off from the coated / dried composition coating film (hereinafter, also referred to as “active material layer”).

It has been empirically clarified that the quality of the performance is almost proportional to the binding ability between the active materials, the adhesion ability between the active material and the current collector, and the powder drop resistance. Therefore, in the present specification, these may be comprehensively expressed by using the term “adhesion” below.

In recent years, from the viewpoint of meeting the demands for high output and high energy density of power storage devices, studies on using a material having a large lithium occlusion as an active material have been promoted. For example, as disclosed in Patent Document 1, a method of utilizing a silicon material having a maximum theoretical occlusion of lithium of about 4,200 mAh / g as an active material is promising.

However, an active material using such a material having a large amount of lithium occlusion is accompanied by a large volume change due to the occlusion and release of lithium. For this reason, when a conventionally used electrode binder is applied to such a material having a large lithium occlusion, the active material cannot be maintained and the active material is peeled off, which is remarkable with charging and discharging. The capacity is reduced.

As a technique for improving the adhesion of the binder for the electrode, a technique for controlling the surface acid amount of the particulate binder particles (see Patent Documents 2 and 3) and a binder having an epoxy group or a hydroxy group are used as described above. Techniques for improving the characteristics (see Patent Documents 4 and 5) and the like have been proposed. Further, a technique has been proposed in which the active material is bound by the rigid molecular structure of polyimide to suppress the volume change of the active material (see Patent Document 6). Further, a technique using a water-soluble polymer such as polyacrylic acid (see Patent Documents 7 and 8) has also been proposed.

Japanese Unexamined Patent Publication No. 2004-185810 International Publication No. 2011/096463 International Publication No. 2013/191080 Japanese Unexamined Patent Publication No. 2010-205722 Japanese Unexamined Patent Publication No. 2010-3703 Japanese Unexamined Patent Publication No. 2011-204592 JP-A-2007-294323 International Publication No. 2018/070423

However, as the binder for electrodes as disclosed in Patent Documents 1 to 8, a new active material typified by a silicon material having a large amount of lithium occlusion and a large volume change accompanying the occlusion / release of lithium is practically used. It could not be said that the adhesion was sufficient for the conversion. When such an electrode binder is used, the electrode deteriorates due to the active material falling off due to repeated charging and discharging, so that there is a problem that the durability required for practical use cannot be sufficiently obtained.

Therefore, some aspects of the present invention provide a composition for a power storage device capable of producing a power storage device electrode which is excellent in flexibility and adhesion and exhibits good charge / discharge durability characteristics. In addition, some aspects of the present invention provide a slurry for a power storage device electrode containing the composition. Further, some aspects of the present invention provide a power storage device electrode which is excellent in adhesion and exhibits good charge / discharge durability characteristics. Further, some aspects of the present invention provide a power storage device having excellent charge / discharge durability characteristics.

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

One aspect of the composition for a power storage device according to the present invention is
Containing the polymer (A) and the liquid medium (B),
When the total of the repeating units contained in the polymer (A) is 100 parts by mass, the polymer (A) becomes
5 to 90 parts by mass of the repeating unit (a1) represented by the following structural formula (1),
5 to 90 parts by mass of repeating unit (a2) derived from unsaturated carboxylic acid,
It contains 5 to 90 parts by mass of a repeating unit (a3) derived from (meth) acrylamide.
The solubility of the polymer (A) in water at 25 ° C. and 1 atm is 1 g or more with respect to 100 g of water.

In one aspect of the composition for a power storage device,
The viscosity of the 10% by mass aqueous solution of the polymer (A) at pH 9 can be 500 to 150,000 mPa · s / 30 rpm.

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

One aspect of the slurry for power storage device electrodes according to the present invention is
The composition for a power storage device according to any one of the above embodiments and an active material are contained.

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

In any aspect of the storage device electrode slurry,
It can 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 storage device electrode slurry,
Thickeners can be further included.

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

One aspect of the power storage device according to the present invention is
The storage device electrode of the above-described embodiment is provided.

According to the composition for a power storage device according to the present invention, since flexibility and adhesion can be improved, a power storage device electrode exhibiting good charge / discharge durability characteristics can be manufactured. The composition for a power storage device according to the present invention exerts the above-mentioned effect particularly when the power storage device electrode contains a material having a large lithium occlusion as an active material, for example, a carbon material such as graphite or a silicon material. That is, since a material having a large lithium occlusion can be used as the active material, the battery performance is also improved.

Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be noted that the present invention is not limited to the embodiments described below, but should be understood to include various modifications implemented without changing the gist of the present invention.

In addition, "(meth) acrylic acid-" in this specification is a concept including 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, the numerical range described by using "~" means that the numerical values described before and after "~" are included as the lower limit value and the upper limit value.

1. 1. Composition for power storage device The composition for power storage device according to the embodiment of the present invention contains a polymer (A) and a liquid medium (B). The composition for a power storage device according to the present embodiment is for producing a power storage device electrode (active material layer) having improved binding ability between active materials, adhesion ability between the active material and a current collector, and powder drop resistance. It can be used as a material, or it can be used as a material for forming a protective film for suppressing a short circuit caused by dendrites generated during charging and discharging.

Hereinafter, each component contained in the composition for a power storage device according to the present embodiment will be described in detail.

1.1. Polymer (A)
The composition for a power storage device according to this embodiment contains a polymer (A). The polymer (A) is a repeating unit (a1) represented by the following structural formula (1) when the total of the repeating units contained in the polymer (A) is 100 parts by mass (hereinafter, simply "repeated"). Unit (a1) ”) 5 to 90 parts by mass, and repeating unit (a2) derived from unsaturated carboxylic acid (hereinafter, also simply referred to as“ repeating unit (a2) ”) 5 to 90 parts by mass. It contains 5 to 90 parts by mass of a repeating unit (a3) derived from (meth) acrylamide (hereinafter, also simply referred to as “repeating unit (a3)”). Further, the polymer (A) may contain a repeating unit derived from another monomer copolymerizable therewith, in addition to the repeating unit. Hereinafter, the repeating unit constituting the polymer (A), the physical properties of the polymer (A), and the method for synthesizing the polymer (A) will be described in this order.

1.1.1. Repeating unit constituting the polymer (A) 1.1.1.1. Repeat unit (a1) represented by structural formula (1)
The polymer (A) contains a repeating unit represented by the following structural formula (1).

The content ratio of the repeating unit (a1) represented by the structural formula (1) is 5 to 90 parts by mass when the total of the repeating units contained in the polymer (A) is 100 parts by mass. The lower limit of the content ratio of the repeating unit (a1) is preferably 7 parts by mass, more preferably 10 parts by mass. The upper limit of the content ratio of the repeating unit (a1) is preferably 85 parts by mass, more preferably 80 parts by mass. When the polymer (A) contains the repeating unit (a1) in the above range, the dispersibility of the active material and the filler is improved. Further, it is considered that a high capacity can be maintained because the current collector, the active material, and the active material can be firmly bonded to each other and the peeling of the mixture layer due to repeated charging and discharging can be suppressed.

The polymer having a repeating unit represented by the above structural formula (1) is, for example, a copolymer obtained by copolymerizing a vinyl ester with another monomer copolymerizable as needed. It can be obtained by saponification in a mixed solvent of an aqueous organic solvent and water in the presence of an alkali containing an alkali metal. That is, vinyl alcohol itself is unstable and cannot be used directly as a monomer, but by saponifying the polymer obtained by using vinyl ester as a monomer, the resulting polymer is vinyl. It is an embodiment in which alcohol is polymerized as a monomer.

Examples of the vinyl ester include vinyl acetate, vinyl propionate, vinyl pivalate and the like, but vinyl acetate is preferable because the saponification reaction easily proceeds. One of these vinyl esters may be used alone, or two or more thereof may be used in combination.

1.1.1.2. Repeating unit derived from unsaturated carboxylic acid (a2)
The content ratio of the repeating unit (a2) derived from the unsaturated carboxylic acid is 5 to 90 parts by mass when the total of the repeating units contained in the polymer (A) is 100 parts by mass. The lower limit of the content ratio of the repeating unit (a2) is preferably 7 parts by mass, more preferably 10 parts by mass. The upper limit of the content ratio of the repeating unit (a2) is preferably 85 parts by mass.
More preferably, it is 80 parts by mass. When the polymer (A) contains the repeating unit (a2) in the above range, the dispersibility of the active material and the filler is improved. Furthermore, it has a high affinity with the silicon material and exhibits good charge / discharge durability characteristics by suppressing the swelling of the silicon material.

The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. , One or more selected from these can be used. Among these, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

1.1.1.3. Repeating unit derived from (meth) acrylamide (a3)
The content ratio of the repeating unit (a3) derived from (meth) acrylamide is 5 to 90 parts by mass when the total of the repeating units contained in the polymer (A) is 100 parts by mass. The lower limit of the content ratio of the repeating unit (a3) is preferably 7 parts by mass, more preferably 10 parts by mass. The upper limit of the content ratio of the repeating unit (a3) is preferably 85 parts by mass, more preferably 80 parts by mass. When the polymer (A) contains the repeating unit (a3) in the above range, the dispersibility of the active material and the filler is improved. In addition, the flexibility of the obtained active material layer becomes appropriate, and the adhesion between the current collector and the active material layer becomes good. Further, since the bonding ability between the active materials containing the carbon material such as graphite and the silicon material can be enhanced, an active material layer having better flexibility and adhesion to the current collector can be obtained.

The (meth) acrylamide is not particularly limited, but is limited to acrylamide, methacrylamide, N-isopropylacrylamide, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-diacetoneacrylamide, N, N-diethylmethacryl. Examples thereof include amide, N, N-dimethylaminopropylacrylamide, N, N-dimethylaminopropyl methacrylamide, N-methylol methacrylamide, N-methylol acrylamide, diacetone acrylamide, maleic acid amide, acrylamide tert-butyl sulfonic acid and the like. , One or more selected from these can be used.

1.1.1.4. Other Repeating Units The polymer (A) may contain repeating units derived from other monomers copolymerizable with the repeating units (a1) to (a3). Such repeating units include a repeating unit (a4) derived from an unsaturated carboxylic acid ester (hereinafter, also simply referred to as “repeating unit (a4)”) and a repeating unit (a5) derived from a compound having a sulfonic acid group. ) (Hereinafter, also simply referred to as "repeating unit (a5)"), a repeating unit derived from a cationic monomer, and the like.

<Repeating unit derived from unsaturated carboxylic acid ester (a4)>
When the polymer (A) contains a repeating unit (a4) derived from an unsaturated carboxylic acid ester, the content ratio of the repeating unit (a4) is 100 mass by mass of the total of the repeating units contained in the polymer (A). In terms of parts, it is preferably 0 to 30 parts by mass. The lower limit of the content ratio of the repeating unit (a4) is preferably 3 parts by mass, more preferably 5 parts by mass. The upper limit of the content ratio of the repeating unit (a4) is preferably 25 parts by mass, more preferably 20 parts by mass. When the polymer (A) contains the repeating unit (a4) in the above range, the affinity between the polymer (A) and the electrolytic solution is improved, and the binder becomes an electric resistance component in the power storage device. In addition to suppressing the increase in resistance, it may be possible to prevent a decrease in adhesion due to excessive absorption of the electrolytic solution.

Among unsaturated carboxylic acid esters, (meth) acrylic acid ester can be preferably used. Specific examples of the (meth) acrylic acid ester include, for example, methyl (meth) acrylic acid, ethyl (meth) acrylic acid, n-propyl (meth) acrylic acid, isopropyl (meth) acrylic acid, and n (meth) acrylic acid. -Butyl, isobutyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, ( N-octyl acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylol propane tri (meth) acrylate, Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, allyl (meth) acrylate, 2-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylic 2-Hydroxypropyl acid, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, glycerin mono (meth) ) Acrylic, glycerinji (meth) acrylate and the like can be mentioned, and one or more selected from these can be used. Among these, one or more selected from methyl (meth) acrylate, ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate is preferable. It is particularly preferable that it is 2-hydroxyethyl acrylate.

<Repeating unit (a5) derived from a compound having a sulfonic acid group>
When the polymer (A) contains a repeating unit (a5) derived from a compound having a sulfonic acid group, the content ratio of the repeating unit (a5) is 100, which is the total of the repeating units contained in the polymer (A). In terms of parts by mass, it is preferably 0 to 30 parts by mass. The lower limit of the content ratio of the repeating unit (a5) is preferably 3 parts by mass, and more preferably 5 parts by mass. The upper limit of the content ratio of the repeating unit (a5) is preferably 27 parts by mass, more preferably 25 parts by mass.

The compound having a sulfonic acid group is not particularly limited, but is vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, sulfobutyl (meth) acrylate, 2-acrylamide-2. -Methylpropanesulfonic acid, 2-hydroxy-3-acrylamidepropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, alkali salts thereof and the like can be mentioned, and one or more selected from these should be used. Can be done.

<Repeating unit derived from cationic monomer>
The polymer (A) may contain a repeating unit derived from a cationic monomer. The cationic monomer is not particularly limited, but is at least one monomer selected from the group consisting of a secondary amine (salt), a tertiary amine (salt) and a quaternary ammonium salt. Is preferable. Specific examples of these cationic monomers are not particularly limited, but are 2- (dimethylamino) ethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate methyl quaternary chloride quaternary salt, and 2- (meth) acrylate. Ethyl (diethylamino), 3- (dimethylamino) propyl (meth) acrylate, 3- (diethylamino) propyl (meth) acrylate, 4- (dimethylamino) phenyl (meth) acrylate, 2- (meth) acrylate [(3,5-Dimethylpyrazolyl) carbonylamino] ethyl, 2- (meth) acrylate 2- (0- [1'-methylpropylideneamino] carboxyamino) ethyl, 2- (1-aziridinyl) (meth) acrylate Ethyl, metacloylcholine chloride, tris isocyanurate (2-acryloyloxyethyl), 2-vinylpyridine, quinaldine red, 1,2-di (2-pyridyl) ethylene, 4'-hydrazino-2-stilbazole dihydrochloride water Japanese product, 4- (4-dimethylaminostyryl) quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichloromid, 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-hepten-4-) Inyl) -N-methyl-1-naphthylmethylamine hydrochloride and the like can be mentioned, and one or more selected from these can be used.

1.1.2. Physical characteristics of polymer (A) 1.1.2.1. Solubility in water Polymer (A) is a water-soluble polymer. When the polymer (A) is a water-soluble polymer, the surface of the active material is easily coated by the polymer (A). As a result, expansion of the active material during charging / discharging can be suppressed, so that it is easy to obtain a power storage device exhibiting good charge / discharging durability characteristics. The "water-soluble polymer" in the present invention refers to a polymer having a solubility in water at 25 ° C. and 1 atm of 1 g or more with respect to 100 g of water.

11.2.2. Viscosity When the viscosity of an aqueous solution of the polymer (A) having a solid content concentration of 10% and pH 9 is measured at a temperature of 25 ° C. using a B-type viscometer, it is preferably 500 to 150,000 mPa · s / 30 rpm, and more. It is preferably 1,000 to 150,000 mPa · s / 30 rpm, and particularly preferably 2,000 to 150,000 mPa · s / 30 rpm. When the viscosity of the aqueous solution of the polymer (A) is within the above range, the dispersibility of the active material and the filler becomes good, and a homogeneous active material layer and a protective film can be easily produced. As a result, an electrode or the like without structural defects can be obtained, which is preferable because it exhibits good charge / discharge characteristics. This viscosity measurement can be measured in accordance with JIS Z 8803. As the B-type viscometer, for example, "RB-80L" and "TVB-10" manufactured by Toki Sangyo Co., Ltd. can be used.

11.2.3. Weight average molecular weight (Mw)
The weight average molecular weight (Mw) of the polymer (A) is preferably 10,000 or more and 2,000,000 or less, more preferably 30,000 or more and 1,500,000 or less, and particularly preferably 50. It is 000 or more and 1,000,000 or less. When the weight average molecular weight (Mw) of the polymer (A) is within the above range, the adhesion is good and it is easy to obtain a power storage device having excellent charge / discharge characteristics.

1.1.3. Method for synthesizing polymer (A) As a method for synthesizing polymer (A), there are mainly two types of synthesis methods. Hereinafter, each synthesis method will be described.

<First synthesis method>
As a first method for synthesizing the polymer (A), vinyl acetate is homopolymerized to obtain polyvinyl acetate, and then polyvinyl acetate is saponified to obtain polyvinyl alcohol, which is necessary for the obtained polyvinyl alcohol. Examples thereof include a method of graft-copolymerizing a monomer.

As a method for polymerizing polyvinyl acetate, any method such as bulk polymerization or solution polymerization can be used. Examples of the initiator used for the polymerization of polyvinyl acetate include azo-based initiators such as azobisisobutyronitrile and organic peroxides such as benzoyl peroxide and bis (4-tert-butylcyclohexyl) peroxydicarbonate. Things etc. can be mentioned.

The saponification reaction of polyvinyl acetate can be carried out, for example, by a method of saponification in an organic solvent in the presence of a saponification catalyst.

Examples of the organic solvent include methanol, ethanol, propanol, ethylene glycol, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, benzene, toluene and the like. These may be used alone or in combination of two or more. Of these, methanol is preferred.

Examples of the saponification catalyst include basic catalysts such as sodium hydroxide, potassium hydroxide and sodium alkoxide, and acidic catalysts such as sulfuric acid and hydrochloric acid. Of these, sodium hydroxide is preferable from the viewpoint of saponification rate.

The method of graft-copolymerizing the monomer required for polyvinyl alcohol can be carried out by solution polymerization. Examples of the solvent used include water, dimethyl sulfoxide, N-methylpyrrolidone and the like.

As the initiator used for the graft copolymerization, for example, an organic peroxide such as benzoyl peroxide, an azo compound such as azobisisobutyronitrile, potassium peroxodisulfate, ammonium peroxodisulfate and the like can be used.

The graft copolymer thus synthesized is a copolymer in which side branches of a polymer composed of necessary monomers are formed on the main chain of polyvinyl alcohol. In addition to the graft copolymer (that is, the polymer (A)), the composition for a power storage device according to the present embodiment includes only a polyvinyl alcohol homopolymer and other monomers that are not involved in the graft copolymerization. A polymer composed of the same may be mixed.

When the composition for a power storage device according to the present embodiment contains the above-mentioned graft copolymer, the binding property with the negative electrode active material and the current collector is improved. Therefore, by using a slurry for a negative electrode containing this composition for a power storage device, a lithium ion secondary battery having excellent cycle characteristics and rate characteristics, and an electrode (negative electrode) from which such a lithium ion secondary battery can be obtained can be obtained. It becomes possible to manufacture. Therefore, the composition for a power storage device in this embodiment is suitable for a lithium ion secondary battery.

Further, by using a positive electrode slurry containing this composition for a power storage device, a lithium ion secondary battery using a high potential positive electrode active material and having excellent cycle characteristics and rate characteristics, and such a lithium ion secondary battery It is possible to obtain an electrode (positive electrode) from which a battery can be obtained. Therefore, the composition for a power storage device according to the present embodiment is suitable for a lithium ion secondary battery.

<Second synthesis method>
As a second method for synthesizing the polymer (A), there is a method of saponifying the copolymer after obtaining a copolymer of a vinyl ester and a necessary monomer.

Since the copolymer of the vinyl ester and the required monomer is obtained in the form of powder, the vinyl ester and the required monomer are polymerized in a suspended state in an aqueous solution containing a polymerization catalyst and a dispersant. It is preferably obtained by a suspension polymerization method using polymer particles.

Examples of the polymerization catalyst include organic peroxides such as benzoyl peroxide and lauryl peroxide, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. Of these, lauryl peroxide is particularly preferable.

The amount of the polymerization catalyst added is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and particularly preferably 0, based on 100 parts by mass of the total mass of the monomer. 1 to 3 parts by mass. When the amount of the polymerization catalyst added is within the above range, the polymerization reaction can proceed smoothly, and the binding force of the obtained polymer (A) may be improved.

The dispersant for carrying out the polymerization can be appropriately selected depending on the type and amount of the monomer used. Examples of such a dispersant include polyvinyl alcohol (partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol), poly (meth) acrylic acid and salts thereof, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose. Such as water-soluble polymers; water-insoluble inorganic compounds such as calcium phosphate and magnesium silicate can be mentioned. These dispersants may be used alone or in combination of two or more.

The amount of the dispersant used depends on the type of the monomer used and the like, but is preferably 0.01 to 10 parts by mass, more preferably 0, with respect to 100 parts by mass of the total mass of the monomer. It is 05 to 5 parts by mass.

Further, a water-soluble salt such as an alkali metal salt or an alkaline earth metal salt can be added in order to adjust the surface active action of the dispersant. Examples of such water-soluble salts include sodium chloride, potassium chloride, calcium chloride, lithium chloride, anhydrous sodium sulfate, potassium sulfate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, trisodium phosphate, and trisodium phosphate. Examples include potassium, and one or more of these can be used.

The amount of the water-soluble salt used depends on the type and amount of the dispersant used, but is usually 0.01 to 10% by mass based on 100% by mass of the total mass of the dispersant aqueous solution.

In the second synthesis method, the temperature at which the monomer is polymerized is preferably -20 to + 20 ° C., more preferably -10 to + 10 ° C., relative to the 10-hour half-life temperature of the polymerization catalyst. For example, the 10-hour half-life temperature of lauryl peroxide is about 62 ° C.

In the second synthesis method, the time for polymerizing the monomer is usually several hours to several tens of hours, although it depends on the type and amount of the polymerization catalyst used, the polymerization temperature and the like.

After completion of the polymerization reaction, the synthesized copolymer is separated by a method such as centrifugation or filtration to obtain a hydrous cake. The obtained hydrous cake-like copolymer can be used as it is or, if necessary, dried and used for the saponification reaction.

The weight average molecular weight of the copolymer before saponification thus obtained is preferably 10,000 to 10,000,000, more preferably 50,000 to 5,000,000. By keeping the weight average molecular weight of the copolymer before saponification within the above range, the binding force tends to be further improved. Therefore, even if the electrode mixture is a slurry, the slurry can be easily applied thickly.

The saponification reaction can be carried out, for example, in the presence of an alkali containing an alkali metal, only in an aqueous organic solvent, or in a mixed solvent of an aqueous organic solvent and water. As the alkali containing an alkali metal used in the saponification reaction, known alkalis can be used, but alkali metal hydroxide is preferable, and sodium hydroxide and potassium hydroxide are selected from the viewpoint of high reactivity. Especially preferable.

The amount of the alkali is preferably 60 to 140 mol%, more preferably 80 to 120 mol%, based on 100 mol% of the total number of moles of the monomer.

For the saponification reaction, it is preferable to use only an aqueous organic solvent or a mixed solvent of an aqueous organic solvent and water. Examples of the aqueous organic solvent include methanol, ethanol, n-propanol, and the like.
Lower alcohols such as isopropanol, n-butanol, tert-butanol; ketones such as acetone and methyl ethyl ketone; and mixtures thereof. Among these, lower alcohols are preferable, and methanol and ethanol are more preferable because a polymer (A) having an excellent binding effect and excellent resistance to mechanical shear can be obtained.

The mass ratio of the solvent used in the saponification reaction to the aqueous organic solvent and water (aqueous organic solvent: water) is preferably 2: 8 to 10: 0, more preferably 3: 7 to 8: 2. is there. When the mass ratio is within the above range, the solvent affinity of the copolymer before saponification and the solvent affinity of the copolymer after saponification are excellent, and the saponification reaction may proceed smoothly. is there. In addition, the binding force of the obtained polymer (A) may be improved.

In the second synthesis method, the temperature at which the copolymer is saponified is preferably 20 to 80 ° C, more preferably 20 to 60 ° C, although it depends on the molar ratio of the monomers. When the temperature for saponification is within the above range, the saponification reaction can proceed smoothly, and the occurrence of side reactions such as a decrease in molecular weight due to alkali may be suppressed.

The time of the saponification reaction varies depending on the type and amount of alkali used, but the reaction is usually completed in about several hours.

When the saponification reaction is completed, it usually becomes a dispersion of a paste or slurry-like copolymer saponified product. By solid-liquid separation by a conventionally known method such as centrifugation or filtration, and drying the liquid-containing copolymer saponified product obtained by thoroughly washing with a lower alcohol such as methanol, spherical single particles or spherical particles are aggregated. A copolymer saponified product, that is, a polymer (A) can be obtained as the aggregated particles.

The conditions for drying the liquid-containing copolymer saponified product are usually preferably at a temperature of 30 to 120 ° C. under normal pressure or reduced pressure.

The drying time is usually several hours to several tens of hours, although it depends on the pressure and temperature at the time of drying.

1.2. Liquid medium (B)
The composition for a power storage device according to the present embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium may contain a non-aqueous medium other than water. Examples of such a non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these can be used. can do. By using an aqueous medium as the liquid medium (B) in the composition for a power storage device according to the present embodiment, the degree of adverse effect on the environment is reduced, and the safety for the handling operator is also increased.

The content ratio 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, and particularly preferably not substantially contained in 100 parts by mass of the aqueous medium. preferable. Here, "substantially free" means that a non-aqueous medium is not intentionally added as a liquid medium, and the non-aqueous medium inevitably mixed in when producing a composition for a power storage device. May include.

1.3. Other Additives The composition for a power storage device according to the present embodiment may contain additives other than the above-mentioned components, if necessary. Examples of such additives include polymers other than the polymer (A), preservatives, thickeners, and the like.

<Polymer other than polymer (A)>
The composition for a power storage device according to the present embodiment may contain a polymer other than the polymer (A). Such polymers are not particularly limited, but include SBR (styrene butadiene rubber) -based polymers, unsaturated carboxylic acid esters, acrylic polymers containing these derivatives as constituent units, PVDF (polyvinylidene fluoride), and the like. Fluorine-based polymers and the like can be mentioned. These polymers may be used alone or in combination of two or more. By containing a polymer other than the polymer (A), flexibility and adhesion may be further improved.

<Preservative>
The composition for a power storage device according to the present embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold and the like to generate foreign substances when the composition for a power storage device is stored. Examples of the preservative include compounds described in Japanese Patent No. 5999399.

<Thickener>
The composition for a power storage device according to the present embodiment may contain a thickener. By containing the thickener, the coatability thereof and the charge / discharge characteristics of the obtained power storage device may be further improved.

Examples of such a thickener 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 alcohols, modified polyvinyl alcohols, and ethylene-vinyl alcohol copolymers; copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, and fumaric acid and vinyl esters. Examples thereof include water-soluble polymers such as saponified products. Among these, alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly (meth) acrylic acid and the like are preferable.

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

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

1.4. Physical characteristics of composition for power storage device 1.4.1. Content The lower limit of the solid content concentration of the composition for a power storage device according to the present embodiment is not particularly limited, but is preferably 1% by mass, more preferably 2% by mass, from the viewpoint of enhancing the binding property. Particularly preferably, it is 5% by mass. The upper limit of the solid content concentration of the composition for a power storage device according to the present embodiment is not particularly limited, but is preferably 50% by mass from the viewpoint of processability such as easy coating on a current collector. It is more preferably 35% by mass, and particularly preferably 20% by mass.

Similarly, the content of the liquid medium (B) in the composition for the power storage device according to the present embodiment is not particularly limited, but is preferably 50 to 99% by mass, more preferably 65 to 98% by mass. Particularly preferably, it is 80 to 95% by mass.

The content ratio of the polymer (A) in the composition for the power storage device according to the present embodiment is a total of 100 of the polymer (A), the polymer other than the polymer (A) contained if necessary, 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 with respect to parts by mass.

1.4.2. pH
The pH of the composition for a power storage device according to the present embodiment is preferably 5 to 12, more preferably 5.5 to 11.5, and particularly preferably 6 to 11. When the pH of the composition for a power storage device is within the above range, the polymer (A) is easily dissolved in the liquid medium (B), so that the viscosity of the composition for a power storage device can be increased. As a result, the stability of the slurry is improved, and problems such as insufficient leveling property and liquid dripping can be suppressed when the slurry is applied, and the storage capacity has both good electrical characteristics and adhesion. It becomes easy to manufacture the device electrode.

The term "pH" as used herein refers to physical properties measured as follows. That is, it is a value measured in accordance with JIS Z8802: 2011 with a pH meter using a glass electrode calibrated with a neutral phosphate standard solution and a borate standard solution as a pH standard solution at 25 ° C. Examples of such a pH meter include "HM-7J" manufactured by DKK-TOA CORPORATION and "D-51" manufactured by HORIBA, Ltd.

It should be noted that the pH of the composition for a power storage device is affected by the monomer composition constituting the polymer (A), but it is not determined only by the monomer composition. That is, it is generally known that the pH of the composition for a power storage device changes depending on the polymerization conditions and the like even if the monomer composition is the same, and the examples of the present specification show only one example. Absent.

For example, even if the polymer composition is the same, all the unsaturated carboxylic acids are charged into the polymerization reaction solution from the beginning, and then other monomers are added in sequence, or a monomer other than the unsaturated carboxylic acid is added. The amount of carboxyl groups derived from the unsaturated carboxylic acid exposed on the surface of the obtained polymer is different from that in the case of charging the polymerization reaction solution and finally adding the unsaturated carboxylic acid. It is considered that the pH of the composition for the power storage device is significantly different even if the order in which the monomers are added is changed by the polymerization method.

2. 2. Slurry for power storage device The slurry for power storage device according to the embodiment of the present invention contains the above-mentioned composition for power storage device. As described above, the above-mentioned composition for a power storage device can be used as a material for forming a protective film for suppressing a short circuit caused by dendrites generated during charging and discharging, and the active materials can be used together. It can also be used as a material for producing a power storage device electrode (active material layer) having improved binding ability, adhesion ability between an active material and a current collector, and powder drop resistance. Therefore, a slurry for a power storage device for forming a protective film (hereinafter, also referred to as a “slurry for a protective film”) and a slurry for a power storage device for forming an active material layer of a power storage device electrode (hereinafter, “power storage device”). It is also referred to as "slurry for electrodes").

2.1. Protective film slurry The term "protective film slurry" as used herein means that a protective film 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 the electrode or a separator or both. It refers to the dispersion liquid used for this purpose. The protective film slurry according to the present embodiment may be composed only of the above-mentioned composition for a power storage device, or may further contain an inorganic filler. Hereinafter, each component contained in the protective film slurry according to the present embodiment will be described in detail. Since the composition for the power storage device is as described above, the description thereof will be omitted.

2.1.1. Inorganic filler The slurry for a protective film according to the present embodiment can improve the toughness of the protective film formed by containing the inorganic filler. As the inorganic filler, at least one metal oxide particle selected from the group consisting of silica, titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), and magnesium oxide (magnesia) can be used. preferable. Among these, titanium oxide and aluminum oxide are preferable from the viewpoint of further improving the toughness of the protective film. Further, as the 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 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. As a result, damage to the separator can be reduced, and the inorganic filler can be prevented from clogging the microporous separator.

The protective film slurry according to the present embodiment preferably contains 0.1 to 20 parts by mass of the above-mentioned composition for a power storage device in terms of solid content with respect to 100 parts by mass of the inorganic filler. It is more preferable that the content is 10 parts by mass. When the content ratio of the composition for a power storage device is within the above range, the balance between the toughness of the protective film formed and the permeability of lithium ions is good, and as a result, the resistance increase rate of the obtained power storage device is lowered. can do.

2.1.2. Liquid medium As the protective film slurry according to the present embodiment, the material described in "1.2. Liquid medium (B)" of the above-mentioned composition for a power storage device can be used as needed. The amount of the liquid medium added can be adjusted as necessary so that the optimum viscosity of the slurry can be obtained according to the coating method and the like.

2.1.3. Other Additives As the protective film slurry according to the present embodiment, an appropriate amount of the material described in "1.3. Other Additives" of the above-mentioned energy storage device composition can be used as needed.

2.2. Slurry for current collector electrodes The term "slurry for current collector electrodes" as used herein is used to apply this to the surface of a current collector and then dry it to form an active material layer on the surface of the current collector. It refers to the dispersion liquid that is produced. The slurry for a power storage device electrode according to the present embodiment contains the above-mentioned composition for a power storage device and an active material.

In general, a slurry for a power storage device electrode 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 the power storage device electrode according to the present embodiment can improve the flexibility and the adhesiveness only by the above-mentioned polymer (A). Of course, the slurry for the power storage device electrode according to the present embodiment may contain a polymer other than the polymer (A) or a thickener in order to further improve the adhesion.

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

2.2.1. Polymer (A)
Since the slurry for the power storage device electrode according to the present embodiment contains the above-mentioned composition for the power storage device, it contains the polymer (A). The composition, physical properties, and synthesis method of the polymer (A) are as described above, and thus the description thereof will be omitted.

The content ratio of the polymer (A) in the slurry for the power storage device electrode according to the present embodiment is preferably 1 to 8 parts by mass, and more preferably 1 to 7 parts by mass with respect to 100 parts by mass of the active material. , Particularly preferably 1.5 to 6 parts by mass. When the content ratio of the polymer (A) is within the above range, the dispersibility of the active material in the slurry becomes good, and the coatability of the slurry becomes also excellent. Even when the slurry for the power storage device electrode according to the present embodiment contains a polymer other than the polymer (A) or a thickener, the content ratio of the polymer (A) is preferably in the above range. ..

2.2.2. Active material Examples of the active material used in the slurry for the electrode of the power storage device 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. conductive polymers such as polyacene, a X _B Y _O Z _(where, a is an alkali metal or a transition metal, at least one B is selected cobalt, nickel, aluminum, tin, transition metals manganese, O is Represents an oxygen atom, X, Y and Z are numbers in the range of 1.10>X> 0.05, 4.00>Y> 0.85 and 5.00>Z> 1.5, respectively.) Examples thereof include the represented composite metal oxide and other metal oxides. Specific examples of these include compounds described in Japanese Patent No. 5999399.

The slurry for power storage device electrodes according to the present embodiment can be used when producing any power storage device electrode of the positive electrode and the negative electrode, 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 when producing a positive electrode, there is a problem that the charge / discharge characteristics are not sufficient and the adhesion is inferior. Lithium iron phosphate has a fine primary particle size and is known to be a secondary aggregate thereof. When charging and discharging are repeated, the aggregation collapses in the active material layer and the active materials are separated from each other. It is considered that one of the factors is that the conductive network inside the active material layer is easily broken due to the peeling from the current collector.

However, the electricity storage device electrode produced by using the energy storage device electrode slurry according to the present embodiment does not cause the above-mentioned problems even when lithium iron phosphate is used as the positive electrode active material, and has good electricity. Can show specific characteristics. It is considered that the reason for this is that the polymer (A) can firmly bind lithium iron phosphate, and at the same time, it can maintain a state in which lithium iron phosphate is firmly bound even during charging and discharging. ..

On the other hand, when producing a negative electrode, it is preferable that the active material exemplified above contains a silicon material. Since the silicon material has a large occlusion amount of lithium per unit weight as compared with other active materials, the storage capacity of the power storage device can be increased by containing the silicon material as the negative electrode active material, and as a result. , The output and energy density of the power 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 carbon material due to charge and discharge is smaller than that of silicon material, the influence of volume change of silicon material can be mitigated by using a mixture of silicon material and carbon material as the negative electrode active material. The adhesion ability between the material layer and the current collector can be further improved.

When silicon (Si) is used as an active material, silicon has a high capacity, but causes a large volume change when occluding lithium. For this reason, the silicon material has a property that it is pulverized by repeated expansion and contraction, causing peeling from the current collector and peeling between active materials, and the conductive network inside the active material layer is easily broken. As a result, the charge / discharge durability characteristics are extremely deteriorated in a short time.

However, the power storage device electrode produced by using the storage device electrode slurry according to the present embodiment can exhibit good electrical characteristics without causing the above-mentioned problems even when a silicon material is used. it can. The reason for this is that the polymer (A) can firmly bind the silicon material, and at the same time, the polymer (A) expands and contracts even if the silicon material expands in volume due to occlusion of lithium, resulting in silicon. It is considered that this is because the material can be maintained in a tightly bound state.

The content ratio 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%. It is particularly preferable to set it to ~ 40% by mass. When the content ratio of the silicon material in 100% by mass of the active material is within the above range, a power storage device having an excellent balance between the improvement of the output and energy density of the power storage device and the 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 means a volume average particle size calculated from the particle size distribution measured by using a particle size distribution measuring device based on a laser diffraction method. Examples of such a laser diffraction type particle size distribution measuring device include the HORIBA LA-300 series and the HORIBA LA-920 series (all manufactured by HORIBA, Ltd.).

2.2.3. Other Additives In addition to the above-mentioned components, other components may be added to the slurry for the power storage device electrode according to the present embodiment, if necessary. Examples of such components include polymers other than the polymer (A), thickeners, conductivity-imparting agents, liquid media (excluding those brought in from the composition for power storage devices), pH adjusters, and the like. Examples include corrosion inhibitors. The polymer and thickener other than the polymer (A) can be selected from the compounds exemplified in the above-mentioned "1.3. Other additives" and used for the same purpose and content ratio.

<Conductivity imparting agent>
A conductivity-imparting agent may be added to the slurry for the power storage device electrode according to the present embodiment for the purpose of imparting conductivity and buffering the volume change of the active material due to the inflow and outflow of lithium ions.

Specific examples of the conductivity-imparting agent include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, and carbon such as fullerene. Among these, acetylene black and furnace black can be preferably used. The content ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material.

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

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

<pH adjuster / corrosion inhibitor>
A pH adjuster or a corrosion inhibitor may be added to the slurry for the power storage device electrode according to the present embodiment for the purpose of suppressing corrosion of the current collector according to the type of the active material.

Examples of the pH adjuster include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide and the like. , Sulfuric acid, ammonium sulfate, sodium hydroxide, potassium hydroxide are preferable.

Corrosion inhibitors include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, molybdate. Examples thereof include ammonium, sodium molybdate, potassium molybdate, and the like, and among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferable.

2.2.4. Method for Producing Slurry for Power Storage Device Electrode The slurry for power storage device electrode according to the present embodiment is manufactured by any method as long as it contains the above-mentioned composition for power storage device and an active material. However, it can be produced by, for example, the method described in Japanese Patent No. 5999399.

3. 3. Power storage device electrode The power storage device electrode according to an embodiment of the present invention includes a current collector, an active material layer formed by applying and drying the above-mentioned slurry for the power storage device electrode on the surface of the current collector. It is equipped with. Such a power storage device electrode is formed by applying the above-mentioned slurry for a power storage device electrode 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. In the power storage device electrode produced in this manner, an active material layer containing the above-mentioned polymer (A), an active material, and an optional component added as needed is bonded onto a current collector. Therefore, it is excellent in flexibility and adhesion, and exhibits good charge / discharge durability characteristics.

The current collector is not particularly limited as long as it is made of a conductive material, and examples thereof include the current collector described in Japanese Patent No. 5999399.

The method for applying the slurry for the power storage device electrode to the current collector is also not particularly limited, and for example, the slurry can be applied by the method described in Japanese Patent No. 5999399.

When a silicon material is used as the active material in the power storage device electrode according to the present embodiment, the content ratio of the silicon element in 100 parts by mass of the active material layer is preferably 2 to 40 parts by mass, more preferably 2 to 35 parts by mass. It is a mass portion, and particularly preferably 3 to 30 parts by mass. When the content of the silicon element in the active material layer is within the above range, in addition to improving the storage capacity of the power storage device produced by using the silicon element, an active material layer having a uniform distribution of silicon elements can be obtained. ..

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

4. Power Storage Device The power storage device according to the embodiment of the present invention can be manufactured according to a conventional method by providing the above-mentioned power storage device electrode, further containing an electrolytic solution, and using parts such as a separator. As a specific manufacturing method, for example, a negative electrode and a positive electrode are overlapped with each other via a separator, and the negative electrode and the positive electrode are stored in a battery container by winding or folding according to the shape of the battery, and an electrolytic solution is injected into the battery container. The method of sealing the battery can be mentioned. The shape of the battery can be an appropriate shape such as a coin type, a cylindrical type, a square type, or a laminated type.

The electrolytic solution may be in the form of a liquid or a gel, and depending on the type of the active material, a known electrolytic solution used in the power storage device that effectively exhibits the function as a battery may be selected. The electrolytic solution can be a solution in which the electrolyte is dissolved in a suitable solvent. Examples of these electrolytes and solvents include compounds described in Japanese Patent No. 5999399.

The above-mentioned power storage device can be applied to a lithium ion secondary battery, an electric double layer capacitor, a lithium ion capacitor, etc., which require discharge at a large current density. Of these, lithium ion secondary batteries are particularly preferable. In the power storage device electrode and the power storage device according to the present embodiment, known members for a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor can be used as members other than the composition for the power storage device. is there.

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. In the present specification, the polymer (A) obtained in Example 1 is referred to as "polymer (A1)", and similarly, the polymer (A) obtained in Example 2 is referred to as "polymer". (A2) ”, the polymer (A) obtained in Example 8 is referred to as“ polymer (A8) ”and the like. Further, the polymer obtained in Comparative Example 1 is referred to as "polymer (B1)", and similarly, the polymer obtained in Comparative Example 5 is referred to as "polymer (B5)" or the like.

5.1. Example 1
5.1.1. Preparation of composition for power storage device and evaluation of physical properties (1) Preparation of composition for power storage device 600 parts by mass of vinyl acetate and 400 parts by mass of methanol are charged, nitrogen gas is bubbled to deoxidize, and then bis (bi) as a polymerization initiator. 0.2 parts by mass of 4-tert-butylcyclohexyl) peroxydicarbonate was charged and polymerized at 65 ° C. for 4 hours. The solid content concentration of the polymerization solution at the time of stopping the polymerization was 45% by mass, and the polymerization rate of vinyl acetate obtained from the solid content was 80%. Methanol vapor was blown into the obtained polymerization solution to remove unreacted vinyl acetate, and then diluted with methanol so that the concentration of polyvinyl acetate was 40% by mass.
Next, 20 parts by mass of a methanol solution of sodium hydroxide having a concentration of 10% by mass was added to 1200 parts by mass of the diluted polyvinyl acetate solution, and a saponification reaction was carried out at 30 ° C. for 1.5 hours. The saponified solution was neutralized with acetic acid, filtered and dried at 100 ° C. for 2 hours to give polyvinyl alcohol (PVA). The average degree of polymerization of the obtained PVA was 330, and the degree of saponification was 90 mol%. The average degree of polymerization and the degree of saponification of PVA were measured by a method according to JIS K 6726.
Next, 900 parts by mass of water, 0.5 parts by mass of tert-butyl hydrooxide (manufactured by Nichiyu, Perbutyl H), 70 parts by mass of PVA obtained above, 25 parts by mass of acrylic acid, and 5 parts by mass of acrylamide were added to a 100 L autoclave. In addition, the reaction was carried out at 70 ° C. for 18 hours. Then, using a 5 wt% sodium hydroxide aqueous solution, a transparent composition for a power storage device having a solid content concentration of 10% and a pH of 9.0 was obtained.

(2) Viscosity measurement The temperature of the composition for a power storage device having a solid content concentration of 10% and a pH of 9.0 obtained above was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model "RB-80L"). The viscosity at 25 ° C. was measured according to JIS Z 8803. The results are shown in Table 1 below.

(3) Solubility in Water The composition for a power storage device having a pH of 9.0 obtained above was diluted by adding water so that the polymer (A1) was 1% by mass. The transparency of the diluted composition for a power storage device thus obtained was visually confirmed at 1 atm and 23 ° C. The results are shown in Table 1 below. If the composition for the power storage device is transparent, it is judged to be "water-soluble" and is described as "A", and if the composition for the power storage device is translucent or cloudy, it is judged to be "water-insoluble" and described as "B". ..

5.1.2. Preparation of slurry for power storage device electrode (1) Synthesis of silicon material (active material) A mixture of crushed silicon dioxide powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) at a temperature of 1100 to 1600 ° C. In an electric furnace adjusted to the range, heat treatment was performed for 10 hours under a nitrogen stream (0.5 NL / min), and the silicon oxide represented by the composition formula SiO _x (x = 0.5 to 1.1) was used. A powder (average particle size 8 μm) was obtained. 300 g of this silicon oxide powder was charged into a batch type heating furnace, and the temperature was raised from room temperature (25 ° C.) to 1100 ° C. at a heating rate of 300 ° C./h while maintaining a reduced pressure of 100 Pa by a vacuum pump. .. Next, while maintaining the pressure in the heating furnace at 2000 Pa, heat treatment (graphite film treatment) was performed at 1100 ° C. for 5 hours while introducing methane gas at a flow rate of 0.5 NL / min. After completion of the graphite coating treatment, the mixture was cooled to room temperature at a temperature lowering 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) whose surface is coated with graphite, and its average particle size is 10.5 μm, and the entire obtained graphite-coated silicon oxide is 100. The proportion of the graphite coating in the mass% was 2% by mass.

(2) Preparation of Slurry for Storage Device Electrode 4 parts by mass (solid content conversion value, above) of the polymer (A1) in a biaxial planetary mixer (manufactured by Primex Co., Ltd., trade name "TK Hibismix 2P-03") (Added as a composition for a power storage device with a solid content concentration of 10% and a pH of 9.0), artificial graphite, which is highly crystalline graphite as a negative electrode active material (manufactured by Hitachi Kasei Kogyo Co., Ltd., trade name "MAG") 76 parts by mass (solid content conversion value), 19 parts by mass (solid content conversion value) of the graphite coating film silicon oxide powder obtained above, carbon as a conductivity imparting agent (made by Denka Co., Ltd., acetylene black) Was added in an amount of 1 part by mass and stirred at 60 rpm for 1 hour to obtain a paste. Water is added to the obtained paste to adjust the solid content concentration to 48% by mass, and then a stirring defoaming machine (manufactured by Shinky Co., Ltd., trade name "Awatori Rentaro") is used at 200 rpm for 2 minutes. A slurry for a power storage device electrode containing 20% by mass of Si in the negative electrode active material by stirring and mixing at 1800 rpm for 5 minutes and further under reduced pressure (about 2.5 × 10 ⁴ Pa) at 1800 rpm for 1.5 minutes. C / Si = 80/20) was prepared.

5.1.3. Manufacture and evaluation of power storage device (1) Manufacture of power storage device electrode (negative electrode) On the surface of a current collector made of copper foil with a thickness of 20 μm, the slurry for power storage device electrode (C / Si = 80/20) obtained above. Was uniformly applied by the 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. Then, the energy storage device electrode (negative electrode) was obtained by press working with a roll press machine 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 Using a knife, 10 cuts in each of the vertical and horizontal directions from the active material layer to the depth reaching the current collector are made on the surface of the electrode sheet obtained above. I made a notch on the grid. An adhesive tape having a width of 18 mm (manufactured by Nichiban Co., Ltd., trade name "Cellotape" (registered trademark) specified in JIS Z1522) was attached to this notch and immediately peeled off, and the degree of shedding of the active material was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.
(Evaluation criteria)
・ 5 points: No dropout of the active material layer.
・ 4 points: 1 to 5 pieces of active material layer were dropped.
・ 3 points: 6 to 20 active material layers were dropped.
-2 points: 21 to 40 pieces of active material layer were dropped.
-Point 1: The number of active material layers dropped is 41 or more.

(3) Manufacture of counter electrode (positive electrode) A biaxial planetary mixer (manufactured by Primix Corporation, product name "TK Hibismix 2P-03") and a binder for electrochemical device electrodes (manufactured by Kureha Co., Ltd., product name "KF") 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 , 100 parts by mass (solid content equivalent) of LiCoO ₂ (manufactured by Hayashi Kasei Co., Ltd.) and 36 parts by mass of N-methylpyrrolidone (NMP) having an average particle diameter of 5 μm were added as the positive electrode active material, and the mixture was stirred at 60 rpm for 2 hours. It was. NMP was added to the obtained paste to adjust the solid content concentration to 65% by mass, and then using a stirring defoaming machine (manufactured by Shinky Co., Ltd., trade name "Awatori Rentaro"), 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 slurry for a positive electrode. 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 removing the solvent was 80 μm, and heated at 120 ° C. for 20 minutes to remove the solvent. .. Then, a counter electrode (positive electrode) was obtained by press working with a roll press machine so that the density of the active material layer was 3.0 g / cm ³ .

(4) Assembly of Lithium Ion Battery Cell A two-pole coin cell (treasure) obtained by punching and molding the negative electrode manufactured above to a diameter of 15.95 mm in a glove box Ar-substituted so that the dew point is -80 ° C or lower. It was placed on the product name "HS Flat Cell" manufactured by Izumi Co., Ltd. Next, a separator made of a polypropylene porous film punched to a diameter of 24 mm (manufactured by Cellguard Co., Ltd., trade name "Cellguard # 2400") was placed, and further, 500 μL of an electrolytic solution was injected so as not to allow air to enter, and then the above A lithium ion battery cell (storage device) was assembled by placing a positive electrode produced in 1 above, punched and molded to a diameter of 16.16 mm, and sealing the exterior body of the bipolar coin cell with a screw. The electrolytic solution used here is a solution in which LiPF ₆ is dissolved in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio) at a concentration of 1 mol / L.

(5) Evaluation of charge / discharge cycle characteristics The power storage device manufactured above was charged at a constant current (1.0 C) in a constant temperature bath adjusted to 25 ° C, and the voltage became 4.2 V. At that time, charging was continued at a constant voltage (4.2 V), and when the current value reached 0.01 C, charging was completed (cutoff). After that, discharge was started at a constant current (1.0 C), and when the voltage reached 3.0 V, the discharge was completed (cutoff), 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. The evaluation results are shown in Table 1 below.
Capacity retention rate (%) = (Discharge capacity in the 100th cycle) / (Discharge capacity in the 1st cycle)
(Evaluation criteria)
・ 5 points: Capacity retention rate is 95% or more.
-4 points: Capacity retention rate is 90% or more and less than 95%.
-3 points: Capacity retention rate 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 rate is 75% or more and less than 80%.
-0 points: Capacity retention rate is less than 75%.

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

5.2. Examples 2 to 13, Comparative Examples 1 to 6
In the above "5.1.1. Preparation and evaluation of physical properties of composition for power storage device (1) Preparation of composition for power storage device", the types and amounts of each monomer are shown in Table 1 or Table 2 below, respectively. A composition for a power storage device having a solid content concentration of 10% and a pH of 9.0 was obtained in the same manner except as described above.

Further, a slurry for a power storage device electrode was prepared in the same manner as in Example 1 except that the composition for a power storage device prepared above was used, and a power storage device electrode and a power storage device were produced, respectively. Evaluated in the same way.

5.3. Example 14
A composition for a power storage device having a solid content concentration of 10% and a pH of 9.0 was obtained in the same manner as in Example 2 above. Next, 1 mass of thickener (trade name "CMC2200", manufactured by Daicel Co., Ltd.) was added to the biaxial planetary mixer (manufactured by Primex Co., Ltd., trade name "TK Hibismix 2P-03") as a pre-added component. 1 part by mass (solid content equivalent value, added as an aqueous solution with a concentration of 2% by mass) and the polymer (A2) (solid content equivalent value, for a power storage device having a solid content concentration of 10% and a pH of 9.0 obtained above) 76 parts by mass (solid content conversion value) of artificial graphite (manufactured by Hitachi Kasei Kogyo Co., Ltd., trade name "MAG"), which is highly crystalline graphite as the negative electrode active material (added as a composition), the graphite obtained above. 19 parts by mass (solid content conversion value) of the coating film silicon oxide powder 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 stirred at 60 rpm for 1 hour. 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 (in terms of solid content), and the mixture was further stirred for 1 hour to obtain a paste. Water is added to the obtained paste to adjust the solid content concentration to 48% by mass, and then a stirring defoaming machine (manufactured by Shinky Co., Ltd., trade name "Awatori Rentaro") is used at 200 rpm for 2 minutes. A slurry for a power storage device electrode containing 20% by mass of Si in the negative electrode active material by stirring and mixing at 1800 rpm for 5 minutes and further under reduced pressure (about 2.5 × 10 ⁴ Pa) at 1800 rpm for 1.5 minutes. C / Si = 80/20) was prepared.

A power storage device electrode and a power storage device were produced in the same manner as in Example 1 except that the slurry for power storage device electrodes prepared above was used, and evaluated in the same manner as in Example 1.

5.4. Examples 15-19, Comparative Examples 7-12
The slurry for the power storage device electrode was prepared in the same manner as in Example 14 except that the composition of the slurry for the power storage device electrode was changed as shown in Table 3 below, and the power storage device electrode and the power storage device were respectively produced. It was evaluated in the same manner as in 14.

As the acrylic polymer and the fluorine-based polymer shown in Table 3 below, the polymers obtained by the following synthesis methods were used, respectively.

<Synthesis of acrylic polymer>
150 parts by mass of water and 0.2 parts by mass of sodium dodecylbenzenesulfonate were charged into a separable flask having a capacity of 7 liters, and the inside of the separable flask was sufficiently replaced with nitrogen.
On the other hand, in another container, 60 parts by mass of water, an ether sulfate type emulsifier as an emulsifier (trade name "Adecaria Soap SR1025", manufactured by ADEKA Co., Ltd.) is placed in 0.8 parts by mass in terms of solid content and 2 as a monomer. , 2,2-Trifluoroethyl methacrylate 20 parts by mass, cyclohexyl methacrylate 12 parts by mass, acrylonitrile 8 parts by mass, methyl methacrylate 5 parts by mass, 2-ethylhexyl acrylate by 50 parts by mass, and acrylic acid 5 parts by mass. A monomer emulsifying solution containing a mixture of the above monomers was prepared with sufficient stirring.
When the temperature inside the separable flask was started and the temperature inside reached 60 ° C., 0.5 parts by mass of ammonium persulfate was added as a polymerization initiator. Then, when the temperature inside the separable flask reaches 70 ° C., the addition of the monomer emulsion prepared above is started, and the monomer is maintained while maintaining the temperature inside the separable flask at 70 ° C. The emulsion was added slowly over 3 hours. Then, the temperature inside the separable flask was raised to 85 ° C., and this temperature was maintained for 3 hours to carry out the polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then ammonium water was added to adjust the pH to 7.6 to obtain an acrylic polymer dispersion having a solid content concentration of 30%.

<Synthesis of fluorine-based polymer>
After sufficiently replacing the inside of an autoclave with an internal volume of about 6 L equipped with an electromagnetic stirrer with nitrogen, 2.5 L of deoxidized pure water and 25 g of ammonium perfluorodecanoate as an emulsifier were charged, and the temperature was 60 ° C. while stirring at 350 rpm. The temperature was raised to. Next, a mixed gas composed of 70% vinylidene fluoride (VDF) and 30% propylene hexafluoride (HFP), which are monomers, was charged until the internal pressure reached 20 kg / cm ² . 25 g of a Freon 113 solution containing 20% of diisopropylperoxydicarbonate as a polymerization initiator was press-fitted using nitrogen gas to initiate polymerization. A mixed gas consisting of 60.2% VDF and 39.8% HFP was sequentially press-fitted so that the internal pressure was maintained at 20 kg / cm ² during the polymerization, and the pressure was maintained at 20 kg / cm ² . Further, since the polymerization rate decreases as the polymerization progresses, after 3 hours, the same amount of the same polymerization initiator solution as before was press-fitted using nitrogen gas, and the reaction was continued for another 3 hours. Then, the reaction solution was cooled and the stirring was stopped at the same time, and the reaction was stopped after releasing the unreacted monomer to obtain a polymer dispersion having a solid content concentration of 40%. As a result of analyzing the obtained polymer by ¹⁹ F-NMR, the mass composition ratio of each monomer was VDF / HFP = 21/4.
Next, after the inside of the separable flask having a capacity of 7 L was sufficiently replaced with nitrogen, the polymer dispersion obtained in the above step was added to the polymer dispersion by 25 parts by mass in terms of polymer, and the emulsifier "Adecaria Soap SR1025" (trade name, stock). (Manufactured by ADEKA) 0.5 parts by mass, 30 parts by mass of methyl methacrylate, 40 parts by mass of 2-ethylhexyl acrylate and 5 parts by mass of methacrylic acid, and 130 parts by mass of water are sequentially charged, stirred at 70 ° C. for 3 hours, and weighted. The coalescence absorbed the monomer. Next, 20 mL of a tetrahydrofuran solution containing 0.5 parts by mass of azobisisobutyronitrile as an oil-soluble polymerization initiator was added, the temperature was raised to 75 ° C., the reaction was carried out for 3 hours, and the reaction was further carried out at 85 ° C. for 2 hours. Was done. Then, after cooling, the reaction was stopped, and the pH was adjusted to 7 with a 2.5N aqueous sodium hydroxide solution to obtain a fluorine-based polymer dispersion having a solid content concentration of 40%.

5.5. Example 20
In Example 1, "polymer (A9) 3.0 parts by mass (solid content conversion value)" is used instead of "PVDF 4.0 parts by mass (solid content conversion value)" used as the positive electrode binder. A slurry for a power storage device electrode was prepared in the same manner as in Example 9 above, and a power storage device electrode and a power storage device were respectively produced and evaluated in the same manner as in Example 9 above.

5.6. Examples 21-22 and Comparative Examples 13-14
The slurry for the power storage device electrode was adjusted in the same manner as in Example 20 except that the composition of the slurry for the power storage device electrode was changed as shown in Table 4 below to prepare the power storage device electrode and the power storage device, respectively. It was evaluated in the same manner as 20.

5.7. Evaluation Results Tables 1 and 2 below summarize the polymer compositions, physical characteristics, and evaluation results used in Examples 1 to 13 and Comparative Examples 1 to 6. Table 3 below summarizes the slurry compositions for power storage device electrodes used in Examples 14 to 19 and Comparative Examples 7 to 12, and the evaluation results. Table 4 below summarizes the slurry compositions for power storage device electrodes used in Examples 20 to 22 and Comparative Examples 13 to 14, and the evaluation results. In each table, the numerical value of each component represents a mass part.

The abbreviations of each monomer in Table 1 and Table 2 above represent the following compounds, respectively.
<Polyvinyl alcohol>
-PVA: Polyvinyl alcohol <unsaturated carboxylic acid>
-TA: Itaconic acid-AA: Acrylic acid-MAA: Methacrylic acid <(meth) acrylamide>
-AAM: Acrylamide-MAM: Methacrylamide <unsaturated carboxylic acid ester>
-HEMA: 2-hydroxyethyl methacrylate-HEA: 2-hydroxyethyl acrylate <Compound having a sulfonic acid group>
・ NASS: Sodium styrene sulfonate

As is clear from the above Tables 1 and 2, the slurry for the electricity storage device electrode prepared by using the composition for the electricity storage device according to the present invention shown in Examples 1 to 13 is the case of Comparative Examples 1 to 6. It was found that the active materials having a large volume change due to charging and discharging can be suitably bonded to each other, and the adhesion between the active material layer and the current collector can be maintained well. As a result, a power storage device electrode capable of suppressing peeling of the active material layer and maintaining good charge / discharge characteristics even though the active material repeatedly expands and contracts in volume by repeating charging and discharging Obtained. It was also found that the power storage device (lithium ion secondary battery) provided with these power storage device electrodes has good charge / discharge rate characteristics. The reason for this is that the power storage device electrodes according to Examples 1 to 13 shown in Tables 1 and 2 above can reduce the change in film thickness of the active material layer due to charging and discharging as compared with the cases of Comparative Examples 1 to 6. 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 slurry for the current collector electrode prepared by using the composition for the current collector according to the present invention shown in Examples 14 to 19 is the case of Comparative Examples 7 to 12. In comparison with the above, even when a thickener or another polymer is used in combination, active materials having a large volume change due to charge / discharge can be suitably bonded to each other, and the active material layer and current collector can be bonded to each other. It was found that the adhesion of the body can be maintained well.

Further, as is clear from the results in Table 4 above, the slurry for the storage device electrode prepared by using the storage device composition according to the present invention shown in Examples 20 to 22 is the case of Comparative Examples 13 and 14. It was found that the battery had good battery characteristics even when used for the positive electrode.

The present invention is not limited to the above embodiment, and various modifications are possible. The present invention includes substantially the same configurations as those described in the embodiments (eg, configurations with the same function, method and result, or configurations with the same purpose and effect). The present invention also includes a configuration in which a non-essential part of the configuration described in the above embodiment is replaced with another configuration. Further, the present invention also includes a configuration that exhibits the same effects as the configuration described in the above embodiment or a configuration that can achieve the same object. Further, the present invention also includes a configuration in which a known technique is added to the configuration described in the above embodiment.

Claims (9)

It contains a water-soluble polymer (A) and a liquid medium (B).
When the total of the repeating units contained in the water-soluble polymer (A) is 100 parts by mass, the polymer (A) becomes
5 to 90 parts by mass of the repeating unit (a1) represented by the following structural formula (1),
5 to 90 parts by mass of repeating unit (a2) derived from unsaturated carboxylic acid,
It contains 5 to 90 parts by mass of a repeating unit (a3) derived from (meth) acrylamide.
A composition for a power storage device, wherein the water-soluble polymer (A) has a solubility in water at 25 ° C. and 1 atm of 1 g or more with respect to 100 g of water.

The composition for a power storage device according to claim 1, wherein the viscosity of the 10% by mass aqueous solution of the water-soluble polymer (A) at pH 9 is 500 to 150,000 mPa · s / 30 rpm. The composition for a power storage device according to claim 1 or 2, wherein the liquid medium (B) is water. A slurry for a power storage device electrode containing the composition for a power storage device according to any one of claims 1 to 3 and an active material. The slurry for a power storage device electrode according to claim 4, which contains a silicon material as the active material. The slurry for a power storage device electrode according to claim 4 or 5, further containing at least one polymer selected from the group consisting of a styrene-butadiene copolymer, an acrylic polymer, and a fluorine-based polymer. The slurry for a power storage device electrode according to any one of claims 4 to 6, further containing a thickener. A current collector comprising an active material layer formed by applying and drying the slurry for a power storage device electrode according to any one of claims 4 to 7 on the surface of the current collector. Device electrode. A power storage device including the power storage device electrode according to claim 8.