JP7143114B2 - 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 usually manufactured 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. be. 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 hydroxyl 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.

On the other hand, lithium-containing phosphate compounds having an olivine structure (olivine-type lithium-containing phosphate compounds) have attracted attention as positive electrode active materials with high safety. The olivine-type lithium-containing phosphate compound has high thermal stability because phosphorus and oxygen are covalently bonded, and does not release oxygen even at high temperatures.

However, the olivine-type lithium-containing phosphate compound has a Li ion absorption/desorption voltage of around 3.4 V, and thus has a low output voltage. Attempts have been made to improve the properties of peripheral materials such as electrode binders and electrolytes (see Patent Documents 7 to 9).

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 JP 2007-294323 A WO2010/113940 JP 2012-216322 A

However, the electrode binders disclosed in Patent Documents 1 to 6 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.

In addition, in the techniques for improving the properties of peripheral materials such as electrode binders and electrolytic solutions as disclosed in the above-mentioned Patent Documents 7 to 9, electricity storage equipped with a positive electrode using an olivine-type lithium-containing phosphate compound as a positive electrode active material It has been difficult to sufficiently improve the charge/discharge endurance characteristics of devices.

Accordingly, some aspects of the present invention provide a composition for an electricity storage device that is capable of producing an electricity storage device electrode that exhibits excellent adhesion and good charge/discharge durability. Moreover, some aspects of the present invention provide a slurry for an electricity storage device electrode containing the composition. Moreover, some aspects of the present invention provide an electricity storage device electrode that exhibits excellent adhesion and 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 a polymer (A), a polymer (B), and a liquid medium (C),
When the total of repeating units contained in the polymer (A) is 100 parts by mass, the polymer (A) contains 50 parts by mass or more of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group. ,
When the total of repeating units contained in the polymer (B) is 100 parts by mass, the polymer (B) contains 0 parts by mass or more and 50 parts by mass of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group. contains less than

In one aspect of the power storage device composition,
When the polymer (A) is subjected to differential scanning calorimetry (DSC) according to JIS K7121, an endothermic peak can be observed in the temperature range of -20°C to 80°C.

In any aspect of the power storage device composition,
The solubility of the polymer (A) in water at 25° C. and 1 atm can be 1 g or more per 100 g of water.

In any aspect of the power storage device composition,
The unsaturated carboxylic acid ester having a hydroxyl group may be at least one selected from the group consisting of hydroxyethyl (meth)acrylate and glycerin mono(meth)acrylate.

In any aspect of the power storage device composition,
The polymer (A) may further contain 1 to 40 parts by mass of repeating units derived from (meth)acrylamide.

In any aspect of the power storage device composition,
The polymer (B) may further contain 50 to 100 parts by mass of repeating units derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group).

In any aspect of the power storage device composition,
The polymer (B) may further contain 20 to 70 parts by mass of repeating units derived from a conjugated diene compound and 0.5 to 30 parts by mass of repeating units derived from an unsaturated carboxylic acid.

In any aspect of the power storage device composition,
The polymer (B) may further contain 1 to 30 parts by mass of repeating units derived from a (meth)acrylamide compound.

In any aspect of the power storage device composition,
When the content of the polymer (A) is Ma parts by mass and the content of the polymer (B) is Mb parts by mass, the value of Mb/Ma can be 0.5 to 5.0. .

In any aspect of the power storage device composition,
The polymer (B) may be particles having a number average particle diameter of 50 nm or more and 1000 nm or less.

In any aspect of the power storage device composition,
The liquid medium (C) 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 one aspect of the electricity storage device electrode slurry,
As the active material, at least one selected from the group consisting of an olivine-type lithium-containing phosphate compound, lithium cobaltate, lithium nickelate, lithium manganate, and ternary lithium nickel-cobalt-manganeseate can be contained.

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.

Since the composition for an electricity storage device according to the present invention has excellent adhesiveness, it is possible to manufacture an electricity storage device electrode exhibiting good charge/discharge durability characteristics. 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. In addition, the composition for an electricity storage device according to the present invention exhibits the above effects particularly when the electrode of the electricity storage device contains an olivine-type lithium-containing phosphoric acid compound as an active material.

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". In addition, "~ (meth)acrylate" is a concept that includes both "~ acrylate" and "~ methacrylate".

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 a polymer (A), a polymer (B), and a liquid medium (C). 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 (A)
The polymer (A) contained in the electricity storage device composition according to the present embodiment may be in the form of latex dispersed in the liquid medium (C), or dissolved in the liquid medium (C). However, it is preferably dissolved in the liquid medium (C). When the polymer (A) is dissolved in the liquid medium (C), the stability of the electricity storage device electrode slurry (hereinafter also simply referred to as "slurry") prepared by mixing with the active material is good. and it is preferable because the slurry can be applied to the current collector well.

In the polymer (A), the repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group (hereinafter also referred to as "repeating unit (a1)") is added to the total repeating units in the polymer (A). is 100 parts by mass, it contains 50 parts by mass or more. In addition to the repeating unit (a1), the polymer (A) may contain repeating units derived from other monomers copolymerizable therewith. Other monomers include, for example, (meth)acrylamide, unsaturated carboxylic acids, unsaturated carboxylic acid esters (excluding unsaturated carboxylic acid esters having a hydroxyl group), α,β-unsaturated nitrile compounds, cationic mono Examples include monomers, conjugated diene compounds, aromatic vinyl compounds, and the like.

Hereinafter, the repeating units constituting the polymer (A), the 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 Polymer (A) <Repeating Unit Derived from Unsaturated Carboxylic Acid Ester Having a Hydroxyl Group>
The polymer (A) preferably contains repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group in an amount of 50 parts by mass or more when the total of repeating units in the polymer (A) is 100 parts by mass. is 51 parts by mass or more, more preferably 55 parts by mass or more, and particularly preferably 60 to 100 parts by mass. When the polymer (A) contains the repeating unit derived from an unsaturated carboxylic acid ester having a hydroxyl group within the above range, the dispersibility of the active material and filler is improved, and a uniform active material layer or protective film can be produced. Since it becomes possible, structural defects are eliminated, and good charge/discharge characteristics are exhibited. Furthermore, by containing the repeating unit derived from an unsaturated carboxylic acid ester having a hydroxyl group within the above range, the surface of the active material is coated with the polymer (A), and expansion of the active material during charging and discharging can be suppressed. , to exhibit good charge-discharge endurance characteristics.

Examples of unsaturated carboxylic acid esters having a hydroxyl group include 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 monomethacrylate are preferred. In addition, these monomers may be used individually by 1 type, and may be used in combination of 2 or more type.

<Repeating unit derived from (meth)acrylamide>
The polymer (A) preferably further contains repeating units derived from (meth)acrylamide. When the polymer (A) contains repeating units derived from (meth)acrylamide, the lower limit of the content of the repeating units derived from (meth)acrylamide is 100 in total of the repeating units in the polymer (A). When expressed as parts by mass, it is preferably 1 part by mass, more preferably 3 parts by mass, and particularly preferably 5 parts by mass. The upper limit of the content of repeating units derived from (meth)acrylamide is preferably 40 parts by mass, more preferably 35 parts by mass. When the content of repeating units derived from (meth)acrylamide is within the above range, the glass transition temperature (Tg) of the resulting polymer (A) is favorable. As a result, the bonding ability between active materials containing a carbon material such as graphite or a silicon material can be enhanced. In addition, the resulting active material layer has better flexibility and adhesion to the current collector. Since the Tg of the polymer (A) is suitable, the flexibility of the active material layer to be obtained is moderate, and the adhesion between the current collector and the active material layer is good.

Examples of (meth)acrylamide include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N , N-dimethylaminopropyl acrylamide, N,N-dimethylaminopropyl methacrylamide, N-methylol methacrylamide, N-methylol acrylamide, diacetone acrylamide, maleic acid amide, acrylamide t-butylsulfonic acid and the like. These (meth)acrylamides may be used singly or in combination of two or more.

<Other repeating units>
The polymer (A) may contain, in addition to the above repeating units, repeating units derived from other monomers copolymerizable therewith. Examples of such monomers include unsaturated carboxylic acids, unsaturated carboxylic acid esters (excluding the unsaturated carboxylic acid esters having a hydroxyl group), α,β-unsaturated nitrile compounds, conjugated diene compounds, aromatic vinyl compounds. , cationic monomers, and the like.

Specific examples of the unsaturated carboxylic acid include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. can be.

As the unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), (meth)acrylate is preferred. Specific examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl ( meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, Allyl (meth)acrylate, ethylene di(meth)acrylate and the like can be mentioned, and one or more selected from these can be used.

Specific examples of the α,β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like, and one or more selected from these. be able to. Among these, one or more selected from acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is particularly preferable.

Specific examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear Conjugated pentadienes, substituted and side-chain conjugated hexadienes, and the like can be mentioned, and one or more selected from these can be used. Among these, 1,3-butadiene is particularly preferred.

Specific examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and at least one selected from these. can be done. Among these, styrene is particularly preferred.

The cationic monomer is preferably at least one monomer selected from the group consisting of secondary amines (salts), tertiary amines (salts) and quaternary ammonium salts. Specific examples of these cationic monomers include 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5) (meth)acrylate -dimethylpyrazolyl)carbonylamino]ethyl, 2-(0-[1'-methylpropylideneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate,
Methacroylcholine chloride, tris(2-acryloyloxyethyl)isocyanurate, 2-vinylpyridine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride 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- inyl)-N-methyl-1-naphthylmethylamine hydrochloride and the like. These monomers may be used individually by 1 type, and may be used in combination of 2 or more type.

1.1.2. Properties of polymer (A) <solubility in water>
Polymer (A) is preferably a water-soluble polymer. When the polymer (A) is a water-soluble polymer, the surface of the active material is easily coated with the polymer (A). As a result, expansion of the active material during charge/discharge can be suppressed, so that an electricity storage device exhibiting good charge/discharge durability can be easily obtained. The "water-soluble polymer" in the present invention means a polymer having a solubility in water of 1 g or more per 100 g of water at 25°C and 1 atm.

<Endothermic properties>
The polymer (A) preferably exhibits an endothermic peak in the temperature range of -20°C to 80°C when subjected to differential scanning calorimetry (DSC) according to JIS K7121. Since such a polymer (A) has a low glass transition temperature (Tg), it is possible to increase the bonding ability between active materials containing a carbon material such as graphite or a silicon material, and the obtained active material The flexibility of the layer becomes appropriate, and the adhesion between the current collector and the active material layer becomes good.

<Weight average molecular weight (Mw)>
The polymer (A) preferably has a polystyrene equivalent weight average molecular weight (Mw) of 1,000 or more, more preferably 10,000 or more, as determined by gel permeation chromatography (GPC). 000 or more is particularly preferred. When the weight-average molecular weight (Mw) of the polymer (A) is within the above range, the adhesion is good, and an electricity storage device with excellent charge/discharge characteristics can be easily obtained.

1.1.3. Method for Synthesizing Polymer (A) The method for synthesizing the polymer (A) is not particularly limited, but polymerization in the presence of a known chain transfer agent, polymerization initiator, etc. in a solvent containing water as a main component is preferred. . A particularly preferred form of polymerization is aqueous solution polymerization. The chain transfer agent used in synthesizing the polymer (A) is preferably a water-soluble chain transfer agent such as hypophosphites, phosphorous acids, thiols, secondary alcohols and amines. Thiols such as mercaptoacetic acid, 2-mercaptosuccinic acid, 3-mercaptopropionic acid and 3-mercapto-1,2-propanediol are particularly preferred. These water-soluble chain transfer agents may be used alone or in combination of two or more. The amount of the chain transfer agent used is preferably 5.0 parts by mass or less with respect to 100 parts by mass of the total mass of the monomers to be polymerized.

The polymerization initiator used in synthesizing the polymer (A) is preferably a water-soluble radical initiator, and persulfates such as lithium persulfate, potassium persulfate, sodium persulfate and ammonium persulfate, and 4,4′-azobis(4 -cyanovaleric acid) are particularly preferred. The amount of the polymerization initiator used is preferably 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the total mass of the monomers to be polymerized.

The polymerization temperature during the synthesis of the polymer (A) is not particularly limited, but it should be synthesized in the range of 30 to 95° C., taking into account the production time and the conversion rate (reaction rate) of the monomers to the copolymer. is preferred, and 50 to 85°C is more preferred. Moreover, it is also possible to use a pH adjuster, a metal ion sealing agent such as EDTA or a salt thereof, for the purpose of improving production stability during polymerization.

Further, before or after the polymerization, the pH may be adjusted with a common neutralizing agent such as ammonia, organic amine, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. In that case, the pH is adjusted to 5-11. is preferably adjusted within the range of It is also possible to use a metal ion sequestering agent such as EDTA or a salt thereof.

1.2. Polymer (B)
The polymer (B) contained in the electricity storage device composition according to the present embodiment may be in the form of latex dispersed in the liquid medium (C), or dissolved in the liquid medium (C). However, it is preferably in the form of a latex in which particles of the polymer (B) are dispersed in the liquid medium (C). When the polymer (B) is in the form of latex dispersed in the liquid medium (C), the stability of the slurry prepared by mixing with the active material is improved, and the slurry is applied to the current collector. It is preferable because it becomes good.

In the polymer (B), the repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group is 0 parts by mass or more and 50 parts by mass when the total of repeating units in the polymer (B) is 100 parts by mass. contains less than Moreover, the polymer (B) may contain repeating units derived from other monomers. Other monomers include, for example, unsaturated carboxylic acid esters (excluding unsaturated carboxylic acid esters having hydroxyl groups), conjugated diene compounds, unsaturated carboxylic acids, (meth)acrylamides, aromatic vinyl compounds, α, β - Unsaturated nitrile compounds, other monomers, and the like.

Hereinafter, the repeating units constituting the polymer (B), the properties of the polymer (B), and the method for synthesizing the polymer (B) will be described in this order.

1.2.1. Repeating Unit Constituting Polymer (B) <Repeating Unit Derived from Unsaturated Carboxylic Acid Ester Having a Hydroxyl Group>
The polymer (B) contains repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group, when the total number of repeating units in the polymer (B) is 100 parts by mass, 0 parts by mass or more and less than 50 parts by mass. contains. The lower limit of the content of the repeating unit derived from the unsaturated carboxylic acid ester having a hydroxyl group is preferably 1 part by mass, more preferably 3 parts by mass. The upper limit of the content of repeating units derived from unsaturated carboxylic acid esters having hydroxyl groups is preferably 50 parts by mass, more preferably 40 parts by mass, and particularly preferably 30 parts by mass. When the polymer (B) contains a repeating unit derived from an unsaturated carboxylic acid ester having a hydroxyl group within the above range, the active material does not agglomerate when the slurry to be described later is produced, and the active material is favorably produced. A dispersed slurry can be made. As a result, the polymer (B) is distributed nearly uniformly in the active material layer produced by applying and drying the slurry, so that an electricity storage device electrode with very few binding defects can be produced. That is, the bonding ability between active materials and the adhesion ability between the active material layer and the current collector can be dramatically improved. Examples of the unsaturated carboxylic acid ester having a hydroxyl group are the same as those for the polymer (A).

<Repeating Unit Derived from Unsaturated Carboxylic Acid Ester>
When the polymer (B) has a repeating unit derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), the polymer (B) has a good affinity with the electrolytic solution and can be polymerized in the electricity storage device. It is possible to suppress an increase in internal resistance due to the combination (B) becoming an electrical resistance component, and to prevent a decrease in adhesion due to excessive absorption of the electrolytic solution.

The lower limit of the content of the repeating unit derived from the unsaturated carboxylic acid ester is preferably 0 part by mass, and 1 part by mass when the total of the repeating units in the polymer (B) is 100 parts by mass. Part is more preferred. The upper limit is preferably 50 parts by mass, more preferably 45 parts by mass, and particularly preferably 40 parts by mass. When the content of the repeating unit derived from the unsaturated carboxylic acid ester is within the above range, the obtained polymer (B) has better affinity with the electrolytic solution, and the polymer (B) can be generated in the electricity storage device. It is possible to suppress an increase in internal resistance due to the formation of an electrical resistance component, and to prevent a decrease in adhesion due to excessive absorption of the electrolytic solution. Examples of the unsaturated carboxylic acid ester are the same as those for the polymer (A).

<Repeating unit derived from conjugated diene compound>
When the polymer (B) has a repeating unit derived from a conjugated diene compound, it becomes easy to produce a polymer excellent in viscoelasticity and strength. That is, when the polymer (B) has a repeating unit derived from a conjugated diene compound, a strong binding force can be imparted to the obtained polymer. Since rubber elasticity derived from the conjugated diene compound is imparted to the polymer, it becomes possible to follow changes such as volume contraction and volume expansion of the active material containing a carbon material such as graphite or a silicon material. As a result, it is considered that the adhesion can be further improved, and the charge/discharge durability can be improved over a long period of time.

The lower limit of the content of repeating units derived from the conjugated diene compound is preferably 20 parts by mass and 25 parts by mass when the total of repeating units in the polymer (B) is 100 parts by mass. 30 parts by mass is particularly preferable. The upper limit is preferably 70 parts by mass, more preferably 65 parts by mass, and particularly preferably 60 parts by mass. When the content of repeating units derived from a conjugated diene compound is within the above range, a polymer having excellent viscoelasticity and strength can be easily produced. Examples of the conjugated diene compound are the same as those for the polymer (A).

<Repeating Unit Derived from Unsaturated Carboxylic Acid>
When the polymer (B) has a repeating unit derived from an unsaturated carboxylic acid, the adhesion of the polymer (B) can be improved. Specific examples of the unsaturated carboxylic acid include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and at least one selected from these. can be done. The polymer (B) preferably has two or more types of repeating units derived from the unsaturated carboxylic acids exemplified above. It is more preferable to use together with one or more kinds of dicarboxylic acids such as acids. Monocarboxylic acid can enhance the effect of improving the bonding ability between active materials containing silicon materials, and dicarboxylic acid can enhance the effect of improving the adhesion ability between the active material layer and the current collector. Therefore, by using a monocarboxylic acid and a dicarboxylic acid in combination, the adhesion of the polymer (B) can be dramatically improved.

The lower limit of the content of repeating units derived from unsaturated carboxylic acid is preferably 0.5 parts by mass when the total of repeating units in the polymer (B) is 100 parts by mass. Parts by mass are more preferred. The upper limit is preferably 30 parts by mass, more preferably 28 parts by mass, and particularly preferably 25 parts by mass. When the content ratio of repeating units derived from unsaturated carboxylic acid is within the above range, the polymer (B) has a bonding ability between active materials having a polar functional group on the surface, such as an active material containing a silicon material. And/or the adhesion ability between the active material layer and the current collector is improved. In addition, since the dispersion stability of the active material is improved during preparation of the slurry, aggregates are less likely to occur, and an increase in slurry viscosity over time can be suppressed.

<Repeating unit derived from (meth)acrylamide>
The polymer (B) may have repeating units derived from (meth)acrylamide. When the polymer (B) has repeating units derived from (meth)acrylamide, the content of the repeating units derived from (meth)acrylamide is based on the total repeating units in the polymer (B) being 100 parts by mass. In this case, the lower limit is preferably 0 parts by mass, more preferably 1 part by mass. The upper limit is preferably 30 parts by mass, more preferably 25 parts by mass, and particularly preferably 20 parts by mass. When the content of repeating units derived from (meth)acrylamide is within the above range, the polymer (B) has a binding ability between active materials having a polar functional group on its surface, such as an active material containing a silicon material. In addition, both the adhesion ability between the active material layer and the current collector are improved. In addition, since the dispersion stability of the active material is improved during preparation of the slurry, aggregates are less likely to occur, and an increase in viscosity of the slurry over time can be suppressed. As a result, the active material layer can be uniformly formed, and the progression of deterioration of the active material layer can be suppressed by, for example, uniformly applying a potential to the active material layer.

<Repeating Unit Derived from Aromatic Vinyl Compound>
When the polymer (B) has a repeating unit derived from an aromatic vinyl compound, the glass transition temperature (Tg) of the polymer (B) is suitable, so that the resulting active material layer has moderate flexibility. , the adhesion ability between the current collector and the active material layer is improved.

The lower limit of the content of the repeating unit derived from the aromatic vinyl compound is preferably 10 parts by mass, and 15 parts by mass when the total of the repeating units in the polymer (B) is 100 parts by mass. is more preferable, and 20 parts by mass is particularly preferable. The upper limit is preferably 60 parts by mass, more preferably 55 parts by mass, and particularly preferably 50 parts by mass. When the content of repeating units derived from an aromatic vinyl compound is within the above range, the resulting polymer tends to have a suitable Tg. As a result, the bonding ability between active materials containing a carbon material such as graphite or a silicon material can be enhanced. In addition, the resulting active material layer has better flexibility and adhesion to the current collector. Examples of the aromatic vinyl compound are the same as those for the polymer (A).

<Repeating Unit Derived from α,β-Unsaturated Nitrile Compound>
When the polymer (B) has a repeating unit derived from an α,β-unsaturated nitrile compound, the polymer (B) can be moderately swollen by the electrolytic solution described below. That is, the presence of the nitrile group allows the electrolytic solution to permeate the network structure of the polymer chains, widening the network spacing, so that the solvated lithium ions easily pass through the network structure and move. As a result, it is considered that the diffusibility of lithium ions is improved. As a result, the electrode resistance can be reduced, so that better charge/discharge characteristics of the electrode can be achieved.

The lower limit of the content of repeating units derived from the α,β-unsaturated nitrile compound is preferably 0 parts by mass when the total number of repeating units in the polymer (B) is 100 parts by mass. , more preferably 2 parts by mass, and particularly preferably 5 parts by mass. The upper limit is preferably 50 parts by mass, more preferably 45 parts by mass, and particularly preferably 40 parts by mass. When the content of the repeating unit derived from the α,β-unsaturated nitrile compound is within the above range, the affinity with the electrolytic solution to be used is excellent, the adhesion and strength are excellent, and the mechanical properties and electrical properties are improved. A composition for an electricity storage device that is excellent in balance with properties can be produced. Examples of the α,β-unsaturated nitrile compound are the same as those for the polymer (A).

<Other repeating units>
The polymer (B) contained in the electricity storage device composition according to the present embodiment can contain, in addition to the repeating units described above, repeating units derived from monomers copolymerizable therewith.

Specific examples of such monomers include vinylidene fluoride, ethylene tetrafluoride, propylene hexafluoride, 1,1,2,2-tetrafluoro-1,2-bis[(trifluorovinyl)oxy] Fluorinated compounds having ethylenically unsaturated bonds such as ethane; carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; acid anhydrides of ethylenically unsaturated dicarboxylic acids; aminoethylacrylamide, dimethylaminomethylmethacrylamide, methylamino Examples include aminoalkylamides of ethylenically unsaturated carboxylic acids such as propylmethacrylamide, and one or more selected from these.

<Preferred Embodiment of Polymer (B)>
From the viewpoint of obtaining a binder composition having more excellent adhesion, the polymer (B) preferably has any one of the following aspects.

(First aspect)
When the total of repeating units in the polymer (B) is 100 parts by mass, 0 parts by mass or more and less than 50 parts by mass of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group and an unsaturated carboxylic acid ester ( A polymer (B-1) containing 50 to 100 parts by mass of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group.
The polymer (B-1) preferably further contains 0.5 to 5 parts by mass of repeating units derived from an unsaturated carboxylic acid. The polymer (B-1) may further contain 1 to 30 parts by mass of repeating units derived from (meth)acrylamide. The polymer (B-1) may be composite particles in which a polymer having these repeating units and a fluorine-containing polymer are combined.

(Second aspect)
When the total of repeating units in the polymer (B) is 100 parts by mass, the repeating unit derived from an unsaturated carboxylic acid ester having a hydroxyl group is 0 parts by mass or more and less than 50 parts by mass, and the repeating unit derived from a conjugated diene compound A polymer (B-2) containing 20 to 70 parts by mass of repeating units and 0.5 to 30 parts by mass of repeating units derived from an unsaturated carboxylic acid.
The polymer (B-2) preferably further contains 1 to 50 parts by mass of repeating units derived from an aromatic vinyl compound. In addition, the polymer (B-2) may further contain 1 to 30 parts by mass of repeating units derived from (meth)acrylamide.

1.2.2. Properties of polymer (B) <solubility in water>
Polymer (B) is preferably a water-insoluble polymer. Since the polymer (B) is a water-insoluble polymer, the function of the polymer (B) as a binder (that is, the binding ability between active materials and the adhesion ability between the active material layer and the current collector) is enhanced. It is preferable because it is easily exhibited. The term "water-insoluble polymer" as used in the present invention means a polymer having a solubility in water of less than 1 g per 100 g of water at 25° C. and 1 atm.

<Tetrahydrofuran (THF) insoluble matter>
The THF-insoluble content of the polymer (B) is preferably 75% by mass or more, more preferably 80% by mass or more. It has been empirically confirmed that this THF-insoluble content is approximately proportional to the amount of insoluble content in the electrolytic solution used in the electric storage device. Therefore, it is preferable to use the polymer (B) having a THF-insoluble content within the above range, because the elution of the polymer (B) into the electrolytic solution can be suppressed even when charging and discharging are repeated over a long period of time.

The THF-insoluble portion of polymer (B) was obtained by immersing 1 g of polymer (B) in 400 mL of tetrahydrofuran (THF) and shaking at 50° C. for 3 hours, and then filtering the THF phase through a 300-mesh wire mesh. It can be calculated by the following formula (1) from the measured value of the mass (Y (g)) of the residue obtained by removing the dissolved THF by evaporation after separating the insoluble matter.
THF insoluble matter (%) = ((1-Y)/1) x 100 (1)

<Endothermic properties>
The polymer (B) preferably has only one endothermic peak in the temperature range of -40°C to 30°C when measured by differential scanning calorimetry (DSC) according to JIS K7121. The endothermic peak temperature (that is, the glass transition temperature (Tg)) is preferably in the range of -30°C to 25°C, more preferably in the range of -25°C to 20°C. When the polymer (B) has only one endothermic peak in the DSC analysis and the peak temperature is within the above range, the polymer (B) exhibits good adhesion to the active material layer. It is preferable because it can impart better flexibility and adhesiveness.

<Number average particle size>
When the polymer (B) is in the form of latex dispersed as particles in the liquid medium (C), the number average particle size of the polymer (B) is preferably in the range of 50 to 1,000 nm, preferably 90 It is more preferably in the range of ~750 nm. When the number average particle size of the polymer (B) is within the above range, the polymer (B) is easily adsorbed on the surface of the active material, so that the polymer (B) follows the movement of the active material. can 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 diameter of the polymer (B) is the cumulative frequency of the number of particles when the particle size distribution is measured using a particle size distribution measuring device based on the measurement principle of the light scattering method, and the particles are accumulated from small particles. is the value of the particle diameter (D50) at which is 50%. Examples of such particle size distribution analyzers include Coulter LS230, LS100, and LS13 320 (manufactured by Beckman Coulter, Inc.) and FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.).

<Weight average molecular weight (Mw)>
The polymer (B) preferably has a weight average molecular weight (Mw) in terms of polystyrene by gel permeation chromatography (GPC) of 10,000 or more, more preferably 100,000 or more. 000 or more is particularly preferred. When the weight-average molecular weight (Mw) of the polymer (A) is within the above range, the adhesion is good, and an electricity storage device with excellent charge/discharge characteristics can be easily obtained.

1.2.3. Method for producing the polymer (B) The method for synthesizing the polymer (B) is not particularly limited, but for example, an emulsion polymerization method performed in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. can depend on Examples of known emulsifiers, chain transfer agents and polymerization initiators include compounds described in Japanese Patent No. 599399 and the like.

The emulsion polymerization method for synthesizing the polymer (B) may be carried out by one-stage polymerization or may be carried out by multi-stage polymerization of two or more stages.

When the synthesis of the polymer (B) is carried out by one-step polymerization, the mixture of the above monomers is preferably reacted at 40 to 80° C. in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc. can be by emulsion polymerization for 4 to 18 hours.

When the polymer (B) is 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 40 to 95% by mass, more preferably in the range of 45 to 90% by mass. By carrying out the first-stage polymerization with such an amount of monomers, it is possible to obtain particles of the polymer (B) that are excellent in dispersion stability and are less likely to form aggregates, and that the composition for an electricity storage device changes over time. This is preferable because it also suppresses a significant increase in viscosity.

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. However, when using a monomer highly reactive with a diene monomer such as an α,β-unsaturated nitrile compound as the monomer, the reaction heat is released all at once because the polymerization reaction progresses rapidly. may occur, making it difficult to control the temperature of the polymerization. Therefore, preferably 10 to 60% by mass, more preferably 15 to 50% by mass of these monomers are subjected to the second-stage polymerization in order to further stabilize the temperature control of the polymerization.

Moreover, it is preferable to use a monomer mixture containing an unsaturated carboxylic acid, (meth)acrylamide, and an unsaturated carboxylic acid ester having a hydroxyl group as the monomers used in the second-stage polymerization. The content of the unsaturated carboxylic acid, (meth)acrylamide, and unsaturated carboxylic acid ester having a hydroxyl group in the monomer mixture used in the second-stage polymerization is preferably 50% by mass or more, more preferably 75% by mass. More preferably, it is 100% by mass.

From the viewpoint of the dispersibility of the resulting polymer, 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 24 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 6 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.

Even if the synthesis of the polymer (B) is carried out by one-step polymerization or by two-step polymerization, by adding a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed, , the pH is preferably adjusted to about 3-6, preferably 3.5-5.5, more preferably 4-5. 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 (B) 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 (B).

(B) When the polymer is a fluorine-containing polymer particle, as a specific embodiment, (1) a polymer particle having a repeating unit derived from a monomer having a fluorine atom is synthesized by one-step polymerization. (2) a composite particle having a polymer X having a repeating unit derived from a monomer having a fluorine atom and a polymer Y having a repeating unit derived from an unsaturated carboxylic acid; aspects. Among these, from the viewpoint of excellent oxidation resistance, composite particles are preferable, and the composite particles are more preferably polymer alloy particles. Examples of the method for producing such composite particles include the method described in JP-A-2014-081996.

1.3. liquid medium (C)
The composition for an electricity storage device according to this embodiment contains a liquid medium (C). The liquid medium (C) 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 (C), 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 producing the composition for an electricity storage device. may contain

1.4. 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 (A) and polymer (B), preservatives, thickeners, and the like. Examples of antiseptics include compounds described in Japanese Patent No. 599399 and the like.

By containing a thickener, the composition for an electricity storage device according to the present embodiment may be able to further improve the applicability and the charge/discharge characteristics of the obtained electricity storage device.

Examples of such thickeners include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; ammonium salts or alkali metal salts of the above cellulose compounds; polyvinyl alcohol, modified polyvinyl alcohol, ethylene-vinyl alcohol copolymers, and the like. polyvinyl alcohol-based (co)polymers; and water-soluble polymers such as saponified copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid and fumaric acid, and vinyl esters. Among these, particularly preferred thickeners include alkali metal salts of carboxymethylcellulose and alkali metal salts of poly(meth)acrylic acid.

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.

1.5. Physical Properties of Composition for Electricity Storage Device <Content Ratio of Polymer (A) and Polymer (B)>
When the content of the polymer (A) is Ma parts by mass and the content of the polymer (B) is Mb parts by mass, the power storage device composition according to the present embodiment has a value of Mb/Ma It is preferably 0.5 to 5.0, more preferably 0.6 to 4.5, and particularly preferably 0.7 to 4.0. When the blending balance of the polymer (A) and the polymer (B) in the electricity storage device composition is within the above range, the surface of the active material of the polymer (A) is coated to suppress the expansion of the active material. Due to the synergistic effect of the effect and the adhesion ability of the polymer (B) between the active material and the current collector and the bonding ability between the active materials, not only excellent adhesion but also very good charge / discharge durability characteristics are exhibited. An electrical storage device electrode is obtained.

<pH>
The pH of the power storage device composition according to the present embodiment is preferably 3 to 8, more preferably 3.5 to 8, and particularly preferably 3.5 to 7.8. If the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling and liquid dripping when applying the slurry, and an electricity storage device electrode having both good electrical properties and adhesion can be obtained. Easier to manufacture.

"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.

In the slurry prepared using the power storage device composition having a pH within the above range, the low pH corrodes the surface of the active material to an extent that does not deteriorate the charge/discharge characteristics, and the surface of the active material is exposed to the atmosphere and adheres to contamination. The active material surface can be cleaned. As a result, in the obtained active material layer, it is possible to suppress the hindrance of intercalation and deintercalation of lithium ions between the active material and the electrolytic solution, and it is possible to develop good charge-discharge characteristics.

Although it is not denied that the pH of the electricity storage device composition is affected by the composition of the monomers constituting the polymer (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 electricity storage device composition changes depending on the polymerization conditions and the like even if the monomer composition is the same, and the examples of the present application merely show an example thereof.

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.

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 “1.3. Liquid Medium (C)” 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 “1.4. 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. Hereinafter, components contained in the slurry for electricity storage device electrodes according to the present embodiment will be described. In addition, since it is as above-mentioned about the composition for electrical storage devices, description is abbreviate|omitted.

2.2.1. 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.

Examples of the carbon material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon fiber.

Examples of the silicon material include silicon simple _substance , silicon _{oxide ,} silicon _alloy , and the like. Si ₂ N ₂ O, Si oxide composites represented by SiO _x (0<x≦2) (for example, materials described in JP-A-2004-185810 and JP-A-2005-259697), and silicon materials described in JP-A-2004-185810. As the silicon oxide, a silicon oxide represented by a composition formula of SiO _x (0<x<2, preferably 0.1≦x≦1) is preferable. The silicon alloy is preferably an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron and molybdenum. Silicon alloys of these transition metals are preferably used because they have high electronic conductivity and high strength. In addition, when the active material contains these transition metals, the transition metal present on the surface of the active material is oxidized to form an oxide having a hydroxyl group on the surface. preferable. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The content of silicon in the silicon alloy is preferably 10 mol % or more, more preferably 20 to 70 mol %, based on all metal elements in the alloy. The silicon material may be single crystal, polycrystal or amorphous.

As the oxide containing lithium atoms, for example, one or more selected from lithium atom-containing oxides (olivine-type lithium-containing phosphate compounds) represented by the following general formula (2) and having an olivine-type crystal structure. is mentioned.

Li _1-x M _x (AO ₄ ) (2)
(In formula (2), M is at least one selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge and Sn is a metal ion of a species, A is at least one selected from the group consisting of Si, S, P and V, and x is a number that satisfies the relationship 0<x<1.)
The value of x in general formula (2) is selected according to the valences of M and A so that the overall valence of general formula (2) is zero.

Examples of olivine-type lithium-containing phosphate compounds include lithium cobaltate, lithium nickelate, lithium manganate, ternary lithium nickel-cobalt _manganate , _LiFePO4 , _LiCoPO4 , _LiMnPO4 , _{Li0.90Ti0.05Nb} . _{0.05Fe0.30Co0.30Mn0.30PO4 and the like .} Among these, LiFePO ₄ (lithium iron phosphate) is particularly preferable because the raw material iron compound is readily available and inexpensive.

The average particle size of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

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 producing a positive electrode, among the active materials exemplified above, it is preferable to use an oxide containing a lithium atom, an olivine-type lithium-containing phosphate compound is more preferable, and lithium iron phosphate (LiFePO ₄ ) is particularly preferable. . Lithium iron phosphate is particularly preferred because the iron compound used as the starting material is readily available and inexpensive.

By the way, when lithium iron phosphate is used as the positive electrode active material, there is a problem that the charging/discharging 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 (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. It is thought that it is from

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. As such a mixture, a carbon-coated silicon material obtained by forming a coating of a carbon material on the surface of a silicon material can also be used. By using the carbon-coated silicon material, the effect of volume change accompanying charging and discharging of the silicon material can be effectively mitigated by the carbon material present on the surface. It becomes easy to improve the adhesion ability.

When silicon (Si) is used as an active material, silicon can occlude up to 22 lithium atoms per 5 atoms (5Si+22Li→Li ₂₂ Si ₅ ). As a result, the theoretical capacity of silicon reaches 4200 mAh/g. However, silicon undergoes a large volume change when absorbing lithium. Specifically, the carbon material expands in volume up to about 1.2 times by absorbing lithium, whereas the silicon material expands in volume up to about 4.4 times by 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 (A) can strongly bind the silicon material, and at the same time, even if the silicon material expands in volume due to the absorption of lithium, the polymer (A) expands and contracts to form silicon. It is believed that this is because the material can be maintained in a strongly bonded state.

The content of the silicon material in 100 parts by mass of the active material is preferably 1 part by mass or more, more preferably 1 to 50 parts by mass, further preferably 5 to 45 parts by mass. It is particularly preferable to set the amount to 40 parts by mass. When the content of the silicon material in 100 parts by mass of the active material is within the above range, it is possible to obtain an electricity storage device having an excellent balance between improved output and energy density of the electricity storage device and charge/discharge durability characteristics.

When a silicon material and a carbon material are used together as the active material, the amount of the silicon material used is preferably 4 to 40 parts by mass, preferably 5 to 35 parts by mass, when the total mass of the active material is 100 parts by mass. is more preferable, and 5 to 30 parts by mass is particularly preferable. When the amount of the silicon material used is within the above range, the volume expansion of the carbon material is small relative to the volume expansion of the silicon material due to lithium absorption, so the volume change due to charging and discharging of the active material layer containing these active materials is small. can be reduced, and the adhesion between the current collector and the active material layer can be further improved.

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.). This particle size distribution measuring apparatus evaluates not only the primary particles of the active material, but also the secondary particles formed by agglomeration of the primary particles. Therefore, the average particle diameter obtained by this particle size distribution measuring apparatus can be used as an indicator of the state of dispersion of the active material contained in the slurry for electricity storage device electrodes. The average particle size of the active material can also be measured by centrifuging the slurry to sediment the active material, removing the supernatant, and measuring the sedimented active material by the above method. .

The proportion of the active material used is preferably such that the total content of the polymer (A) and the polymer (B) with respect to 100 parts by mass of the active material is 0.1 to 25 parts by mass. More preferably, it is used in a proportion of 0.5 to 15 parts by mass. By setting it as such a usage ratio, it is possible to manufacture an electrode having excellent adhesiveness, low electrode resistance, and excellent charge-discharge characteristics.

2.2.2. Other Additives 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, conductivity-imparting agents, thickeners, liquid media (excluding those brought in from the composition for electric storage devices), pH adjusters, corrosion inhibitors, and the like.

<Electric conductivity imparting agent>
Specific examples of the conductivity imparting agent include carbon and the like in lithium ion secondary batteries. Examples of carbon include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black and furnace black can be preferably used.
The proportion of the conductivity imparting agent used 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. .

<Thickener>
A thickener may be added from the viewpoint of improving the coatability of the slurry for electricity storage device electrodes. Specific examples of the thickener include the compounds described in "1.4. Other Additives". The proportion of the thickener used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the active material.

<Liquid medium>
Since the electricity storage device electrode slurry according to the present embodiment contains the above-described electricity storage device composition, the electricity storage device electrode slurry contains the liquid medium (C) contained in the electricity storage device composition. In the electricity storage device electrode slurry according to the present embodiment, in addition to the liquid medium (C) brought from the electricity storage device composition, if necessary, a liquid medium other than the liquid medium (C) may be added. good.

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 (C) contained in the electricity storage device composition. It is preferable to select and use from among the liquid media described for the liquid medium (C) in the composition for an electricity storage device.

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, and ammonium chloride. Among these, sulfuric acid and ammonium sulfate are preferred.

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.

2.2.3. 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 by the method described in Japanese Patent No. 599399, for example.

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 (A), the polymer (B) and the active material described above, and optional components added as necessary, on the current collector. are bound together, it exhibits excellent adhesion and 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. 599399 can be used.

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 following procedure. i.e.
(1) Using a fluorescent X-ray spectrometer (manufactured by Spectris, product name: "Panalytical MagixPRO"), a prepared sample having a known silicon element content is measured at a plurality of points to create a calibration curve.
(2) Scrape off 3 g of the entire active material layer from the electricity storage device electrode (do not collect only a part in the depth direction) with a spatula or the like, mix with a mortar or the like so that the whole is uniform, and then remove a 3 cm diameter piece. press onto a disc-shaped plate. If the active material layer alone cannot be formed, an adhesive agent having a known elemental composition may be used as appropriate. As such a coagulant, for example, styrene/maleic acid resin, boric acid powder, cellulose powder and the like can be used. Moreover, even when the silicon content is high and the linearity of the calibration curve cannot be ensured, the sample can be diluted with the above-mentioned coagulant for measurement. When using the above-mentioned coagulant, it is preferable to use the same coagulant for the sample for preparing the calibration curve in order to avoid deviation of the calibration curve due to the matrix effect.
(3) The obtained plate is set in a fluorescent X-ray analyzer for analysis, and the silicon element content is calculated from the calibration curve. When the above coagulant is used, the silicon element content is calculated after subtracting the weight of the coagulant.

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.

As the electrolyte for lithium ion secondary batteries, any conventionally known lithium salt can be used, and specific examples thereof include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO ₂ and LiAsF ₆ . , _LiSbF6 , _LiB10Cl10 , _LiAlCl4 , LiCl, LiBr, _{LiB ( C2H5} ) _{4 , LiCF3SO3 , LiCH3SO3 , LiC4F9SO3 ,} Li _{( CF3SO2} ) ₂ Examples include N, lithium lower fatty acid carboxylate, and the like. In the nickel-hydrogen secondary battery, for example, a conventionally known potassium hydroxide aqueous solution having a concentration of 5 mol/liter or more can be used.

The solvent for dissolving the electrolyte is not particularly limited, but specific examples thereof include carbonate compounds such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methylethyl carbonate, and diethyl carbonate; lactone compounds such as butyl lactone; ether compounds such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxide compounds such as dimethylsulfoxide; One or more selected from these can be used. The electrolyte concentration in the electrolytic solution is preferably 0.5 to 3.0 mol/L, more preferably 0.7 to 2.0 mol/L.

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. Synthesis of Polymer (1) Synthesis of Polymers (A1) to (A-26) A polymer (A1) was obtained by the following polymerization. After sufficiently replacing the inside of a separable flask with a capacity of 7 L with nitrogen, 310 parts by mass of water was charged, the internal temperature was raised to 80° C., and then 0.5 parts by mass of sodium persulfate was added. Then, a mixed solution of 50 parts by mass of water and 100 parts by mass of 2-hydroxyethyl acrylate was added dropwise over 1 hour, followed by reaction at 80°C ± 3°C for 2 hours, and reaction at 90°C ± 3°C for 4 hours. gone. Thereafter, the mixture was cooled and adjusted to pH 7 with a 2.5% sodium hydroxide aqueous solution to obtain a composition containing 20 wt% of polymer (A1). A composition containing 20 wt % of the polymer (A1) obtained in this way was designated as a composition for an electricity storage device A1.

Polymers (A2) to (A26) were synthesized in the same manner as in the synthesis example of the polymer (A1) except that the types and content of the monomers used were changed as shown in Tables 1 and 2. to obtain power storage device compositions A2 to A26.

The abbreviations of the components in Tables 1 and 2 represent the following compounds.
<Unsaturated carboxylic acid ester having a hydroxyl group>
・HEA: 2-hydroxyethyl acrylate ・HEMA: 2-hydroxyethyl methacrylate <(meth)acrylamide>
・AAM: acrylamide ・MAAM: methacrylamide <Other monomers>
・MMA: methyl methacrylate ・BA: n-butyl acrylate ・EA: ethyl acrylate

(2) Synthesis of Polymers (B1) to (B13) A composition containing particles of polymer (B1) was obtained by two-stage polymerization as shown below. In the first-stage polymerization, 211 parts by mass of water and 79 parts by mass of a monomer mixture consisting of 33 parts by mass of 1,3-butadiene, 42 parts by mass of styrene, 2 parts by mass of methacrylic acid and 2 parts by mass of acrylic acid were placed in the reactor. , 0.1 parts by mass of t-dodecyl mercaptan as a chain transfer 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 stirred at 60 ° C. Polymerization was carried out for 18 hours, and the reaction was completed at a polymerization conversion rate of 96%. Subsequently, in the second-stage polymerization, 189 parts by mass of water, 21 parts by mass of methacrylic acid, 0.05 parts by mass of potassium persulfate as a polymerization initiator, and 0.1 part by mass of sodium carbonate were added to the reactor. After the addition and the polymerization reaction was continued at 80° C. for 2 hours, the reaction was terminated. The polymerization conversion rate at this time was 98%. Unreacted monomers are removed from the obtained latex of the polymer (B1) (particle dispersion of the polymer (B1)), and after concentration, a 10% aqueous sodium hydroxide solution and water are added to obtain the polymer (B1 ) was adjusted to obtain an electricity storage device composition B1 having a pH of 4.4 and containing 20% of the particles of the polymer (B1).

Polymers (B2) to (B2)-( B13) was synthesized to obtain power storage device compositions B2 to B13. Polymers (B5) to (B8) and (B10) to (B13) were synthesized by one-step polymerization without performing second-step polymerization.

(3) Synthesis of polymers (B14) to (B18) After sufficiently replacing the inside of an autoclave with an internal volume of 6 L equipped with an electromagnetic stirrer with nitrogen, 2.5 L of deoxygenated pure water and perfluorodecane as an emulsifier 25 g of ammonium acid was charged, and the temperature was raised to 60° C. while stirring at 350 rpm. Next, a mixed gas containing 70% vinylidene fluoride (VdDF) 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 diisopropyl peroxydicarbonate as a polymerization initiator was pressurized using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas of 60% VdDF and 40% HFP was successively injected so that the internal pressure was maintained at 20 kg/cm ² to maintain the pressure at 20 kg/cm ² . In addition, since the polymerization rate decreased as the polymerization progressed, after 3 hours, the same amount of the same polymerization initiator solution as before was pressurized using nitrogen gas, and the reaction was further continued for 3 hours. After that, the reaction solution was cooled and the stirring was stopped, and the reaction was stopped after the unreacted monomer was released, thereby obtaining an aqueous dispersion containing 40% of the fluoropolymer particles. As a result of ¹⁹ F-NMR analysis of the obtained fluorine-based polymer, the mass composition ratio of each monomer was VdDF/HFP=21/4.

After sufficiently purging the inside of a separable flask with a capacity of 7 L with nitrogen, 25 parts by mass of the aqueous dispersion containing the particles of the fluoropolymer obtained in the above step in terms of the fluoropolymer, emulsifier "ADEKARIA Soap SR1025" (trade name, manufactured by ADEKA Co., Ltd.) 0.5 parts by mass, cyclohexyl methacrylate (CHMA) 22.5 parts by mass, ethyl acrylate (EA) 48 parts by mass, allyl methacrylate (AMA) 0.5 parts by mass 2 parts by mass of methacrylamide (AAM), 2 parts by mass of acrylic acid (AA) and 130 parts by mass of water were sequentially charged and stirred at 70°C for 3 hours to allow the fluorine-based polymer to absorb the monomers. Then, 20 mL of a tetrahydrofuran solution containing 0.5 parts by mass of azobisisobutyronitrile, which is an oil-soluble polymerization initiator, was added, the temperature was raised to 75°C and the reaction was carried out for 3 hours, and the reaction was further carried out at 85°C for 2 hours. gone. Then, after cooling, the reaction was stopped, and the pH was adjusted to 6.8 with a 2.5N sodium hydroxide aqueous solution to obtain an electricity storage device composition B14 containing 40% of the polymer (B14).

Polymers (B15) to (B18) were synthesized in the same manner as in the synthesis example of polymer (B14), except that the types and content ratios of the monomers used were changed as shown in Table 4, and electricity was stored. Device compositions B15 to B18 were obtained.

The abbreviations of the components in Tables 3 and 4 represent the following compounds, respectively.
<Monomer Having Fluorine Atom>
・VdDF: vinylidene fluoride ・HFP: propylene hexafluoride ・TFE: ethylene tetrafluoride ・2VE: 1,1,2,2-tetrafluoro-1,2-bis[(trifluorovinyl)oxy]ethane <non- Saturated carboxylic acid>
・AA: acrylic acid ・TA: itaconic acid ・MAA: methacrylic acid <(meth)acrylamide>
・AAM: acrylamide ・MAAM: methacrylamide <conjugated diene compound>
・ BD: 1,3-butadiene <aromatic vinyl compound>
・ST: styrene <unsaturated carboxylic acid ester having a hydroxyl group>
・HEA: 2-hydroxyethyl acrylate ・HEMA: 2-hydroxyethyl methacrylate <unsaturated carboxylic acid ester>
・MMA: methyl methacrylate ・CHMA: cyclohexyl methacrylate ・2EHA: 2-ethylhexyl acrylate ・EA: ethyl acrylate ・BA: n-butyl acrylate ・AMA: methyl acrylate <α,β-unsaturated nitrile compound>
・AN: Acrylonitrile

(4) Physical property evaluation <solubility in water>
At 25° C. and 1 atm, it was visually observed whether or not 1 g of each of the polymers (A1) to (A26) obtained above dissolved in 100 g of water. The results are also shown in Tables 1 and 2. In the table, "○" indicates the case of complete dissolution, and "×" indicates the presence of undissolved matter.

<Measurement of number average particle size>
Using a particle size distribution analyzer (manufactured by Otsuka Electronics Co., Ltd., model "FPAR-1000") whose measurement principle is the dynamic light scattering method, the particle size distributions of the polymers (B1) to (B18) obtained above were measured. The number average particle size was obtained from the particle size distribution. The measurement conditions are as follows. The measurement results are also shown in Tables 3 and 4.
(Measurement condition)
・Dispersion medium: water ・Measurement temperature: 25°C
・ Dilution rate: 0.1 wt%
・Scattering angle: 160°
・Light source laser wavelength: 632.8 nm

<Measurement of pH>
The pH of the power storage device compositions B1 to B18 obtained above was measured at 25° C. using a pH meter (manufactured by HORIBA, Ltd.). The measurement results are also shown in Tables 1 to 4.

<Endothermic properties>
For the electricity storage device compositions A1 to A26 and B1 to B18 obtained above, JIS
When measured using a differential scanning calorimeter (manufactured by NETZSCH, DSC204F1 Phoenix) based on K7121, one endothermic peak of each polymer was observed. The temperature at which the endothermic peak is observed can be regarded as the glass transition temperature (Tg). Tables 1 to 4 also show the glass transition temperature (Tg) of each polymer.

5.2. Example 1
5.2.1. Preparation of power storage device composition The power storage device composition A1 and the power storage device composition B5 obtained above were added to 1.5 parts by mass of the polymer (A1) and 2.0 parts by mass of the polymer (B5). A composition for an electricity storage device used in Example 1 was obtained by adding each corresponding amount and stirring at 60 rpm for 1 hour.

5.2.2. 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 electrodes Add a thickener (trade name “CMC2200”, manufactured by Daicel Corporation) to a biaxial planetary mixer (trade name “TK Hibismix 2P-03” manufactured by Primix Co., Ltd.). 1 part by mass (solid content conversion value, added as an aqueous solution with a concentration of 2% by mass), 94 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 Solid content conversion value), 6 parts by mass of the powder of the graphite-coated silicon oxide film obtained above (solid content conversion value), and 68 parts by mass of water were added and stirred at 60 rpm for 1 hour. Then, the power storage device composition obtained above is added so that the polymer (A1) is 1.5 parts by mass and the polymer (B5) is 2 parts by mass with respect to 100 parts by mass of the active material, and further After stirring for 1 hour, a paste was obtained. After adding water to the obtained paste and adjusting the solid content concentration to 50% 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 5% by mass of Si in the negative electrode active material ( C/Si (5%)) was prepared.

In addition, an electricity storage battery containing no Si in the negative electrode active material was prepared in the same manner as the electricity storage device electrode slurry (C/Si (5%)) except that the amounts of artificial graphite and graphite-coated silicon oxide powder used were adjusted. A device electrode slurry (C), an electricity storage device electrode slurry (C/Si (10%)) containing 10% by mass of Si in the negative electrode active material, and an electricity storage containing 20% by mass of Si in the negative electrode active material A device electrode slurry (C/Si (20%)) was prepared.

5.2.3. 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 (5%)) 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 .

In addition, the type of the electricity storage device electrode slurry to be applied is selected from the electricity storage device electrode slurry (C) containing no Si in the negative electrode active material obtained above, the electricity storage device electrode slurry (C / Si (10%)), or An electricity storage device electrode (negative electrode) containing each of the active materials in the active material layer was produced in the same manner as in the method for producing an electricity storage device electrode described above, except that the electricity storage device electrode slurry (C/Si (20%)) was used. got

(2) 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 Denki Kagaku Kogyo Co., Ltd., trade name "Denka Black 50% pressed product") 3.0 Parts by mass, 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. did 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 .

(3) 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 to prevent air from entering. A lithium ion battery cell (electricity storage device) was assembled by punching and molding the manufactured positive electrode into a diameter of 16.16 mm, and then sealing the exterior 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).

(4) 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 controlled at 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. Charging and discharging were repeated 100 times in this way, and the discharge capacity at the 100th cycle was calculated. The 100-cycle capacity retention rate (%) was obtained by dividing the discharge capacity at the 100th cycle measured in this manner by the discharge capacity at the 1st cycle. When the capacity retention rate at the 100th cycle is 80% or more for all the active materials, it can be judged that the deterioration of the electrode caused by charge-discharge cycles is suppressed and is good.

(5) Evaluation of electrode expansion rate The film thickness of the electricity storage device electrode (negative electrode) produced above was measured and taken as the negative electrode film thickness (X0) before the cycle test. Next, the electric storage device produced above was charged at a constant current (1.0 C) in a constant temperature bath adjusted to 25 ° C. When the voltage reached 4.2 V, the constant voltage ( 4.2 V), and the 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, which was regarded as the first cycle. After repeating charging and discharging 10 times in this manner, the electricity storage device was disassembled and the negative electrode was taken out. The taken-out negative electrode was washed with dimethyl carbonate, dried at room temperature for 12 hours, and the film thickness was measured to obtain the negative electrode film thickness (X1) before the cycle test. The electrode expansion coefficient was a value defined by the following formula.
Electrode expansion rate (%) = (X1/X0) x 100
The electrode expansion rate is 105% or less in the case of the electrode using the electricity storage device electrode slurry (C) containing no Si in the negative electrode active material, and the electricity storage device electrode slurry containing 20% by mass of Si in the negative electrode active material. In the case of an electrode using (C/Si (20%)), when the ratio is 130% or less, the expansion of the electrode caused by charge/discharge cycles is suppressed, and it can be judged to be good.

5.3. Examples 2-21 and Comparative Examples 1-13
In "5.2.1. Preparation of power storage device composition" in Example 1 above, the polymer (A) and polymer (B) were changed to have the content ratios shown in Table 5 or Table 6. A composition for an electricity storage device was obtained in the same manner as in Example 1 except for the above. Furthermore, in the same manner as in Example 1 except that the composition for an electricity storage device thus prepared was used, a slurry for an electricity storage device electrode was prepared, an electricity storage device electrode and an electricity storage device were produced, respectively, and It was evaluated in the same manner as 1.

5.4. Evaluation Results Tables 5 and 6 below summarize the compositions and evaluation results of the electrical storage device compositions used in Examples 1 to 21 and Comparative Examples 1 to 13.

5.5. Example 22
5.5.1. Preparation of power storage device composition The power storage device composition A1 and the power storage device composition B14 obtained above were added to 1.0 parts by mass of the polymer (A1) and 2.0 parts by mass of the polymer (B14). A corresponding amount of each was added, and the mixture was stirred at 60 rpm for 1 hour to obtain an electricity storage device composition used in Example 22.

5.5.2. Production and evaluation of power storage device (1) Preparation of positive electrode slurry and production of positive electrode for power storage device Commercially available nickel-manganese-lithium cobaltate (nickel (Ni), cobalt (Co), manganese (Mn) ratio 1:1:1) 100 parts by mass of active material particles, 3 parts by mass of acetylene black, 1 part by mass of ammonium sulfate and 1 part by mass of water were added and stirred at 90 rpm for 1 hour. Then, the power storage device composition obtained above was added so that the polymer (A1) was 1.0 parts by mass and the polymer (B14) was 2.0 parts by mass with respect to 100 parts by mass of the active material. and further stirred for 1 hour to obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 65%, using a stirring deaerator (manufactured by Thinky Co., Ltd., trade name "Awatori Mixer"), 200 rpm for 2 minutes, 1 , 800 rpm for 5 minutes and then under vacuum (about 5.0×10 ³ 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, the positive electrode was obtained by pressing with a roll press machine so that the density of the active material layer was 3.0 g/cm ³ .

(2) Production of Counter Electrode (Negative Electrode) Of the negative electrodes produced in Example 1, produced using slurry for electricity storage device electrodes (C/Si (10%)) containing 10% by mass of Si in the negative electrode active material. I used what I did.

(3) Assembly of Lithium Ion Battery Cell An electricity storage device was produced in the same manner as in Example 1 except that the electricity storage device electrode produced above was used, and evaluated in the same manner as in Example 1.

(4) Evaluation of the crack rate of the electrode plate The positive electrode plate obtained above was cut into pieces of 2 cm in width and 10 cm in length, and the positive electrode plate was repeatedly bent 100 times along a round bar with a diameter of 2 mm in the width direction. did the test. The size of cracks along the round bar was visually observed and measured, and the crack rate was measured. The crack rate was defined by the following formula (3).
Crack rate (%) = (cracked length (mm) ÷ total electrode plate length (mm)) x 100 (3)
The crack rate was evaluated in increments of 5% by rounding off to make it easier to clarify the difference. Here, an electrode plate with excellent flexibility and adhesion has a low crack rate. A crack rate of 0% is desirable, but a crack rate of up to 20% is permissible when a positive electrode plate and a negative electrode plate are spirally wound with a separator interposed therebetween. However, if the crack rate is greater than 20%, the electrode plate is likely to be cut, making it impossible to manufacture the electrode plate assembly and lowering the productivity of the electrode plate assembly. From this, the crack rate up to 20% was judged to be good.

(5) Evaluation of charge-discharge cycle characteristics The 100-cycle capacity retention rate (%) was calculated in the same manner as in Example 1 for the electricity storage device produced above. In addition, charging and discharging were repeated up to 500 cycles, and the capacity retention rate (%) at 500 cycles was calculated. When the difference between the capacity retention rate at 100 cycles and the capacity retention rate at 500 cycles is 16% or less, it can be judged that the deterioration is suppressed when charging and discharging are repeated, and the battery is good.

5.6. Examples 23-29 and Examples 33-36
In "5.5.1. Preparation of power storage device composition" in Example 22 above, except that the polymer (A) and the polymer (B) were changed to the content ratios shown in Table 7, A composition for an electricity storage device was obtained in the same manner as in Example 22. Furthermore, in the same manner as in Example 22 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, and the was evaluated similarly.

5.7. Example 30
5.7.1. Preparation of power storage device composition The power storage device composition A11 and the power storage device composition B18 obtained above were added to 5.0 parts by mass of the polymer (A11) and 4.0 parts by mass of the polymer (B18). A corresponding amount of each was added, and the mixture was stirred at 60 rpm for 1 hour to obtain an electricity storage device composition used in Example 30.

5.7.2. Preparation of slurry for positive electrode and production of positive electrode for power storage device A biaxial planetary mixer (manufactured by Primix Co., Ltd., trade name “TK Hibis Mix 2P-03”) is added to a thickener (trade name “CMC1120”, manufactured by Daicel Corporation). ) 1 part by mass (in terms of solid content), 100 parts by mass of lithium iron phosphate (LiFePO ₄ ) manufactured by Hosen Co., Ltd., 5 parts by mass of acetylene black, and 68 parts by mass of water, and stirred at 60 rpm for 1 hour. rice field. The lithium iron phosphate was pulverized in an agate mortar and classified using a sieve to have an average particle size (D50 value) of 10 μm. Moreover, the lithium iron phosphate is an example of the positive electrode active material. Then, the power storage device composition obtained above was added so that the polymer (A11) was 5.0 parts by mass and the polymer (B18) was 4.0 parts by mass with respect to 100 parts by mass of the active material. and further stirred for 1 hour to obtain a paste.

After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring deaerator (manufactured by Thinky Co., Ltd., trade name "Awatori Mixer"), 200 rpm for 2 minutes, 1 , 800 rpm for 5 minutes and then under vacuum (about 5.0×10 ³ 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. . After that, the positive electrode was obtained by pressing with a roll press so that the density of the active material layer was 2.0 g/cm ³ .

Thereafter, a negative electrode and an electric storage device were produced in the same manner as in Example 22 above, and evaluated in the same manner as in Example 22 above.

5.8. Examples 31-32 and Comparative Example 14
In "5.7.1. Preparation of power storage device composition" in Example 30 above, except that the polymer (A) and the polymer (B) were changed to the content ratios shown in Table 7, A composition for an electricity storage device was obtained in the same manner as in Example 30 above. Furthermore, in the same manner as in Example 30 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, and was evaluated similarly.

5.9. Evaluation Results Table 7 below summarizes the compositions and evaluation results of the electrical storage device compositions used in Examples 22 to 36 and Comparative Example 14.

The abbreviations of each component in Table 7 represent the following compounds, respectively.
<Active material>
・NMC (111): nickel-manganese-lithium cobaltate (ratio of nickel (Ni), cobalt (Co), manganese (Mn) 1:1:1) active material particles ・NMC (532): nickel-manganese-cobalt Lithium oxide (ratio of nickel (Ni), cobalt (Co), manganese (Mn) 5:3:2) active material particles ・NMC (622): nickel-manganese-lithium cobaltate (nickel (Ni), cobalt (Co ), manganese (Mn) ratio 6:2:2) Active material particles LCO: Lithium cobaltate (LiCoO ₂ ), manufactured by Hayashi Kasei Co., Ltd. LFP: Lithium iron phosphate (LiFePO ₄ ), manufactured by Hosen Co., Ltd. <Conductivity aid>
・AB: Acetylene black

As is clear from Table 5, the electricity storage devices provided with negative electrodes produced using the electricity storage device compositions according to the present invention shown in Examples 1 to 21 performed 100 cycles even when using any active material. The subsequent capacity retention rate was excellent, and the expansion rate of the electrode could be kept low. On the other hand, as is clear from Table 6, in Comparative Examples 1 to 13, as the content of the silicon material in the active material increased, the capacity retention rate after 100 cycles tended to decrease, and the electrode expansion rate could not be kept low.

As is clear from Table 7, the electricity storage devices provided with the positive electrode produced using the electricity storage device composition according to the present invention shown in Examples 22 to 36 can keep the crack rate low, and charge and discharge. It was found that the deterioration when repeated was suppressed. On the other hand, in Comparative Example 14, the crack rate could not be kept low, and it was found that the battery deteriorated at an early stage due to repeated charging and discharging.

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 (14)

Containing a polymer (A), a water-insoluble polymer (B), and water,
When the total of repeating units contained in the polymer (A) is 100 parts by mass, the polymer (A) contains 50 parts by mass or more of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group. ,
When the total number of repeating units contained in the water-insoluble polymer (B) is 100 parts by mass, the number of repeating units derived from the unsaturated carboxylic acid ester having a hydroxyl group in the water-insoluble polymer (B) A power storage device composition having a content of 0 parts by mass and a content of repeating units derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group) of 50 to 100 mass . . Containing a polymer (A), a water-insoluble polymer (B), and water,
When the total of repeating units contained in the polymer (A) is 100 parts by mass, the polymer (A) contains 50 parts by mass or more of repeating units derived from an unsaturated carboxylic acid ester having a hydroxyl group. ,
When the total number of repeating units contained in the water-insoluble polymer (B) is 100 parts by mass, the number of repeating units derived from the unsaturated carboxylic acid ester having a hydroxyl group in the water-insoluble polymer (B) The content ratio is 0 parts by mass, the content ratio of repeating units derived from a conjugated diene compound is 20 to 70 parts by mass, and the content ratio of repeating units derived from an unsaturated carboxylic acid is 0.5 to 30 parts by mass. A composition for an electric storage device. Claim 1 or claim 1, wherein an endothermic peak is observed in a temperature range of -20°C to 80°C when the polymer (A) is subjected to differential scanning calorimetry (DSC) in accordance with JIS K7121. 3. The composition for an electricity storage device according to 2. The composition for an electricity storage device according to any one of claims 1 to 3, wherein the polymer (A) has a solubility in water at 25°C and 1 atm of 1 g or more per 100 g of water. 5. The unsaturated carboxylic acid ester having a hydroxyl group is at least one selected from the group consisting of hydroxyethyl (meth)acrylate and glycerin mono(meth)acrylate, according to any one of claims 1 to 4 . composition for electrical storage devices. The electricity storage device composition according to any one of claims 1 to 5 , wherein the polymer (A) further contains 1 to 40 parts by mass of repeating units derived from (meth)acrylamide. The electricity storage device composition according to any one of claims 1 to 6 , wherein the water-insoluble polymer (B) further contains 1 to 30 parts by mass of repeating units derived from a (meth)acrylamide compound. . When the content of the polymer (A) is Ma parts by mass and the content of the water-insoluble polymer (B) is Mb parts by mass, the value of Mb/Ma is 0.5 to 5.0. The composition for an electricity storage device according to any one of claims 1 to 7 . The composition for an electricity storage device according to any one of claims 1 to 8 , wherein the water-insoluble polymer (B) is particles having a number average particle diameter of 50 nm or more and 1000 nm or less. An electricity storage device electrode slurry containing the electricity storage device composition according to claim 1 and an active material. 11. The electricity storage device electrode slurry according to claim 10 , containing a silicon material as said active material. 11. The method according to claim 10 , wherein the active material contains at least one selected from the group consisting of an olivine-type lithium-containing phosphate compound, lithium cobaltate, lithium nickelate, lithium manganate, and ternary nickel-cobalt-manganese lithium. Slurry for electricity storage device electrodes according to the above. 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 10 to 12 on the surface of the current collector. device electrode. An electricity storage device comprising the electricity storage device electrode according to claim 13 .