Slurry composition for power storage device, slurry for power storage device electrode, power storage device electrode, and power storage device

Abstract

The present invention provides a slurry composition for a power storage device, the slurry composition enabling the production of a power storage device electrode which achieves excellent charge / discharge cycle characteristics by having a reduced internal resistance, while achieving excellent charge / discharge durability characteristics by having improved adhesion.　A slurry composition for a power storage device according to the present invention contains a carboxymethyl cellulose (A), a polymer (B), and a liquid medium (C), wherein: the viscosity of a 1% aqueous solution of the carboxymethyl cellulose (A) as measured using a Brookfield viscometer under a condition of 25°C is 30,000 mPa∙s or more; when the total of repeating units contained in the polymer (B) is taken as 100 mass%, the polymer (B) contains 5-75 mass% of a repeating unit (b1) that is derived from an aromatic vinyl compound and 1-10 mass% of at least one repeating unit selected from the group consisting of a repeating unit (b2) that is derived from an unsaturated carboxylic acid and a repeating unit (b3) that is derived from a compound having a sulfonic acid group; and the swelling ratio is 120 mass% to 250 mass% inclusive when the polymer (B) is immersed in a solvent that is composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under conditions of 70°C and 24 hours.

Description

Slurry composition for energy storage devices, slurry for energy storage device electrodes, energy storage device electrodes and energy storage devices

[0001] The present invention relates to a slurry composition for energy storage devices, a slurry for energy storage device electrodes containing the composition and an active material, an energy storage device electrode prepared by applying and drying the slurry on a current collector, and an energy storage device equipped with the energy storage device electrode.

[0002] In recent years, there has been a growing demand for energy storage devices with high voltage and high energy density to power electronic devices. Lithium-ion batteries and lithium-ion capacitors are among the promising candidates for such devices.

[0003] Electrodes used in such energy storage devices are manufactured by applying and drying a composition (slurry for energy storage device electrodes) containing an active material and a polymer that functions as a binder onto the surface of a current collector. The properties required of the polymer used as a binder include the ability to bond the active materials together, the ability to adhere the active materials to the current collector, abrasion resistance during the electrode winding process, and powder shedding resistance, which prevents fine particles of the active material from falling off the coated and dried composition film (hereinafter also referred to as the "active material layer") even after cutting. By exhibiting good adhesion with such a binder material, the internal resistance of the battery caused by the binder material can be reduced, thereby providing the energy storage device with good charge and discharge characteristics.

[0004] Furthermore, empirically, it has become clear that the bonding ability between the active materials, the adhesion ability between the active materials and the current collector, and the resistance to powder shedding are roughly proportional to the quality of the performance. Therefore, in this specification, these may be collectively referred to as "adhesion."

[0005] Furthermore, in recent years, research and development of electric vehicles equipped with energy storage devices has been actively pursued with the aim of reducing environmental impact. When energy storage devices are installed as a power source for electric vehicles, the devices are required to have battery characteristics such as high capacity, rapid charging, and repeated charge / discharge characteristics.

[0006] Against this backdrop, various binder materials have been proposed to reduce the resistance and improve the charge-discharge durability characteristics of energy storage devices (see, for example, Patent Documents 1 and 2).

[0007] International Publication No. 2015 / 012366, Japanese Patent Publication No. 2017-126456

[0008] However, the binder materials disclosed in the above-mentioned Patent Documents 1 and 2 do not have sufficient repeated charge-discharge characteristics or charge-discharge durability characteristics, and further improvements were needed for application to energy storage devices as power sources for electric vehicles.

[0009] Several aspects of the present invention provide a slurry composition for energy storage devices that enables the manufacture of energy storage device electrodes that have excellent repeated charge-discharge characteristics by reducing internal resistance and excellent charge-discharge durability characteristics by improving adhesion.

[0010] One embodiment of the slurry composition for energy storage devices according to the present invention contains carboxymethylcellulose (A), a polymer (B), and a liquid medium (C), wherein the viscosity of a 1% aqueous solution of carboxymethylcellulose (A), measured using a Brookfield viscometer at 25°C, is 30,000 mPa·s or more, and when the total amount of repeating units contained in the polymer (B) is taken as 100% by mass, the polymer (B) contains 5 to 75% by mass of repeating units (b1) derived from aromatic vinyl compounds, and 1 to 10% by mass of at least one repeating unit selected from the group consisting of repeating units (b2) derived from unsaturated carboxylic acids and repeating units (b3) derived from compounds having sulfonic acid groups, and the swelling rate when the polymer (B) is immersed in a solvent consisting of propylene carbonate and diethyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours is 120% by mass or more and 250% by mass or less.

[0011] In one embodiment of the slurry composition for the energy storage device, the polymer (B) may further contain 0 to 60% by mass of repeating units (b4) derived from a conjugated diene compound.

[0012] In any embodiment of the slurry composition for the energy storage device, the polymer (B) may be polymer particles, and the surface acid content of the polymer particles may be 0.05 mmol / g or more and 1.5 mmol / g or less.

[0013] In any embodiment of the slurry composition for the energy storage device, the polymer (B) may be polymer particles, and the number-average particle diameter of the polymer particles may be 50 nm or more and 500 nm or less.

[0014] In any embodiment of the slurry composition for the energy storage device, the carboxymethylcellulose (A) may have a molecular main chain structure of carboxymethylcellulose, and the side chains of the main chain structure may contain carboxyl groups and sulfonic acid groups.

[0015] In any embodiment of the slurry composition for the energy storage device, when an aqueous solution of carboxymethylcellulose (A) with a solid content of 1% is applied to a surface with a thickness of 100 μm and an area of ​​5 cm × 8 cm, the number of insoluble gels may be 52 or less.

[0016] In any embodiment of the slurry composition for the energy storage device, the viscosity of the 1% aqueous solution of carboxymethylcellulose (A) may be 80,000 mPa·s to 110,000 mPa·s.

[0017] In any embodiment of the slurry composition for the energy storage device, the liquid medium (C) may be water.

[0018] One embodiment of the slurry for energy storage device electrodes according to the present invention contains the slurry composition for energy storage devices according to any of the above embodiments and an active material.

[0019] In one embodiment of the slurry for the electrodes of the energy storage device, the active material may contain graphite and silicon material.

[0020] One embodiment of the energy storage device electrode according to the present invention comprises a current collector and an active material layer formed by applying and drying a slurry for energy storage device electrodes according to any of the above embodiments on the surface of the current collector.

[0021] One embodiment of the energy storage device electrode according to the present invention comprises the energy storage device electrode of the above embodiment.

[0022] According to the slurry composition for energy storage devices of the present invention, carboxymethylcellulose (A) exhibits high viscosity, allowing for high adhesion to electrodes with a small amount of additive, and the polymer (B) effectively suppresses electrode expansion. Furthermore, according to the slurry composition for energy storage devices of the present invention, carboxymethylcellulose (A) improves the dispersibility of the active material and conductive additive, making it easier to form efficient conductive paths in the active material layer. This makes it possible to manufacture energy storage device electrodes with reduced internal resistance, excellent input / output characteristics, and excellent charge-discharge cycle characteristics.

[0023] Preferred embodiments of the present invention will be described in detail below. It should be understood that the present invention is not limited to the embodiments described below, but also includes various modifications that do not alter the essence of the invention.

[0024] In this specification, "(meth)acrylic" means "acrylic" or "methacrylic," "(meth)acrylate" means "acrylate" or "methacrylate," and "(meth)acrylamide" means "acrylamide" or "methacrylamide."

[0025] In this specification, numerical ranges described as "X to Y" are interpreted as including the numerical value X as the lower limit and the numerical value Y as the upper limit.

[0026] 1. Slurry composition for energy storage devices The slurry composition for energy storage devices according to one embodiment of the present invention contains carboxymethylcellulose (A), a polymer (B), and a liquid medium (C). The viscosity of a 1% aqueous solution of carboxymethylcellulose (A), measured using a Brookfield viscometer at 25°C, is 30,000 mPa·s or more. The polymer (B) contains, when the total amount of repeating units contained in the polymer (B) is 100% by mass, 5 to 75 parts by mass of repeating units (b1) derived from aromatic vinyl compounds, and 1 to 10 parts by mass of at least one repeating unit selected from the group consisting of repeating units (b2) derived from unsaturated carboxylic acids and repeating units (b3) derived from compounds having sulfonic acid groups. Furthermore, the polymer (B) has a swelling rate of 120% by mass or more and 250% by mass or less when immersed in a solvent consisting of propylene carbonate and diethyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours.

[0027] The slurry composition for energy storage devices according to this embodiment can be used as a material for producing an electrode (active material layer) for an energy storage device with improved bonding ability between active materials, adhesion ability between active materials and current collectors, and resistance to powder shedding. The components that may be included in the slurry composition for energy storage devices according to this embodiment will be described in detail below.

[0028] 1.1. Carboxymethylcellulose (A) The slurry composition for energy storage devices according to this embodiment contains carboxymethylcellulose (A). The viscosity of a 1% aqueous solution of carboxymethylcellulose (A), measured using a Brookfield viscometer at 25°C, is 30,000 mPa·s or higher. The lower limit of the viscosity of this 1% aqueous solution of carboxymethylcellulose (A) is preferably 60,000 mPa·s, more preferably 80,000 mPa·s, and particularly preferably 85,000 mPa·s. The upper limit of the viscosity of this 1% aqueous solution of carboxymethylcellulose (A) is preferably 120,000 mPa·s, more preferably 110,000 mPa·s, and particularly preferably 105,000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethylcellulose (A) is preferably 60,000 mPa·s to 120,000 mPa·s, more preferably 80,000 mPa·s to 110,000 mPa·s, and particularly preferably 85,000 mPa·s to 105,000 mPa·s. As such, carboxymethylcellulose (A) can exhibit high viscosity, and therefore high adhesion to the electrode can be imparted with a small amount of additive. When the viscosity of carboxymethylcellulose (A) is within the above range, migration of the binder that occurs during electrode drying is suppressed, and thus a reduction in adhesion to the electrode can be suppressed. The measurement method is as described in the examples.

[0029] The number of insoluble gel substances in carboxymethylcellulose (A) is preferably 52 or less, more preferably 42 or less, and even more preferably 32 or less. When the number of insoluble gel substances in carboxymethylcellulose (A) is within the above range, it is thought that the reduction in adhesion to the electrode can be suppressed because there is less gel component during slurry preparation. The measurement method is as described in the examples.

[0030] Furthermore, in carboxymethylcellulose (A), the main chain structure of the molecule is carboxymethylcellulose, but it is preferable that carboxyl groups and sulfonic acid groups are present in the side chains of the main chain structure. By graft polymerization of monomers having carboxyl groups and monomers having sulfonic acid groups onto the uncarboxymethylated hydroxyl functional groups on the glucose units of carboxymethylcellulose, carboxyl groups, sulfonic acid groups, and crosslinking structures are introduced, forming crosslinked water-soluble polymer branched chains in the side chains of carboxymethylcellulose. In carboxymethylcellulose (A) with carboxyl groups, sulfonic acid groups, and crosslinking structures introduced into the side chains, the movement of the molecular chains becomes more difficult due to spatial steric hindrance and hydrogen bonding between carboxylate, sulfonate, and hydroxyl groups, and the viscosity of the aqueous carboxymethylcellulose solution is greatly improved. As a result, the amount added to the electrode plate can be reduced, and process problems such as decreased slurry viscosity, weight instability during coating, decreased tackiness, and electrode plate peeling do not occur, and high battery capacity can be achieved.

[0031] Carboxymethylcellulose (A) can be produced, for example, as follows: Step 1: Carboxymethylcellulose is added to an aqueous ethanol solution under a nitrogen-protected atmosphere and dispersed uniformly. Step 2: The mixed solution obtained in Step 1 is heated to 50-90°C, ammonium persulfate is added as an initiator, and the mixture is kept warm for 1-3 hours. In this way, the hydroxyl groups at the 2nd and 3rd positions of the glucose units in the carboxymethylcellulose molecular chain are activated. Step 3: After the reaction in Step 2 is complete, monomers having carboxyl groups and monomers having sulfonic acid groups are added within 1-5 hours and the mixture is kept warm for 1-3 hours. Step 4: After the reaction in Step 3 is complete, a crosslinking agent is added within 1-5 hours. Step 5: After the reaction in Step 4 is complete, the reaction solution is filtered to obtain a solid of carboxymethylcellulose (A) in which carboxyl groups, sulfonic acid groups, and crosslinking structures have been introduced into the side chains. This is washed several times with acetone solution to remove unreacted monomers, dried, and pulverized to obtain carboxymethylcellulose (A).

[0032] Because carboxyl groups have strong polarity, the introduction of carboxyl groups into the side chains of carboxymethylcellulose (A) results in excellent water solubility, improving its water solubility and dispersibility in the slurry for energy storage device electrodes. This allows for better dispersion and compatibility with other components in the slurry for energy storage device electrodes, and further significantly increases the viscosity of carboxymethylcellulose (A). In addition, since this chemical modification process does not generate additional gelling insoluble particles, it is possible to avoid the phenomenon of the prepared slurry for energy storage device electrodes being unfilterable.

[0033] Examples of monomers having a carboxyl group include mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, 2-propylacrylic acid, and 3,3-dimethylacrylic acid, as well as salts thereof. One or more selected from these can be used. Among these, sodium acrylate is particularly preferred.

[0034] The sulfonic acid group interacts with the carboxyl group to enhance the adhesiveness of carboxymethylcellulose (A). Furthermore, the formation of water-soluble cross-linked polymer chains on the side chains of carboxymethylcellulose (A) can further improve its solubility in water.

[0035] Examples of monomers having a sulfonic acid group include sodium vinylsulfonate, sodium p-styrenesulfonate, and sodium 3-allyloxy-2-hydroxy-1-propanesulfonate, and one or more selected from these can be used. Among these, sodium p-styrenesulfonate is particularly preferred.

[0036] Further, by adding a crosslinking agent, a network structure in which carboxyl groups and sulfonic acid groups are crosslinked can be formed. As a result, polymer branches formed by carboxyl groups and sulfonic acid groups on carboxymethyl cellulose (A) finally form a network-like super-large-scale branch, and the spatial steric hindrance effect can be further enhanced. Also, the movement of the molecular chains of carboxymethyl cellulose (A) becomes more difficult, and its viscosity can be effectively improved.

[0037] Examples of the crosslinking agent include pentaerythritol tetraacrylate, trimethylolpropane triacrylate, vinyl methacrylate, diallyl maleate, diallyl carbonate, etc., and one or more selected from these can be used. Among these, pentaerythritol tetraacrylate or trimethylolpropane triacrylate is preferable, and pentaerythritol tetraacrylate is more preferable.

[0038] When manufacturing the above carboxymethyl cellulose (A), when the mass of carboxymethyl cellulose is a, the mass of the monomer having a carboxyl group is b, the mass of the monomer having a sulfonic acid group is c, and the mass of the crosslinking agent is d, it is preferable that a:b:c:d = 1000:95 - 715:50 - 265:10 - 20. Also, when manufacturing the above carboxymethyl cellulose (A), by satisfying the relationship of the following formula (1), the degree of crosslinking by carboxyl groups and sulfonic acid groups becomes appropriate, and a high-viscosity carboxymethyl cellulose (A) with less gel insoluble matter can be obtained. Further, when manufacturing the above carboxymethyl cellulose (A), by satisfying the relationship of the following formula (2), the modification rate becomes appropriate, and a carboxymethyl cellulose (A) with sufficiently high viscosity can be obtained, and the yield is also improved.

[0039] 1.2. Polymer (B) The slurry composition for a power storage device according to this embodiment contains a polymer (B). The polymer (B) may be in the form of a latex dispersed in the liquid medium (C) or may be in a dissolved state in the liquid medium (C), but is preferably in the form of a latex dispersed in the liquid medium (C). When the polymer (B) is in the form of a latex dispersed in the liquid medium (C), the stability of the slurry for a power storage device electrode (hereinafter also simply referred to as "slurry") prepared by mixing with the active material is good, and the coating property of the slurry on the current collector is good, which is preferable.

[0040] Hereinafter, the repeating units constituting the polymer (B), the physical properties of the polymer (B), and the production method will be described in this order.

[0041] 1.2.1. Repeating units constituting the polymer (B) When the total of the repeating units contained in the polymer (B) is 100% by mass, the polymer (B) contains 5 to 75% by mass of a repeating unit (b1) derived from an aromatic vinyl compound (hereinafter also referred to as "repeating unit (b1)") and at least one repeating unit selected from the group consisting of a repeating unit (b2) derived from an unsaturated carboxylic acid (hereinafter also referred to as "repeating unit (b2)") and a repeating unit (b3) derived from a compound having a sulfonic acid group (hereinafter also referred to as "repeating unit (b3)") in an amount of 1 to 10% by mass. In addition to these repeating units, the polymer (B) may contain repeating units derived from other monomers copolymerizable with these repeating units.

[0042] 1.2.1.1. Repeating Units (b1) The content of repeating units (b1) derived from aromatic vinyl compounds is 5 to 75% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units (b1) is preferably 7% by mass, and more preferably 9% by mass. The upper limit of the content of repeating units (b1) is preferably 70% by mass, and more preferably 65% ​​by mass. The content of repeating units (b1) is preferably 7 to 70% by mass, and more preferably 9 to 65% by mass. By containing repeating units (b1) within the above ranges in polymer (B), the dispersibility of the active material and conductive additive becomes excellent in the liquid medium (C), and good slurry characteristics are obtained, thereby improving coatability. In addition, the permeability of the electrolyte can be improved, resulting in good repeated charge-discharge characteristics.

[0043] The aromatic vinyl compound is not particularly limited, but examples include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, 4-tert-butylstyrene, etc., and one or more selected from these can be used. Among these, styrene is particularly preferred.

[0044] 1.2.1.2. Repeating Units (b2) and Repeating Units (b3) Polymer (B) contains at least one repeating unit selected from the group consisting of repeating units (b2) derived from unsaturated carboxylic acids and repeating units (b3) derived from compounds having sulfonic acid groups (hereinafter also referred to as "repeating units derived from specific acid compounds"). The content of repeating units derived from specific acid compounds is 1 to 10% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units derived from specific acid compounds is preferably 1.5% by mass, and more preferably 2% by mass. The upper limit of the content of repeating units derived from specific acid compounds is preferably 9% by mass, and more preferably 8% by mass. The content of repeating units derived from specific acid compounds is preferably 1.5 to 9% by mass, and more preferably 2 to 8% by mass. By polymer (B) containing repeating units derived from specific acid compounds within the above ranges, the dispersibility of the active material and conductive additive is further improved. Furthermore, the resulting active material layer has appropriate flexibility, resulting in good adhesion between the current collector and the active material layer. In addition, the affinity with the silicon material used as the active material is improved, and the dispersion of the conductive additive near the silicon material results in good charge-discharge durability characteristics.

[0045] The content of repeating units (b2) derived from unsaturated carboxylic acids is preferably 0.5 to 10% by mass, when the total amount of repeating units contained in polymer (B) is taken as 100% by mass. The lower limit of the content of repeating units (b2) is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content of repeating units (b2) is more preferably 9% by mass, and particularly preferably 8% by mass. The content of repeating units (b2) is more preferably 1 to 9% by mass, and particularly preferably 2 to 8% by mass.

[0046] The unsaturated carboxylic acid is not particularly limited, but examples include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, as well as dicarboxylic acid monoesters such as monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate. One or more selected from these can be used. Preferably, one or more selected from acrylic acid, methacrylic acid, itaconic acid, monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate is used as the unsaturated carboxylic acid.

[0047] The content of repeating units (b3) derived from compounds having sulfonic acid groups is preferably 0.5 to 10% by mass, when the total amount of repeating units contained in polymer (B) is taken as 100% by mass. The lower limit of the content of repeating units (b3) is more preferably 0.8% by mass, and particularly preferably 1% by mass. The upper limit of the content of repeating units (b3) is more preferably 8% by mass, and particularly preferably 5% by mass. The content of repeating units (b3) is more preferably 0.8 to 8% by mass, and particularly preferably 1 to 5% by mass.

[0048] Compounds having a sulfonic acid group are not particularly limited, but include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-alyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof.

[0049] 1.2.1.3. Other repeating unit polymers (B) may contain repeating units derived from other monomers copolymerizable with repeating units (b1), (b2), and (b3). Examples of such repeating units include repeating units (b4) derived from conjugated diene compounds (hereinafter also referred to as "repeating unit (b4)"), repeating units (b5) derived from unsaturated carboxylic acid esters (hereinafter also referred to as "repeating unit (b5)"), repeating units (b6) derived from α,β-unsaturated nitrile compounds (hereinafter also referred to as "repeating unit (b6)"), and repeating units (b7) derived from (meth)acrylamide (hereinafter also referred to as "repeating unit (b7)").

[0050] <Repeating units (b4) derived from conjugated diene compounds> The content of repeating units (b4) derived from conjugated diene compounds is preferably 0 to 60% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units (b4) is more preferably 10% by mass, and particularly preferably 20% by mass. The upper limit of the content of repeating units (b4) is more preferably 55% by mass, and particularly preferably 50% by mass. The content of repeating units (b4) is more preferably 10 to 55% by mass, and particularly preferably 20 to 50% by mass. By polymer (B) containing repeating units (b4) within the above ranges, the dispersibility of the active material is improved, and a homogeneous active material layer can be produced, thus eliminating structural defects in the electrode plate and potentially exhibiting good repeated charge-discharge characteristics. Furthermore, the polymer (B) coating the surface of the active material can be given elasticity, and the adhesion can be improved by the expansion and contraction of polymer (B), potentially exhibiting good charge-discharge durability characteristics.

[0051] The conjugated diene compound is not particularly limited, but examples include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene, and one or more selected from these can be used. Among these, 1,3-butadiene is particularly preferred.

[0052] <Repeating units (b5) derived from unsaturated carboxylic acid esters> The content of repeating units (b5) derived from unsaturated carboxylic acid esters is preferably 0.1 to 94% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units (b5) is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content of repeating units (b5) is more preferably 93% by mass, and particularly preferably 92% by mass. The content of repeating units (b5) is more preferably 1 to 93% by mass, and particularly preferably 2 to 92% by mass. By polymer (B) containing repeating units (b5) within the above ranges, the affinity between polymer (B) and the electrolyte is improved, and it may be possible to suppress the increase in internal resistance due to the binder becoming an electrical resistance component in the energy storage device.

[0053] Among unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Specific examples of (meth)acrylic acid esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and tri(meth)acrylic acid. Examples include trimethylolpropane methacrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, hydroxymethyl (meth)acrylate, 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, and glycerin di(meth)acrylate, and one or more selected from these can be used. Among these, it is preferable to use one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl (meth)acrylate.

[0054] <Repeating units (b6) derived from α,β-unsaturated nitrile compounds> The content of repeating units (b6) derived from α,β-unsaturated nitrile compounds is preferably 5 to 40% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units (b6) is more preferably 6% by mass, and particularly preferably 8% by mass. The upper limit of the content of repeating units (b6) is more preferably 35% by mass, and particularly preferably 30% by mass. The content of repeating units (b6) is more preferably 6 to 35% by mass, and particularly preferably 8 to 30% by mass. By polymer (B) containing repeating units (b6) within the above ranges, the affinity between polymer (B) and the electrolyte is improved, and it may be possible to suppress the increase in internal resistance due to polymer (B) becoming an electrical resistance component in the energy storage device.

[0055] Examples of α,β-unsaturated nitrile compounds include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, fumaronitrile, isopropylidene malononitrile, tetracyanoethylene, and vinylidene cyanide, and one or more selected from these can be used. Among these, one or more selected from the group consisting of acrylonitrile, methacrylonitrile, fumaronitrile, isopropylidene malononitrile, and tetracyanoethylene are preferred, and acrylonitrile is particularly preferred.

[0056] <(meth)acrylamide-derived repeating units (b7)> The content of (meth)acrylamide-derived repeating units (b7) is preferably 0.1 to 10% by mass when the total amount of repeating units contained in polymer (B) is 100% by mass. The lower limit of the content of repeating units (b7) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content of repeating units (b7) is more preferably 9% by mass, and particularly preferably 8% by mass. The content of repeating units (b7) is more preferably 0.5 to 9% by mass, and particularly preferably 1 to 8% by mass. When polymer (B) contains repeating units (b7) within the above ranges, the dispersibility of the active material in the slurry may be improved. In addition, the flexibility of the resulting active material layer may be appropriate, and the adhesion between the current collector and the active material layer may be improved.

[0057] Examples of (meth)acrylamides include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, maleic acid amide, etc., and one or more selected from these can be used.

[0058] 1.2.2. Physical Properties of Polymer (B) 1.2.2.1. Electrolyte Swelling Rate When 1 g of film of polymer (B) is immersed in a solvent consisting of propylene carbonate and diethyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours, the swelling rate (also referred to as "electrolyte swelling rate" in this specification) is 120% by mass or more and 250% by mass or less. The lower limit of the electrolyte swelling rate is preferably 130% by mass, and more preferably 150% by mass. The upper limit of the electrolyte swelling rate is preferably 230% by mass, and more preferably 200% by mass. The electrolyte swelling rate is more preferably 130% by mass or more and 230% by mass or less, and particularly preferably 150% by mass or more and 200% by mass or less. When the electrolyte swelling rate of polymer (B) is within the above range, polymer (B) can swell appropriately by absorbing the electrolyte. As a result, solvated lithium ions can easily reach the active material. Furthermore, if the electrolyte swelling rate of polymer (B) is within the aforementioned range, the coating capacity of polymer (B) on the active material decreases, effectively reducing electrode resistance and resulting in good charge-discharge characteristics. The polymer (B) film can be produced by pouring a particle dispersion of polymer (B) into a mold and drying it in a constant temperature bath at 85°C for 24 hours.

[0059] 1.2.2.2. Number-average particle size polymer (B) When polymer particles are present, the number-average particle size of the polymer particles is preferably 50 nm or more and 500 nm or less, more preferably 70 nm or more and 400 nm or less, and particularly preferably 90 nm or more and 250 nm or less. When the number-average particle size of the polymer particles is within the above range, the polymer particles are more likely to adsorb onto the surface of the active material, so that the polymer particles can move along with the movement of the active material. As a result, migration can be suppressed, and the deterioration of electrical properties can be reduced in some cases.

[0060] The number-average particle diameter of polymer particles is the average particle diameter obtained from images of 50 particles observed using a transmission electron microscope (TEM). Examples of transmission electron microscopes include the "H-7650" manufactured by Hitachi High-Tech Corporation.

[0061] 1.2.2.3. Surface Acidity Polymer (B) When polymer particles are present, the surface acidity of the polymer particles is preferably 0.05 mmol / g or more and 1.5 mmol / g or less, more preferably 0.1 mmol / g or more and 1.3 mmol / g or less, and particularly preferably 0.5 mmol / g or more and 1.2 mmol / g or less. When the surface acidity of the polymer particles is within the above range, a stable and homogeneous slurry can be produced. By producing an active material layer using such a homogeneous slurry, an active material layer with uniform dispersion of the active material and polymer particles and small variations in thickness can be obtained. As a result, variations in charge-discharge characteristics within the electrode can be suppressed, and an energy storage device exhibiting good charge-discharge characteristics can be obtained.

[0062] 1.2.3. Method for producing polymer (B) Polymer (B) can be produced by emulsion polymerization, for example, in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. Compounds described in Japanese Patent Publication No. 5999399, etc., can be used as the emulsifier (surfactant), chain transfer agent, and polymerization initiator.

[0063] The emulsion polymerization method for synthesizing polymer (B) may be carried out as a single-step polymerization or as a multi-step polymerization of two or more steps.

[0064] When polymer (B) is synthesized by one-step polymerization, the above monomer mixture can be subjected to emulsion polymerization in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80°C for 4 to 36 hours.

[0065] By setting the total solids content concentration in emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed while maintaining good dispersion stability of the resulting polymer (B) particles. This total solids content concentration is preferably 48% by mass or less, and more preferably 45% by mass or less.

[0066] Whether the synthesis of polymer (B) is carried out as a single-step polymerization or as a multi-step polymerization of two or more steps, it is preferable to adjust the pH to about 4.5 to 10.5, preferably 5.0 to 10.0, and more preferably 5.5 to 9.5, by adding a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed. The neutralizing agent used here is not particularly limited, but examples include metal hydroxides such as sodium hydroxide and lithium hydroxide; ammonia, etc. Setting the pH within the above range ensures good stability of the polymer (B) particle dispersion.

[0067] 1.3. Liquid Medium (C) The slurry composition for energy storage devices according to this embodiment contains a liquid medium (C). The liquid medium (C) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium may contain a non-aqueous medium other than water. Examples of this 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. By using an aqueous medium as the liquid medium (C) in the slurry composition for energy storage devices according to this embodiment, the degree of adverse impact on the environment is reduced, and the safety for handling workers is also increased.

[0068] The proportion of non-aqueous media contained in the aqueous media is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably substantially absent, per 100 parts by mass of aqueous media. Here, "substantially absent" means that non-aqueous media are not intentionally added as a liquid medium, and may contain non-aqueous media that are inevitably mixed in when preparing the slurry composition for energy storage devices.

[0069] 1.4. Other Additives The slurry composition for energy storage devices according to this embodiment may contain additives other than those described above, as needed. Examples of such additives include polymers other than polymer (B) (hereinafter also referred to as "other polymers"), conductive additives, preservatives, thickeners, and the like.

[0070] 1.4.1. Other Polymers The slurry composition for energy storage devices according to this embodiment may contain other polymers that act as binders. Preferably, the other polymer is at least one polymer selected from the group consisting of conjugated diene polymers such as hydrogenated acrylonitrile butadiene rubber and styrene-butadiene copolymers, acrylic polymers containing unsaturated carboxylic acid esters or their derivatives as constituent units, and fluorine polymers such as polyvinylidene fluoride (PVdF). These polymers may be used individually or in combination of two or more. The inclusion of these polymers may further improve flexibility and adhesion. Furthermore, using polymer (B) in combination with other polymers is also preferable from the viewpoint of polymer compatibility. The other polymer may be dissolved in the liquid medium (C) or dispersed in the liquid medium (C) as latex.

[0071] If the slurry composition for energy storage devices according to this embodiment contains other polymers, the content of the other polymers is preferably 5 parts by mass or less, more preferably 0.1 to 4 parts by mass, and particularly preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the total solid content of the slurry composition for energy storage devices.

[0072] 1.4.2. Conductive Additives The slurry composition for the energy storage device according to this embodiment may contain conductive additives. Specific examples of conductive additives include carbon nanotubes, carbon nanofibers, acetylene black, Ketjen black, furnace black, graphite, graphene, fullerene, carbon nanohorns, activated carbon, graphite, carbon fibers, and other carbon-based materials. Among these, at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, acetylene black, furnace black, and graphene is preferred, and carbon nanotubes or acetylene black are more preferred.

[0073] Examples of carbon nanotubes include single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). Furthermore, carbon nanotubes may consist solely of carbon, or their structure may be partially substituted or chemically modified with other elements, or they may be composites with metals (e.g., gold, silver, copper, aluminum, nickel, cobalt, titanium, platinum, etc.).

[0074] From the viewpoint of effectively improving the dispersibility of the conductive additive in the liquid medium (C), the content ratio of the conductive additive is preferably 0.1 to 100 parts by mass, more preferably 1 to 80 parts by mass, and particularly preferably 5 to 50 parts by mass, per 100 parts by mass of polymer (B).

[0075] 1.4.3. Preservatives The slurry composition for energy storage devices according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold, and other foreign substances when the slurry composition for energy storage devices is stored. Specific examples of preservatives include compounds described in Japanese Patent Publication No. 5477610, etc.

[0076] 1.4.4. Thickening Agent The slurry composition for energy storage devices according to this embodiment may contain a thickening agent other than carboxymethylcellulose (A). Examples of commercially available thickening agents include alkali metal salts of carboxymethylcellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0077] If the slurry composition for energy storage devices according to this embodiment contains a thickening agent other than carboxymethylcellulose (A), the content ratio of the thickening agent is preferably 5 parts by mass or less, and more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the total solid content of the slurry composition for energy storage devices.

[0078] 1.5. Physical Properties of the Slurry Composition for Energy Storage Devices 1.5.1. pH The pH of the slurry composition for energy storage devices according to this embodiment is preferably 2.0 to 11.0, more preferably 4.5 to 10.5, even more preferably 5.0 to 10.0, and particularly preferably 5.5 to 9.5. When the pH is within the above range, the carboxymethylcellulose (A) dissolves more easily in the liquid medium (C), and the viscosity of the slurry composition for energy storage devices can be increased. This makes it possible to suppress the occurrence of problems such as insufficient leveling and dripping, and makes it easy to manufacture electrode plates that have both good electrical properties and adhesion.

[0079] In this specification, "pH" refers to a physical property measured as follows: a value measured at 25°C using a pH meter with a glass electrode calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions, in accordance with JIS Z8802:2011. Examples of such pH meters include the "HM-7J" manufactured by Toa DKK Corporation and the "D-51" manufactured by Horiba, Ltd.

[0080] It should be noted that while the pH of the slurry composition for energy storage devices is influenced by the monomer composition of polymer (B), it is not determined solely by the monomer composition. In other words, it is generally known that even with the same monomer composition, the pH of the slurry composition for energy storage devices can change depending on the polymerization conditions, and the examples in this specification merely illustrate one such example.

[0081] 2. Slurry for Energy Storage Device Electrodes "Slurry for energy storage device electrodes" refers to a dispersion used to create an active material layer on the surface of a current collector by applying it to the surface of the current collector and then drying it. The slurry for energy storage device electrodes according to one embodiment of the present invention contains the above-described slurry composition for energy storage devices and an active material. In the slurry for energy storage device electrodes according to this embodiment, carboxymethylcellulose (A) exhibits high viscosity, allowing for high adhesion to the electrode plate with a small amount of additive, and the polymer (B) effectively suppresses electrode expansion. Furthermore, in the slurry for energy storage device electrodes according to this embodiment, carboxymethylcellulose (A) improves the dispersibility of the active material and conductive additive, making it easier to form efficient conductive paths in the active material layer. This makes it possible to manufacture energy storage device electrodes that have reduced internal resistance, excellent input / output characteristics, and excellent charge-discharge cycle characteristics. The components that may be included in the slurry for energy storage device electrodes according to this embodiment will be described below. Note that the slurry composition for energy storage devices is as described above, so its description will be omitted.

[0082] 2.1. Active Materials Examples of active materials used in the electrode slurry for the energy storage device according to this embodiment include positive electrode active materials and negative electrode active materials. Specific examples of these active materials include, for example, carbon materials, silicon materials, oxides containing lithium atoms, sulfur compounds, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacene, and A Ｘ B Ｙ O Ｚ Examples include composite metal oxides represented by (wherein A is an alkali metal or transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, and manganese, O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively) and other metal oxides. Specific examples of these include compounds described in Japanese Patent Publication No. 5999399, etc.

[0083] The slurry for the energy storage device electrode according to this embodiment can be used when manufacturing either the positive or negative electrode of an energy storage device, but it is particularly preferable to use it for the negative electrode.

[0084] When manufacturing the negative electrode, it is preferable to use a silicon material among the active materials exemplified above. Since silicon materials have a larger lithium absorption capacity per unit weight compared to other active materials, including a silicon material as the negative electrode active material can increase the energy storage capacity of the resulting energy storage device, and as a result, the output and energy density of the energy storage device can be increased.

[0085] Furthermore, the negative electrode active material is more preferably a mixture of silicon and carbon materials. Since the volume change of carbon materials during charging and discharging is smaller than that of silicon materials, using a mixture of silicon and carbon materials as the negative electrode active material can mitigate the effects of the volume change of silicon materials, thereby improving the adhesion between the active material layer and the current collector. From the viewpoint of having an even smaller volume change during charging and discharging, graphite is particularly preferred as the carbon material.

[0086] The silicon content in 100% by mass of the active material is preferably 1% by mass or more, more preferably 2 to 50% by mass, even more preferably 3 to 45% by mass, and particularly preferably 5 to 40% by mass. When the silicon content in 100% by mass of the active material is within the above range, an energy storage device can be obtained that has an excellent balance between improved output and energy density of the energy storage device and charge / discharge durability characteristics.

[0087] On the other hand, when manufacturing a positive electrode, among the active materials exemplified above, A Ｘ B Ｙ O Ｚ It is preferable that the composite metal oxide is represented by [formula]. Examples of such composite metal oxides include lithium cobaltate, lithium nickelate, lithium manganeseate, and ternary nickel-cobalt-manganate lithium.

[0088] The active material is preferably particulate. The average particle size of the active material is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm. Here, the average particle size of the active material refers to the volume-average particle size calculated from the particle size distribution measured using a particle size distribution analyzer that uses laser diffraction as its measurement principle. Examples of such laser diffraction particle size distribution analyzers include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by HORIBA, Ltd.).

[0089] 2.2 Other Components In addition to the components described above, other components may be added to the slurry for the energy storage device electrode according to this embodiment as needed. Examples of such components include polymers other than polymer (B), thickeners, liquid media, pH adjusters, corrosion inhibitors, cellulose fibers, etc. As polymers other than polymer (B) and thickeners, compounds exemplified in the section "1.4. Other Additives" above can be appropriately selected and used for the same purpose and in the same proportions.

[0090] <Liquid Medium> In addition to the liquid medium brought in from the slurry composition for the energy storage device, a liquid medium may be further added to the slurry for the energy storage device electrode according to this embodiment. The added liquid medium may be the same type as the liquid medium (C) contained in the slurry composition for the energy storage device, or it may be different, but it is preferable to select and use one of the liquid media exemplified in the section "1.3. Liquid Medium (C)" above.

[0091] In the slurry for energy storage device electrodes according to this embodiment, the content ratio of the liquid medium (including the portion brought in from the energy storage device slurry composition) is preferably such that the solid content concentration in the slurry (meaning the ratio of the total mass of components other than the liquid medium in the slurry to the total mass of the slurry; the same applies hereinafter) is 40 to 80% by mass, and more preferably 50 to 70% by mass.

[0092] <pH adjusters and corrosion inhibitors> Depending on the type of active material, pH adjusters and / or corrosion inhibitors may be further added to the slurry for the electrodes of the energy storage device according to this embodiment for the purpose of suppressing corrosion of the current collector.

[0093] Examples of pH adjusting agents include hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, acetic acid, boric acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, nitric acid, boric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred.

[0094] Examples of corrosion inhibitors include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, potassium molybdate, etc. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0095] <Cellulose Fibers> Cellulose fibers may be further added to the slurry for the electrodes of the energy storage device according to this embodiment. Adding cellulose fibers may improve the adhesion of the active material to the current collector. It is thought that the fibrous cellulose fibers can prevent the active material from falling off and improve its adhesion to the current collector by binding adjacent active materials together in a fibrous manner through linear adhesion or linear contact.

[0096] 2.3. Method for Preparing Slurry for Energy Storage Device Electrodes The slurry for energy storage device electrodes according to this embodiment may be manufactured by any method, as long as it contains the above-described slurry composition for energy storage devices and the active material. From the viewpoint of producing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to manufacture it by adding the active material and any optional additives used as needed to the slurry composition for energy storage devices and mixing them. Specific manufacturing methods include, for example, the method described in Japanese Patent Publication No. 5999399.

[0097] 3. Energy Storage Device Electrode An energy storage device electrode according to one embodiment of the present invention comprises a current collector and an active material layer formed by applying and drying the above-mentioned slurry for energy storage device electrodes on the surface of the current collector. Such an energy storage device electrode can be manufactured by applying the above-mentioned slurry for energy storage device electrodes to the surface of a current collector such as metal foil to form a coating film, and then drying the coating film to form an active material layer. The energy storage device electrode manufactured in this manner has an active material layer that is highly flexible and has good dispersibility of active material and conductive additives bonded to the surface of the current collector, resulting in excellent adhesion and easier formation of efficient conductive paths within the active material layer. This makes it possible to manufacture an energy storage device electrode that has reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics.

[0098] The current collector is not particularly limited as long as it is made of a conductive material, but examples include the current collector described in Japanese Patent Publication No. 5999399.

[0099] In the energy storage device electrode according to this embodiment, when a silicon material is used as the active material, the content of silicon elements in 100 parts by mass of the active material layer is preferably 2 to 30 parts by mass, more preferably 2 to 25 parts by mass, and particularly preferably 3 to 20 parts by mass. When the content of silicon elements in the active material layer is within the above range, the energy storage capacity of the energy storage device made using it is improved, and an active material layer with a uniform distribution of silicon elements is obtained. The content of silicon elements in the active material layer can be measured by a method described, for example, in Japanese Patent Publication No. 5999399.

[0100] 4. Energy Storage Device An energy storage device according to one embodiment of the present invention is equipped with the above-mentioned energy storage device electrodes, further contains an electrolyte, and can be manufactured by conventional methods using components such as separators. Specific manufacturing methods include, for example, stacking a negative electrode and a positive electrode via a separator, winding or folding them according to the battery shape, housing them in a battery container, and then injecting the electrolyte into the battery container and sealing it. The shape of the battery can be a suitable shape, such as coin-type, cylindrical, prismatic, or laminate-type.

[0101] The electrolyte can be in liquid or gel form, and depending on the type of active material, one can select from known electrolytes used in energy storage devices that effectively exhibits battery function. The electrolyte can be a solution in which an electrolyte is dissolved in a suitable solvent. Examples of these electrolytes and solvents include compounds described in, for example, Japanese Patent Publication No. 5999399.

[0102] The energy storage device described above is applicable to lithium-ion secondary batteries, electric double-layer capacitors, and lithium-ion capacitors that require high current density discharge. Among these, lithium-ion secondary batteries are particularly preferred. In the energy storage device electrodes and energy storage device according to this embodiment, components other than the slurry composition for the energy storage device can be those of known lithium-ion secondary batteries, electric double-layer capacitors, and lithium-ion capacitors.

[0103] 5. Examples The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0104] 5.1. Production of Carboxymethylcellulose (A) 5.1.1. Production of Carboxymethylcellulose (A1) Step 1: A 1:1 mixture of 2.5 kg of water and ethanol was added to a 5 L glass reaction vessel, and nitrogen gas was continuously supplied. 1.0 kg of sodium carboxymethylcellulose powder, with a degree of substitution of 0.9 and a viscosity of 1% aqueous solution of 16,000 mPa·s, was added to the mixture. The mixture was stirred at a stirring speed of 100 rpm / min until uniform. Step 2: The temperature was raised to 70°C, and 30 g of aqueous ammonium persulfate solution (ammonium persulfate:water = 2:1) was added as an initiator, and the mixture was kept warm for 1 hour. Step 3: 140 g of sodium acrylate monomer and 50 g of sodium p-styrenesulfonate monomer were added dropwise to the reaction system, with the addition time set to 3 hours. The temperature was strictly controlled, and the mixture was kept warm for another hour after the addition was complete. Step 4: After Step 3 was completed, 10 g of pentaerythritol tetraacrylate was added dropwise as a crosslinking agent, and the addition time was set to 2 hours. Step 5: After confirming that the size of the carboxymethylcellulose particles had grown to 1.2 to 1.4 times the original particle size, a stopping agent was added to stop the reaction. Step 6: The above reaction system was filtered to obtain modified carboxymethylcellulose. This was washed several times with acetone solution to remove residual unreacted monomers, and then dried and ground to obtain 1.1 kg of carboxymethylcellulose (A1).

[0105] 5.1.2. Carboxymethylcellulose (A2) was produced by following the same process as described in "5.1.1. Production of Carboxymethylcellulose (A1)" above, except that 135 g of sodium acrylate monomer and 50 g of sodium p-styrene sulfonate monomer were added in step 3, and 15 g of pentaerythritol tetraacrylate was added in step 4.

[0106] 5.1.3. Carboxymethylcellulose (A3) was produced by following the same process as described in "5.1.1. Production of Carboxymethylcellulose (A1)" above, except that 130 g of sodium acrylate monomer and 50 g of sodium p-styrene sulfonate monomer were added in step 3, and 20 g of pentaerythritol tetraacrylate was added in step 4.

[0107] 5.1.4. Carboxymethylcellulose (A4) Commercially available sodium carboxymethylcellulose (manufactured by Daicel Corporation, product name "CMC2200") was used as is. This sodium carboxymethylcellulose had a degree of substitution of 1.0, and the viscosity of a 1% aqueous solution was 1,500 mPa·s.

[0108] 5.1.5. Carboxymethylcellulose (A5) Commercially available sodium carboxymethylcellulose (manufactured by Nippon Paper Chemical Co., Ltd., product name "MAC500LC") was used as is. This sodium carboxymethylcellulose had a degree of substitution of 0.7, and the viscosity of a 1% aqueous solution was 4,600 mPa·s.

[0109] 5.2. Evaluation of the physical properties of carboxymethylcellulose (1) Viscosity test A viscosity test was performed using a viscometer (Brookfield DV-II). Specifically, 300 g of a 1% aqueous solution of carboxymethylcellulose was placed in a 500 mL beaker and left to stand at a constant temperature of 25°C for 60 minutes. After the temperature stabilized, a 63# or 64# rotor was selected according to the viscosity of the carboxymethylcellulose and the viscometer's measurement range. The test was performed at 12 rpm, 6 rpm, or 3 rpm for 5 minutes, and the value was recorded once the viscosity value stabilized.

[0110] (2) Number of insoluble gel substances in carboxymethylcellulose solution Approximately 3 mL of a 1% aqueous solution of carboxymethylcellulose was taken with a dropper and applied to an A4 film (PET film) to a thickness of 100 μm using an adjustable coater blade to form a uniform liquid film. Immediately thereafter, the number of insoluble gel substances present in a 5 cm × 8 cm area was visually counted under natural light. This measurement was performed three times on the same sample, and the average value is shown.

[0111] (3) Summary The results of the physical property measurements of each carboxymethylcellulose described above are summarized in Table 1 below.

[0112]

[0113] 5.3. Synthesis of Polymers 5.3.1. Synthesis of Polymer (B1) A particle dispersion of polymer (B1) was obtained by a one-step polymerization as shown below. In a reactor, 200 parts by mass of water, a monomer mixture consisting of 13 parts by mass of 1,3-butadiene, 75 parts by mass of styrene, 10 parts by mass of acrylonitrile, and 2 parts by mass of acrylic acid was charged, along with 0.1 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 0.2 parts by mass of sodium alkyldiphenyl ether disulfonate as an emulsifier, and 0.2 parts by mass of potassium persulfate as a polymerization initiator. Polymerization was carried out at 70°C for 12 hours with stirring, and it was confirmed that the polymerization conversion rate was 98%. Unreacted monomers were removed from the particle dispersion of polymer (B1) obtained in this way, and the mixture was concentrated. After adding a 2.5% aqueous sodium hydroxide solution, water was removed using an evaporator to obtain a particle dispersion of polymer (B1) with a solid content of 40% by mass and a pH of 8.0.

[0114] 5.3.2. Except for the types and amounts of synthetic monomers of polymers (B2) to (B10) as shown in Table 2 below, each polymer was synthesized by a one-step polymerization in the same manner as described in "5.3.1. Synthesis of Polymer (B1)" above, and particle dispersions of each polymer were obtained.

[0115] 5.4. Evaluation of Polymer Properties (1) Measurement of Surface Acidity The surface acidity of polymer particles contained in the particle dispersions of each polymer obtained above was measured as follows. First, it was confirmed that 0.005 mol / L sulfuric acid was filled in the reagent bottle at the top of the titration burette of the potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., model "AT-510"), and that the conductivity of ultrapure water was 2 μS or less. Next, the burette was purged to remove air, and the nozzle was de-bubbled. Then, approximately 1 g of the polymer particle dispersion obtained above (in terms of solid content) was taken into a 300 mL beaker, and the sample weight was recorded. After diluting it to 200 mL with ultrapure water, 1 mol / L sodium hydroxide aqueous solution was added dropwise. When the endpoint was reached, it was stirred for about 30 seconds to confirm that the conductivity had stabilized. The RESET button of the measurement program was pressed to put it into measurement standby mode. The START button of the measurement program was pressed to start the measurement with 0.005 mol / L sulfuric acid. The process automatically terminates and saves the file upon reaching the endpoint. The resulting curve was then analyzed, and the surface acid content was calculated from the amount of sulfuric acid used using the following formula (3): Surface acid content (mol / g) = Amount of acid used in the carboxylic acid region of the particle surface [mL] × Acid concentration [mol / L] × Degree of ionization / Sample weight [g] / 1000 .....(3)

[0116] (2) Measurement of number-average particle size The polymer particle dispersion obtained above was diluted to 0.1 wt% latex, and one drop was added to the collodion support membrane using a pipette. Then, one drop of 0.02 wt% osmium tetroxide solution was added to the collodion support membrane using a pipette, and the sample was air-dried for 12 hours to prepare the sample. The sample prepared in this way was observed at a magnification of 10 K using a transmission electron microscope (TEM, Hitachi High-Tech Corporation, model number "H-7650"), and image analysis was performed using the HITACHI EMIP program to calculate the average particle size of 50 randomly selected polymers.

[0117] (3) Measurement of Electrolyte Swelling Rate The polymer particle dispersion obtained above was poured into a mold and dried in a constant temperature bath at 85°C for 24 hours to produce a film. 1 g of this film was immersed in 20 mL of a mixture of propylene carbonate (PC) and diethyl carbonate (DEC) (PC / DEC = 1 / 1 (volume ratio), hereinafter this mixture will be referred to as "PC / DEC"), which will be used as an electrolyte in the manufacture of the energy storage device described later, and shaken at 70°C for 24 hours. Next, the insoluble matter was separated by filtration through a 300 mesh wire mesh, and the weight of the remaining material (Y (g)) obtained by evaporating and removing the dissolved PC / DEC was measured. Furthermore, after absorbing and removing the PC / DEC adhering to the surface of the insoluble matter (film) separated by the above filtration using paper, the weight of the insoluble matter (film) (Z (g)) was measured. Electrolyte swelling rate (mass%) = (Z / (1-Y)) x 100 (4)

[0118] (4) The polymer compositions of the small polymers (B1) to (B10) and the results of the measurement of their respective physical properties are summarized in Table 2 below.

[0119]

[0120] In Table 2 above, the values ​​in the column for each monomer represent "parts by mass," and the abbreviations for each monomer represent the following compounds. <Aromatic vinyl compounds> ST: Styrene, DVB: Divinylbenzene, VT: Vinyltoluene <Unsaturated carboxylic acids> AA: Acrylic acid, MAA: Methacrylic acid, TA: Itaconic acid <Compounds with sulfonic acid groups> NaSS: Sodium styrenesulfonate <Conjugated diene compounds> BD: 1,3-Butadiene <Unsaturated carboxylic acid esters> 2EHA: 2-Ethylhexyl acrylate, MMA: Methyl methacrylate, BA: Butyl acrylate, CHMA: Cyclohexyl methacrylate, EDMA: Ethylene glycol dimethacrylate, HEMA: 2-Hydroxyethyl methacrylate, HEA: 2-Hydroxyethyl acrylate <α,β-unsaturated nitrile compounds> AN: Acrylonitrile <(Meth)acrylamide> AAM: Acrylamide, MAM: Methacrylamide

[0121] 5.5. Example 1 5.5.1. 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 subjected to a heat treatment for 10 hours in an electric furnace with the temperature adjusted to the range of 1100°C to 1600°C under a nitrogen gas flow (0.5 NL / min), resulting in a composition formula SiO ｘ A silicon dioxide powder (average particle size 8 μm) represented by (x = 0.5 to 1.1) was obtained. 300 g of this silicon dioxide powder was placed in a batch heating furnace, and while maintaining a reduced absolute pressure of 100 Pa using a vacuum pump, the temperature was raised from room temperature (25 °C) to 1100 °C at a heating rate of 300 °C / h. Next, while maintaining the pressure inside the heating furnace at 2000 Pa, methane gas was introduced at a flow rate of 0.5 NL / min, and a heat treatment (graphite coating treatment) was performed at 1100 °C for 5 hours. After the graphite coating treatment was completed, the powder was cooled to room temperature at a cooling rate of 50 °C / h to obtain approximately 330 g of graphite-coated silicon dioxide powder. This graphite-coated silicon oxide is a conductive powder (active material) in which the surface of silicon oxide is coated with graphite. Its average particle size is 10.5 μm, and the proportion of the graphite coating when the total amount of the obtained graphite-coated silicon oxide is considered to be 100% by mass is 2% by mass.

[0122] 5.5.2. Preparation of Slurry Composition for Energy Storage Devices A slurry composition for energy storage devices was obtained by adding 0.5 parts by mass of carboxymethylcellulose (A1) (calculated on a solid content basis, added as an aqueous solution with a concentration of 2% by mass) and 4 parts by mass of polymer (B1) (calculated on a solid content basis, added as a particle dispersion of the polymer (B1) obtained above) to a twin-screw planetary mixer (Primix Corporation, product name "TK Hibiscus Mix 2P-03") and stirring at 60 rpm for 20 minutes.

[0123] 5.5.3. Preparation of Slurry for Electrodes of Energy Storage Devices Subsequently, into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK High-Viscosity Mixer 2P-03") into which the slurry composition for energy storage devices has been charged, 90.25 parts by mass (in terms of solid content) of artificial graphite (manufactured by Lionak Corporation, trade name "MAG"), which is highly crystalline graphite as a negative electrode active material, 4.75 parts by mass (in terms of solid content) of the powder of silicon oxide coated with graphite obtained above, and 1 part by mass of carbon (acetylene black, manufactured by Denka Co., Ltd.) as a conductive assistant were charged, and the mixture was stirred at 60 rpm for 1 hour to obtain a paste. Water was added to the obtained paste, and after adjusting the solid content concentration to 48% by mass, using a stirring defoamer (manufactured by Shinky Co., Ltd., trade name "Foam Removing Rintaro"), it was stirred and mixed at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under reduced pressure (about 2.5×10 ４ Pa) to prepare a slurry for electrodes of energy storage devices containing 5% by mass of Si in the negative electrode active material (C / Si = 95 / 5).

[0124] Regarding the slurry for electrodes of energy storage devices obtained above, the pH at 25°C was measured using a pH meter (manufactured by Horiba, Ltd.). The results are shown in Table 3 below.

[0125] Also, regarding the slurry for electrodes of energy storage devices obtained above, the viscosity at 25°C was measured using a rotational viscometer in accordance with JIS Z 8803:2011. The results are shown in Table 3 below.

[0126] 5.5.4. Manufacture and Evaluation of Energy Storage Devices <Manufacture of Energy Storage Device Electrode (Negative Electrode)> On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for electrodes of energy storage devices obtained above (C / Si = 95 / 5) was uniformly applied by the doctor blade method so that the film thickness after drying would be 80 μm, dried at 60°C for 10 minutes, and then dried at 120°C for 10 minutes. Thereafter, by pressing with a roll press so that the density of the active material layer would be 1.5 g / cm ３ ³, an energy storage device electrode (negative electrode) was obtained.

[0127] <Evaluation of Coatability (Smoothness)> A test piece measuring 12 cm wide x 12 cm long was cut from the energy storage device electrode (negative electrode) obtained above, and 36 squares measuring 2 cm x 2 cm were measured using a film thickness gauge (Mitutoyo, model "DIGIMATIC MICROMETER IP65"), and the ratio of the standard deviation to the average value of the film thickness (smoothness) was calculated. Note that if the standard deviation of the active material layer exceeds 2%, it means that the slurry for the energy storage device electrode is not uniformly applied. In such cases, the smoothness of the active material layer formed on the surface of the current collector is impaired in energy storage device electrodes made by applying the slurry for the energy storage device electrode over a large area. As a result, the electrical characteristics are not uniform on the electrode surface, and stable electrical characteristics cannot be achieved, especially when mass-produced. On the other hand, if the standard deviation of the active material layer is 2% or less, it means that the slurry for the energy storage device electrode is uniformly applied. In such cases, electrodes fabricated by applying a slurry for energy storage device electrodes over a large area exhibit good smoothness of the active material layer formed on the surface of the current collector. As a result, the electrical properties become uniform across the electrode surface, enabling stable electrical characteristics, especially in mass production. For this reason, the evaluation criteria for the coatability of the slurry for energy storage device electrodes were established as follows. The results are shown in Table 3 below. (Evaluation Criteria) A: Good smoothness because the standard deviation is 2% or less. B: Poor smoothness because the standard deviation exceeds 2%.

[0128] <Evaluation of Adhesion Strength of Negative Electrode Coating Layer> On the surface of the energy storage device electrode (negative electrode) obtained above, 10 cuts were made vertically and horizontally at 2 mm intervals using a knife, from the active material layer to a depth reaching the current collector, creating a grid pattern. 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Sellotape" (registered trademark), specified in JIS Z 1522:2009) was applied to these cuts and immediately peeled off, and the degree of detachment of the active material was evaluated by visual inspection. The evaluation criteria are as follows. The evaluation results are shown in Table 3 below. (Evaluation Criteria) ・5 points: 0 detached pieces of the active material layer. ・4 points: 1 to 5 detached pieces of the active material layer. ・3 points: 6 to 20 detached pieces of the active material layer. ・2 points: 21 to 40 detached pieces of the active material layer. ・1 point: 41 or more detached pieces of the active material layer.

[0129] <Manufacturing of the Counter Electrode (Positive Electrode)> A twin-shaft planetary mixer (manufactured by Primix Corporation, product name "TK Hibiscus Mix 2P-03") is mixed with 4 parts by mass (solid content equivalent) of electrochemical device electrode binder (manufactured by Kureha Corporation, product name "KF Polymer #1120"), 3.0 parts by mass of conductive additive (manufactured by Denka Co., Ltd., product name "Denka Black 50% Pressed Product"), and LiCoO with an average particle size of 5 μm as the positive electrode active material. ２ 100 parts by mass (solid content equivalent) of (manufactured by Hayashi Chemical Co., Ltd.) and 36 parts by mass of N-methylpyrrolidone (NMP) were added, and the mixture was stirred at 60 rpm for 2 hours. After adding NMP to the resulting paste and adjusting the solid content concentration to 65% by mass, the mixture was stirred and defoamed using a stirring and defoaming machine (manufactured by Shinky Co., Ltd., product name "Awatori Rentaro") at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and further under reduced pressure (approximately 2.5 × 10⁻⁶). ４ A cathode slurry was prepared by stirring and mixing at 1800 rpm for 1.5 minutes in Pa. This cathode slurry was uniformly applied to the surface of a current collector made of aluminum foil using the 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 density of the active material layer was 3.0 g / cm³. ３ The opposite electrode (positive electrode) was obtained by pressing it using a roll press machine in the manner described above.

[0130] <Assembly of Lithium-ion Battery Cell> In a glove box substituted with Ar to maintain a dew point of -80°C or lower, the negative electrode manufactured above was punched out to a diameter of 16.16 mm and placed on a two-electrode coin cell (manufactured by Hosen Co., Ltd., product name "HS Flat Cell"). Next, a separator made of a polypropylene porous membrane punched out to a diameter of 24 mm (manufactured by Cellguard Co., Ltd., product name "Cellguard #2400") was placed on top, and then 500 μL of electrolyte was injected to prevent air from entering. Finally, the positive electrode manufactured above was punched out to a diameter of 15.95 mm and placed on top, and the outer body of the two-electrode coin cell was sealed by closing it with screws to assemble the lithium-ion battery cell (energy storage device). The electrolyte used here was a solvent of propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio) with LiPF６ This is a solution obtained by dissolving [the substance] at a concentration of 1 mole / L.

[0131] <Evaluation of Resistance Increase Rate> The energy storage device manufactured above was placed in a constant temperature bath at 25°C, and charging was started with a constant current (1.0C). When the voltage reached 4.2V, charging was continued at a constant voltage (4.2V), and the charging completion (cutoff) was defined as when the current value reached 0.01C. Subsequently, discharging was started with a constant current (0.05C), and the charging completion (cutoff) was defined as when the voltage reached 3.0V, and the discharge capacity for the 0th cycle was calculated. Furthermore, charging was started with a constant current (1.0C), and when the voltage reached 4.2V, charging was continued at a constant voltage (4.2V), and the charging completion (cutoff) was defined as when the current value reached 0.01C. Subsequently, discharging was started with a constant current (1.0C), and the charging completion (cutoff) was defined as when the voltage reached 3.0V, and the discharge capacity for the 1st cycle was calculated. This charge-discharge cycle was repeated 100 times. After 100 charge-discharge cycles, the same charge-discharge procedure was performed as in the 0th cycle, and the discharge capacity on the 101st cycle was evaluated. The resistance increase rate was calculated using the following formula (5) and evaluated according to the following criteria. The results are shown in Table 3 below. Resistance increase rate (%) = (Discharge capacity on the 101st cycle - Discharge capacity on the 100th cycle) / (Discharge capacity on the 0th cycle - Discharge capacity on the 1st cycle) × 100 ・・・・・(5) (Evaluation criteria) ・5 points: Resistance increase rate of 100% or more and less than 150%. ・4 points: Resistance increase rate of 150% or more and less than 200%. ・3 points: Resistance increase rate of 200% or more and less than 250%. ・2 points: Resistance increase rate of 250% or more and less than 300%. ・1 point: Resistance increase rate of 300% or more and less than 350%. ・0 points: Resistance increase rate of 350% or more.

[0132] <Evaluation of Cycle Characteristics> For the energy storage device fabricated above, charging was started with a constant current (1.0C) in a constant temperature bath controlled at 25°C. When the voltage reached 3.8V, charging was continued at a constant voltage (3.8V), and charging was completed (cutoff) when the current value reached 0.01C. After that, discharging was started with a constant current (1.0C), and discharging was completed (cutoff) when the voltage reached 2.5V, and the discharge capacity of the first cycle was calculated. This charge-discharge cycle was repeated 100 times. The capacity retention rate was calculated using the following formula (6) and evaluated according to the following criteria. The results are shown in Table 3 below. Capacity Retention Rate (%) = Discharge Capacity at 100 Cycles / Discharge Capacity at 1 Cycle .....(6) (Evaluation Criteria) ・5 points: Capacity retention rate of 95% or more. ・4 points: Capacity retention rate of 90% or more but less than 95%. ・3 points: Capacity retention rate of 85% or more but less than 90%. - 2 points: Volume retention rate is 80% or more but less than 85%. - 1 point: Volume retention rate is 75% or more but less than 80%. - 0 points: Volume retention rate is less than 75%.

[0133] <Evaluation of electrode expansion rate> The film thickness of the negative electrode manufactured as described above was measured and taken as the initial film thickness. The energy storage device manufactured as described above was then charged at a constant current (0.2C) in a constant temperature bath controlled at 25°C. When the voltage reached 3.8V, charging was continued at a constant voltage (3.8V), and charging was completed (cutoff) when the current value reached 0.01C. Subsequently, discharge was started at a constant current (0.2C) in a constant temperature bath controlled at 25°C, and discharge was completed (cutoff) when the voltage reached 2.5V, thus completing the chemical conversion charge and discharge process. After that, a contact sensor (manufactured by Keyence Corporation, product name "GT2-H12KLF") was attached to the energy storage device, and the film thickness at that time was taken as the film thickness after chemical conversion. Then, charging was started at a constant current (0.2C), and when the voltage reached 3.8V, charging was continued at a constant voltage (3.8V), and charging was completed (cutoff) when the current value reached 0.01C. Subsequently, discharge was started in a constant temperature bath maintained at 25°C with a constant current (0.2C). Discharge completion (cutoff) was defined as reaching a voltage of 2.5V. The film thickness at the 10th discharge cycle was measured, and the electrode expansion rate was calculated using the following formula (7) and evaluated according to the following criteria. The results are shown in Table 3 below. Electrode expansion rate (%) = (Film thickness at the 10th discharge cycle - Film thickness after chemical conversion) / (Initial film thickness) × 100 ・・・・・(7) (Evaluation criteria) ・5 points: Electrode expansion rate is 40% or less. ・4 points: Electrode expansion rate is greater than 40% but 43% or less. ・3 points: Electrode expansion rate is greater than 43% but 46% or less. ・2 points: Electrode expansion rate is greater than 46% but 50% or less. ・1 point: Electrode expansion rate is greater than 50%.

[0134] 5.6. Examples 2-10 and Comparative Examples 1-9 In Examples 2-10 and Comparative Examples 1-9, the slurry compositions for energy storage devices were obtained by using carboxymethylcellulose, polymer type and amount as described in Table 3 or Table 4 below, respectively, except that the procedure was the same as in Example 1.

[0135] 5.7. Evaluation Results Tables 3 and 4 below summarize the types and content ratios of carboxymethylcellulose and polymers used in Examples 1 to 10 and Comparative Examples 1 to 9, as well as the evaluation results. In Tables 3 and 4 below, the values ​​in the columns for carboxymethylcellulose and polymer represent "parts by mass".

[0136]

[0137]

[0138] As is clear from Tables 3 and 4 above, the slurry for energy storage device electrodes prepared using the slurry compositions for energy storage devices according to the present invention shown in Examples 1 to 10 yielded energy storage device electrodes with excellent properties, compared to Comparative Examples 5 to 7. This was achieved because the polymer (B) effectively bonded the active materials together, suppressing fusion between particles within the electrode, thereby reducing internal resistance and further reducing the electrode plate expansion rate.

[0139] Furthermore, as is clear from Tables 3 and 4 above, the slurry for energy storage device electrodes prepared using the energy storage device slurry compositions according to the present invention shown in Examples 1 to 7, compared to Comparative Examples 1 and 2, contained carboxymethylcellulose (A1) to (A3) as a thickening agent. This allowed for the production of a slurry with a good dispersion state even with a reduced amount of carboxymethylcellulose added, resulting in an energy storage device electrode with excellent adhesion and flexibility. It is presumed that by using carboxymethylcellulose (A1) to (A3), which has carboxyl groups and sulfonic acid groups in its side chains, as a thickening agent for the negative electrode slurry, efficient conductive paths are more easily formed in the active material layer. This reduces internal resistance, resulting in an energy storage device with excellent input / output characteristics and excellent charge-discharge cycle characteristics.

[0140] The present invention is not limited to the embodiments described above, and various modifications are possible. The present invention encompasses configurations that are substantially identical to those 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 encompasses configurations in which non-essential parts of the configurations described in the embodiments are replaced with other configurations. Furthermore, the present invention also encompasses configurations that produce the same effects or achieve the same purpose as the configurations described in the embodiments. Furthermore, the present invention also encompasses configurations that add known technology to the configurations described in the embodiments.

Claims

1. A slurry composition for energy storage devices comprising carboxymethylcellulose (A), a polymer (B), and a liquid medium (C), wherein the viscosity of a 1% aqueous solution of carboxymethylcellulose (A), measured using a Brookfield viscometer at 25°C, is 30,000 mPa·s or more, and when the total amount of repeating units contained in the polymer (B) is taken as 100% by mass, the polymer (B) contains 5 to 75% by mass of repeating units (b1) derived from aromatic vinyl compounds, and 1 to 10% by mass of at least one repeating unit selected from the group consisting of repeating units (b2) derived from unsaturated carboxylic acids and repeating units (b3) derived from compounds having sulfonic acid groups, and the swelling rate when the polymer (B) is immersed in a solvent consisting of propylene carbonate and diethyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours is 120% by mass or more and 250% by mass or less.

2. The slurry composition for energy storage devices according to claim 1, wherein the polymer (B) further contains 0 to 60% by mass of repeating units (b4) derived from a conjugated diene compound.

3. The slurry composition for energy storage devices according to claim 1 or claim 2, wherein the polymer (B) is polymer particles, and the surface acid content of the polymer particles is 0.05 mmol / g or more and 1.5 mmol / g or less.

4. The slurry composition for an energy storage device according to claim 1 or claim 2, wherein the polymer (B) is polymer particles, and the number-average particle diameter of the polymer particles is 50 nm or more and 500 nm or less.

5. The slurry composition for energy storage devices according to claim 1 or claim 2, wherein the carboxymethylcellulose (A) has a molecular main chain structure of carboxymethylcellulose, and the side chains of the main chain structure have carboxyl groups and sulfonic acid groups.

6. The slurry composition for energy storage devices according to claim 1 or 2, wherein when an aqueous solution of carboxymethylcellulose (A) with a solid content of 1% is applied to a surface with a thickness of 100 μm and an area of ​​5 cm × 8 cm, there are 52 or fewer insoluble gels.

7. The slurry composition for energy storage devices according to claim 1 or claim 2, wherein the viscosity of a 1% aqueous solution of carboxymethylcellulose (A) is 80,000 mPa·s to 110,000 mPa·s.

8. The slurry composition for energy storage devices according to claim 1 or claim 2, wherein the liquid medium (C) is water.

9. A slurry for an electrode of an energy storage device, comprising the slurry composition for an energy storage device according to claim 1 or claim 2, and an active material.

10. The slurry for an electrode of an energy storage device according to claim 9, wherein the active material contains graphite and silicon material.

11. An energy storage device electrode comprising a current collector and an active material layer formed by applying and drying the slurry for energy storage device electrodes described in claim 9 on the surface of the current collector.

12. An energy storage device comprising the energy storage device electrodes described in claim 11.

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