Composition for power storage device, slurry for power storage device electrode, power storage device electrode, and power storage device

Abstract

Provided is a composition for a power storage device. By improving dispersibility of a conductive assistant such as CNT, said composition makes it possible to manufacture a power storage device electrode that has excellent adhesion, excellent input / output characteristics through reduction of internal resistance, and excellent charge / discharge cycle characteristics.　A composition for a power storage device according to the present invention contains a polymer (A), a conductive assistant (B), and a liquid medium (C). When the total of repeating units contained in the polymer (A) is 100 mass%, the polymer (A) contains 1-50 mass% of a repeating unit (a1) derived from an aromatic vinyl compound and 20-75 mass% of a repeating unit (a2) derived from an unsaturated carboxylic acid ester. The viscosity of the polymer (A) in an NMP solution having a solid content concentration of 8% is 300-5,000 mPa·s.

Description

Composition for electric storage device, slurry for electric storage device electrode, electric storage device electrode, and electric storage device

[0001] The present invention relates to a composition for an electricity storage device, a slurry for an electricity storage device electrode containing the composition and an active material, an electricity storage device electrode prepared by applying the slurry to a current collector and drying it, and an electricity storage device including the electricity storage device electrode.

[0002] In recent years, there has been a demand for high-voltage, high-energy-density power storage devices as power sources for electronic devices. Lithium-ion batteries and lithium-ion capacitors are expected to be such power storage devices.

[0003] Electrodes used in such electricity storage devices are produced by applying a composition (slurry for electricity storage device electrodes) containing an active material and a polymer that functions as a binder to the surface of a current collector and drying the composition. The properties required of the polymer used as a binder include the ability to bind active materials together and to adhere the active material to the current collector, abrasion resistance during the process of winding the electrode, and resistance to powder shedding, which prevents fine powder of the active material from falling off from the applied and dried composition coating film (hereinafter also referred to as the "active material layer") even during subsequent cutting.

[0004] It has been empirically demonstrated that the bonding ability between the active materials, the adhesion ability between the active material and the current collector, and the resistance to powder shedding are almost proportional to each other in performance. Therefore, in the present specification, these may be collectively referred to as "adhesion."

[0005] Furthermore, in recent years, research and development of electric vehicles equipped with power storage devices has been actively conducted with the aim of reducing the environmental impact. When power storage devices are installed as driving power sources for electric vehicles, the devices are required to have battery properties such as high-capacity rapid charging and durability against repeated charge and discharge.

[0006] Against this background, a method has been proposed in which carbon nanotubes (hereinafter also referred to as "CNTs") are used as a conductive additive in order to improve the electron conductive path in an electricity storage device (see, for example, Patent Document 1).

[0007] Japanese Patent Application Laid-Open No. 2020-001960

[0008] However, conductive additives such as CNTs have poor dispersibility, and if aggregates of CNTs or the like are formed in the slurry for an electric storage device electrode, adhesion may be impaired. Furthermore, if aggregates of CNTs or the like are formed in the active material layer of the electrode, it becomes difficult to form an efficient conductive path, making it difficult to simultaneously achieve high levels of properties such as low resistance and charge / discharge cycle characteristics.

[0009] Some aspects of the present invention provide a composition for an electricity storage device that can produce an electricity storage device electrode that has excellent adhesion, reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics, by improving the dispersibility of a conductive additive such as CNT.

[0010] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized as any of the following aspects.

[0011] One aspect of the composition for an electrical storage device according to the present invention comprises a polymer (A), a conductive additive (B), and a liquid medium (C), wherein the polymer (A) contains, when the total amount of repeating units contained in the polymer (A) is taken as 100 mass%, 1 to 50 mass% of repeating units (a1) derived from an aromatic vinyl compound, and 20 to 75 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester, and the viscosity of the polymer (A) in an NMP solution having a solids concentration of 8% is 300 to 5,000 mPa s.

[0012] In one embodiment of the composition for an electrical storage device, the polymer (A) may further contain 0.5 to 10 mass % of a repeating unit (a3) ​​derived from an unsaturated carboxylic acid.

[0013] In any embodiment of the composition for an electrical storage device, the polymer (A) may further contain 5 to 40 mass % of a repeating unit (a4) derived from an α,β-unsaturated nitrile compound.

[0014] In any of the above embodiments of the composition for an electrical storage device, the polymer (A) may further contain 0.1 to 10 mass % of a repeating unit (a5) derived from a compound having a sulfonic acid group.

[0015] In any of the above embodiments of the composition for an electrical storage device, the polymer (A) may further contain 0.1 to 10 mass % of a repeating unit (a6) derived from (meth)acrylamide.

[0016] In any embodiment of the composition for a storage battery device, the conductive additive (B) may be at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, acetylene black, furnace black, and graphene.

[0017] In any embodiment of the composition for an electrical storage device, the liquid medium (C) may be at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones, and amides.

[0018] In any of the embodiments of the composition for an electrical storage device, the composition may further contain at least one polymer selected from the group consisting of hydrogenated acrylonitrile butadiene rubber, an acrylic polymer, and a fluorine-based polymer.

[0019] In any of the above embodiments of the composition for an electrical storage device, the composition may further contain a thickener.

[0020] One aspect of the slurry for an electrode of an electricity storage device according to the present invention contains the composition for an electricity storage device according to any one of the above aspects and an active material.

[0021] In one embodiment of the slurry for an electric storage device electrode, the active material may be a positive electrode active material.

[0022] In any of the embodiments of the slurry for an electrode of an electricity storage device, the active material may contain a silicon material.

[0023] One aspect of the electricity storage device electrode according to the present invention includes a current collector and an active material layer formed by applying the above-described electricity storage device electrode slurry to the surface of the current collector and drying the applied slurry.

[0024] An aspect of the electricity storage device according to the present invention includes the electricity storage device electrode of the above aspect.

[0025] The composition for an electrical storage device according to the present invention can improve the dispersibility of a conductive additive such as CNT. Furthermore, the composition for an electrical storage device according to the present invention has good dispersibility of a conductive additive such as CNT, resulting in excellent adhesion and facilitating the formation of efficient conductive paths in the active material layer. This makes it possible to produce an electrical storage device electrode that has reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics.

[0026] 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 are implemented within the scope of the present invention.

[0027] In this specification, "poly(meth)acrylic acid" refers to "polyacrylic acid" or "polymethacrylic acid", "(meth)acrylate" refers to "acrylate" or "methacrylate", and "(meth)acrylamide" refers to "acrylamide" or "methacrylamide".

[0028] In this specification, a numerical range described as "X to Y" is interpreted as including the numerical value X as the lower limit and the numerical value Y as the upper limit.

[0029] 1. Composition for Electrical Storage Devices A composition for electrical storage devices according to one embodiment of the present invention contains a polymer (A), a conductive additive (B), and a liquid medium (C). The polymer (A) contains 1 to 50 mass% of repeating units (a1) derived from an aromatic vinyl compound and 20 to 75 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester, where the total amount of repeating units contained in the polymer (A) is taken as 100 mass%. The polymer (A) has a viscosity of 300 to 5,000 mPa·s in an NMP solution having a solids concentration of 8%. Note that "NMP" in this specification is an abbreviation for N-methyl-2-pyrrolidone.

[0030] The composition for an electricity storage device according to this embodiment can be used as a material for producing an electricity storage device electrode (active material layer) that has improved bonding ability between active materials, improved adhesion ability between the active material and a current collector, and improved resistance to powder shedding. Components that can be contained in the composition for an electricity storage device according to this embodiment are described in detail below.

[0031] 1.1. Polymer (A) The composition for an electrical storage device according to this embodiment contains a polymer (A). A conductive additive (B), such as CNT, generally has high coagulation properties and is difficult to uniformly disperse in a liquid medium (C). Furthermore, if the conductive additive (B) is not well dispersed, an active material layer obtained using an electrical storage device electrode slurry containing the conductive additive (B) may not form efficient conductive paths, and various properties of the conductive additive (B) may not be fully exhibited. In this regard, the composition for an electrical storage device according to this embodiment contains a polymer (A), thereby improving the dispersibility of the conductive additive (B), such as CNT, in the liquid medium (C). Furthermore, by using a composition for an electrical storage device containing a polymer (A) and a conductive additive (B), the structure of the conductive additive (B) is appropriately dispersed, enabling the formation of efficient conductive paths.

[0032] The repeating units constituting the polymer (A), the physical properties of the polymer (A), and the production method thereof will be described below in this order.

[0033] 1.1.1. Repeating units constituting polymer (A) When the total repeating units contained in polymer (A) is taken as 100% by mass, polymer (A) contains 1 to 50% by mass of repeating units (a1) (hereinafter also referred to as "repeating units (a1)") derived from an aromatic vinyl compound and 20 to 75% by mass of repeating units (a2) (hereinafter also referred to as "repeating units (a2)") derived from an unsaturated carboxylic acid ester. In addition to repeating units (a1) and repeating units (a2), polymer (A) may contain repeating units derived from other monomers copolymerizable with these repeating units.

[0034] 1.1.1.1. Repeating Unit (a1) Derived from an Aromatic Vinyl Compound The content of the repeating unit (a1) derived from an aromatic vinyl compound is 1 to 50% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content of the repeating unit (a1) is preferably 5% by mass, more preferably 9% by mass. The upper limit of the content of the repeating unit (a1) is preferably 47% by mass, more preferably 45% by mass. The content of the repeating unit (a1) is preferably 5 to 47% by mass, more preferably 9 to 45% by mass. By containing the repeating unit (a1) within the above range in the polymer (A), the dispersibility of the conductive additive (B), such as CNT, is excellent in the liquid medium (C), resulting in good slurry properties and improved coatability. Furthermore, the permeability of the electrolyte can be improved, resulting in good repeated charge / discharge characteristics.

[0035] The aromatic vinyl compound is not particularly limited, but examples thereof 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.

[0036] 1.1.1.2. Repeating Unit (a2) Derived from Unsaturated Carboxylic Acid Ester The content of the repeating unit (a2) derived from an unsaturated carboxylic acid ester is 20 to 75% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content of the repeating unit (a2) is preferably 23% by mass, and more preferably 25% by mass. The upper limit of the content of the repeating unit (a2) is preferably 70% by mass, and more preferably 65% ​​by mass. The content of the repeating unit (a2) is preferably 23 to 70% by mass, and more preferably 25 to 65% by mass. When the polymer (A) contains the repeating unit (a2) within the above range, the affinity between the polymer (A) and the electrolyte solution is improved, and an increase in internal resistance due to the polymer (A) becoming an electrical resistance component in the electricity storage device can be suppressed.

[0037] Among unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Specific examples of (meth)acrylic acid esters include 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, trimethylolpropane tri(meth)acrylate, tetra ... Examples include pentaerythritol di(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, glycerin di(meth)acrylate, dimethyl itaconate, diethyl itaconate, and dibutyl itaconate, and one or more selected from these may be used. Among these, 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, 2-hydroxyethyl (meth)acrylate, dimethyl itaconate, diethyl itaconate, and dibutyl itaconate are preferred.

[0038] 1.1.1.3. Other Repeating Units In addition to the repeating units (a1) and (a2), the polymer (A) may contain repeating units derived from other monomers copolymerizable therewith. Examples of such repeating units include a repeating unit (a3) ​​derived from an unsaturated carboxylic acid (hereinafter also referred to as "repeating unit (a3)"), a repeating unit (a4) derived from an α,β-unsaturated nitrile compound (hereinafter also referred to as "repeating unit (a4)"), a repeating unit (a5) derived from a compound having a sulfonic acid group (hereinafter also referred to as "repeating unit (a5)"), a repeating unit (a6) derived from (meth)acrylamide (hereinafter also referred to as "repeating unit (a6)"), and a repeating unit (a7) derived from a conjugated diene compound (hereinafter also referred to as "repeating unit (a7)").

[0039] <Repeating Unit (a3) ​​Derived from Unsaturated Carboxylic Acid> The polymer (A) may contain a repeating unit (a3) ​​derived from an unsaturated carboxylic acid. The content of the repeating unit (a3) ​​is preferably 0.5 to 10% by mass, where the total amount of repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content of the repeating unit (a3) ​​is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content of the repeating unit (a3) ​​is more preferably 9% by mass, and particularly preferably 8% by mass. The content of the repeating unit (a3) ​​is more preferably 1 to 9% by mass, and particularly preferably 2 to 8% by mass. By containing the repeating unit (a3) ​​within the above range in the polymer (A), the dispersibility of the conductive additive (B) may be further improved. Furthermore, the affinity with the silicon material used as the active material may be improved, and the conductive additive (B) may be dispersed in the vicinity of the silicon material, thereby exhibiting good charge / discharge durability characteristics.

[0040] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and dicarboxylic acid monoesters such as monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid, methacrylic acid, itaconic acid, monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate.

[0041] <Repeating Unit (a4) Derived from an α,β-Unsaturated Nitrile Compound> The content of the repeating unit (a4) derived from an α,β-unsaturated nitrile compound is preferably 5 to 40% by mass, when the total amount of repeating units contained in the polymer (A) is taken as 100% by mass. The lower limit of the content of the repeating unit (a4) is more preferably 6% by mass, and particularly preferably 8% by mass. The upper limit of the content of the repeating unit (a4) is more preferably 35% by mass, and particularly preferably 30% by mass. The content of the repeating unit (a4) is more preferably 6 to 35% by mass, and particularly preferably 8 to 30% by mass. When the polymer (A) contains the repeating unit (a4) within the above range, the affinity between the polymer (A) and the liquid medium (C) is improved. Furthermore, the affinity between the polymer (A) and the electrolyte is improved, which may prevent an increase in internal resistance in an electricity storage device due to the polymer (A) becoming an electrical resistance component.

[0042] The α,β-unsaturated nitrile compound is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, fumaronitrile, isopropylidenemalononitrile, tetracyanoethylene, vinylidene cyanide, etc., and one or more selected from these can be used. Among these, one or more selected from the group consisting of acrylonitrile, methacrylonitrile, fumaronitrile, isopropylidenemalononitrile, and tetracyanoethylene are preferred, and acrylonitrile is particularly preferred.

[0043] <Repeating Unit (a5) Derived from a Compound Having a Sulfonic Acid Group> The polymer (A) may contain a repeating unit (a5) derived from a compound having a sulfonic acid group. The content of the repeating unit (a5) is preferably 0.1 to 10 mass% when the total amount of repeating units contained in the polymer (A) is taken as 100 mass%. The lower limit of the content of the repeating unit (a5) is more preferably 0.5 mass%, and particularly preferably 1 mass%. The upper limit of the content of the repeating unit (a5) is more preferably 8 mass%, and particularly preferably 5 mass%. The content of the repeating unit (a5) is more preferably 0.5 to 8 mass%, and particularly preferably 1 to 5 mass%. By containing the repeating unit (a5) in the polymer (A) within the above range, the dispersibility of the active material and conductive additive may be improved. Furthermore, 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. Furthermore, since the bonding ability between active materials containing a carbon material such as graphite and a silicon material can be enhanced, an active material layer having better flexibility and adhesion to the current collector can be obtained in some cases.

[0044] Specific examples of the compound having a sulfonic acid group include, but are not limited to, compounds having a sulfonic acid group such as 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, and 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof.

[0045] <Repeating Unit (a6) Derived from (Meth)acrylamide> The content of the repeating unit (a6) derived from (meth)acrylamide is preferably 0.1 to 10% by mass, relative to the total amount of repeating units contained in the polymer (A) taken as 100% by mass. The lower limit of the content of the repeating unit (a6) is more preferably 0.5% by mass, and particularly preferably 0.8% by mass. The upper limit of the content of the repeating unit (a6) is more preferably 9% by mass, and particularly preferably 8% by mass. The content of the repeating unit (a6) is more preferably 0.5 to 9% by mass, and particularly preferably 0.8 to 8% by mass. By including the repeating unit (a6) in the polymer (A) within the above range, the dispersibility of the active material and filler in the slurry may be improved. Furthermore, the flexibility of the resulting active material layer may be appropriate, which may improve the adhesion between the current collector and the active material layer.

[0046] The (meth)acrylamide is not particularly limited, but examples thereof 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, and maleic acid monoamide, and one or more selected from these may be used.

[0047] 1.1.2. Physical Properties of Polymer (A) 1.1.2.1. Viscosity The viscosity of the polymer (A) in an NMP solution with a solids concentration of 8% is 300 to 5,000 mPa·s. The lower limit of the viscosity is preferably 400 mPa·s, and more preferably 500 mPa·s. The upper limit of the viscosity is preferably 4,500 mPa·s, and more preferably 4,000 mPa·s. The viscosity is preferably 400 to 4,500 mPa·s, and more preferably 500 to 4,000 mPa·s. When the viscosity is within the above range, the adsorption stability of the polymer (A) to the conductive additive (B) is increased, and the dispersibility of the conductive additive (B) in the liquid medium (C) can be effectively improved. This improves adhesion and makes it easier to form efficient conductive paths in the active material layer, making it possible to manufacture an energy storage device electrode that reduces internal resistance, has excellent input / output characteristics, and also has excellent charge / discharge cycle characteristics.

[0048] The viscosity of an NMP solution of polymer (A) having a solids concentration of 8% is a value measured at a temperature of 25° C. using a Brookfield viscometer in accordance with JIS Z 8803: 2011. As the Brookfield viscometer, for example, “RB-80L” or “TVB-10” manufactured by Toki Sangyo Co., Ltd. can be used.

[0049] 1.1.2.2. Weight-Average Molecular Weight (Mw) The weight-average molecular weight (Mw) of the polymer (A) is preferably 200,000 or more and 15,000,000 or less, more preferably 500,000 or more and 12,000,000 or less, and particularly preferably 1,000,000 or more and 10,000,000 or less. When the weight-average molecular weight (Mw) of the polymer (A) is within the above range, the polymer (A) exhibits high adsorption stability to the conductive additive (B), effectively improving the dispersibility of the conductive additive (B) in the liquid medium (C). This improves adhesion and facilitates the formation of efficient conductive paths in the active material layer, thereby reducing internal resistance and enabling the production of an electricity storage device electrode with excellent input / output characteristics and excellent charge / discharge cycle characteristics. The weight-average molecular weight of the polymer (A) can be measured, for example, using a GPC method under the following conditions.

[0050] 10 mg of an aqueous dispersion of polymer (A) with a solids concentration of 20% by mass was mixed with 5 mL of THF, left to stand at 25°C for 16 hours, and then passed through a 0.45 μm membrane filter to obtain a measurement sample. Next, using the resulting measurement sample, the weight-average molecular weight (Mw) of the THF-soluble component was determined by gel permeation chromatography (RI detection) using the following column under the following measurement conditions. [Measurement conditions] Temperature: 35°C Solvent: THF Flow rate: 1.0 mL / min Concentration: 0.2% by mass Sample injection volume: 100 μL [Column] Tosoh Corporation's "GPC TSKgel α-2500" (30 cm x 2 columns) was used. (Measurement was performed under conditions where the linear correlation equation between Log10 (Mw) and elution time between Mw 1,000 and 20,000,000 was 0.98 or higher.)

[0051] 1.1.3. Method for Producing Polymer (A) The method for producing polymer (A) is not particularly limited, but can be, for example, an emulsion polymerization method carried out in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, compounds described in Japanese Patent No. 5,999,399, etc. can be used.

[0052] The emulsion polymerization method for synthesizing the polymer (A) may be carried out in a single-stage polymerization or in a multi-stage polymerization such as two or more stages.

[0053] When polymer (A) is synthesized by single-stage polymerization, the mixture of the above-mentioned monomers can be emulsion-polymerized in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80°C for preferably 4 to 36 hours.

[0054] By controlling the total solids concentration in the emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed in a state in which the dispersion stability of the resulting polymer (A) particles is good. This total solids concentration is preferably 48% by mass or less, and more preferably 45% by mass or less.

[0055] Whether the synthesis of polymer (A) is carried out as a single-stage polymerization or as a multi-stage polymerization (two or more stages), it is preferable to add a neutralizing agent to the polymerization mixture after the completion of emulsion polymerization to adjust the pH to about 4.5 to 10.5, preferably 5 to 10, and more preferably 5.5 to 9.5. The neutralizing agent used here is not particularly limited, but examples include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia, etc. Setting the pH within the above range improves the stability of polymer (A). By concentrating the polymerization mixture after the neutralization treatment, the solids concentration can be increased while maintaining the good stability of polymer (A).

[0056] 1.2. Conductive Aid (B) The composition for an electrical storage device according to this embodiment contains a conductive aid (B). Specific examples of the conductive aid (B) include carbon such as carbon nanotubes, carbon nanofibers, acetylene black, ketjen black, furnace black, graphite, graphene, fullerene, carbon nanohorns, activated carbon, graphite, and carbon fibers. 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 are particularly preferred.

[0057] Examples of carbon nanotubes include single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT). Carbon nanotubes may be composed of only carbon, or may have a structure in which a portion of the structure is substituted with or chemically modified by other elements, or may be a composite with a metal (e.g., gold, silver, copper, aluminum, nickel, cobalt, titanium, platinum, etc.).

[0058] From the viewpoint of effectively improving the dispersibility of the conductive auxiliary (B) in the liquid medium (C), the content of the conductive auxiliary (B) in the composition for a storage battery device 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, relative to 100 parts by mass of the polymer (A).

[0059] 1.3. Liquid Medium (C) The composition for an electrical storage device according to this embodiment contains a liquid medium (C). The liquid medium (C) is not particularly limited, but may be an aliphatic hydrocarbon such as hexane, heptane, octane, decane, or dodecane; an alicyclic hydrocarbon such as cyclohexane, cycloheptane, cyclooctane, or cyclodecane; an aromatic hydrocarbon such as toluene, xylene, mesitylene, naphthalene, or tetralin; a ketone such as methylhexyl ketone or dipropyl ketone; an ester such as butyl acetate, butyl butyrate, or methyl butanoate; an ether such as dibutyl ether, tetrahydrofuran, or anisole; or a (mono-, di-, tri-, or poly)ethylene glycol mono-, di-, tri-, or poly(ethylene glycol) ... Examples of the liquid medium (C) that can be used include glycol ethers such as methyl ether, (mono-, di-, tri-, or poly)ethylene glycol dimethyl ether, and ethylene glycol phenyl ether; lactams such as β-lactam, γ-lactam, σ-lactam, N-methyl-2-pyrrolidone, and 2-pyrrolidone; lactones such as α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone; and amides such as N-methylacetamide, dimethylacetamide, N-methylformamide, and dimethylformamide. These liquid media (C) can be used singly or in combination of two or more.

[0060] The liquid medium (C) may contain water as long as it contains an organic solvent as the main solvent. The phrase "containing an organic solvent as the main solvent" means that the organic solvent accounts for more than 50% by mass when the total mass of the liquid medium (C) is taken as 100% by mass.

[0061] 1.4 Other Additives The composition for an electrical storage device according to this embodiment may contain additives other than the components described above, as necessary. Examples of such additives include polymers other than the polymer (A) (hereinafter also referred to as "other polymers"), preservatives, thickeners, etc.

[0062] 1.4.1. Other Polymers The composition for an electrical storage device according to this embodiment may contain other polymers. Examples of other polymers include, but are not limited to, conjugated diene polymers such as hydrogenated acrylonitrile butadiene rubber and styrene-butadiene copolymers, acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as structural units, and fluorine-containing polymers such as polyvinylidene fluoride (PVdF). These polymers may be used alone or in combination of two or more. The inclusion of these polymers may further improve flexibility and adhesion. Furthermore, using polymer (A) 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 may be in the form of a latex dispersed in the liquid medium (C).

[0063] When the composition for a storage battery device according to this embodiment contains another polymer, the content of the other polymer 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, relative to 100 parts by mass of the total solid content of the composition for a storage battery device.

[0064] 1.4.2. Preservatives The composition for an electrical storage device according to this embodiment may contain a preservative. The inclusion of a preservative may prevent the growth of bacteria, mold, and the like and the generation of foreign matter when the composition for an electrical storage device is stored. Specific examples of preservatives include compounds described in Japanese Patent No. 5,477,610, etc.

[0065] The composition for an electricity storage device according to this embodiment may contain a thickener. By containing a thickener, it may be possible to further improve the coatability of the slurry and the charge / discharge characteristics of the resulting electricity storage device.

[0066] Specific examples of thickeners include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the cellulose compounds or the poly(meth)acrylic acid; polyvinyl alcohol (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer; and water-soluble polymers such as saponified copolymers of vinyl esters with unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid. Among these, alkali metal salts of carboxymethyl cellulose and alkali metal salts of poly(meth)acrylic acid are preferred.

[0067] Commercially available thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0068] When the composition for a storage battery device according to this embodiment contains a thickener, the content of the thickener is preferably 5 parts by mass or less, and more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the total solid content of the composition for a storage battery device.

[0069] 2. Slurry for Electricity Storage Device Electrodes The term "slurry for electricity storage device electrodes" refers to a dispersion liquid used to form an active material layer on the surface of a current collector by applying the slurry to the surface of the current collector and then drying. A slurry for electricity storage device electrodes according to one embodiment of the present invention contains the above-described composition for electricity storage devices and an active material. The slurry for electricity storage device electrodes according to this embodiment exhibits good dispersibility of the conductive additive (B) such as CNT contained in the composition for electricity storage devices, resulting in good storage stability. Furthermore, the slurry for electricity storage device electrodes according to this embodiment exhibits excellent dispersibility of the active material and conductive additive (B), resulting in good coatability, thereby enhancing the surface smoothness of the coating film (particularly the linearity and flatness at the coated edge). Below, each component contained in the slurry for electricity storage device electrodes according to this embodiment will be described. The composition for electricity storage devices has been described above, so a detailed description will be omitted.

[0070] 2.1 Active Material Active materials used in the slurry for an electrode of an electricity storage device according to this embodiment include a positive electrode active material and a negative electrode active material. Specific examples of these include carbon materials, silicon materials, oxides containing lithium atoms, sulfur compounds, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacenes, A Ｘ B Ｙ O Ｚ (wherein A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, and manganese, O is an oxygen atom, and X, Y, and Z are numbers within the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively), as well as other metal oxides. Specific examples of these include compounds described in Japanese Patent No. 5,999,399.

[0071] The slurry for an electricity storage device electrode according to this embodiment can be used when producing either a positive electrode or a negative electrode for an electricity storage device, but is particularly preferably used for a positive electrode.

[0072] When preparing a positive electrode, among the active materials exemplified above, AＸ B Ｙ O Ｚ It is preferable that the composite metal oxide is represented by the formula: Examples of such composite metal oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and ternary nickel cobalt manganese oxide.

[0073] On the other hand, when preparing a negative electrode, among the active materials exemplified above, it is preferable to use one containing a silicon material. Since silicon materials have a larger lithium absorption capacity per unit weight than other active materials, by containing a silicon material as a negative electrode active material, the storage capacity of the obtained electricity storage device can be increased, and as a result, the output and energy density of the electricity storage device can be increased.

[0074] The negative electrode active material is preferably a mixture of a silicon material and a carbon material. Since the volume change of a carbon material during charging and discharging is smaller than that of a silicon material, the use of a mixture of a silicon material and a carbon material as the negative electrode active material can mitigate the effect of the volume change of the silicon material and further improve the adhesion between the active material layer and the current collector.

[0075] The content of the silicon material 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 content of the silicon material in 100% by mass of the active material is within the above range, an electricity storage device can be obtained that has an excellent balance between improved output and energy density of the electricity storage device and charge / discharge durability characteristics.

[0076] The active material is preferably in the form of particles. The average particle diameter of the active material is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm. Here, the average particle diameter of the active material refers to the volume average particle diameter calculated from the particle size distribution measured using a particle size distribution measuring device that uses laser diffraction as its measurement principle. Examples of such laser diffraction particle size distribution measuring devices include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by HORIBA, Ltd.).

[0077] 2.2. Other Components In addition to the components described above, other components may be added to the slurry for an electrical storage device electrode according to this embodiment as needed. Examples of such components include a polymer other than the polymer (A), a thickener, a liquid medium, a pH adjuster, a corrosion inhibitor, and cellulose fiber. The polymer other than the polymer (A) and the thickener may be appropriately selected from the compounds exemplified in "1.4. Other Additives" above, and may be used for the same purpose and in the same content ratio.

[0078] <Liquid Medium> A liquid medium may be further added to the slurry for an electrical storage device electrode according to this embodiment in addition to the liquid medium carried over from the electrical storage device composition. The liquid medium to be added may be the same as or different from the liquid medium (C) contained in the electrical storage device composition, but is preferably selected from the liquid media exemplified in "1.3. Liquid Medium (C)" above.

[0079] The content of the liquid medium (including the portion carried over from the composition for a storage battery device) in the slurry for an electrode of a storage battery device according to this embodiment is preferably such that the solids concentration in the slurry (meaning the proportion of the total mass of the components other than the liquid medium in the slurry to the total mass of the slurry; the same applies hereinafter) is 40 to 80 mass%, and more preferably 50 to 70 mass%.

[0080] <pH Adjuster / Corrosion Inhibitor> A pH adjuster and / or a corrosion inhibitor may be further added to the slurry for an electricity storage device electrode according to this embodiment, depending on the type of active material, for the purpose of suppressing corrosion of the current collector.

[0081] Examples of pH adjusters include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, and potassium hydroxide. Of these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred.

[0082] Examples of the corrosion inhibitor include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, and potassium molybdate. Of these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0083] <Cellulose Fiber> Cellulose fiber may be further added to the slurry for an electricity storage device electrode according to this embodiment. Adding cellulose fiber may improve the adhesion of the active material to the current collector. It is believed that the fibrous cellulose fiber bonds adjacent active materials together in a fibrous form through linear adhesion or linear contact, thereby preventing the active material from falling off and improving the adhesion to the current collector.

[0084] 2.3. Method for Preparing Slurry for Electrical Storage Device Electrode The electrical storage device electrode slurry according to this embodiment may be produced by any method as long as it contains the electrical storage device composition and active material described above. From the viewpoint of producing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to produce the slurry by adding the active material and optional additive components used as needed to the electrical storage device composition and mixing them. Specific examples of the production method include the method described in Japanese Patent No. 5,999,399.

[0085] 3. Electricity Storage Device Electrode An electricity 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-described electricity storage device electrode slurry to the surface of the current collector. Such an electricity storage device electrode can be produced by applying the above-described 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. The electricity storage device electrode produced in this manner has an active material layer, in which a conductive additive such as CNTs is well dispersed, bonded to the surface of the current collector. This provides excellent adhesion, facilitating the formation of efficient conductive paths within the active material layer. This makes it possible to produce an electricity storage device electrode that has reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics.

[0086] The current collector is not particularly limited as long as it is made of a conductive material, and examples thereof include the current collectors described in Japanese Patent No. 5,999,399 and the like.

[0087] In the electricity storage device electrode according to this embodiment, when a silicon material is used as the active material, the content of elemental silicon 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 elemental silicon in the active material layer is within this range, the electricity storage capacity of the electricity storage device produced using the active material layer is improved, and an active material layer with a uniform distribution of elemental silicon is obtained. The content of elemental silicon in the active material layer can be measured, for example, by the method described in Japanese Patent No. 5,999,399.

[0088] 4. Energy Storage Device An energy storage device according to one embodiment of the present invention includes the above-described energy storage device electrodes, further contains an electrolyte solution, and can be manufactured by a conventional method using components such as a separator. Specific manufacturing methods include, for example, stacking a negative electrode and a positive electrode with a separator interposed therebetween, and then wrapping or folding the stack according to the battery shape to house the stack in a battery container, and then injecting an electrolyte solution into the battery container and sealing it. The battery can have any suitable shape, such as a coin shape, a cylindrical shape, a rectangular shape, or a laminate shape.

[0089] The electrolyte may be liquid or gel, and may be selected from known electrolytes used in energy storage devices to effectively demonstrate the functions of the battery, depending on the type of active material. The electrolyte may be a solution in which an electrolyte is dissolved in a suitable solvent. Examples of such electrolytes and solvents include compounds described in Japanese Patent No. 5,999,399.

[0090] The above-described electricity storage device can be applied to lithium ion secondary batteries, electric double layer capacitors, lithium ion capacitors, and the like that require discharge at a high current density. Among these, lithium ion secondary batteries are particularly preferred. In the electricity storage device electrode and electricity storage device according to this embodiment, known materials for lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors can be used as components other than the electricity storage device composition.

[0091] 5. Examples The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are by mass unless otherwise specified.

[0092] 5.1. Example 1 5.1.1. Polymer Synthesis A polymer (A1) dispersion was obtained by single-stage polymerization as shown below. A 3-L separable flask was charged with 500 parts by mass of water, 0.8 parts by mass of 4,4'-azobis(4-cyanovaleric acid), 0.64 parts by mass of sodium bicarbonate, 1 part by mass of styrene, 67 parts by mass of 2-ethylhexyl acrylate, 1 part by mass of acrylic acid, 30 parts by mass of acrylonitrile, and 1 part by mass of sodium styrenesulfonate. Nitrogen bubbling was performed for 30 minutes, and then the reaction was carried out at 70°C for 5 hours. The mixture was then cooled to obtain an aqueous polymer (A1) dispersion with a solids concentration of 15%. The polymerization conversion of polymer (A1) at this time was 99%.

[0093] Next, 1 part by mass of 2,6-di-tert-butyl-p-cresol was added as an antioxidant. This aqueous dispersion of polymer (A1) was added dropwise to 3,000 parts by mass of a 0.5% aqueous calcium chloride solution. The resulting aggregates were washed with water, and a portion of the resulting aggregates was dried at 80°C, and the entire amount was recovered.

[0094] The polymer (A1) obtained above was added to N-methyl-2-pyrrolidone (NMP) and stirred overnight to dissolve the polymer (A1) in NMP, adjusting the content of the polymer (A1) to 8% by mass. The viscosity of this NMP solution of polymer (A1) at 25°C was measured using a B-type viscometer and found to be 820 mPa s.

[0095] 5.1.2. Physical Properties of Polymer <Evaluation of NMP Solubility> The aqueous dispersion of polymer (A1) obtained above was added to an aqueous calcium chloride solution, and the solution was subjected to a water-washing step and a drying step to obtain a coagulated polymer (A1). The obtained polymer (A1) was diluted with N-methyl-2-pyrrolidone to a concentration of 1 mass %. The transparency of the thus obtained 1 mass % NMP solution of the polymer was confirmed visually at 1 atmosphere and 23°C. The evaluation criteria were as follows. The results are shown in Table 1 below. (Evaluation Criteria) - When the 1 mass % NMP solution of the polymer was transparent, it was judged to be "soluble" and indicated as "A". - When the 1 mass % NMP solution of the polymer was translucent or cloudy, it was judged to be "insoluble" and indicated as "B".

[0096] 5.1.3 Preparation and Evaluation of Composition for Electrical Storage Device Preparation of Composition for Electrical Storage Device 1,000 parts by mass of NMP was added as a liquid medium to a container containing 4 parts by mass of single-walled carbon nanotubes (SWCNT, manufactured by OCSiAl Corporation, product name "TUBALL") and 20 parts by mass of the polymer (A1) obtained above. Ultrasonic dispersion was then carried out for 10 minutes, and the mixture was then passed five times using a high-pressure homogenizer (manufactured by Yoshida Kikai Kogyo Co., Ltd., product name "Nanovata") under 100 MPa to prepare a composition for an electrical storage device.

[0097] <Evaluation of CNT Dispersibility> The composition for use in an electrical storage device obtained above was subjected to a shear rate-shear viscosity evaluation in an environment of 25°C using an Anton Paar rheometer (MCR-500 model) with a 25 mm diameter, 2° cone plate as the measuring tool, under conditions of reciprocating motion between 1 (1 / s) and 1,000 (1 / s). The shear viscosity was read at 5 (1 / s) on the way there and back, and the rate of change (%) was calculated. The evaluation criteria were as follows. The results are shown in Table 1 below. (Evaluation Criteria) - Rate of change of 50% or less: The conductive additive dispersant is easy to handle due to small hysteresis and low structural viscosity. - Rate of change of 50% or more: The conductive additive dispersant is difficult to handle due to large hysteresis and high structural viscosity.

[0098] 5.1.4. Preparation of Slurry for Lithium-Ion Secondary Battery Positive Electrode Two parts by mass of polyvinylidene fluoride (Arkema, trade name "HSV1810"), 100 parts by mass of NMC811 (Beijing Dangsheng, trade name "ME-83SC") as a positive electrode active material, 3 parts by mass of acetylene black, and 25 parts by mass of NMP were added to a two-axis planetary mixer (Primix Corporation, trade name "TK Hibismix 2P-03") to prepare a slurry with a solids concentration of approximately 80%, and the mixture was stirred at 60 rpm for 1 hour. NMC811 is lithium nickel manganese cobalt oxide (LiNi ０．８ Mn ０．１ Co ０．１ O ２ ) is an abbreviation for

[0099] After stirring for 1 hour to obtain a paste, 0.1 parts by mass of the composition for an electrical storage device containing about 2% by mass of the polymer (A1) obtained above was added, and NMP was added to obtain a slurry with a solids concentration of 65%. The mixture was stirred using a stirring defoamer (manufactured by Thinky Corporation, product name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then further stirred under vacuum (about 5.0 × 10 ３ The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at 1000 kPa (2000 kPa) to prepare a slurry for a lithium ion secondary battery positive electrode.

[0100] 5.1.5. Preparation and Evaluation of Positive Electrode for Lithium Ion Secondary Battery <Preparation of Positive Electrode for Lithium Ion Secondary Battery> The slurry for the positive electrode for lithium ion secondary battery obtained above was uniformly applied to the surface of a current collector made of aluminum foil with a thickness of 20 μm by a doctor blade method so that the film thickness after drying would be 100 μm, and the slurry was dried at 120° C. for 20 minutes. Thereafter, the density of the formed film (positive electrode active material layer) was 3.0 g / cm ３ The resultant was pressed using a roll press machine so as to obtain a positive electrode for a lithium ion secondary battery.

[0101] <Evaluation of Electrode Condition> The lithium-ion secondary battery positive electrode obtained above was cut into a 10 cm x 10 cm piece, and the number of broken bubble marks on the surface was visually counted. The evaluation criteria were as follows. The evaluation results are shown in Table 1 below. Those with no particle marks in the active material layer indicated reduced coating defects due to residual emulsifier, and good cycle characteristics. (Evaluation Criteria) 5 points: If there were no broken bubble marks, there were no coating defects due to residual emulsifier, and the result was good. 4 points: If there were 1 to 5 broken bubble marks, there were almost no coating defects due to residual emulsifier, and the result was good. 3 points: If there were 6 to 10 broken bubble marks, there were few coating defects due to residual emulsifier, and the result was good. 2 points: If there were 11 to 15 broken bubble marks, there were some coating defects due to residual emulsifier, and the result was difficult to use. 1 point: If the number of broken particle traces is 16 or more, there are many coating defects due to residual emulsifier, and the coating cannot be used.

[0102] <Evaluation of Adhesion Strength> A knife was used to make 10 incisions in each direction, 2 mm apart, on the surface of the lithium-ion secondary battery positive electrode obtained above, from the active material layer to the current collector, creating a grid pattern. An 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Cellotape" (registered trademark), as defined in JIS Z1522:2009) was attached to the incisions and immediately peeled off, and the degree of active material loss was evaluated by visual inspection. The evaluation criteria were as follows. The evaluation results are shown in Table 1 below. (Evaluation Criteria) 5 points: 0 active material layers lost. 4 points: 1 to 5 active material layers lost. 3 points: 6 to 20 active material layers lost. 2 points: 21 to 40 active material layers lost. 1 point: 41 or more active material layers lost.

[0103] 5.1.6. Fabrication and Evaluation of Lithium-Ion Secondary Batteries <Preparation of Slurry for Lithium-Ion Secondary Battery Negative Electrode> 1 part by mass (solid content equivalent) of a thickener (manufactured by Daicel Corporation, product name "CMC2200"), 100 parts by mass (solid content equivalent) of graphite as the negative electrode active material, and 68 parts by mass of water were added to a biaxial planetary mixer (manufactured by Primix Corporation, product name "TK Hivismix 2P-03"), and the mixture was stirred at 60 rpm for 1 hour.

[0104] Next, SBR (trade name "TRD105A" manufactured by ENEOS Materials Corporation) was added in an amount equivalent to 2 parts by mass (solid content equivalent), and the mixture was further stirred for 1 hour to obtain a paste. Water was added to the obtained paste to adjust the solid content to 50%, and then the mixture was stirred and mixed using a stirring defoamer (trade name "Awatori Rentaro" manufactured by Thinky Corporation) at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then under vacuum at 1800 rpm for 1.5 minutes to prepare a slurry for a lithium-ion secondary battery negative electrode.

[0105] <Preparation of negative electrode for lithium ion secondary battery> The slurry for the negative electrode for lithium ion secondary battery prepared above was uniformly applied to the surface of a current collector made of copper foil with a thickness of 20 μm by a doctor blade method so that the film thickness after drying would be 80 μm, and the slurry was dried at 120° C. for 20 minutes. After that, the density of the formed film (negative electrode active material layer) was 1.9 g / cm ３ The negative electrode for a lithium ion secondary battery was obtained by pressing the negative electrode using a roll press machine so that the negative electrode became as follows:

[0106] <Assembly of Lithium-Ion Secondary Battery> In a glove box purged with Ar so that the dew point was −80° C. or less, the negative electrode produced above was punched out to 50 mm × 25 mm, to which a Ni tab was welded, and placed on a 56 mm × 32 mm polypropylene sheet. Next, a separator made of a polypropylene porous film punched out to 55 mm × 30 mm (manufactured by Celgard Co., Ltd., product name “Celgard #2400”) was placed, and the positive electrode produced above was punched out to 48 mm × 23 mm and then welded to an Al tab. A 56 mm × 32 mm polypropylene sheet was then placed on top of it. The structure was fixed by attaching 2 mm × 5 mm Kapton tape to the top and bottom of the long sides of the structure, and the structure was sandwiched between two 6 cm × 11 cm laminate films so that the center was located, and the three sides were heat-sealed at 180° C. with a width of 1 cm. After that, 650 μL of electrolyte was injected, and the remaining side was vacuum-sealed to assemble a lithium-ion battery cell (electricity storage device). The electrolyte used here was a solution of LiPF in a solvent of ethylene carbonate / dimethyl carbonate = 3 / 7 (mass ratio). ６ at a concentration of 1 mol / L, and 2 mass % of fluoroethyl carbonate and 1 mass % of vinyl carbonate were dissolved in the solution.

[0107] <Evaluation of Resistance Increase Rate> The lithium ion secondary battery prepared above was charged at a constant current (1.0 C) in a thermostatic chamber controlled at 25°C. When the voltage reached 4.25 V, charging was continued at a constant voltage (4.25 V). Charging was completed (cut-off) when the current reached 0.01 C. Discharge was then initiated at a constant current (0.05 C). Discharge was completed (cut-off) when the voltage reached 2.5 V, and the discharge capacity at the 0th cycle was calculated. Charging was then initiated at a constant current (1.0 C). When the voltage reached 4.25 V, charging was continued at a constant voltage (4.25 V). Charge was completed (cut-off) when the current reached 0.01 C. Discharge was then initiated at a constant current (1.0 C). Discharge was completed (cut-off) when the voltage reached 2.5 V, and the discharge capacity at the 1st cycle was calculated. Charge and discharge were repeated 100 times in this manner. After repeating charge and discharge 100 times, charge and discharge were performed in the same manner as in the 0th cycle, and the discharge capacity in the 101st cycle was evaluated. The resistance increase rate was calculated using the following formula (1) and evaluated according to the following criteria. The results are shown in Table 1 below. Resistance increase rate (%) = (discharge capacity at 101st cycle - discharge capacity at 100th cycle) / (discharge capacity at 0th cycle - discharge capacity at 1st cycle) x 100 (1) (Evaluation criteria) - 5 points: Resistance increase rate is 100% or more and less than 110%. - 4 points: Resistance increase rate is 110% or more and less than 120%. - 3 points: Resistance increase rate is 120% or more and less than 130%. - 2 points: Resistance increase rate is 130% or more and less than 140%. - 1 point: Resistance increase rate is 140% or more and less than 150%. - 0 point: Resistance increase rate is 150% or more.

[0108] <Evaluation of Cycle Characteristics> The lithium-ion secondary battery fabricated above was charged at a constant current (1.0 C) in a thermostatic chamber controlled at 25°C. When the voltage reached 4.25 V, charging was continued at a constant voltage (4.25 V). Charging was completed (cutoff) when the current reached 0.01 C. Discharge was then initiated at a constant current (1.0 C). Discharge was completed (cutoff) when the voltage reached 2.5 V, and the discharge capacity at the first cycle was calculated. This cycle was repeated 100 times. The capacity retention was calculated using the following formula (2) and evaluated according to the following criteria. The results are shown in Table 1 below. Capacity Retention (%) = (Discharge Capacity at 100th Cycle / Discharge Capacity at 1st Cycle) × 100 (2) (Evaluation Criteria) 5 points: Capacity retention of 95% or more. 4 points: Capacity retention of 90% or more but less than 95%. 3 points: Capacity retention of 85% or more but less than 90%.・2 points: Capacity retention rate is 80% or more but less than 85%. ・1 point: Capacity retention rate is 75% or more but less than 80%. ・0 point: Capacity retention rate is less than 75%.

[0109] In the measurement conditions, "1 C" refers to the current value at which a cell having a certain electrical capacity is discharged at a constant current until discharge is complete in 1 hour. For example, "0.1 C" refers to the current value at which discharge is completed in 10 hours, and "10 C" refers to the current value at which discharge is completed in 0.1 hours.

[0110] 5.2. Examples 2 to 16 and Comparative Examples 1 to 6 Each polymer was synthesized by single-stage polymerization in the same manner as in Example 1, except that the types and amounts of monomers were as shown in Tables 1 and 2 below, respectively, and each test was carried out in the same manner as in Example 1.

[0111] 5.3 Evaluation results of Examples 1 to 16 and Comparative Examples 1 to 6 Tables 1 and 2 below show the polymer compositions, measurement results of each physical property, and evaluation results used in Examples 1 to 16 and Comparative Examples 1 to 6. The numerical values ​​representing the polymer compositions shown in Tables 1 and 2 below represent parts by mass.

[0112]

[0113]

[0114] The polymer numbers used in each example are listed in the lines below each example number and each comparative example number in Tables 1 and 2. The abbreviations for the monomers in Tables 1 and 2 represent the following compounds. <Monomers> (Aromatic vinyl compounds) ST: Styrene VT: Vinyltoluene 4tBST: 4-tert-butylstyrene (Unsaturated carboxylic acid esters) MMA: Methyl methacrylate TADB: Dibutyl itaconate TADM: Dimethyl itaconate TADE: Diethyl itaconate BA: Butyl acrylate 2EHA: 2-ethylhexyl acrylate HEMA: Hydroxyethyl methacrylate CHMA: Cyclohexyl methacrylate (Unsaturated carboxylic acids) TA: Itaconic acid TAMB: Monobutyl itaconate TAMM: Monomethyl itaconate TAME: Monoethyl itaconate AA: Acrylic acid MAA: Methacrylic acid (α,β-Unsaturated nitrile compounds) AN: Acrylonitrile DMP: Isopropylidenemalononitrile FN: Fumaronitrile TCE: Tetracyanoethylene (compound with sulfonic acid group) NaSS: Sodium styrenesulfonate VS: Vinyl sulfonic acid ((meth)acrylamide) AAM: Acrylamide MAM: Methacrylamide

[0115] As is clear from Tables 1 and 2, by including polymer (A) as a dispersant, a composition with excellent dispersibility of conductive additive (B) can be obtained. Therefore, a slurry prepared using a composition containing polymer (A) and conductive additive (B) has excellent dispersibility and storage stability of the active material and conductive additive, resulting in good coatability and high surface smoothness of the coating film.

[0116] Furthermore, the positive electrodes of the electricity storage devices of Examples 1 to 16 were formed by bonding an active material layer containing the electricity storage device composition according to the present invention, an active material, and optional components added as needed to the surface of a current collector, and therefore had excellent adhesion and facilitated the formation of efficient conductive paths in the active material layer. This is presumably why electricity storage devices with reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics could be manufactured.

[0117] 5.4 Examples 17 to 22 In Examples 17 to 22, changes in the amount and type of conductive additive were investigated. In Examples 17 to 22, tests were conducted in the same manner as in Example 1, except that the amount of polymer (A1) prepared in Example 1, the amount of conductive additive, and the type of conductive additive were as shown in Table 3 below.

[0118]

[0119] In Table 3 above, the abbreviations for the conductive additive (B) represent the following compounds: (Conductive additive (B)) TUBALL: SWCNT, manufactured by OCSiAl Corporation Cnano: MWCNT, manufactured by Cnano Technology Corporation VGCF: Vapor-phase carbon nanofiber, manufactured by Resonac Corporation Super CT: Furnace black, manufactured by TIMCAL Corporation AB: Acetylene black, manufactured by Denka Company Limited, trade name "Denka Black (registered trademark)"

[0120] As is clear from Table 3 above, by including polymer (A) as a dispersant, a composition with excellent dispersibility of conductive aid (B) can be obtained, regardless of the contents of polymer (A) and conductive aid (B) or the type of conductive aid (B). Therefore, a slurry prepared using a composition containing polymer (A) and conductive aid (B) has excellent dispersibility and storage stability of the active material and conductive aid, and therefore has good coatability and high surface smoothness of the coating film.

[0121] Furthermore, the positive electrodes of the electricity storage devices of Examples 17 to 22 were formed by bonding an active material layer containing the electricity storage device composition according to the present invention, an active material, and optional components added as needed to the surface of a current collector. Therefore, regardless of the contents of the polymer (A) and the conductive additive (B) or the type of the conductive additive (B), the positive electrodes exhibited excellent adhesion and facilitated the formation of efficient conductive paths in the active material layer. This is presumably why electricity storage devices were produced that had reduced internal resistance, excellent input / output characteristics, and excellent charge / discharge cycle characteristics.

[0122] 5.5. Examples 23 to 26 In Examples 23 to 26, an investigation was conducted into replacing polyvinylidene fluoride (manufactured by Arkema, product name "HSV1810") contained in a slurry for a positive electrode of a lithium ion secondary battery with another polymer. In Examples 23 to 26, each test was performed in the same manner as in Example 1, except that the type of composition for an electricity storage device and the type of binder were as shown in Table 4 below.

[0123]

[0124] In Table 4 above, the abbreviations for the conductive additive and binder component represent the following compounds: (Conductive additive) TUBALL: SWCNT, manufactured by OCSiAl (Binder component) PVdF: Polyvinylidene fluoride, manufactured by Arkema, trade name "HSV1810", HNBR: Hydrogenated acrylonitrile butadiene rubber, manufactured by Lanxess, trade name "Telban 3467".

[0125] As is clear from Table 4 above, the evaluation results were good even when the binder component was changed from polyvinylidene fluoride (manufactured by Arkema, product name "HSV1810") to HNBR, polymer (A1), or polymer (A5). In addition, the evaluation results were also good when the dispersant for the conductive additive was changed from polymer (A1) to polymer (A5).

[0126] 5.6 Timing of Mixing Conductive Aid The timing of mixing the conductive aid was investigated. In Comparative Examples 7 and 8 in Table 5 below, the polymer and conductive aid (SWCNT, manufactured by OCSiAl, "TUBALL") were not mixed into a paste in advance as in Example 1, but the following production method was used.

[0127] <Preparation of Slurry for Lithium-Ion Secondary Battery Positive Electrode in Comparative Examples 7 and 8> 2 parts by mass of polyvinylidene fluoride (manufactured by Arkema, trade name "HSV1810"), 100 parts by mass of NMC811 (trade name "ME-83SC", manufactured by Beijing Dangsheng Co., Ltd.) as a positive electrode active material, 3 parts by mass of acetylene black, 0.1 parts by mass of a conductive additive (SWCNT, manufactured by OCSiAl Corporation, "TUBALL"), 0.5 parts by mass of a polymer (A1) NMP solution or a polymer (B1) NMP solution in terms of solids content, and 20 parts by mass of NMP were added to a two-shaft planetary mixer (manufactured by Primix Corporation, trade name "TK Hibismix 2P-03") to prepare a slurry having a solids concentration of about 80%, and the mixture was stirred at 60 rpm for 1 hour.

[0128] After stirring for 1 hour to obtain a paste, NMP was added to adjust the solid content of the slurry to 65%. The mixture was then deaerated using a stirring deaerator (Thinky Corporation, product name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then further deaerated under vacuum (approximately 5.0 × 10 ３ The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at 1000 kPa (2000 kPa) to prepare a slurry for a lithium ion secondary battery positive electrode.

[0129] Using the thus obtained slurry for a lithium ion secondary battery positive electrode, a positive electrode for a lithium ion secondary battery was produced in the same manner as in Example 1, and various tests were carried out in the same manner as in Example 1.

[0130]

[0131] The evaluation results in Table 5 above reveal that by dispersing the conductive additive in polymer (A) in advance to obtain a composition for a storage battery device, an electrode with excellent dispersibility of the conductive additive can be obtained.

[0132] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially identical to 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 parts of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention also includes configurations that achieve the same effects or purposes as the configurations described in the above embodiments. Furthermore, the present invention also includes configurations in which publicly known technology is added to the configurations described in the above embodiments.

Claims

1. A composition for an electrical storage device comprising: a polymer (A); a conductive assistant (B); and a liquid medium (C); wherein, when the total amount of repeating units contained in the polymer (A) is taken as 100% by mass, the polymer (A) contains: 1 to 50% by mass of repeating units (a1) derived from an aromatic vinyl compound; and 20 to 75% by mass of repeating units (a2) derived from an unsaturated carboxylic acid ester; and wherein the viscosity of the polymer (A) in an NMP solution having a solids concentration of 8% is 300 to 5,000 mPa·s.

2. The composition for an electrical storage device according to claim 1, wherein the polymer (A) further contains 0.5 to 10 mass % of a repeating unit (a3) ​​derived from an unsaturated carboxylic acid.

3. The composition for use in an electrical storage device according to claim 1 or 2, wherein the polymer (A) further contains 5 to 40 mass % of a repeating unit (a4) derived from an α,β-unsaturated nitrile compound.

4. The composition for an electrical storage device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 mass % of a repeating unit (a5) derived from a compound having a sulfonic acid group.

5. The composition for use in an electrical storage device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 mass % of a repeating unit (a6) derived from (meth)acrylamide.

6. A composition for storage devices according to claim 1 or claim 2, wherein the conductive assistant (B) is at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, acetylene black, furnace black and graphene.

7. A composition for an electrical storage device according to claim 1 or 2, wherein the liquid medium (C) is at least one selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, esters, ethers, glycol ethers, lactams, lactones and amides.

8. A composition for an electrical storage device according to claim 1 or 2, further comprising at least one polymer selected from the group consisting of hydrogenated acrylonitrile butadiene rubber, an acrylic polymer and a fluorine-based polymer.

9. The composition for an electrical storage device according to claim 1 or 2, further comprising a thickener.

10. A slurry for an electrode of a storage battery device, comprising the composition for a storage battery device according to claim 1 and an active material.

11. The slurry for an electrode of a storage battery device according to claim 10, wherein the active material is a positive electrode active material.

12. The slurry for an electric storage device electrode according to claim 10, which contains a silicon material as the active material.

13. An electricity storage device electrode comprising: a current collector; and an active material layer formed by applying the slurry for an electricity storage device electrode according to claim 10 to the surface of the current collector and drying it.

14. An electricity storage device comprising the electricity storage device electrode according to claim 13.