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

Abstract

Provided is a power storage device binder composition that has excellent adhesion and that can enhance charge / discharge durability characteristics of a power storage device.　A power storage device binder composition according to the present invention contains a polymer (A) and a liquid medium (B). If the total of repeating units contained in the polymer (A) is 100 mass%, the polymer (A) contains 1-40 mass% of repeating units (a1) derived from an unsaturated carboxylic acid ester having an alicyclic hydrocarbon group and 45-90 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester having an aliphatic hydrocarbon group (excluding the unsaturated carboxylic acid ester having an alicyclic hydrocarbon group), and the swelling ratio of the polymer (A) when the polymer (A) is immersed in a solvent comprising a propylene carbonate and a diethyl carbonate with a volume fraction of 1:1 at 70°C for 24 hours is 120-200 mass%.

Description

[Technical Field]

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

[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] In recent years, lithium-containing phosphate compounds with a highly safe olivine structure (olivine-type lithium-containing phosphate compounds) have been adopted as positive electrode active materials for energy storage devices. Olivine-type lithium-containing phosphate compounds have high thermal stability because phosphorus and oxygen are covalently bonded, and they do not release oxygen even at high temperatures.

[0006] However, olivine-type lithium-containing phosphate compounds have a low output voltage because the Li-ion absorption / release voltage is around 3.4V. To compensate for this drawback, attempts have been made to improve the properties of peripheral materials such as electrode binders and electrolytes (see Patent Documents 1-3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-294323 [Patent Document 2] International Publication No. 2010 / 113940 [Patent Document 3] Japanese Patent Publication No. 2012-216322 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] While techniques for improving the properties of peripheral materials such as electrode binders and electrolytes, as disclosed in the above-mentioned Patent Documents 1 to 3, improve the output voltage of energy storage devices equipped with a positive electrode using an olivine-type lithium-containing phosphate compound as the positive electrode active material, it has been difficult to sufficiently improve the charge-discharge durability characteristics of the energy storage device.

[0009] Therefore, several embodiments of the present invention provide a binder composition for energy storage devices that has excellent adhesion and can improve the charge-discharge durability characteristics of the energy storage device. Furthermore, several embodiments of the present invention provide a slurry for energy storage device electrodes that has excellent adhesion and can improve the charge-discharge durability characteristics of the energy storage device. Furthermore, several embodiments of the present invention provide an energy storage device that has excellent adhesion and can improve the charge-discharge durability characteristics of the energy storage device. [Means for solving the problem]

[0010] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in any of the following embodiments.

[0011] One embodiment of the binder composition for energy storage devices according to the present invention is: It contains a polymer (A) and a liquid medium (B), When the total amount of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) is Repeating units (a1) derived from unsaturated carboxylic acid esters having alicyclic hydrocarbon groups (1-40% by mass), It contains 45 to 90% by mass of repeating units (a2) derived from unsaturated carboxylic acid esters having aliphatic hydrocarbon groups (excluding the aforementioned unsaturated carboxylic acid esters having alicyclic hydrocarbon groups), The polymer (A) is immersed in a solvent consisting of propylene carbonate and diethyl carbonate in a volume fraction ratio of 1:1 at 70°C for 24 hours, and its swelling rate is 120% by mass or more and 200% by mass or less.

[0012] In one embodiment of the binder composition for the energy storage device, The polymer (A) may further contain 0.1 to 10% by mass of repeating units (a5) derived from an unsaturated carboxylic acid.

[0013] In any of the aspects of the binder composition for an electricity storage device described above, the polymer (A) may further contain 1 to 14% by mass of a repeating unit (a6) derived from an aromatic vinyl compound.

[0014] In any of the aspects of the binder composition for an electricity storage device described above, the total content of the repeating unit (a1) and the repeating unit (a2) contained in the polymer (A) may be 70% by mass or more.

[0015] In any of the aspects of the binder composition for an electricity storage device described above, when differential scanning calorimetry (DSC) is performed on the polymer (A) in accordance with JIS K7121:2012, an endothermic peak may be observed in a temperature range of -60°C to 60°C.

[0016] In any of the aspects of the binder composition for an electricity storage device described above, the polymer (A) is polymer particles, the number average particle diameter of the polymer particles may be 50 nm or more and 500 nm or less.

[0017] In any of the aspects of the binder composition for an electricity storage device described above, the surface acid content of the polymer (A) may be 0.05 mmol / g or more and 3 mmol / g or less.

[0018] One aspect of the slurry for an electricity storage device electrode according to the present invention is comprising the binder composition for an electricity storage device according to any one of the above aspects, and an active material.

[0019] In one aspect of the slurry for an electricity storage device electrode described above, the active material may be a positive electrode active material.

[0020] In one aspect of the slurry for an electricity storage device electrode described above, a silicon material may be contained as the active material.

[0021] One embodiment of the energy storage device electrode according to the present invention is: The device 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.

[0022] One aspect of the energy storage device according to the present invention is: The device comprises an energy storage device electrode according to the above embodiment. [Effects of the Invention]

[0023] According to the binder composition for energy storage devices of the present invention, an energy storage device with excellent charge-discharge durability characteristics is provided due to its excellent adhesion. [Modes for carrying out the invention]

[0024] 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.

[0025] In this specification, "(meth)acrylic acid~" refers to "acrylic acid~" or "methacrylic acid~". Also, "~(meth)acrylate" refers to "~acrylate" or "~methacrylate".

[0026] 1. Binder composition for energy storage devices A binder composition for an energy storage device according to one embodiment of the present invention contains a polymer (A) and a liquid medium (B). The polymer (A) contains, when the total amount of repeating units contained in the polymer (A) is 100% by mass, 1 to 40% by mass of repeating units (a1) derived from an unsaturated carboxylic acid ester having an alicyclic hydrocarbon group and 45 to 90% by mass of repeating units (a2) derived from an unsaturated carboxylic acid ester having an aliphatic hydrocarbon group (excluding the aforementioned unsaturated carboxylic acid ester having an alicyclic hydrocarbon group). Furthermore, the polymer (A) has a swelling rate of 120% by mass or more and 200% 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 binder composition for energy storage devices according to this embodiment can be used as a material for producing an energy storage device electrode (active material layer) with improved bonding ability between active materials, adhesion ability between active materials and current collectors, and resistance to powder shedding. It can also be used as a material for forming a protective film to suppress short circuits caused by dendrites generated during charging and discharging. The components contained in the binder composition for energy storage devices according to this embodiment will be described in detail below.

[0028] 1.1. Polymerization (A) The binder composition for energy storage devices according to this embodiment contains polymer (A). Polymer (A) contains 1 to 40% by mass of repeating units (a1) (hereinafter also simply referred to as "repeating unit (a1)") derived from unsaturated carboxylic acid esters having alicyclic hydrocarbon groups, and 45 to 90% by mass of repeating units (a2) (hereinafter also simply referred to as "repeating unit (a2)") derived from unsaturated carboxylic acid esters having aliphatic hydrocarbon groups, when the total amount of repeating units contained in polymer (A) is 100% by mass. Polymer (A) may also contain repeating units derived from other monomers copolymerizable thereto, in addition to the aforementioned repeating units.

[0029] The polymer (A) contained in the binder composition for energy storage devices according to this embodiment may be in the form of latex dispersed in the liquid medium (B) or dissolved in the liquid medium (B), but it is preferable that it be in the form of latex dispersed in the liquid medium (B). It is preferable that the polymer (A) is in the form of latex dispersed in the liquid medium (B) because it improves the stability of the slurry for energy storage device electrodes (hereinafter also simply referred to as "slurry") produced by mixing it with the active material, and also improves the applicability of the slurry to the current collector.

[0030] The following will explain the repeating units that make up polymer (A), the physical properties of polymer (A), and the manufacturing method, in that order.

[0031] 1.1.1. Repeating units constituting polymer (A) 1.1.1.1. Repeating units (a1) derived from unsaturated carboxylic acid esters having alicyclic hydrocarbon groups The content of repeating units (a1) derived from unsaturated carboxylic acid esters having alicyclic hydrocarbon groups is 1 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 repeating units (a1) is preferably 1% by mass, more preferably 3% by mass, and particularly preferably 10% by mass. The upper limit of the content of repeating units (a1) is preferably 40% by mass, more preferably 35% by mass, and particularly preferably 30% by mass. By containing repeating units (a1) within the above ranges in polymer (A), swelling of polymer (A) in the electrolyte is moderately suppressed, and the coating properties of polymer (A) on the active material during electrode fabrication are maintained. As a result, Li insertion and removal into the active material becomes easier, and the internal resistance can be reduced, resulting in good charge-discharge characteristics.

[0032] The unsaturated carboxylic acid ester having an alicyclic hydrocarbon group is not particularly limited, but examples include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate, and one or more can be selected from these. Of these, cyclohexyl (meth)acrylate is particularly preferred.

[0033] 1.1.1.2. Repeating units (a2) derived from unsaturated carboxylic acid esters having an aliphatic hydrocarbon group. The content of repeating units (a2) derived from unsaturated carboxylic acid esters having aliphatic hydrocarbon groups (excluding the aforementioned unsaturated carboxylic acid esters having alicyclic hydrocarbon groups) is 45 to 90% 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 repeating units (a2) is preferably 45% by mass, more preferably 50% by mass, and particularly preferably 55% by mass. The upper limit of the content of repeating units (a2) is preferably 90% by mass, more preferably 85% by mass, and particularly preferably 80% by mass. By containing repeating units (a2) within the above ranges in polymer (A), the dispersibility of the active material and filler is improved, making it possible to produce a uniform active material layer and protective film. As a result, structural defects in the electrode plate are eliminated, and good charge-discharge characteristics are achieved. Furthermore, the polymer (A) coating the surface of the active material can be given elasticity, and the adhesion can be improved by the expansion and contraction of polymer (A), resulting in good charge-discharge durability characteristics.

[0034] In this invention, an unsaturated carboxylic acid ester having both an alicyclic hydrocarbon group and an aliphatic hydrocarbon group is defined as belonging to the category of unsaturated carboxylic acid esters having an alicyclic hydrocarbon group.

[0035] The unsaturated carboxylic acid ester having an aliphatic hydrocarbon group is not particularly limited, but (meth)acrylic acid esters are preferred. Specific examples of such (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, and others, and one or more can be selected from these. Of these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is preferred, and one or more selected from n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is more preferred.

[0036] 1.1.1.3. Other Repeating Units Polymer (A) may contain repeating units derived from other monomers copolymerizable with repeating units (a1) and (a2). Examples of such repeating units include repeating units derived from polyfunctional (meth)acrylic acid esters (a3) ​​(hereinafter also simply referred to as "repeating unit (a3)"), repeating units derived from other unsaturated carboxylic acid esters (a4) (hereinafter also simply referred to as "repeating unit (a4)"), repeating units derived from unsaturated carboxylic acids (a5) (hereinafter also simply referred to as "repeating unit (a5)"), repeating units derived from aromatic vinyl compounds (a6) (hereinafter also simply referred to as "repeating unit (a6)"), repeating units derived from (meth)acrylamide (a7) (hereinafter also simply referred to as "repeating unit (a7)"), repeating units derived from α,β-unsaturated nitrile compounds (a8) (hereinafter also simply referred to as "repeating unit (a8)"), repeating units derived from compounds having sulfonic acid groups (a9) (hereinafter also simply referred to as "repeating unit (a9)"), and repeating units derived from cationic monomers.

[0037] <Repeating unit (a3) ​​derived from polyfunctional (meth)acrylic acid ester> Polymer (A) may contain repeating units (a3) ​​derived from polyfunctional (meth)acrylic acid esters. The inclusion of repeating units (a3) ​​in polymer (A) may make it easier to suppress the swelling rate of polymer (A) in the electrolyte.

[0038] In this invention, "polyfunctional" means having one or more functional groups selected from polymerizable double bonds and epoxy groups, in addition to the polymerizable double bond of the (meth)acrylic acid ester.

[0039] Specific examples of polyfunctional (meth)acrylic acid esters include glycidyl (meth)acrylate, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene di(meth)acrylate, and one or more of these can be selected. Of these, one or more selected from allyl (meth)acrylate and ethylene glycol di(meth)acrylate are preferred, and allyl (meth)acrylate is particularly preferred.

[0040] The content of repeating units (a3) ​​in polymer (A) is preferably 0.1 to 10% by mass, and more preferably 1 to 8% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. A content of repeating units (a3) ​​within the above range is preferable because it makes it easier to suppress the swelling rate of polymer (A) in the electrolyte as described above. When the content is above the lower limit, the swelling rate of polymer (A) can be suppressed, the coating on the active material can be maintained, the insertion and removal of Li ions cannot be inhibited, and the increase in internal resistance can be suppressed. As a result, good charge and discharge characteristics are observed. On the other hand, when the content is below the upper limit, polymer (A) becomes flexible, which can impart flexibility to the electrode, making it less likely for structural defects to occur. As a result, good charge and discharge characteristics are observed.

[0041] <Repeating units derived from other unsaturated carboxylic acid esters (a4)> Polymer (A) may contain repeating units (a4) derived from other unsaturated carboxylic acid esters. In the present invention, other unsaturated carboxylic acid esters refer to unsaturated carboxylic acid esters other than the alicyclic hydrocarbon esters, the aliphatic hydrocarbon esters, and the polyfunctional (meth)acrylic acid esters.

[0042] Other unsaturated carboxylic acid esters include unsaturated carboxylic acid esters having a hydroxyl group and unsaturated carboxylic acid esters having a phenoxy group. Examples of unsaturated carboxylic acid esters having a hydroxyl group are not particularly limited, but include 2-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, and glycerin mono(meth)acrylate. Examples of unsaturated carboxylic acid esters having a phenoxy group include phenoxydiethylene glycol (meth)acrylate. Of these, 2-hydroxyethyl (meth)acrylate and glycerin mono(meth)acrylate are preferred. One or more of these can be used as other unsaturated carboxylic acid esters.

[0043] The content of repeating units (a4) in polymer (A) is preferably 0 to 10% by mass, and more preferably 1 to 8% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. When polymer (A) contains repeating units (a4) within the above range, the dispersibility of the active material and filler 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.

[0044] <Repeating units derived from unsaturated carboxylic acids (a5)> Polymer (A) may contain repeating units (a5) derived from an unsaturated carboxylic acid. 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, and one or more selected from these can be used. Preferably, one or more selected from acrylic acid, methacrylic acid, and itaconic acid are used as the unsaturated carboxylic acid.

[0045] The content of repeating units (a5) derived from unsaturated carboxylic acids is preferably 0.1 to 10% by mass, and more preferably 1 to 8% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. By polymer (A) containing repeating units (a5) within the above range, the dispersibility of the active material and filler is improved. This makes it possible to produce a uniform active material layer and protective film, eliminating structural defects in the electrode plate and resulting in good charge-discharge characteristics.

[0046] <Repeating units derived from aromatic vinyl compounds (a6)> Polymer (A) may contain repeating units (a6) derived from an aromatic vinyl compound. The aromatic vinyl compound is not particularly limited, but examples include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used.

[0047] The content of repeating units (a6) derived from aromatic vinyl compounds is preferably 1 to 14% by mass, and more preferably 2 to 12% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. By containing repeating units (a6) within the above range, polymer (A) exhibits good binding strength to positive electrode active materials and the like used as active materials. As a result, an energy storage device electrode with excellent flexibility and adhesion can be obtained.

[0048] <(meth)acrylamide-derived repeating unit (a7)> Polymer (A) may contain repeating units (a7) derived from (meth)acrylamide. Examples of (meth)acrylamide 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, acrylamide tert-butylsulfonic acid, and one or more selected from these can be used.

[0049] The content of repeating units (a7) derived from (meth)acrylamide is preferably 0 to 5% by mass, and more preferably 1 to 4% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. When polymer (A) contains repeating units (a7) within the above range, the dispersibility of the active material and filler 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.

[0050] <Repeating unit (a8) derived from α,β-unsaturated nitrile compounds> Polymer (A) may contain repeating units (a8) derived from an α,β-unsaturated nitrile compound. The α,β-unsaturated nitrile compound is not particularly limited, but examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and one or more selected from these can be used. Among these, one or more selected from acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0051] The content of repeating units (a8) derived from α,β-unsaturated nitrile compounds is preferably 0 to 10% by mass, and more preferably 1 to 8% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. By polymer (A) containing repeating units (a8) within the above range, it is possible to improve the affinity of polymer (A) with the electrolyte. This may facilitate the insertion and removal of Li ions and result in good charge and discharge characteristics.

[0052] <Repeating unit (a9) derived from a compound having a sulfonic acid group> Polymer (A) may contain repeating units (a9) derived from a compound having a sulfonic acid group. The compound having a sulfonic acid group is not particularly limited, but examples 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, and one or more selected from these can be used.

[0053] The content of repeating units (a9) derived from compounds having sulfonic acid groups is preferably 0 to 10% by mass, and more preferably 1 to 6% by mass, when the total amount of repeating units contained in polymer (A) is taken as 100% by mass. When polymer (A) contains repeating units (a9) within the above range, the dispersibility of the active material and filler is improved. As a result, it becomes possible to produce a uniform active material layer and protective film, which eliminates structural defects in the electrode plate and may result in good charge-discharge characteristics.

[0054] <Repeating units derived from cationic monomers> Polymer (A) may contain repeating units derived from a cationic monomer. The cationic monomer is not particularly limited, but it is preferably at least one monomer selected from the group consisting of secondary amines (salts), tertiary amines (salts), and quaternary ammonium salts. Specific examples of these cationic monomers are not particularly limited, but include 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate methyl chloride quaternary salt, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(0-[1'-methylpropyleneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methachloroylcholinchloride, and tris(2-acryloyloxyethyl) isocyanurate. Examples include 2-vinylpyridine, quinaldine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazole dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichlormid, N-allylbenzylamine, N-allylaniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-heptene-4-inyl)-N-methyl-1-naphthylmethylamine hydrochloride, and one or more selected from these can be used.

[0055] 1.1.2. Physical properties of polymer (A) 1.1.2.1. Electrolyte swelling rate When polymer (A) 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 (hereinafter also referred to as "electrolyte swelling rate") is 120% by mass or more and 200% by mass or less, preferably 130% by mass or more and 190% by mass or less, and more preferably 130% by mass or more and 180% by mass or less. When the electrolyte swelling rate of polymer (A) is within the above range, polymer (A) 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 is within the above range, the coating effect of polymer (A) on the active material becomes low, effectively reducing electrode resistance and exhibiting good charge-discharge characteristics.

[0056] 1.1.2.2.Number average particle size When the polymer (A) is in the form of particles, the number-average particle diameter of the particles is preferably 50 nm to 500 nm, more preferably 60 nm to 450 nm, and particularly preferably 70 nm to 400 nm. When the number-average particle diameter of the polymer (A) particles is within the above range, the polymer (A) particles are more easily adsorbed onto the surface of the active material, so that the polymer (A) particles can move along with the movement of the active material. As a result, migration can be suppressed, which may reduce the deterioration of electrical properties.

[0057] The number-average particle size of polymer (A) particles can be calculated from the average particle size 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-Technologies Corporation.

[0058] 1.1.2.3. Glass transition temperature Polymer (A) preferably has an endothermic peak in the temperature range of -60°C to 60°C when measured by differential scanning calorimetry (DSC) in accordance with JIS K7121:2012. The temperature of this endothermic peak (i.e., the glass transition temperature (Tg)) is more preferably in the range of 60°C or lower, and particularly preferably in the range of 50°C or lower. When the peak temperature is within the above range, polymer (A) is preferable because it can impart better flexibility and tackiness to the active material layer.

[0059] 1.1.2.4. Surface acid content When the polymer (A) is in the form of particles, the surface acid content of the particles is preferably 0.05 mmol / g or more and 3 mmol / g or less, more preferably 0.1 mmol / g or more and 2.8 mmol / g or less, and particularly preferably 0.2 mmol / g or more and 2.5 mmol / g or less. When the surface acid content of the polymer (A) particles is within the above range, a stable and homogeneous slurry can be produced. When an active material layer is produced using such a homogeneous slurry, an active material layer with uniform dispersion of the active material and polymer (A) particles and with little variation in thickness is 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.

[0060] 1.1.3. Method for producing polymer (A) The method for producing polymer (A) is not particularly limited, but can be carried out by emulsion polymerization in the presence of known emulsifiers (surfactants), chain transfer agents, polymerization initiators, etc. Compounds described in Japanese Patent Publication No. 5999399, etc., can be used as emulsifiers (surfactants), chain transfer agents, and polymerization initiators.

[0061] The emulsion polymerization method for synthesizing polymer (A) may be carried out as a single-step polymerization or as a multi-step polymerization of two or more steps.

[0062] When polymer (A) 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.

[0063] When polymer (A) is synthesized by two-step polymerization, it is preferable to set the polymerization steps as follows.

[0064] The proportion of monomers used in the first stage polymerization is preferably in the range of 20 to 99% by mass, and more preferably in the range of 25 to 99% by mass, relative to the total mass of monomers (the sum of the mass of monomers used in the first stage polymerization and the mass of monomers used in the second stage polymerization). By performing the first stage polymerization with such a proportion of monomers, it is possible to obtain polymer (A) particles that have excellent dispersion stability and are less prone to agglomeration. In addition, it is preferable that the increase in viscosity of the binder composition for energy storage devices over time is suppressed.

[0065] The types and proportions of monomers used in the second polymerization step may be the same as, or different from, the types and proportions of monomers used in the first polymerization step.

[0066] The polymerization conditions at each stage are preferably as follows, from the viewpoint of the dispersibility of the particles of the resulting polymer (A). • First stage polymerization; preferably at a temperature of 40-80°C; preferably for a polymerization time of 2-36 hours; preferably with a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more. • Second stage polymerization; preferably at a temperature of 40-80°C; preferably for a polymerization time of 2-18 hours.

[0067] 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 (A) particles. This total solids content concentration is preferably 48% by mass or less, and more preferably 45% by mass or less.

[0068] Whether polymer (A) is synthesized as a single-step polymerization or as a two-step polymerization, it is preferable to add a neutralizing agent to the polymerization mixture after emulsion polymerization is complete. The pH range is preferably adjusted 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 ensures good stability of polymer (A). After the neutralization treatment, the polymerization mixture can be concentrated to increase the solid content concentration while maintaining the good stability of polymer (A).

[0069] 1.1.4. Content ratio of polymer (A) The content of polymer (A) in the binder composition for energy storage devices according to this embodiment is preferably 10 to 100% by mass, more preferably 20 to 95% by mass, and particularly preferably 25 to 90% by mass, based on 100% by mass of the polymer components. Here, the polymer components include polymer (A), polymers other than polymer (A) described later, and thickeners, etc.

[0070] 1.2. Liquid media (B) The binder composition for energy storage devices according to this embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium may contain a non-aqueous medium other than water. Examples of such non-aqueous media include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, and sulfone compounds, and one or more selected from these can be used. By using an aqueous medium as the liquid medium (B) in the binder composition for energy storage devices according to this embodiment, the degree of adverse impact on the environment is reduced, and safety for handling workers is also increased.

[0071] The content of non-aqueous media in the aqueous media is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially absent, based on 100% by mass of the 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 binder composition for energy storage devices.

[0072] 1.3. Other Additives The binder 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 (A), preservatives, thickeners, and the like.

[0073] 1.3.1. Polymers other than polymer (A) The binder composition for energy storage devices according to this embodiment may contain polymers other than polymer (A). Such polymers are not particularly limited, but examples include acrylic polymers containing unsaturated carboxylic acid esters or their derivatives as constituent units, and fluorine-based polymers such as PVDF (polyvinylidene fluoride). These polymers may be used individually or in combination of two or more. The inclusion of these polymers may further improve flexibility and adhesion.

[0074] 1.3.2. Preservatives The binder composition for energy storage devices according to this embodiment may contain a preservative. By including a preservative, it may be possible to suppress the growth of bacteria, mold, and other foreign substances when the binder composition for energy storage devices is stored. Specific examples of preservatives include compounds described in Japanese Patent Publication No. 5477610, etc.

[0075] 1.3.3. Thickening Agents The binder composition for energy storage devices according to this embodiment may contain a thickening agent. By including a thickening agent, it may be possible to further improve the applicability of the slurry and the charge / discharge characteristics of the resulting energy storage device.

[0076] Specific examples of thickeners include cellulose compounds such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose; polysaccharides such as alginic acid; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the aforementioned cellulose compounds or poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; and water-soluble polymers such as saponified copolymers of unsaturated carboxylic acids and vinyl esters, including (meth)acrylic acid, maleic acid, and fumaric acid. Among these, alkali metal salts of carboxymethylcellulose and alkali metal salts of poly(meth)acrylic acid are preferred.

[0077] Examples of commercially available thickeners include alkali metal salts of carboxymethylcellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0078] If the binder composition for energy storage devices according to this embodiment contains a thickening agent, the proportion of the thickening agent is preferably 5% by mass or less, and more preferably 0.1 to 3% by mass, based on 100% by mass of the total solid content of the binder composition for energy storage devices.

[0079] 1.4. pH of binder composition for energy storage devices The pH of the binder composition for energy storage devices according to this embodiment is preferably 4.5 to 10.5, more preferably 5 to 10, and particularly preferably 5.5 to 9.5. When the pH is within this range, problems such as insufficient leveling and liquid dripping can be suppressed. As a result, it becomes easier to manufacture energy storage device electrodes that achieve both good electrical characteristics and adhesion.

[0080] 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.

[0081] Furthermore, while the pH of a binder composition for energy storage devices may be affected by the monomer composition constituting the polymer (A), 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 a binder composition for energy storage devices can change depending on the polymerization conditions, etc., and the examples in this specification merely illustrate one such example.

[0082] For example, even with the same monomer composition, the amount of carboxyl groups derived from the unsaturated carboxylic acid exposed on the surface of the resulting polymer will differ depending on whether all unsaturated carboxylic acids are added to the polymerization reaction solution from the beginning, followed by the sequential addition of other monomers, or whether the monomers other than the unsaturated carboxylic acid are added to the polymerization reaction solution first, with the unsaturated carboxylic acid being added last. Thus, even simply changing the order in which monomers are added during polymerization can significantly alter the pH of the binder composition for energy storage devices.

[0083] 2. Slurry for energy storage devices A slurry for energy storage devices according to one embodiment of the present invention contains the above-described binder composition for energy storage devices. The above-described binder composition for energy storage devices can be used as a material for producing a protective film to suppress short circuits caused by dendrites generated during charging and discharging, or as a material for producing an energy storage device electrode (active material layer) with improved bonding ability between active materials, adhesion ability between active materials and current collectors, and resistance to powder shedding. For this reason, the slurry for energy storage devices for producing a protective film (hereinafter also referred to as "slurry for protective film") and the slurry for energy storage devices for producing the active material layer of the energy storage device electrode (hereinafter also referred to as "slurry for energy storage device electrode") will be described separately.

[0084] 2.1. Slurry for protective film "Protective film slurry" refers to a dispersion used to create a protective film on the surface of an electrode or separator, or both, by applying it to the surface of the electrode or separator, or both, and then drying it. The protective film slurry according to this embodiment may consist only of the above-described binder composition for energy storage devices, or it may further contain an inorganic filler. An example of an inorganic filler is the inorganic filler described in Japanese Patent Application Publication No. 2020-184461.

[0085] 2.2. 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 this embodiment contains the above-mentioned binder composition for energy storage devices and an active material. The components contained in the slurry for energy storage device electrodes according to this embodiment will be described below.

[0086] 2.2.1. Polymer (A) The composition, physical properties, and manufacturing method of polymer (A) are as described above, so no further explanation is provided.

[0087] The polymer component content in the slurry for the electrodes of the energy storage device according to this embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass, per 100 parts by mass of active material. When the polymer component content is within the above range, the dispersibility of the active material in the slurry is good, and the applicability of the slurry is also excellent. Here, the polymer component includes polymer (A), polymers other than polymer (A) added as needed, and thickeners, etc.

[0088] 2.2.2.Active material 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 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 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.

[0089] 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 positive electrode.

[0090] Examples of the lithium atom-containing oxide include one or more selected from lithium atom-containing oxides (olivine-type lithium-containing phosphate compounds) that are represented by the following general formula (1) and have an olivine-type crystal structure.

[0091] Li 1-x M x(AO4) ·····(1) (In formula (1), M is an ion of at least one metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge and Sn; A is at least one selected from the group consisting of Si, S, P and V; and x is a number satisfying the relationship 0<x<1.) Furthermore, the value of x in the general formula (1) is selected according to the valences of M and A such that the overall valence of the general formula (1) is 0.

[0092] Examples of the olivine-type lithium-containing phosphate compound include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4 and the like. Among these, LiFePO4 (lithium iron phosphate) is particularly preferable because the iron compound used as a raw material is easily available and inexpensive.

[0093] The average particle diameter of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 µm, more preferably in the range of 1 to 25 µm, and particularly preferably in the range of 1 to 20 µm.

[0094] In addition, the active material layer may contain active materials exemplified below. For example, conductive polymers such as polyacene; A X B Y O Z (where 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 represents an oxygen atom; and X, Y and Z are numbers falling within the ranges of 1.10>X>0.05, 4.00>Y>0.85, and 5.00>Z>1.5 respectively). Other examples include composite metal oxides represented by the above formula, other metal oxides, and the like. Examples of such composite metal oxides include lithium cobaltate, lithium nickelate, lithium manganate, ternary lithium nickel cobalt manganate, and the like.

[0095] Energy storage device electrodes fabricated using the slurry for energy storage device electrodes according to this embodiment can exhibit good electrical properties even when an oxide containing lithium atoms is used as the positive electrode active material. This is because polymer (A) can firmly bind the oxide containing lithium atoms, and at the same time, can maintain a state in which the oxide containing lithium atoms is firmly bound even during charging and discharging.

[0096] On the other hand, when manufacturing a negative electrode, it is preferable to use an active material that contains carbon material among the examples given above. Since carbon material undergoes smaller volume changes during charging and discharging than silicon material, using a mixture of silicon and carbon material as the negative electrode active material can mitigate the effects of volume changes in the silicon material, thereby further improving the adhesion between the active material layer and the current collector.

[0097] 2.2.3. Other ingredients 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 (A), thickeners, liquid media, conductive additives, pH adjusters, corrosion inhibitors, cellulose fibers, etc. As polymers other than polymer (A) and thickeners, appropriate selections can be made from the compounds exemplified in "1.3. Other Additives" above and used for the same purpose and in the same proportions.

[0098] <Liquid media> In addition to the portion brought in from the binder 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 (B) contained in the binder 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 "1.2. Liquid Medium (B)" above.

[0099] The content ratio of the liquid medium (including the amount brought in from the binder composition for an electricity storage device) in the slurry for an electricity storage device electrode according to the present embodiment is preferably such that the solid content concentration in the slurry (refers to 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 30 to 70% by mass, and more preferably 40 to 60% by mass.

[0100] <Conductive auxiliary agent> A conductive auxiliary agent may be further added to the slurry for an electricity storage device electrode according to the present embodiment for the purposes of imparting conductivity and buffering the volume change of the active material caused by the entry and exit of lithium ions.

[0101] Specific examples of the conductive auxiliary agent include carbons such as activated carbon, acetylene black, Ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotubes. Among these, acetylene black or carbon nanotubes can be preferably used. The content ratio of the conductive auxiliary agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass, relative to 100 parts by mass of the active material.

[0102] <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 the present embodiment for the purpose of suppressing corrosion of the current collector depending on the type of the active material.

[0103] Examples of the pH adjuster include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferable. The pH adjuster can also be selected and used from the neutralizing agents described in the production method of the polymer (A).

[0104] 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.

[0105] <Cellulose Fiber> Cellulose fibers may be further added to the slurry for the energy storage device electrodes according to this embodiment. Adding cellulose fibers may improve the adhesion of the active material to the current collector. It is believed that the fibrous cellulose fibers bind adjacent active materials together through linear adhesion or linear contact, thereby preventing the active material from falling off and improving adhesion to the current collector.

[0106] 2.2.4. Method for preparing slurry for electrodes of energy storage devices The slurry for the electrodes of the energy storage device according to this embodiment may be manufactured by any method, as long as it contains the above-described binder 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 binder composition for energy storage devices and mixing them. Specific manufacturing methods include, for example, the method described in Japanese Patent Publication No. 5999399.

[0107] 3. Energy storage device electrodes 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. In the energy storage device electrode manufactured in this manner, an active material layer containing the above-mentioned polymer (A), active material, and optionally added components is bonded to the surface of the current collector. As a result, excellent adhesion is obtained, and an energy storage device with excellent charge-discharge durability characteristics can be obtained.

[0108] 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.

[0109] 4. Energy storage devices An energy storage device according to one embodiment of the present invention comprises 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 any suitable shape, such as coin-type, cylindrical, prismatic, or laminate-type.

[0110] 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 such electrolytes and solvents include compounds described in Japanese Patent Publication No. 5999399, etc.

[0111] 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 binder composition for the energy storage device can be those of known lithium-ion secondary batteries, electric double-layer capacitors, and lithium-ion capacitors.

[0112] 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.

[0113] 5.1. Example 1 5.1.1. Preparation of binder compositions for energy storage devices 150 parts by mass of water and 0.2 parts by mass of sodium dodecylbenzenesulfonate were placed in a 7-liter separable flask, and the inside of the separable flask was thoroughly purged with nitrogen. Meanwhile, in a separate container, 60 parts by mass of water, 0.8 parts by mass of an ether sulfate-type emulsifier (product name "ADEKA Soap SR1025", manufactured by ADEKA Corporation) in terms of solid content, and 1 part by mass of cyclohexyl methacrylate (CHMA), 3 parts by mass of acrylonitrile (AN), 58 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of n-butyl acrylate (BA), 5 parts by mass of n-butyl methacrylate (BMA), 5 parts by mass of ethyl acrylate (EA), 2 parts by mass of allyl methacrylate (AMA), 2 parts by mass of acrylamide (AAM), 10 parts by mass of styrene (ST), 1 part by mass of sodium styrene sulfonate (NASS), and 3 parts by mass of acrylic acid (AA) were added and thoroughly stirred to prepare a monomer emulsion containing the mixture of the above monomers. The temperature inside the separable flask was started to rise, and when the internal temperature reached 60°C, 0.5 parts by mass of ammonium persulfate was added as a polymerization initiator. When the internal temperature of the separable flask reached 70°C, the addition of the monomer emulsion prepared above was started, and the monomer emulsion was slowly added over 3 hours while maintaining the internal temperature of the separable flask at 70°C. After that, the internal temperature of the separable flask was raised to 85°C and maintained at this temperature for 3 hours to carry out the polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then ammonium water was added to adjust the pH to 8.0, thereby obtaining an aqueous dispersion containing 30% by mass of particles consisting of polymer (A).

[0114] 5.1.2. Evaluation of the physical properties of polymer (A) For the polymer (A) obtained above, the electrolyte swelling rate, glass transition temperature (Tg), pH, number-average particle size, and surface acid content were measured. For the measurement of pH, number-average particle size, and surface acid content, an aqueous dispersion of polymer (A) was used as the measurement sample. The measurement results are shown in Table 1.

[0115] (1) Measurement of electrolyte swelling rate A film was prepared by drying the polymer (A) obtained above in a constant temperature bath at 40°C for 24 hours. 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") and left to stand 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. The electrolyte swelling rate was calculated using the following formula. Electrolyte swelling rate (mass%)=(Z / (1-Y))×100

[0116] (2) Measurement of glass transition temperature The polymer (A) obtained above was measured using a differential scanning calorimeter (NETZSCH, DSC204F1 Phoenix) in accordance with JIS K7121:2012, and the temperature of the endothermic peak was determined.

[0117] (3) pH measurement The pH of the aqueous dispersion of polymer (A) obtained above was measured at 25°C using a pH meter (manufactured by Horiba, Ltd.).

[0118] (4) Measurement of number-average particle size The aqueous dispersion of polymer (A) obtained above was diluted to 0.1 wt% latex, and one drop of this solution was added to a collodion support membrane using a pipette. Then, one drop of 1 wt% phosphotungstic acid 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 10K using a transmission electron microscope (TEM, Hitachi High-Technologies Corporation, model number "H-7650"), and image analysis was performed using the HITACHI EMIP program to calculate the number-average particle size of 50 randomly selected polymer (A) particles.

[0119] (5) Measurement of surface acid content The surface acid content of the polymer (A) particles 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 (A) obtained above (in terms of solid content) was taken into a 300 mL beaker, and its sample weight was recorded. After diluting it to 200 mL with ultrapure water, 1 mol / L sodium hydroxide aqueous solution was added dropwise. Once the endpoint was reached, the mixture 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. Surface acid content (mmol / g) = Amount of acid used in the carboxylic acid region on the particle surface [mL] × Acid concentration [mol / L] × Degree of ionization / Sample weight [g] / 1000

[0120] 5.1.3. Preparation of slurry for the positive electrode of a non-aqueous secondary battery In a twin-screw planetary mixer (manufactured by Primix Corporation, product name "TK Hibiscus Mix 2P-03"), 2 parts by mass of the polymer (A) (calculated on a solid content basis, added as an aqueous dispersion of polymer (A) obtained above), 100 parts by mass of NMC622 (product name "ME-8A", manufactured by Beijing Dangsheng Co., Ltd.) as a positive electrode active material, 5 parts by mass of acetylene black, 1 part by mass of a thickener (product name "CMC2200", manufactured by Daicel Corporation), and 20 parts by mass of water were added, and the mixture was stirred at 60 rpm for 1 hour. Note that NMC622 is an example of a positive electrode active material.

[0121] The mixture was then stirred for 1 hour to obtain a paste. Water was added to the resulting paste to adjust the solid content to 70%, and then a stirring and degassing machine (manufactured by Thinky Co., Ltd., product name "Awatori Rentaro") was used to stir at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and finally under vacuum (approximately 5.0 × 10). 3 A slurry for the positive electrode of a non-aqueous secondary battery was prepared by stirring and mixing at 1800 rpm for 1.5 minutes at Pa.

[0122] 5.1.4. Fabrication and property evaluation of positive electrodes for non-aqueous secondary batteries 5.1.4.1. Fabrication of positive electrodes for non-aqueous secondary batteries The non-aqueous secondary battery positive electrode slurry obtained above was uniformly applied to the surface of a current collector made of 20 μm thick aluminum foil using the doctor blade method so that the film thickness after drying would be 100 μm, and then dried at 120°C for 20 minutes. After that, the density of the formed film (positive electrode active material layer) was 3.0 g / cm³. 3 A positive electrode for a non-aqueous secondary battery was obtained by press processing using a roll press machine to achieve the desired result.

[0123] 5.1.4.2. Evaluation of physical properties of positive electrodes for non-aqueous secondary batteries <Evaluation of adhesion strength> On the surface of the positive electrode for the non-aqueous secondary battery obtained above, ten cuts were made vertically and horizontally at 2 mm intervals using a knife, to a depth from the active material layer to 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 Z1522:2009) was applied to these cuts and immediately peeled off, and the degree of active material detachment was evaluated by visual inspection. The evaluation criteria are as follows. The evaluation results are shown in Table 1. (Evaluation Criteria) • 5 points: There are 0 instances of active material layer shedding. • 4 points: 1 to 5 layers of the active material have been detached. • 3 points: There are 6 to 20 detached active material layers. • 2 points: 21 to 40 active material layers have been detached. • 1 point: More than 41 active material layers have been lost.

[0124] <Evaluation of the number of fractured polymer particles (maintenance of particle shape) in the positive electrode coating layer> The surface of the positive electrode for the non-aqueous secondary battery obtained above was observed using a scanning electron microscope (SEM, JEOL Ltd., model number "JSM-6360LA") to observe the polymer (A) particles, and the number of particles destroyed by pressing per 100 polymer (A) particles was measured. In this measurement, if the boundary between particles could be confirmed, the particle shape was maintained and it was judged to be an undestroyed particle; if the boundary between particles could not be confirmed, the particle was crushed and judged to be a destroyed particle. The evaluation criteria are as follows. The evaluation results are shown in Table 1. (Evaluation Criteria) • 5 points: When the number of destroyed particles is 10 or less, the interface of the polymer particles is very resistant to adhesion and is excellent. • 4 points: When the number of destroyed particles is between 11 and 20, the interface of the polymer particles is less likely to be compressed, indicating good performance. • 3 points: If the number of destroyed particles is between 21 and 30, the interface of the compressed polymer particles may be present, but the product is still usable. • 2 points: If the number of destroyed particles is between 31 and 40, it is unusable because a large number of interfaces of the compressed polymer particles are observed. • 1 point: If the number of destroyed particles is 41 or more, it is unusable because a large number of interfaces of the compressed polymer particles are observed.

[0125] 5.1.5. Fabrication and physical property evaluation of non-aqueous secondary batteries (1) Preparation of slurry for aqueducts of non-aqueducts and fabrication of aqueducts for non-aqueducts of secondary batteries In a twin-shaft planetary mixer (product name "TK Hibiscus Mix 2P-03" manufactured by Primix Corporation), 1 part by mass (based on solid content) of a thickening agent (product name "CMC2200" manufactured by Daicel Corporation), 100 parts by mass (based on solid content) of graphite as a negative electrode active material, and 68 parts by mass of water were added, and the mixture was stirred at 60 rpm for 1 hour.

[0126] Next, an amount equivalent to 2 parts by mass (in terms of solid content) of SBR (product name "TRD105A", manufactured by JSR Corporation) was added, and the mixture was stirred for another 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 and defoaming machine (manufactured by Thinky Co., Ltd., product name "Awatori Rentaro") 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 the negative electrode of a non-aqueous secondary battery.

[0127] Next, the non-aqueous secondary battery negative electrode slurry prepared above was uniformly applied to the surface of a current collector made of 20 μm thick copper foil using the doctor blade method, so that the film thickness after drying would be 80 μm, and then dried at 120°C for 20 minutes. After that, the density of the formed film (negative electrode active material layer) was 1.9 g / cm³. 3 By press-forming the material using a roll press machine, a negative electrode for a non-aqueous secondary battery was obtained.

[0128] (2) Assembly of non-aqueous secondary batteries (lithium-ion batteries) In a glove box where the dew point was substituted with Ar to -80°C or lower, the negative electrode for the non-aqueous secondary battery prepared above was punched out into a circular shape with a diameter of 15.95 mm and placed on a two-electrode coin cell (manufactured by Hosen Co., Ltd., product name "HS Flat Cell").

[0129] Next, a separator made of a porous polypropylene membrane punched into a 24mm diameter circle (manufactured by Cellguard Co., Ltd., product name "Cellguard #2400") was placed on top of the negative electrode for a non-aqueous secondary battery.

[0130] Furthermore, after injecting 500 μL of electrolyte to prevent air from entering, the positive electrode for the non-aqueous secondary battery prepared above was punched out into a circular shape with a diameter of 16.16 mm, placed on top of the separator, and the outer body of the two-electrode coin cell was sealed by screwing it shut, thereby assembling a lithium-ion battery cell (an example of a non-aqueous secondary battery). The electrolyte used here was a solution of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio) in which LiPF6 was dissolved at a concentration of 1 mol / L.

[0131] (3) Evaluation of physical properties of non-aqueous secondary batteries <Evaluation of cycle characteristics> For the non-aqueous secondary batteries manufactured as described above, charging was started at a constant current (1.0C) in a constant temperature bath maintained at 25°C. Charging continued at a constant voltage (4.2V) when the voltage reached 4.2V, and charging was completed (cutoff) when the current reached 0.01C. Discharging was then started at a constant current (1.0C), and discharge was completed (cutoff) when the voltage reached 3.0V. The discharge capacity for the first cycle was calculated. This charge-discharge cycle was repeated 100 times. The capacity retention rate was calculated using the following formula and evaluated according to the following criteria. The evaluation results are shown in Table 1. Capacity retention rate (%) = (Discharge capacity at 100 cycles) / (Discharge capacity at 1 cycle) (Evaluation Criteria) • 5 points: Capacity retention rate is 95% or higher. • 4 points: Capacity retention rate is between 90% and less than 95%. • 3 points: Capacity retention rate is between 85% and less than 90%. • 2 points: Capacity retention rate is between 80% and less than 85%. • 1 point: Capacity retention rate is between 75% and less than 80%. • 0 points: Capacity retention rate is less than 75%.

[0132] <Evaluation of resistance increase rate> For the non-aqueous secondary battery manufactured as described above, charging was started at a constant current (1.0C) in a constant temperature bath maintained at 25°C. Charging continued at a constant voltage (4.2V) when the voltage reached 4.2V, and the charging was completed (cutoff) when the current reached 0.01C. Discharging was then started at a constant current (0.05C), and the discharge capacity for the first cycle was calculated when the voltage reached 3.0V. Furthermore, charging was started again at a constant current (1.0C), and charging continued at a constant voltage (4.2V) when the voltage reached 4.2V, and the charging was completed (cutoff) when the current reached 0.01C. Discharging was then started at a constant current (1.0C), and the discharge capacity for the first cycle was calculated when the voltage reached 3.0V. This process was repeated 100 times. After 100 charge-discharge cycles, the same charge-discharge procedure as in the 0th cycle was performed, and the discharge capacity on the 101st cycle was evaluated. The resistance increase rate was calculated using the following formula and evaluated according to the following criteria. Resistance increase rate (%) = (Discharge capacity at cycle 101 - Discharge capacity at cycle 100) / (Discharge capacity at cycle 0 - Discharge capacity at cycle 1) × 100 (Evaluation Criteria) • 5 points: Resistance increase rate is between 100% and 110%. • 4 points: Resistance increase rate is between 110% and less than 120%. • 3 points: Resistance increase rate is between 120% and 130%. • 2 points: Resistance increase rate is between 130% and 140%. • 1 point: Resistance increase rate is between 140% and 150%. • 0 points: Resistance increase rate is 150% or more.

[0133] In the measurement conditions, "1C" refers to the current value at which a cell with a certain electrical capacity will complete discharge in one hour. For example, "0.1C" refers to the current value at which discharge will complete in 10 hours, and "10C" refers to the current value at which discharge will complete in 0.1 hours.

[0134] 5.2. Examples 2-14, Comparative Examples 1-6 In the section "5.1.1. Preparation of Binder Composition for Energy Storage Devices" above, aqueous dispersions containing 30% by mass of polymer particles were obtained in the same manner as described in Table 1 or Table 2, except that the types and amounts of each monomer were as shown. Otherwise, a slurry for energy storage device electrodes was prepared in the same manner as in Example 1, and energy storage device electrodes and energy storage devices were fabricated and evaluated in the same manner as in Example 1.

[0135] [Table 1]

[0136] [Table 2]

[0137] The abbreviations for each monomer in Tables 1 and 2 represent the following monomers, respectively. <Unsaturated carboxylic acid esters having alicyclic hydrocarbon groups> • CHMA: Cyclohexyl methacrylate • CHA: Cyclohexyl Acrylate <Unsaturated carboxylic acid esters containing aliphatic hydrocarbon groups> • 2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate BMA: n-butyl methacrylate • MMA: Methyl methacrylate • EA: Ethyl acrylate <Polyfunctional (meth)acrylic acid esters> • EDMA: Ethylene glycol dimethacrylate AMA: Allyl methacrylate <Other unsaturated carboxylic acid esters> HEMA: 2-hydroxyethyl methacrylate • HEA: 2-hydroxyethyl acrylate GLM: Glycerin monomethacrylate <Unsaturated carboxylic acids> TA: Itaconic acid AA: Acrylic acid • MAA: Methacrylic acid <Aromatic vinyl compounds> ·ST: Styrene DVB: Divinylbenzene <(meth)acrylamide> · AAM: Acrylamide • MAM: Methacrylamide <α,β-unsaturated nitrile compounds> AN: Acrylonitrile <Compounds containing sulfonic acid groups> • NASS: Sodium styrene sulfonate

[0138] 5.3. Examples 15-20 In Example 12, a slurry for energy storage device electrodes was prepared in the same manner as in Example 12, except that the content ratios of polymer (A), CMC (product name "CMC2200", manufactured by Daicel Corporation), and alginic acid (product name "Sodium Alginate 80-120", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were as shown in Table 3. Energy storage device electrodes and energy storage devices were then fabricated and evaluated in the same manner as in Example 12. The results are shown in Table 3.

[0139] [Table 3]

[0140] 5.4. Example 21 In Example 5, the binder used in the slurry for the negative electrode of a non-aqueous secondary battery was changed from TRD105A to polymer (A) prepared in Example 5, and the adhesion strength and cycle characteristics were evaluated in the same manner as in Example 5. The results are shown in Table 4.

[0141] [Table 4]

[0142] 5.5. Evaluation Results As is clear from Tables 1 and 2 above, the slurry for energy storage device electrodes prepared using the binder compositions for energy storage devices according to the present invention shown in Examples 1 to 14 was able to bind the active materials together more effectively than in Comparative Examples 1 to 6, resulting in energy storage device electrodes with good charge-discharge durability characteristics. The reason for this is that the polymer (A) contained in the binder compositions of Examples 1 to 14 shown in Tables 1 and 2 above has a relatively low electrolyte swelling rate of 120 to 200% by mass, which maintains coating properties on the active materials, and as a result facilitates the insertion and removal of lithium ions. This prevents the penetration of electrolyte between active materials from being inhibited, resulting in low resistance, and consequently exhibiting good charge-discharge durability characteristics.

[0143] As is clear from the results in Table 3 above, the slurry for energy storage device electrodes according to the present invention, which uses polymer (A) and a thickener in combination, allows for more favorable bonding of active materials and maintains good adhesion between the active material layer and the current collector. In particular, the slurry for energy storage device electrodes prepared using the binder compositions for energy storage devices shown in Examples 17 and 18 allows for favorable bonding of active materials and maintains good adhesion between the active material layer and the current collector, even when alginic acid is used as a thickener.

[0144] As is clear from the results in Table 4 above, the slurry for the electrode of an energy storage device prepared using the binder composition for energy storage devices according to the present invention shown in Example 21 showed good results even when a negative electrode active material was used. It is thought that the improved electrolyte affinity facilitated the deintercalation and insertion of Li ions into the negative electrode active material, resulting in lower resistance and thus good charge-discharge characteristics.

[0145] 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. It contains a polymer (A) and a liquid medium (B), When the total amount of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) is 1 to 40% by mass of repeating units (a1) derived from unsaturated carboxylic acid esters having alicyclic hydrocarbon groups, It contains 45 to 90% by mass of repeating units (a2) derived from an unsaturated carboxylic acid ester having an aliphatic hydrocarbon group (excluding the aforementioned unsaturated carboxylic acid ester having an alicyclic hydrocarbon group), The polymer (A) has a swelling rate of 120% by mass or more and 200% 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. The polymer (A) is polymer particles, The number-average particle diameter of the polymer particles is 50 nm or more and 500 nm or less. A binder composition for energy storage devices, wherein the surface acid content of the polymer (A) is 0.05 mmol / g or more and 3 mmol / g or less.

2. The binder composition for energy storage devices according to claim 1, wherein the polymer (A) further contains 0.1 to 10% by mass of repeating units (a5) derived from an unsaturated carboxylic acid.

3. The binder composition for energy storage devices according to claim 1 or claim 2, wherein the polymer (A) further contains 1 to 14% by mass of repeating units (a6) derived from an aromatic vinyl compound.

4. The binder composition for energy storage devices according to claim 1 or claim 2, wherein the total amount of the repeating unit (a1) and the repeating unit (a2) in the polymer (A) is 70% by mass or more.

5. Differential scanning calorimetry was performed on the polymer (A) in accordance with JIS K7121:2012. A binder composition for an energy storage device according to claim 1 or 2, wherein an endothermic peak is observed in the temperature range of -60°C to 60°C when determinant saturation (DSC) is performed.

6. A slurry for an electrode of an energy storage device, comprising the binder composition for an energy storage device described in claim 1 and an active material.

7. The slurry for electrodes of an energy storage device according to claim 6, wherein the active material is a positive electrode active material.

8. The slurry for an electrode of an energy storage device according to claim 6, wherein the active material contains a silicon material.

9. An energy storage device electrode comprising a current collector and an active material layer formed by applying and drying a slurry for energy storage device electrodes according to any one of claims 6 to 8 on the surface of the current collector.

10. A storage device comprising the storage device electrodes described in claim 9.

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