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

Abstract

Provided is a binder composition for a power storage device with which it is possible to fabricate a power storage device electrode that has excellent adhesion and in which electrode expansion associated with repeated charging / discharging is suppressed, and to improve cycle service-life properties of the power storage device.　A binder composition for a power storage device according to the present invention contains a polymer (A) and a liquid medium (B), the polymer (A) containing, when the total of repeating units included in the polymer (A) is 100 parts by mass, 50-80 parts by mass of a repeating unit (a1) derived from a conjugated diene compound, 15-49 parts by mass of a repeating unit (a2) derived from an aromatic vinyl compound, and 0.1-10 parts by mass of a repeating unit (a3) derived from unsaturated carboxylic acid. The tan δ of the dynamic viscoelasticity of the polymer (A) (loss modulus / storage modulus) has one peak top in the range of -50℃ to 10℃ inclusive, and one peak top in the range of 150℃ to 250°C inclusive. When the tan δ of the peak top in the range of -50℃ to 10℃ inclusive is tan δ (Tp1) and the tan δ of the peak top in the range 150℃ to 250°C inclusive is tan δ (Tp2), the relationship of expression (1) is satisfied.　(1): tan δ (Tp2) / tan δ (Tp1) < 0.5

Description

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

[0001] The present invention relates to a binder composition for an electricity storage device, a slurry for an electricity storage device electrode, an electricity storage device electrode, and an electricity storage device.

[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 energy storage devices are produced by applying a composition (slurry for energy 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 polymer used as a binder is required to have the ability to bond active materials together and to adhere to the current collector, as well as resistance to powder shedding, which prevents fine powder of the active material from falling off from the active material layer when the applied and dried composition coating (hereinafter also referred to as the "active material layer") is cut. Such binder materials exhibit good adhesion and reduce the internal resistance of the battery due to the binder material, thereby imparting good charge / discharge characteristics to the energy storage device.

[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] On the other hand, in order to further increase the capacity of energy storage devices, the use of materials with a large lithium ion storage capacity has been investigated. Active materials using materials with a large lithium ion storage capacity undergo large volume changes due to the absorption and desorption of lithium ions. Therefore, when conventional electrode binders are used with such materials with a large lithium storage capacity, adhesion cannot be maintained, resulting in peeling of the active material and a significant decrease in capacity during charging and discharging.

[0006] Techniques proposed for improving the adhesion of electrode binders include a technique for controlling the surface acid content of particulate binder particles (see Patent Documents 1 and 2) and a technique for improving the above properties by using a binder having an epoxy group or a hydroxy group (see Patent Documents 3 and 4). Also proposed is a technique for constraining the active material with the rigid molecular structure of polyimide to suppress volumetric changes of the active material (see Patent Document 5).

[0007] International Publication No. 2011 / 096463 International Publication No. 2013 / 191080 JP 2010-205722 A JP 2010-3703 A JP 2011-204592 A

[0008] However, the electrode binders disclosed in the above Patent Documents 1 to 5 do not have sufficient adhesion for practical use of new active materials, such as silicon materials, which have a large lithium ion occlusion capacity and undergo large volume changes due to the occlusion and release of lithium ions. When such electrode binders are used, the active material falls off due to repeated charge and discharge, causing deterioration of the electrode, and there is a problem in that the durability required for practical use cannot be obtained.

[0009] Some aspects of the present invention provide a binder composition for an electricity storage device that can produce an electricity storage device electrode that has excellent adhesion and in which electrode expansion due to repeated charge and discharge is suppressed, and that can improve the cycle life characteristics of the electricity storage device.

[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 binder composition for an electrical storage device according to the present invention comprises a polymer (A) and a liquid medium (B), wherein, when the total number of repeating units contained in the polymer (A) is 100 parts by mass, the polymer (A) contains 50 to 80 parts by mass of repeating units (a1) derived from a conjugated diene compound, 15 to 49 parts by mass of repeating units (a2) derived from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating units (a3) ​​derived from an unsaturated carboxylic acid, wherein the polymer (A) has one peak top in the range of −50° C. or higher and 10° C. or lower and one peak top in the range of 150° C. or higher and 250° C. or lower, When tan δ at the peak top in the range of -50°C or higher and 10°C or lower is defined as tan δ(Tp1), and tan δ at the peak top in the range of 150°C or higher and 250°C or lower is defined as tan δ(Tp2), the relationship of the following formula (1) is satisfied: tan δ(Tp2) / tan δ(Tp1)<0.5 (1)

[0012] In one embodiment of the binder composition for a storage battery device, the polymer (A) may have a proton relaxation time of 1500 ms or more when a latex having a solids concentration of 10% is measured by a CPMG method in pulse NMR.

[0013] In any embodiment of the binder composition for a storage battery device, the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) ​​may be 80 parts by mass or more.

[0014] In any of the above-described binder compositions for a storage battery device, the polymer (A) may further contain 0.1 to 10 parts by mass of a repeating unit (a4) derived from an unsaturated carboxylic acid ester.

[0015] In any of the above-described binder compositions for a storage battery device, the polymer (A) may further contain 0.1 to 10 parts by mass of a repeating unit (a5) derived from an α,β-unsaturated nitrile compound.

[0016] In any of the above-mentioned binder compositions for a storage battery device, the polymer (A) may have an electrolyte swelling degree of 100 to 350%.

[0017] In any of the above-described binder compositions for a storage battery device, the polymer (A) may be polymer particles, and the number average particle diameter of the polymer particles may be 50 nm or more and 500 nm or less.

[0018] In any one of the above-described binder compositions for a storage battery device, the polymer particles may have a surface acid amount of 0.05 mmol / g or more and 1 mmol / g or less.

[0019] In any of the above-described binder compositions for a storage battery device, the liquid medium (B) may be water.

[0020] One aspect of the slurry for an electrode of an electricity storage device according to the present invention contains the binder 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 electrode of an electricity storage device, the active material may contain a silicon material.

[0022] 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 electricity storage device electrode slurry according to any one of the above aspects to the surface of the current collector and drying the applied slurry.

[0023] An aspect of the electricity storage device according to the present invention includes the electricity storage device electrode of the above aspect.

[0024] The binder composition for an electricity storage device according to the present invention makes it possible to produce an electricity storage device electrode that has excellent adhesion and in which electrode expansion due to repeated charge and discharge is suppressed, thereby improving the cycle life characteristics of the electricity storage device.

[0025] FIG. 1 is a graph showing the relationship between the measurement temperature and tan δ in the dynamic viscoelasticity measurement of the film prepared in Example 5.

[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, "(meth)acrylic acid..." refers to "acrylic acid..." or "methacrylic 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. Binder Composition for Electrical Storage Device A binder composition for an electrical storage device according to one embodiment of the present invention contains a polymer (A) and a liquid medium (B). The polymer (A) contains, relative to 100 parts by mass of the total repeating units contained in the polymer (A), 50 to 80 parts by mass of repeating units (a1) derived from a conjugated diene compound, 15 to 49 parts by mass of repeating units (a2) derived from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating units (a3) ​​derived from an unsaturated carboxylic acid. The polymer (A) has one peak top in the dynamic viscoelasticity tan δ (loss modulus / storage modulus) range of -50°C to 10°C and one peak top in the range of 150°C to 250°C, and when the tan δ of the peak top in the range of -50°C to 10°C is tan δ(Tp1) and the tan δ of the peak top in the range of 150°C to 250°C is tan δ(Tp2), the relationship of the following formula (1) is satisfied: tan δ(Tp2) / tan δ(Tp1)<0.5 (1)

[0030] The binder 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) having improved bonding ability between active materials, improved adhesion ability between the active material and a current collector, and improved resistance to powder shedding, or as a material for producing a protective film for suppressing short circuits caused by dendrites that occur during charge and discharge. Each component contained in the binder composition for an electricity storage device according to this embodiment will be described in detail below.

[0031] 1.1. Polymer (A) The binder composition for an electricity storage device according to this embodiment contains a polymer (A). The polymer (A) may be in a latex state dispersed in a liquid medium (B) described below, or may be dissolved in the liquid medium (B), but is preferably in a latex state dispersed in the liquid medium (B). When the polymer (A) is in a latex state dispersed in the liquid medium (B), the stability of a slurry for an electricity storage device electrode (hereinafter also referred to as "slurry") prepared by mixing the polymer (A) with an active material is improved, and the coating properties of the slurry on a current collector are also improved, which is preferable.

[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 parts by mass, polymer (A) contains 50 to 80 parts by mass of repeating units (a1) (hereinafter also referred to simply as "repeating units (a1)") derived from a conjugated diene compound, 15 to 49 parts by mass of repeating units (a2) (hereinafter also referred to simply as "repeating units (a2)") derived from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating units (a3) ​​(hereinafter also referred to simply as "repeating units (a3)") derived from an unsaturated carboxylic acid. In addition to repeating units (a1), (a2), and (a3), polymer (A) may also contain repeating units derived from other monomers copolymerizable with these repeating units.

[0034] 1.1.1.1. Repeating Unit (a1) Derived from a Conjugated Diene Compound The content of the repeating unit (a1) derived from a conjugated diene compound is 50 to 80 parts by mass, where the total amount of repeating units contained in the polymer (A) is 100 parts by mass. The lower limit of the content of the repeating unit (a1) is preferably 52 parts by mass, more preferably 55 parts by mass. The upper limit of the content of the repeating unit (a1) is preferably 78 parts by mass, more preferably 75 parts by mass. By containing the repeating unit (a1) within the above range in the polymer (A), the dispersibility of the active material and filler is improved, making it possible to prepare a homogeneous active material layer and protective film, thereby eliminating structural defects in the electrode plate and exhibiting good repeated charge-discharge characteristics. In addition, the polymer (A) coating the surface of the active material can be imparted with elasticity, and the elasticity of the polymer (A) can improve adhesion, thereby exhibiting good charge-discharge durability characteristics.

[0035] The conjugated diene compound is not particularly limited, but examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc., and one or more selected from these can be used. Among these, 1,3-butadiene is particularly preferred.

[0036] 1.1.1.2. Repeating Unit (a2) Derived from an Aromatic Vinyl Compound The content of the repeating unit (a2) derived from an aromatic vinyl compound is 15 to 49 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a2) is preferably 17 parts by mass, more preferably 20 parts by mass. The upper limit of the content of the repeating unit (a2) is preferably 47 parts by mass, more preferably 45 parts by mass. By containing the repeating unit (a2) within the above range in the polymer (A), fusion between the polymers (A) dispersed in the active material layer is suppressed, resulting in good slurry properties and improved coatability. Furthermore, the permeability of the electrolyte is improved, resulting in good repeated charge / discharge characteristics. Furthermore, the polymer (A) may exhibit good binding strength with silicon materials, graphite, and other active materials, resulting in an electricity storage device electrode with excellent adhesion.

[0037] The aromatic vinyl compound is not particularly limited, but examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used. Among these, styrene is particularly preferred.

[0038] 1.1.1.3. 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) ​​derived from an unsaturated carboxylic acid is preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a3) ​​is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the content of the repeating unit (a3) ​​is preferably 9 parts by mass, more preferably 8 parts by mass. By containing the repeating unit (a3) ​​in the polymer (A) within the above range, the adhesion between the current collector and the active material layer can be improved, and the adhesion strength of the electrode may be improved.

[0039] The unsaturated carboxylic acid is not particularly limited, but includes monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc., and one or more selected from these can be used. Among these, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0040] 1.1.1.4. Other Repeating Units In addition to the repeating units (a1), (a2), and (a3), the polymer (A) may contain repeating units derived from other monomers copolymerizable with the repeating units (a1), (a2), and (a3). Examples of such repeating units include a repeating unit (a4) derived from an unsaturated carboxylic acid ester (hereinafter also referred to simply as "repeating unit (a4)"), a repeating unit (a5) derived from an α,β-unsaturated nitrile compound (hereinafter also referred to simply as "repeating unit (a5)"), a repeating unit (a6) derived from (meth)acrylamide (hereinafter also referred to simply as "repeating unit (a6)"), a repeating unit (a7) derived from a compound having a sulfonic acid group (hereinafter also referred to simply as "repeating unit (a7)"), and a repeating unit derived from a cationic monomer.

[0041] <Repeating Unit (a4) Derived from Unsaturated Carboxylic Acid Ester> The polymer (A) may contain a repeating unit (a4) derived from an unsaturated carboxylic acid ester. The content of the repeating unit (a4) is preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a4) is preferably 1 part by mass, more preferably 2 parts by mass. The upper limit of the content of the repeating unit (a4) is preferably 9 parts by mass, more preferably 8 parts by mass. When the polymer (A) contains the repeating unit (a4) 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 binder becoming an electrical resistance component in the electricity storage device may be suppressed.

[0042] 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, tri(meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, methyl ... Examples of suitable acrylates include trimethylolpropane acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, and glycerin di(meth)acrylate. Among these, preferred are one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl (meth)acrylate, with methyl (meth)acrylate being particularly preferred.

[0043] <Repeating Unit (a5) Derived from an α,β-Unsaturated Nitrile Compound> The polymer (A) may contain a repeating unit (a5) derived from an α,β-unsaturated nitrile compound. The content of the repeating unit (a5) is preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a5) is preferably 1 part by mass, more preferably 2 parts by mass. The upper limit of the content of the repeating unit (a5) is preferably 9 parts by mass, more preferably 8 parts by mass. By containing the repeating unit (a5) in the polymer (A) within the above range, it is possible to reduce the dissolution of the polymer (A) in the electrolyte solution, improve the affinity between the polymer (A) and the electrolyte solution, and in some cases suppress an increase in internal resistance in an electricity storage device due to the binder becoming an electrical resistance component.

[0044] The α,β-unsaturated nitrile compound is not particularly limited, and examples thereof 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 the group consisting of acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0045] <Repeating Unit (a6) Derived from (Meth)acrylamide> The polymer (A) may contain a repeating unit (a6) derived from (meth)acrylamide. The content of the repeating unit (a6) is preferably 0 to 8 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a6) is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the content of the repeating unit (a6) is preferably 7 parts by mass, more preferably 6 parts by mass. When the polymer (A) contains the repeating unit (a6) 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 amide, and one or more selected from these may be used.

[0047] <Repeating Unit (a7) Derived from a Compound Having a Sulfonic Acid Group> The polymer (A) may contain a repeating unit (a7) derived from a compound having a sulfonic acid group. The content of the repeating unit (a7) is preferably 0 to 8 parts by mass, relative to 100 parts by mass of the total repeating units contained in the polymer (A). The lower limit of the content of the repeating unit (a7) is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the content of the repeating unit (a7) is preferably 7 parts by mass, more preferably 6 parts by mass. When the polymer (A) contains the repeating unit (a7) within the above range, the dispersibility of the active material and filler is improved, which may enable the production of a homogeneous active material layer or protective film. Furthermore, adhesion to the current collector is improved, and structural defects in the electrode plate are reduced, which may result in good charge / discharge characteristics.

[0048] The compound having a sulfonic acid group is not particularly limited, but examples thereof include compounds 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, acrylamido tert-butylsulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid, as well as alkali salts thereof, and one or more compounds selected from these can be used.

[0049] <Repeating Units Derived from Cationic Monomers> The polymer (A) may contain repeating units derived from a cationic monomer. The cationic monomer is not particularly limited, but 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 the cationic monomer 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'-methylpropylideneamino]carboxyamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methcroylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, and 2-vinylpiperidinyl. Examples of the surfactant include lysine, 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-hepten-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, and the like. One or more surfactants selected from these may be used.

[0050] 1.1.2. Physical Properties of Polymer (A) 1.1.2.1. Dynamic Viscoelasticity When the dynamic viscoelasticity of polymer (A) is measured, there is one peak top of tan δ (loss modulus / storage modulus) in the range of -50°C to 10°C and one peak top in the range of 150°C to 250°C. When the tan δ of the peak top in the range of -50°C to 10°C is tan δ(Tp1) and the tan δ of the peak top in the range of 150°C to 250°C is tan δ(Tp2), the relationship of the following formula (1) is satisfied: tan δ(Tp2) / tan δ(Tp1)<0.5 (1)

[0051] The measurement sample in this dynamic viscoelasticity measurement is a film of polymer (A). The film of polymer (A) is prepared by drying polymer (A) at 40°C for 24 hours to prepare a uniform film with a thickness of 1.0±0.3 mm, and then drying this film in a vacuum dryer at 160°C for 30 minutes, and then cutting it into 10 mm x 10 mm strips. Next, using the dynamic viscoelasticity measurement device described below, the measurement sample is fixed on a parallel plate (product name "PP-12") and measured in a temperature range of -70°C to 250°C under the following measurement conditions. Measurement conditions: shear mode, measurement frequency 0.01 to 1 Hz, temperature rise rate 0.1°C / min Dynamic viscoelasticity measurement device: Model "MCR 301" manufactured by Anton Paar

[0052] The "tan δ(Tp2) / tan δ(Tp1)" value of the polymer (A) used in this embodiment is less than 0.5, preferably 0.48 or less, and more preferably 0.45 or less. When the "tan δ(Tp2) / tan δ(Tp1)" value of the polymer (A) is within the above range, it indicates that there is a large amount of polymer component near the peak top temperature of tan δ(Tp1). In addition, it indicates high viscosity at temperatures near the peak top temperature of tan δ(Tp1), and it is believed that this high viscosity can ensure adhesion to the active material mainly composed of carbon materials. It also indicates that the polymer (A) is highly crosslinked at temperatures near the peak top temperature of tan δ(Tp2). When the polymer (A) is hard, the binder is not crushed by the expansion and contraction of the Si active material during repeated charge and discharge, and the particle shape can be maintained, which is thought to maintain adhesion to the active material and suppress electrode expansion. Furthermore, since the internal resistance can be reduced by increasing the permeability of the electrolyte solution into the active material, an electrode exhibiting good repeated charge-discharge characteristics can be produced. Furthermore, since the polymer (A) used in this embodiment can improve adhesion, an electrode exhibiting good charge-discharge durability characteristics can be produced.

[0053] The temperature Tp1 (°C) of the peak top of tan δ in the dynamic viscoelasticity measurement of the polymer (A) is preferably in the temperature range of −38°C or higher and 8°C or lower, more preferably −35°C or higher and 5°C or lower. It is also preferable that one peak top exists in the above temperature range. The presence of one Tp in the above temperature range indicates high viscosity in the same temperature range. It is believed that this high viscosity enables the polymer (A) to maintain a high binding strength in the same temperature range and to exhibit good adhesion.

[0054] The temperature Tp2 (°C) of the peak top of tan δ in the dynamic viscoelasticity measurement of the polymer (A) is preferably in the temperature range of 155°C or higher and 245°C or lower, more preferably 160°C or higher and 240°C or lower. It is also preferable that one peak top exists in the above temperature range. The presence of one Tp in the above temperature range indicates that a polymer with a high content of hydrophilic polymer has been formed in the same temperature range. It is believed that a high content of hydrophilic polymer in the polymer (A) in the same temperature range contributes to the hardness of the polymer (A) and reduces its internal resistance.

[0055] The temperature Tp of the peak top of tan δ can be adjusted by adjusting the monomer composition during polymerization of the polymer (A).

[0056] The tan δ (Tp1) of the polymer (A) is preferably 0.5 to 1.2, more preferably 0.55 to 1.15, and particularly preferably 0.6 to 1.10. The tan δ (Tp1) of the polymer (A) being within the above range indicates that the polymer (A) is viscous but not too hard, and has sufficient binding strength to maintain the electrode structure.

[0057] The tan δ (Tp2) of the polymer (A) is preferably 0.01 to 0.4, more preferably 0.03 to 0.38, and particularly preferably 0.05 to 0.35. The fact that the tan δ (Tp2) of the polymer (A) is within the above range indicates that the polymer (A) is not too soft, suppresses fusion between particles, and has sufficient hardness to withstand the expansion and contraction of Si.

[0058] Methods for adjusting tan δ (Tp) include changing the glass transition temperature or gel content of the polymer (A), or changing the method of adding monomers during polymerization of the polymer (A).

[0059] 1.1.2.2. Pulse NMR Transverse relaxation time T of protons present in an aqueous dispersion of polymer (A) adjusted to a solids concentration of 10% Ａ When measured by pulsed NMR, the relaxation time T ０ In contrast, T Ａ <T ０ holds true.

[0060] The measurement is performed using a pulsed nuclear magnetic resonance spectrometer "minispec mq20 manufactured by BRUKER Corporation," using hydrogen nuclei as the measurement nuclei, and measuring the transverse relaxation time (spin-spin relaxation time) of protons by the CPMG method (Carr-Purcell Meiboom-Gill method) under the measurement conditions of a measurement temperature of 25°C, a frequency of 20 MHz, and a 90-180° pulse interval of 0.04 tau. It is preferable to adjust the pH of the aqueous dispersion to 8.0 during the measurement.

[0061] The transverse relaxation time T of protons present in the aqueous dispersion of polymer (A) Ａ is preferably 1500 ms or more, more preferably 1550 ms or more, and particularly preferably 1600 ms or more. The transverse relaxation time of protons measured by pulse NMR is measured as the relaxation time of all the constituent components of the measurement sample. Therefore, in the case of an aqueous dispersion of polymer (A) having a solids concentration of 10%, the relaxation time T Ａ is obtained as the average value of the relaxation times of protons present in 10% of polymer (A) and 90% of water.

[0062] relaxation time T Ａ The relaxation time T Ａ It is believed that the longer the distance, the more hydrophobic the surface of the polymer (A) becomes, and the more effectively it is adsorbed onto the surface of the active material, thereby exhibiting excellent adhesion and the effect of suppressing the expansion of the electrode.

[0063] 1.1.2.3. Number Average Particle Diameter When the polymer (A) is in the form of particles, the number average particle diameter of the particles is preferably 50 nm or more and 500 nm or less, more preferably 70 nm or more and 480 nm or less, and particularly preferably 90 nm or more and 450 nm or less. When the number average particle diameter of the polymer (A) particles is within the above range, the polymer (A) particles are easily adsorbed to the surface of the active material, and therefore, the polymer (A) particles can move along with the movement of the active material. As a result, migration can be suppressed, which may reduce deterioration of electrical properties.

[0064] The number average particle size of the polymer (A) particles is the average value of particle sizes obtained from images of 50 particles observed with a transmission electron microscope (TEM), such as the "H-7650" manufactured by Hitachi High-Technologies Corporation.

[0065] 1.1.2.4. Surface Acidity When the polymer (A) is in the form of particles, the surface acidity of the particles is preferably 0.05 mmol / g or more and 1 mmol / g or less, more preferably 0.07 mmol / g or more and 0.95 mmol / g or less, and particularly preferably 0.10 mmol / g or more and 0.90 mmol / g or less. When the surface acidity of the polymer (A) particles is within the above range, a stable and homogeneous slurry can be prepared. When an active material layer is prepared using such a homogeneous slurry, an active material layer in which the active material and polymer (A) particles are uniformly dispersed and with little variation in thickness can be obtained. As a result, variation in charge / discharge characteristics within the electrode can be suppressed, resulting in an electricity storage device exhibiting good charge / discharge characteristics. The surface acidity of the polymer (A) can be measured by the method described in the Examples below.

[0066] 1.1.2.5. Electrolyte Swelling Degree When polymer (A) is immersed in a solvent consisting of ethylene carbonate and ethyl methyl carbonate in a 1:1 volume fraction at 70°C for 24 hours, the swelling degree (hereinafter also referred to as "electrolyte swelling degree") is preferably 100% to 350%, more preferably 110% to 250%, and particularly preferably 120% to 200%. When the electrolyte swelling degree 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, effectively reducing electrode resistance and achieving better charge / discharge characteristics. Furthermore, when the electrolyte swelling degree of polymer (A) is within the above range, no significant volume change occurs when polymer (A) absorbs the electrolyte, resulting in excellent adhesion.

[0067] 1.1.3. Method for Producing Polymer (A) <Polymerization Step> The polymerization step for polymer (A) is not particularly limited, but can be, for example, an emulsion polymerization method carried out in the presence of a known emulsifier, chain transfer agent, polymerization initiator, etc.

[0068] Examples of the emulsifier include anionic surfactants such as sulfate salts of higher alcohols, alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkyldiphenyletherdisulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, naphthalenesulfonic acid-formalin condensates, and sulfate salts of nonionic surfactants; nonionic surfactants such as alkyl esters of polyethylene glycol, alkylphenyl ethers of polyethylene glycol, and alkyl ethers of polyethylene glycol; and fluorine-based surfactants such as perfluorobutylsulfonates, perfluoroalkyl group-containing phosphate esters, perfluoroalkyl group-containing carboxylates, and perfluoroalkylethylene oxide adducts, and at least one selected from these can be used.

[0069] Specific examples of the chain transfer agent and polymerization initiator include compounds described in Japanese Patent No. 5,999,399.

[0070] 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.

[0071] 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 a temperature of 0 to 80°C for a polymerization time of preferably 4 to 36 hours.

[0072] When the synthesis of the polymer (A) is carried out by two-stage polymerization, it is preferable to set the polymerization in each stage as follows.

[0073] The proportion of the monomer used in the first-stage polymerization is preferably in the range of 20 to 99 mass %, more preferably in the range of 25 to 99 mass %, based on the total mass of the monomers (the sum of the mass of the monomers used in the first-stage polymerization and the mass of the monomers used in the second-stage polymerization). By carrying out the first-stage polymerization at such a proportion of the monomers, it is possible to obtain particles of polymer (A) that are excellent in dispersion stability and are less likely to form aggregates, and it is also preferable because an increase in viscosity over time of the binder composition for an electrical storage device after coagulation is suppressed.

[0074] The types and proportions of monomers used in the second-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization.

[0075] The polymerization conditions for each stage are preferably as follows, from the viewpoint of the dispersibility of the particles of the resulting polymer (A): First-stage polymerization: A temperature of preferably 0 to 80°C; A polymerization time of preferably 2 to 36 hours; A polymerization conversion rate of preferably 50% by mass or more, more preferably 60% by mass or more. Second-stage polymerization: A temperature of preferably 0 to 80°C; A polymerization time of preferably 2 to 18 hours.

[0076] When the synthesis of the polymer (A) is carried out by three-stage polymerization, it is preferable to set the polymerization in each stage as follows.

[0077] The proportion of the monomer used in the first-stage polymerization is preferably in the range of 20 to 90 mass %, more preferably in the range of 25 to 80 mass %, based on the total mass of the monomers (the sum of the mass of the monomers used in the first-stage polymerization, the mass of the monomers used in the second-stage polymerization, and the mass of the monomers used in the third-stage polymerization). By carrying out the first-stage polymerization at such a proportion of the monomers, it is possible to obtain particles of polymer (A) that are excellent in dispersion stability and are less likely to form aggregates, and it is also preferable because an increase in viscosity over time of the binder composition for an electrical storage device after coagulation is suppressed.

[0078] The types and proportions of monomers used in the second-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization.

[0079] The types and proportions of monomers used in the third-stage polymerization may be the same as or different from the types and proportions of monomers used in the first-stage polymerization and the types and proportions of monomers used in the second-stage polymerization.

[0080] From the viewpoint of the dispersibility of the particles of the resulting polymer (A), the polymerization conditions for each stage are preferably as follows: First-stage polymerization: preferably a temperature of 0 to 80°C; preferably a polymerization time of 2 to 36 hours; preferably a polymerization conversion of 50% by mass or more, more preferably 60% by mass or more. Second-stage polymerization: preferably a temperature of 0 to 80°C; preferably a polymerization time of 2 to 18 hours. Third-stage polymerization: preferably a temperature of 0 to 80°C; preferably a polymerization time of 2 to 9 hours.

[0081] 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 45% by mass or less, and more preferably 40% by mass or less.

[0082] Whether the synthesis of polymer (A) is carried out by single-stage polymerization or multi-stage polymerization, it is preferable to neutralize the polymerization mixture after the completion of emulsion polymerization by adding a neutralizing agent. The neutralizing agent used here is not particularly limited, but examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; etc.

[0083] 1.2. Liquid Medium (B) The binder composition for a storage battery device 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 this non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, and sulfone compounds, and one or more selected from these may be used. By using an aqueous medium as the liquid medium (B), the binder composition for a storage battery device according to this embodiment has a reduced adverse effect on the environment and is safer for workers handling the binder composition.

[0084] The content of the non-aqueous medium in the aqueous medium is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably substantially free of the non-aqueous medium, per 100 parts by mass of the aqueous medium. Here, "substantially free of the non-aqueous medium" means that the non-aqueous medium is not intentionally added as a liquid medium, and the binder composition for an electrical storage device may contain a non-aqueous medium that is inevitably mixed in when the binder composition for an electrical storage device is prepared.

[0085] 1.3 Other Additives The binder composition for an electricity 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), preservatives, thickeners, etc.

[0086] <Polymers Other Than Polymer (A)> The binder composition for an electrical storage device according to this embodiment may contain a polymer other than the polymer (A). Examples of such polymers include, but are not limited to, acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as structural units, and fluorine-containing polymers such as PVDF (polyvinylidene fluoride). These polymers may be used alone or in combination of two or more. The inclusion of these polymers may further improve flexibility and adhesion.

[0087] <Preservative> The binder composition for a storage battery device according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold, and the like, and the generation of foreign matter, when the binder composition for a storage battery device is stored. Specific examples of preservatives include the compounds described in Japanese Patent No. 5,477,610, etc.

[0088] <Thickener> The binder 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.

[0089] Examples of thickeners include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the above-mentioned cellulose compounds or poly(meth)acrylic acid; modified polyvinyl alcohol, polyethylene oxide; polyvinylpyrrolidone, polycarboxylic acid, oxidized starch, starch phosphate, casein, various modified starches, chitin, and chitosan derivatives. Among these, cellulose-based polymers are preferred.

[0090] Commercially available thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0091] When the binder composition for a storage battery device according to this embodiment contains a thickener, the content of the thickener is preferably 5% by mass or less, and more preferably 0.1 to 3% by mass, relative to 100% by mass of the total solid content of the binder composition for a storage battery device.

[0092] 1.4. pH of the binder composition for an electricity storage device The pH of the binder composition for an electricity storage device according to this embodiment is preferably 6.0 to 9.5, more preferably 6.3 to 9.2, and particularly preferably 6.5 to 9.0. When the pH is within this range, problems such as insufficient leveling and dripping can be suppressed, making it easier to produce an electricity storage device electrode that combines good electrical properties and adhesion.

[0093] In this specification, "pH" refers to a physical property measured as follows: It is a value measured at 25°C using a pH meter using a glass electrode calibrated with a neutral phosphate standard solution and a borate standard solution as pH standard solutions, in accordance with JIS Z8802:2011. Examples of such pH meters include the "HM-7J" manufactured by DKK-TOA Corporation and the "D-51" manufactured by HORIBA, Ltd.

[0094] Although it is not denied that the pH of the binder composition for an electricity storage device is 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 the pH of a binder composition for an electricity storage device changes depending on the polymerization conditions, etc., even if the monomer composition is the same, and the examples in the present specification merely show one example.

[0095] 2. Slurry for Electricity Storage Devices A slurry for an electricity storage device according to one embodiment of the present invention contains the above-described binder composition for an electricity storage device. The above-described binder composition for an electricity storage device can be used as a material for producing a protective film for suppressing short circuits caused by dendrites that occur during charging and discharging, or 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 the current collector, and improved resistance to powder shedding. Hereinafter, the slurry for an electricity storage device for producing a protective film (hereinafter also referred to as "slurry for protective film") and the slurry for an electricity storage device for producing an active material layer of an electricity storage device electrode (hereinafter also referred to as "slurry for electricity storage device electrode") will be described separately.

[0096] 2.1. Slurry for Protective Film The term "slurry for protective film" refers to a dispersion liquid used to form a protective film on the surface of an electrode or a separator, or both, by applying the slurry to the surface of an electrode or a separator, or both, and then drying the dispersion liquid. The slurry for protective film according to this embodiment may consist solely of the binder composition for an electrical storage device described above, or may further contain an inorganic filler. Examples of inorganic fillers include the inorganic fillers described in JP 2020-184461 A.

[0097] 2.2. Slurry for Electricity Storage Device Electrode The term "slurry for electricity storage device electrode" refers to a dispersion liquid used for forming an active material layer on the surface of a current collector by applying the dispersion liquid to the surface of the current collector and then drying the same. The slurry for electricity storage device electrode according to this embodiment contains the above-described binder composition for electricity storage devices and an active material.

[0098] Generally, a slurry for an electric storage device electrode often contains a binder component such as an SBR copolymer and a thickener such as carboxymethyl cellulose to improve adhesion. On the other hand, the slurry for an electric storage device electrode according to this embodiment can improve adhesion even when it contains only the polymer (A) described above as the polymer component. Of course, the slurry for an electric storage device electrode according to this embodiment may contain a polymer other than the polymer (A) or a thickener to further improve adhesion. The components contained in the slurry for an electric storage device electrode according to this embodiment will be described below.

[0099] 2.2.1 Polymer (A) The composition, physical properties, production method, etc. of the polymer (A) are as described above, and therefore further explanation is omitted.

[0100] The content of the polymer component in the slurry for an electrical storage device electrode 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 the active material. When the content of the polymer component is within this range, the dispersibility of the active material in the slurry is good, and the coating properties of the slurry are also excellent. Here, the polymer component includes the polymer (A), a polymer other than the polymer (A) that is added as needed, a thickener, and the like.

[0101] Active materials used in the slurry for an electrode of an electric 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.

[0102] The slurry for an electrode of an electricity storage device according to this embodiment can be used when producing either a positive electrode or a negative electrode, but is particularly preferably used for a negative electrode.

[0103] When preparing a negative electrode, among the active materials exemplified above, those containing a silicon material and / or a carbon material are preferred, and a mixture of a silicon material and a carbon material is more preferred. Silicon materials have a larger lithium absorption capacity per unit weight than other active materials, which can increase the storage capacity of the resulting energy storage device. As a result, the output and energy density of the energy storage device can be increased. Meanwhile, carbon materials undergo smaller volume changes during charging and discharging than silicon materials. Therefore, by using a mixture of a silicon material and a carbon material as the negative electrode active material, the effect of the volume change of the silicon material can be mitigated, and the adhesion between the active material layer and the current collector can be further improved.

[0104] When silicon (Si) is used as an active material, while it has a high capacity, it undergoes a large volume change when absorbing lithium ions. As a result, silicon materials tend to pulverize due to repeated expansion and contraction, causing peeling from the current collector and separation of active material particles, which can easily disrupt the conductive network within the active material layer. This property causes the charge / discharge durability of the energy storage device to deteriorate dramatically in a short period of time.

[0105] In this respect, the electricity storage device electrode produced using the electricity storage device electrode slurry according to this embodiment can exhibit good electrical properties without the above-mentioned problems even when a silicon material is used. The reason for this is thought to be that the polymer (A) can firmly bind the silicon material, and at the same time, even when the silicon material expands in volume due to lithium occlusion, the polymer (A) expands and contracts, thereby maintaining the state in which the silicon material is firmly bound.

[0106] 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 10 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.

[0107] The negative electrode active material is preferably in the form of particles, and the average particle size of the negative electrode active material is preferably 0.1 to 100 μm, and more preferably 1 to 20 μm.

[0108] On the other hand, when preparing a positive electrode, among the active materials exemplified above, an oxide containing lithium atoms is preferred. Examples of the oxide containing lithium atoms include one or more oxides represented by the following general formula (2) and selected from lithium manganate, lithium nickelate, lithium cobaltate, and lithium manganese nickel cobaltate.

[0109] Li １－ｘ M ｘ (A.O. ４) (2) (In formula (2), M is at least one metal ion 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 of 0<x<1.) The value of x in general formula (2) is selected depending on the valences of M and A so that the valence of the entire general formula (2) is 0.

[0110] Examples of olivine-type lithium-containing phosphate compounds include LiFePO ４ , LiCoPO ４ , LiMnPO ４ , Li ０．９０ Ti ０．０５ Nb ０．０５ Fe ０．３０ Co ０．３０ Mn ０．３０ P.O. ４ Among these, LiFePO is particularly preferred. ４ (Lithium iron phosphate) is preferred because the iron compound that serves as the raw material is readily available and inexpensive.

[0111] The average particle size of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

[0112] The active material layer may contain the following active materials: conductive polymers such as polyacene; 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), and other metal oxides.

[0113] Examples of the composite metal oxide include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and ternary nickel cobalt manganese oxide.

[0114] The electricity storage device electrode produced using the electricity storage device electrode slurry according to this embodiment can exhibit good electrical properties even when an oxide containing lithium atoms is used as the positive electrode active material, which is thought to be because the polymer (A) can firmly bind the oxide containing lithium atoms and can maintain the state in which the oxide containing lithium atoms is firmly bound even during charge and discharge.

[0115] 2.2.3. Other Components In addition to the components described above, the slurry for an electricity storage device electrode according to this embodiment may contain, as necessary, components such as a polymer other than the polymer (A), a thickener, a liquid medium, a conductive aid, a pH adjuster, a corrosion inhibitor, an antioxidant, and cellulose fiber. The polymer other than the polymer (A) and the thickener may be appropriately selected from the compounds exemplified in the above section "1.3. Other Additives" and used for the same purpose and in the same content ratio.

[0116] <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 binder composition for an electrical storage device. The liquid medium to be added may be the same as or different from the liquid medium (B) contained in the binder composition for an electrical storage device, but is preferably selected from the liquid media exemplified in the above section "1.2. Liquid medium (B)".

[0117] The content of the liquid medium (including the portion carried over from the binder 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 30 to 70 mass%, and more preferably 40 to 60 mass%.

[0118] <Conductive Aid> A conductive aid may be further added to the slurry for an electricity storage device electrode according to this embodiment for the purposes of imparting conductivity and buffering the volume change of the active material due to the inflow and outflow of lithium ions.

[0119] Specific examples of the conductive additive include activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, fullerene, carbon nanotubes, and other carbons. Among these, acetylene black, ketjen black, and carbon nanotubes are preferably used. The content of the conductive additive 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, per 100 parts by mass of the active material.

[0120] <pH Adjuster> A pH adjuster 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.

[0121] 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. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred. Furthermore, a neutralizing agent selected from those described in the production method for polymer (A) can also be used.

[0122] <Corrosion Inhibitor> 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.

[0123] 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.

[0124] <Cellulose Fiber> Cellulose fiber may be further added to the slurry for an electricity storage device electrode according to this embodiment. Known cellulose fibers can be used. 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 state through linear adhesion or linear contact, thereby preventing the active material from falling off and improving the adhesion to the current collector.

[0125] 2.2.4. Method for Preparing Slurry for Electricity Storage Device Electrode The slurry for an electricity storage device electrode according to this embodiment may be produced by any method as long as it contains the above-described binder composition for an electricity storage device and active material. 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 binder composition for an electricity storage device and mixing them. Specific production methods include, for example, the method described in Japanese Patent No. 5,999,399.

[0126] 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 bound to the surface of the current collector, the active material layer containing the above-described polymer (A), an active material, and optional components added as needed. This results in excellent adhesion and suppressed expansion of the electrode due to repeated charge and discharge, resulting in excellent charge and discharge durability.

[0127] 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.

[0128] 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% by mass of the active material layer is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and particularly preferably 3 to 10% 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.

[0129] 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.

[0130] The electrolyte may be liquid or gel, and may be selected from known electrolytes used in power 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.

[0131] 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, components other than the binder composition for electricity storage devices can be known components for lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors.

[0132] 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.

[0133] 5.1 Example 1 5.1.1 Preparation of Binder Composition for Electrical Storage Devices Example 1 A binder composition for electrical storage devices containing polymer (A1) was obtained by two-stage polymerization as shown below. A reactor was charged with 300 parts by mass of water, a monomer mixture consisting of 50 parts by mass of 1,3-butadiene, 35 parts by mass of styrene, 5 parts by mass of acrylonitrile, 1 part by mass of sodium styrenesulfonate, 1 part by mass of itaconic acid, and 1 part by mass of acrylamide, 0.1 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 0.1 parts by mass of sodium alkyldiphenyl ether disulfonate as an emulsifier, and 1.0 part by mass of potassium persulfate as a polymerization initiator. The mixture was polymerized at 70°C for 18 hours with stirring, and the polymerization conversion was confirmed to be 95%. Next, 50 parts by mass of water, 1 part by mass of itaconic acid, 1 part by mass of acrylic acid, 1 part by mass of methacrylic acid, 1 part by mass of hydroxyethyl methacrylate, 1 part by mass of hydroxyethyl acrylate, 1 part by mass of acrylonitrile, and 1 part by mass of sodium styrenesulfonate were further added to the reactor, and polymerization was carried out for 12 hours at 75° C., after which it was confirmed that the polymerization conversion rate was 98%. From the particle dispersion of polymer (A1) thus obtained, unreacted monomers were removed and the mixture was concentrated, and a 5% aqueous solution of sodium hydroxide was added, followed by removing water using an evaporator, thereby obtaining a binder composition for an electrical storage device containing particles of polymer (A1) with a solids concentration of 40% by mass and a pH of 7.0.

[0134] 5.1.2. Evaluation of Physical Properties of Binder Composition for Electrical Storage Devices <Method for Measuring Polymerization Conversion Rate> The polymerization conversion rate in the synthesis of the above polymer was measured as follows. After polymerization for a predetermined time, the reaction solution was extracted and placed in a pre-weighed aluminum dish (X (g)), and the weight of the reaction solution (Y (g)) was measured. This was dried at 155°C for 15 minutes using a hot air dryer. The aluminum dish was removed and allowed to cool, and then its weight (Z (g)) was measured. The polymerization conversion rate (%) was calculated from the weights X, Y, and Z measured in this way using the following formula (3): Polymerization conversion rate (%) = ((Z-X) / Y) x 100 (3)

[0135] <Measurement of Number Average Particle Diameter> One drop of the latex obtained by diluting the binder composition for a storage battery device obtained above to 0.1 wt % was pipetted onto a collodion support film, and then one drop of a 0.02 wt % osmium tetroxide solution was pipetted onto the collodion support film and air-dried for 12 hours to prepare a sample. The sample thus prepared was observed using a transmission electron microscope (TEM, Hitachi High-Tech Corporation, model number "H-7650") at a magnification of 10K (magnification), and image analysis was performed using the HITACHI EMIP program to calculate the number average particle diameter of 50 randomly selected particles of polymer (A1). The resulting number average particle diameter of polymer (A1) was 190 nm. The measurement results are shown in Table 1 below.

[0136] <pH Measurement> The pH of the binder composition for an electricity storage device obtained above was measured at 25° C. using a pH meter (manufactured by Horiba, Ltd.), and it was confirmed that the pH was 7.0. The results are shown in Table 1 below.

[0137] <Measurement of Electrolyte Swelling Degree> The polymer (A1) obtained above was dried in a thermostatic chamber at 85°C for 24 hours to produce a film. 1 g of this film was immersed in 20 mL of a mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC = 1 / 1 (volume ratio), hereinafter, this mixed solution will be referred to as "EC / EMC") used as an electrolyte solution in the production of an electricity storage device described below, and shaken at 70°C for 24 hours. Next, the insoluble matter was separated by filtration through a 300-mesh wire netting, and the weight (Y (g)) of the residue obtained by evaporating and removing the soluble EC / EMC was measured. Furthermore, the EC / EMC adhering to the surface of the insoluble matter (film) separated by the filtration was absorbed and removed by paper, and the weight (Z (g)) of the insoluble matter (film) was measured. The degree of swelling in an electrolyte solution was measured according to the following formula (4), and the degree of swelling in an electrolyte solution of the polymer (A1) was found to be 171% by mass: Degree of swelling in an electrolyte solution (mass%)=(Z / (1−Y))×100 (4)

[0138] <Measurement of Surface Acid Amount> The surface acid amount of particles of polymer (A1) contained in the binder composition for a storage battery device obtained above was measured as follows. First, it was confirmed that 0.005 mol / L sulfuric acid was filled in the titration burette and the reagent bottle on the top of the main body of a potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., Model "AT-510"), and it was confirmed that the conductivity of the ultrapure water was 2 μS or less. Next, purging was performed to remove air from the burette, and further bubbles were removed from the nozzle. Thereafter, approximately 1 g of the binder composition for a storage battery device obtained above, converted to solids, was placed in a 300 mL beaker, and the sample weight was recorded. Ultrapure water was added to dilute the mixture to 200 mL, and then a 1 mol / L aqueous sodium hydroxide solution was added dropwise. After reaching the endpoint, the mixture was stirred for approximately 30 seconds, and the conductivity was confirmed to have stabilized. The RESET button of the measurement program was pressed to enter measurement standby mode. The START button of the measurement program was pressed to start measurement using 0.005 mol / L sulfuric acid. When the end point is reached, the process is automatically terminated and the file is saved. The obtained curve was analyzed, and the surface acid amount was calculated from the amount of sulfuric acid used using the following formula (5). As a result, the surface acid amount of polymer (A1) was found to be 0.37 mmol / g. The results are shown in Table 1 below. Surface acid amount (mmol / g) = Amount of acid used in carboxylic acid region on particle surface [mL] × Acid concentration [mol / L] × Ionization degree / Sample weight [g] / 1000 (5)

[0139] <Pulse NMR> The transverse relaxation time T of protons present in an aqueous dispersion of polymer (A1) adjusted to a solids concentration of 10% Ａ was measured by pulse NMR. The measurement was carried out using a pulse nuclear magnetic resonance spectrometer "minispec mq20 manufactured by BRUKER Corporation," with hydrogen nuclei as the measurement nuclei, and the transverse relaxation time (spin-spin relaxation time) of water protons was measured by the CPMG method (Carr-Purcell Meiboom-Gill method) under the measurement conditions of a measurement temperature of 25°C, a frequency of 20 MHz, and a 90-180° pulse interval of 0.04 tau. The pH of the aqueous dispersion was adjusted to 8.0 during the measurement. As a result, the transverse relaxation time T Ａ The measurement results are shown in Table 1 below.

[0140] <Measurement of Dynamic Viscoelasticity> The polymer (A1) obtained above was dried at 40°C for 24 hours to produce a uniform film with a thickness of 1.0±0.3 mm. This film was then dried in a vacuum dryer at 160°C for 30 minutes. The film was removed from the vacuum dryer and cut into 10 mm x 10 mm strips to serve as measurement samples. Next, using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, model "MCR 301"), the measurement sample was fixed to a parallel plate (product name "PP-12") and dynamic viscoelasticity was measured in a temperature range of -70°C to 250°C under measurement conditions of shear mode, measurement frequency of 0.01 to 1 Hz, and temperature rise rate of 0.1°C / min. As a result, the peak top of tan δ on the low temperature side (tan δ-1) was observed at 8°C, and its value was 0.96. The peak top of tan δ on the high temperature side (tan δ-2) was observed at 192°C, and its value was 0.05. In Tables 1 to 3 below, the peak top of tan δ on the low temperature side is represented as "tan δ-1," and the peak top of tan δ on the high temperature side is represented as "tan δ-2." Figure 1 shows, as an example, a graph illustrating the relationship between measurement temperature and tan δ in the dynamic viscoelasticity measurement of the film produced in Example 5.

[0141] 5.1.3. Preparation of Slurry for Electricity Storage Device Electrode <Synthesis of Silicon Material (Active Material)> A mixture of pulverized silicon dioxide powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was heat-treated in an electric furnace adjusted to a temperature in the range of 1100°C to 1600°C under a nitrogen gas flow (0.5 NL / min) for 10 hours to produce a silicon material having the composition formula SiO ｘA silicon oxide powder (average particle size 8 μm) represented by the formula (x = 0.5 to 1.1) was obtained. 300 g of this silicon oxide powder was placed in a batch-type heating furnace, and while maintaining a reduced pressure of 100 Pa absolute using a vacuum pump, the temperature was increased from room temperature (25°C) to 1100°C at a heating rate of 300°C / h. Next, while maintaining the pressure inside the heating furnace at 2000 Pa, methane gas was introduced at a flow rate of 0.5 NL / min, and a heat treatment (graphite coating treatment) was carried out at 1100°C for 5 hours. After completion of the graphite coating treatment, the powder was cooled to room temperature at a temperature decrease rate of 50°C / h, yielding approximately 330 g of graphite-coated silicon oxide powder. This graphite-coated silicon oxide was a conductive powder (active material) in which the surface of silicon oxide was coated with graphite, and had an average particle size of 10.5 μm. The proportion of the graphite coating was 2 mass% when the entire obtained graphite-coated silicon oxide was taken as 100 mass%.

[0142] <Preparation of Slurry for Electricity Storage Device Electrode> To a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK Hibismix 2P-03"), 1 part by mass (solid content equivalent, added as an aqueous solution with a concentration of 2% by mass) of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), 4 parts by mass (solid content equivalent, added as the binder composition for an electricity storage device obtained above) of the polymer (A1), 85.5 parts by mass (solid content equivalent) of highly crystalline artificial graphite (manufactured by Resonac Inc., trade name "MAG") as a negative electrode active material, 9.5 parts by mass (solid content equivalent) of the graphite-coated silicon oxide powder obtained above, and 1 part by mass of carbon (manufactured by Denka Company, acetylene black) as a conductive additive were added, and the mixture was stirred at 60 rpm for 1 hour to obtain a paste. Water was added to the obtained paste to adjust the solid content concentration to 48% by mass, and then the mixture was deaerated using a stirring deaerator (manufactured by Thinky Corporation, product name "Awatori Rentaro") at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then under reduced pressure (approximately 2.5 × 10 ４ The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at 1000 kPa (C / Si=90 / 10) to prepare a slurry for an electricity storage device electrode containing 10 mass % of Si in the negative electrode active material.

[0143] <Slurry Stability Test> Approximately 1 mL of a C / Si = 90 / 10 slurry was measured using a Physica MCR301 manufactured by Anton Paar, and the slurry viscosity behavior was measured using a 25 mm diameter cone plate under conditions of a GAP of 1 mm and 25°C, starting with a shear rate of 1 (1 / s). When the shear rate reached 1000 (1 / s), the shear rate was again slowed to 1 (1 / s). The measurement was defined as proceeding from 1 to 1000 (1 / s), and as returning from 1000 to 1 (1 / s), and the evaluation criteria were as follows: (Evaluation criteria) 5 points: The viscosity at 100 (1 / s) on the return is within ±8% of the viscosity at 100 (1 / s) on the outward movement. 4 points: The viscosity at 100 (1 / s) on the return is within ±10% of the viscosity at 100 (1 / s) on the outward movement. 3 points: The viscosity at 100 (1 / s) on the return is within ±15% of the viscosity at 100 (1 / s) on the outward movement. 2 points: The viscosity at 100 (1 / s) on the return is within ±20% of the viscosity at 100 (1 / s) on the outward movement. 1 point: The viscosity at 100 (1 / s) on the return is greater than ±20% of the viscosity at 100 (1 / s) on the outward movement.

[0144] 5.1.4. Production and Evaluation of Electricity Storage Device <Production of Electricity Storage Device Electrode (Negative Electrode)> The slurry for an electricity storage device electrode (C / Si=90 / 10) obtained 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 80° C. for 5 minutes, and then dried at 120° C. for 5 minutes. After that, the density of the active material layer was 1.6 g / cm ３ The mixture was pressed using a roll press machine so that an electricity storage device electrode (negative electrode) was obtained.

[0145] <Evaluation of Adhesion Strength of Negative Electrode Coating Layer> A knife was used to make a grid pattern of 10 incisions, 2 mm apart, vertically and horizontally, from the active material layer to a depth reaching the current collector. An 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Cellotape" (registered trademark), as defined in JIS Z1522) was attached to the incisions and immediately peeled off, and the degree of active material loss was evaluated visually. 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.

[0146] <Production of Counter Electrode (Positive Electrode)> A two-axis planetary mixer (manufactured by Primix Corporation, product name "TK Hibismix 2P-03") was charged with 4 parts by mass (solid content equivalent) of a binder for electrochemical device electrodes (manufactured by Kureha Corporation, product name "KF Polymer #1120"), 3.0 parts by mass of a conductive additive (manufactured by Denka Company Limited, product name "Denka Black 50% Pressed Product"), and 1.0 parts by mass of LiCoO 4 with an average particle diameter of 5 μm as a positive electrode active material. ２ 100 parts by mass (solid content equivalent) of PEG-400 (manufactured by Hayashi Chemical Co., Ltd.) and 36 parts by mass of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 2 hours. NMP was added to the obtained paste to adjust the solid content concentration to 65% by mass, and then the mixture was stirred at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and further under reduced pressure (approximately 2.5 × 10 ４ The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at a pressure of 1000 Pa (2000 psi). The slurry was then uniformly applied to the surface of an aluminum foil current collector by a doctor blade method so that the thickness of the coating after solvent removal would be 80 μm. The coating was then heated at 120° C. for 20 minutes to remove the solvent. After that, the density of the active material layer was 3.0 g / cm. ３ The resultant was pressed by a roll press machine to obtain a counter electrode (positive electrode).

[0147] <Assembly of Lithium-Ion Battery Cell> In a glove box purged with Ar to maintain a dew point of −80°C or less, the negative electrode produced above was punched out to a diameter of 16.16 mm and placed on a two-electrode coin cell (manufactured by Hosen Co., Ltd., product name "HS Flat Cell"). Next, a separator made of a polypropylene porous membrane punched out to a diameter of 24 mm (manufactured by Celgard Co., Ltd., product name "Celgard #2400") was placed on top. 300 μL of electrolyte was then poured in to prevent air from entering. The positive electrode produced above was punched out to a diameter of 15.95 mm and placed on top. The exterior body of the two-electrode coin cell was then screwed shut and sealed to assemble a lithium-ion battery cell (power storage device). The electrolyte used here was a 1 / 1 (mass ratio) ethylene carbonate / ethyl methyl carbonate solvent containing LiPF ６ It is a solution in which the above is dissolved at a concentration of 1 mol / L.

[0148] <Evaluation of Cycle Characteristics> The lithium-ion secondary battery fabricated above was charged at a constant current (1.0 C) in a thermostatic chamber maintained at 25°C. When the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 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 (6) 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 First Cycle) (6) (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%.

[0149] <Evaluation of Resistance Increase Rate> The power storage device manufactured above was placed in a thermostatic chamber at 25 ° C., and charging was initiated at a constant current (1.0 C). When the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The point at which the current value reached 0.01 C was considered to be the end of charging (cut-off). Thereafter, discharging was initiated at a constant current (0.05 C). The point at which the voltage reached 3.0 V was considered to be the end of discharge (cut-off), and the discharge capacity at the 0th cycle was calculated. Further, charging was initiated at a constant current (1.0 C), and when the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The point at which the current value reached 0.01 C was considered to be the end of charging (cut-off). Thereafter, discharging was initiated at a constant current (1.0 C). The point at which the voltage reached 3.0 V was considered to be the end of discharge (cut-off), and the discharge capacity at the first cycle was calculated. In this manner, 100 charge-discharge cycles were performed. 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 (7) and evaluated according to the following criteria: 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 (7) (Evaluation criteria) - 5 points: Resistance increase rate is 100% or more and less than 150%. - 4 points: Resistance increase rate is 150% or more and less than 200%. - 3 points: Resistance increase rate is 200% or more and less than 250%. - 2 points: Resistance increase rate is 250% or more and less than 300%. - 1 point: Resistance increase rate is 300% or more and less than 350%. - 0 point: Resistance increase rate is 350% or more.

[0150] <Evaluation of electrode plate expansion coefficient> The film thickness of the negative electrode produced above was measured and taken as the initial film thickness. Then, for the electricity storage device produced above, charging was started at a constant current (0.2 C) in a thermostatic bath controlled at 25 ° C., and when the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The point at which the current value reached 0.01 C was considered to be the end of charge (cut-off). Thereafter, discharging was started at a constant current (0.2 C) in a thermostatic bath controlled at 25 ° C., and when the voltage reached 2.5 V, discharge was considered to be the end of discharge (cut-off), completing the chemical charge and discharge. Thereafter, a contact sensor (manufactured by Keyence Corporation, product name "GT2-H12KLF") was attached to the electricity storage device, and the film thickness at that point was considered to be the film thickness after chemical formation. Then, charging was started at a constant current (0.2 C), and when the voltage reached 4.2 V, charging was continued at a constant voltage (4.2 V). The point at which the current value reached 0.01 C was considered to be the end of charge (cut-off). Thereafter, discharge was initiated at a constant current (0.2 C) in a thermostatic chamber maintained at 25°C. The point when the voltage reached 2.5 V was considered the point at which discharge was completed (cutoff). The film thickness at the time of the 10th discharge cycle was measured, and the electrode plate expansion coefficient was calculated using the following formula (8), and evaluated according to the following criteria. The results are shown in Table 1 below. Electrode plate expansion coefficient (%) = ((film thickness at the 10th discharge cycle) - (film thickness after chemical formation)) / (initial film thickness) × 100 (8) (Evaluation criteria) 5 points: Electrode plate expansion coefficient is 40% or less. 4 points: Electrode plate expansion coefficient is more than 40% but not more than 43%. 3 points: Electrode plate expansion coefficient is more than 43% but not more than 46%. 2 points: Electrode plate expansion coefficient is more than 46% but not more than 50%. 1 point: Electrode plate expansion coefficient is more than 50%.

[0151] 5.2. Examples 2 to 15 and Comparative Examples 1 to 6 In Examples 2 to 15 and Comparative Examples 1 and 3 to 6, the types and amounts of monomers were as shown in Tables 1 to 3 below, respectively, and each polymer was synthesized by two-stage polymerization in the same manner as in Example 1 to obtain each binder composition for an electricity storage device.

[0152] In Comparative Example 2, the types and amounts of monomers were as shown in Table 3 below, and the polymer was synthesized by single-stage polymerization to obtain a binder composition for an electricity storage device. All other operations were carried out in the same manner as in Example 1.

[0153] 5.3. Evaluation Results Tables 1 to 3 below show the polymer compositions, the measurement results of each physical property, and the evaluation results used in Examples 1 to 15 and Comparative Examples 1 to 6. The values ​​representing the polymer compositions shown in Tables 1 to 3 below represent parts by mass.

[0154]

[0155]

[0156]

[0157] The polymer numbers synthesized in each example are listed in the lines below the example numbers and comparative example numbers in Tables 1 to 3. The monomers in Tables 1 to 3 represent the following compounds, respectively. <Conjugated diene compounds> BD: 1,3-butadiene <Aromatic vinyl compounds> ST: Styrene ・DVB: Divinylbenzene <Unsaturated carboxylic acids> TA: Itaconic acid ・AA: Acrylic acid ・MAA: Methacrylic acid <Unsaturated carboxylic acid esters> MMA: Methyl methacrylate ・BA: Butyl acrylate ・2EHA: 2-ethylhexyl acrylate ・CHMA: Cyclohexyl methacrylate ・EDMA: Ethylene glycol dimethacrylate ・HEMA: 2-hydroxyethyl methacrylate ・HEA: 2-hydroxyethyl acrylate <α,β-Unsaturated nitrile compounds> AN: Acrylonitrile <(Meth)acrylamide> ・AAM: Acrylamide ・MAM: Methacrylamide <Compounds having a sulfonic acid group> NASS: Sodium styrenesulfonate

[0158] In Examples 1 to 15, a slurry for an electric storage device electrode was used that contained the electric storage device binder composition of the present invention and an active material containing a silicon material. By including the electric storage device binder composition of Examples 1 to 15, the binder particles were not destroyed by the active material, which undergoes large volume changes during charge and discharge, and were able to maintain their particle shape. This was found to favorably bind the active materials together, reducing the electrode plate expansion rate and maintaining good adhesion between the active material layer and the current collector. Furthermore, it was found that the ability of the binder particles to maintain their particle shape increased the permeability of the electrolyte and suppressed the rate of increase in resistance. As a result, it is presumed that an electric storage device electrode was obtained that suppressed peeling of the active material layer and reduced electrode plate expansion, even when the volume of the active material repeatedly expanded and contracted during repeated charge and discharge, thereby exhibiting good cycle characteristics.

[0159] 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 liquid medium (B) comprising a polymer (A), wherein, when the total amount of repeating units contained in the polymer (A) is taken as 100 parts by mass, the polymer (A) comprises 50 to 80 parts by mass of repeating units (a1) derived from a conjugated diene compound, 15 to 49 parts by mass of repeating units (a2) derived from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating units (a3) ​​derived from an unsaturated carboxylic acid, wherein the polymer (A) has one peak top of dynamic viscoelasticity tan δ (loss modulus / storage modulus) in the range of -50°C or higher and 10°C or lower, and one peak top in the range of 150°C or higher and 250°C or lower, A binder composition for an electrical storage device, which satisfies the relationship of the following formula (1) when tan δ(Tp1) is the tan δ of the peak top in the range of -50°C or more and 10°C or less, and tan δ(Tp2) is the tan δ of the peak top in the range of 150°C or more and 250°C or less: tan δ(Tp2) / tan δ(Tp1)<0.5 (1) 2. The binder composition for an electrical storage device according to claim 1, wherein a proton relaxation time when a latex of the polymer (A) having a solids concentration of 10% is measured by a CPMG method of pulse NMR is 1,500 ms or more.

3. A binder composition for a storage battery device according to claim 1 or 2, wherein the total amount of the repeating unit (a1), the repeating unit (a2) and the repeating unit (a3) ​​is 80 parts by mass or more.

4. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 parts by mass of a repeating unit (a4) derived from an unsaturated carboxylic acid ester.

5. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) further contains 0.1 to 10 parts by mass of a repeating unit (a5) derived from an α,β-unsaturated nitrile compound.

6. The binder composition for an electrical storage device according to claim 1 or 2, wherein the polymer (A) has a degree of swelling in an electrolyte of 100 to 350%.

7. The binder composition for a storage battery device according to claim 1 or 2, wherein the polymer (A) is in the form of polymer particles, and the number average particle size of the polymer particles is 50 nm or more and 500 nm or less.

8. The binder composition for a storage battery device according to claim 7, wherein the polymer particles have a surface acid amount of 0.05 mmol / g or more and 1 mmol / g or less.

9. The binder composition for an electrical storage device according to claim 1 or 2, wherein the liquid medium (B) is water.

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

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

12. 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 or 11 onto the surface of the current collector and drying it.

13. An electricity storage device comprising the electricity storage device electrode according to claim 12.

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