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

Abstract

Provided is a power storage device binder composition with which it is possible to manufacture a power storage device electrode having superior repeated charging / discharging characteristics by reducing internal resistance, and superior charging / discharging durability characteristics in high temperatures by improving adhesion.　A power storage device binder composition according to the present invention contains a polymer (A) and a liquid medium (B), the polymer (A) containing, when the total of repeating units contained in the polymer (A) is defined as 100 mass%, 15-60 mass% of a repeating unit (a1) derived from a conjugated diene compound, and 1-10 mass% of a repeating unit (a2) derived from unsaturated carboxylic acid, one peak top of the dynamic viscoelasticity tan δ(loss modulus / storage modulus) of the polymer (A) being present in the range of at least -40°C to less than 50°C, and one peak top being present in the range of 50-150°C, inclusive, and when the tan δ of the peak top of the range of at least -40°C to less than 50°C is defined as tan δ (Tp1) and the tan δ of the peak top of the range 50-150°C, inclusive, is defined as tan δ (Tp2), the relationship of expression (1) is satisfied.　tan δ (Tp2) / tan δ (Tp1) ≥ 0.5 (1)

Description

Technical Field

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

Background Art

[0002] In recent years, there has been a demand for power storage devices having a high voltage and a high energy density as a power source for driving electronic devices. As such power storage devices, lithium ion batteries, lithium ion capacitors, etc. are expected.

[0003] An electrode used in such a power storage device is manufactured by applying and drying a composition (slurry for a power storage device electrode) containing an active material and a polymer functioning as a binder on the surface of a current collector. The characteristics required for the polymer used as a binder include the binding ability between active materials, the adhesion ability between the active material and the current collector, the abrasion resistance in the process of winding the electrode, and the resistance to powder falling, such that fine powder of the active material does not fall off from the applied and dried composition coating film (hereinafter, also referred to as "active material layer") even by subsequent cutting. By such a binder material exhibiting good adhesion and reducing the internal resistance of the battery caused by the binder material, good charge and discharge characteristics can be imparted to the power storage device.

[0004] In addition, it has been empirically clarified that the binding ability between the above active materials, the adhesion ability between the active material and the current collector, and the resistance to powder falling are almost in a proportional relationship in terms of performance. Therefore, in this specification, these may sometimes be represented using the term "adhesion" including the above.

[0005] Furthermore, in recent years, for the purpose of reducing environmental impact, research and development of electric vehicles equipped with power storage devices have been actively carried out. When a power storage device is installed as a drive power source for an electric vehicle, high input / output characteristics that allow frequent charging and discharging are required, and for this purpose, it is important to reduce resistance. Also, in summer, the temperature inside the vehicle can reach as high as 50°C or more, so the power storage device is required to have durability at high temperatures.

[0006] Under such circumstances, various binder materials have been proposed to reduce the resistance of power storage devices and improve charge / discharge durability characteristics (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the binder materials disclosed in Patent Documents 1 and 2 above do not have sufficient repeated charge / discharge characteristics and durability at high temperatures, and further improvement has been required for application to power storage devices as drive power sources for electric vehicles.

[0009] Therefore, some aspects of the present invention provide a binder composition for a power storage device capable of manufacturing a power storage device electrode that has excellent charge-discharge cycle characteristics by reducing internal resistance and has excellent charge-discharge durability characteristics at high temperatures by improving adhesion. Further, some aspects of the present invention provide a slurry for a power storage device electrode containing the binder composition. Additionally, some aspects of the present invention provide a power storage device electrode that has excellent charge-discharge cycle characteristics by reducing internal resistance and has excellent charge-discharge durability characteristics at high temperatures by improving adhesion. Furthermore, some aspects of the present invention provide a power storage device that has excellent charge-discharge cycle characteristics and excellent charge-discharge durability characteristics at high temperatures.

Means for Solving the Problems

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

[0011] One aspect of the binder composition for a power storage device according to the present invention is containing a polymer (A) and a liquid medium (B), when the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 15 to 60% by mass of a repeating unit (a1) derived from a conjugated diene compound and 1 to 10% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid, and the polymer (A) has one peak top of tanδ (loss elastic modulus / storage elastic modulus) of the dynamic viscoelasticity in the range of -40°C or higher and less than 50°C and one peak top in the range of 50°C or higher and 150°C or lower, when the tanδ of the peak top in the range of -40°C or higher and less than 50°C is defined as tanδ(Tp1) and the tanδ of the peak top in the range of 50°C or higher and 150°C or lower is defined as tanδ(Tp2), the following relationship of formula (1) is satisfied. tanδ(Tp2) / tanδ(Tp1)≧0.5 (1)

[0012] In one aspect of the binder composition for the power storage device, the polymer (A) may further contain 35 to 75% by mass of a repeating unit (a3) derived from an aromatic vinyl compound, and in this case, the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) can be 80% by mass or more.

[0013] In one aspect of the binder composition for the power storage device, the polymer (A) may contain at least one of a repeating unit (a4) derived from an unsaturated carboxylic acid ester and a repeating unit (a5) derived from an α,β-unsaturated nitrile compound, and in this case, the total amount of the repeating unit (a1), the repeating unit (a2), the repeating unit (a4), and the repeating unit (a5) can be 65% by mass or more.

[0014] In any aspect of the binder composition for the power storage device, the Martens hardness calculated using a pico indenter of the polymer (A) may be 15 MPa or more.

[0015] In any aspect of the binder composition for the power storage device, the polymer (A) is polymer particles, and the number average particle diameter of the polymer particles may be 50 nm or more and 500 nm or less.

[0016] In any aspect of the binder composition for the power storage device, the liquid medium (B) may be water.

[0017] One aspect of the slurry for the power storage device electrode according to the present invention contains the binder composition for the power storage device in any of the above aspects and an active material.

[0018] In one aspect of the slurry for the power storage device electrode, The active material may contain a silicon material.

[0019] One aspect of the electrode of the power storage device according to the present invention is a current collector and an active material layer formed by applying and drying the slurry for the electrode of the power storage device in any of the above aspects on the surface of the current collector.

[0020] One aspect of the power storage device according to the present invention is equipped with the electrode of the power storage device in the above aspect.

Advantages of the Invention

[0021] According to the binder composition for the power storage device of the present invention, the internal resistance can be reduced, so that the repeated charge and discharge characteristics are excellent, and the adhesion can be improved, so that a power storage device electrode excellent in charge and discharge durability characteristics at high temperatures can be manufactured. The binder composition for the power storage device according to the present invention exhibits the above effects particularly when the power storage device electrode contains a material having a large lithium storage amount, such as a carbon material like graphite or a silicon material, as the active material. Thus, since a material having a large lithium storage amount can be used as the active material of the power storage device electrode, the battery performance is also improved.

Brief Description of the Drawings

[0022]

Figure 1

Modes for Carrying Out the Invention

[0023] Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, but also includes various modifications implemented within the scope of not changing the gist of the present invention.

[0024] In addition, the term "(meth)acrylic acid~" in this specification is a concept that includes both "acrylic acid~" and "methacrylic acid~". Similarly, the term "~(meth)acrylate" is a concept that includes both "~acrylate" and "~methacrylate". Similarly, the term "(meth)acrylamide" is a concept that includes both "acrylamide" and "methacrylamide".

[0025] In this specification, a numerical range described as "A~B" is interpreted as including numerical value A as the lower limit value and including numerical value B as the upper limit value.

[0026] In this specification, "under high temperature" generally refers to an environment in a temperature range of approximately 40°C to 80°C.

[0027] 1. Binder Composition for Energy Storage Device The binder composition for an energy storage device according to an embodiment of the present invention contains a polymer (A) and a liquid medium (B). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 15 to 60% by mass of repeating units (a1) derived from a conjugated diene compound and 1 to 10% by mass of repeating units (a2) derived from an unsaturated carboxylic acid. Further, there is one peak top of tanδ (loss elastic modulus / storage elastic modulus) of the dynamic viscoelasticity of the polymer (A) in the range of -40°C or higher and less than 50°C, and there is one in the range of 50°C or higher and 150°C or lower. When the tanδ of the peak top in the range of -40°C or higher and less than 50°C is tanδ(Tp1) and the tanδ of the peak top in the range of 50°C or higher and 150°C or lower is tanδ(Tp2), the following relationship of formula (1) is satisfied. tanδ(Tp2) / tanδ(Tp1)≧0.5 (1)

[0028] The binder composition for a power storage device according to the present embodiment can also be used as a material for producing a power storage device electrode (active material layer) with improved binding ability between active materials, adhesion ability between the active material and the current collector, and powder falling resistance, and can also be used as a material for forming a protective film for suppressing a short circuit caused by dendrites generated during charge and discharge. Hereinafter, each component contained in the binder composition for a power storage device according to the present embodiment will be described in detail.

[0029] 1.1. Polymer (A) The binder composition for a power storage device according to the present embodiment contains a polymer (A). When the total of the repeating units contained in the polymer (A) is 100% by mass, the repeating unit (a1) derived from a conjugated diene compound (hereinafter, also simply referred to as "repeating unit (a1)") is 15 to 60% by mass, and the repeating unit (a2) derived from an unsaturated carboxylic acid (hereinafter, also simply referred to as "repeating unit (a2)") is 1 to 10% by mass. Further, in addition to the above repeating units, the polymer (A) may contain repeating units derived from other monomers copolymerizable therewith.

[0030] The polymer (A) contained in the binder composition for a power storage device according to the present embodiment may be in the form of a latex dispersed in the liquid medium (B) or may be in a state dissolved in the liquid medium (B), but it is preferably in the form of a latex dispersed in the liquid medium (B). When the polymer (A) is in the form of a latex dispersed in the liquid medium (B), the stability of the slurry for a power storage device electrode (hereinafter, also simply referred to as "slurry") prepared by mixing with the active material is improved, and the coatability of the slurry on the current collector is also improved, which is preferable.

[0031] Hereinafter, the repeating units constituting the polymer (A), the physical properties of the polymer (A), and the production method will be described in this order.

[0032] 1.1.1. Repeating units constituting the polymer (A) 1.1.1.1. Repeating unit (a1) derived from a conjugated diene compound The content ratio of the repeating unit (a1) derived from the conjugated diene compound is 15 to 60% by mass based on 100% by mass of the total repeating units contained in the polymer (A). The lower limit of the content ratio of the repeating unit (a1) is preferably 17% by mass, more preferably 20% by mass. The upper limit of the content ratio of the repeating unit (a1) is preferably 57% by mass, more preferably 55% by mass. When the polymer (A) contains the repeating unit (a1) within the above range, the dispersibility of the active material and the filler becomes good, and it becomes possible to produce a uniform active material layer and a protective film. As a result, structural defects of the electrode plate disappear, and good charge-discharge cycle characteristics are exhibited. In addition, the polymer (A) covering the surface of the active material can be imparted with stretchability, and the adhesion can be improved by the stretching of the polymer (A), so that good charge-discharge durability characteristics are exhibited.

[0033] The conjugated diene compound is not particularly limited, and 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.

[0034] 1.1.1.2. Repeating unit (a2) derived from unsaturated carboxylic acid The content ratio of the repeating unit (a2) derived from the unsaturated carboxylic acid is 1 to 10% by mass based on 100% by mass of the total repeating units contained in the polymer (A). The lower limit of the content ratio of the repeating unit (a2) is preferably 1.2% by mass, more preferably 1.5% by mass. The upper limit of the content ratio of the repeating unit (a 2 ) is preferably 9% by mass, more preferably 8% by mass. When the polymer (A) contains the repeating unit (a2) within the above range, the dispersibility of the active material and the filler becomes good. In addition, the affinity with the silicon material used as the active material is improved, and the swelling of the silicon material is suppressed, so that good charge-discharge durability characteristics are exhibited.

[0035] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0036] 1.1.1.3. Other repeating units In addition to the repeating units (a1) to (a2), the polymer (A) may contain a repeating unit derived from another monomer copolymerizable therewith. Examples of such a repeating unit include a repeating unit (a3) derived from an aromatic vinyl compound (hereinafter also simply referred to as "repeating unit (a3)"), a repeating unit (a4) derived from an unsaturated carboxylic acid ester (hereinafter also simply referred to as "repeating unit (a4)"), a repeating unit (a5) derived from an α,β-unsaturated nitrile compound (hereinafter also simply referred to as "repeating unit (a5)"), a repeating unit (a6) derived from (meth)acrylamide (hereinafter also simply referred to as "repeating unit (a6)"), a repeating unit (a7) derived from a compound having a sulfonic acid group (hereinafter also simply referred to as "repeating unit (a7)"), a repeating unit derived from a cationic monomer, and the like.

[0037] <Repeating unit (a3) derived from an aromatic vinyl compound> When the content ratio of the repeating unit (a3) derived from the aromatic vinyl compound is 35 to 75% by mass based on 100% by mass of the total repeating units contained in the polymer (A), it is preferable. The lower limit of the content ratio of the repeating unit (a3) is preferably 38% by mass, more preferably 40% by mass. The upper limit of the content ratio of the repeating unit (a3) is preferably 72% by mass, more preferably 70% by mass. By containing the repeating unit (a3) in the above range in the polymer (A), the fusion of the polymers (A) dispersed in the electrode is suppressed, the permeability of the electrolytic solution is improved, and thus good charge-discharge cycle characteristics may be exhibited. Further, good adhesion to graphite or the like used as the active material may be shown, and a storage device electrode excellent in adhesion can be obtained.

[0038] The aromatic vinyl compound is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used.

[0039] When the polymer (A) contains the repeating unit (a3) derived from the aromatic vinyl compound, when the total of the repeating units contained in the polymer (A) is 100% by mass, the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) is preferably 80% by mass or more, more preferably 85% by mass or more. When the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) is in the above range, the dispersibility of the active material and the filler is good, and the fusion of the polymers (A) dispersed in the electrode can be suppressed, and the adhesion and the permeability of the electrolytic solution are improved, so that good charge-discharge cycle characteristics and good charge-discharge durability characteristics are exhibited.

[0040] <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. When the total of the repeating units contained in the polymer (A) is 100% by mass, the content ratio of the repeating unit (a4) is preferably 0 to 60% by mass. The lower limit of the content ratio of the repeating unit (a4) is preferably 1% by mass, more preferably 2% by mass. The upper limit of the content ratio of the repeating unit (a4) is preferably 55% by mass, more preferably 50% by mass. When the polymer (A) contains the repeating unit (a4) within the above range, the affinity between the polymer (A) and the electrolytic solution becomes good, and it is possible to suppress an increase in internal resistance due to the binder becoming an electric resistance component in the power storage device, and it may be possible to prevent a decrease in adhesion due to excessive absorption of the electrolytic solution.

[0041] Among the unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Specific examples of the (meth)acrylic acid esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate, etc. One or more selected from these can be used. Among them, it is preferably 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, and particularly preferably methyl (meth)acrylate.

[0042] <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. When the total of the repeating units contained in the polymer (A) is 100% by mass, the content ratio of the repeating unit (a5) is preferably 0 to 60% by mass. The lower limit of the content ratio of the repeating unit (a5) is preferably 0.5% by mass, more preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a5) is preferably 55% by mass, more preferably 50% by mass. When the polymer (A) contains the repeating unit (a5) within the above range, it becomes possible to reduce the dissolution of the polymer (A) in the electrolytic solution, and it may be possible to suppress the decrease in adhesion due to the electrolytic solution. Further, it may be possible to suppress an increase in internal resistance due to the dissolved polymer component becoming an electric resistance component in the power storage device.

[0043] 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 preferable, and acrylonitrile is particularly preferable.

[0044] When the polymer (A) contains at least one of a repeating unit (a4) derived from an unsaturated carboxylic acid ester and a repeating unit (a5) derived from an α,β-unsaturated nitrile compound, when the total of the repeating units contained in the polymer (A) is 100% by mass, the total amount of the repeating unit (a1), the repeating unit (a2), the repeating unit (a4) and the repeating unit (a5) is preferably 65% by mass or more, more preferably 68% by mass or more. When the total amount of the repeating unit (a1), the repeating unit (a2), the repeating unit (a4) and the repeating unit (a5) is within the above range, the dispersibility of the active material and the filler becomes good, and the fusion of the polymers (A) dispersed in the electrode can be suppressed, and the adhesion and the permeability of the electrolytic solution are improved, so that good charge-discharge cycle characteristics and good charge-discharge durability characteristics are exhibited.

[0045] <Repeating unit (a6) derived from (meth)acrylamide> Polymer (A) may contain a repeating unit (a6) derived from (meth)acrylamide. When the total of the repeating units contained in polymer (A) is 100% by mass, the content ratio of the repeating unit (a6) is preferably 0 to 10% by mass. The lower limit of the content ratio of the repeating unit (a6) is preferably 1% by mass, more preferably 2% by mass. The upper limit of the content ratio of the repeating unit (a6) is preferably 8% by mass, more preferably 5% by mass. When 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. Further, the flexibility of the obtained active material layer may become appropriate, and the adhesion between the current collector and the active material layer may be improved. Furthermore, since the binding ability between active materials containing a carbon material such as graphite or a silicon material can be enhanced, an active material layer with better flexibility and adhesion to the current collector may be obtained.

[0046] (Meth)acrylamide is not particularly limited, and 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, maleic amide, acrylamide tert-butylsulfonic acid, etc., and one or more selected from these can 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. When the total of the repeating units contained in the polymer (A) is 100% by mass, the content ratio of the repeating unit (a7) is preferably 0 to 10% by mass. The lower limit of the content ratio of the repeating unit (a7) is preferably 0.5% by mass, more preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a7) is preferably 8% by mass, more preferably 5% by mass.

[0048] The compound having a sulfonic acid group is not particularly limited, and 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-methylpropane sulfonic acid, 2-hydroxy-3-acrylamidopropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and alkali salts thereof. One or more selected from these can be used.

[0049] <Repeating unit derived from a cationic monomer> 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 amine (salt), tertiary amine (salt), and quaternary ammonium salt. Specific examples of these cationic monomers are not particularly limited, but include 2-(dimethylamino)ethyl (meth)acrylate, methyl 4-quaternary salt of dimethylaminoethyl (meth)acrylate chloride, 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, methacryloylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, 2-vinylpyridine, quinacridine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazoles dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichloramide, 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, etc. One or more selected from these can be used.

[0050] 1.1.2. Physical properties of the polymer (A) 1.1.2.1. Dynamic viscoelasticity When measuring the dynamic viscoelasticity of the polymer (A), there is one peak top of tanδ (loss elastic modulus / storage elastic modulus) in the range of -40°C or higher and less than 50°C, and one in the range of 50°C or higher and 150°C or lower. When the tanδ of the peak top in the range of -40°C or higher and less than 50°C is defined as tanδ(Tp1), and the tanδ of the peak top in the range of 50°C or higher and 150°C or lower is defined as tanδ(Tp2), the following relationship of formula (1) is satisfied. tanδ(Tp2) / tanδ(Tp1)≧0.5 (1)

[0051] The measurement sample in this dynamic viscoelasticity measurement is a film of the polymer (A). The film of the polymer (A) is obtained by drying the polymer (A) at 40°C for 24 hours to produce a uniform film with a thickness of 1.0 ± 0.3 mm, drying this film in a vacuum dryer at 160°C for 30 minutes, and then cutting it into strips of 10 mm × 10 mm. Then, using the following dynamic viscoelasticity measurement device, the measurement sample is fixed with a parallel plate (product name "PP-12"), and measured in the temperature range of -70°C to 180°C under the following measurement conditions. · Measurement conditions: shear mode, measurement frequency 0.01 - 1 Hz, heating rate 0.1°C / min · Dynamic viscoelasticity measurement device: manufactured by Anton Paar, model "MCR 301"

[0052] The value of "tanδ(Tp2) / tanδ(Tp1)" of the polymer (A) used in this embodiment is 0.5 or more, preferably 0.75 or more, and more preferably 1 or more. When the value of "tanδ(Tp2) / tanδ(Tp1)" of the polymer (A) is within the above range, it indicates that the viscosity is high at a temperature near the peak top temperature of tanδ(Tp1), and it is considered that the adhesiveness can be ensured by this high viscosity. Also, it indicates that the polymer (A) is hard at a temperature near the peak top temperature of tanδ(Tp2), that is, a high crosslinking. Since the polymer (A) is hard, it can maintain its particle shape without being crushed like other binders during electrode formation, and thus it is considered that the permeability of the electrolyte to the active material can be increased. Thus, the polymer (A) used in this embodiment can reduce the internal resistance by increasing the permeability of the electrolyte to the active material, so that an electrode showing good charge-discharge cycle characteristics can be fabricated. Also, since the polymer (A) used in this embodiment can improve the adhesiveness, an electrode showing good charge-discharge durability characteristics at high temperatures can be fabricated.

[0053] The temperature Tp1 (°C) of the peak top of tanδ in the dynamic viscoelasticity measurement of the polymer (A) preferably exists in a temperature range of preferably -35°C or more and 45°C or less, more preferably -30°C or more and 40°C or less. Also, preferably, there is one peak top in the above temperature range. The presence of one Tp in the above temperature range indicates that the viscosity is high in the same temperature range. It is considered that due to this high viscosity, the high adhesive force of the polymer (A) in the same temperature range can be maintained, and good adhesiveness can be exhibited.

[0054] The temperature Tp2 (°C) at the peak top of tanδ in the dynamic viscoelasticity measurement of the polymer (A) preferably exists in the temperature range of 60°C or higher and 145°C or lower, more preferably 70°C or higher and 140°C or lower. Further, it is preferable that there is one peak top in the above temperature range. The presence of one Tp in the above temperature range indicates that a polymer with a homogeneous cross-linked composition is formed in the same temperature range. It is considered that a large amount of the homogeneous cross-linked composition of the polymer (A) in the same temperature range can exhibit the hardness of the polymer (A) and reduce the internal resistance.

[0055] Examples of the method for adjusting the temperature Tp at the peak top of tanδ include the method of adjusting the monomer composition during the polymerization of the polymer (A).

[0056] The tanδ (Tp1) of the polymer (A) is preferably 0.01 to 0.5, more preferably 0.01 to 0.45, and particularly preferably 0.01 to 0.4. The fact that the tanδ (Tp1) of the polymer (A) is within the above range indicates that the polymer (A) has viscosity but is not too hard and has sufficient adhesive force to hold the electrode structure.

[0057] The tanδ (Tp2) of the polymer (A) is preferably 0.1 to 3, more preferably 0.2 to 2.5, and particularly preferably 0.3 to 2. The fact that the tanδ (Tp2) of the polymer (A) is within the above range indicates that the polymer (A) is not too soft and has sufficient hardness to suppress the fusion of particles.

[0058] Examples of the method for adjusting tanδ (Tp) include changing the glass transition temperature or gel content of the polymer (A), or changing the monomer addition method during the polymerization of the polymer (A).

[0059] 1.1.2.2. Martens hardness The Martens hardness calculated using the picoin-denter of the polymer (A) used in this embodiment is preferably 15 MPa or more, more preferably 20 MPa or more, and particularly preferably 25 MPa or more. The fact that the Martens hardness of the polymer (A) is within the above range indicates that the polymer (A) is hard. Because the polymer (A) is hard, it can maintain its particle shape without being crushed like other binders during electrode formation, so it is considered that the permeability of the electrolyte to the active material can be increased. Such a polymer (A) can reduce the internal resistance by increasing the permeability of the electrolyte to the active material, so an electrode with good charge-discharge cycle characteristics can be fabricated.

[0060] The Martens hardness of the polymer (A) can be measured using a picoin-denter. The measurement sample in this picoin-denter is a thin film of the polymer (A). The thin film of the polymer (A) is formed by adding about 1 g of the polymer (A) onto a 1 cm × 1 cm Si wafer and forming a coating film using spin coating under the following apparatus and conditions, and drying the coating film on a hot plate at 150 °C for 30 minutes. For this measurement sample, the Martens hardness is calculated using the following picoin-denter under the following test conditions. · Spin coating rotation conditions: Coating was performed according to 150 rpm × 5 s, 250 rpm × 5 s, 1000 rpm × 30 s. · Spin coater: Mikasa Co., Ltd., model "MS-A-150" · Picoin-denter test conditions: Pressed in for 5 s at a pressure of 0.1 mN, kept for 1 s, and then released over 5 s · Picoin-denter: Manufactured by Helmut Fischer, model "HM500"

[0061] 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 60 nm or more and 450 nm or less, and particularly preferably 70 nm or more and 400 nm or less. When the number-average particle diameter of the particles of the polymer (A) is within the above range, the particles of the polymer (A) are likely to adsorb on the surface of the active material, so that the particles of the polymer (A) can follow and move as the active material moves. As a result, migration can be suppressed, and thus deterioration of electrical characteristics may be reduced.

[0062] Incidentally, the number-average particle diameter of the particles of the polymer (A) can be calculated from the average value of the particle diameters obtained from the images of 50 particles observed by a transmission electron microscope (TEM). Examples of the transmission electron microscope include "H-7650" manufactured by Hitachi High-Technologies Corporation.

[0063] 1.1.2.4. Degree of swelling in electrolyte The degree of swelling of the polymer (A) in the electrolyte is preferably 100 to 500% by mass, more preferably 120 to 450% by mass, and particularly preferably 140 to 400% by mass. When the degree of swelling in the electrolyte is within the above range, the polymer (A) can swell moderately with respect to the electrolyte. As a result, the solvated lithium ions can easily reach the active material, reducing the internal resistance of the electrode and realizing better charge-discharge cycle characteristics. Also, when the degree of swelling in the electrolyte is within the above range, a large volume change does not occur, so the adhesion is also excellent. The degree of swelling of the polymer (A) in the electrolyte can be measured by the method described in the examples below.

[0064] 1.1.3. Method for producing the polymer (A) The method for producing the polymer (A) is not particularly limited, and for example, it can be carried out by an emulsion polymerization method in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, the compounds described in Japanese Patent No. 5999399 and the like can be used.

[0065] The emulsion polymerization method for synthesizing the polymer (A) may be carried out by one-stage polymerization or by multi-stage polymerization of two or more stages.

[0066] When the polymer (A) is synthesized by one-stage polymerization, the above monomer mixture can be subjected to emulsion polymerization in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80 °C, preferably for 4 to 36 hours.

[0067] When the polymer (A) is synthesized by two-stage polymerization, the polymerization in each stage is preferably set as follows.

[0068] The usage ratio of the monomers used in the first-stage polymerization is preferably in the range of 20 to 100% by mass, more preferably in the range of 25 to 100% by 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 with such a usage ratio of the monomers, it is possible to obtain particles of the polymer (A) having excellent dispersion stability and being less likely to form aggregates, and it is also preferable that the viscosity increase of the binder composition for the power storage device over time is suppressed.

[0069] The type and usage ratio of the monomers used in the second-stage polymerization may be the same as or different from the type and usage ratio of the monomers used in the first-stage polymerization.

[0070] From the viewpoint of the dispersibility of the particles of the polymer (A) obtained, the polymerization conditions in each stage are preferably as follows. · First-stage polymerization; preferably a temperature of 40 to 80 °C: preferably a polymerization time of 2 to 36 hours: preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more. · Second-stage polymerization; preferably a temperature of 40 to 80 °C; preferably a polymerization time of 2 to 18 hours.

[0071] By setting the total solid concentration in emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed with good dispersion stability of the particles of the resulting polymer (A). This total solid concentration is preferably 48% by mass or less, more preferably 45% by mass or less.

[0072] Whether the synthesis of the polymer (A) is carried out by one-stage polymerization or by a two-stage polymerization method, after the completion of emulsion polymerization, it is preferable to adjust the pH to about 4.5 to 10.5, preferably 5 to 10, more preferably 5.5 to 9.5 by adding a neutralizing agent to the polymerization mixture. The neutralizing agent used here is not particularly limited, and examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia and the like. By setting the pH range as described above, the stability of the polymer (A) becomes good. After the neutralization treatment, by concentrating the polymerization mixture, the solid content concentration can be increased while maintaining good stability of the polymer (A).

[0073] 1.1.4. Content ratio of polymer (A) The content ratio of the polymer (A) in the binder composition for the power storage device according to the present embodiment is preferably 10 to 100% by mass, more preferably 20 to 95% by mass, and particularly preferably 25 to 90% by mass in 100% by mass of the polymer component. Here, the polymer component includes the polymer (A), polymers other than the polymer (A) described later, and thickeners and the like.

[0074] 1.2. Liquid medium (B) The binder composition for a power storage device according to this embodiment contains a liquid medium (B). As the liquid medium (B), an aqueous medium containing water is preferable, and water is more preferable. The above aqueous medium can contain a non-aqueous medium other than water. Examples of this non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. By using an aqueous medium as the liquid medium (B) in the binder composition for a power storage device according to this embodiment, the degree of adverse impact on the environment is reduced, and the safety for handling workers is also increased.

[0075] The content ratio of the non-aqueous medium contained in the aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially not contained in 100% by mass of the aqueous medium. Here, "substantially not contained" means to the extent that a non-aqueous medium is not intentionally added as the liquid medium, and may include non-aqueous media that are unavoidably mixed in when preparing the binder composition for a power storage device.

[0076] 1.3. Other additives The binder composition for a power storage device according to this embodiment can contain additives other than the above-described components as necessary. Examples of such additives include polymers other than the polymer (A), preservatives, thickeners, etc.

[0077] 1.3.1. Polymers other than the polymer (A) The binder composition for a power storage device according to this embodiment may contain a polymer other than the polymer (A). Such polymers are not particularly limited, but include acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as constituent units, fluorine-based polymers such as PVDF (polyvinylidene fluoride), etc. These polymers may be used alone or in combination of two or more. By containing these polymers, flexibility and adhesion may be further improved.

[0078] 1.3.2. Antiseptic The binder composition for a power storage device according to this embodiment may contain an antiseptic. By containing an antiseptic, it may be possible to suppress the growth of bacteria, mold, etc. and the generation of foreign substances when the binder composition for a power storage device is stored. Specific examples of the antiseptic include compounds described in Japanese Patent No. 5477610 and the like.

[0079] 1.3.3. Thickener The binder composition for a power storage device according to this embodiment may contain a thickener. By containing a thickener, the coating property of the slurry and the charge-discharge characteristics of the resulting power storage device may be further improved.

[0080] Specific examples of the thickener include, for example, cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the cellulose compound or the poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer; and water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid and vinyl esters. Among these, alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly(meth)acrylic acid, etc. are preferable.

[0081] Examples of commercially available products of these thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0082] When the binder composition for a power storage device according to this embodiment contains a thickener, the content ratio of the thickener is preferably 5% by mass or less, more preferably 0.1 to 3% by mass, based on 100% by mass of the total solid content of the binder composition for a power storage device.

[0083] 1.4. pH of the Binder Composition for the Power Storage Device The pH of the binder composition for the power storage device according to the present embodiment is preferably 5 to 10, more preferably 6 to 9.5, and particularly preferably 6.5 to 9. When the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling property and liquid dripping, and it becomes easy to manufacture a power storage device electrode that achieves both good electrical characteristics and adhesion.

[0084] As used herein, "pH" refers to the physical property measured as follows. At 25 °C, it is the value measured in accordance with JIS Z8802:2011 using a pH meter with a glass electrode calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions. Examples of such pH meters include "HM-7J" manufactured by Toa DKK Corporation and "D-51" manufactured by Horiba, Ltd.

[0085] It should be noted that although it is not denied that the pH of the binder composition for the power storage device is affected by the monomer composition constituting the polymer (A), it is added that it is not determined only by the monomer composition. That is, it is generally known that even with the same monomer composition, the pH of the binder composition for the power storage device changes depending on polymerization conditions and the like, and the examples in the present specification only show an example thereof.

[0086] For example, even with the same monomer composition, when all unsaturated carboxylic acids are charged into the polymerization reaction solution from the beginning and then other monomers are sequentially added, and when monomers other than unsaturated carboxylic acids are charged into the polymerization reaction solution and finally unsaturated carboxylic acid is added, the amount of carboxy groups derived from unsaturated carboxylic acids exposed on the surface of the resulting polymer is different. It is considered that just changing the order of adding monomers by the polymerization method in this way will result in a significant difference in the pH of the binder composition for the power storage device.

[0087] 2. Slurry for the Power Storage Device The slurry for a power storage device according to an embodiment of the present invention contains the above-described binder composition for a power storage device. The above-described binder composition for a power storage device can be used as a material for forming a protective film for suppressing a short circuit caused by dendrites generated during charge and discharge, and can also be used as a material for forming a power storage device electrode (active material layer) with improved binding ability between active materials, adhesion ability between the active material and the current collector, and resistance to powder falling. Therefore, the slurry for a power storage device for forming a protective film (hereinafter, also referred to as "slurry for protective film") and the slurry for a power storage device for forming the active material layer of the power storage device electrode (hereinafter, also referred to as "slurry for power storage device electrode") will be described separately.

[0088] 2.1. Slurry for protective film The "slurry for protective film" refers to a dispersion liquid used to form a protective film on the surface of the electrode or separator or both surfaces thereof after applying it to the surface of the electrode or separator or both surfaces thereof and drying. The slurry for protective film according to the present embodiment may be composed only of the above-described binder composition for a power storage device, or may further contain an inorganic filler. Hereinafter, each component contained in the slurry for protective film according to the present embodiment will be described in detail. Since the binder composition for a power storage device has been described above, the description thereof will be omitted.

[0089] 2.1.1. Inorganic filler The slurry for protective film according to the present embodiment can improve the toughness of the protective film by containing an inorganic filler. As the inorganic filler, it is preferable to use at least one kind of inorganic oxide particles selected from the group consisting of silica, titanium oxide (titania), aluminum oxide (alumina), zirconium oxide (zirconia), and magnesium oxide (magnesia). Among these, titanium oxide particles or aluminum oxide particles are preferable from the viewpoint of further improving the toughness of the protective film. Further, as the titanium oxide, rutile-type titanium oxide is more preferable.

[0090] The average particle diameter of the inorganic filler is preferably 1 μm or less, more preferably 0.1 to 0.8 μm. In addition, the average particle diameter of the inorganic filler is preferably larger than the average pore diameter of the separator which is a porous membrane. Thereby, damage to the separator can be reduced, and it is possible to prevent the inorganic filler from clogging the micropores of the separator.

[0091] The slurry for the protective film according to the present embodiment preferably contains 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, in terms of solid content, of the above-described binder composition for the power storage device with respect to 100 parts by mass of the inorganic filler. When the content ratio of the binder composition for the power storage device is within the above range, the balance between the toughness of the protective film and the lithium ion permeability becomes good, and as a result, the resistance increase rate of the obtained power storage device can be further reduced.

[0092] 2.1.2. Liquid medium In the slurry for the protective film according to the present embodiment, in addition to the carry-in from the binder composition for the power storage device, a liquid medium may be further added. The addition amount of the liquid medium can be adjusted as necessary so as to obtain an optimal slurry viscosity according to the coating method and the like. Examples of such a liquid medium include the materials described in the above “1.2. Liquid medium (B)”.

[0093] 2.1.3. Other components The slurry for the protective film according to the present embodiment can use an appropriate amount of the materials described in the above “1.3. Other additives” as necessary.

[0094] 2.2. Slurry for the power storage device electrode The “slurry for the power storage device electrode” refers to a dispersion liquid used to form an active material layer on the surface of a current collector after being applied to the surface of the current collector and dried. The slurry for the power storage device electrode according to the present embodiment contains the above-described binder composition for the power storage device and an active material.

[0095] Generally, slurries for power storage device electrodes often contain a binder component such as an SBR copolymer and a thickener such as carboxymethyl cellulose in order to improve adhesion. On the other hand, the slurry for power storage device electrodes according to the present embodiment can improve adhesion even when it contains only the polymer (A) described above as the polymer component. Of course, the slurry for power storage device electrodes according to the present embodiment may further contain a polymer other than the polymer (A) or a thickener in order to further improve adhesion. Hereinafter, the components contained in the slurry for power storage device electrodes according to the present embodiment will be described.

[0096] 2.2.1. Polymer (A) The composition, physical properties, manufacturing method, etc. of the polymer (A) are as described above, so the description will be omitted.

[0097] The content ratio of the polymer component in the slurry for power storage device electrodes according to the present 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 with respect to 100 parts by mass of the active material. When the content ratio of the polymer component is within the above range, the dispersibility of the active material in the slurry becomes good, and the coatability of the slurry is also excellent. Here, the polymer component includes the polymer (A), a polymer other than the polymer (A) added as necessary, and a thickener and the like.

[0098] 2.2.2. Active Material Examples of the active material used in the slurry for power storage device electrodes according to the present embodiment include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacene, A X B Y O Z(However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively.) Composite metal oxides represented by the formula, and other metal oxides, etc. may be mentioned. Specific examples thereof include compounds described in Japanese Patent No. 5999399 and the like.

[0099] The slurry for a power storage device electrode according to the present embodiment can be used when manufacturing any of the positive and negative electrodes of the power storage device electrode, and it is preferably used for both the positive and negative electrodes.

[0100] When using lithium iron phosphate as the positive electrode active material, there were problems that the charge and discharge characteristics were not sufficient and the adhesion was poor. Lithium iron phosphate has a fine primary particle size and is known to be its secondary aggregate. When repeating charge and discharge, aggregation collapses in the active material layer, causing separation between the active materials, which is considered to be one of the factors for easy peeling from the current collector and easy disconnection of the conductive network inside the active material layer.

[0101] The power storage device electrode manufactured using the slurry for a power storage device electrode according to the present embodiment can exhibit good electrical characteristics without causing the above problems even when using lithium iron phosphate as the positive electrode active material. The reason for this is considered to be that the polymer (A) can firmly bind lithium iron phosphate and at the same time can maintain the state of firmly binding lithium iron phosphate even during charge and discharge.

[0102] On the other hand, when manufacturing the negative electrode, among the above-exemplified active materials, it is preferable to contain a silicon material. Since the silicon material has a larger lithium storage amount per unit weight compared to other active materials, by containing the silicon material as the negative electrode active material, the storage capacity of the obtained power storage device can be increased, and as a result, the output and energy density of the power storage device can be increased.

[0103] Further, as the negative electrode active material, a mixture of a silicon material and a carbon material is more preferable. Since the volume change accompanying charge and discharge of the carbon material is smaller than that of the silicon material, by using a mixture of the silicon material and the carbon material as the negative electrode active material, the influence of the volume change of the silicon material can be mitigated, and the adhesion ability between the active material layer and the current collector can be further improved.

[0104] When silicon (Si) is used as the active material, while silicon has a high capacity, it undergoes a large volume change when storing lithium. For this reason, the silicon material has the property of being pulverized by repeated expansion and contraction, causing peeling from the current collector and separation between the active materials, and the conductive network inside the active material layer is easily disconnected. Due to this property, the charge-discharge durability characteristics of the power storage device deteriorate extremely in a short time.

[0105] The power storage device electrode produced using the slurry for a power storage device electrode according to this embodiment can exhibit good electrical characteristics without causing the above-mentioned problems even when a silicon material is used. The reason for this is considered 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 by storing lithium, the polymer (A) can expand and contract to maintain the state of firmly binding the silicon material.

[0106] The content ratio 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, still more preferably 3 to 45% by mass, and particularly preferably 10 to 40% by mass. When the content ratio of the silicon material in 100% by mass of the active material is within the above range, a power storage device excellent in the balance between the output and energy density improvement of the power storage device and the charge-discharge durability characteristics can be obtained.

[0107] The shape of the active material is preferably particulate. The average particle size of the active material is preferably 0.1 to 100 μm, more preferably 1 to 20 μm. Here, the average particle size of the active material refers to the volume average particle size calculated from the particle size distribution measured using a particle size distribution measuring device with the laser diffraction method as the measurement principle. Examples of such a laser diffraction type particle size distribution measuring device include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by Horiba, Ltd.).

[0108] 2.2.3. Other Components In the slurry for a power storage device electrode according to this embodiment, other components may be added as necessary in addition to the components described above. Examples of such components include polymers other than polymer (A), thickeners, liquid media, conductivity-imparting agents, pH adjusters, corrosion inhibitors, cellulose fibers, and the like. The polymers other than polymer (A) and the thickeners can be appropriately selected from the compounds exemplified in "1.3. Other Additives" above and used in the same purpose and content ratio.

[0109] <Liquid Medium> In the slurry for a power storage device electrode according to this embodiment, in addition to the carry-over from the binder composition for a power storage device, a liquid medium may be further added. The added liquid medium may be of the same type as the liquid medium (B) contained in the binder composition for a power storage device, or may be different, but it is preferably selected from the liquid media exemplified in "1.2. Liquid Medium (B)" above and used.

[0110] The content ratio of the liquid medium (including the carry-over from the binder composition for a power storage device) in the slurry for a power storage device electrode according to this embodiment is preferably such that the solid content concentration in the slurry (the ratio 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% by mass, and more preferably 40 to 60% by mass.

[0111] <Conductive agent> In the slurry for a power storage device electrode according to this embodiment, a conductive agent may be further added for the purpose of imparting conductivity and buffering the volume change of the active material due to the ingress and egress of lithium ions.

[0112] Specific examples of the conductive agent include carbons such as activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black or ketjen black can be preferably used. The content ratio of the conductive agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material.

[0113] <pH adjuster and corrosion inhibitor> In the slurry for a power storage device electrode according to this embodiment, a pH adjuster and / or a corrosion inhibitor may be further added for the purpose of suppressing the corrosion of the current collector according to the type of the active material.

[0114] Examples of the pH adjuster include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferable. It can also be selected and used from among the neutralizing agents described in the method for producing the polymer (A).

[0115] 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, potassium molybdate, etc. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferable.

[0116] <Cellulose fiber> Cellulose fiber may be further added to the slurry for the power storage device electrode according to this embodiment. By adding cellulose fiber, the adhesion of the active material to the current collector may be improved. It is considered that the fibrous cellulose fiber can prevent the active material from falling off and improve the adhesion to the current collector by fibrously binding adjacent active materials by wire adhesion or wire contact.

[0117] The average fiber length of the cellulose fiber can be selected from a wide range of 0.1 to 1000 μm. For example, it is preferably 1 to 750 μm, more preferably 1.3 to 500 μm, still more preferably 1.4 to 250 μm, and particularly preferably 1.8 to 25 μm. If the average fiber length is within the above range, the surface smoothness (coating uniformity) may be good, and the adhesion of the active material to the current collector may be improved.

[0118] The fiber length of the cellulose fiber may be uniform, and the coefficient of variation of the fiber length ([standard deviation of fiber length / average fiber length] × 100) is, for example, preferably 0.1 to 100, more preferably 0.5 to 50, and particularly preferably 1 to 30. The maximum fiber length of the cellulose fiber is, for example, preferably 500 μm or less, more preferably 300 μm or less, still more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0119] When the average fiber length of the cellulose fiber is 5 times or less with respect to the average thickness of the active material layer, it is advantageous because the surface smoothness (coating film uniformity) and the adhesion of the active material to the current collector are further improved. The average fiber length of the cellulose fiber is preferably 0.01 to 5 times, more preferably 0.02 to 3 times, and particularly preferably 0.03 to 2 times with respect to the average thickness of the active material layer.

[0120] The average fiber diameter of the cellulose fiber is preferably 1 nm to 10 μm, more preferably 5 nm to 2.5 μm, still more preferably 20 nm to 700 nm, and particularly preferably 30 nm to 200 nm. When the average fiber diameter is within the above range, the occupied volume of the fiber does not become too large, and the packing density of the active material may be increased. Therefore, the cellulose fiber is preferably a cellulose nanofiber having a nanometer-sized average fiber diameter (for example, a cellulose nanofiber having an average fiber diameter of 10 nm to 500 nm, preferably about 25 nm to 250 nm).

[0121] The fiber diameter of the cellulose fiber is also uniform, and the coefficient of variation of the fiber diameter ([standard deviation of fiber diameter / average fiber diameter] × 100) is preferably 1 to 80, more preferably 5 to 60, and particularly preferably 10 to 50. The maximum fiber diameter of the cellulose fiber is preferably 30 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.

[0122] The ratio of the average fiber length to the average fiber diameter (aspect ratio) of the cellulose fiber is, for example, preferably 10 to 5000, more preferably 20 to 3000, and particularly preferably 50 to 2000. When the aspect ratio is within the above range, the adhesion of the active material to the current collector becomes good, and the surface smoothness (coating film uniformity) of the electrode may become good without weakening the breaking strength of the fiber.

[0123] In the present invention, the average fiber length, the standard deviation of the fiber length distribution, the maximum fiber length, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter may be values calculated from fibers (n = about 20) measured based on electron micrographs.

[0124] The material of the cellulose fiber may be a polysaccharide having a β-1,4-glucan structure. Examples of the cellulose fiber include natural cellulose fibers (pulp fibers) such as cellulose fibers derived from higher plants (e.g., wood fibers (wood pulp such as softwood and hardwood), bamboo fibers, sugarcane fibers, seed hair fibers (e.g., cotton linter, bombax cotton, kapok, etc.), bast fibers (e.g., hemp, kozo, mitsumata, etc.), leaf fibers (e.g., manila hemp, New Zealand hemp, etc.)), cellulose fibers derived from animals (e.g., ascidian cellulose, etc.), cellulose fibers derived from bacteria (e.g., cellulose contained in nata de coco, etc.), and chemically synthesized cellulose fibers (e.g., rayon, cellulose esters (such as cellulose acetate), cellulose ethers (e.g., hydroxyalkyl celluloses such as hydroxyethyl cellulose (HEC) and hydroxypropyl cellulose, alkyl celluloses such as methyl cellulose and ethyl cellulose, etc., cellulose derivatives, etc.)). These cellulose fibers may be used alone or in combination of two or more.

[0125] Among these cellulose fibers, cellulose fibers derived from pulp such as cellulose fibers derived from higher plants (e.g., wood fibers (wood pulp such as softwood and hardwood) and seed hair fibers (such as cotton linter pulp)) are preferred because it is easy to prepare nanofibers having an appropriate aspect ratio.

[0126] The method for manufacturing the cellulose fiber is not particularly limited, and depending on the target fiber length and fiber diameter, conventional methods such as those described in Japanese Patent Publication No. 60-19921, Japanese Patent Application Laid-Open No. 2011-26760, Japanese Patent Application Laid-Open No. 2012-25833, Japanese Patent Application Laid-Open No. 2012-36517, Japanese Patent Application Laid-Open No. 2012-36518, Japanese Patent Application Laid-Open No. 2014-181421, etc. may be used.

[0127] 2.2.4. Method for Preparing Slurry for Electrodes of Energy Storage Devices The slurry for electrodes of the energy storage device according to this embodiment may be manufactured by any method as long as it contains the above-described binder composition for the energy storage device and the active material. From the viewpoint of manufacturing a slurry having better dispersibility and stability more efficiently and inexpensively, it is preferable to add the active material and optional additive components used as necessary to the binder composition for the energy storage device and mix them. Specific manufacturing methods include, for example, the methods described in Japanese Patent No. 5999399 and the like.

[0128] 3. Electrodes of Energy Storage Devices The electrode of the energy storage device according to an embodiment of the present invention includes a current collector and an active material layer formed by applying and drying the above-described slurry for electrodes of the energy storage device on the surface of the current collector. Such an electrode of the energy storage device can be manufactured by applying the above-described slurry for electrodes of the energy storage device on 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 electrode of the energy storage device manufactured in this way has an active material layer containing the above-described polymer (A), the active material, and optional components added as necessary bound to the surface of the current collector, and thus has excellent charge-discharge cycle characteristics and excellent charge-discharge durability characteristics at high temperatures.

[0129] 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. 5999399 and the like.

[0130] In the storage device electrode according to this embodiment, when a silicon material is used as the active material, the content ratio of silicon element in 100% by mass of the active material layer is preferably 2 to 30% by mass, more preferably 2 to 20% by mass, and particularly preferably 3 to 10% by mass. When the content of silicon element in the active material layer is within the above range, in addition to the improvement of the storage capacity of the storage device manufactured using the same, an active material layer with a uniform distribution of silicon element can be obtained. The content of silicon element in the active material layer can be measured, for example, by the method described in Japanese Patent No. 5999399.

[0131] 4. Storage device The storage device according to an embodiment of the present invention includes the above-described storage device electrode, further contains an electrolytic solution, and can be manufactured according to a conventional method using components such as a separator. As a specific manufacturing method, for example, a method of laminating a negative electrode and a positive electrode via a separator, winding, folding, etc. according to the battery shape, storing them in a battery container, injecting an electrolytic solution into the battery container, and sealing it can be mentioned. The shape of the battery can be an appropriate shape such as a coin type, a cylindrical type, a rectangular type, a laminate type, etc.

[0132] The electrolytic solution may be liquid or gel, and may be selected from known electrolytic solutions used in storage devices according to the type of active material so as to effectively exhibit the function as a battery. The electrolytic solution can be a solution in which an electrolyte is dissolved in an appropriate solvent. Examples of such electrolytes and solvents include compounds described in Japanese Patent No. 5999399.

[0133] The above-described storage device is applicable to a lithium ion secondary battery, an electric double layer capacitor, a lithium ion capacitor, etc. that require discharge at a high current density. Among these, a lithium ion secondary battery is particularly preferable. In the storage device electrode and the storage device according to this embodiment, members other than the binder composition for the storage device can be members known for use in lithium ion secondary batteries, electric double layer capacitors, or lithium ion capacitors.

[0134] 5. Examples Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[0135] 5.1. Example 1 5.1.1. Preparation and Physical Property Evaluation of Binder Composition for Energy Storage Device (1) Preparation of Binder Composition for Energy Storage Device A binder composition for an energy storage device containing polymer (A) was obtained by two-stage polymerization as shown below. Into a reactor, 200 parts by mass of water, a monomer mixture consisting of 15 parts by mass of 1,3-butadiene, 15 parts by mass of styrene, and 2 parts by mass of acrylic acid, 0.1 part by mass of tert-dodecyl mercaptan as a chain transfer agent, 0.2 part by mass of sodium alkyl diphenyl ether disulfonic acid as an emulsifier, and 0.2 part by mass of potassium persulfate as a polymerization initiator were charged, and polymerization was carried out at 70 °C for 12 hours while stirring. After confirming that the polymerization conversion rate was 90%, 200 parts by mass of water, 55 parts by mass of styrene, 3 parts by mass of acrylic acid, 5 parts by mass of methyl methacrylate, and 5 parts by mass of acrylonitrile were further added to the reactor, and polymerization was carried out at 75 °C for 12 hours. After confirming that the polymerization conversion rate was 98%, unreacted monomers were removed from the thus-obtained particle dispersion of polymer (A) and concentrated. After adding a 2.5% aqueous sodium hydroxide solution, water was removed using an evaporator to obtain a binder composition for an energy storage device containing particles of polymer (A) with a solid content concentration of 40% by mass and a pH of 8.0.

[0136] (2) Measurement of Number Average Particle Diameter A latex obtained by diluting the binder composition for the power storage device obtained above to 0.1 wt% was dropped dropwise onto a collodion support film with a pipette, and further, a 0.02 wt% osmium tetroxide solution was dropped dropwise onto the collodion support film with a pipette and air-dried for 12 hours to prepare a sample. The sample thus prepared was observed at a magnification of 10K using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corporation, model number "H-7650"), and image analysis was performed using the program of HITACHI EMIP, and the number average particle diameter of 50 randomly selected polymer (A) particles was calculated. The measurement results are shown in Table 1.

[0137] (3) Measurement of pH Regarding the binder composition for the power storage device obtained above, when the pH at 25 °C was measured using a pH meter (manufactured by Horiba, Ltd.), it was confirmed that the pH was 8.0.

[0138] (4) Measurement of electrolyte swelling degree The polymer (A) obtained above was dried in a constant temperature bath at 85 °C for 24 hours to prepare a film. 1 g of this film was immersed in 20 mL of a mixed solution composed of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) (EC / DEC / EMC = 1 / 1 / 1 (volume ratio), hereinafter this mixed solution is referred to as "EC / DEC / EMC") and shaken at 70 °C for 24 hours. Then, after filtering through a 300-mesh wire mesh to separate the insoluble matter, the weight (Y (g)) of the residue obtained by evaporating and removing the dissolved EC / DEC / EMC was measured. Also, after removing the EC / DEC / EMC adhering to the surface of the insoluble matter (film) separated by the above filtration by absorbing it with paper, the weight (Z (g)) of the insoluble matter (film) was measured. When the electrolyte swelling degree was measured by the following formula (2), the electrolyte swelling degree of the above polymer (A) was 160 mass%. Electrolyte swelling degree (mass%) = (Z / (1 - Y)) × 100 (2)

[0139] (5) Measurement of dynamic viscoelasticity The polymer (A) obtained above was dried at 40 °C for 24 hours to prepare a uniform film with a thickness of 1.0 ± 0.3 mm. This film was dried in a vacuum dryer at 160 °C for 30 minutes. The film taken out from the vacuum dryer and cut into strips of 10 mm × 10 mm was used as a measurement sample. Next, using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, model "MCR 301"), the measurement sample was fixed with a parallel plate (product name "PP-12"), and dynamic viscoelasticity was measured in the temperature range of -70 °C to 180 °C under the measurement conditions of shear mode, measurement frequency of 0.01 to 1 Hz, and temperature rising speed of 0.1 °C / min. As a result, the peak top of tanδ on the low temperature side (tanδ-1) was observed at 10 °C, and its value was 0.02. Also, the peak top of tanδ on the high temperature side (tanδ-2) was observed at 120 °C, and its value was 1.0. In Tables 1 to 3 below, the peak top of tanδ on the low temperature side is represented as "tanδ-1", and the tanδ on the high temperature side is represented as "tanδ-2".

[0140] (6) Measurement of Martens hardness About 1 g of the polymer (A) obtained above was added onto a Si wafer of about 1 cm × 1 cm, and a thin film was prepared using a spin coater (manufactured by Mikasa Co., Ltd., model "MS-A-150") and dried on a hot plate. When the Martens hardness of this thin film was calculated using a micro indenter (manufactured by Helmut Fischer, model "HM500"), it was 300 MPa.

[0141] 5.1.2. Preparation of slurry for the electrode of the energy storage device (1) Synthesis of silicon material (active material) A mixture of pulverized silicon dioxide powder (average particle diameter 10 μm) and carbon powder (average particle diameter 35 μm) was heat-treated in an electric furnace with the temperature adjusted in the range of 1100 °C to 1600 °C under a nitrogen stream (0.5 NL / min) for 10 hours, and the composition formula is SiO xSilicon oxide powder (average particle size 8 μm) represented by (x = 0.5 to 1.1) was obtained. 300 g of this silicon oxide powder was charged into a batch heating furnace, and while maintaining a reduced pressure of 100 Pa absolute pressure with a vacuum pump, the temperature was raised from room temperature (25 °C) to 1100 °C at a heating rate of 300 °C / h. Next, while maintaining the pressure in the heating furnace at 2000 Pa, methane gas was introduced at a flow rate of 0.5 NL / min, and a heat treatment (graphite coating treatment) was performed at 1100 °C for 5 hours. After the graphite coating treatment was completed, it was cooled to room temperature at a cooling rate of 50 °C / h to obtain approximately 330 g of graphite-coated silicon oxide powder. This graphite-coated silicon oxide is a conductive powder (active material) in which the surface of silicon oxide is coated with graphite, its average particle size is 10.5 μm, and when the entire obtained graphite-coated silicon oxide is taken as 100% by mass, the proportion of the graphite coating is 2% by mass.

[0142] (2) Preparation of slurry for storage device electrode Into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK Hibis Mix 2P-03"), 1 part by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation, added as an aqueous solution with a solid content conversion value and a concentration of 2% by mass), 4 parts by mass of polymer (A) (solid content conversion value, added as the binder composition for the storage device obtained above), 90.25 parts by mass of artificial graphite (manufactured by Showa Denko Materials Co., Ltd., trade name "MAG"), which is highly crystalline graphite as the negative electrode active material (solid content conversion value), 4.75 parts by mass of the graphite-coated silicon oxide powder obtained above (solid content conversion value), and 1 part by mass of carbon (acetylene black, manufactured by Denka Co., Ltd.) as a conductivity-imparting agent were charged and 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 using a stirring and defoaming machine (manufactured by Shin-Kee Co., Ltd., trade name "Awa Toriren Taro"), it was stirred and mixed at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under reduced pressure (about 2.5×10 4 Pa) to prepare a slurry for a storage device electrode containing 5% by mass of Si in the negative electrode active material (C / Si = 95 / 5).

[0143] In addition, a slurry for a storage device electrode (C / Si = 100 / 0) that does not contain Si in the negative electrode active material was prepared in the same manner as the slurry for a storage device electrode (C / Si = 95 / 5), except that the usage amounts of artificial graphite and silicon-coated graphite powder were adjusted.

[0144] 5.1.3. Manufacture and Evaluation of Storage Devices (1) Manufacture of Storage Device Electrode (Negative Electrode) On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for a storage device electrode (C / Si = 95 / 5 or C / Si = 100 / 0) obtained above was uniformly applied by the doctor blade method so that the film thickness after drying would be 80 μm, dried at 60 °C for 10 minutes, and then dried at 120 °C for 10 minutes. Thereafter, by pressing with a roll press so that the density of the active material layer would be 1.5 g / cm 3 a storage device electrode (negative electrode) was obtained.

[0145] (2) Evaluation of Adhesion Strength of Negative Electrode Coating Layer On the surface of the storage device electrode obtained above, using a knife, ten cuts were made vertically and horizontally at 2 mm intervals reaching from the active material layer to the depth of the current collector to create a grid of cuts. An adhesive tape with a width of 18 mm (manufactured by Nichiban Co., Ltd., trade name "Cellotape" (registered trademark), specified in JIS Z1522) was attached to these cuts and immediately peeled off, and the degree of dropout of the active material was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 1. (Evaluation Criteria) · 5 points: The number of dropouts of the active material layer is 0. · 4 points: The number of dropouts of the active material layer is 1 - 5. · 3 points: The number of dropouts of the active material layer is 6 - 20. · 2 points: The number of dropouts of the active material layer is 21 - 40. · 1 point: The number of dropouts of the active material layer is 41 or more.

[0146] (3) Manufacture of Counter Electrode (Positive Electrode) To a two-axis planetary mixer (manufactured by Primix Corporation, product name "TK Hibiscus Mix 2P-03"), 4 parts by mass (in terms of solid content) of a binder for electrochemical device electrodes (manufactured by Kuraray Co., Ltd., product name "KF Polymer #1120"), 3.0 parts by mass of a conductive assistant (manufactured by Denka Co., Ltd., product name "Denka Black 50% pressed product"), 100 parts by mass (in terms of solid content) of LiCoO with an average particle diameter of 5 μm as a positive electrode active material 2 (manufactured by Hayashi Kasei Co., Ltd.) and 36 parts by mass of N-methylpyrrolidone (NMP) were added, and stirring was carried out at 60 rpm for 2 hours. NMP was added to the obtained paste, and after adjusting the solid content concentration to 65% by mass, using a stirring and defoaming machine (manufactured by Shin-Kei Co., Ltd., product name "Awa Toriren Tarou"), stirring and mixing were carried out at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under reduced pressure (about 2.5×10 4 Pa) to prepare a positive electrode slurry. This positive electrode slurry was uniformly applied onto the surface of a current collector made of aluminum foil by the doctor blade method so that the film thickness after solvent removal was 80 μm, and heated at 120 °C for 20 minutes to remove the solvent. Then, by pressing with a roll press machine so that the density of the active material layer was 3.0 g / cm 3 , a counter electrode (positive electrode) was obtained.

[0147] (4) Assembly of lithium-ion battery cells In a glove box purged with Ar so that the dew point was -80 °C or lower, a negative electrode manufactured above and punched and formed into a diameter of 15.95 mm was placed on a two-pole coin cell (manufactured by Hozen Co., Ltd., product name "HS Flat Cell"). Next, a separator made of a polypropylene porous membrane punched into a diameter of 24 mm (manufactured by Celgard LLC, product name "Celgard #2400") was placed, and after injecting 500 μL of electrolyte so that no air entered, a positive electrode manufactured above and punched and formed into a diameter of 16.16 mm was placed, and the outer body of the two-pole coin cell was closed and sealed with a screw to assemble a lithium-ion battery cell (power storage device). The electrolyte used here was LiPF in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio)6 It is a solution dissolved at a concentration of 1 mol / L.

[0148] (5) Evaluation of charge-discharge cycle characteristics Regarding the power storage device manufactured above, in a thermostatic bath adjusted to 60°C, charging was started at a constant current (1.0C), and when the voltage reached 4.2V, charging was continued at a constant voltage (4.2V). The point when the current value reached 0.01C was defined as the end of charging (cut-off). Then, discharging was started at a constant current (1.0C), and the point when the voltage reached 3.0V was defined as the end of discharging (cut-off), and the discharge capacity of the first cycle was calculated. In this way, 100 charge-discharge cycles were repeated. The capacity retention rate was calculated by the following formula (3) and evaluated according to the following criteria. The evaluation results are shown in Table 1. Capacity retention rate (%) =(Discharge capacity of the 100th cycle) / (Discharge capacity of the first cycle) (3) (Evaluation criteria) · 5 points: The capacity retention rate is 95% or more. · 4 points: The capacity retention rate is 90% or more and less than 95%. · 3 points: The capacity retention rate is 85% or more and less than 90%. · 2 points: The capacity retention rate is 80% or more and less than 85%. · 1 point: The capacity retention rate is 75% or more and less than 80%. · 0 point: The capacity retention rate is less than 75%.

[0149] (6) Evaluation of resistance at high temperature Regarding the power storage device manufactured above, in a thermostat adjusted to 60°C, charging was started at a constant current (1.0C), and when the voltage reached 4.2V, charging was continued at a constant voltage (4.2V). When the current value reached 0.01C, the charging was completed (cut-off). Thereafter, discharging was started at a constant current (0.05C), and when the voltage reached 3.0V, the discharging was completed (cut-off), and the discharge capacity at the 0th cycle was calculated. Further, charging was started at a constant current (1.0C), and when the voltage reached 4.2V, charging was continued at a constant voltage (4.2V). When the current value reached 0.01C, the charging was completed (cut-off). Thereafter, discharging was started at a constant current (1.0C), and when the voltage reached 3.0V, the discharging was completed (cut-off), and the discharge capacity at the 1st cycle was calculated. In this way, 100 charge-discharge cycles were repeated. After repeating 100 charge-discharge cycles, charge-discharge was performed in the same manner as in the 0th cycle, the discharge capacity at the 101st cycle was evaluated, the resistance increase rate was calculated by the following formula (4), and the evaluation was made according to the following criteria. Resistance increase rate (%) =(Discharge capacity at the 101st cycle - Discharge capacity at the 100th cycle) / (Discharge capacity at the 0th cycle - Discharge capacity at the 1st cycle) × 100 (4) (Evaluation criteria) ·5 points: The resistance increase rate is 100% or more and less than 150%. ·4 points: The resistance increase rate is 150% or more and less than 200%. ·3 points: The resistance increase rate is 200% or more and less than 250%. ·2 points: The resistance increase rate is 250% or more and less than 300%. ·1 point: The resistance increase rate is 300% or more and less than 350%. ·0 points: The resistance increase rate is 350% or more.

[0150] Note that in the measurement conditions, "1C" indicates the current value at which a cell having a certain capacitance is discharged at a constant current and the discharge ends in 1 hour. For example, "0.1C" indicates the current value at which the discharge ends in 10 hours, and "10C" indicates the current value at which the discharge ends in 0.1 hour.

[0151] 5.2. Examples 2 to 12, Comparative Examples 1 to 5 In the above "5.1.1. Preparation and Physical Property Evaluation of Binder Composition for Energy Storage Device (1) Preparation of Binder Composition for Energy Storage Device", except that the types and amounts of each monomer and the amount of emulsifier were as described in Tables 1 to 3 below, binder compositions for energy storage devices containing polymer particles with a solid content concentration of 40% by mass were obtained in the same manner, and each physical property was evaluated. In addition, Fig. 1 shows a graph representing the relationship between the measurement temperature and tanδ in the dynamic viscoelasticity measurement of the film prepared in Example 3.

[0152] Furthermore, except that the binder compositions for energy storage devices prepared above were used, slurry for energy storage device electrodes was prepared in the same manner as in Example 1 above, energy storage device electrodes and energy storage devices were manufactured respectively, and evaluated in the same manner as in Example 1 above.

[0153] 5.3. Example 13 In Example 4, except that the thickener was 0.9 parts by mass of CMC (trade name "CMC2200", manufactured by Daicel Corporation) and 0.1 parts by mass of CNF (trade name "Cellish KY-100G", manufactured by Daicel Corporation, fiber diameter 0.07 μm), slurry for energy storage device electrodes was prepared in the same manner as in Example 4, energy storage device electrodes and energy storage devices were manufactured respectively, and evaluated in the same manner as in Example 1 above. The results are shown in Table 4 below.

[0154] 5.4. Example 14 In Example 4, except that the thickener was 0.8 parts by mass of CMC (trade name "CMC2200", manufactured by Daicel Corporation) and 0.2 parts by mass of CNF (trade name "Cellish KY-100G", manufactured by Daicel Corporation, fiber diameter 0.07 μm), slurry for energy storage device electrodes was prepared in the same manner as in Example 4, energy storage device electrodes and energy storage devices were manufactured respectively, and evaluated in the same manner as in Example 1 above. The results are shown in Table 4 below.

[0155] 5.5. Evaluation Results Tables 1 to 3 below show the polymer compositions, the results of measuring each physical property, and the results of each evaluation used in Examples 1 to 12 and Comparative Examples 1 to 5. Table 4 below shows the polymer component compositions used in Examples 13 and 14 and the results of each evaluation.

[0156]

Table 1

[0157]

Table 2

[0158]

Table 3

[0159]

Table 4

[0160] The abbreviations of the monomers and thickeners in the above Tables 1 to 4 represent the following compounds, respectively. <Conjugated diene compound> · BD: 1,3 - butadiene <Unsaturated carboxylic acid> · TA: Itaconic acid · AA: Acrylic acid · MAA: Methacrylic acid <Aromatic vinyl compound> · ST: Styrene · DVB: Divinylbenzene <Unsaturated carboxylic acid ester> · 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 compound> ·AN: Acrylonitrile <(Meth)acrylamide> ·AAM: Acrylamide ·MAM: Methacrylamide <Compound having a sulfonic acid group> ·NASS: Sodium styrene sulfonate <Thickener> ·CMC: Trade name "CMC2200", manufactured by Daicel Corporation, Sodium carboxymethyl cellulose ·CNF: Trade name "Cellish KY-100G", manufactured by Daicel Corporation, Microfibrillar cellulose, fiber diameter 0.07 μm

[0161] As is clear from Table 1 to Table 2 above, the slurry for a power storage device electrode prepared using the binder composition for a power storage device according to the present invention shown in Examples 1 to 12 can preferably bind active materials to each other and suppress the fusion of particles in the electrode as compared with the cases of Comparative Examples 1 to 5. As a result, the internal resistance can be reduced, and a power storage device electrode having good charge and discharge durability characteristics at high temperatures can be obtained. The reason for this is that the polymer (A) contained in the binder compositions of Examples 1 to 12 shown in Table 1 to Table 2 above has one peak top temperature Tp (°C) of tan δ-1 in the range of -40°C or more and less than 50°C as compared with the cases of Comparative Examples 1 to 5 shown in Table 3 above, which suggests high viscosity. It is presumed that this can maintain a high binding force. Furthermore, the peak top temperature Tp (°C) of tan δ-2 of the polymer (A) exists in the range of 50°C or more and 150°C or less, which suggests that the crosslinking degree of the polymer on the high temperature side is high. As a result, it becomes possible to maintain the particle shape of the binder during electrode formation. Thereby, it is presumed that the permeability of the electrolyte between the active materials is not inhibited and a low resistance can be achieved, and as a result, good repeated charge and discharge characteristics and good charge and discharge durability characteristics at high temperatures are shown.

[0162] Also, as is clear from the results in Table 4 above, the slurry for a power storage device electrode prepared using the binder composition for a power storage device according to the present invention shown in Examples 13 and 14 can suitably bind active materials to each other even when CNF as a thickener is used in combination, and it has been found that the adhesion between the active material layer and the current collector can be maintained well.

[0163] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations having the same functions, methods, and results, or configurations having the same objectives and effects). 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 includes configurations that exhibit the same operational effects as the configurations described in the above embodiments or configurations that can achieve the same objectives. Furthermore, the present invention also includes configurations in which known techniques are added to the configurations described in the above embodiments.

Claims

1. Comprising a polymer (A) and a liquid medium (B), when the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) is, 15 to 60% by mass of repeating units (a1) derived from a conjugated diene compound, 1 to 10% by mass of repeating units (a2) derived from an unsaturated carboxylic acid, containing, there is one peak top of tanδ (loss elastic modulus / storage elastic modulus) of the dynamic viscoelasticity of the polymer (A) in the range of -40°C or higher and less than 50°C, and one in the range of 50°C or higher and 150°C or lower, when the tanδ of the peak top in the range of -40°C or higher and less than 50°C is tanδ(Tp1) and the tanδ of the peak top in the range of 50°C or higher and 150°C or lower is tanδ(Tp2), a binder composition for a power storage device that satisfies the relationship of the following formula (1). tanδ(Tp2) / tanδ(Tp1) ≥ 0.5 (1)

2. The polymer (A) further contains 35 to 75% by mass of repeating units (a3) derived from an aromatic vinyl compound, The binder composition for a power storage device according to claim 1, wherein the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) is 80% by mass or more.

3. The polymer (A) contains at least one of repeating units (a4) derived from an unsaturated carboxylic acid ester and repeating units (a5) derived from an α,β-unsaturated nitrile compound, The binder composition for a power storage device according to claim 1, wherein the total amount of the repeating unit (a1), the repeating unit (a2), the repeating unit (a4), and the repeating unit (a5) is 65% by mass or more.

4. The binder composition for a power storage device according to any one of claims 1 to 3, wherein the Martens hardness calculated using a pico indenter of the polymer (A) is 15 MPa or more.

5. The polymer (A) is polymer particles, The binder composition for a power storage device according to any one of claims 1 to 4, wherein the number average particle diameter of the polymer particles is 50 nm or more and 500 nm or less.

6. The binder composition for a power storage device according to any one of claims 1 to 5, wherein the liquid medium (B) is water.

7. A slurry for a power storage device electrode containing the binder composition for a power storage device according to any one of claims 1 to 6 and an active material.

8. The slurry for a storage device electrode according to claim 7, containing a silicon material as the active material.

9. A storage device electrode comprising a current collector and an active material layer formed by applying and drying the slurry for a storage device electrode according to claim 7 or claim 8 on the surface of the current collector.

10. A storage device comprising the storage device electrode according to claim 9.

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