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

Abstract

Provided is a binder composition for a power storage device, which has excellent adhesion, is capable of producing a power storage device electrode in which expansion of the electrode accompanying repeated charging and discharging is suppressed, and is capable of improving the cycle life characteristics of the power storage device. This binder composition for an electricity storage device contains a polymer (A) and a liquid medium (B), and when the total of the repeating units contained in the polymer (A) is taken as 100 parts by mass, the content of the repeating units contained in the polymer (A) is less than or equal to 100 parts by mass. The polymer (A) contains 50-80 parts by mass of a repeating unit (a1) derived from a conjugated diene compound, 15-49 parts by mass of a repeating unit (a2) derived from an aromatic vinyl compound, and 0.1-10 parts by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid, and the peak top of the dynamic viscoelasticity tan [delta] (loss elastic modulus / storage elastic modulus) is 1 in the range of-50 DEG C to 10 DEG C; the present invention is characterized in that there is one in the range of 150 DEG C to 250 DEG C, and when the tan [delta] at the peak top in the range of-50 DEG C to 10 DEG C is represented by tan [delta] (Tp1) and the tan [delta] at the peak top in the range of 150 DEG C to 250 DEG C is represented by tan [delta] (Tp2), the relationship represented by formula (1) is satisfied. (1) tan [delta] (Tp2) / tan [delta] (Tp1) < 0.5.

Description

Technical Field

[0001] This invention relates to adhesive compositions for energy storage devices, slurries for electrodes of energy storage devices, electrodes for energy storage devices, and energy storage devices. Background Technology

[0002] In recent years, high-voltage and high-energy-density energy storage devices have become essential power sources for electronic devices. Lithium-ion batteries and lithium-ion capacitors are among the most anticipated such devices.

[0003] The electrodes used in such energy storage devices are manufactured by coating the surface of the current collector with a composition containing active materials and a polymer that functions as a binder (energy storage device electrode slurry) and then drying it. The desired properties of the polymer used as a binder include the ability of the active materials to bond with each other and the ability of the active materials to adhere tightly to the current collector, as well as the resistance to powdering when the coated and dried composition film (hereinafter also referred to as the "active material layer") is cut. By ensuring good adhesion through such a binder material, the internal resistance of the battery caused by the binder material is reduced, thus imparting good charge and discharge characteristics to the energy storage device.

[0004] It should be noted that experience shows that the binding ability of the aforementioned active materials to each other, the adhesion ability of the active materials to the current collector, and the performance of anti-dust shedding are roughly proportional. Therefore, in this specification, the term "adhesion" is sometimes used to refer to these properties.

[0005] On the other hand, in order to achieve higher capacity in energy storage devices, materials with high lithium-ion absorption capacity have been studied. The active material obtained using materials with high lithium-ion absorption capacity exhibits significant volume changes due to lithium-ion absorption and release. Therefore, if conventional electrode binders are used with such materials with high lithium absorption capacity, it is impossible to maintain a tight seal, leading to active material peeling and a significant capacity reduction with each charge and discharge cycle.

[0006] As a technique for improving the adhesion of electrode binders, techniques for controlling the surface acidity of particulate binder particles have been proposed (see Patent Documents 1 and 2), and techniques for using binders with epoxy groups and hydroxyl groups to improve the above properties have been proposed (see Patent Documents 3 and 4). In addition, a technique for using the rigid molecular structure of polyimide to bind the active material and suppress the volume change of the active material has been proposed (see Patent Document 5).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2011 / 096463

[0010] Patent Document 2: International Publication No. 2013 / 191080

[0011] Patent Document 3: Japanese Patent Application Publication No. 2010-205722

[0012] Patent Document 4: Japanese Patent Application Publication No. 2010-3703

[0013] Patent Document 5: Japanese Patent Application Publication No. 2011-204592 Summary of the Invention

[0014] However, the electrode binders disclosed in Patent Documents 1-5 above cannot be said to provide sufficient adhesion when applying novel active materials, such as silicon materials, which have a large lithium-ion adsorption capacity and a large volume change associated with lithium-ion adsorption and release. If such electrode binders are used, the active material will detach due to repeated charging and discharging, leading to electrode deterioration. Therefore, there is a problem that the durability required for practical application cannot be fully obtained.

[0015] Some aspects of the present invention involve providing an adhesive composition for a storage device that can produce storage device electrodes with excellent sealing while suppressing electrode expansion during repeated charging and discharging, and can improve the cycle life characteristics of the storage device.

[0016] This invention is made to solve at least a part of the above-mentioned problems and can be implemented in any of the following ways.

[0017] One embodiment of the adhesive composition for energy storage devices of the present invention comprises a polymer (A) and a liquid medium (B).

[0018] When the total number of repeating units contained in the polymer (A) is set to 100 parts by mass, the polymer (A) contains:

[0019] 50–80 parts by mass of repeating unit (a1) from conjugated diene compounds

[0020] 15–49 parts by mass of repeating unit (a2) from aromatic vinyl compounds, and

[0021] 0.1–10 parts by mass from repeating units (a3) ​​of unsaturated carboxylic acids,

[0022] The dynamic viscoelasticity of the polymer (A) exhibits one tanδ (loss modulus / storage modulus) peak in the range of -50℃ to 10℃, and another peak in the range of 150℃ to 250℃.

[0023] When the tanδ of the peak in the range of -50℃ to 10℃ is set as tanδ(Tp1), and the tanδ of the peak in the range of 150℃ to 250℃ is set as tanδ(Tp2), the following relationship (1) is satisfied.

[0024] tanδ(Tp2) / tanδ(Tp1)<0.5 (1).

[0025] In one embodiment of the above-mentioned adhesive composition for storage devices, the relaxation time of protons when latex containing 10% solids of the above-mentioned polymer (A) is measured by pulsed NMR CPMG method can be 1500 ms or more.

[0026] In any of the above-described adhesive compositions for energy storage devices, the total amount of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) ​​may be 80 parts by mass or more.

[0027] In any of the above-described adhesive compositions for storage devices, the polymer (A) may further contain 0.1 to 10 parts by mass of repeating units (a4) derived from unsaturated carboxylic acid esters.

[0028] In any of the above-described adhesive compositions for storage devices, the polymer (A) may further contain 0.1 to 10 parts by mass of repeating units (a5) from α,β-unsaturated nitrile compounds.

[0029] In any of the above-mentioned adhesive compositions for storage devices, the electrolyte swelling ratio of the polymer (A) can be 100 to 350%.

[0030] In any of the above-mentioned adhesive compositions for storage devices, the polymer (A) is polymer particles, and the number-average particle size of the polymer particles can be 50 nm to 500 nm.

[0031] In any of the above-mentioned adhesive compositions for storage devices, the surface acidity of the polymer particles can be 0.05 mmol / g to 1 mmol / g.

[0032] In any of the above-mentioned adhesive compositions for energy storage devices, the liquid medium (B) may be water.

[0033] One embodiment of the slurry for the electrode of the energy storage device of the present invention comprises an adhesive composition for energy storage devices and an active substance according to any of the above embodiments.

[0034] In one embodiment of the slurry for the electrodes of the aforementioned energy storage device, silicon material may be included as the active material.

[0035] One embodiment of the energy storage device electrode of the present invention comprises: a current collector and an active material layer formed by coating the surface of the current collector with a slurry for energy storage device electrode of any of the above embodiments and drying it.

[0036] One embodiment of the energy storage device of the present invention includes the energy storage device electrodes of the above embodiment.

[0037] The adhesive composition for energy storage devices according to the present invention can produce energy storage device electrodes that exhibit excellent sealing while suppressing electrode expansion during repeated charging and discharging, thereby improving the cycle life characteristics of the energy storage device. Attached Figure Description

[0038] Figure 1 This is a graph showing the relationship between the measurement temperature and tanδ in the dynamic viscoelasticity measurement of the membrane prepared in Example 5. Detailed Implementation

[0039] The preferred embodiments of the present invention will now be described in detail. It should be noted that the present invention is not limited to the embodiments described below, but can be understood to include various modifications implemented without altering the spirit of the invention.

[0040] In this specification, "(meth)acrylic acid ~" means "acrylic acid ~" or "methacrylic acid ~", "~(meth)acrylate" means "~acrylate" or "~methacrylate", and "(meth)acrylamide" means "acrylamide" or "methacrylamide".

[0041] In this specification, a numerical range such as "X~Y" can be interpreted as including the value X as the lower limit and the value Y as the upper limit.

[0042] 1. Adhesive composition for energy storage devices

[0043] An adhesive composition for an energy storage device according to one embodiment of the present invention comprises a polymer (A) and a liquid medium (B). When the total number of repeating units contained in the polymer (A) is set to 100 parts by mass, the polymer (A) contains 50 to 80 parts by mass of repeating units (a1) from a conjugated diene compound, 15 to 49 parts by mass of repeating units (a2) from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating units (a3) ​​from an unsaturated carboxylic acid. Furthermore, the polymer (A) has one peak in the dynamic viscoelasticity tanδ (loss modulus / storage modulus) in the range of -50°C to 10°C and one peak in the range of 150°C to 250°C. When the tanδ of the peak in the range of -50°C to 10°C is set to tanδ(Tp1), and the tanδ of the peak in the range of 150°C to 250°C is set to tanδ(Tp2), the following relationship (1) is satisfied.

[0044] tanδ(Tp2) / tanδ(Tp1)<0.5 (1)

[0045] The adhesive composition for energy storage devices according to this embodiment can be used as a material for manufacturing energy storage device electrodes (active material layers) that improves the bonding ability between active materials, the adhesion between active materials and current collectors, and resistance to powder shedding. It can also be used as a material for manufacturing a protective film to suppress short circuits caused by dendrites generated during charging and discharging. Hereinafter, each component included in the adhesive composition for energy storage devices according to this embodiment will be described in detail.

[0046] 1.1. Polymer (A)

[0047] The adhesive composition for energy storage devices according to this embodiment contains a polymer (A). The polymer (A) can be in a latex form dispersed in a liquid medium (B) described later, or it can be dissolved in the liquid medium (B), preferably in a latex form dispersed in the liquid medium (B). If the polymer (A) is in a latex form dispersed in the liquid medium (B), the stability of the energy storage device electrode slurry (hereinafter also referred to as "slurry") prepared by mixing with the active material becomes good, and the coating properties of the slurry on the current collector also become good, which is therefore preferred.

[0048] The following descriptions will be presented in the order of repeating units constituting polymer (A), physical properties of polymer (A), and manufacturing method.

[0049] 1.1.1. Repeating units constituting polymer (A)

[0050] When the total number of repeating units contained in polymer (A) is set to 100 parts by mass, polymer (A) contains 50 to 80 parts by mass of repeating unit (a1) (hereinafter also simply referred to as "repeating unit (a1)") from a conjugated diene compound, 15 to 49 parts by mass of repeating unit (a2) (hereinafter also simply referred to as "repeating unit (a2)") from an aromatic vinyl compound, and 0.1 to 10 parts by mass of repeating unit (a3) ​​(hereinafter also simply referred to as "repeating unit (a3)") from an unsaturated carboxylic acid. In addition to repeating units (a1), repeating units (a2), and repeating units (a3), polymer (A) may also contain repeating units from other monomers that can copolymerize with them.

[0051] 1.1.1.1. Repeating unit (a1) from conjugated diene compounds

[0052] When the total number of repeating units contained in polymer (A) is set to 100 parts by mass, the content of repeating units (a1) from the conjugated diene compound is 50 to 80 parts by mass. The lower limit of the content of repeating units (a1) is preferably 52 parts by mass, more preferably 55 parts by mass. The upper limit of the content of repeating units (a1) is preferably 78 parts by mass, more preferably 75 parts by mass. By containing repeating units (a1) in polymer (A) within the above range, the dispersion of active material and filler becomes good, and a homogeneous active material layer and protective film can be formed. Therefore, structural defects of the electrode plate are reduced, and good charge-discharge characteristics are exhibited. In addition, polymer (A) can impart stretchability to the surface of the coated active material. The stretching of polymer (A) can improve the adhesion, thus exhibiting good charge-discharge durability characteristics.

[0053] The conjugated diene compound is not particularly limited, and examples include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene, etc., and one or more of them may be used. Among them, 1,3-butadiene is particularly preferred.

[0054] 1.1.1.2. Repeating units (a2) from aromatic vinyl compounds

[0055] When the total number of repeating units contained in polymer (A) is set to 100 parts by mass, the content of repeating units (a2) from aromatic vinyl compounds is 15 to 49 parts by mass. The lower limit of the content of repeating units (a2) is preferably 17 parts by mass, more preferably 20 parts by mass. The upper limit of the content of repeating units (a2) is preferably 47 parts by mass, more preferably 45 parts by mass. By including repeating units (a2) in polymer (A) within the above range, the fusion of polymers (A) dispersed in the active material layer can be suppressed, resulting in good slurry properties and improved coatability. In addition, due to the improved permeability of the electrolyte, good repeated charge-discharge characteristics are exhibited. Furthermore, it sometimes exhibits good adhesion to silicon materials, graphite, etc., used as active materials, resulting in electrodes for energy storage devices with excellent adhesion.

[0056] As an aromatic vinyl compound, there is no particular limitation, and examples include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used. Among them, styrene is particularly preferred.

[0057] 1.1.1.3. Repeating unit (a3) ​​from unsaturated carboxylic acids

[0058] Polymer (A) may contain repeating units (a3) ​​derived from unsaturated carboxylic acids. When the total number of repeating units in polymer (A) is set to 100 parts by mass, the proportion of repeating units (a3) ​​derived from unsaturated carboxylic acids is preferably 0.1 to 10 parts by mass. The lower limit of the proportion of repeating units (a3) ​​is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the proportion of repeating units (a3) ​​is preferably 9 parts by mass, more preferably 8 parts by mass. By including repeating units (a3) ​​within the above range in polymer (A), the adhesion between the current collector and the active material layer can be improved, resulting in increased electrode adhesion strength.

[0059] The unsaturated carboxylic acid is not particularly limited, and examples include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. One or more of these can be used. Preferably, one or more of acrylic acid, methacrylic acid, and itaconic acid are used.

[0060] 1.1.1.4. Other repeating units

[0061] In addition to repeating units (a1), (a2), and (a3), polymer (A) may also contain repeating units from other monomers that can copolymerize with it. Examples of such repeating units include repeating units (a4) from unsaturated carboxylic acid esters (hereinafter also simply referred to as "repeating unit (a4)"), repeating units (a5) from α,β-unsaturated nitrile compounds (hereinafter also simply referred to as "repeating unit (a5)"), repeating units (a6) from (meth)acrylamide (hereinafter also simply referred to as "repeating unit (a6)"), repeating units (a7) from compounds having sulfonic acid groups (hereinafter also simply referred to as "repeating unit (a7)"), and repeating units from cationic monomers.

[0062] <Repeating unit (a4) from unsaturated carboxylic acid esters>

[0063] Polymer (A) may contain repeating units (a4) derived from unsaturated carboxylic acid esters. When the total number of repeating units in polymer (A) is set to 100 parts by mass, the proportion of repeating units (a4) is preferably 0.1 to 10 parts by mass. The lower limit of the proportion of repeating units (a4) is preferably 1 part by mass, more preferably 2 parts by mass. The upper limit of the proportion of repeating units (a4) is preferably 9 parts by mass, more preferably 8 parts by mass. By including repeating units (a4) within the above range in polymer (A), the affinity between polymer (A) and the electrolyte becomes good, and in some cases, the increase in internal resistance in the energy storage device caused by the binder becoming a resistive component can be suppressed.

[0064] Among unsaturated carboxylic acid esters, (meth)acrylates are preferred. Specific examples of (meth)acrylates include, for instance, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol dimethacrylate, and propylene glycol dimethacrylate. Diol esters, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 6-hydroxyhexyl methacrylate, glyceryl mono(meth)acrylate, and glyceryl di(meth)acrylate, etc., may be used, with one or more selected from them. Preferably, one or more selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl methacrylate are used, with methyl methacrylate being particularly preferred.

[0065] <Repeating unit (a5) from α,β-unsaturated nitrile compounds>

[0066] Polymer (A) may contain repeating units (a5) from α,β-unsaturated nitrile compounds. When the total number of repeating units contained in polymer (A) is set to 100 parts by mass, the content of repeating units (a5) is preferably 0.1 to 10 parts by mass. The lower limit of the content of repeating units (a5) is preferably 1 part by mass, more preferably 2 parts by mass. The upper limit of the content of repeating units (a5) is preferably 9 parts by mass, more preferably 8 parts by mass. By containing repeating units (a5) in polymer (A) within the above range, the solubility of polymer (A) in electrolyte can be reduced, the affinity of polymer (A) for electrolyte becomes good, and sometimes the increase in internal resistance caused by the binder becoming a resistive component in energy storage devices can be suppressed.

[0067] The α,β-unsaturated nitrile compound is not particularly limited, and examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, dicyanoethylene, etc., and one or more selected from these can be used. Among them, one or more selected from acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0068] <Repeating unit (a6) from (meth)acrylamide>

[0069] Polymer (A) may contain repeating units (a6) derived from (meth)acrylamide. When the total number of repeating units in polymer (A) is set to 100 parts by mass, the proportion of repeating units (a6) is preferably 0 to 8 parts by mass. The lower limit of the proportion of repeating units (a6) is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the proportion of repeating units (a6) is preferably 7 parts by mass, more preferably 6 parts by mass. By including repeating units (a6) in polymer (A) within the above range, the dispersion of the active material and filler in the slurry becomes better. Furthermore, the resulting active material layer has moderate flexibility, and the adhesion between the current collector and the active material layer is improved.

[0070] As for (meth)acrylamide, there is no particular limitation, and examples include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethylacrylamide, N,N-diethylacrylamide, N,N-diethylmethylacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethylacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethylacrylamide, diacetoneacrylamide, maleamide, etc., and one or more of them may be used.

[0071] <Repeating unit (a7) from compounds containing sulfonic acid groups>

[0072] Polymer (A) may contain repeating units (a7) from compounds having sulfonic acid groups. When the total number of repeating units contained in polymer (A) is set to 100 parts by mass, the content ratio of repeating units (a7) is preferably 0 to 8 parts by mass. The lower limit of the content ratio of repeating units (a7) is preferably 0.5 parts by mass, more preferably 1 part by mass. The upper limit of the content ratio of repeating units (a7) is preferably 7 parts by mass, more preferably 6 parts by mass. By containing repeating units (a7) in polymer (A) within the above range, the dispersion of active materials and fillers becomes better, and a homogeneous active material layer and protective film can be formed. In addition, the adhesion to the current collector is improved, and the structural defects of the electrode plate are reduced, thus exhibiting good charge and discharge characteristics.

[0073] The compounds having a sulfonic acid group are not particularly limited, and examples include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, sulfobutyl (meth) acrylate, 2-acrylamide-2-methylpropanesulfonic acid, acrylamide tert-butyl sulfonic acid, 2-hydroxy-3-acrylamide propanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and their base salts, etc., and one or more of them may be used.

[0074] <Repeating units from cationic monomers>

[0075] Polymer (A) may contain repeating units derived from cationic monomers. The cationic monomer is not particularly limited, but is preferably selected from at least one monomer chosen from secondary amines (salts), tertiary amines (salts), and quaternary ammonium salts. Specific examples of cationic monomers include 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate chloromethyl quaternary ammonium salt, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(O-[1'-methylpropylideneamino]carboxylamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacryloylcholine chloride, and tris(2-acryloyloxy)isocyanate. Ethyl ester, 2-vinylpyridine, quinalidine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazyl-2-stilbene dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazolium, diallylamine, diallylamine hydrochloride, triallylamine, diallyl dimethylammonium chloride, dichloropropyleneamine, N-allyl benzylamine, N-allyl aniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-heptene-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, etc., may be selected from one or more of them.

[0076] 1.1.2. Physical properties of polymer (A)

[0077] 1.1.2.1. Dynamic viscoelasticity

[0078] When measuring the dynamic viscoelasticity of polymer (A), there is one peak of tanδ (loss modulus / storage modulus) in the range of -50℃ to 10℃ and another peak in the range of 150℃ to 250℃. Moreover, when the tanδ of the peak in the range of -50℃ to 10℃ is set as tanδ(Tp1) and the tanδ of the peak in the range of 150℃ to 250℃ is set as tanδ(Tp2), the following relationship (1) is satisfied.

[0079] tanδ(Tp2) / tanδ(Tp1)<0.5 (1)

[0080] The test sample in this dynamic viscoelasticity determination was a film of polymer (A). The polymer (A) film was obtained as follows: polymer (A) 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 then dried in a vacuum dryer at 160°C for 30 minutes and cut into 10 mm × 10 mm rectangles. Next, using the dynamic viscoelasticity determination apparatus described below, the test sample was fixed using parallel plates (product name "PP-12"), and the determination was performed in the temperature range of -70°C to 250°C under the following conditions.

[0081] Measurement conditions: Shear mode, measurement frequency 0.01~1Hz, heating rate 0.1℃ / min

[0082] Dynamic viscoelasticity measuring apparatus: Anton Paar, model "MCR 301"

[0083] In this embodiment, the value of "tanδ(Tp2) / tanδ(Tp1)" of the polymer (A) is less than 0.5, preferably 0.48 or less, and more preferably 0.45 or less. If the value of "tanδ(Tp2) / tanδ(Tp1)" of the polymer (A) is within the above range, it indicates that there is a higher polymer content near the peak temperature of tanδ(Tp1). Furthermore, it indicates that the viscosity is higher at temperatures near the peak temperature of tanδ(Tp1), and it is believed that this high viscosity can primarily ensure the tightness with the active material composed of carbon materials. In addition, high cross-linking is observed at temperatures near the peak temperature of tanδ(Tp2), i.e., the polymer (A) is relatively hard. It is believed that if the polymer (A) is relatively hard, the binder will not deform due to the expansion and contraction of the Si active material during repeated charging and discharging, and the particle shape can be maintained. Therefore, the adhesion with the active material can be maintained, and the expansion of the electrode can be suppressed. Furthermore, by increasing the permeability of the electrolyte into the active material, the internal resistance can be reduced, and thus an electrode exhibiting good repeated charging and discharging characteristics can be produced. In addition, the polymer (A) used in this embodiment can improve the adhesion, thus enabling the fabrication of an electrode that exhibits good charge-discharge durability characteristics.

[0084] The temperature Tp1 (°C) of the peak of tanδ in the dynamic viscoelasticity determination of polymer (A) is preferably within a temperature range of -38°C to 8°C, more preferably -35°C to 5°C. Furthermore, it is preferable that there is one peak within the above temperature range. The presence of one Tp within the above temperature range indicates higher viscosity within that temperature range. It is believed that due to this higher viscosity, polymer (A) can maintain higher adhesive strength within this temperature range, exhibiting good adhesion.

[0085] The temperature Tp2 (°C) of the peak of tanδ in the dynamic viscoelasticity measurement of polymer (A) is preferably within a temperature range of 155°C to 245°C, more preferably 160°C to 240°C. Furthermore, it is preferable that there is one peak within the above temperature range. The presence of one Tp within the above temperature range indicates that a polymer with a higher content of hydrophilic polymers has formed within this temperature range. It is believed that the higher content of hydrophilic polymers in polymer (A) within this temperature range indicates that polymer (A) is harder and can reduce internal resistance.

[0086] Methods for adjusting the temperature Tp at the peak of tanδ include adjusting the monomer composition during the polymerization of polymer (A).

[0087] The tanδ (Tp1) of polymer (A) is preferably 0.5 to 1.2, more preferably 0.55 to 1.15, and particularly preferably 0.6 to 1.10. The tanδ (Tp1) of polymer (A) being within the above range indicates that polymer (A) is viscous but not rigid, and has sufficient adhesive force to maintain the electrode structure.

[0088] The tanδ (Tp2) of polymer (A) is preferably 0.01 to 0.4, more preferably 0.03 to 0.38, and particularly preferably 0.05 to 0.35. A tanδ (Tp2) of polymer (A) within the above range indicates that polymer (A) is not too soft, inhibits the fusion of particles, and has sufficient hardness to withstand the expansion and contraction of Si.

[0089] Methods for adjusting tanδ(Tp) include changing the glass transition temperature of polymer (A), altering the gel content, or changing the monomer addition method during polymer (A) polymerization.

[0090] 1.1.2.2. Pulsed NMR

[0091] The transverse relaxation time T of protons in an aqueous dispersion of polymer (A) adjusted to a solid content of 10% was determined using pulsed NMR. A When the measurement is performed, T is the relaxation time relative to elemental water, T A <T0 is established.

[0092] The transverse relaxation time (spin-spin relaxation time) of the proton was determined using a pulsed nuclear magnetic resonance (PMR) apparatus, a Minispec MQ20 ​​manufactured by BRUKER Corporation, with the hydrogen nucleus as the analyte. The determination was conducted at a temperature of 25°C, a frequency of 20 MHz, and a pulse interval of 0.04 tau between 90 and 180° pulses. It should be noted that the pH of the aqueous dispersion was preferably prepared to 8.0 for the determination.

[0093] The transverse relaxation time T of protons present in the aqueous dispersion of polymer (A) A Preferably, it is 1500 ms or more, more preferably 1550 ms or more, and particularly preferably 1600 ms or more. The transverse relaxation time of the protons, determined by pulse NMR, is measured in the form of the overall relaxation time of the constituent components of the sample. Therefore, when it is an aqueous dispersion of polymer (A) with a solid component concentration of 10%, the relaxation time T A It is obtained as the average relaxation time of protons present in 10% polymer (A) and 90% water.

[0094] The greater the interaction between the surface of polymer (A) and water molecules, the longer the relaxation time T. A The shorter the relaxation time T, the stronger the hydrophilicity of the particle surface. A The shorter the time, the stronger the hydrophobicity, and the longer the relaxation time T. A The longer the relaxation time T, the better. Therefore, the relaxation time T is considered to be... A The longer the length, the stronger the hydrophobicity of the polymer (A) surface, and the more effectively it is adsorbed onto the surface of the active material, thus exhibiting excellent adhesion and electrode expansion suppression effect.

[0095] 1.1.2.3. Number-average particle size

[0096] When polymer (A) is in the form of particles, the number average particle size is preferably 50 nm to 500 nm, more preferably 70 nm to 480 nm, and particularly preferably 90 nm to 450 nm. If the number average particle size of polymer (A) is within the above range, the particles of polymer (A) readily adsorb onto the surface of the active material, and thus can move along with the active material. As a result, migration can be suppressed, and therefore, degradation of electrical properties can sometimes be reduced.

[0097] It should be noted that the number-average particle size of polymer (A) is the average particle size obtained from images of 50 particles observed using a transmission electron microscope (TEM). Examples of transmission electron microscopes include the "H-7650" manufactured by Hitachi High Technology Co., Ltd.

[0098] 1.1.2.4. Surface acidity

[0099] When polymer (A) is in the form of particles, the surface acidity of these particles is preferably 0.05 mmol / g to 1 mmol / g, more preferably 0.07 mmol / g to 0.95 mmol / g, and particularly preferably 0.10 mmol / g to 0.90 mmol / g. If the surface acidity of the polymer (A) particles is within the above range, a stable and homogeneous slurry can be produced. When an active material layer is prepared using such a homogeneous slurry, an active material layer with uniformly dispersed active material and polymer (A) particles and a small thickness deviation can be obtained. As a result, deviations in charge-discharge characteristics within the electrode can be suppressed, thus obtaining a storage device exhibiting excellent charge-discharge characteristics. The surface acidity of polymer (A) can be measured according to the method described in the examples below.

[0100] 1.1.2.5. Electrolyte swelling ratio

[0101] The swelling degree (hereinafter also referred to as "electrolyte swelling ratio") of polymer (A) when immersed in a solvent consisting of ethylene carbonate and methyl ethyl carbonate in a volume fraction of 1:1 at 70°C for 24 hours is preferably 100% to 350%, more preferably 110% to 250%, and particularly preferably 120% to 200%. If the electrolyte swelling ratio of polymer (A) is within the above range, polymer (A) can swell appropriately by absorbing the electrolyte. As a result, solvated lithium ions can easily reach the active material, thus effectively reducing electrode resistance and achieving better charge-discharge characteristics. In addition, if the electrolyte swelling ratio of polymer (A) is within the above range, polymer (A) will not undergo a large volume change even if it absorbs the electrolyte, thus exhibiting excellent adhesion.

[0102] 1.1.3. Method for manufacturing polymer (A)

[0103] <Polymerization Process>

[0104] The polymerization process of polymer (A) is not particularly limited, for example, it can be based on emulsion polymerization in the presence of known emulsifiers, chain transfer agents, polymerization initiators, etc.

[0105] Examples of emulsifiers include anionic surfactants such as sulfated salts of higher alcohols, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabirates, naphthalene sulfonic acid, formaldehyde condensates, and sulfated salts of nonionic surfactants; nonionic surfactants such as alkyl esters of polyethylene glycol, alkylphenyl ethers of polyethylene glycol, and alkyl ethers of polyethylene glycol; and fluorinated surfactants such as perfluorobutyl sulfonates, perfluoroalkyl phosphates, perfluoroalkyl carboxylates, and perfluoroalkyl ethylene oxide adducts. One or more of these can be used.

[0106] As specific examples of chain transfer agents and polymerization initiators, compounds described in Japanese Patent No. 5999399 and the like can be used.

[0107] Emulsion polymerization for synthesizing polymer (A) can be carried out in one step or in multiple steps (two or more steps).

[0108] In the case of synthesizing polymer (A) by one-step polymerization, it can be carried out by emulsion polymerization of the above-mentioned monomer mixture in the presence of appropriate emulsifiers, chain transfer agents, polymerization initiators, etc., at a temperature preferably 0 to 80°C and a polymerization time preferably 4 to 36 hours.

[0109] In the case of synthesizing polymer (A) by two-step polymerization, the polymerization settings for each step are preferably set as follows.

[0110] The proportion of monomers used in the first polymerization step is preferably in the range of 20% to 99% by mass, more preferably in the range of 25% to 99% by mass, relative to the total mass of monomers (the sum of the mass of monomers used in the first polymerization step and the mass of monomers used in the second polymerization step). By performing the first polymerization step with such a monomer usage ratio, polymer (A) particles with excellent dispersion stability and low tendency to form aggregates can be obtained, and the viscosity increase over time of the solidified adhesive composition for energy storage devices is also suppressed, which is therefore preferred.

[0111] The types and proportions of monomers used in the second polymerization step can be the same as or different from those used in the first polymerization step.

[0112] From the viewpoint of the dispersion of the particles of the obtained polymer (A), the polymerization conditions for each step are preferred as follows.

[0113] The first step is polymerization; the preferred temperature is 0 to 80°C; the preferred polymerization time is 2 to 36 hours; the preferred polymerization conversion rate is 50% by mass or more, and more preferably 60% by mass or more.

[0114] The second step is polymerization; preferably at a temperature of 0–80°C; preferably for a polymerization time of 2–18 hours.

[0115] When polymer (A) is synthesized by three-step polymerization, the preferred polymerization steps are as follows.

[0116] The proportion of monomers used in the first polymerization step is preferably in the range of 20 to 90% by mass, more preferably in the range of 25 to 80% by mass, relative to the total mass of monomers (the sum of the mass of monomers used in the first polymerization step, the mass of monomers used in the second polymerization step, and the mass of monomers used in the third polymerization step). By performing the first polymerization step with such a monomer usage ratio, it is possible to obtain polymer (A) particles with excellent dispersion stability and low tendency to form aggregates, and the viscosity increase over time of the solidified adhesive composition for energy storage devices is also suppressed, which is therefore preferred.

[0117] The types and proportions of monomers used in the second polymerization step can be the same as or different from those used in the first polymerization step.

[0118] The types and proportions of monomers used in the third polymerization step can be the same as or different from those used in the first polymerization step and the second polymerization step.

[0119] From the viewpoint of the dispersion of the particles of the obtained polymer (A), the polymerization conditions for each step are preferred as follows.

[0120] The first step is polymerization; the preferred temperature is 0 to 80°C; the preferred polymerization time is 2 to 36 hours; the preferred polymerization conversion rate is 50% by mass or more, and more preferably 60% by mass or more.

[0121] The second step is polymerization; preferably at a temperature of 0–80°C; preferably for a polymerization time of 2–18 hours.

[0122] The third step is polymerization; preferably at a temperature of 0–80°C; preferably for a polymerization time of 2–9 hours.

[0123] By keeping the total solids concentration in the emulsion polymerization at 50% by mass or less, the polymerization reaction can be carried out under conditions where the particle dispersion stability of the resulting polymer (A) is good. This total solids concentration is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0124] Whether the synthesis of polymer (A) is carried out by one-step polymerization or by multi-step polymerization, it is preferable to add a neutralizing agent to the polymerization mixture after the emulsion polymerization is completed. There are no particular limitations on the neutralizing agent used herein; examples include metal hydroxides such as sodium hydroxide and potassium hydroxide, and ammonia.

[0125] 1.2. Liquid medium (B)

[0126] The adhesive composition for energy storage devices of this embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium may contain a non-aqueous medium other than water. Examples of such non-aqueous media include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. By using an aqueous medium as the liquid medium (B), the adhesive composition for energy storage devices of this embodiment reduces the degree of adverse environmental impact and improves the safety of operators.

[0127] The proportion of non-aqueous media in the aqueous medium is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably substantially non-existent, out of 100 parts by mass of the aqueous medium. Here, "substantially non-existent" means to the extent that a non-aqueous medium is not intentionally added as a liquid medium, and may contain non-aqueous media that are unavoidably mixed in when preparing the adhesive composition for storage devices.

[0128] 1.3. Other additives

[0129] The adhesive composition for energy storage devices according to this embodiment may contain additives other than the components described above, as needed. Examples of such additives include polymers other than polymer (A), preservatives, tackifiers, etc.

[0130] <Polymers other than polymer (A)>

[0131] The adhesive composition for energy storage devices according to this embodiment may contain polymers other than polymer (A). Such polymers are not particularly limited, and examples include acrylic polymers containing unsaturated carboxylic acid esters or their derivatives as constituent units, fluoropolymers such as PVDF (polyvinylidene fluoride), etc. One of these polymers may be used alone, or two or more may be used in combination. The inclusion of these polymers further improves flexibility and adhesion.

[0132] <Preservatives>

[0133] The adhesive composition for storage devices according to this embodiment may contain a preservative. Sometimes, by containing a preservative, it is possible to inhibit the growth of bacteria, mold, etc., and the generation of foreign matter during the storage of the adhesive composition for storage devices. Specific examples of preservatives include compounds described in Japanese Patent No. 5477610 and the like.

[0134] <Tackifier>

[0135] The adhesive composition for energy storage devices according to this embodiment may contain a tackifier. Sometimes, by containing a tackifier, the coatability of the slurry and the charge / discharge characteristics of the resulting energy storage device can be further improved.

[0136] Examples of tackifiers include, for example, cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; the above-mentioned cellulose compounds or ammonium or alkali metal salts of the above-mentioned poly(meth)acrylic acid; modified polyvinyl alcohol, polyethylene oxide; polyvinylpyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, chitosan derivatives, etc. Among these, cellulose-based polymers are preferred.

[0137] Commercially available products that serve as these tackifiers include, for example, alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Co., Ltd.).

[0138] When the adhesive composition for storage devices in this embodiment contains a tackifier, the proportion of the tackifier is preferably 5% by mass or less, and more preferably 0.1 to 3% by mass, relative to 100% by mass of the total solid content of the adhesive composition for storage devices.

[0139] 1.4. pH of the adhesive composition for energy storage devices

[0140] The pH of the adhesive composition for the energy storage device in this embodiment is preferably 6.0 to 9.5, more preferably 6.3 to 9.2, and particularly preferably 6.5 to 9.0. If the pH is within the above range, insufficient leveling and dripping can be suppressed, making it easier to manufacture energy storage device electrodes that have both good electrical properties and good sealing.

[0141] In this manual, "pH" refers to the physical property measured as follows: It is a value measured according to JIS Z8802:2011 using a pH meter with a glass electrode calibrated at 25°C using neutral phosphate and borate standard solutions as pH standard solutions. Examples of such pH meters include the "HM-7J" manufactured by Toa Denpa Co., Ltd., and the "D-51" manufactured by Horiba Manufacturing Co., Ltd.

[0142] It should be noted that while the pH of the adhesive composition for energy storage devices is undeniably influenced by the monomer components constituting the polymer (A), it is not solely determined by the monomer components. That is, it is generally believed that even with the same monomer components, the pH of the adhesive composition for energy storage devices can change due to polymerization conditions, etc. The examples in this specification are merely one example.

[0143] 2. Slurry for energy storage equipment

[0144] One embodiment of the present invention provides a slurry for a storage device containing the aforementioned binder composition for a storage device. This binder composition can be used as a material for fabricating a protective film to suppress short circuits caused by dendrites generated during charging and discharging, and also as a material for fabricating a storage device electrode (active material layer) that improves the bonding ability between active materials, the adhesion between the active material and the current collector, and resistance to powdering. Hereinafter, the slurry for a storage device used to fabricate a protective film (hereinafter also referred to as "slurry for protective film") and the slurry for a storage device used to fabricate the active material layer of the storage device electrode (hereinafter also referred to as "slurry for storage device electrode") will be described separately.

[0145] 2.1. Slurry for protective film

[0146] "Protective film slurry" refers to a dispersion liquid used to form a protective film on the surface of an electrode or a separator, or both, by applying it to the surface of the electrode or a separator and then drying it. The protective film slurry of this embodiment may consist solely of the aforementioned adhesive composition for energy storage devices, or it may further contain inorganic fillers. Examples of inorganic fillers include those described in Japanese Patent Application Publication No. 2020-184461.

[0147] 2.2. Electrode paste for energy storage devices

[0148] "Electrode slurry for energy storage devices" refers to a dispersion liquid used to form an active material layer on the surface of a current collector after being coated onto the surface of the current collector and then dried. The electrode slurry for energy storage devices of this embodiment contains the above-described binder composition for energy storage devices and the active material.

[0149] Generally, electrode pastes for energy storage devices mostly contain binder components such as SBR-based copolymers and tackifiers such as carboxymethyl cellulose to improve adhesion. On the other hand, the electrode paste for energy storage devices of this embodiment can also improve adhesion when it contains only the aforementioned polymer (A) as a polymer component. Of course, the electrode paste for energy storage devices of this embodiment can contain polymers other than polymer (A) and tackifiers to further improve adhesion. Hereinafter, the components contained in the electrode paste for energy storage devices of this embodiment will be described.

[0150] 2.2.1. Polymer (A)

[0151] The composition, physical properties, and manufacturing method of polymer (A) are as described above, therefore, the description is omitted.

[0152] Relative to 100 parts by mass of the active material, the polymer component in the electrode slurry of the energy storage device according to this embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass. If the polymer component content is within the above range, the active material in the slurry has good dispersibility, and the slurry has excellent coatability. Here, the polymer component includes polymer (A), polymers other than polymer (A) added as needed, and tackifiers, etc.

[0153] 2.2.2. Active substances

[0154] Examples of active materials used in the electrode paste of the energy storage device according to this embodiment include positive electrode active materials and negative electrode active materials. Specific examples include, for instance, carbon materials, silicon materials, oxides containing lithium atoms, sulfur compounds, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyphenylene oxide, and A. X B Y O Z (Where A represents an alkali metal or transition metal, B represents at least one transition metal selected from cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively.) This refers to composite metal oxides, other metal oxides, etc. Specific examples include compounds described in Japanese Patent No. 5999399, etc.

[0155] The electrode paste for the energy storage device of this embodiment can also be used when making either the positive or negative electrode, and is particularly preferred for the negative electrode.

[0156] When fabricating the negative electrode, it is preferable to further contain silicon and / or carbon materials in the active material exemplified above, and more preferably a mixture of silicon and carbon materials. Since silicon materials have a larger lithium absorption per unit weight compared to other active materials, the energy storage capacity of the resulting energy storage device can be increased. As a result, the output and energy density of the energy storage device can be improved. On the other hand, carbon materials exhibit smaller volume changes during charging and discharging compared to silicon materials. Therefore, by using a mixture of silicon and carbon materials as the negative electrode active material, the influence of volume changes in silicon materials can be mitigated, and the adhesion between the active material layer and the current collector can be further improved.

[0157] When silicon (Si) is used as the active material, it offers high capacity, but it also undergoes significant volume changes when absorbing lithium ions. Therefore, silicon materials exhibit the following properties: micronization due to repeated expansion and contraction leads to peeling from the current collector, separation of the active material from each other, and easy disruption of the conductive network within the active material layer. Due to this property, the charge / discharge durability of energy storage devices deteriorates drastically within a short period.

[0158] In this respect, the energy storage device electrode made using the energy storage device electrode paste of this embodiment does not exhibit the problems described above, even when using silicon material, and can show good electrical characteristics. The reason for this is that the polymer (A) can firmly bond the silicon material, and even if the silicon material expands in volume by absorbing lithium, the polymer (A) will expand and contract, thereby maintaining a state in which the silicon material is firmly bonded.

[0159] The proportion of silicon material in 100% by mass of the active material is preferably 1% by mass or more, more preferably 2 to 50% by mass, even more preferably 3 to 45% by mass, and particularly preferably 10 to 40% by mass. If the proportion of silicon material in 100% by mass of the active material is within the above range, an energy storage device with excellent balance between improved output and energy density and charge / discharge durability can be obtained.

[0160] The shape of the negative electrode active material is preferably particulate. The average particle size of the negative electrode active material is preferably 0.1 to 100 μm, more preferably 1 to 20 μm.

[0161] On the other hand, when manufacturing a positive electrode, an oxide containing lithium atoms is preferred among the active materials exemplified above. As an oxide containing lithium atoms, for example, one or more of lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, and lithium manganese nickel cobalt oxide can be represented by the following general formula (2).

[0162] Li 1－x M x (AO4) (2)

[0163] (In formula (2), M is at least one metal ion selected from Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge and Sn, A is at least one metal ion selected from Si, S, P and V, and x is a number that satisfies the relationship 0 < x < 1.)

[0164] It should be noted that the value of x in the above general formula (2) is selected in such a way that the overall value of the above general formula (2) is 0 based on the values ​​of M and A.

[0165] Examples of olivine-type lithium phosphate compounds include LiFePO4, LiCoPO4, LiMnPO4, and Li 0.90 Ti 0.0 5Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4, etc. Among them, LiFePO4 (lithium iron phosphate) is particularly preferred because iron compounds as raw materials are readily available and inexpensive.

[0166] The average particle size of the olivine-type lithium phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

[0167] In addition, the active material layer may contain the following examples of active materials. For example, conductive polymers such as poly(phenylene oxide) can be cited; A X B Y O Z (Where A represents an alkali metal or transition metal, B represents at least one transition metal selected from cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively.) This refers to composite metal oxides, other metal oxides, etc.

[0168] Examples of the aforementioned composite metal oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and ternary lithium nickel cobalt manganese oxide.

[0169] The battery electrode made using the battery electrode paste of this embodiment exhibits good electrical characteristics even when using an oxide containing lithium atoms as the positive electrode active material. This is because the polymer (A) can firmly bond the oxide containing lithium atoms, and maintains this firm bonding even during charging and discharging.

[0170] 2.2.3. Other components

[0171] In addition to the components described above, the electrode slurry for the energy storage device of this embodiment may also contain polymers other than polymer (A), thickeners, liquid media, conductive additives, pH adjusters, corrosion inhibitors, antioxidants, cellulose fibers, etc., as needed. As polymers other than polymer (A) and thickeners, appropriate selections can be made from the compounds exemplified in the section “1.3. Other Additives” above, and they can be used according to the same purpose and proportions.

[0172] <Liquid Medium>

[0173] In addition to the portion introduced by the adhesive composition for the energy storage device, a liquid medium may be further added to the slurry for the electrode of the energy storage device in this embodiment. The added liquid medium may be the same as or different from the liquid medium (B) contained in the adhesive composition for the energy storage device. Preferably, it is selected from the liquid media exemplified in the above-mentioned "1.2. Liquid Medium (B)".

[0174] The liquid medium (including the portion introduced by the binder composition for energy storage devices) in the slurry for electrodes of the energy storage device in this embodiment refers to the concentration of solid components in the slurry (which refers to the proportion of the total mass of the components other than the liquid medium in the slurry to the total mass of the slurry. The same applies below.) is preferably 30 to 70% by mass, and more preferably 40 to 60% by mass.

[0175] <Conductive additives>

[0176] In this embodiment, conductive additives can be further added to the electrode slurry of the energy storage device to impart conductivity, while buffering the volume change of the active material caused by the entry and exit of lithium ions.

[0177] Specific examples of conductive additives include activated carbon, acetylene black, Ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotubes. Among these, acetylene black, Ketjen black, or carbon nanotubes are preferred. The proportion of the conductive additive relative to 100 parts by weight of the active material is preferably 20 parts by weight or less, more preferably 1 to 15 parts by weight, and particularly preferably 2 to 10 parts by weight.

[0178] <pH adjuster>

[0179] In this embodiment, a pH adjuster can be further added to the electrode slurry of the energy storage device to inhibit corrosion of the current collector according to the type of active material.

[0180] Examples of pH adjusters include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, and potassium hydroxide. Sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred. Alternatively, neutralizing agents described in the manufacturing method of polymer (A) may also be used.

[0181] <Corrosion Inhibitor>

[0182] In this embodiment, corrosion inhibitors can be further added to the electrode slurry of the energy storage device to suppress corrosion of the current collector depending on the type of active material.

[0183] Examples of corrosion inhibitors include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, and potassium molybdate. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferred.

[0184] Cellulose Fiber

[0185] Cellulose fibers can be further added to the electrode slurry of the energy storage device in this embodiment. Known materials can be used as cellulose fibers. Adding cellulose fibers can sometimes improve the adhesion between the active material and the current collector. It is believed that by using fibrous cellulose fibers to bond adjacent active materials together through line adhesion or line contact, fibrous material detachment can be prevented, and adhesion to the current collector can be improved.

[0186] 2.2.4. Preparation method of electrode paste for energy storage devices

[0187] The electrode slurry for the energy storage device according to this embodiment can be manufactured by any method as long as it contains the above-described binder composition for energy storage devices and the active substance. From the viewpoint of manufacturing a slurry with better dispersibility and stability more efficiently and cheaply, it is preferable to manufacture it by adding the active substance and any additives to the binder composition for energy storage devices and mixing them together. As a specific manufacturing method, for example, the method described in Japanese Patent No. 5999399 can be cited.

[0188] 3. Electrodes of energy storage devices

[0189] An embodiment of the present invention provides an electrode for a storage device comprising: a current collector and an active material layer formed by coating the surface of the current collector with the aforementioned slurry for a storage device electrode and drying it. The storage device electrode can be manufactured by coating the surface of a current collector, such as a metal foil, with the aforementioned slurry for a storage device electrode to form a coating film, and then drying the coating film to form an active material layer. Since the storage device electrode manufactured in this way is formed by bonding an active material layer containing the aforementioned polymer (A), the active material, and any other components added as needed to the surface of the current collector, it exhibits excellent adhesion, and the expansion of the electrode during repeated charging and discharging is suppressed, resulting in excellent charge-discharge durability.

[0190] As a current collector, there are no particular restrictions as long as it is made of a conductive material; for example, the current collector described in Japanese Patent No. 5999399 can be cited.

[0191] When silicon material is used as the active material in the electrode of the energy storage device in this embodiment, the silicon content in 100% by mass of the active material layer is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and particularly preferably 3 to 10% by mass. If the silicon content in the active material layer is within the above range, the energy storage capacity of the energy storage device manufactured using this active material layer is increased, and an active material layer with uniform silicon distribution is obtained. The silicon content in the active material layer can be determined by, for example, the method described in Japanese Patent No. 5999399.

[0192] 4. Energy storage devices

[0193] One embodiment of the energy storage device of the present invention includes the aforementioned energy storage device electrodes and further contains an electrolyte. It can be manufactured using conventional methods using components such as separators. As a specific manufacturing method, examples include overlapping the negative and positive electrodes with a separator in between, winding or folding them according to the battery shape to house them in a battery container, then injecting electrolyte into the battery container and sealing it. The battery shape can be suitable, such as coin-shaped, cylindrical, square, or laminated.

[0194] The electrolyte can be a liquid or a gel; any electrolyte that effectively performs its function as a battery can be selected from known electrolytes used in energy storage devices, depending on the type of active material. The electrolyte can be a solution obtained by dissolving an electrolyte in a suitable solvent. Examples of such electrolytes and solvents include compounds described in Japanese Patent No. 5999399, etc.

[0195] The aforementioned energy storage device can be used in lithium-ion secondary batteries, double-layer capacitors, or lithium-ion capacitors that require discharge at high current densities. Lithium-ion secondary batteries are particularly preferred. In the energy storage device electrodes and energy storage device of this embodiment, components other than the binder composition for energy storage devices can use known components for lithium-ion secondary batteries, double-layer capacitors, or lithium-ion capacitors.

[0196] 5. Examples

[0197] The present invention will now be specifically described based on embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, "parts" and "%" in the embodiments and comparative examples are quality standards.

[0198] 5.1. Example 1

[0199] 5.1.1. Preparation of adhesive composition for energy storage devices

[0200] <Example 1>

[0201] A binder composition for storage devices containing polymer (A1) was obtained through a two-step polymerization process as shown below. 300 parts by weight of water, a monomer mixture consisting of 50 parts by weight of 1,3-butadiene, 35 parts by weight of styrene, 5 parts by weight of acrylonitrile, 1 part by weight of sodium styrene sulfonate and itaconic acid, 1 part by weight of acrylamide, 0.1 part by weight of tert-dodecyl mercaptan as a chain transfer agent, 0.1 part by weight of sodium alkyl diphenyl ether disulfonate as an emulsifier, and 1.0 part by weight of potassium persulfate as a polymerization initiator were added to the reactor. Polymerization was carried out at 70°C for 18 hours with stirring, and the polymerization conversion rate was confirmed to be 95%. Next, 50 parts by weight of water, 1 part by weight of itaconic acid, 1 part by weight of acrylic acid, 1 part by weight of methacrylic acid, 1 part by weight of hydroxyethyl methacrylate, 1 part by weight of hydroxyethyl acrylate, 1 part by weight of acrylonitrile, and 1 part by weight of sodium styrene sulfonate were further added to the reactor. After polymerization at 75°C for 12 hours, the polymerization conversion rate was confirmed to be 98%. Unreacted monomers were removed from the particle dispersion of polymer (A1) thus obtained and the mixture was concentrated. After adding 5% sodium hydroxide aqueous solution, water was removed using an evaporator, thereby obtaining an adhesive composition for energy storage devices containing polymer (A1) particles with a solid content concentration of 40% by mass and a pH of 7.0.

[0202] 5.1.2. Physical property evaluation of adhesive compositions for energy storage devices

[0203] <Methods for Determining Polymerization Conversion Rate>

[0204] The polymerization conversion rate in the synthesis of the above polymers was determined as follows.

[0205] The reaction solution that has undergone polymerization for a specified time is extracted and placed into a pre-weighed aluminum dish (X (g)), and the weight of the reaction solution (Y (g)) is measured. It is then dried in a hot air dryer at 155°C for 15 minutes. The aluminum dish is removed, cooled, and then weighed (Z (g)). Based on the values ​​of X, Y, and Z obtained from these measurements, the polymerization conversion rate (%) is calculated according to the following formula (3).

[0206] Polymerization conversion rate (%) = ((Z-X) / Y) × 100 (3)

[0207] <Determination of Number-Average Particle Size>

[0208] One drop of latex diluted to 0.1 wt% with the aforementioned adhesive composition for energy storage devices was added to the collodion support film using a pipette. Then, one drop of 0.02 wt% osmium tetroxide solution was added to the collodion support film using a pipette, and the film was air-dried for 12 hours to prepare the sample. The prepared sample was observed at 10K magnification using a transmission electron microscope (TEM, Hitachi High Technology Co., Ltd., model "H-7650"). Image analysis was performed using the HITACHI EMIP program to calculate the number-average particle size of 50 randomly selected polymer (A1) particles. The result showed that the number-average particle size of polymer (A1) was 190 nm. The measurement results are shown in Table 1 below.

[0209] <pH Measurement>

[0210] The pH of the above-obtained adhesive composition for energy storage devices was measured at 25°C using a pH meter (manufactured by Horiba Manufacturing Co., Ltd.), and the result confirmed that the pH was 7.0. The results are shown in Table 1 below.

[0211] <Determination of Electrolyte Swelling Ratio>

[0212] The polymer (A1) obtained above was dried in a constant temperature bath at 85°C for 24 hours to prepare a membrane. 1 g of this membrane was immersed in 20 mL of a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) used as the electrolyte in the manufacture of the energy storage device described later (EC / EMC = 1 / 1 (capacity ratio), hereinafter referred to as "EC / EMC"), and shaken at 70°C for 24 hours. Next, after filtering with a 300-mesh metal mesh to separate the insoluble matter, the weight (Y (g)) of the residue obtained after evaporating the dissolved EC / EMC was measured. In addition, the EC / EMC adhering to the surface of the insoluble matter (membrane) separated by the filtration was removed by absorbing it with paper, and the weight (Z (g)) of the insoluble matter (membrane) was measured. The electrolyte swelling rate was determined according to the following formula (4), and the electrolyte swelling rate of the above polymer (A1) was 171% by mass.

[0213] Electrolyte swelling ratio (mass%) = (Z / (1-Y)) × 100 (4)

[0214] <Determination of Surface Acidity>

[0215] The surface acidity of the polymer (A1) particles in the above-obtained adhesive composition for storage devices was determined as follows. First, it was confirmed that the burette and reagent bottle on the upper part of the potentiometric titration apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., model "AT-510") were filled with 0.005 mol / L sulfuric acid, and that the conductivity of the ultrapure water was below 2 μS. Next, air was expelled from the burette, and air bubbles were removed from the nozzle. Then, approximately 1 g of the above-obtained adhesive composition for storage devices (converted to solids) was added to a 300 mL beaker, and the sample weight was recorded. Ultrapure water was added to dilute to 200 mL, and then a 1 mol / L sodium hydroxide aqueous solution was added dropwise. The mixture was stirred for approximately 30 seconds upon reaching the endpoint to confirm that the conductivity had stabilized. The RESET button of the measurement program was pressed to enter the measurement standby state. The START button of the measurement program was pressed to begin the measurement using 0.005 mol / L sulfuric acid. The process automatically terminates and saves the file upon reaching the endpoint. The resulting curve is then analyzed, and the surface acid content is calculated using the following formula (5) based on the amount of sulfuric acid used. The result shows that the surface acid content of the polymer (A1) is 0.37 mmol / g. The results are presented in Table 1 below.

[0216] Surface acid content (mmol / g) = Amount of acid used in the carboxylic acid region on the particle surface [mL] × Acid concentration [mol / L] × Degree of ionization / Sample weight [g] / 1000 (5)

[0217] <Pulse NMR>

[0218] The transverse relaxation time T of protons in an aqueous dispersion of polymer (A1) adjusted to a solid content of 10% was determined by pulsed NMR. A The transverse relaxation time (spin-spin relaxation time) of water protons was determined using a pulsed nuclear magnetic resonance (PMR) apparatus, a Minispec MQ20 ​​(BRUKER), with the analyte being a hydrogen nucleus. The measurement conditions were 25°C, 20MHz, and a 90-180° pulse interval of 0.04 tau. It should be noted that the pH of the aqueous dispersion was prepared to 8.0 for the measurement. The results showed that the transverse relaxation time T of the protons present in the aqueous dispersion of polymer (Al) was... A The result was 2120 ms. The measurement results are shown in Table 1 below.

[0219] <Determination of Dynamic Viscoelasticity>

[0220] The polymer (A1) 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 then dried in a vacuum dryer at 160°C for 30 minutes. The film was removed from the vacuum dryer, and 10 mm × 10 mm rectangles were cut out as samples for measurement. Next, a dynamic viscoelasticity measuring apparatus (AntonPaar, model "MCR 301") was used, with parallel plates (product name "PP-12") used to fix the sample. Dynamic viscoelasticity was measured in a temperature range of -70°C to 250°C under the following conditions: shear mode, measurement frequency 0.01–1 Hz, and heating rate 0.1°C / min. The results showed that a tanδ peak (tanδ-1) was observed at 8°C on the low-temperature side, with a value of 0.96. Furthermore, a tanδ peak (tanδ-2) was observed at 192°C on the high-temperature side, with a value of 0.05. It should be noted that in Tables 1 to 3 below, the peak 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". Additionally, in Figure 1 The graph shown in Example 5 illustrates the relationship between the measurement temperature and tanδ in the dynamic viscoelasticity test of the membrane prepared in Example 5.

[0221] 5.1.3. Preparation of electrode paste for energy storage devices

[0222] <Synthesis of Silicon Materials (Active Substances)>

[0223] A mixture of pulverized silica powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was heated in an electric furnace at a temperature adjusted to 1100℃–1600℃ under a nitrogen flow (0.5 NL / min) for 10 hours to obtain SiO2. x (x = 0.5–1.1) represents silicon oxide powder (average particle size 8 μm). 300 g of this silicon oxide powder was added to an intermittent heating furnace, and while maintaining a reduced absolute pressure of 100 Pa using a vacuum pump, the temperature was increased from room temperature (25 °C) to 1100 °C at a rate of 300 °C / h. Then, the pressure inside the furnace was maintained at 2000 Pa, and methane gas was introduced at a flow rate of 0.5 NL / min while the furnace was heated at 1100 °C for 5 hours (graphite coating treatment). After the graphite coating treatment, the powder was cooled to room temperature at a rate of 50 °C / h, thus obtaining approximately 330 g of graphite-coated silicon oxide powder. This graphite-coated silicon oxide is a conductive powder (active material) with a graphite coating on the surface of silicon oxide, with an average particle size of 10.5 μm. The proportion of graphite coating is 2 by mass when the total amount of the obtained graphite-coated silicon oxide is set to 100% by mass.

[0224] <Preparation of Electrode Paste for Energy Storage Devices>

[0225] Add 1 part by mass of tackifier (trade name "CMC2200", manufactured by Daicel Co., Ltd., in the form of a 2% by mass aqueous solution), 4 parts by mass of polymer (Al) (in the form of the binder composition for energy storage devices obtained above), 85.5 parts by mass of highly crystalline graphite, i.e., artificial graphite (manufactured by Resonac Co., Ltd., trade name "MAG") as a negative electrode active material, 9.5 parts by mass of the graphite-coated silica powder obtained above, and 1 part by mass of carbon (manufactured by Denka Co., Ltd., acetylene black) as a conductive additive to a twin-shaft planetary mixer (PRIMIX Co., Ltd., trade name "TK HIVIS MIX 2P-03), and stir at 60 rpm for 1 hour to obtain a paste. Water was added to the obtained paste, and the concentration of solids was adjusted to 48% by mass. The mixture was then stirred and mixed at 200 rpm for 2 minutes, followed by stirring at 1800 rpm for 5 minutes using a degassing mixer (Thinky Co., Ltd., trade name "Hotori Rentarō"). The mixture was then further stirred under reduced pressure (approximately 2.5 × 10⁻⁶). 4 Pa) was stirred at 1800 rpm for 1.5 minutes to prepare a slurry for energy storage devices containing 10% by mass Si in the negative electrode active material (C / Si = 90 / 10).

[0226] <Stability Test of Slurry>

[0227] Using an AntonPaar Physica MCR301, approximately 1 mL of slurry with a C / Si ratio of 90 / 10 was measured. Using a 25 mm diameter conical plate with a 1 mm gap (GAP) and at 25°C, the shear rate was increased from 1 (1 / s) to 1000 (1 / s), then decreased back to 1 (1 / s) to obtain the above slurry viscosity behavior. The range from 1 to 1000 (1 / s) is defined as the upward movement of the measurement, and the range from 1000 to 1 (1 / s) is defined as the downward movement. The evaluation criteria are as follows.

[0228] (Evaluation Criteria)

[0229] 5 points: The viscosity at time 100 (1 / s) above the moving average is within ±8% of the viscosity at time 100 (1 / s) below the moving average.

[0230] 4 points: The viscosity at time 100 (1 / s) above the moving average is within ±10% of the viscosity at time 100 (1 / s) below the moving average.

[0231] 3 points: The viscosity at time 100 (1 / s) above the moving average is within ±15% of the viscosity at time 100 (1 / s) below the moving average.

[0232] 2 points: The viscosity at time 100 (1 / s) above the moving average is within ±20% of the viscosity at time 100 (1 / s) below the moving average.

[0233] 1 point: The viscosity at time 100 (1 / s) above the moving average is greater than ±20% at time 100 (1 / s) below the moving average.

[0234] 5.1.4. Manufacturing and Evaluation of Energy Storage Equipment

[0235] <Manufacturing of Electrodes (Negative Electrode) for Energy Storage Devices>

[0236] The electrode paste (C / Si = 90 / 10) obtained above was uniformly coated onto the surface of a 20 μm thick copper foil current collector with a dried film thickness of 80 μm using a doctor blade method. The coating was dried at 80°C for 5 minutes, followed by drying at 120°C for 5 minutes. Then, a rolling mill was used for stamping to achieve a density of 1.6 g / cm³ for the active material layer. 3 Thus, the electrode (negative electrode) of the energy storage device is obtained.

[0237] <Evaluation of the Adhesion Strength of the Negative Electrode Coating>

[0238] On the surface of the electrode of the aforementioned energy storage device, a checkerboard grid pattern is created by making 10 longitudinal and 10 transverse cuts at 2mm intervals, extending from the active material layer to the depth of the current collector. An 18mm wide adhesive tape (manufactured by NICHIBAN Co., Ltd., trade name "Cellotape" (registered trademark), JIS Z1522) is applied to these cuts and immediately peeled off. The degree of active material detachment is evaluated visually. The evaluation criteria are as follows. The evaluation results are shown in Table 1 below.

[0239] (Evaluation Criteria)

[0240] 5 points: 0 active substance layers were detached.

[0241] 4 points: 1 to 5 active substance layers were shed.

[0242] 3 points: The number of active substance layers detached is 6 to 20.

[0243] 2 points: 21 to 40 active substance layers were shed.

[0244] 1 point: More than 41 active substance layers are detached.

[0245] <Manufacturing of the counter electrode (positive electrode)>

[0246] Add 4 parts by weight (converted solids value) of electrode binder for electrochemical devices (manufactured by KUREHA Co., Ltd., trade name "KF Polymer #1120"), 3.0 parts by weight of conductive additive (manufactured by Denka Co., Ltd., trade name "Denka Black 50% Pressed Product"), 100 parts by weight (converted solids value) of LiCoO2 (manufactured by Hayashi Kasei Co., Ltd.) with an average particle size of 5 μm, and 36 parts by weight of N-methylpyrrolidone (NMP) to a twin-shaft planetary mixer (PRIMIX Co., Ltd., trade name "TK HIVIS MIX 2P-03) and stir at 60 rpm for 2 hours. NMP was added to the obtained paste to adjust the solids concentration to 65% by mass. Then, using a degassing mixer (Thinky Co., Ltd., trade name "Hotori Rentarō"), the mixture was stirred at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and finally mixed under reduced pressure (approximately 2.5 × 10⁻⁶). 4 The positive electrode slurry was prepared by stirring at 1800 rpm for 1.5 minutes. The slurry was then uniformly coated onto the surface of an aluminum foil current collector using a doctor blade to achieve a film thickness of 80 μm after solvent removal. The film was then heated at 120°C for 20 minutes to remove the solvent. Finally, the film was pressed using a roller press to achieve a density of 3.0 g / cm³ for the active material layer. 3 Thus, the counter electrode (positive electrode) is obtained.

[0247] <Assembly of Lithium-ion Battery Cells>

[0248] In a glove box where the dew point is below -80°C after Ar replacement, the negative electrode, which was punched into a 16.16 mm diameter form, is placed on a bipolar button cell (manufactured by Hosen Co., Ltd., trade name "HS-Flat Cell"). Next, a separator (manufactured by Celgard Co., Ltd., trade name "Celgard #2400") made of a polypropylene porous membrane punched into a 24 mm diameter is placed on top. Then, 300 μL of electrolyte is injected to prevent air ingress. The positive electrode, which was punched into a 15.95 mm diameter form, is then placed on top. The casing of the bipolar button cell is then sealed with screws, thereby assembling a lithium-ion battery cell (energy storage device). The electrolyte used here is a solution of LiPF6 dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0249] <Evaluation of Cyclic Characteristics>

[0250] For the lithium-ion secondary battery fabricated above, charging was initiated in a constant temperature bath at 25°C with a constant current (1.0C). Charging continued at a constant voltage (4.2V) until the voltage reached 4.2V, and the charging was considered complete (cut-off) when the current reached 0.01C. Then, discharging was initiated with a constant current (1.0C), and the discharging was considered complete (cut-off) when the voltage reached 2.5V. The discharge capacity of the first cycle was calculated. This charge-discharge cycle was repeated 100 times. The capacity retention rate was calculated according to the following formula (6), and evaluated according to the following criteria. The results are shown in Table 1 below.

[0251] Capacity retention rate (%) = (Discharge capacity in the 100th cycle) / (Discharge capacity in the 1st cycle) (6)

[0252] (Evaluation Criteria)

[0253] 5 points: Capacity retention rate is above 95%.

[0254] 4 points: Capacity retention rate is above 90% and less than 95%.

[0255] 3 points: Capacity retention rate is above 85% and less than 90%.

[0256] 2 points: Capacity retention rate is above 80% and less than 85%.

[0257] 1 point: Capacity retention rate is above 75% and less than 80%.

[0258] 0 points: Capacity retention rate is less than 75%.

[0259] <Evaluation of the rate of increase in resistance>

[0260] The manufactured energy storage device was placed in a constant temperature bath at 25°C and charged with a constant current (1.0C). Charging continued at a constant voltage (4.2V) until the voltage reached 4.2V, and the charging was considered complete (cut-off) when the current reached 0.01C. Then, discharging began with a constant current (0.05C), and the discharging was considered complete (cut-off) when the voltage reached 3.0V. The discharge capacity of the 0th cycle was calculated. Next, charging was started with a constant current (1.0C), and charging continued at a constant voltage (4.2V) until the voltage reached 4.2V, and the charging was considered complete (cut-off) when the current reached 0.01C. Then, discharging began with a constant current (1.0C), and the discharging was considered complete (cut-off) when the voltage reached 3.0V. The discharge capacity of the 1st cycle was calculated. This charge-discharge cycle was repeated 100 times. After repeating the charge and discharge cycle 100 times, the charge and discharge cycle was performed in the same way as the 0th cycle. The discharge capacity of the 101st cycle was evaluated. The resistance rise rate was calculated according to the following formula (7), and the evaluation was carried out according to the following criteria.

[0261] Resistance rise rate (%) = (Discharge capacity of the 101st cycle - Discharge capacity of the 100th cycle) / (Discharge capacity of the 0th cycle - Discharge capacity of the 1st cycle) × 100 (7)

[0262] (Evaluation Criteria)

[0263] 5 points: The rate of increase in resistance is greater than 100% and less than 150%.

[0264] 4 points: The rate of increase in resistance is greater than 150% but less than 200%.

[0265] 3 points: The rate of increase in resistance is greater than 200% but less than 250%.

[0266] 2 points: The rate of increase in resistance is greater than 250% but less than 300%.

[0267] 1 point: The rate of increase in resistance is greater than 300% but less than 350%.

[0268] 0 points: Resistance rise rate is above 350%.

[0269] <Evaluation of Plate Expansion Rate>

[0270] The film thickness of the negative electrode manufactured above is measured and taken as the initial film thickness. Then, for the energy storage device manufactured above, charging is initiated in a thermostatic bath at 25°C with a constant current (0.2C). Charging continues at a constant voltage (4.2V) until the current reaches 0.01C, at which point charging is considered complete (cut-off). Then, discharging is initiated in the thermostatic bath at 25°C with a constant current (0.2C). Discharging is considered complete (cut-off) until the voltage reaches 2.5V, completing the formation charge-discharge process. Then, a contact sensor (manufactured by KEYENCE, product name "GT2-H12KLF") is installed on the energy storage device, and the film thickness at this moment is taken as the formed film thickness. Charging is then initiated again with a constant current (0.2C), and charging continues at a constant voltage (4.2V) until the voltage reaches 4.2V. Charging is considered complete (cut-off) until the current reaches 0.01C. Then, discharge was started in a constant temperature bath at 25°C with a constant current (0.2C). The moment when the voltage reached 2.5V was taken as the end of the discharge (cut-off). The film thickness at the 10th discharge cycle was measured, and the plate expansion rate was calculated according to the following formula (8). The results were evaluated according to the following criteria. The results are shown in Table 1 below.

[0271] Electrode expansion rate (%) = ((film thickness at the 10th discharge cycle) - (film thickness after formation)) / (initial film thickness) × 100 、、、、、(8)

[0272] (Evaluation Criteria)

[0273] 5 points: The plate expansion rate is below 40%.

[0274] 4 points: The plate expansion rate is greater than 40% and less than 43%.

[0275] 3 points: The plate expansion rate is greater than 43% and less than 46%.

[0276] 2 points: The plate expansion rate is greater than 46% and less than 50%.

[0277] 1 point: The plate expansion rate is greater than 50%.

[0278] 5.2. Examples 2-15, Comparative Examples 1-6

[0279] In Examples 2-15, Comparative Examples 1, 3-6, the types and amounts of monomers were as described in Tables 1-3 below. Each polymer was synthesized using the same two-step polymerization as in Example 1 to obtain the adhesive composition for each energy storage device. Otherwise, all procedures were carried out in the same manner as in Example 1.

[0280] In Comparative Example 2, the types and amounts of monomers were as described in Table 3 below, and a polymer was synthesized by one-step polymerization to obtain an adhesive composition for energy storage devices. Otherwise, all procedures were carried out in the same manner as in Example 1.

[0281] 5.3 Evaluation Results

[0282] Tables 1 to 3 below show the polymer compositions, property test results, and evaluation results used in Examples 1 to 15 and Comparative Examples 1 to 6. It should be noted that the numerical values ​​representing polymer compositions shown in Tables 1 to 3 below are parts by mass.

[0283]

[0284]

[0285]

[0286] It should be noted that the following row after the example and comparative example numbers in Tables 1 to 3 above lists the polymer numbers synthesized in each example. The monomers in Tables 1 to 3 above represent the following compounds.

[0287] <Conjugated diene compounds>

[0288] BD: 1,3-Butadiene

[0289] <Aromatic Vinyl Compounds>

[0290] ST: Styrene

[0291] DVB: Divinylbenzene

[0292] <Unsaturated carboxylic acids>

[0293] TA: Itaconic acid

[0294] AA: Acrylic acid

[0295] MAA: Methacrylic acid

[0296] <Unsaturated carboxylic acid esters>

[0297] MMA: Methyl methacrylate

[0298] BA: Butyl acrylate

[0299] 2EHA: 2-Ethylhexyl acrylate

[0300] CHMA: Cyclohexyl methacrylate

[0301] EDMA: Ethylene glycol dimethacrylate

[0302] HEMA: 2-Hydroxyethyl methacrylate

[0303] HEA: 2-Hydroxyethyl Acrylate

[0304] <α,β-unsaturated nitrile compounds>

[0305] AN: Acrylonitrile

[0306] <(meth)acrylamide>

[0307] AAM: Acrylamide

[0308] MAM: Methacrylamide

[0309] <Compounds with sulfonic acid groups>

[0310] NASS: Sodium styrene sulfonate

[0311] In Examples 1-15, a slurry comprising the binder composition for energy storage devices of the present invention and an active material containing silicon was used as the electrode slurry for the energy storage device. By using the binder composition for energy storage devices of Examples 1-15, the binder particles were not destroyed due to the large volume changes of the active material accompanying charge and discharge, and the particle shape was maintained. This demonstrates that proper adhesion between the active materials reduces the plate expansion rate and maintains good adhesion between the active material layer and the current collector. Furthermore, it shows that because the binder particles maintain their particle shape, the permeability of the electrolyte is improved, and the rate of resistance increase is suppressed. These results suggest that even with repeated charge and discharge, and repeated volume expansion and contraction caused by the active material, plate expansion can be reduced while suppressing peeling of the active material layer, resulting in an energy storage device electrode with good cycle characteristics.

[0312] This invention is not limited to the embodiments described above and various modifications are possible. This invention includes configurations that are substantially the same as those described in the embodiments (e.g., configurations with the same function, method, and result, or configurations with the same purpose and effect). Furthermore, this invention includes configurations obtained by replacing non-essential parts of the configurations described in the above embodiments with other configurations. In addition, this invention also includes configurations that achieve the same effect as those described in the above embodiments or that can achieve the same purpose. Furthermore, this invention also includes configurations incorporating known technologies into the configurations described in the above embodiments.

Claims

1. An adhesive composition for energy storage devices, comprising a polymer (A) and a liquid medium (B). When the total number of repeating units contained in the polymer (A) is set to 100 parts by mass, the polymer (A) contains: 50–80 parts by mass of repeating unit (a1) from conjugated diene compounds 15–49 parts by mass of repeating unit (a2) from aromatic vinyl compounds, and 0.1–10 parts by mass from repeating units (a3) ​​of unsaturated carboxylic acids, The tanδ peak of the dynamic viscoelasticity of the polymer (A) has one peak in the range of -50℃ to 10℃ and another peak in the range of 150℃ to 250℃. The tanδ of the dynamic viscoelasticity is the loss modulus / storage modulus. When the tanδ of the peak in the range of -50℃ to 10℃ is set as tanδ(Tp1), and the tanδ of the peak in the range of 150℃ to 250℃ is set as tanδ(Tp2), the following relationship (1) is satisfied. tanδ(Tp2) / tanδ(Tp1)<0.5 (1).

2. The adhesive composition for energy storage devices according to claim 1, wherein, When the latex of the polymer (A) with a solid content of 10% was measured by pulsed NMR CPMG, the relaxation time of the protons was greater than 1500 ms.

3. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The total quantity of the repeating unit (a1), the repeating unit (a2), and the repeating unit (a3) ​​is 80 parts by mass or more.

4. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer (A) further contains 0.1 to 10 parts by mass of repeating units (a4) from unsaturated carboxylic acid esters.

5. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer (A) further contains 0.1 to 10 parts by mass of repeating units (a5) from α,β-unsaturated nitrile compounds.

6. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The electrolyte swelling rate of the polymer (A) is 100-350%.

7. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer (A) is polymer particles. The number-average particle size of the polymer particles is 50 nm to 500 nm.

8. The adhesive composition for energy storage devices according to claim 7, wherein, The surface acidity of the polymer particles is 0.05 mmol / g to 1 mmol / g.

9. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The liquid medium (B) is water.

10. A paste for electrodes of a storage device, comprising the binder composition for storage devices as described in claim 1 and an active substance.

11. The slurry for electrodes of energy storage devices according to claim 10, wherein, The active material contains silicon.

12. An electrode for a storage device, comprising: a current collector, and an active material layer formed by coating the surface of the current collector with the slurry for the storage device electrode of claim 10 or 11 and drying it.

13. An energy storage device comprising the energy storage device electrode as described in claim 12.

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