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

Abstract

Provided is a binder composition for an electricity storage device, which is capable of producing an electricity storage device electrode having excellent input / output characteristics and excellent charge / discharge durability characteristics at high temperatures by reducing internal resistance. This binder composition for an electricity storage device contains a polymer (A) and a liquid medium (B), and is characterized in that the value of spin-spin relaxation time (T2) of the polymer (A) measured by pulse NMR is 0.8 msec or less at 100 DEG C, and the value of the spin-spin relaxation time (T2) of the polymer (A) measured by pulse NMR is 0.5 msec or less when the total of the repeating units contained in the polymer (A) is 100 mass%. The polymer (A) contains 4 mass% or more of a repeating unit (a1) derived from an unsaturated carboxylic acid having a value of "monomer molecular weight (g / mol) / number of carboxylic acid functional groups" of less than 85 and / or a repeating unit (a2) derived from an unsaturated carboxylic acid having a value of "monomer molecular weight (g / mol) / number of carboxylic acid functional groups" of 85 or more.

Description

Technical Field

[0001] The present invention relates to an adhesive composition for energy storage devices, a slurry for energy storage device electrodes containing the adhesive composition and an active substance, an energy storage device electrode formed by coating the slurry onto a current collector and drying it, and an energy storage device having the energy storage device electrode. Background Technology

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

[0003] Electrodes for such energy storage devices are manufactured by coating a composition (a paste for energy storage device electrodes) onto the surface of a current collector and then drying it. This composition (a paste for energy storage device electrodes) contains active materials and a polymer that acts as a binder. Required properties of the polymer used as a binder include the ability of the active materials to bond with each other, the adhesion between the active materials and the current collector, and resistance to powdering when the coating film (hereinafter also referred to as the "active material layer") formed by coating and drying is cut, preventing the micro-powder of the active materials from detaching from the active material layer. By ensuring good adhesion of this binder material, the internal resistance of the energy storage device caused by the binder material is reduced, thereby imparting good charge and discharge characteristics to the energy storage device.

[0004] Furthermore, in recent years, research and development of electric vehicles equipped with energy storage devices has become increasingly popular in order to reduce environmental impact. When energy storage devices are used as the driving power source for electric vehicles, high input-output characteristics that can be frequently and repeatedly charged and discharged are required. Therefore, it is important to reduce the internal resistance of the energy storage devices.

[0005] Against this backdrop, efforts should be made to improve the low resistance and charge / discharge durability of energy storage devices, leading to the development of various binder materials (for example, see Patent Documents 1-2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2015 / 012366

[0009] Patent Document 2: Japanese Patent Application Publication No. 2017-126456 Summary of the Invention

[0010] However, the adhesive materials disclosed in the aforementioned patent documents 1-2 are insufficient in terms of having both high-level charge-discharge durability and low resistivity. Further improvements are required in order to make them suitable for use as energy storage devices for electric vehicle drive power supplies.

[0011] One aspect of the present invention is to provide an adhesive composition for energy storage devices, which enables the manufacture of energy storage device electrodes with excellent input / output characteristics and excellent charge / discharge durability at high temperatures by reducing internal resistance.

[0012] This invention was made to solve at least a part of the above-mentioned problems and can be implemented in any of the following ways.

[0013] One embodiment of the adhesive composition for energy storage devices of the present invention comprises:

[0014] Polymer (A) and liquid medium (B).

[0015] The spin-spin relaxation time (T2) of the polymer (A) measured by pulsed NMR is less than 0.8 msec at 100 °C.

[0016] When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains at least 4% by mass repeating units (a1) of unsaturated carboxylic acids with a value of less than 85 for "monomer molecular weight (g / mol) / number of carboxylic acid functional groups" and repeating units (a2) of unsaturated carboxylic acids with a value of 85 or more for "monomer molecular weight (g / mol) / number of carboxylic acid functional groups".

[0017] In one embodiment of the adhesive composition for the aforementioned energy storage device,

[0018] The polymer (A) described above may contain repeating units (a1) and repeating units (a2) derived from unsaturated carboxylic acids.

[0019] In one embodiment of the adhesive composition for the aforementioned energy storage device,

[0020] When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) may contain 4% or more and less than 30% by mass of the repeating units (a1) derived from unsaturated carboxylic acids and 2% or more and less than 10% by mass of the repeating units (a2) derived from unsaturated carboxylic acids.

[0021] In any of the above-mentioned adhesive compositions for energy storage devices,

[0022] In the polymer (A) described above, the value of "the content of the repeating unit (a1) from the unsaturated carboxylic acid [mass%] / the content of the repeating unit (a2) from the unsaturated carboxylic acid [mass%]" can be 1 or more.

[0023] In any of the above-mentioned adhesive compositions for energy storage devices,

[0024] The polymer (A) may further contain 10% to 70% by mass of repeating units (a3) ​​derived from conjugated diene compounds.

[0025] In any of the above-mentioned adhesive compositions for energy storage devices,

[0026] The polymer (A) may further contain 10% to 40% by mass of repeating units (a4) derived from α,β-unsaturated nitrile compounds.

[0027] In any of the above-mentioned adhesive compositions for energy storage devices,

[0028] The liquid medium (B) mentioned above can be water.

[0029] In any of the above-mentioned adhesive compositions for energy storage devices,

[0030] The polymer (A) mentioned above consists of polymer particles.

[0031] The average Z-particle size of the polymer particles can be 50 nm to 500 nm.

[0032] In any of the above-mentioned adhesive compositions for energy storage devices,

[0033] The polymer particles described above can satisfy the following relationship (3).

[0034] 41.1×T2+2237.4÷PS+48.3<100・・・・・(3)

[0035] (In equation (3), T2 represents the spin-spin relaxation time (T2) of the polymer particles at 100℃ as determined by pulsed NMR, and PS represents the Z-average particle size (nm) of the polymer particles.)

[0036] One embodiment of the electrode paste for energy storage devices of the present invention includes:

[0037] The above-mentioned adhesive composition and active substance for energy storage devices.

[0038] In one embodiment of the electrode paste for the aforementioned energy storage device,

[0039] The aforementioned active material may contain silicon.

[0040] One embodiment of the electrode of the energy storage device of the present invention includes:

[0041] The current collector and the active material layer are formed by coating the surface of the current collector with the electrode paste of the energy storage device as described above and then drying it.

[0042] One embodiment of the energy storage device of the present invention comprises:

[0043] The electrodes of the energy storage device described above.

[0044] The binder composition for energy storage devices of the present invention reduces internal resistance, resulting in excellent input / output characteristics. Furthermore, it enhances the bonding ability of active materials, enabling the manufacture of energy storage device electrodes with excellent charge-discharge durability at high temperatures. The binder composition for energy storage devices of the present invention exhibits these effects particularly well when the energy storage device electrode contains materials with high lithium absorption, such as carbon materials like graphite or silicon materials as active materials. In this way, materials with high lithium absorption can be used as active materials in the energy storage device electrode, thus improving battery performance. Detailed Implementation

[0045] 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, and it should be understood that various modifications implemented without altering the spirit of the invention are also included within the scope of the present invention.

[0046] In this specification, “(meth)acrylic acid ~” means “acrylic acid ~” or “methacrylic acid ~”. Similarly, “~(meth)acrylate” means “~acrylate” or “~methacrylate”. Likewise, “(meth)acrylamide” means “acrylamide” or “methacrylamide”.

[0047] 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.

[0048] In this specification, "high temperature" refers to an environment with a temperature range of approximately 40°C to 80°C.

[0049] 1. Adhesive composition for energy storage devices

[0050] 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), wherein the value of the spin-spin relaxation time (T2) of the polymer (A) measured based on pulse NMR is less than 0.8 msec at 100°C, and when the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains at least 4% by mass of repeating units (a1) of unsaturated carboxylic acids with a value of less than 85 in "monomer molecular weight (g / mol) / number of carboxylic acid functional groups" and repeating units (a2) of unsaturated carboxylic acids with a value of 85 or more in "monomer molecular weight (g / mol) / number of carboxylic acid functional groups".

[0051] The adhesive composition for energy storage devices according to this embodiment can also be used as a material for making energy storage device electrodes (active material layers) that improve the bonding ability between active materials, or as a material for making protective films that suppress short circuits caused by dendritic crystal formation during charging and discharging. Hereinafter, the components contained in the adhesive composition for energy storage devices according to this embodiment will be described in detail.

[0052] 1.1. Polymer (A)

[0053] The binder composition for energy storage devices according to this embodiment includes a polymer (A). The polymer (A) included in the binder composition for energy storage devices according to this embodiment can be a latex dispersed in a liquid medium (B) or dissolved in the liquid medium (B), but is preferably a latex dispersed in the liquid medium (B). If the polymer (A) is a latex dispersed in the liquid medium (B), the slurry for the energy storage device electrode (hereinafter, also simply referred to as "slurry") prepared by mixing with the active material has good stability. Furthermore, the slurry has good coating properties for the current collector, which is therefore preferred. Furthermore, if the polymer (A) is a latex dispersed in the liquid medium (B), it is easier to maintain the particle shape of the polymer (A) during the fabrication of the energy storage device electrode, improving the permeability of the electrolyte inside the electrode and increasing lithium-ion conductivity. This reduces internal resistance, thus easily resulting in an energy storage device electrode with excellent input / output characteristics.

[0054] The following descriptions will be presented in the order of repeating units constituting polymer (A), physical properties of polymer (A), and manufacturing method.

[0055] 1.1.1. Repeating units constituting polymer (A)

[0056] 1.1.1.1. Repeating unit (a1) from unsaturated carboxylic acids

[0057] Polymer (A) preferably contains repeating units (a1) (hereinafter also referred to as "repeating units (a1)") derived from unsaturated carboxylic acids with a monomer molecular weight (g / mol) / number of carboxylic acid functional groups of less than 85. When the total number of repeating units contained in polymer (A) is 100% by mass, the proportion of repeating units (a1) is preferably 4% by mass or more and less than 30% by mass. The proportion of repeating units (a1) is more preferably 6% by mass or more, particularly preferably 8% by mass or more. The proportion of repeating units (a1) is more preferably 27% by mass or less, particularly preferably 25% by mass or less. By containing repeating units (a1) within the above range, polymer (A) exhibits good dispersibility of the active material and filler. Furthermore, by improving the affinity with the silicon material used as the active material, structural damage to the active material layer caused by the expansion and contraction of the silicon material is suppressed, thereby exhibiting good charge-discharge durability characteristics.

[0058] There are no particular limitations on the unsaturated carboxylic acids used, but examples include acrylic acid (72.1 g), itaconic acid (65.0 g), maleic acid (58.1 g), fumaric acid (58.0 g), monocarboxylic acids, and dicarboxylic acids (including anhydrides), etc., and one or more of these can be used. Here, the value in parentheses represents the value of "monomer molecular weight (g / mol) / number of carboxylic acid functional groups". Among these, one or more selected from acrylic acid and itaconic acid are preferred.

[0059] 1.1.1.2. Repeating unit (a2) from unsaturated carboxylic acids

[0060] Polymer (A) preferably contains repeating units (a2) derived from unsaturated carboxylic acids with a monomer molecular weight (g / mol) / number of carboxylic acid functional groups of 85 or more (hereinafter also referred to as "repeating units (a2)"). When the total number of repeating units contained in polymer (A) is 100% by mass, the content of repeating units (a2) is preferably 2% by mass or more and less than 10% by mass. The content of repeating units (a2) is more preferably 3% by mass or more, particularly preferably 4% by mass or more. The content of repeating units (a2) is more preferably 8% by mass or less, particularly preferably 6% by mass or less. By containing repeating units (a2) within the above range, polymer (A) exhibits good dispersibility of the active material and filler. In addition, by improving the affinity with the silicon material used as the active material, the structural damage of the active material layer caused by the expansion and contraction of the silicon material is suppressed, thereby exhibiting good charge and discharge durability characteristics.

[0061] There are no particular limitations on the unsaturated carboxylic acids, but examples include monocarboxylic acids (including anhydrides) such as methacrylic acid (86.1), crotonic acid (86.1), ethyl mono-2-(methacryloyloxy)succinate (230.2), 1-(2-acryloyloxyethyl) phthalate (132.1), and 1-(2-methacryloyloxyethyl) phthalate (139.1). One or more of these can be used. Here, the values ​​in parentheses represent the value of "monomer molecular weight (g / mol) / number of carboxylic acid functional groups". Among these, methacrylic acid is preferred.

[0062] Polymer (A) preferably comprises the aforementioned repeating unit (a1) and repeating unit (a2). In the above case, when the total number of repeating units contained in polymer (A) is set to 100% by mass, the total amount of repeating unit (a1) and repeating unit (a2) is preferably 6% by mass or more and less than 35% by mass, more preferably 8% by mass or more and less than 30% by mass. If the total amount of repeating unit (a1) and repeating unit (a2) is within the above range, the dispersion of the active material and filler is further improved, and the fusion of polymer (A) dispersed in the electrode can be suppressed, improving the binding capacity and electrolyte permeability, thus exhibiting good repeated charge-discharge characteristics and good input-output characteristics.

[0063] 1.1.1.3. Other repeating units

[0064] In addition to the repeating units (a1) and (a2) mentioned above, polymer (A) may contain repeating units from other monomers that can copolymerize with them. Examples of such repeating units include repeating units (a3) ​​from conjugated diene compounds (hereinafter also referred to as "repeating unit (a3)"), repeating units (a4) from α,β-unsaturated nitrile compounds (hereinafter also referred to as "repeating unit (a4)"), repeating units (a5) from aromatic vinyl compounds (hereinafter also referred to as "repeating unit (a5)"), repeating units (a6) from unsaturated carboxylic acid esters (hereinafter also referred to as "repeating unit (a6)"), repeating units (a7) from (meth)acrylamide (hereinafter also referred to as "repeating unit (a7)"), repeating units (a8) from compounds having sulfonic acid groups (hereinafter also referred to as "repeating unit (a8)"), and repeating units from cationic monomers.

[0065] <Repeating unit (a3) ​​from conjugated diene compounds>

[0066] Polymer (A) may contain repeating units (a3) ​​derived from a conjugated diene compound. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a3) ​​derived from the conjugated diene compound is preferably 10% to 70% by mass. The proportion of repeating units (a3) ​​is more preferably 17% by mass or more, particularly preferably 20% by mass or more. The proportion of repeating units (a3) ​​is more preferably 65% ​​by mass or less, particularly preferably 60% by mass or less. By containing repeating units (a3) ​​within the above range, polymer (A) exhibits good dispersion of the active material and filler, enabling the formation of a uniform active material layer and protective film. Consequently, structural defects in the electrode plate sometimes disappear, resulting in good repeated charge-discharge characteristics. Furthermore, the polymer (A) can impart stretchability to the surface of the coated active material, and the polymer (A) can improve its binding capacity through stretching, thus sometimes exhibiting good charge-discharge durability characteristics.

[0067] The repeating unit (a3) ​​from the conjugated diene compound is preferably a repeating unit that has not been hydrogenated by oil layer hydrogenation or water layer hydrogenation. By containing the unhydrogenated repeating unit (a3) ​​from the conjugated diene compound, the polymer (A) can be endowed with stretchability, and sometimes the polymer (A) can further improve its adhesion through stretching.

[0068] The conjugated diene compound is not particularly limited, but examples include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene, and one or more of these can be used. Among these, 1,3-butadiene is particularly preferred.

[0069] <From repeating unit (a4) of α,β-unsaturated nitrile compounds>

[0070] Polymer (A) may contain repeating units (a4) from α,β-unsaturated nitrile compounds. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a4) is preferably 0% to 60% by mass. The proportion of repeating units (a4) is more preferably 0.5% by mass or more, particularly preferably 1% by mass or more. The proportion of repeating units (a4) is more preferably 55% by mass or less, particularly preferably 50% by mass or less. By containing repeating units (a4) within the above range, polymer (A) can sometimes reduce its solubility in the electrolyte, suppressing the decrease in binding capacity caused by the electrolyte. Furthermore, it can sometimes suppress the increase in internal resistance caused by polymer components dissolved in the energy storage device becoming resistive components.

[0071] The α,β-unsaturated nitrile compound is not particularly limited, but examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, isopropylene malononitrile, fumaric acid, tetracyanoethylene, etc., and one or more selected from these can be used. Among these, one or more selected from acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is particularly preferred.

[0072] <Repeating unit (a5) from aromatic vinyl compounds>

[0073] Polymer (A) may contain repeating units (a5) derived from aromatic vinyl compounds. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a5) is preferably 35% to 75% by mass. More preferably, the proportion of repeating units (a5) is 38% by mass or more, and particularly preferably 40% by mass or more. More preferably, the proportion of repeating units (a5) is 72% by mass or less, and particularly preferably 70% by mass or less. By containing repeating units (a5) within the above range, polymer (A) can suppress the fusion of polymers (A) dispersed in the electrode, improving electrolyte permeability, and thus sometimes exhibiting good input / output characteristics. Furthermore, it sometimes exhibits good binding ability to graphite and the like used as active materials. Therefore, electrodes for energy storage devices with excellent high-temperature durability are sometimes obtained.

[0074] As an aromatic vinyl compound, there is no particular limitation, but examples include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more of these can be used.

[0075] <Repeating unit (a6) from unsaturated carboxylic acid esters>

[0076] Polymer (A) may contain repeating units (a6) derived from unsaturated carboxylic acid esters. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a6) is preferably 0% to 15% by mass. More preferably, the proportion of repeating units (a6) is 1% by mass or more, particularly preferably 2% by mass or more. More preferably, the proportion of repeating units (a6) is 12% by mass or less, particularly preferably 10% by mass or less. By containing repeating units (a6) within the above range, polymer (A) exhibits good affinity with the electrolyte, and can sometimes suppress the increase in internal resistance in energy storage devices caused by the binder becoming a resistive component. Furthermore, it can sometimes prevent a decrease in binding capacity due to excessive absorption of electrolyte.

[0077] Among unsaturated carboxylic acid esters, (meth)acrylates are preferred. Specific examples of (meth)acrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, nonyl methacrylate, decyl methacrylate, ethylene glycol dimethacrylate, and propylene glycol dimethacrylate. Glycol esters, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl methacrylate, 2-hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 6-hydroxyhexyl methacrylate, glyceryl mono(meth)acrylate, glyceryl di(meth)acrylate, etc., may be used, with one or more selected from these. Among these, one or more selected from methyl methacrylate, n-butyl methacrylate, allyl methacrylate, and ethylene glycol di(meth)acrylate are preferred, with methyl methacrylate being particularly preferred.

[0078] <Repeating unit (a7) from (meth)acrylamide>

[0079] Polymer (A) may contain repeating units (a7) derived from (meth)acrylamide. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a7) is preferably 0% to 10% by mass. More preferably, the proportion of repeating units (a7) is 1% by mass or more, particularly preferably 2% by mass or more. More preferably, the proportion of repeating units (a7) is 8% by mass or less, particularly preferably 5% by mass or less. By containing repeating units (a7) within the above range, polymer (A) sometimes exhibits good dispersibility of active materials and fillers in the slurry. Furthermore, it can improve the binding ability of active materials containing carbon materials such as graphite and silicon materials, thus sometimes exhibiting good high-temperature durability in energy storage devices using these two types of active materials.

[0080] There is no particular limitation on (meth)acrylamide, but examples such as acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, diacetone acrylamide, maleamide, acrylamide tert-butylsulfonic acid, etc., may be used, and one or more of these may be used.

[0081] <Repeating unit (a8) from compounds containing sulfonic acid groups>

[0082] Polymer (A) may contain repeating units (a8) from compounds having sulfonic acid groups. When the total number of repeating units in polymer (A) is set to 100% by mass, the proportion of repeating units (a8) is preferably 0% to 10% by mass. More preferably, the proportion of repeating units (a8) is 0.5% by mass or more, particularly preferably 1% by mass or more. More preferably, the proportion of repeating units (a8) is 8% by mass or less, particularly preferably 5% by mass or less.

[0083] The compound having a sulfonic acid group is not particularly limited, but examples include vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, sulfobutyl (meth) acrylate, 2-acrylamide-2-methylpropane sulfonic acid, 2-hydroxy-3-acrylamide propane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and their salts, etc., and one or more of these compounds may be used.

[0084] <Repeating units from cationic monomers>

[0085] Polymer (A) may contain repeating units from cationic monomers. While not particularly limited in its choice of cationic monomers, it is preferably selected from at least one of secondary amines (salts), tertiary amines (salts), and quaternary ammonium salts. Specific examples of these cationic monomers are not particularly limited, but examples include 2-(dimethylamino)ethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate chloromethane quaternary salt, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(O-[1'-methylpropyleneamino]carboxylamino)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacryloyloxyethyltrimethylammonium chloride, and tri(isocyanuric acid) 2-Acryloyloxyethyl ester, 2-vinylpyridine, quinalidine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazine-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 use one or more selected from these.

[0086] 1.1.2. Physical properties of polymer (A)

[0087] 1.1.2.1. Pulsed NMR

[0088] When measuring the pulsed NMR of polymer (A), the spin-spin relaxation time (T2), obtained as the time constant of the spin-spin relaxation of the proton, is less than 0.8 msec at 100 °C.

[0089] In this embodiment, the spin-spin relaxation time T2 of polymer (A) is determined using the CPMG (Carr-Purcell-Meiboom-Gill) method with a pulsed NMR (nuclear magnetic resonance) apparatus. A pulsed NMR apparatus is used to evaluate the motility of polymer molecules based on the mobility (relaxation time) of hydrogen atoms in the polymer chain; in this embodiment, the CPMG method is used as the sequence.

[0090] The CPMG method using a pulsed NMR apparatus can itself employ known methods, such as those described in Japanese Patent Application Publication No. 2020-085776. Specifically, the T2 relaxation curve (free induction decay curve) obtained by measuring the spin-spin relaxation time T2 (transverse relaxation time) is curve-fitted into the following equation (1) or the following equation (2), thereby separating it into two components.

[0091] [Mathematical Formula 1]

[0092]

[0093] In equation (1), n ​​is the number of separated components; in the measurement of this invention, n = 2. T is the observation time. T2 i This refers to the relaxation time of each component. A i It is the intensity of each component i at t=0, and is proportional to the amount of component i. Here, in the order of component 1 < component 2, the component with the longer relaxation time becomes component 2, therefore, the component with higher molecular mobility becomes component 2.

[0094] [Mathematical Formula 2]

[0095]

[0096] In equation (2), t is the observation time. T21 is the relaxation time of component 1, and T22 is the relaxation time of component 2. A1 is the intensity of component 1 at t=0, and A2 is the intensity of component 2 at t=0.

[0097] The relaxation time T2 of each component when performing fitting based on equation (1) or equation (2) i The relaxation time T21 of component 1 can be any value without particular limitation. In this invention, the relaxation time T21 of component 1 can be less than 3 ms (e.g., 0.1 to 2.5 ms), and the relaxation time T22 of component 2 can be greater than 2 ms (e.g., 2.5 to 70 ms) (where T21 < T22). In this invention, among the two separated components, the relaxation time T21 of component 1 is defined as the spin-spin relaxation time (T2).

[0098] The sample for pulse NMR measurement was a membrane of polymer (A). The membrane of polymer (A) was prepared as follows: polymer (A) was dried at 40°C for 24 hours to prepare a uniform membrane with a thickness of 1.0 ± 0.3 mm. The membrane was then dried in a vacuum dryer at 160°C for 30 minutes and cut into rectangles of 10 mm × 5 mm.

[0099] The polymer (A) used in this embodiment is characterized by a low T2 at 100°C. This is considered to indicate low polymer chain mobility at the drying temperatures of the slurry and electrodes, suppressing excessive coating of the active material by the polymer (A) during drying and ensuring low resistance in the energy storage device. On the other hand, the T2 value is less dependent on large deformations such as polymer chain breakage, and the binding ability of the active material to each other is enhanced even under strong stresses generated by electrode pressing.

[0100] The polymer (A) has a T2 of less than 0.8 msec at 100°C, but preferably less than 0.75 msec, and more preferably less than 0.7 msec.

[0101] Methods for adjusting the T2 of polymer (A) include adjusting the monomer composition during polymerization, adjusting the free radical polymerization initiator, adjusting the chain transfer agent, and adjusting the polymerization temperature. It is believed that T2 is not simply determined by the monomer composition, but is complexly influenced by multiple factors such as monomer chain distribution, stereoregularity, molecular weight, polymer chain end structure, and degree of crosslinking. Especially in particulate polymers, the T2 value changes significantly by altering conditions such as monomer composition, initiator dosage, chain transfer dosage, and polymerization temperature during polymerization. Therefore, even with the same monomer composition, copolymers with different T2 values ​​can be obtained.

[0102] 1.1.2.2. Z-mean particle size

[0103] When polymer (A) is in the form of particles, the Z-average particle size of these particles is preferably 50 nm to 500 nm, more preferably 60 nm to 450 nm, and particularly preferably 70 nm to 400 nm. If the Z-average particle size of polymer (A) is within the above range, the balance between adhesion and coating on the surface of the active material is good, and it is possible to achieve both the adhesive force required to maintain the electrode structure and the low resistance of the electrode at a high level.

[0104] It should be noted that the Z-mean particle size of polymer (A) can be determined by dynamic light scattering (DLS). Examples of particle size measuring devices using DLS include the "FPAR-1000" manufactured by Otsuka Electronics Co., Ltd. For the analytical method, cumulative analysis is used.

[0105] DLS determination is performed using a dispersion of polymer (A). Sometimes, the DLS method overestimates the measured value due to the influence of trace amounts of coarse particles and foreign matter; therefore, the test solution is filtered with a filter with a pore size of 1–3 μm.

[0106] When the polymer (A) is in the form of particles, it is preferable to satisfy the following relationship (3).

[0107] 41.1×T2+2237.4÷PS+48.3<100 ・・・・・(3)

[0108] T2: The spin-spin relaxation time (T2) of polymer (A) at 100 °C, determined by pulsed NMR.

[0109] PS: Z-average particle size (nm) of polymer particles

[0110] Equation (3) above is an empirical formula obtained by statistical analysis of a large amount of experimental data. By satisfying the above range, the balance between the adhesiveness and coating properties of the active material of the adhesive can be improved, and it has both high cycle characteristics and low resistance of the equipment.

[0111] 1.1.2.3. Electrolyte swelling degree

[0112] The electrolyte swelling degree of polymer (A) is preferably 150–450% by mass, more preferably 160–440% by mass, and particularly preferably 170–430% by mass. If the electrolyte swelling degree is within the above range, polymer (A) can adequately swell in the electrolyte. As a result, solvated lithium ions can easily reach the active material, reducing the internal resistance of the electrode and achieving further improved input / output characteristics. Furthermore, if the electrolyte swelling degree is within the above range, no large volume change occurs, thus the binding ability of the active materials is also excellent. The electrolyte swelling degree of polymer (A) can be determined by the method described in the examples below.

[0113] 1.1.2.4. Number of disrupting particles of polymer (A) in the negative electrode coating layer

[0114] In the negative electrode coating layer, the polymer (A) particles preferably maintain their particle shape. The number of broken polymer (A) particles in the negative electrode coating layer is preferably 30 or less per 100 polymer (A) particles, more preferably 20 or less, and particularly preferably 10 or less. If the number of broken polymer (A) particles is within the above range, there are enough polymer (A) particles maintaining their particle shape in the negative electrode coating layer to maintain adhesion to the active material while forming a conductive path for the electrolyte. That is, separation of the active materials from each other can be suppressed, and the conductive network inside the active material layer can be maintained. Therefore, even at high temperatures, a negative electrode for an energy storage device with excellent charge-discharge durability can be obtained.

[0115] 1.1.3. Method for manufacturing polymer (A)

[0116] There are no particular limitations on the manufacturing method of polymer (A). For example, emulsion polymerization can be carried out in the presence of known emulsifiers (surfactants), chain transfer agents, polymerization initiators, etc. As emulsifiers (surfactants), chain transfer agents, and polymerization initiators, compounds described in Patent No. 5999399, etc., can be used.

[0117] Emulsion polymerization for synthesizing polymer (A) can be carried out in a single stage or in a multi-stage process involving two or more stages.

[0118] When polymer (A) is synthesized by a single-stage polymerization, for the mixture of the above-mentioned monomers, emulsion polymerization can be carried out in the presence of appropriate emulsifiers, chain transfer agents, polymerization initiators, etc., preferably at 35 to 85°C and preferably for 4 to 36 hours.

[0119] When polymer (A) is synthesized by two-stage polymerization, the polymerization stages are preferably set as follows.

[0120] The proportion of monomers used in the first stage polymerization 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 stage polymerization and the mass of monomers used in the second stage polymerization). By using such a proportion of monomers in the first stage polymerization, it is possible to obtain polymer particles (A) with excellent dispersion stability and low agglomeration rate, while also suppressing the viscosity increase of the adhesive composition for energy storage devices over time, which is preferable.

[0121] The types and proportions of monomers used in the second stage of polymerization can be the same as or different from those used in the first stage of polymerization.

[0122] From the viewpoint of the dispersion of the particles of the obtained polymer (A), the polymerization conditions for each stage are preferably set as follows.

[0123] • First stage polymerization: preferably a temperature of 35 to 80°C, preferably a polymerization time of 2 to 36 hours, preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more.

[0124] • Second stage polymerization: preferably at a temperature of 40 to 85°C, preferably for a polymerization time of 2 to 18 hours.

[0125] By keeping the total solids concentration in the emulsion polymerization at 50% by mass or less, the resulting polymer (A) exhibits good particle dispersion stability and allows the polymerization reaction to proceed. This total solids concentration is preferably 48% by mass or less, and more preferably 45% by mass or less.

[0126] Whether polymer (A) is synthesized via a single-stage polymerization or a multi-stage polymerization method, it is preferable to adjust the pH to approximately 4.5–10.5, more preferably 5–10, and even more preferably 5.5–9.5, by adding a neutralizing agent to the polymerization mixture after emulsion polymerization. The neutralizing agent used here is not particularly limited, and examples include metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; ammonia, ethylamine, diethylamine, triethylamine, 2-mercaptoethylamine, glycine, lysine, glutamic acid, 2-aminoethanethiol, and cysteine. By setting the pH within the aforementioned range, the polymer (A) exhibits good stability. After neutralization, the polymerization mixture is concentrated, thereby maintaining the good stability of polymer (A) while increasing the concentration of solid components.

[0127] 1.1.4. Proportion of Polymer (A)

[0128] The proportion of polymer (A) in the adhesive composition for energy storage devices according to this embodiment is preferably 10 to 100% by mass of the polymer component, more preferably 20 to 95% by mass, and particularly preferably 25 to 90% by mass. Here, the polymer component includes polymer (A), polymers other than polymer (A) described later, and thickeners, etc.

[0129] 1.2. Liquid medium (B)

[0130] The adhesive composition for energy storage devices according to this embodiment includes a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium may also 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) in the adhesive composition for energy storage devices according to this embodiment, the degree of negative environmental impact is reduced, and the safety for operators is increased.

[0131] The proportion of non-aqueous media contained in the aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially non-existent, out of 100% by mass of the aqueous medium. Here, "substantially non-existent" means the degree to which non-aqueous media are not intentionally added as a liquid medium, and may include non-aqueous media that are unavoidably mixed in when preparing the adhesive composition for storage devices.

[0132] 1.3. Other additives

[0133] The adhesive composition for energy storage devices according to this embodiment may contain additives other than those described above, as needed. Examples of such additives include polymers other than polymer (A), preservatives, thickeners, etc.

[0134] 1.3.1. Polymers other than polymer (A)

[0135] The adhesive composition for energy storage devices according to this embodiment may contain polymers other than polymer (A). Such polymers are not particularly limited, but examples include acrylic polymers containing unsaturated carboxylic acid esters or their derivatives as constituent units, fluoropolymers such as PVDF (polyvinylidene fluoride), etc. One of these polymers may be used alone, or two or more may be used in combination. Containing these polymers sometimes further improves flexibility and bonding strength.

[0136] 1.3.2. Preservatives

[0137] The adhesive composition for storage devices according to this embodiment may contain a preservative. By containing a preservative, it is sometimes possible to inhibit the growth of bacteria, mold, and other foreign matter during the storage of the adhesive composition for storage devices. Specific examples of preservatives include compounds described in Patent No. 5477610 and the like.

[0138] 1.3.3. Thickeners

[0139] The adhesive composition for energy storage devices according to this embodiment may contain a thickener. By containing a thickener, the coatability of the slurry and the charge / discharge characteristics of the resulting energy storage device can sometimes be further improved.

[0140] Specific examples of thickeners include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the aforementioned cellulose compounds or poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; and water-soluble polymers such as saponifications of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid with vinyl esters. Among these, alkali metal salts of carboxymethyl cellulose and alkali metal salts of poly(meth)acrylic acid are preferred.

[0141] Commercially available products that serve as these thickeners include, for example, alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (and above, manufactured by Daicel Co., Ltd.).

[0142] When the adhesive composition for storage devices in this embodiment contains a thickener, the content of the thickener is preferably 5% by mass or less, and more preferably 0.1 to 3% by mass, relative to 100% by mass of the total solid content of the adhesive composition for storage devices.

[0143] 1.4. pH of adhesive compositions for energy storage devices

[0144] The pH of the adhesive composition for the energy storage device in this embodiment is preferably 5 to 10, more preferably 6 to 9.5, and particularly preferably 6.5 to 9. If the pH is within the above range, problems such as insufficient leveling and liquid dripping can be suppressed, making it easier to manufacture energy storage device electrodes that have both good electrical properties and good sealing.

[0145] In this manual, "pH" refers to a physical property measured as follows: The value was measured at 25°C using a pH meter with a glass electrode, according to JIS Z8802:2011. The glass electrode was calibrated using neutral phosphate and borate standard solutions as pH standard solutions. Examples of such pH meters include the "HM-7J" manufactured by Toa DKK Corporation and the "D-51" manufactured by Horiba Manufacturing Co., Ltd.

[0146] It should be noted that the pH of the adhesive composition for energy storage devices is not denied to be affected by the monomer composition constituting the polymer (A), but incidentally, it is not solely determined by the monomer composition. That is, generally speaking, it is known that even with the same monomer composition, the pH of the adhesive composition for energy storage devices can change due to polymerization conditions, etc., and the examples in this application specification are merely illustrative examples.

[0147] For example, even with the same monomer composition, the amount of carboxyl groups from the unsaturated carboxylic acid exposed on the surface of the resulting polymer differs depending on whether the unsaturated carboxylic acid is added sequentially after all the unsaturated carboxylic acid has been initially added to the polymerization reaction solution, or whether monomers other than the unsaturated carboxylic acid are added last, with the unsaturated carboxylic acid being added last. Thus, it is believed that even simply changing the order in which monomers are added during the polymerization process can significantly alter the pH of the adhesive composition for energy storage devices.

[0148] 2. Slurry for energy storage equipment

[0149] One embodiment of the present invention provides a slurry for a storage device containing the aforementioned adhesive composition for a storage device. This adhesive composition can also be used as a material for fabricating a protective film that suppresses short circuits caused by dendritic crystallization accompanying charging and discharging; it can also be used as a material for fabricating electrodes (active material layers) in a storage device, which improves the bonding ability between active materials, the adhesion between the active materials and the current collector, and resistance to powdering. Therefore, the slurry for a storage device used for fabricating a protective film (hereinafter also referred to as "slurry for protective film") and the slurry for a storage device used for fabricating the active material layer of the electrodes (hereinafter also referred to as "slurry for storage device electrodes") will be described separately.

[0150] 2.1. Slurry for protective film

[0151] "Protective film slurry" refers to a dispersion liquid used to coat the surface of an electrode or a separator, or both, and then dry it to form a protective film on the surface of the electrode or a separator, or both. 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.

[0152] 2.2. Electrode paste for energy storage devices

[0153] "Electrode slurry for energy storage devices" refers to a dispersion liquid that is coated onto the surface of a current collector and then dried to create an active material layer on the surface of the current collector. The electrode slurry for energy storage devices of this embodiment contains the above-mentioned binder composition for energy storage devices and the active material.

[0154] Generally, to improve bonding strength, electrode slurries for energy storage devices mostly contain binder components such as SBR-based copolymers and thickeners such as carboxymethyl cellulose. On the other hand, even when the electrode slurry for energy storage devices in this embodiment contains only the aforementioned polymer (A) as a polymer component, bonding strength can still be improved. Of course, to further improve bonding strength, the electrode slurry for energy storage devices in this embodiment may contain polymers other than polymer (A) and thickeners. The components contained in the electrode slurry for energy storage devices of this embodiment will be described below.

[0155] 2.2.1. Polymer (A)

[0156] The composition, properties, and manufacturing methods of polymer (A) are as described above, and therefore will not be explained further.

[0157] Relative to 100 parts by mass of the active material, the polymer component in the slurry for the electrode of the energy storage device according to this embodiment is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass, even 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 thickeners, etc.

[0158] 2.2.2. Active substances

[0159] Examples of active materials used in the electrode paste for the energy storage device in this embodiment include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, and conductive polymers such as polyphenylene oxide. X B Y O Z (Where A is an alkali metal or transition metal, B is selected from at least one transition metal such as cobalt, nickel, aluminum, tin, and manganese, O represents an oxygen atom, and X, Y, and Z are numbers in the range of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively.) This refers to composite metal oxides, other metal oxides, etc. Specific examples include compounds described in Japanese Patent No. 5999399, etc.

[0160] The slurry for the electrode of the energy storage device in this embodiment can also be used when making either the positive or negative electrode of the energy storage device, but is preferably used for both the positive and negative electrodes.

[0161] When lithium iron phosphate is used as the positive electrode active material, there are issues with insufficient charge-discharge characteristics and poor binding capacity. One of the main reasons is believed to be that lithium iron phosphate has a fine primary particle size, and it is known to be a secondary aggregate. During repeated charge and discharge, it aggregates and disintegrates in the active material layer, causing the active material to separate from each other, peel off from the current collector, and the conductive network inside the active material layer is easily broken.

[0162] Faced with this problem, if an energy storage device electrode made using the electrode slurry of this embodiment is adopted, the aforementioned problems will not occur even when lithium iron phosphate is used as the positive electrode active material, and good electrical characteristics can be exhibited. The reason for this is that the polymer (A) can firmly bind the lithium iron phosphate and maintain the state of firm binding of the lithium iron phosphate even during charging and discharging.

[0163] On the other hand, when manufacturing the negative electrode, the active material exemplified above preferably contains silicon. Silicon has a higher lithium absorption per unit weight than other active materials; therefore, by using silicon as the negative electrode active material, the energy storage capacity of the resulting energy storage device can be increased, resulting in improved output and energy density of the energy storage device.

[0164] Furthermore, a mixture of silicon and carbon materials is more preferably used as the negative electrode active material. Since the volume change of carbon materials during charging and discharging is smaller than that of silicon materials, by using a mixture of silicon and carbon materials as the negative electrode active material, the influence of the volume change of silicon materials can be mitigated, and the binding ability between the active materials can be further improved.

[0165] When silicon (Si) is used as the active material, it has high capacity, but it also undergoes a large volume change when absorbing lithium. Therefore, silicon materials are prone to micronization due to repeated expansion and contraction, peeling off from the current collector, causing the active material to separate from each other, and the conductive network inside the active material layer is easily broken. Due to this property, the charge-discharge durability of energy storage devices deteriorates drastically in a short period of time.

[0166] Faced with such a problem, if an energy storage device electrode made using the energy storage device electrode paste of this embodiment is adopted, even when using silicon material, the problems described above will not occur, and good electrical characteristics can be exhibited. The reason for this is that the polymer (A) can firmly bond the silicon material, and even if the silicon material expands in volume due to lithium adsorption, the polymer (A) will expand and contract to maintain the state of firmly bonding the silicon material.

[0167] The silicon material content in 100% by mass of the active material is preferably 1% by mass or more, more preferably 2 to 50% by mass, further preferably 3 to 45% by mass, and particularly preferably 10 to 40% by mass. If the silicon material content 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.

[0168] The active material is preferably in particulate form. The average particle size of the active material is preferably 0.1–100 μm, more preferably 1–20 μm. Here, the average particle size of the active material refers to the volume average particle size calculated based on the particle size distribution obtained by measuring the particle size distribution using a particle size distribution measuring device based on laser diffraction. Examples of such laser diffraction particle size distribution measuring devices include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by Horiba Manufacturing Co., Ltd.).

[0169] 2.2.3. Other components

[0170] In addition to the components described above, other components may be added to the electrode slurry of the energy storage device according to this embodiment, as needed. Examples of such components include polymers other than polymer (A), thickeners, liquid media, conductive additives, pH adjusters, corrosion inhibitors, cellulose fibers, etc. As polymers other than polymer (A) and thickeners, appropriate compounds may be selected from those exemplified in the section "1.3. Other Additives" above, and used for the same purpose and in the same proportions.

[0171] <Liquid Medium>

[0172] In the electrode slurry of this embodiment, in addition to the components from the binder composition for energy storage devices, a liquid medium may be further added. The added liquid medium may be the same type as the liquid medium (B) contained in the binder composition for energy storage devices, or it may be different, but it is preferable to select from the liquid media exemplified in the above-mentioned "1.2. Liquid Medium (B)".

[0173] The liquid medium (including components derived from the binder composition for energy storage devices) in the slurry for electrodes of the energy storage device in this embodiment is preferably 30 to 70% by mass, more preferably 40 to 60% by mass.

[0174] <Conductive additives>

[0175] With the aim of imparting conductivity while buffering the volume change of the active material caused by the entry and exit of lithium ions, conductive additives may be further added to the electrode slurry of the energy storage device in this embodiment.

[0176] 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.

[0177] <pH adjuster / corrosion inhibitor>

[0178] To suppress corrosion of the current collector, the electrode slurry of the energy storage device in this embodiment may be further supplemented with a pH adjuster and / or a corrosion inhibitor, depending on the type of active material.

[0179] Examples of pH adjusters include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, and potassium hydroxide. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferred. Alternatively, neutralizing agents described in the manufacturing method of polymer (A) may also be used.

[0180] 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.

[0181] Cellulose Fiber

[0182] Cellulose fibers can be further added to the electrode slurry of the energy storage device in this embodiment. Adding cellulose fibers can sometimes improve the adhesion of the active material to the current collector. It is believed that fibrous cellulose fibers can bond adjacent active materials together fibrously through wire bonding or wire contact, preventing the active material from falling off while improving the adhesion to the current collector.

[0183] 2.2.4. Preparation method of electrode paste for energy storage devices

[0184] The electrode slurry for energy storage devices 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 active material. From the viewpoint of manufacturing a slurry with better dispersibility and stability more efficiently and inexpensively, it is preferable to add active material and any additives as needed to the binder composition for energy storage devices, and then manufacture it by mixing them. As a specific manufacturing method, for example, the method described in Japanese Patent No. 5999399 can be cited.

[0185] 3. Electrodes of energy storage devices

[0186] 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 electrode is 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. The electrode manufactured in this way is formed by bonding an active material layer comprising the aforementioned polymer (A), the active material, and any other components added as needed to the surface of the current collector. Therefore, it exhibits excellent input / output characteristics by reducing internal resistance and excellent charge / discharge durability at high temperatures.

[0187] 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.

[0188] In the electrode of the energy storage device according to this embodiment, when silicon material is used as the active material, the silicon content in 100% by mass of the active material layer is preferably 2 to 30% by mass, more preferably 2 to 20% by mass, and particularly preferably 3 to 10% by mass. If the silicon content in the active material layer is within the above range, the energy storage capacity of the energy storage device made therefrom is increased, and in addition, an active material layer with uniform silicon distribution can be obtained. The silicon content in the active material layer can be determined, for example, by the method described in Japanese Patent No. 5999399, etc.

[0189] 4. Energy storage devices

[0190] One embodiment of the energy storage device of the present invention includes the aforementioned energy storage device electrodes, and may further contain an electrolyte, use components such as separators, and is manufactured according to conventional methods. Specific manufacturing methods include, for example, overlapping the negative and positive electrodes via a separator, winding or folding them according to the battery shape to house them in a battery container, injecting electrolyte into the battery container, and sealing it. The battery shape can be suitable, such as coin-shaped, cylindrical, square, or laminated.

[0191] The electrolyte can be liquid or gel-like; any electrolyte that effectively performs its battery function can be selected from known electrolytes used in energy storage devices, based 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.

[0192] The aforementioned energy storage device can be applied to lithium-ion secondary batteries, double-layer capacitors, lithium-ion capacitors, etc., which require high current density discharge. Among these, 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 the energy storage device can be known components for lithium-ion secondary batteries, double-layer capacitors, or lithium-ion capacitors.

[0193] 5. Examples

[0194] The present invention will now be specifically described with reference to embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, "parts" and "%" in the embodiments and comparative examples refer to quality standards.

[0195] 5.1. Example 1

[0196] 5.1.1. Preparation and property evaluation of adhesive compositions for energy storage devices

[0197] (1) Preparation of adhesive composition for energy storage devices

[0198] A binder composition for energy storage devices comprising polymer (A) was obtained through a two-stage polymerization process as shown below. In the first stage, 300 parts by mass of water, a monomer mixture consisting of 25 parts by mass of 1,3-butadiene, 6.5 parts by mass of styrene, 12.5 parts by mass of acrylonitrile, 10 parts by mass of acrylic acid, and 2 parts by mass of methacrylic acid were added to a reactor. 0.1 parts by mass of tert-dodecyl mercaptan as a chain transfer agent, 0.2 parts by mass of sodium dodecyl diphenyl ether disulfonate as an emulsifier, 0.1 parts by mass of cumene hydroperoxide as a polymerization initiator, 0.1 parts by mass of sodium ascorbate as a reducing agent, 0.002 parts by mass of sodium dithionite as other polymerization aids, 0.001 parts by mass of ferric sulfate (II) heptahydrate, and 0.01 parts by mass of disodium dihydrogen ethylenediaminetetraacetate were also added. The reaction was initiated at 40°C with stirring, and after 8 hours, the polymerization conversion rate was confirmed to be over 60%. Next, as a second stage, 25 parts by mass of 1,3-butadiene, 6.5 parts by mass of styrene, 12.5 parts by mass of acrylonitrile, 0.3 parts by mass of potassium persulfate as an initiator, and 0.15 parts by mass of sodium metabisulfite as a reducing agent were added to the reactor. The polymerization temperature was appropriately raised to 80°C, and after 8 hours of polymerization, the polymerization conversion rate was confirmed to be above 95%. It should be noted that the polymerization conversion rate was calculated according to the determination method described below. Unreacted monomers were removed from the particle dispersion of polymer (A) thus obtained and the mixture was concentrated. After adding 2.5% aqueous sodium hydroxide solution, the water was removed using an evaporator, thereby obtaining a binder composition for energy storage devices containing polymer (A) particles with a solid content concentration of 40% by mass and a pH of 6.0.

[0199] (2) Determination of polymerization conversion rate

[0200] Extract the reaction solution that has been polymerized for a specified time and place it into a pre-measured aluminum dish (X (g)). Measure the weight of the reaction solution (Y (g)). Dry it at 155°C for 15 minutes using a hot air dryer. Remove the aluminum dish, allow it to cool, and measure the weight of the aluminum dish (Z (g)). Calculate the polymerization conversion using the following formula (4).

[0201] Polymerization conversion rate = ((Z-X) / Y) × 100... (4)

[0202] (3) Determination of Z-mean particle size

[0203] The Z-mean particle size of polymer (A) was determined using dynamic light scattering. Specifically, first, a laser was irradiated with the adhesive composition for the energy storage device obtained above, and the intensity of the scattered light from the particles of polymer (A) was measured over time in microseconds. Then, the detected scattering intensity distribution originating from the particles of polymer (A) was applied to a normal distribution, and the Z-mean particle size of polymer (A) was determined using a cumulative analysis method for calculating the mean particle size. The Z-mean particle size was measured using a high-concentration particle size analyzer (Otsuka Electronics Co., Ltd., "FPAR-1000"). This particle size measuring device is equipped with data analysis software that automatically analyzes the measurement data, thereby calculating the Z-mean particle size. The measurement results are shown in Table 1. It should be noted that the units digit is rounded.

[0204] (4) Determination of T2

[0205] The adhesive composition for energy storage devices 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, and 10 mm × 5 mm rectangles were cut out as samples for measurement. These samples were filled into sample tubes, and T2 at 100°C was calculated using a benchtop TD-NMR spectrometer (manufactured by Bruker Corporation, trade name "TD-NMR minispec mq20"). The measurement results are shown in Table 1. It should be noted that the third decimal place is rounded.

[0206] 5.1.2. Preparation of electrode paste for energy storage devices

[0207] (1) Synthesis of silicon materials (active substances)

[0208] A mixture of pulverized silica powder (average particle size 10 μm) and carbon powder (average particle size 35 μm) was heat-treated for 10 hours in an electric furnace at a temperature ranging from 1100 °C to 1600 °C under a nitrogen flow (0.5 NL / min) to obtain a product with the composition SiO x(x = 0.5–1.1) represents silicon oxide powder (average particle size 8 μm). 300 g of this silicon oxide powder was loaded into a batch 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, while maintaining the pressure inside the furnace at 2000 Pa, methane gas was introduced at a flow rate of 0.5 NL / min, and a heat treatment (graphite coating treatment) was performed at 1100 °C for 5 hours. After the graphite coating treatment, 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, assuming the total amount of the obtained graphite-coated silicon oxide is 100% by mass.

[0209] (2) Preparation of electrode paste for energy storage devices

[0210] In a twin-shaft planetary mixer (manufactured by PRIMIX Co., Ltd., trade name "TK HIVISMIX 2P-03"), 1 part by weight of thickener (trade name "CMC2200", manufactured by Daicel Co., Ltd., added as a 2% by weight aqueous solution), 4 parts by weight of polymer (A, added as a binder composition for storage devices obtained above), 90.25 parts by weight of highly crystalline graphite, i.e., artificial graphite (manufactured by Resonac Co., Ltd., trade name "MAG") as a negative electrode active material, 4.75 parts by weight of graphite-coated silicon oxide powder obtained above, and 1 part by weight of carbon (manufactured by DENKA Co., Ltd., acetylene black) as a conductive additive were added, and the mixture was stirred at 60 rpm for 1 hour to obtain a paste. Water was added to the obtained paste, and the concentration of solid components was adjusted to 48% 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 further stirred under reduced pressure (approximately 2.5 × 10⁻⁶). 4 The negative electrode active material containing 5% by mass Si was stirred and mixed at 1800 rpm for 1.5 minutes to prepare a slurry for energy storage devices (C / Si = 95 / 5).

[0211] 5.1.3. Manufacturing and Evaluation of Energy Storage Equipment

[0212] (1) Manufacturing of electrodes (negative electrodes) for energy storage devices

[0213] On the surface of a current collector composed of a 20 μm thick copper foil, a paste for the electrode of a storage device (C / Si = 95 / 5) obtained above is uniformly coated using a doctor blade method to achieve a dried film thickness of 80 μm. The paste is dried at 60°C for 10 minutes, followed by drying at 120°C for 10 minutes. Then, the active material layer is dried at a density of 1.5 g / cm³. 3 The electrode (negative electrode) of the energy storage device is obtained by pressing it with a roller press.

[0214] (2) Manufacturing of the counter electrode (positive electrode)

[0215] In a twin-shaft planetary mixer (manufactured by PRIMIX Co., Ltd., trade name "TK HIVISMIX 2P-03"), 4 parts by weight (converted solid content value) of binder for electrochemical equipment electrodes (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 "DENKABLACK 50% Pressed Product"), 100 parts by weight (converted solid content value) of LiCoO2 (manufactured by HAYASHI Chemical Co., Ltd.) with an average particle size of 5 μm as the positive electrode active material, and 36 parts by weight of N-methylpyrrolidone (NMP) were added and stirred 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 stirring degassing machine (THINKY Co., Ltd., trade name "Awa Tori Rentaro"), the mixture was stirred at 200 rpm for 2 minutes, then at 1800 rpm for 5 minutes, and further stirred 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 with a thickness of 80 μm after solvent removal using a doctor blade. The coating was heated at 120°C for 20 minutes to remove the solvent. The active material layer density was then [not specified]. 3 The positive electrode is obtained by stamping with a roller press.

[0216] (3) Assembly of lithium-ion battery cells

[0217] Inside a glove box where Ar replacement was performed with a dew point below -80°C, a 16.16 mm diameter negative electrode was punched and molded, and then placed on a two-pole button cell (manufactured by Hosen Co., Ltd., trade name "HS FLAT CELL"). Next, a separator (manufactured by Celgard Co., Ltd., trade name "Celgard #2400") with a 24 mm diameter punched hole was placed on top. Then, 500 μL of electrolyte was injected to prevent air from entering, followed by a 15.95 mm diameter positive electrode, and the two-pole button cell casing was screwed on and sealed, thus assembling a lithium-ion battery cell (energy storage device). The electrolyte used here is a solution formed by dissolving LiPF6 at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0218] (4) Evaluation of charge-discharge cycle characteristics

[0219] In a constant temperature bath at 60°C, the energy storage device manufactured above was charged with a constant current (1.0C). At a voltage of 4.2V, charging continued with a constant voltage (4.2V), and the charging ended (cut off) when the current reached 0.01C. Then, discharge was initiated with a constant current (1.0C), and the discharge ended (cut off) when the voltage reached 3.0V. The discharge capacity of the first cycle was calculated. This charging and discharging process was repeated 100 times. The capacity retention rate was calculated using the following formula (5), and evaluated according to the following criteria. The evaluation results are shown in Table 1.

[0220] Capacity retention rate (%)

[0221] = (Discharge capacity in the 100th cycle) / (Discharge capacity in the 1st cycle) ... (5)

[0222] (Evaluation Criteria)

[0223] • 5 points: Capacity retention rate is above 95%.

[0224] • 4 points: Capacity retention rate is above 90% and less than 95%.

[0225] • 3 points: Capacity retention rate is above 85% and less than 90%.

[0226] • 2 points: Capacity retention rate is above 80% and less than 85%.

[0227] • Point 1: Capacity retention rate is 75% or higher but less than 80%.

[0228] • 0 point: Capacity retention rate is less than 75%.

[0229] (5) Resistance evaluation at high temperature

[0230] In a constant-temperature bath at 60°C, the aforementioned energy storage device was initially charged with a constant current (1.0C). When the voltage reached 4.2V, charging continued at a constant voltage (4.2V), and the charging ended (cut off) when the current reached 0.01C. Then, discharge began with a constant current (0.05C), and the discharge ended (cut off) when the voltage reached 3.0V. The discharge capacity of the 0th cycle was calculated. Next, charging began with a constant current (1.0C), and charging continued at a constant voltage (4.2V), and the charging ended (cut off) when the current reached 0.01C. Then, discharge began with a constant current (1.0C), and the discharge ended (cut off) when the voltage reached 3.0V. The discharge capacity of the 1st cycle was calculated. This charging and discharging cycle was repeated 100 times. After 100 cycles of charging and discharging, the same charging and discharging process as in the 0th cycle was performed. The discharge capacity of the 101st cycle was evaluated, and the resistance rise rate was calculated using the following formula (6). The evaluation was carried out according to the following criteria.

[0231] Resistance rise rate (%)

[0232] = (Discharge capacity of the 100th cycle - Discharge capacity of the 101st cycle) / (Discharge capacity of the 0th cycle - Discharge capacity of the 1st cycle) × 100... (6)

[0233] (Evaluation Criteria)

[0234] • 5 points: The rate of increase in resistance is 100% or more but less than 150%.

[0235] • 4 points: The rate of increase in resistance is greater than 150% but less than 200%.

[0236] • 3 points: The rate of increase in resistance is greater than 200% but less than 250%.

[0237] • 2 points: The rate of increase in resistance is greater than 250% but less than 300%.

[0238] • Point 1: The rate of increase in resistance is greater than 300% but less than 350%.

[0239] • 0 point: Resistance rise rate is 350% or more.

[0240] It should be noted that in the measurement conditions, "1C" represents the current value at which the discharge ends within 1 hour when a battery with a certain capacitance is subjected to constant current discharge. For example, "0.1C" refers to the current value at which the discharge ends after 10 hours, and "10C" refers to the current value at which the discharge ends after 0.1 hours.

[0241] 5.2. Examples 2-13, Comparative Examples 1-9

[0242] In the section “5.1.1. Preparation and Property Evaluation of Adhesive Compositions for Storage Devices (1) Preparation of Adhesive Compositions for Storage Devices” above, the types and amounts of each monomer and the polymerization temperature conditions are operated in the same manner as those recorded in Tables 1 to 3 below, respectively, to obtain adhesive compositions for storage devices containing polymer particles with a solid content concentration of 40% by mass, and the properties of each composition are evaluated. It should be noted that for examples where no numerical values ​​are recorded in the second stage, the adhesive composition for storage devices is obtained through single-stage polymerization.

[0243] 5.3. Evaluation Results

[0244] Tables 1 to 3 below show the polymer composition, property test results, and evaluation results used in Examples 1 to 13 and Comparative Examples 1 to 9. It should be noted that the numerical values ​​of the polymer composition shown in Tables 1 to 3 below represent parts by mass.

[0245]

[0246]

[0247]

[0248] The abbreviations for monomers and thickeners in Tables 1 to 4 above refer to the following compounds.

[0249] <Unsaturated carboxylic acids>

[0250] •AA: Acrylic acid

[0251] • ITA: Itaconic acid

[0252] •FA: Fumaric acid

[0253] •MAA: Methacrylic acid

[0254] • HO-MS: 1-(2-methacryloyloxyethyl) succinate

[0255] •CB-1: 1-(2-methacryloyloxyethyl) phthalate

[0256] <Conjugated diene compounds>

[0257] •BD: 1,3-Butadiene

[0258] • IP: Isoprene

[0259] <α,β-unsaturated nitrile compounds>

[0260] •AN: Acrylonitrile

[0261] MAN: Methacrylonitrile

[0262] • FN: Fumarium

[0263] <Aromatic Vinyl Compounds>

[0264] •ST: Styrene

[0265] • DVB: Divinylbenzene

[0266] <Unsaturated carboxylic acid esters>

[0267] • MMA: Methyl methacrylate

[0268] •BA: Butyl acrylate

[0269] • EGDMA: Ethylene glycol dimethacrylate

[0270] • AMA: Allyl Methacrylate

[0271] <Initiator>

[0272] • KPS: Potassium persulfate

[0273] • CHP: Cumene hydroperoxide

[0274] • ACVA: 4,4'-azobis(4-cyanopentanoic acid)

[0275] <Reducing agent>

[0276] • Na2S2O5: Sodium metabisulfite

[0277] • ACA: L-Ascorbic Acid

[0278] <Chain transfer agent>

[0279] •tDM: tert-dodecyl mercaptan

[0280] • αMSD: α-methylstyrene dimer

[0281] <Other Polymerization Auxiliaries>

[0282] • NaHCO3: Sodium bicarbonate

[0283] •FeSO4: Ferric(II) sulfate heptahydrate

[0284] •EDTA-2Na: Disodium dihydrogen ethylenediaminetetraacetate

[0285] • Na2S2O4: Sodium dithionite

[0286] As can be clearly seen from Tables 1 to 3 above, the energy storage device electrodes made using the binder compositions for energy storage devices of the present invention shown in Examples 1 to 13, compared to Comparative Examples 1 to 9, exhibit reduced internal resistance by allowing the active materials to adhere appropriately to each other, thus suppressing the fusion of particles within the electrode. Furthermore, the energy storage device electrodes made using the binder compositions for energy storage devices of the present invention shown in Examples 1 to 13 exhibit excellent charge-discharge durability characteristics at high temperatures. Compared to Comparative Examples 1 to 9 shown in Table 3, the polymer (A) contained in the binder compositions for energy storage devices of Examples 1 to 13 shown in Tables 1 to 2 has a T2 value below 0.8, indicating low polymer chain mobility. Therefore, it is speculated that this suppresses particle fusion, results in excessive coating of active materials, and exhibits high input-output characteristics. Furthermore, the polymer (A) contained in the adhesive compositions for energy storage devices in Examples 1 to 13 contains more than 4% by mass of repeating units derived from unsaturated carboxylic acids compared to Comparative Examples 8 and 9. Therefore, it is presumed that the ability of the active substances to bind to each other in the high-temperature electrolyte is excellent, which helps to improve the charge-discharge durability characteristics at high temperatures.

[0287] This invention is not limited to the embodiments described above and can be modified in various ways. 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. Moreover, this invention also includes configurations that have the same effect or can achieve the same purpose as the configurations described in the above embodiments. Furthermore, this invention also includes configurations obtained by adding known techniques to the configurations described in the above embodiments.

Claims

1. An adhesive composition for an energy storage device, comprising a polymer (A) and a liquid medium (B). The spin-spin relaxation time (T2) of the polymer (A), as measured by pulsed NMR, is below 0.8 msec at 100 °C. When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains at least 4% by mass repeating units (a1) of unsaturated carboxylic acids with a value of less than 85 for "monomer molecular weight (g / mol) / number of carboxylic acid functional groups" and repeating units (a2) of unsaturated carboxylic acids with a value of 85 or more for "monomer molecular weight (g / mol) / number of carboxylic acid functional groups".

2. The adhesive composition for energy storage devices according to claim 1, wherein, The polymer (A) contains repeating units (a1) and repeating units (a2) derived from unsaturated carboxylic acids.

3. The adhesive composition for energy storage devices according to claim 2, wherein, When the total number of repeating units contained in the polymer (A) is set to 100% by mass, the polymer (A) contains 4% or more and less than 30% by mass of repeating units (a1) from unsaturated carboxylic acids and 2% or more and less than 10% by mass of repeating units (a2) from unsaturated carboxylic acids.

4. The adhesive composition for energy storage devices according to claim 2 or 3, wherein, In the polymer (A), the value of "the content of the repeating unit (a1) from the unsaturated carboxylic acid [mass%] / the content of the repeating unit (a2) from the unsaturated carboxylic acid [mass%]" is 1 or more.

5. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer (A) further contains 10% to 70% by mass of repeating units (a3) ​​derived from a conjugated diene compound.

6. The adhesive composition for energy storage devices according to claim 1 or 2, wherein, The polymer (A) further contains 10% to 40% by mass of repeating units (a4) from α,β-unsaturated nitrile compounds.

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

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

9. The adhesive composition for energy storage devices according to claim 8, wherein, The polymer particles satisfy the following relationship (3). 41.1×T2+2237.4÷PS+48.3<100・・・・・(3) In equation (3), T2 represents the value of the spin-spin relaxation time (T2) of the polymer particles at 100℃ as determined by pulse NMR, and PS represents the Z-average particle size (nm) of the polymer particles.

10. A paste for electrodes of a storage device, comprising the binder composition for a storage device as described in claim 1 or 2 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, wherein the active material layer is formed by coating the surface of the current collector with the slurry for the storage device electrode of claim 10 and then drying it.

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

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