Coating liquid for energy storage devices and negative electrode protective films

Abstract

To provide a power storage device in which a negative electrode protective film is thin and which can exhibit high battery characteristics.SOLUTION: There is provided a power storage device including a very thin negative electrode protective film having a film thickness of 0.2-19 μm. In a coating liquid for the negative electrode protective film which contains a polymer, a lithium salt compound, and a solvent, ethylene glycol dimethyl ether and / or diethylene glycol dimethyl ether is used as the solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to energy storage devices such as lithium-ion batteries, and to a coating liquid for forming a negative electrode protective film to protect the negative electrode used in energy storage devices. [Background technology]

[0002] Energy storage devices such as lithium-ion rechargeable batteries and electrochemical capacitors are used in electronic devices such as mobile phones, laptops, and camcorders. Recently, due to growing environmental awareness and the development of related laws, their application in vehicles such as electric vehicles and hybrid electric vehicles, as well as in batteries for home power storage, is also progressing.

[0003] Energy storage devices consist of a positive electrode, a negative electrode, and an electrolyte. As the applications of energy storage devices advance, there is a growing demand for higher performance, and improvements are being made to components such as electrodes.

[0004] Furthermore, Patent Document 1 discloses a battery in which a polymer solid electrolyte containing a lithium salt compound is interposed between the electrolyte and the electrode layer. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-087711 [Overview of the project] [Problems that the invention aims to solve]

[0006] When forming a protective film between the negative electrode and electrolyte as shown in Patent Document 1, a coating liquid for the negative electrode protective film is applied to the negative electrode and electrolyte. However, depending on the material of the negative electrode and electrolyte, there was a problem that adverse effects such as corrosion or reaction of the negative electrode and electrolyte may occur during the application or drying of the coating liquid for the negative electrode protective film. This tendency was particularly pronounced when lithium-based compounds were used as the active material for the negative electrode, or when inorganic solid electrolytes were used as the electrolyte. Therefore, it was necessary to apply the coating to a separate substrate, dry it to form the negative electrode protective film, and then laminate it onto the negative electrode. However, peeling the negative electrode protective film from the substrate and laminating the negative electrode protective film onto the negative electrode could not be done unless the film was of a certain thickness or higher. [Means for solving the problem]

[0007] The inventors of the present invention conducted diligent research to solve the above problems. They found that the above problems can be solved by using ethylene glycol dimethyl ether and / or diethylene glycol dimethyl ether as a solvent in an energy storage device equipped with a very thin negative electrode protective film, and in a coating liquid for the negative electrode protective film containing a polymer, a lithium salt compound, and a solvent. The present invention was completed by further research based on this finding.

[0008] In other words, the present invention provides inventions in the following embodiments. Item 1: An energy storage device comprising a positive electrode, an inorganic solid electrolyte, a negative electrode protective film containing a lithium salt compound with a thickness of 0.2 to 19 μm, and a negative electrode containing one of the following as the negative electrode active material: a lithium-based compound, graphite, or a silicon-based compound. Item 2: The energy storage device described in Item 1, wherein the 180° peel strength of the negative electrode protective film and the negative electrode is 0.1 to 10.0 N / cm as specified in JIS Z 0237:2009. Item 3: The energy storage device according to item 1 or 2, wherein the negative electrode contains a lithium-based compound as the negative electrode active material. Item 4: An energy storage device according to any one of items 1 to 3, wherein the inorganic solid electrolyte is an oxide-based inorganic solid electrolyte or a sulfide-based inorganic solid electrolyte. Item 5: A coating solution for a negative electrode protective film containing (A) a polymer, (B) a lithium salt compound, (C) ethylene glycol dimethyl ether, and / or diethylene glycol dimethyl ether. [Effects of the Invention]

[0009] The energy storage device of the present invention exhibits high battery performance because the thickness of the negative electrode protective film is extremely thin.

[0010] By using the coating liquid for negative electrode protective films of the present invention, the negative electrode and electrolyte are not adversely affected during the application or drying of the coating liquid for negative electrode protective films, making it possible to achieve high battery performance in energy storage devices equipped with the formed negative electrode protective film. [Modes for carrying out the invention]

[0011] In this specification, numbers connected by "~" represent a numerical range that includes the numbers before and after "~" as the lower and upper limits, respectively. If multiple lower and upper limits are listed separately, any lower and upper limits may be selected and connected by "~".

[0012] "1. Energy storage devices" The energy storage device of the present invention comprises a positive electrode, an inorganic solid electrolyte, a negative electrode protective film containing a lithium salt compound with a thickness of 0.2 to 19 μm, and a negative electrode. The negative electrode protective film is characterized by being interposed (laminated) between the negative electrode and the electrolyte.

[0013] In the energy storage device of the present invention, both the positive electrode and the negative electrode can be those of known type, but examples include electrodes that have a positive electrode material layer or a negative electrode material layer on the current collector.

[0014] For the positive electrode and the negative electrode, known current collectors can be used. Specifically, for the positive electrode, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium are used as the current collector. For the negative electrode, metals such as copper, nickel, stainless steel, gold, platinum, and titanium are used as the current collector.

[0015] In addition, the positive electrode material layer and the negative electrode material layer each contain at least a positive electrode active material and a negative electrode active material, and may further contain a conductive auxiliary agent, a binder, and a thickener.

[0016] The positive electrode active material used in the present invention is a lithium metal-containing composite oxide powder having a composition of any one of LiMO2, LiM2O4, Li2MO3, and LiMEO4. Here, M in the formula mainly consists of transition metals and includes at least one of Co, Mn, Ni, Cr, Fe, and Ti. Although M consists of transition metals, in addition to transition metals, Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. may also be added. E includes at least one of P and Si. The particle diameter of the positive electrode active material is preferably 50 μm or less, and more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li / Li+) or more.

[0017] Specific examples of the positive electrode active material include lithium cobaltate, lithium nickelate, lithium nickel / cobalt / manganese (ternary system), spinel-type lithium manganate, lithium iron phosphate, and the like.

[0018] The negative electrode active material used in the present invention is graphite, a lithium-based compound (lithium and lithium alloys (Li-Si alloy, Li-Sn alloy, etc.)), Si, SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiO x (0 < x ≤ 2, SiO, etc.), SnSiO xThese are silicon-based compounds such as LiSiO. In the case of powder, the particle size is preferably 10 nm to 100 μm, and more preferably 20 nm to 20 μm.

[0019] The active material content in the positive electrode material layer and the negative electrode material layer may be, for example, 100% by mass, more preferably 99.9 to 50% by mass, more preferably 99.5 to 70% by mass, and even more preferably 99 to 85% by mass.

[0020] When using conductive additives, known conductive additives can be used, such as graphite, furnace black, acetylene black, Ketjen black or other conductive carbon blacks, carbon fibers such as carbon nanotubes, or metal powders. One or more of these conductive additives may be used.

[0021] When a conductive additive is used, the content of the conductive additive is not particularly limited, but the upper limit is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the total amount of active material. Examples of the lower limit of the content of the conductive additive are usually 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.5 parts by mass or more, and 2 parts by mass or more.

[0022] As a binder, one or more compounds selected from fluororesins such as PVdF, fluororubber, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber, acrylic polymers, vinyl polymers, and the ion-conducting polymers described above can be used. These binders are added in amounts of 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 3 parts by mass, relative to 100 parts by mass of the active material.

[0023] Specific examples of thickeners include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose and their salts (alkali metal salts such as sodium salts, ammonium salts), polyvinyl alcohol, polyacrylates, polyethylene oxide, etc. One or more of these thickeners may be used. These thickeners are added in amounts of 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, relative to 100 parts by mass of the active material. Furthermore, if the viscosity of the coating solution is low, a thickener can be used in combination.

[0024] The positive electrode material layer and negative electrode material layer may contain lithium salt compounds such as LiBF4, LiPF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2(LiTFSI), LiN(SFO2)2(LiFSI), LiN(C2F5SO2)2, and LiN[CF3SC(C2F5SO2)3]2, along with ion-conducting polymers such as ethylene oxide / allyl glycidyl ether binary copolymer, ethylene oxide / glycidyl methacrylate binary copolymer, ethylene oxide / glycidyl acrylate binary copolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl methacrylate terpolymer, and ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl acrylate terpolymer.

[0025] The method for manufacturing the positive electrode and negative electrode, which comprise a current collector and positive electrode material layer and negative electrode material layer, is not particularly limited and general methods can be used. For example, a paste (coating liquid) of the positive electrode material and negative electrode material, consisting of a positive electrode active material or negative electrode active material, a conductive additive, a binder, and optionally a thickener and solvent, is uniformly applied to the surface of the current collector to an appropriate thickness using methods such as the doctor blade method or the silkscreen method.

[0026] For example, in the doctor blade method, the negative electrode active material powder, positive electrode active material powder, conductive assistant, binder, etc. are dispersed in water to form a slurry, coated on a metal electrode substrate, and then made uniform to an appropriate thickness by a blade having a predetermined slit width. After coating the active material, the electrode is dried, for example, with hot air at 100 °C or under reduced pressure at 80 °C to remove the excess organic solvent. The dried electrode is manufactured by press molding with a pressing device.

[0027] The inorganic solid electrolyte is preferably an oxide-based solid electrolyte or a sulfide-based solid electrolyte, and more preferably a sulfide-based solid electrolyte. The inorganic solid electrolyte is generally an aggregate of inorganic solid particles constituting the electrolyte.

[0028] The oxide-based solid electrolyte is not particularly limited as long as it contains oxygen, has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electron insulation.

[0029] Specific compounds constituting the oxide-based solid electrolyte include Li x La y TiO3 [x = 0.3 to 0.7, y = 0.3 to 0.7] (LLT), Li x La y Zr z M m O n (M is at least one element of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, x satisfies 5 ≤ x ≤ 10, y satisfies 1 ≤ y ≤ 4, z satisfies 1 ≤ z ≤ 4, m satisfies 0 ≤ m ≤ 2, and n satisfies 5 ≤ n ≤ 20.) Li x B y M z O n (In the formula, M is at least one element of C, S, Al, Si, Ga, Ge, In, Sn, x satisfies 0 ≤ x ≤ 5, y satisfies 0 ≤ y ≤ 1, z satisfies 0 ≤ z ≤ 1, and n satisfies 0 ≤ n ≤ 6.) Li x (Al, Ga) y (Ti, Ge) z Si a P m On (wherein 1≦x≦3, 0≦y≦1, 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13), Li (3-2x) M x DO(x represents a number between 0 and 0.1, M represents a divalent metal atom, and D represents a halogen atom or a combination of two or more halogen atoms), Li x Si y O z (1≦x≦5, 0 <y≦3、1≦z≦10)、Li x S y O z (1≦x≦3, 0 <y≦2、1≦z≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 GeO4, La having a perovskite crystal structure 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li (1+x+y) (Al,Ga) x (Ti,Ge) (2-x) Si y P (3-y) O 12 (where 0≦x≦1, 0≦y≦1), Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include the above. Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON (in which some of the oxygen in lithium phosphate is replaced with nitrogen), and LiPOD (where D is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.). LiAON (where A is at least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used.

[0030] Among them, Lix La y TiO3 [x=0.3~0.7, y=0.3~0.7] (LLT), Li x La y Zr z M m O n (M is at least one element from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, x satisfies 5 ≤ ​​x ≤ 10, y satisfies 1 ≤ y ≤ 4, z satisfies 1 ≤ z ≤ 4, m satisfies 0 ≤ m ≤ 2, and n satisfies 5 ≤ ​​n ≤ 20.) Li7La3Zr2O 12 (LLZ), Li3BO3, Li3BO3-Li2SO4, Li3BO3-Li2CO3, Li x (Al,Ga) y (Ti,Ge) z Si a P m O n (However, 1≦x≦3, 0≦y≦1, 0≦z≦2, 0≦a≦1, 1≦m≦7, 3≦n≦13) are preferred. These may be used individually or in combination of two or more types.

[0031] Sulfide-based solid electrolytes are not particularly limited as long as they contain sulfur, have ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and possess electronic insulating properties. For example, lithium-ion conductive inorganic solid electrolytes satisfying the composition shown in the following formula can be cited.

[0032] Li a M b P c S d A e In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. Among these, B, Sn, Si, Al, and Ge are preferred, and Sn, Al, and Ge are more preferred. A represents I, Br, Cl, and F, with I and Br being preferred, and I being particularly preferred. a to e represent the composition ratio of each element, where a:b:c:d:e satisfies 1 to 12:0 to 1:1:2 to 12:0 to 5. a is further preferably 1 to 9, and more preferably 1.5 to 4. b is preferably 0 to 0.5. d is further preferably 3 to 7, and more preferably 3.25 to 4.5. e is further preferably 0 to 3, and more preferably 0 to 2.

[0033] In the formula, the composition ratio of Li, M, P, S, and A is preferably such that b and e are 0, more preferably b=0, e=0 and the ratio of a, c, and d (a:c:d) is a:c:d=1~9:1:3~7, and even more preferably b=0, e=0 and a:c:d=1.5~4:1:3.25~4.5.

[0034] When the sulfide-based solid electrolyte is a Li / P / S system, the ratio of Li2S to P2S5 is preferably 60:40 to 85:15 in molar ratio of Li2S:P2S5, and preferably 65:35 to 80:20.

[0035] Specific examples of sulfide-based solid electrolytes include Li2S / SiS2, Li2S-SiS2 / P2S5, Li2S / P2S5, Li2S / GeS2, Li2S / GeS2 / Ga2S3, Li2S / B2S3, Li2S / Ga2S3, Li2S / Al2S3, Li2S / GeS2 / P2S5, Li2S / Al2S3 / P2S5, Li2S / P2S3, Li2S / P2S3 / P2S5, Li2S / SiS2 / Li4SiO4, Li2S / SiS2 / Li3PO4, LiX / Li2S / P2S5, LiX / Li2S / SiS2, LiX / Li2S / B2S3 (where X is a halogen atom (Br, Cl, or I)), etc.

[0036] When the inorganic solid electrolyte is in particulate form, the particle size can be, for example, 0.01 to 100 μm, preferably 0.1 to 20 μm.

[0037] The negative electrode protective film of the present invention contains a lithium salt compound and has a film thickness of 0.2 to 19 μm.

[0038] The negative electrode protective film of the present invention is preferably 0.2 to 19 μm thick, and more preferably 0.5 to 15 μm thick.

[0039] The adhesion between the negative electrode protective film of the present invention and the negative electrode is preferably such that the 180° peel strength specified in JIS Z 0237:2009 is 0.1 to 10.0 N / cm, more preferably 0.2 to 8.0 N / cm, and particularly preferably 0.5 to 5.0 N / cm. Having this level of adhesion is preferable because it exhibits excellent charge-discharge cycle performance.

[0040] The negative electrode protective film of the present invention contains a lithium salt compound. Preferred lithium salt compounds are those with a broad potential window, such as those commonly used in lithium-ion batteries. Examples of lithium salt compounds include, but are not limited to, LiBF4, LiPF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2(LiTFSI), LiN(SFO2)2(LiFSI), LiN(C2F5SO2)2, and LiN[CF3SC(C2F5SO2)3]2. These may be used individually or in combination of two or more.

[0041] The lithium salt compound content is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more, per 100 parts by mass of polymer. The upper limit is preferably 900 parts by mass or less, more preferably 800 parts by mass or less, particularly preferably 700 parts by mass or less, and may be 500 parts by mass or less, or 300 parts by mass or less.

[0042] Examples of polymers used in the negative electrode protective film include polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyphosphazene, polysiloxane, polyvinyl fluoride, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polyether polymers, with polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, and polyether polymers being preferred.

[0043] The polyether polymer preferably has constituent units derived from alkylene oxide, and more preferably has constituent units derived from ethylene oxide.

[0044] The polyether polymer preferably contains a constituent unit derived from the monomer of formula (1), and optionally has a constituent unit derived from formula (2) and / or formula (3). Only one type of monomer represented by each formula may be used, or two or more types may be mixed and used.

[0045] [ka]

[0046] [ka]

[0047] [In formula (2), R is an alkyl group having 1 to 12 carbon atoms, or -CH2O(CH2CH2O) n R 4 And R 4 [where n is an alkyl group with 1 to 6 carbon atoms, and n is a number from 0 to 12.]

[0048] The compound of formula (2) can be obtained from commercial sources or easily synthesized by general ether synthesis methods from epihalohydrins and alcohols. A phenyl group is an example of the aryl group. Examples of commercially available compounds include propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, t-butyl glycidyl ether, benzyl glycidyl ether, 1,2-epoxydodecane, 1,2-epoxyoctane, 1,2-epoxyheptane, 2-ethylhexyl glycidyl ether, 1,2-epoxydecane, 1,2-epoxyhexane, glycidylphenyl ether, 1,2-epoxypentane, and glycidyl isopropyl ether. Among these commercially available products, propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, and glycidyl isopropyl ether are preferred, with propylene oxide, butylene oxide, methyl glycidyl ether, and ethyl glycidyl ether being particularly preferred. In the monomer represented by formula (2) obtained by synthesis, R is -CH2O(CR 1 R 2 R 3 ) is preferred, R 1 , R 2 , R 3 At least one of them is -CH2O(CH2CH2O)nR 4 It is preferable that this is the case. 4 A C1-C6 alkyl group is preferred, and a C1-C4 alkyl group is more preferred. n is 0-6, and 0-4 is more preferred.

[0049] [ka]

[0050] [In formula (3), R 5 This represents a group containing an ethylenically unsaturated group.

[0051] The monomers used in formula (3) include allyl glycidyl ether, 4-vinylcyclohexyl glycidyl ether, α-terpinyl glycidyl ether, cyclohexenyl methyl glycidyl ether, p-vinylbenzyl glycidyl ether, allylphenyl glycidyl ether, vinyl glycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-pentene, 4,5-epoxy-2-pentene, 1,2-epoxy-5,9-cyclododecanediene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5-cyclooctene, glycidyl acrylate, glycidyl methacrylate, glycidyl sorbate, glycidyl cinnamate, glycidyl crotate, and glycidyl-4-hexenoate. Preferably, allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate are used.

[0052] In a polyether polymer, the molar ratio of the constituent units derived from the monomer of formula (1), the constituent units derived from the monomer of formula (2), and the constituent units derived from the monomer of formula (3) is 1 It is determined by 1H-NMR spectroscopy. The constituent units derived from the monomer of formula (1) are preferably present in an amount of 30 mol% or more, more preferably 45 mol% or more, particularly preferably 60 mol% or more, preferably 100 mol% or less, more preferably 96 mol% or less, and particularly preferably 93.5 mol% or less. The constituent units derived from the monomer of formula (2) may be 0 mol% or more, 3 mol% or more, 5 mol% or more, 70 mol% or less, 59 mol% or less, or 39 mol% or less. The constituent units derived from the monomer of formula (3) may be 0 mol% or more, 1 mol% or more, 1.5 mol% or more, 2 mol% or more, 3 mol% or more, 20 mol% or less, 15 mol% or less, or 12 mol% or less.

[0053] In a polyether polymer, the constituent units may consist only of constituent units derived from the monomer of formula (1), constituent units derived from the monomer of formula (2), and constituent units derived from the monomer of formula (3), or they may also consist of constituent units derived from other monomers. Preferably, the total molar ratio of constituent units derived from the monomer of formula (1), constituent units derived from the monomer of formula (2), and constituent units derived from the monomer of formula (3) in the polyether polymer is 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, and particularly preferably 100 mol%.

[0054] Specific examples of polyether polymers include ethylene oxide / allyl glycidyl ether binary copolymer, ethylene oxide / glycidyl methacrylate binary copolymer, ethylene oxide / glycidyl acrylate binary copolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl methacrylate terpolymer, and ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl acrylate terpolymer.

[0055] The weight-average molecular weight of the polyether polymer is not particularly limited, but may be between 10,000 and 3,000,000, more preferably between 50,000 and 2,500,000, and especially preferably between 100,000 and 2,000,000. The weight-average molecular weight is calculated by gel permeation chromatography (GPC) using dimethylformamide (DMF) as the solvent, on a standard polystyrene basis.

[0056] Polyether polymers can be synthesized, for example, as follows: a ring-opening polymerization catalyst is used, along with a coordination anion initiator such as an organoaluminum-based catalyst system, an organozinc-based catalyst system, or an organotin-phosphate condensate catalyst system, or a K2 counterion. +Polyether(i) can be obtained by reacting each monomer with an anionic initiator such as potassium alkoxide, diphenylmethyl potassium, or potassium hydroxide in the presence or absence of a solvent at a reaction temperature of 10 to 120°C under stirring. Coordinating anionic initiators are preferred in terms of degree of polymerization and the properties of the resulting copolymer, and among them, organotin-phosphate condensate catalyst systems are particularly preferred due to their ease of handling.

[0057] The polymer content is preferably 1 to 95% by mass, more preferably 2 to 90% by mass, and particularly preferably 15 to 80% by mass, with the entire negative electrode protective film being 100% by mass.

[0058] Furthermore, the negative electrode protective film may contain a room-temperature molten salt. A room-temperature molten salt is a salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which the power supply is expected to operate normally. The temperature range in which the power supply is expected to operate normally has an upper limit of about 120°C, and in some cases about 60°C, and a lower limit of about -40°C, and in some cases about -20°C.

[0059] Room-temperature molten salts are also called ionic liquids, and pyridine-based, aliphatic amine-based, and alicyclic amine-based quaternary ammonium organic cations are known. Examples of quaternary ammonium organic cations include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions. Imidazolium cations are particularly preferred.

[0060] Examples of tetraalkylammonium ions include, but are not limited to, trimethylethylammonium ions, trimethylethylammonium ions, trimethylpropylammonium ions, trimethylhexylammonium ions, tetrapentylammonium ions, and triethylmethylammonium ions.

[0061] Examples of alkylpyridinium ions include, but are not limited to, N-methylpyridinium ions, N-ethylpyridinium ions, N-propylpyridinium ions, N-butylpyridinium ions, 1-ethyl-2-methylpyridinium ions, 1-butyl-4-methylpyridinium ions, and 1-butyl-2,4-dimethylpyridinium ions.

[0062] Examples of imidazolium cations include, but are not limited to, 1,3-dimethylimidazolium ions, 1-ethyl-3-methylimidazolium ions, 1-methyl-3-ethylimidazolium ions, 1-methyl-3-butylimidazolium ions, 1-butyl-3-methylimidazolium ions, 1,2,3-trimethylimidazolium ions, 1,2-dimethyl-3-ethylimidazolium ions, 1,2-dimethyl-3-propylimidazolium ions, and 1-butyl-2,3-dimethylimidazolium ions.

[0063] These room-temperature molten salts containing cations may be used individually or in combination of two or more types.

[0064] If the negative electrode protective film contains a room-temperature molten salt, its content is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, per 100 parts by mass of polymer.

[0065] The negative electrode protective film may contain plasticizers. While not particularly limited, dicyano compounds and ether compounds are preferred as plasticizers. When plasticizers are added, it is preferable that they crosslink the polymer, i.e., form a polymer crosslinked product. This crosslinking is preferably chemical, as it can suppress the leakage of plasticizer from the gel film.

[0066] Examples of dicyano compounds include succinonitrile, glutalonitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, and 1,8-dicyanooctane.

[0067] Examples of ether compounds include linear ether compounds and branched ether compounds.

[0068] Examples of linear ether compounds include triglyme (triethylene glycol dimethyl ether) and tetraglyme (tetraethylene glycol dimethyl ether).

[0069] Examples of branched ether compounds include the following highly branched ether compounds. [ka] [ka]

[0070] If the negative electrode protective film contains a plasticizer, the plasticizer content is preferably 10 to 1000 parts by mass, more preferably 20 to 900 parts by mass, per 100 parts by mass of polymer.

[0071] The negative electrode protective film may contain a filler. The filler is not particularly limited, but any material that is electrochemically stable and electrically insulating may be used, and inorganic and organic fillers are used. Specific examples of inorganic fillers include inorganic oxides such as silica, alumina, alumina silicate, zirconia, potassium titanate, barium titanate, and lithium aluminate, and inorganic nitrides such as aluminum nitride and silicon nitride. Specific examples of organic fillers include acrylic resins (such as polymethyl methacrylate), styrene resins, fluororesins, urethane resins, polyolefin resins, styrene-butadiene copolymers, styrene-methyl methacrylate copolymers, and polyalkylene oxides (such as polyethylene oxide). These fillers can be used individually or in combination of two or more types.

[0072] The shape of the filler is not particularly limited and can be spherical, flattened, needle-shaped, columnar, or irregular. The particle size of the filler can be measured by dynamic light scattering (dispersion medium: water). The average particle size of the filler is preferably 0.1 to 19 μm, and more preferably 0.2 to 15 μm.

[0073] If a filler is included, the filler content may be in the range of 1 to 80 parts by mass, preferably in the range of 10 to 80 parts by mass, and more preferably in the range of 15 to 50 parts by mass, per 100 parts by mass of polymer.

[0074] The manufacturing method of the energy storage device of the present invention is not particularly limited, and it consists of at least a positive electrode, a negative electrode, an electrolyte, and a negative electrode protective film, and is manufactured by known methods. For example, in the case of a coin-type lithium-ion battery, a positive electrode, an electrolyte, a negative electrode, and a negative electrode protective film are placed between the negative electrode and the electrolyte, and then inserted into an outer casing. After that, it is joined to a sealing body by tab welding or the like, the sealing body is sealed, and then crimped to obtain the battery. The shape of the battery is not limited, but examples include coin-type, cylindrical, and sheet-type batteries, and a structure in which two or more batteries are stacked is also possible.

[0075] The following examples of methods for manufacturing the energy storage device of the present invention can also be disclosed. 1) The positive electrode and the inorganic solid electrolyte are stacked. 2) In a laminate of a positive electrode and an inorganic solid electrolyte, the coating liquid for the negative electrode protective film described in section 2. Coating liquid for negative electrode protective film is applied to the surface of the inorganic solid electrolyte, and then a negative electrode protective film is formed on the inorganic solid electrolyte. 3) A negative electrode is further laminated onto a laminate of a positive electrode and electrolyte having a negative electrode protective film on the surface of an inorganic solid electrolyte.

[0076] The following examples of methods for manufacturing the energy storage device of the present invention can also be disclosed. 1) After applying the coating liquid for a negative electrode protective film described in section 2, "Coating liquid for negative electrode protective film," of the present invention to the surface of the negative electrode, a negative electrode protective film is formed on the negative electrode. 2) A negative electrode having a negative electrode protective film on its surface, a positive electrode, and an inorganic solid electrolyte are laminated together. The positive electrode and the inorganic solid electrolyte may be laminated separately, or a laminate of the positive electrode and the inorganic solid electrolyte may be laminated together.

[0077] The method for forming the negative electrode protective film of the present invention is not particularly limited, but examples include casting an inorganic solid electrolyte or a negative electrode, removing the solvent, and then producing the negative electrode protective film by heating or irradiation with active energy rays such as ultraviolet light.

[0078] Crosslinking reactions can be carried out by heating at room temperature to around 200°C for 10 minutes to 24 hours if using heat. If using ultraviolet light, xenon lamps, mercury lamps, high-pressure mercury lamps, and metal halide lamps can be used, and the reaction can be carried out by irradiation at a wavelength of 365 nm and a light intensity of 1 to 50 mW / cm² for 0.1 to 30 minutes, for example.

[0079] "2. Coating liquid for negative electrode protective film" The coating liquid for the negative electrode protective film of the present invention contains (A) a polymer, (B) a lithium salt compound, (C) ethylene glycol dimethyl ether, and / or diethylene glycol dimethyl ether.

[0080] Examples of polymers used in the coating liquid for the negative electrode protective film of the present invention include polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyphosphazene, polysiloxane, polyvinyl fluoride, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polyether polymers, with polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, and polyether polymers being preferred.

[0081] The polyether polymer preferably has constituent units derived from alkylene oxide, and more preferably has constituent units derived from ethylene oxide.

[0082] The polyether polymer preferably contains a constituent unit derived from the monomer of formula (1), and optionally has a constituent unit derived from formula (2) and / or formula (3). Only one type of monomer represented by each formula may be used, or two or more types may be mixed and used.

[0083] [ka]

[0084] [ka]

[0085] [In formula (2), R is an alkyl group having 1 to 12 carbon atoms, or -CH2O(CH2CH2O) n R 4 And R 4 [where n is an alkyl group with 1 to 6 carbon atoms, and n is a number from 0 to 12.]

[0086] The compound of formula (2) can be obtained from commercial sources or easily synthesized by general ether synthesis methods from epihalohydrins and alcohols. A phenyl group is an example of the aryl group. Examples of commercially available compounds include propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, t-butyl glycidyl ether, benzyl glycidyl ether, 1,2-epoxydodecane, 1,2-epoxyoctane, 1,2-epoxyheptane, 2-ethylhexyl glycidyl ether, 1,2-epoxydecane, 1,2-epoxyhexane, glycidylphenyl ether, 1,2-epoxypentane, and glycidyl isopropyl ether. Among these commercially available products, propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, and glycidyl isopropyl ether are preferred, with propylene oxide, butylene oxide, methyl glycidyl ether, and ethyl glycidyl ether being particularly preferred. In the monomer represented by formula (1) obtained by synthesis, R is -CH2O(CR 1 R 2 R 3 ) is preferred, R 1 , R 2 , R 3 At least one of them is -CH2O(CH2CH2O)nR 4 It is preferable that this is the case. 4 A C1-C6 alkyl group is preferred, and a C1-C4 alkyl group is more preferred. n is 0-6, and 0-4 is more preferred.

[0087] [ka]

[0088] [In formula (3), R 5 This represents a group containing an ethylenically unsaturated group.

[0089] The monomers used in formula (3) include allyl glycidyl ether, 4-vinylcyclohexyl glycidyl ether, α-terpinyl glycidyl ether, cyclohexenyl methyl glycidyl ether, p-vinylbenzyl glycidyl ether, allylphenyl glycidyl ether, vinyl glycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-pentene, 4,5-epoxy-2-pentene, 1,2-epoxy-5,9-cyclododecanediene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5-cyclooctene, glycidyl acrylate, glycidyl methacrylate, glycidyl sorbate, glycidyl cinnamate, glycidyl crotate, and glycidyl-4-hexenoate. Preferably, allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate are used.

[0090] In a polyether polymer, the molar ratio of the constituent units derived from the monomer of formula (1), the constituent units derived from the monomer of formula (2), and the constituent units derived from the monomer of formula (3) is 1 It is determined by 1H-NMR spectroscopy. The constituent units derived from the monomer of formula (1) are preferably present in an amount of 30 mol% or more, more preferably 45 mol% or more, particularly preferably 60 mol% or more, preferably 100 mol% or less, more preferably 96 mol% or less, and particularly preferably 93.5 mol% or less. The constituent units derived from the monomer of formula (2) may be 0 mol% or more, 3 mol% or more, 5 mol% or more, 70 mol% or less, 59 mol% or less, or 39 mol% or less. The constituent units derived from the monomer of formula (3) may be 0 mol% or more, 1 mol% or more, 1.5 mol% or more, 2 mol% or more, 3 mol% or more, 20 mol% or less, 15 mol% or less, or 12 mol% or less.

[0091] In a polyether polymer, the constituent units may consist only of constituent units derived from the monomer of formula (1), constituent units derived from the monomer of formula (2), and constituent units derived from the monomer of formula (3), or they may also consist of constituent units derived from other monomers. Preferably, the total molar ratio of constituent units derived from the monomer of formula (1), constituent units derived from the monomer of formula (2), and constituent units derived from the monomer of formula (3) in the polyether polymer is 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more, and particularly preferably 100 mol%.

[0092] Specific examples of polyether polymers include ethylene oxide / allyl glycidyl ether binary copolymer, ethylene oxide / glycidyl methacrylate binary copolymer, ethylene oxide / glycidyl acrylate binary copolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl methacrylate terpolymer, and ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl acrylate terpolymer.

[0093] The weight-average molecular weight of the polyether polymer is not particularly limited, but may be between 10,000 and 3,000,000, more preferably between 50,000 and 2,500,000, and especially preferably between 100,000 and 2,000,000. The weight-average molecular weight is calculated by gel permeation chromatography (GPC) using dimethylformamide (DMF) as the solvent, on a standard polystyrene basis.

[0094] Polyether polymers can be synthesized, for example, as follows: a ring-opening polymerization catalyst is used, along with a coordination anion initiator such as an organoaluminum-based catalyst system, an organozinc-based catalyst system, or an organotin-phosphate condensate catalyst system, or a K2 counterion. +Polyether(i) can be obtained by reacting each monomer with an anionic initiator such as potassium alkoxide, diphenylmethyl potassium, or potassium hydroxide in the presence or absence of a solvent at a reaction temperature of 10 to 120°C under stirring. Coordinating anionic initiators are preferred in terms of degree of polymerization and the properties of the resulting copolymer, and among them, organotin-phosphate condensate catalyst systems are particularly preferred due to their ease of handling.

[0095] Examples of polymer content in the coating liquid for the negative electrode protective film include, preferably, 5 to 95% by mass, more preferably 5 to 50% by mass, and even more preferably 6 to 30% by mass, based on 100% by mass of the entire coating liquid for the negative electrode protective film.

[0096] The lithium salt compound used in the coating solution for the negative electrode protective film of the present invention is preferably a lithium salt compound having a broad potential window, such as those commonly used in lithium-ion batteries. Examples of lithium salt compounds include, but are not limited to, LiBF4, LiPF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2(LiTFSI), LiN(SFO2)2(LiFSI), LiN(C2F5SO2)2, and LiN[CF3SC(C2F5SO2)3]2. These may be used individually or in mixtures of two or more types.

[0097] The lithium salt compound content is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more, per 100 parts by mass of polymer, with an upper limit of 900 parts by mass or less, more preferably 800 parts by mass or less, and particularly preferably 700 parts by mass or less.

[0098] The coating liquid for the negative electrode protective film of the present invention contains ethylene glycol dimethyl ether (glyme) and diethylene glycol dimethyl ether (diglyme).

[0099] The content of ethylene glycol dimethyl ether (glyme) and diethylene glycol dimethyl ether (diglyme) is preferably 20 to 1400 parts by mass, more preferably 50 to 900 parts by mass, per 100 parts by mass of polymer.

[0100] The coating liquid for the negative electrode protective film of the present invention preferably contains ethylene glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), and a plasticizer in a total amount of 200 to 1500 parts by mass, more preferably 300 to 1300 parts by mass, and particularly preferably 400 to 1200 parts by mass, per 100 parts by mass of polymer.

[0101] Furthermore, the coating liquid for the negative electrode protective film may contain a room-temperature molten salt. A room-temperature molten salt is a salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which the power supply is expected to operate normally. The temperature range in which the power supply is expected to operate normally has an upper limit of about 120°C, and in some cases about 60°C, and a lower limit of about -20°C, and in some cases about -15°C.

[0102] Room-temperature molten salts are also called ionic liquids, and pyridine-based, aliphatic amine-based, and alicyclic amine-based quaternary ammonium organic cations are known. Examples of quaternary ammonium organic cations include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, and piperidinium ions. Imidazolium cations are particularly preferred.

[0103] Examples of tetraalkylammonium ions include, but are not limited to, trimethylethylammonium ions, trimethylethylammonium ions, trimethylpropylammonium ions, trimethylhexylammonium ions, tetrapentylammonium ions, and triethylmethylammonium ions.

[0104] Examples of alkylpyridinium ions include, but are not limited to, N-methylpyridinium ions, N-ethylpyridinium ions, N-propylpyridinium ions, N-butylpyridinium ions, 1-ethyl-2-methylpyridinium ions, 1-butyl-4-methylpyridinium ions, and 1-butyl-2,4-dimethylpyridinium ions.

[0105] Examples of imidazolium cations include, but are not limited to, 1,3-dimethylimidazolium ions, 1-ethyl-3-methylimidazolium ions, 1-methyl-3-ethylimidazolium ions, 1-methyl-3-butylimidazolium ions, 1-butyl-3-methylimidazolium ions, 1,2,3-trimethylimidazolium ions, 1,2-dimethyl-3-ethylimidazolium ions, 1,2-dimethyl-3-propylimidazolium ions, and 1-butyl-2,3-dimethylimidazolium ions.

[0106] These room-temperature molten salts containing cations may be used individually or in combination of two or more types.

[0107] If the coating liquid for the negative electrode protective film contains a room-temperature molten salt, its content is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, per 100 parts by mass of polymer.

[0108] The coating liquid for the negative electrode protective film may contain plasticizers, etc. While not particularly limited, dicyano compounds and ether compounds are preferred as plasticizers.

[0109] Examples of dicyano compounds include succinonitrile, glutalonitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, and 1,8-dicyanooctane.

[0110] Examples of ether compounds include linear ether compounds and branched ether compounds.

[0111] Examples of linear ether compounds include triglyme (triethylene glycol dimethyl ether) and tetraglyme (tetraethylene glycol dimethyl ether).

[0112] Examples of branched ether compounds include the following highly branched ether compounds. [ka] [ka]

[0113] If the coating liquid for the negative electrode protective film contains a plasticizer, the plasticizer content is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, per 100 parts by mass of polymer.

[0114] The negative electrode protective film may contain a filler. The filler is not particularly limited, but any material that is electrochemically stable and electrically insulating may be used, and inorganic and organic fillers are used. Specific examples of inorganic fillers include inorganic oxides such as silica, alumina, alumina silicate, zirconia, potassium titanate, barium titanate, and lithium aluminate, and inorganic nitrides such as aluminum nitride and silicon nitride. Specific examples of organic fillers include acrylic resins (such as polymethyl methacrylate), styrene resins, fluororesins, urethane resins, polyolefin resins, styrene-butadiene copolymers, styrene-methyl methacrylate copolymers, and polyalkylene oxides (such as polyethylene oxide). These fillers can be used individually or in combination of two or more types.

[0115] The shape of the filler is not particularly limited and can be spherical, flattened, needle-shaped, columnar, or irregular. The particle size of the filler can be measured by dynamic light scattering (dispersion medium: water). The average particle size of the filler is preferably 0.1 to 19 μm, and more preferably 0.2 to 15 μm.

[0116] If a filler is included, the filler content may be in the range of 1 to 80 parts by mass, preferably in the range of 10 to 80 parts by mass, and more preferably in the range of 15 to 50 parts by mass, per 100 parts by mass of polymer.

[0117] The coating liquid for the negative electrode protective film of the present invention may contain a reaction initiator, such as a thermal reaction initiator or a photoreaction initiator, and may also contain a crosslinking aid.

[0118] As a thermal reaction initiator, a radical initiator selected from organic peroxides, azo compounds, etc., is used. As organic peroxides, those commonly used for crosslinking applications such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, and peroxyesters are used, and as azo compounds, those commonly used for crosslinking applications such as azonitrile compounds, azoamide compounds, and azoamidine compounds are used. The amount of radical initiator added varies depending on the type, but is usually in the range of 0.1 to 10 parts by mass per 100 parts by mass of polymer.

[0119] Radical initiators such as alkylphenones, benzophenones, acylphosphine oxides, titanocenes, triazines, bisimidazoles, and oxime esters are used as photoinitiators. The amount of these radical polymerization initiators added varies depending on the type, but is usually in the range of 0.01 to 5.0 parts by mass per 100 parts by mass of polymer.

[0120] As the crosslinking aid, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, triallyl isocyanurate, maleimide, phenyl maleimide, maleic anhydride, etc. can be arbitrarily used. The content of the crosslinking aid is in the range of 5 to 50 parts by mass based on 100 parts by mass of the polymer.

[0121] In the present application, it can also be described as a power storage device including a negative electrode protective film obtained by using the "2. Coating liquid for negative electrode protective film", and a positive electrode, an inorganic solid electrolyte, a negative electrode protective film containing a lithium salt compound with a film thickness of 0.2 to 19 μm, a lithium-based compound, graphite, or a silicon-based compound as a negative electrode active material using the negative electrode protective film.

Example

[0122] The present invention will be described more specifically in the following examples, but the present invention is not limited thereto.

[0123] In this example, a negative electrode with a protective film formed thereon was produced, and the evaluation of the peeling strength of the protective film was carried out. Also, a coin cell was produced, and the performance evaluation of the charge-discharge characteristics of the coin cell was carried out in the following experiments.

[0124] The polymer was measured by the following method. 〔Composition molar ratio〕 1 It was determined from the signal intensity ratio derived from the composition unit by H-NMR spectrum. 〔Weight average molecular weight〕 Gel permeation chromatography (GPC) measurement was performed, and the weight average molecular weight was calculated in terms of standard polystyrene. The GPC measurement was carried out at 60 °C using RID-6A manufactured by Shimadzu Corporation, SHODEX KD-807, KD-806, KD-806M, and KD-803 columns manufactured by Showa Denko K.K., and DMF as the solvent.

[0125] [Synthesis example (Production of catalyst for polyether polymerization)] A three-necked flask equipped with a stirrer, thermometer, and distillation apparatus contained 10 g of tributyltin chloride and 35 g of tributyl phosphate. The mixture was heated at 250°C for 20 minutes under a nitrogen stream while stirring, and the distillate was removed to obtain a solid condensed substance as the residue. This substance was used as a polymerization catalyst in the following polymerization examples.

[0126] [Polymerization Example 1: Polymer 1] The inside of a 3L glass four-necked flask was purged with nitrogen, and 1 g of the condensation substance shown in the catalyst synthesis example and a glycidyl ether compound (a) with a moisture content adjusted to 10 ppm or less were added as polymerization catalysts: [ka] 114 g of compound (a), 12 g of allyl glycidyl ether, 0.10 g of n-butanol, and 1000 g of n-hexane as a solvent were charged. While monitoring the polymerization rate of compound (a) by gas chromatography, 136 g of ethylene oxide was added sequentially. The polymerization temperature was set to 20°C and the reaction was carried out for 10 hours. The polymerization reaction was stopped by adding 1 mL of methanol. After removing the polymer by decantation, it was dried at 40°C under normal pressure for 24 hours, and then at 45°C under reduced pressure for 10 hours to obtain 210 g of polymer. The molar ratio of the obtained polymer was ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol%, and the weight-average molecular weight was 1.5 million.

[0127] [Polymerization Example 2: Polymer 2] In polymerization example 1, 130 g of glycidyl ether compound (a), 0.13 g of n-butanol, and 1000 g of n-hexane as a solvent were charged. While monitoring the polymerization rate of compound (a) by gas chromatography, 135 g of ethylene oxide was added sequentially. The polymerization temperature was set to 20°C, and the reaction was carried out for 10 hours. The polymerization reaction was stopped by adding 1 mL of methanol. After removing the polymer by decantation, it was dried at 40°C under atmospheric pressure for 24 hours, and then at 45°C under reduced pressure for 10 hours to obtain 220 g of polymer. The molar ratio of the obtained polymer was ethylene oxide / diethylene glycol methylglycidyl ether = 80 / 20 mol%, and the weight-average molecular weight was 1.8 million.

[0128] Fabrication of a negative electrode with a protective film formed on it Example 1 (1) A negative electrode coating solution 1 was prepared by completely dissolving 100 parts by mass of ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol% ternary copolymer (weight-average molecular weight 1.5 million) as a polymer, 116 parts by mass of LiN(CF3SO2)2 (abbreviation: LiTFSI) as a lithium salt compound, 200 parts by mass of triethylene glycol dimethyl ether (triglyme) as a plasticizer, 40 parts by mass of trimethylolpropane trimethacrylate (abbreviation: TMPTMA) as a crosslinking aid, and 3 parts by mass of benzophenone as a radical initiator in 700 parts by mass of ethylene glycol dimethyl ether (monoglyme) as a polymer.

[0129] (2) In an argon glove box, the negative electrode coating solution 1 described in (1) above was drop-coated onto the metallic lithium on the copper / metallic lithium laminated foil. After drying at room temperature for 10 minutes, the solvent was removed under vacuum at 50°C for 1 hour. Then, UV irradiation of 1 J / cm² was performed in an argon glove box. 2 Crosslinking was performed using [a specific method] to create a negative electrode 1 in which a 15 μm thick negative electrode protective film 1 was laminated.

[0130] Fabrication of a negative electrode with a protective film formed on it - Example 2 In the same manner as in Example 1, a negative electrode 2 was fabricated by varying the amount of negative electrode coating liquid 1 dropped onto the metallic lithium of the copper / metallic lithium laminated foil, thereby creating a negative electrode 2 with a 0.5 μm thick negative electrode protective film 2.

[0131] Fabrication of a negative electrode with a protective film formed on it - Example 3 In the same manner as in Example 1, a negative electrode 3 was fabricated by varying the amount of negative electrode coating liquid 1 dropped onto the metallic lithium of the copper / metallic lithium laminated foil, thereby creating a negative electrode protective film 3 with a thickness of 19 μm.

[0132] Fabrication of a negative electrode with a protective film formed on it - Example 4 In the same manner as in Example 1, a negative electrode 4 was fabricated by varying the amount of negative electrode coating liquid 1 dropped onto the metallic lithium of the copper / metallic lithium laminated foil, thereby creating a negative electrode protective film 4 with a thickness of 0.2 μm.

[0133] Fabrication of a negative electrode with a protective film formed on it - Example 5 A negative electrode coating solution 2 was prepared in the same manner as in Example 1, except that the plasticizer in negative electrode coating solution 1 was changed from triglyme to tetraethylene glycol dimethyl ether (tetraglyme), and the coating solvent was changed from monoglyme to diethylene glycol dimethyl ether (diglyme). A negative electrode 5 was prepared by drop coating onto a copper / metallic lithium laminated foil, as in Example 1, to which a 15 μm thick negative electrode protective film 5 was laminated.

[0134] Fabrication of a negative electrode with a protective film formed on it - Example 6 In the same manner as in Example 1, a negative electrode 6 was fabricated by varying the amount of negative electrode coating liquid 1 dropped onto the metallic lithium of the copper / metallic lithium laminated foil, thereby creating a negative electrode protective film 6 with a thickness of 12 μm.

[0135] Fabrication of a negative electrode with a protective film formed on it: Comparative Example 1 In the same manner as in Example 1, a negative electrode 7 was fabricated by varying the amount of negative electrode coating liquid 1 dropped onto the metallic lithium of the copper / metallic lithium laminated foil, thereby creating a negative electrode protective film 7 with a thickness of 50 μm.

[0136] Fabrication of a negative electrode with a protective film formed on it: Comparative Example 2 A negative electrode coating solution 3 was prepared in the same manner as in Example 1, except that the solvent in negative electrode coating solution 1 was changed from monoglyme to acetonitrile. A negative electrode 8 was then fabricated by drop coating onto the metallic lithium of a copper / metallic lithium laminated foil, similar to Example 1, to which a 15 μm thick negative electrode protective film 8 was laminated. However, the lithium of the negative electrode discolored, and the negative electrode protective film peeled off from the negative electrode, making it impossible to measure the peel strength and battery characteristics.

[0137] Peel strength test of negative electrode protective film The adhesion between the negative electrode protective film and the metallic lithium negative electrode was measured according to the 180° peel strength specified in JIS Z 0237:2009. The results are shown in Table 1.

[0138] Example of positive electrode fabrication (1) NCM (LiNi 0.5 Co 0.2 Mn 0.3 To 100 parts by mass of O2, 3 parts by mass of acetylene black and 3 parts by mass of graphite were added as conductive additives, and 3 parts by mass of polyvinylidene fluoride (PVdF) was added as a binder. This mixture was then added to an NMP solution so that the solid content of the slurry was 35% by mass, and thoroughly mixed to obtain a cathode slurry. The obtained cathode slurry was coated onto a 20 μm thick aluminum current collector using a die coater, dried at 100°C for more than 12 hours, and then pressed with a roll press to produce a cathode precursor with a thickness of 18 μm (basis weight 6.0 mg / cm²). 2 , positive electrode density 3.0g / cm 3 , porosity 26%).

[0139] (2) A coating solution for cathode impregnation was prepared by completely dissolving 100 parts by mass of ethylene oxide / diethylene glycol methyl glycidyl ether = 80 / 20 mol% binary copolymer (weight-average molecular weight 1.8 million) as a polymer, 412 parts by mass of LiBF as a lithium salt compound, 200 parts by mass of triglyme as a plasticizer, and 10 parts by mass of TMPTMA as a crosslinking aid in 700 parts by mass of acetonitrile.

[0140] (3) Inside the argon glove box, the coating solution of (2) was drop-coated onto the precursor of the positive electrode of (1). Then, by allowing it to stand for 2 hours, while removing the solvent, a positive electrode for an inorganic solid electrolyte secondary battery impregnated with a polymer electrolyte in the voids within the positive electrode was fabricated.

[0141] Examples of actual manufacturing of sulfide-based electrolyte secondary batteries 1-5, comparative manufacturing example 1 Examples of the fabrication of a negative electrode with a protective film formed inside an argon glove box Using the negative electrodes obtained in Examples 1 to 5 and Comparative Example 1, the positive electrode obtained in the example of the fabrication of the positive electrode, and as the inorganic solid electrolyte, a sulfide-based electrolyte (film thickness: 300 μm) obtained by the mechanical milling method with a Li2S / P2S5 = 70 / 30 mol% composition, after laminating the positive electrode, the inorganic solid electrolyte, and the negative electrode in that order, they were caulked to manufacture a test 2032-type coin battery.

[0142] Example of Manufacturing a Secondary Battery with Oxide-Based Electrolytes (2) Examples of the fabrication of a negative electrode with a protective film formed inside an argon glove box The negative electrode obtained in Example 6, the positive electrode obtained in the example of the fabrication of the positive electrode, and as the inorganic solid electrolyte, Li7La3Zr2O 12 (film thickness: 500 μm) was used. After laminating the positive electrode, the inorganic solid electrolyte, and the negative electrode in that order, they were caulked to manufacture a test 2032-type coin battery.

[0143] [Evaluation of the fabricated battery] As an evaluation of the fabricated battery, a charge-discharge test was conducted using a charge-discharge device, and the discharge capacity at the third charge-discharge cycle was determined. The charge-discharge test conditions were CCCV charge up to 4.2 V at a current corresponding to 0.1C (10-hour rate) (0.01C cut-off), and then CCCV discharge up to 2.5 V at a current corresponding to 0.1C (0.01C cut-off). The test temperature was set to a 60°C environment. The results are shown in Table 1.

[0144] The aforementioned negative electrode protective film is a thin film and has sufficient peel strength with respect to the negative electrode. From the results of the examples and the comparative example, it can be seen that an inorganic solid electrolyte secondary battery in which the protective film is disposed between the negative electrode and the inorganic solid electrolyte has excellent battery characteristics (charge-discharge cycle capacity maintenance).

[0145] [Table 1] [Industrial applicability]

[0146] The inorganic solid electrolyte secondary battery of the present invention exhibits excellent charge and discharge characteristics and is suitable for use in large-scale battery applications such as in-vehicle applications like electric vehicles and hybrid electric vehicles, as well as storage batteries for household power storage.

Claims

1. An energy storage device comprising a positive electrode, an inorganic solid electrolyte, a negative electrode protective film containing a lithium salt compound with a thickness of 0.2 to 19 μm, and a negative electrode containing one of the following as the negative electrode active material: a lithium-based compound, graphite, or a silicon-based compound, An energy storage device in which the negative electrode protective film and the negative electrode have a 180° peel strength of 0.1 to 10.0 N / cm as specified in JIS Z 0237:2009.

2. The energy storage device according to claim 1, wherein the negative electrode contains a lithium-based compound as the negative electrode active material.

3. The energy storage device according to claim 1 or 2, wherein the inorganic solid electrolyte is an oxide-based inorganic solid electrolyte or a sulfide-based inorganic solid electrolyte.

4. The energy storage device according to claim 1 or 2, wherein the negative electrode protective film is a coating liquid for negative electrode protective films containing (A) a polymer, (B) a lithium salt compound, (C) ethylene glycol dimethyl ether, and / or diethylene glycol dimethyl ether.

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