Negative electrode protective film

Abstract

It was found that a gap is generated between an electrode in a power storage device and a protecting film through charging / discharging of the power storage device, when the protecting film is formed between a negative electrode and an electrolyte. Due to the generated gap, there has been a problem that a sufficient battery characteristic cannot be obtained.　A negative electrode protecting film containing a lithium salt compound, wherein the film-thickness change proportion when being pressed for 10 minutes at a pressure of 1 MPa at 25ºC is 1-20%, and the film-thickness change rate when being left for 10 minutes after releasing pressing pressure is -1% to 5%, when the film thickness of the negative electrode protecting film before pressing is defined as 100%.

Description

Technical Field

[0001] The present invention relates to a negative electrode protective film for protecting a negative electrode used in a power storage device such as a lithium ion battery.

Background Art

[0002] Power storage devices such as lithium ion secondary batteries and electrochemical capacitors are used in electronic devices such as mobile phones, notebook computers, and camcorders. Recently, due to the increasing awareness of environmental protection and the improvement of related laws, applications as in-vehicle use such as electric vehicles and hybrid electric vehicles and as power storage batteries for household power storage have also been progressing.

[0003] In a power storage device, it is composed of a positive electrode, a negative electrode, and an electrolyte. As the application of the power storage device progresses, at the same time, higher performance is required for the power storage device, and improvements in members such as electrodes are being advanced.

[0004] Further, Patent Document 1 discloses a battery in which a polymer solid electrolyte containing a lithium salt compound is interposed between an electrolyte and an electrode layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] In other words, the present invention provides inventions in the following embodiments. Item 1 A negative electrode protective film containing a lithium salt compound, A negative electrode protective film in which the film thickness before pressing is taken as 100%, and the rate of change in film thickness after pressing at a temperature of 25°C and a pressure of 1 MPa for 10 minutes is 1 to 20%, and the rate of change in film thickness after being left for 10 minutes after the press pressure is released is -1 to 5%. Item 2: The negative electrode protective film according to Item 1, wherein the ionic conductivity at 25°C is 0.1 to 10 mS / cm. Item 3 The negative electrode protective film according to Item 1 or 2, wherein the rate of change in film thickness (X1) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and the rate of change in film thickness (X2) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and left standing for 10 minutes after the press pressure is released are in the relationship X1 > X2. A negative electrode with a negative electrode protective film, comprising a negative electrode and a negative electrode protective film according to any one of items 1 to 3 laminated on the surface of the negative electrode. Item 5: An energy storage device containing a positive electrode, an electrolyte, a negative electrode protective film as described in any one of items 1 to 3, and a negative electrode. Item 6: The energy storage device according to Item 5, wherein the electrolyte is a solid electrolyte. [Effects of the Invention]

[0009] By using the negative electrode protective film of the present invention, it becomes possible to achieve high battery performance in energy storage devices. Although the details of this mechanism are not entirely clear, it is thought that, for example, by providing a negative electrode protective film that has certain mechanical properties during pressing and releasing during charging and discharging, appropriate followability is obtained between the negative electrode and the electrolyte. [Modes for carrying out the invention]

[0010] 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 "~".

[0011] "1. Negative electrode protective film" The negative electrode protective film of the present invention contains a lithium salt compound, Taking the thickness of the negative electrode protective film before pressing as 100%, the rate of change in film thickness (X1) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes is 1 to 20%, and the rate of change in film thickness (X2) when left for 10 minutes after the press pressure is released is -1 to 5%. In this invention, the rate of change in film thickness is more specifically the rate of reduction in film thickness. That is, taking the thickness of the negative electrode protective film before pressing as 100% (reference), the rate of reduction in film thickness of the negative electrode protective film immediately after pressing at a temperature of 25°C and a pressure of 1 MPa for 10 minutes is 1 to 20% (the negative electrode protective film becomes 80 to 99%). Furthermore, taking the thickness of the negative electrode protective film before pressing as 100% (reference), the rate of reduction in film thickness of the negative electrode protective film when the pressure from the press is released and it is left to stand at a temperature of 25°C and atmospheric pressure for 10 minutes is -1 to 5% (the negative electrode protective film becomes 95% to 101%). In the negative electrode protective film of the present invention, the film thickness change rate (X1) and the film thickness change rate (X2) can be suitably adjusted, for example, by the blending ratio of the plasticizer and the crosslinking aid described later.

[0012] 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.

[0013] The negative electrode protective film of the present invention is preferably formed from a polymer composition comprising a lithium salt compound and a polymer. The lithium salt compound content is preferably, at a lower limit, 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 the polymer. At an upper limit, it 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.

[0014] 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.

[0015] The polyether polymer preferably has constituent units derived from alkylene oxide, and more preferably has constituent units derived from ethylene oxide.

[0016] 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.

[0017] [ka]

[0018] [ka]

[0019] [In formula (2), R is an alkyl group having 1 to 12 carbon atoms, or -CH2O(CH2CH2O) n R 4 and R 4 is an alkyl group having 1 to 6 carbon atoms, and n is a number from 0 to 12.]

[0020] The compound of formula (2) can be easily synthesized by obtaining it from commercially available products or by a general ether synthesis method from epihalohydrin and alcohol. Examples of the aryl group include a phenyl group. Examples of compounds available from commercially available products 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-epoxydodecane, 1,2-epoxyhexane, glycidyl phenyl ether, 1,2-epoxypentane, glycidyl isopropyl ether, etc. Among these commercially available products, propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether, butyl glycidyl ether, glycidyl isopropyl ether are preferred, and propylene oxide, butylene oxide, methyl glycidyl ether, ethyl glycidyl ether are particularly preferred. In the monomer represented by formula (2) obtained by synthesis, R is -CH2O(CR 1 R 2 R 3 ) is preferred, and at least one of 1 R 2 R 3 R is preferably -CH2O(CH2CH2O)nR 4 . R 4 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms. n is preferably from 0 to 6, more preferably from 0 to 4.

[0021] [ka]

[0022] [In formula (3), R 5 This represents a group containing an ethylenically unsaturated group.

[0023] 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.

[0024] 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.

[0025] 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, particularly preferably 98 mol% or more, and preferably 100 mol%.

[0026] Specific examples of polyether polymers include ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl methacrylate terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl acrylate terpolymer, ethylene oxide / allyl glycidyl ether binary copolymer, ethylene oxide / glycidyl methacrylate binary copolymer, and ethylene oxide / glycidyl acrylate binary copolymer.

[0027] 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.

[0028] 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.

[0029] The polymer content in the negative electrode protective film is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, with the entire negative electrode protective film being 100% by mass. Examples include 5 to 50% by mass, 5 to 30% by mass, 5 to 20% by mass, 10 to 30% by mass, and 10 to 20% by mass.

[0030] 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.

[0031] 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.

[0032] Examples of tetraalkylammonium ions include, but are not limited to, trimethylethylammonium ions, trimethylethylammonium ions, trimethylpropylammonium ions, trimethylhexylammonium ions, tetrapentylammonium ions, and triethylmethylammonium ions.

[0033] 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.

[0034] 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.

[0035] These room-temperature molten salts containing cations may be used individually or in combination of two or more types.

[0036] 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.

[0037] The negative electrode protective film may contain plasticizers, etc. While not particularly limited, dicyano compounds and ether compounds are preferred as plasticizers. When a plasticizer is added, it is preferable that it crosslinks the polymer, i.e., that it is a polymer crosslinked product. This crosslinking is preferably chemical crosslinking, which can suppress the outflow of the plasticizer from the negative electrode protective film. The negative electrode protective film of the present invention allows for suitable adjustment of the film thickness change rate by adjusting the blending ratio of the plasticizer and the crosslinking aid described later.

[0038] Examples of dicyano compounds include succinonitrile, glutalonitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, and 1,8-dicyanooctane.

[0039] Examples of ether compounds include linear ether compounds and branched ether compounds.

[0040] Examples of linear ether compounds include triglyme (triethylene glycol dimethyl ether) and tetraglyme (tetraethylene glycol dimethyl ether).

[0041] Examples of branched ether compounds include the following highly branched ether compounds. [ka] [ka]

[0042] If the negative electrode protective film contains a plasticizer, the plasticizer content is preferably 10 to 380 parts by mass, more preferably 50 to 350 parts by mass, and particularly preferably 125 to 300 parts by mass, per 100 parts by mass of polymer.

[0043] 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.

[0044] 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 20 μm, more preferably 0.2 to 15 μm, and may be 1 to 15 μm.

[0045] 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 60 parts by mass, and more preferably in the range of 15 to 50 parts by mass, per 100 parts by mass of polymer.

[0046] The negative electrode protective film has a film thickness change rate of 1 to 20%, preferably 2 to 20%, and particularly preferably 2 to 15%, when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes, with the film thickness of the negative electrode protective film before pressing being 100%. This is represented by the following formula. X1(%) = [(A1-A2) / A1] × 100 Film thickness of the negative electrode protective film before pressing: A1 Film thickness after pressing at 25°C and 1 MPa for 10 minutes: A2 Film thickness change rate when pressed at 25°C and 1 MPa for 10 minutes: X1

[0047] The negative electrode protective film has a film thickness change rate of -1 to 5%, preferably 0 to 5%, and particularly preferably 0 to 4%, when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes, with the film thickness of the negative electrode protective film before pressing set to 100%, and left to stand for 10 minutes after the press pressure is released. This is represented by the following formula. X2(%) = [(A1-A3) / A1] × 100 Film thickness of the negative electrode protective film before pressing: A1 Film thickness after pressing at 25°C and 1 MPa for 10 minutes, followed by 10 minutes of resting after the pressure was released: A3 Change in film thickness after pressing at 25°C and 1 MPa for 10 minutes, followed by 10 minutes of standing time after the pressure is released: X2

[0048] For the negative electrode protective film, the rate of change in film thickness (X1) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and the rate of change in film thickness (X2) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and then left to stand for 10 minutes after the press pressure is released should satisfy the relationship X1 > X2, but it is preferable that 0.05 ≤ X2 / X1 ≤ 0.95, more preferably 0.1 ≤ X2 / X1 ≤ 0.95, and even more preferably 0.2 ≤ X2 / X1 ≤ 0.90.

[0049] The thickness of the negative electrode protective film (thickness of the negative electrode protective film before pressing) can be appropriately adjusted according to the size of the energy storage device (size of the negative electrode, etc.). For example, the thickness ranges are 0.1-200 μm, 0.1-50 μm, 0.1-30 μm, 0.2-200 μm, 0.2-50 μm, 0.2-30 μm, 0.5-200 μm, 0.5-50 μm, 0.5-30 μm, 1-200 μm, 1-50 μm, 1-30 μm, 2-200 μm, 2-50 μm, 2-30 μm, 5-200 μm, 5-50 μm, 5-30 μm, 10-200 μm, 10-50 μm, and 10-30 μm. Preferably, the particle size is in the range of 0.1 μm to 200 μm, more preferably 0.2 μm to 100 μm, even more preferably 0.2 μm to 50 μm, and particularly preferably 0.5 μm to 30 μm.

[0050] The negative electrode protective film preferably has an ionic conductivity of 0.1 to 10 mS / cm at 25°C, more preferably 0.3 to 9 mS / cm, and particularly preferably 0.4 to 8 mS / cm.

[0051] In the present invention, the negative electrode protective film is preferably a gel film. A gel is a swollen body in which a polymer forms a three-dimensional network structure through chemical bonding (such as covalent bonds, ionic bonds, or coordination bonds) or through intermolecular interactions such as crystallization or molecular entanglement, and holds solvent molecules in its voids.

[0052] The method for manufacturing the negative electrode protective film of the present invention is not particularly limited, but it is formed using the negative electrode protective film composition described in section "2. Composition for negative electrode protective film". The negative electrode protective film composition contains a polymer, a lithium salt compound, etc., preferably a plasticizer, and optionally a filler, and if necessary, it is mixed and dissolved in an organic solvent, and the composition is cast onto a substrate (e.g., a PET film or a Teflon® plate), and after removing the solvent, the negative electrode protective film is produced by heating or irradiation with active energy rays such as ultraviolet light. Alternatively, the negative electrode protective film can also be produced by casting the composition onto the surface of the negative electrode or electrolyte.

[0053] "2. Composition for negative electrode protective film" As the polymer used in the composition for the negative electrode protective film, the polymer described in section "1. Negative Electrode Protective Film" can be used.

[0054] As the lithium salt compound used in the composition for the negative electrode protective film, the lithium salt compound described in section "1. Negative Electrode Protective Film" can be used. In terms of content, it is preferable that the lower limit is 5 parts by mass or more, more preferably 8 parts by mass or more, and particularly preferable 10 parts by mass or more, per 100 parts by mass of polymer, and the upper limit is preferably 900 parts by mass or less, more preferably 800 parts by mass or less, and particularly preferable 700 parts by mass or less.

[0055] As the plasticizer used in the composition for the negative electrode protective film, the plasticizer described in section "1. Negative Electrode Protective Film" can be used, and the content is preferably 10 to 380 parts by mass, more preferably 50 to 350 parts by mass, and particularly preferably 125 to 300 parts by mass, per 100 parts by mass of polymer.

[0056] As fillers used in the negative electrode protective film composition, fillers described in section "1. Negative Electrode Protective Film" can be used. If a filler is included, its content may be in the range of 1 to 80 parts by mass, preferably in the range of 10 to 60 parts by mass, and more preferably in the range of 15 to 50 parts by mass, per 100 parts by mass of polymer.

[0057] To crosslink the negative electrode protective film composition, a reaction initiator can be used, such as a thermal reaction initiator or a photoreaction initiator, and a crosslinking aid may also be included.

[0058] 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.

[0059] 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.

[0060] As crosslinking aids, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, triallyl isocyanurate, maleimide, phenyl maleimide, maleic anhydride, etc., can be used as desired. The content of the crosslinking aid is preferably in the range of 25 to 60 parts by mass, and more preferably in the range of 30 to 50 parts by mass, based on 100 parts by mass of the polymer.

[0061] The negative electrode protective film composition may contain water or an organic solvent. Examples of organic solvents include toluene, xylene, benzene, acetonitrile, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, glyme (ethylene glycol dimethyl ether), diglyme (diethylene glycol dimethyl ether), and THF (tetrahydrofuran).

[0062] The water or organic solvent content is preferably 20 to 1400 parts by mass, more preferably 50 to 900 parts by mass, per 100 parts by mass of polymer.

[0063] The composition for the negative electrode protective film of the present invention preferably contains a total amount of water or organic solvent and plasticizer of 200 to 1500 parts by mass, more preferably 300 to 1200 parts by mass, and particularly preferably 400 to 1000 parts by mass, per 100 parts by mass of polymer.

[0064] 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. For example, the electrolyte may be heated to a wavelength of 365 nm with a light intensity of 1-50 mW / cm². 2 This can be done by irradiating for 0.1 to 30 minutes.

[0065] "3. Energy Storage Devices" The energy storage device of the present invention comprises a positive electrode, an electrolyte, a negative electrode protective film as described in section "1. Negative Electrode Protective Film," and a negative electrode. The negative electrode protective film is characterized by being interposed between the negative electrode and the electrolyte. Preferably, the negative electrode protective film is in contact with both the negative electrode and the electrolyte. In addition, in the present invention, a negative electrode with a negative electrode protective film may be laminated on the surface of the negative electrode and applied to the energy storage device. Alternatively, the negative electrode protective film can be laminated on the surface of the electrolyte, and the electrolyte and negative electrode can be arranged so that the negative electrode protective film is located on the negative electrode side, thereby applying the negative electrode protective film to the energy storage device.

[0066] In the energy storage device of the present invention, both the positive electrode and the negative electrode can be those of known origin, but examples include electrodes that have a positive electrode material layer or a negative electrode material layer on the current collector.

[0067] Known current collectors can be used for the positive and negative electrodes. Specifically, for the positive electrode, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium can be used as current collectors. For the negative electrode, metals such as copper, nickel, stainless steel, gold, platinum, and titanium can be used as current collectors.

[0068] Furthermore, 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 also contain a conductive additive, a binder, and a thickener.

[0069] The positive electrode active material used in this invention is a lithium metal-containing composite oxide powder having one of the following compositions: LiMO2, LiM2O4, Li2MO3, or LiMEO4. Here, M mainly consists of a transition metal and contains at least one of Co, Mn, Ni, Cr, Fe, or Ti. Although M consists of a transition metal, other elements such as Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, and B may also be added. E contains at least one of P and Si. The particle size 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.

[0070] Specific examples of positive electrode active materials include lithium cobalt oxide, lithium nickel oxide, nickel / cobalt / lithium manganese oxide (ternary system), spinel-type lithium manganese oxide, and lithium iron phosphate.

[0071] The negative electrode active material used in this invention is either a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (intercalary compound) capable of intercalating and releasing alkali metal ions such as lithium ions, or a metal such as lithium, aluminum-based compounds, tin-based compounds, silicon-based compounds, or titanium-based compounds capable of intercalating and releasing alkali metal ions such as lithium ions. In the case of powder, the particle size is preferably 10 nm to 100 μm, and more preferably 20 nm to 20 μm. It may also be used as a mixed active material of metal and carbon material.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 2 parts by mass, relative to 100 parts by mass of the active material.

[0076] 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.

[0077] 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.

[0078] 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, a solvent such as water or N-methyl-2-pyrrolidone (NMP), and a thickener as needed, 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.

[0079] For example, in the doctor blade method, negative electrode active material powder, positive electrode active material powder, conductive additive, binder, etc., are dispersed in water to form a slurry, which is then applied to a metal electrode substrate. After application, the slurry is uniformly spread to an appropriate thickness using a blade with a predetermined slit width. After the active material is applied, the electrodes are dried to remove excess organic solvent, for example, by using hot air at 100°C or under reduced pressure at 80°C. After drying, the electrodes are manufactured by press molding using a press device.

[0080] The electrolyte is preferably a solid electrolyte, preferably a polymer solid electrolyte or an inorganic solid electrolyte, and more preferably an oxide-based solid electrolyte or a sulfide-based solid electrolyte. In general, an inorganic solid electrolyte is an aggregate of inorganic solid particles that constitute the electrolyte.

[0081] Oxide-based solid electrolytes are not particularly limited as long as they contain oxygen, have ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and possess electronic insulating properties.

[0082] Specific compounds that make up oxide-based solid electrolytes include Li x 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.) Li x B y M z O n (In the formula, M is at least one element from C, S, Al, Si, Ga, Ge, In, and 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 O n (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 La, which has a perovskite crystal structure, is GeO4. 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) Siy P (3-y) O 12 Examples include Li7La3Zr2O12, which has a garnet-type crystal structure (where 0≦x≦1 and 0≦y≦1). Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON, which is lithium phosphate with some of the oxygen replaced by 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.

[0083] Among them, Li x 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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. [Examples]

[0091] The present invention will be described in more detail in the following examples, but the present invention is not limited thereto.

[0092] In this example, a protective film composition for the negative electrode was fabricated, and the physical properties of the film were evaluated. Separately, a coin cell was fabricated using the negative electrode with the protective film formed on it, and the charge-discharge characteristics of the coin cell were evaluated in the following experiment.

[0093] The polymer was measured using the following method. [Composition molar ratio] 1The signal intensity ratio derived from the compositional units was determined by 1H-NMR spectroscopy. [Weight average molecular weight] Gel permeation chromatography (GPC) measurements were performed, and the weight-average molecular weight was calculated based on standard polystyrene equivalents. GPC measurements were performed at 60°C using Shimadzu RID-6A, Showa Denko K.K.'s Showdex KD-807, KD-806, KD-806M, and KD-803 columns, and DMF as the solvent.

[0094] [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.

[0095] [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.

[0096] [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.

[0097] [Example of negative electrode fabrication] (1) 100 parts by mass of artificial graphite (particle size 10 μm) was used as the negative electrode active material. 2 parts by mass of vapor-grown carbon fiber (VGCF) was added as a conductive additive, 3 parts by mass of styrene-butadiene rubber (SBR) as a binder, and 2 parts by mass of sodium carboxymethylcellulose as a thickener. Water was then added to achieve a solid content concentration of 35% by mass, and the mixture was thoroughly mixed to obtain a negative electrode slurry. The obtained negative electrode slurry was applied to a copper current collector with a thickness of 16.5 μm using a die coater, dried at 100°C for 12 hours or more, and then pressed using a roll press to produce a 30 μm thick negative electrode for an inorganic solid electrolyte secondary battery (basis weight 4.0 mg / cm²). 2 , negative electrode density 1.1g / cm 3 , porosity 26%)

[0098] <Example 1> Preparation of composition 1 for negative electrode protective film A negative electrode protective film composition 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 tetraethylene glycol dimethyl ether (tetraglyme) 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 coating solvent.

[0099] Fabrication of a negative electrode with a protective film formed on it Composition 1 for the negative electrode protective film was drop-coated onto the negative electrode precursor in an argon glove box. After drying at room temperature for 10 minutes, the solvent was removed under vacuum at 50°C for 1 hour. Then, UV irradiation at 1 J / cm² was applied in the argon glove box. 2 Crosslinking was performed using [a specific method] to create a negative electrode 1 (negative electrode with negative electrode protective film) with a 15 μm thick negative electrode protective film 1 layered on top.

[0100] <Example 2> Preparation of composition 2 for negative electrode protective film A negative electrode protective film composition 2 was prepared in the same manner as negative electrode protective film composition 1, except that the type of plasticizer was changed to triethylene glycol dimethyl ether (triglime).

[0101] Fabrication of a negative electrode with a protective film formed on it A negative electrode 2 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 2, and a negative electrode 2 with a thickness of 15 μm was laminated on it.

[0102] <Example 3> Preparation of composition 3 for negative electrode protective film A negative electrode protection composition 3 was prepared in the same manner as negative electrode protection composition 1, except that 20 parts by mass of nanosilica (manufactured by Admatex, particle size 0.2-0.4 μm) were added.

[0103] Fabrication of a negative electrode with a film formed on it A negative electrode 3 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 3.

[0104] <Example 4> Preparation of composition 4 for negative electrode protective film A negative electrode protective film composition 4 was prepared in the same manner as negative electrode protective composition 1, except that the amount of LiTFSI was changed to 150 parts by mass and the amount of tetraglyme to 280 parts by mass.

[0105] Fabrication of a negative electrode with a protective film formed on it A negative electrode 4 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 4, and a negative electrode 4 with a thickness of 15 μm was laminated on it.

[0106] <Example 5> Preparation of composition 5 for negative electrode protective film A negative electrode protective film composition 5 was prepared in the same manner as negative electrode protective composition 1, except that the amount of LiTFSI was changed to 160 parts by mass and the amount of tetraglyme was changed to 300 parts by mass.

[0107] Fabrication of a negative electrode with a protective film formed on it A negative electrode 5 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 5. A negative electrode 5 with a thickness of 15 μm was laminated on it.

[0108] <Example 6> Fabrication of a negative electrode with a protective film formed on it Using the negative electrode protective film composition 1, a negative electrode 6 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, with a negative electrode protective film 6 having a thickness of 0.5 μm laminated on it.

[0109] <Example 7> Fabrication of a negative electrode with a protective film formed on it Using composition 1 for negative electrode protective film, a negative electrode 7 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, with a 30 μm thick negative electrode protective film 7 laminated on top.

[0110] <Comparative Example 1> Preparation of composition 6 for negative electrode protective film A negative electrode protective film composition 6 was prepared in the same manner as negative electrode protective film composition 1, except that the amount of LiTFSI was changed to 36 parts by mass and the amount of TMPTMA to 5 parts by mass, and a plasticizer was not used.

[0111] Fabrication of a negative electrode with a protective film formed on it A negative electrode 8 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 6, and a negative electrode 8 with a thickness of 15 μm was laminated on it.

[0112] <Comparative Example 2> Preparation of composition 7 for negative electrode protective film A negative electrode protective film composition 7 was prepared in the same manner as negative electrode protective film composition 1, except that the amount of LiTFSI was changed to 180 parts by mass and the amount of tetraglyme was changed to 400 parts by mass.

[0113] Fabrication of a negative electrode with a protective film formed on it A negative electrode 9 (negative electrode with negative electrode protective film) was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 7, and a negative electrode 9 with a thickness of 15 μm was laminated on it.

[0114] <Comparative Example 3> Preparation of composition 8 for negative electrode protective film A negative electrode protective film composition 8 was prepared in the same manner as negative electrode protective film composition 1, except that the amount of polymer was changed to 10 parts by mass, the amount of LiTFSI to 75 parts by mass, and the amount of TMPTMA to 10 parts by mass.

[0115] Fabrication of a negative electrode with a protective film formed on it A negative electrode 10 was fabricated in the same manner as in Example 1, except that negative electrode protective film composition 1 was replaced with negative electrode protective film composition 8, and a negative electrode 10 with a thickness of 15 μm was laminated on it.

[0116] Press test of protective film Press tests were conducted on negative electrode protective films 1-10 using a dynamic viscoelasticity tester (Rheogel-E, manufactured by UBM Corporation). A pressure of 1 MPa was applied at 25°C for 10 minutes, pressing the sample sheet in the thickness direction. The thickness at that time was measured, and the thickness after releasing the pressure and letting it stand for 10 minutes was also measured. The rate of change in film thickness was calculated using the following formula. The results are shown in Table 1. X1(%) = [(A1-A2) / A1] × 100 Film thickness of the negative electrode protective film before pressing: A1 Film thickness after pressing at 25°C and 1 MPa for 10 minutes: A2 Percentage change in film thickness when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes (indicated as "Percentage change in thickness during pressing" in the table): X1 X2(%) = [(A1-A3) / A1] × 100 Film thickness of the negative electrode protective film before pressing: A1 Film thickness after pressing at 25°C and 1 MPa for 10 minutes, followed by 10 minutes of resting after the pressure was released: A3 The percentage change in film thickness after pressing at 25°C and 1 MPa for 10 minutes, followed by a 10-minute period of resting after the pressure was released (indicated as "Percentage change in thickness before and after testing" in the table): X2

[0117] Ionic conductivity measurement of protective films The ionic conductivity of protective films 1-10 was measured using negative electrodes 1-10 as samples with a dynamic viscoelasticity tester (AMETEK Science Instruments potentiostat PMC-1000) at 25°C. Negative electrodes 1-10 were sandwiched between SUS electrodes, and the ionic conductivity of the protective films was calculated from the bulk resistance of the protective films using the complex impedance method with an AC method at a voltage of 30mV and a frequency range of 10Hz-10MHz.

[0118] Example of positive electrode fabrication (1) NCM (LiNi 0.5 Co 0.2 Mn 0.3To 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%).

[0119] (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.

[0120] (3) The coating solution from (2) was applied dropwise onto the cathode precursor from (1) in an argon glove box. After that, the mixture was left to stand for 2 hours to remove the solvent and impregnate the voids in the cathode with a polymer electrolyte, thereby creating an inorganic solid electrolyte cathode for secondary batteries.

[0121] Examples of manufacturing practices for oxide-based electrolyte secondary batteries Fabrication example of a negative electrode with a protective film formed inside an argon glove box: Negative electrodes obtained in Examples 1-7 and Comparative Examples 1-3, positive electrode obtained in the example of positive electrode fabrication, and Li7La3Zr2O as the inorganic solid electrolyte. 12 Using a film thickness of 500 μm, a test 2032 type coin cell was manufactured by stacking the positive electrode, inorganic solid electrolyte, and negative electrode in that order, then crimping them together.

[0122] [Evaluation of the manufactured battery] The fabricated batteries were evaluated by performing charge-discharge tests using a charge-discharge device. The discharge capacity at the third charge-discharge cycle and the retention rate of the discharge capacity at the 50th cycle relative to the discharge capacity at the third cycle were determined. The charge-discharge test conditions were as follows: CCCV charging to 4.2V with a current equivalent to 0.1C (10-hour rate) (0.01C cut-off), followed by CCCV discharging to 2.5V with a current equivalent to 0.1C (0.01C cut-off). The test temperature was 60°C. The results are shown in Table 1.

[0123] The aforementioned negative electrode protective film possesses film strength, flexibility, binding properties, and ion conductivity. From the results of the examples and comparative examples, it can be seen that inorganic solid electrolyte secondary batteries in which this protective film is placed between the negative electrode and the inorganic solid electrolyte exhibit superior battery characteristics (discharge capacity, maintenance of charge-discharge cycle capacity).

[0124] [Table 1] [Industrial applicability]

[0125] 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. A negative electrode protective film containing a lithium salt compound, The negative electrode protective film comprises a polymer, The aforementioned polymer is a polyether polymer. Taking the thickness of the negative electrode protective film before pressing as 100%, the rate of change in film thickness after pressing at a temperature of 25°C and a pressure of 1 MPa for 10 minutes is 1 to 20%, and the rate of change in film thickness after being left for 10 minutes after the press pressure is released is -1 to 5%. The negative electrode protective film is such that the rate of change in film thickness (X1) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and the rate of change in film thickness (X2) when pressed at a temperature of 25°C and a pressure of 1 MPa for 10 minutes and then left to stand for 10 minutes after the press pressure is released are in the relationship X1 > X2.

2. The negative electrode protective film according to claim 1, wherein the ionic conductivity at 25°C is 0.1 to 10 mS / cm.

3. A negative electrode with a negative electrode protective film, comprising a negative electrode and a negative electrode protective film according to claim 1 or 2 laminated on the surface of the negative electrode.

4. An energy storage device comprising a positive electrode, an electrolyte, a negative electrode protective film according to claim 1 or 2, and a negative electrode.

5. The energy storage device according to claim 4, wherein the electrolyte is a solid electrolyte.

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