Electrodes and secondary batteries

Abstract

Provided is an electrode comprising an electrode active material layer and a polymer layer formed upon the electrode active material layer, wherein the polymer layer contains inorganic particles and a copolymer that contains fluoromonomer units and amide-bond-containing monomer units.

Description

[Technical Field]

[0001] The present disclosure relates to an electrode and a secondary battery. [Background technology]

[0002] Patent Document 1 describes a lithium ion secondary battery that includes a positive electrode, a negative electrode, a polymer layer, and a lithium ion-permeable insulating layer, wherein the positive electrode includes a positive electrode active material layer containing a positive electrode active material capable of absorbing and desorbing lithium, and a positive electrode current collector, the negative electrode includes a negative electrode active material layer formed by a vapor phase method and containing an alloy-based negative electrode active material, and a negative electrode current collector, the polymer layer is formed on the surface of the negative electrode active material layer and contains a first polymer and first inorganic oxide particles, and the lithium ion-permeable insulating layer is disposed so as to be interposed between the positive electrode and the negative electrode.

[0003] Patent Document 2 describes a composition characterized by containing an inorganic filler, a copolymer of a fluoromonomer and a polymerizable vinyl compound having an amide bond, and a solvent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-250968 [Patent Document 2] International Publication No. 2020 / 054210 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure aims to provide an electrode that can be used to obtain a secondary battery in which the storage capacity is less likely to decrease even after storage at high temperatures and the resistance is less likely to increase even after repeated charging and discharging. [Means for solving the problem]

[0006] According to a first aspect of the present disclosure, there is provided an electrode comprising an electrode active material layer and a polymer layer formed on the electrode active material layer, wherein the polymer layer contains a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit, and inorganic particles. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide an electrode that can obtain a secondary battery that is resistant to a decrease in storage capacity even after storage at high temperatures and a resistance that is resistant to an increase in resistance even after repeated charge and discharge. DETAILED DESCRIPTION OF THE INVENTION

[0008] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0009] The electrode of the present disclosure comprises an electrode active material layer and a polymer layer formed on the electrode active material layer.

[0010] Patent Document 1 describes that in a lithium ion secondary battery using an alloy-based negative electrode active material, by forming a polymer layer containing a first polymer and first inorganic oxide particles on the surface of the negative electrode active material layer, a lithium ion secondary battery can be obtained that has excellent battery performance such as charge / discharge cycle characteristics and output characteristics, a long service life, and very little deterioration in the battery characteristics even with an increased number of charge / discharge cycles, and that is also highly safe against internal short circuits.

[0011] However, it has been found that the method proposed in Patent Document 1, in which a polymer layer containing a first polymer and first inorganic oxide particles is formed on the surface of a negative electrode active material layer, is prone to a decrease in storage capacity when stored at high temperatures, and furthermore, it is not possible to sufficiently suppress an increase in resistance after repeated charging and discharging of the secondary battery.

[0012] Therefore, the inventors have intensively investigated means for obtaining a secondary battery in which the storage capacity is resistant to decrease even after storage at high temperatures and the resistance is resistant to increase even after repeated charge and discharge. As a result, it has been found that by forming a polymer layer containing a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit and inorganic particles on an electrode active material layer, it is possible to obtain an electrode that can be used to obtain a secondary battery in which the storage capacity is resistant to decrease even after storage at high temperatures and the resistance is resistant to increase even after repeated charge and discharge.

[0013] That is, the electrode of the present disclosure is an electrode comprising an electrode active material layer and a polymer layer formed on the electrode active material layer, and the polymer layer contains a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit, and inorganic particles. Therefore, by using the electrode of the present disclosure as an electrode for a secondary battery, a secondary battery can be obtained in which the storage capacity is unlikely to decrease even after storage at high temperatures, and the resistance is unlikely to increase even after repeated charge and discharge.

[0014] The following describes in more detail embodiments of the electrodes of the present disclosure.

[0015] The electrode of the present disclosure comprises an electrode active material layer and a polymer layer formed on the electrode active material layer.

[0016] (polymer layer) The polymer layer of the electrode of the present disclosure contains a copolymer and inorganic particles and is formed on the electrode active material layer. As long as the polymer layer is formed on the electrode active material layer, it may be formed directly on the electrode active material layer without any other layer therebetween, or may be formed on the electrode active material layer via any other layer. However, since the effect of forming the polymer layer can be fully obtained, it is preferable that the polymer layer be formed directly on the electrode active material layer without any other layer therebetween.

[0017] (copolymer) The copolymer contained in the polymer layer contains a fluoromonomer unit and an amide bond-containing monomer unit.

[0018] The fluoromonomers forming the fluoromonomer unit include (1) sp 2 Examples include olefins having a fluorine atom bonded to a hybridized carbon atom, (2) monomers represented by the general formula: CH2=CX-COORf (wherein X is Cl, H or an alkyl group, and Rf is a fluoroalkyl group), (3) monomers represented by the general formula: CH2=CH-Rf (wherein Rf is a fluoroalkyl group), and (4) monomers represented by the general formula: CH2=CH-ORf (wherein Rf is a fluoroalkyl group).

[0019] The alkyl group may be an alkyl group having 1 to 3 carbon atoms, and a methyl group is preferred.

[0020] The fluoroalkyl group is preferably a linear or branched fluoroalkyl group having 1 to 12 carbon atoms.

[0021] As the fluoromonomer, (1) is preferred because it allows the introduction of fluorine atoms bonded to carbon atoms constituting the polymer main chain into the copolymer, thereby further improving the performance of the secondary battery. Also preferred are vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, monofluoroethylene, trifluorostyrene, and fluoropolymers represented by the general formula: CX2=CXRf 1 (Wherein, X is independently H or F, at least one of X is F, Rf 1 is more preferably at least one selected from the group consisting of fluoromonomers represented by a straight-chain or branched fluoroalkyl group having 1 to 12 carbon atoms.

[0022] The fluoromonomer is more preferably at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and 2,3,3,3-tetrafluoropropene, as this can further improve the performance of the secondary battery, and tetrafluoroethylene is particularly preferred.

[0023] The amide bond-containing monomer that forms the amide bond-containing monomer unit contains an amide bond and a polymerizable vinyl group. The amide bond is a bond between a carbonyl group and a nitrogen atom. Examples of the polymerizable vinyl group include vinyl, allyl, vinyl ether, vinyl ester, and acrylic groups.

[0024] Examples of the amide bond-containing monomer include N-vinyl lactam compounds such as N-vinyl-β-propiolactam, N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, and N-vinyl-heptolactam; acyclic N-vinyl amide compounds such as N-vinyl formamide and N-methyl-N-vinyl acetamide; acyclic N-allyl amide compounds such as N-allyl-N-methylformamide and allyl urea; N-allyl lactam compounds such as 1-(2-propenyl)-2-pyrrolidone; and acrylamide compounds such as (meth)acrylamide, N,N-dimethylacrylamide, and N-isopropylacrylamide.

[0025] The amide bond-containing monomer also includes [ka] (In the formula, R 11 and R 12 are independently H or an alkyl group having 1 to 10 carbon atoms), [ka] (In the formula, R 11 and R 12 are independently H or an alkyl group having 1 to 10 carbon atoms).

[0026] The amide bond-containing monomer is preferably a monomer having a lactam ring. The lactam ring is not particularly limited as long as it is a ring formed by an amide bond and carbon atoms, and may be a monocyclic or polycyclic ring, but a monocyclic ring is preferred. The lactam ring may also have any substituent. Examples of lactam rings include an α-lactam ring, a β-lactam ring, a γ-lactam ring, a δ-lactam ring, an ε-caprolactam ring, and an ω-heptalactam ring.

[0027] The amide bond-containing monomer may have a structure in which the remaining atomic group, obtained by removing one or more hydrogen atoms bonded to the carbon or nitrogen atom that forms the lactam ring, is directly or indirectly bonded to a polymerizable vinyl group. For example, the amide bond-containing monomer may have a structure in which the remaining atomic group, obtained by removing one hydrogen atom bonded to the carbon or nitrogen atom that forms the lactam ring, is bonded to a vinyl group or an allyl group.

[0028] As the amide bond-containing monomer, at least one selected from the group consisting of N-vinyl-β-propiolactam, N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-ε-caprolactam, and N-vinyl-heptolactam is preferred, at least one selected from the group consisting of N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, and N-vinyl-ε-caprolactam is more preferred, and N-vinyl-2-pyrrolidone is even more preferred, because it can further improve the performance of secondary batteries.

[0029] The copolymer may contain other monomer units in addition to the fluoromonomer units and the amide bond-containing monomer units. The other monomers are not particularly limited as long as they are copolymerizable with the fluoromonomers and the amide bond-containing monomers. Examples of the other monomer units include vinyl ester monomer units, vinyl ether monomer units, (meth)acrylic monomer units having polyethylene glycol in the side chain, vinyl monomer units having polyethylene glycol in the side chain, (meth)acrylic monomer units having a long-chain hydrocarbon group, and vinyl monomer units having a long-chain hydrocarbon group.

[0030] The content of the fluoromonomer units in the copolymer is preferably 75 to 7 mol % based on the total monomer units, and the content of the amide bond-containing monomer units in the copolymer is preferably 25 to 93 mol % based on the total monomer units, since this can further improve the performance of the secondary battery.

[0031] The content of fluoromonomer units in the copolymer is more preferably 60 mol% or less, even more preferably 55 mol% or less, particularly preferably 50 mol% or less, most preferably 45 mol% or less, more preferably 15 mol% or more, even more preferably 20 mol% or more, particularly preferably 35 mol% or more, and most preferably 40 mol% or more.

[0032] The content of amide bond-containing monomer units in the copolymer is more preferably 40 mol% or more, even more preferably 45 mol% or more, particularly preferably 50 mol% or more, and most preferably 55 mol% or more, more preferably 85 mol% or less, even more preferably 80 mol% or less, particularly preferably 65 mol% or less, and most preferably 60 mol% or less.

[0033] The content of other monomer units in the copolymer is preferably 50 mol% or less, more preferably 35 mol% or less, even more preferably 25 mol% or less, still more preferably 15 mol% or less, particularly preferably 5 mol% or less, and preferably 0 mol% or more.

[0034] The copolymer may also be a copolymer containing substantially only fluoromonomer units and amide bond-containing monomer units.

[0035] The composition of the copolymer is, for example, 1 H-NMR and 19 It can be measured by F-NMR.

[0036] The weight-average molecular weight (polystyrene equivalent) of the copolymer is preferably 10,000 to 500,000, more preferably 15,000 or more, even more preferably 20,000 or more, particularly preferably 30,000 or more, and more preferably 400,000 or less, because this can further improve the performance of the secondary battery. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0037] (Method of producing copolymer) The copolymer can be suitably produced by a production method in which a fluoromonomer, an amide bond-containing monomer, and, if necessary, other monomers are polymerized in a reactor.

[0038] As the polymerization method, methods such as suspension polymerization, emulsion polymerization, and solution polymerization can be used.

[0039] Among various polymerization methods, a polymerization method using a fluorine-containing solvent is preferred because it allows the production of a copolymer having a high molecular weight. The copolymer can be suitably produced, for example, by a production method in which at least a fluoromonomer and an amide bond-containing monomer are polymerized in a fluorine-containing solvent to obtain the copolymer.

[0040] Examples of fluorine-containing solvents include hydrochlorofluoroalkanes such as CH3CClF2, CH3CCl2F, CF3CF2CCl2H, and CF2ClCF2CFHCl; chlorofluoroalkanes such as CF2ClCFClCF2CF3 and CF3CFClCFClCF3; perfluoroalkanes such as perfluorocyclobutane, CF3CF2CF2CF3, CF3CF2CF2CF2CF3, and CF3CF2CF2CF2CF2CF3; perfluoroalkanes such as CF2HCF2CF2CF2H, CF3CFHCF2CF2CF3, CF3CF2CF2CF2CF2H, CF3CF2CFHCF2CF3, CF3CFHCFHCF2CF3, CF2HCF2CF2CF2CF2H, CF2HCFHCF2CF2CF3, and CF3CF Examples include hydrofluorocarbons such as 2CF2CF2CF2CF2H, CF3CH(CF3)CF3CF2CF3, CF3CF(CF3)CFHCF2CF3, CF3CF(CF3)CFHCFHCF3, CF3CH(CF3)CFHCF2CF3, CF2HCF2CF2CF2CF2CF2H, CF3CF2CF2CF2CH2CH3, and CF3CH2CF2CH3; (perfluoroalkyl)alkyl ethers such as F(CF2)4OCH3, F(CF2)4OC2H5, (CF3)2CFOCH3, and F(CF2)3OCH3; and hydrofluoroalkyl ethers such as CF3CH2OCF2CHF2, CHF2CF2CH2OCF2CHF2, and CF3CF2CH2OCF2CHF2.

[0041] The fluorine-containing solvent is preferably at least one selected from the group consisting of hydrofluorocarbons, (perfluoroalkyl) alkyl ethers, and hydrofluoroalkyl ethers, and more preferably hydrofluoroalkyl ethers, because it allows the production of a copolymer having a higher molecular weight.

[0042] Of these, the fluorine-containing solvent is preferably at least one selected from the group consisting of CF3CH2CF2CH3, CF3CH2OCF2CHF2, CHF2CF2CH2OCF2CHF2 and CF3CF2CH2OCF2CHF2, and more preferably CF3CH2OCF2CHF2.

[0043] In the above polymerization, a polymerization initiator, a surfactant and a chain transfer agent can be used, and conventionally known ones can be used for each of them.

[0044] As the polymerization initiator, a radical polymerization initiator can be used. Examples of the polymerization initiator include: dialkyl peroxycarbonates such as di-normal propyl peroxydicarbonate, diisopropyl peroxydicarbonate, and di-sec-butyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-hexyl peroxy 2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, and t-amyl peroxypivalate; Dialkyl peroxides such as di-t-butyl peroxide; Di[fluoro(or fluorochloro)acyl]peroxides; are some of the most representative examples.

[0045] Di[fluoro(or fluorochloro)acyl]peroxides include diacyl peroxides represented by [(RfCOO)-]2 (Rf is a perfluoroalkyl group, an ω-hydroperfluoroalkyl group, or a fluorochloroalkyl group).

[0046] Examples of di[fluoro(or fluorochloro)acyl]peroxides include di(ω-hydro-dodecafluoroheptanoyl)peroxide, di(ω-hydro-tetradecafluorooctanoyl)peroxide, di(ω-hydro-hexadecafluorononanoyl)peroxide, di(perfluorobutyryl)peroxide, di(perfluoroparyl)peroxide, di(perfluorohexanoyl)peroxide, di(perfluoroheptanoyl)peroxide, di(perfluorooctanoyl)peroxide, di(perfluorononanoyl)peroxide, di(ω-chloro-hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, Examples of the peroxide include di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundecafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undecachlorotriacontafluorodocosanoyl) peroxide.

[0047] Polymerization in the presence of a chain transfer agent allows the solution viscosity, weight-average molecular weight, etc. of the resulting copolymer to be appropriately adjusted. Examples of chain transfer agents include hydrocarbons such as ethane, isopentane, n-hexane, and cyclohexane; aromatics such as toluene and xylene; ketones such as acetone; acetates such as ethyl acetate and butyl acetate; alcohols such as methanol and ethanol; mercaptans such as methyl mercaptan; and halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, and methyl chloride.

[0048] The polymerization temperature is not particularly limited, but is preferably 0 to 95°C, more preferably 15 to 95°C, from the viewpoint of the polymerization rate and the cost required for temperature control.

[0049] The polymerization pressure is not particularly limited, but is preferably 0.3 to 1.5 MPaG, more preferably 0.4 MPaG or more, and more preferably 1.0 MPaG or less, from the viewpoints of the polymerization rate and the pressure resistance of the reactor.

[0050] After the polymerization is completed, if the copolymer is obtained as a slurry, the polymer can be recovered by removing the slurry from the reactor, washing and drying it.

[0051] (Inorganic particles) The inorganic particles contained in the polymer layer are preferably inorganic particles containing at least one element selected from the group consisting of Mg, Al, Si, Ti, Zr, and Ba. The inorganic particles are preferably inorganic particles (excluding electrode active materials).

[0052] The inorganic particles are preferably at least one selected from the group consisting of metal oxide particles and metal hydroxide particles, and more preferably metal oxide particles containing at least one element selected from the group consisting of Mg, Al, Si, Ti, Zr, and Ba.

[0053] The metal oxide particles are preferably particles of at least one type selected from the group consisting of MgO, Al2O3, SiO2, TiO2, ZrO2 and BaO.

[0054] The metal hydroxide particles are preferably at least one type of particles selected from the group consisting of Mg(OH)2, Al(OH)3 and Zr(OH)4.

[0055] Among these, the inorganic particles are preferably at least one type of particles selected from the group consisting of MgO, Al2O3, SiO2 and ZrO2, and more preferably Al2O3 particles.

[0056] The average particle size of the inorganic particles is preferably 25 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, particularly preferably 1 μm or less, and preferably 0.02 μm or more. The average particle size of the inorganic particles is a value obtained by measurement using a transmission electron microscope, a laser particle size distribution analyzer, or the like.

[0057] In the polymer layer, the content ratio of the copolymer to the inorganic particles [(copolymer) / (inorganic particles)] is preferably 0.1 / 99.9 to 49.9 / 50.1 by mass, more preferably 1 / 99 or more, even more preferably 5 / 95 or more, particularly preferably 10 / 90 or more, more preferably 45 / 55 or less, and even more preferably 40 / 60 or less.

[0058] (Method for forming polymer layer) The polymer layer can be formed, for example, by preparing a composition containing the copolymer and inorganic particles and coating the composition on the electrode active material layer.

[0059] The coating method is not particularly limited as long as it can cover the surface of the electrode active material layer with a polymer layer formed from the composition. For example, a method of applying the composition to the electrode active material layer and drying the coating film can be used. More specific examples of coating methods include roll-coating the composition onto the electrode active material layer, dipping the electrode active material layer into the composition, and applying the composition to the electrode active material layer and then immersing it in an appropriate coagulation solution. Alternatively, a film can be prepared using the composition, and the resulting film and the electrode active material layer can be laminated by a method such as lamination. An example of a method of preparing a film using the composition is to cast the composition onto a film having a smooth surface, such as a polyester film or an aluminum film, and then peel it off.

[0060] The composition containing the copolymer and the inorganic particles preferably further contains a solvent.

[0061] Examples of the solvent include water; nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran, dioxane, ethyl cellosolve, methyl cellosolve, diglyme, and triglyme; aromatic hydrocarbon solvents such as xylene, toluene, and solvent naphtha; aliphatic hydrocarbon solvents such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, and mineral spirits; fluorine-containing solvents such as CF3CH2CF2CH3, CF3CH2OCF2CHF2, CHF2CF2CH2OCF2CHF2, and CF3CF2CH2OCF2CHF2; and mixed solvents thereof.

[0062] (electrode active material layer) The electrode active material layer may contain an electrode active material and a binder. The electrode of the present disclosure may be used as either a positive electrode or a negative electrode. Therefore, the electrode active material may be a positive electrode active material or a negative electrode active material. The positive electrode may include a positive electrode active material layer containing a positive electrode active material and a binder, and a polymer layer formed on the positive electrode active material layer. The negative electrode may include a negative electrode active material layer containing a negative electrode active material and a binder, and a polymer layer formed on the negative electrode active material layer.

[0063] The electrode usually includes a current collector, and the electrode active material layer is formed on the current collector. The electrode active material layer may be formed on one side or both sides of the current collector. When the electrode active material layer is formed on both sides of the current collector, the polymer layer may be formed only on the electrode active material layer on one side, or on the electrode active material layers on both sides.

[0064] Hereinafter, embodiments of the positive electrode and the negative electrode will be described in more detail.

[0065] (positive electrode) The positive electrode comprises a positive electrode active material layer containing a positive electrode active material and a binder, and a polymer layer formed on the positive electrode active material layer. By forming a polymer layer containing a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit and inorganic particles on the positive electrode active material layer, a secondary battery can be obtained that is resistant to a decrease in storage capacity even after storage at high temperatures and is resistant to an increase in resistance even after repeated charge and discharge.

[0066] (Cathode active material) There are no particular limitations on the positive electrode active material as long as it is capable of electrochemically absorbing and releasing lithium ions.

[0067] The positive electrode active material is preferably a positive electrode active material containing at least one alkali metal selected from the group consisting of Li, Na, and K, and more preferably a positive electrode active material containing at least one alkali metal selected from the group consisting of Li, Na, and K and at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge.

[0068] Among these, the positive electrode active material is preferably a material containing lithium and at least one transition metal, such as a lithium transition metal composite oxide or a lithium-containing transition metal phosphate compound.

[0069] The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of the lithium transition metal composite oxide include lithium-cobalt composite oxides such as LiCoO2, lithium-nickel composite oxides such as LiNiO2, lithium-manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and those in which some of the transition metal atoms that make up the main part of these lithium transition metal composite oxides have been substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and Si. Examples of the substituted oxides include lithium-nickel-manganese composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-cobalt-manganese composite oxide, lithium-manganese-aluminum composite oxide, and lithium-titanium composite oxide. More specifically, LiNi 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiMn 1.8 Al 0.2 O4, LiMn 1.5 Ni 0.5 O4, Li4Ti5O 12 , LiNi 0.82 Co 0.15 Al 0.03 Examples include O2.

[0070] The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples of the lithium-containing transition metal phosphate compound include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and lithium transition metal phosphate compounds in which a portion of the transition metal atoms that constitute the main components of these lithium transition metal phosphate compounds has been substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

[0071] In particular, from the viewpoint of high voltage, high energy density, charge / discharge cycle characteristics, etc., LiCoO2, LiNiO2, LiMn2O4, LiNi 0.82 Co 0.15 Al 0.03 O2, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2 and LiFePO4 are preferred.

[0072] (binder) As the binder, a polymer (excluding a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit) can be used.

[0073] Any material can be used as a binder as long as it is safe for the solvents and electrolyte used in electrode production. Examples include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

[0074] (Conductive material) The positive electrode active material layer may further contain a conductive material, such as carbon materials such as graphite, carbon black, carbon nanotubes, carbon fibers, and acetylene black.

[0075] With respect to the content of each component in the positive electrode active material layer, when the mass of the electrode active material layer is taken as 100 mass%, it is preferable that the content of the positive electrode active material is 80.0 to 99.8 mass%, the content of the conductive material is 0.1 to 10.0 mass%, and the content of the binder is 0.1 to 10.0 mass%.

[0076] The positive electrode usually further includes a positive electrode current collector, and a positive electrode active material layer is formed on the positive electrode current collector. The positive electrode active material layer may be formed on one side or both sides of the positive electrode current collector. When positive electrode active material layers are formed on both sides of the positive electrode current collector, a polymer layer may be formed only on the positive electrode active material layer on one side, or on the positive electrode active material layers on both sides.

[0077] Examples of the material for the positive electrode current collector include metals such as aluminum, titanium, and tantalum, and alloys thereof, with aluminum and its alloys being preferred.

[0078] The positive electrode active material layer may be formed by a conventional method, for example, by adding a binder, a thickener, a conductive material, a solvent, etc. to the positive electrode active material to form a slurry positive electrode mixture, which is then applied to a current collector, dried, and pressed to increase density.

[0079] Examples of thickeners include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, and casein.

[0080] Examples of the solvent for the positive electrode mixture include the same solvents as those that may be contained in the composition for forming the polymer layer.

[0081] (Negative electrode) The negative electrode comprises a negative electrode active material layer containing a negative electrode active material and a binder, and a polymer layer formed on the negative electrode active material layer. By forming a polymer layer containing a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit and inorganic particles on the negative electrode active material layer, a secondary battery can be obtained that is resistant to a decrease in storage capacity even after storage at high temperatures and is resistant to an increase in resistance even after repeated charge and discharge.

[0082] (Negative electrode active material) Examples of the negative electrode active material include carbonaceous materials capable of absorbing and desorbing lithium ions, such as pyrolysis products of organic materials under various pyrolysis conditions, artificial graphite, and natural graphite; metal oxide materials capable of absorbing and desorbing lithium ions, such as tin oxide and silicon oxide; lithium metal; various lithium alloys; etc. Two or more of these negative electrode active materials may be used in combination.

[0083] The negative electrode active material is preferably a negative electrode active material containing a carbonaceous material or a negative electrode active material containing a compound containing at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti.

[0084] Examples of compounds containing at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti include lithium alloys containing lithium and at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti, and metal oxides containing at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti.

[0085] Carbonaceous materials include: (1) Natural graphite, (2) Artificial carbonaceous materials and artificial graphite materials; carbonaceous materials {for example, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or oxidized versions of these pitches, needle coke, pitch coke, and partially graphitized carbon materials, furnace black, acetylene black, pitch-based carbon fiber, and other organic pyrolysis products; carbonizable organic materials (for example, coal tar pitch ranging from soft pitch to hard pitch, coal-based heavy oils such as carbonized liquefied oil, atmospheric residue, straight-run heavy oils such as vacuum residue, cracked petroleum heavy oils such as ethylene tar produced as a by-product during the thermal decomposition of crude oil, naphtha, etc.); aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; N-ring compounds such as phenazine and acridine; S-ring compounds such as thiophene and bithiophene; biphenyl; terphenyl; carbonaceous materials obtained by heat-treating the following at least once in the range of 400 to 3200°C: organic polymers such as polyphenylenes, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophenes and polystyrene, natural polymers such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and polysaccharides represented by saccharose, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin), and carbonized products thereof, or solutions of carbonizable organic substances dissolved in low-molecular-weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonized products thereof; (3) A carbonaceous material in which the negative electrode active material layer is made of at least two or more carbonaceous materials having different crystallinities and / or has an interface where the carbonaceous materials having different crystallinities are in contact with each other; (4) A carbonaceous material in which the negative electrode active material layer is made of at least two or more kinds of carbonaceous materials having different orientations and / or has an interface where the carbonaceous materials having different orientations are in contact with each other; The material selected from the above is preferable because it has a good balance between initial irreversible capacity and high current density charge / discharge characteristics.

[0086] (binder) As the binder, a polymer (excluding a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit) can be used. Examples of the binder include the same binders that can be contained in the positive electrode active material layer.

[0087] With regard to the content of each component in the negative electrode active material layer, when the mass of the negative electrode active material layer is taken as 100 mass %, the content of the negative electrode active material is preferably 99.9 to 80.0 mass % and the content of the binder is preferably 0.1 to 20.0 mass %.

[0088] The negative electrode usually further includes a negative electrode current collector, and a negative electrode active material layer is formed on the negative electrode current collector. The negative electrode active material layer may be formed on one side or both sides of the negative electrode current collector. When a negative electrode active material layer is formed on both sides of the negative electrode current collector, a polymer layer may be formed only on the negative electrode active material layer on one side, or on the negative electrode active material layers on both sides.

[0089] Examples of the material for the negative electrode current collector include copper, nickel, stainless steel, etc. Among these, copper is preferred from the viewpoints of ease of processing into a thin film and cost.

[0090] The negative electrode active material layer may be formed by a conventional method, for example, by adding a binder, a thickener, a conductive material, a solvent, and the like to the negative electrode active material to form a slurry-like negative electrode mixture, which is then applied to a current collector, dried, and then pressed to increase density.

[0091] Examples of the thickener include the same thickeners that can be used in forming the positive electrode active material layer.

[0092] Examples of conductive materials for the negative electrode include metal materials such as copper and nickel; and carbon materials such as graphite and carbon black.

[0093] Examples of the solvent for the negative electrode mixture include the same solvents as those that may be contained in the composition for forming the polymer layer.

[0094] (Electrode applications) The electrode of the present disclosure can be used in electrochemical devices. Examples of electrochemical devices include batteries such as secondary batteries and capacitors. The battery may be a primary battery, a storage battery (secondary battery), or a power storage element. The battery may be a non-aqueous electrolyte battery. Non-aqueous electrolyte batteries include all batteries equipped with an electrolyte and a power generation element. Examples of non-aqueous electrolyte batteries include lithium ion primary batteries, lithium ion secondary batteries, nickel-metal hydride batteries, lithium ion capacitors, and electric double layer capacitors.

[0095] (Secondary battery) The electrode of the present disclosure can be particularly suitably used as an electrode for a secondary battery, and among the secondary batteries, a lithium ion secondary battery is particularly preferred.

[0096] Secondary batteries are a secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, the secondary battery comprising the electrode of the present disclosure as the positive electrode; a secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, and comprising the electrode of the present disclosure as the negative electrode; a secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, the secondary battery comprising the electrode of the present disclosure as the positive electrode and the electrode of the present disclosure as the negative electrode; The present invention may take any of the following forms:

[0097] The non-aqueous electrolyte may be prepared by dissolving a known electrolyte salt in a known organic solvent for dissolving electrolyte salts.

[0098] The organic solvent for dissolving the electrolyte salt is not particularly limited, and one or more of the following can be used: hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and vinylene carbonate; and fluorine-containing solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate. Any of the conventionally known electrolytes can be used, such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCl, LiBr, CH3SO3Li, CF3SO3Li, and cesium carbonate.

[0099] The shape of the secondary battery is arbitrary, and examples thereof include cylindrical, rectangular, laminated, coin, large, etc. The shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

[0100] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0101] <1> According to a first aspect of the present disclosure, Provided is an electrode comprising an electrode active material layer and a polymer layer formed on the electrode active material layer, wherein the polymer layer contains a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit, and inorganic particles. <2> According to a second aspect of the present disclosure, There is provided an electrode according to a first aspect, wherein the fluoromonomer is at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and 2,3,3,3-tetrafluoropropene. <3> According to a third aspect of the present disclosure, There is provided an electrode according to the first or second aspect, wherein the amide bond-containing monomer has a lactam ring. <4> According to a fourth aspect of the present disclosure, There is provided an electrode according to any one of the first to third aspects, wherein the amide bond-containing monomer is N-vinyl-2-pyrrolidone. <5> According to a fifth aspect of the present disclosure, There is provided an electrode according to any one of the first to fourth aspects, wherein the content of fluoromonomer units in the copolymer is 75 to 7 mol % based on all monomer units, and the content of amide bond-containing monomer units in the copolymer is 25 to 93 mol % based on all monomer units. <6> According to a sixth aspect of the present disclosure, According to any one of the first to fifth aspects, there is provided an electrode in which the inorganic particles contain at least one element selected from the group consisting of Mg, Al, Si, Ti, Zr and Ba. <7> According to a seventh aspect of the present disclosure, There is provided an electrode according to any one of the first to sixth aspects, wherein the content ratio of the copolymer to the inorganic particles [(copolymer) / (inorganic particles)] is 0.1 / 99.9 to 49.9 / 50.1 in mass ratio. <8> According to an eighth aspect of the present disclosure, There is provided an electrode according to any one of the first to seventh aspects, wherein the electrode active material layer contains an electrode active material and a binder, and the binder contains a polymer (excluding a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit). <9> According to a ninth aspect of the present disclosure, According to an eighth aspect, there is provided an electrode in which the electrode active material is a positive electrode active material. <10> According to a tenth aspect of the present disclosure, According to a ninth aspect, there is provided an electrode, wherein the positive electrode active material is a positive electrode active material containing at least one alkali metal selected from the group consisting of Li, Na and K. <11> According to an eleventh aspect of the present disclosure, According to a ninth or tenth aspect, there is provided an electrode, wherein the positive electrode active material is a positive electrode active material containing at least one alkali metal selected from the group consisting of Li, Na, and K, and at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. <12> According to a twelfth aspect of the present disclosure, According to any one of the ninth to eleventh aspects, there is provided an electrode, wherein the electrode active material layer further contains a conductive material. <13> According to a thirteenth aspect of the present disclosure, When the mass of the electrode active material layer is 100% by mass, The content of the positive electrode active material is 80.0 to 99.8 mass %, The content of the conductive material is 0.1 to 10.0 mass %, The binder content is 0.1 to 10.0 mass%. According to a twelfth aspect, there is provided an electrode. <14> According to a fourteenth aspect of the present disclosure, According to an eighth aspect, there is provided an electrode, wherein the electrode active material is a negative electrode active material. <15> According to a fifteenth aspect of the present disclosure, According to a fourteenth aspect, there is provided an electrode, wherein the negative electrode active material is a negative electrode active material containing a carbonaceous material, or a negative electrode active material containing a compound containing at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti. <16> According to a sixteenth aspect of the present disclosure, When the mass of the electrode active material layer is 100% by mass, The content of the negative electrode active material is 99.9 to 80.0 mass %, The binder content is 0.1 to 20.0 mass% According to a fourteenth or fifteenth aspect there is provided an electrode. <17> According to a seventeenth aspect of the present disclosure, According to any one of the first to sixteenth aspects, there is provided an electrode for use in an electrochemical device. <18> According to an eighteenth aspect of the present disclosure, There is provided a secondary battery comprising an electrode according to any one of the first to seventeenth aspects. [Example]

[0102] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0103] The values ​​in the examples were measured by the following methods.

[0104] <Monomer composition of polymer> Using an NMR analyzer (Agilent Technologies, VNS400MHz), 1 H-NMR and 19 The monomer composition of the polymer was measured by F-NMR in the deuterated chloroform solution state.

[0105] <Weight average molecular weight> Measurement was performed by gel permeation chromatography (GPC). Calculations were made using data measured using Tosoh AS-8010, CO-8020, and columns (three GMHHR-H columns connected in series) and Shimadzu RID-10A, with dimethylformamide (DMF) as the solvent at a flow rate of 1.0 ml / min (reference: polystyrene).

[0106] In the examples and comparative examples, the following copolymers and inorganic particles were used.

[0107] (copolymer) Copolymer a (composition ratio: tetrafluoroethylene (TFE) / N-vinyl-2-pyrrolidone (VP) = 41 / 59, weight average molecular weight: 320,000) Copolymer b (composition ratio: TFE / VP=38 / 62, weight average molecular weight: 240,000) ·Copolymer c (composition ratio: TFE / VP=33 / 67, weight average molecular weight: 97,000) Copolymer d (composition ratio: vinylidene fluoride (VdF) / hexafluoropropylene (HFP) = 93 / 7, weight average molecular weight: 320,000)

[0108] (Inorganic particles) Inorganic particle X: aluminum oxide (particle diameter: 0.7 μm) Inorganic particle Y: silicon dioxide (particle size: 0.6 μm) Inorganic particles Z: zirconium dioxide (particle size: 0.4 μm) Inorganic particles W: magnesium oxide (particle diameter: 0.6 μm)

[0109] Examples 1 to 7, Comparative Examples 1 to 2 <Preparation of electrolyte> Ethylene carbonate, a high-dielectric constant solvent, and ethyl methyl carbonate and dimethyl carbonate, low-viscosity solvents, were mixed in a volume ratio of 30:30:40, and LiPF6 was added to this mixture to give a concentration of 1.1 mol / L to obtain a non-aqueous electrolyte solution.

[0110] <Preparation of positive electrode> Li(Ni) as a positive electrode active material 1 / 3 Mn 1 / 3 Co 1 / 3 90 parts by weight of 2024 sintered aluminum oxide, 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to form a slurry. The resulting slurry was applied to one side of a 15 μm thick aluminum foil that had previously been coated with a conductive additive, dried, and roll-pressed in a press. The resultant was cut into a shape with an active material layer size of 50 mm wide and 30 mm long, and an uncoated area of ​​5 mm wide and 9 mm long to form a positive electrode.

[0111] <Preparation of negative electrode> 98 parts by mass of carbonaceous material (graphite) was mixed with 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) as a thickener and binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was applied to one side of a 10 μm thick copper foil, dried, and rolled in a press. The resulting foil was cut into a shape with an active material layer measuring 52 mm wide and 32 mm long, and an uncoated portion measuring 5 mm wide and 9 mm long to form a negative electrode.

[0112] The positive electrode obtained above was treated with a composition containing a copolymer and inorganic particles as follows: In Comparative Example 2, however, the positive electrode obtained above was used as is without the treatment described below.

[0113] <Coating treatment (dip method)> The copolymer and inorganic particles were mixed in the ratios shown in Table 1, and then the resulting mixture was mixed with HFE-347pc-f (CF3CH2OCF2CHF2) to prepare a composition with a solids concentration of 10% by mass. The positive electrode obtained above was immersed in the composition for 1 minute, and then the immersed material was recovered from the composition. The immersed material was washed with HFE-347pc-f to remove any deposits on the surface of the immersed material, and then the washed immersed material was dried to obtain a positive electrode with a polymer layer formed on the positive electrode active material layer. The formation of a polymer layer on the active material layer was confirmed using a scanning electron microscope (SEM) or by measuring the thickness and weight.

[0114] <Fabrication of aluminum laminated cells> A positive electrode having a polymer layer (a positive electrode not having a polymer layer in Comparative Example 2) and a negative electrode were arranged opposite each other with a 20 μm-thick microporous polyethylene film (separator) interposed therebetween, and the nonaqueous electrolyte solution obtained above was poured into the battery. After the nonaqueous electrolyte solution had sufficiently permeated the separator and the like, the battery was sealed, pre-charged, and aged to prepare a lithium ion secondary battery (aluminum laminate cell).

[0115] <Measurement of battery characteristics> The resulting aluminum laminate cell was subjected to a high-temperature storage test and a low-temperature cycle test, and the resistance increase rate was measured as follows.

[0116] <High temperature storage test> At 25°C, the battery was charged to 4.35 V at a constant current equivalent to 0.2 C, then discharged to 3.0 V at a constant current of 0.2 C. This was repeated for two cycles to stabilize the battery. For the third cycle, the battery was charged to 4.35 V at a constant current of 0.2 C, then charged at a constant voltage of 4.35 V until the current value reached 0.05 C, and then discharged to 3.0 V at a constant current of 0.2 C to determine the initial discharge capacity. The battery was then charged to 4.35 V at a constant current of 0.2 C, and then charged at a constant voltage of 4.35 V until the current value reached 0.05 C, and a storage test was performed. Here, 1C represents the current value required to discharge the battery's standard capacity in one hour, 5C represents five times that current value, 0.1C represents one-tenth of that current value, and 0.2C represents one-fifth of that current value.

[0117] After the initial characteristic evaluation, the charged secondary battery was stored at high temperature for 672 hours at 60°C. After the battery was cooled sufficiently, it was discharged at 0.5C to 3V at 25°C, then charged at a constant current of 0.2C to 4.35V, then charged at a constant voltage of 4.35V until the current value reached 0.05C, and finally discharged at a constant current of 0.2C to 3.0V to determine the storage capacity.

[0118] The capacity retention rate (%) was calculated based on the following formula. Capacity retention rate (%)=(storage capacity) / (initial discharge capacity)×100

[0119] <Measurement of resistance increase rate after low-temperature cycle test> At 25°C, the battery was charged to 4.2V at a constant current equivalent to 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This cycle was repeated twice to stabilize the battery. The secondary battery prepared above was then charged to 4.2V at a constant current of 0.2C in a -5°C environment, then charged at a constant voltage of 4.2V until the current value reached 0.05C, and then discharged to 3.0V at a constant current of 0.2C to determine the initial discharge capacity. Charge and discharge were repeated in the same manner, and a 200-cycle test was performed.

[0120] The resistance of the battery stabilized as described above when calculating the initial discharge capacity and the resistance after the cycle test were measured. The measurement temperature was −10° C. The resistance increase rate after the low-temperature cycle test was calculated based on the following formula. Resistance increase rate (%) = Resistance after 200 cycles (Ω) / Resistance after calculating initial discharge capacity (Ω) × 100

[0121] The results are shown in Table 1.

[0122] [Table 1]

[0123] Examples 8 to 14, Comparative Examples 3 to 4 <Preparation of electrolyte> High-dielectric-constant solvents, ethylene carbonate and monofluoroethylene carbonate, and low-viscosity solvent, ethyl methyl carbonate, were mixed in a volume ratio of 30:5:65, and LiPF6 was added to the mixture to give a concentration of 1.0 mol / L to obtain a nonaqueous electrolyte solution.

[0124] <Preparation of positive electrode> 90% by mass of LiMnO4 as a positive electrode active material, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent to form a slurry. The resulting slurry was applied to one side of a 15 μm thick aluminum foil that had previously been coated with a conductive additive, dried, and roll-pressed in a press. The resultant was cut into a shape with an active material layer size of 50 mm wide and 30 mm long, and an uncoated area of ​​5 mm wide and 9 mm long to form a positive electrode.

[0125] <Preparation of negative electrode> To 98 parts by mass of artificial graphite, 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) were added as thickeners and binders, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was applied to one side of a 10 μm thick copper foil, dried, and rolled in a press. The resulting foil was cut into a shape with an active material layer measuring 52 mm wide and 32 mm long, and an uncoated portion measuring 5 mm wide and 9 mm long to form a negative electrode.

[0126] The negative electrode obtained above was treated with a composition containing a copolymer and inorganic particles as follows: In Comparative Example 4, however, the negative electrode obtained above was used as is without the treatment described below.

[0127] <Coating treatment (dip method)> The copolymer and inorganic particles were mixed in the ratios shown in Table 2, and then the resulting mixture was mixed with HFE-347pc-f (CF3CH2OCF2CHF2) to prepare a composition with a solids concentration of 10% by mass. The negative electrode obtained above was immersed in the composition for 1 minute, and then the immersed material was recovered from the composition. The immersed material was washed with HFE-347pc-f to remove any deposits on the surface of the immersed material, and then the washed immersed material was dried to obtain a negative electrode with a polymer layer formed on the negative electrode active material layer. The formation of the polymer layer on the active material layer was confirmed using a scanning electron microscope (SEM) or by measuring the thickness and weight.

[0128] <Fabrication of aluminum laminated cells> The above-mentioned positive electrode and the negative electrode having a polymer layer (in Comparative Example 4, the negative electrode having no polymer layer) were arranged opposite each other with a 20 μm-thick microporous polyethylene film (separator) interposed therebetween, and the nonaqueous electrolyte solution obtained above was poured into the battery. After the nonaqueous electrolyte solution had sufficiently permeated the separator and the like, the battery was sealed, pre-charged, and aged to prepare a lithium ion secondary battery (aluminum laminate cell).

[0129] <Measurement of battery characteristics> The resulting aluminum laminate cell was subjected to a high-temperature storage test and a low-temperature cycle test, and the resistance increase rate was measured as follows.

[0130] <High temperature storage test> At 25°C, the battery was charged to 4.35 V at a constant current equivalent to 0.2 C, then discharged to 3.0 V at a constant current of 0.2 C. This was repeated for two cycles to stabilize the battery. For the third cycle, the battery was charged to 4.35 V at a constant current of 0.2 C, then charged at a constant voltage of 4.35 V until the current value reached 0.05 C, and then discharged to 3.0 V at a constant current of 0.2 C to determine the initial discharge capacity. The battery was then charged to 4.35 V at a constant current of 0.2 C, and then charged at a constant voltage of 4.35 V until the current value reached 0.05 C, and a storage test was performed. Here, 1C represents the current value required to discharge the battery's standard capacity in one hour, 5C represents five times that current value, 0.1C represents one-tenth of that current value, and 0.2C represents one-fifth of that current value.

[0131] After the initial characteristic evaluation, the charged secondary battery was stored at high temperature for 528 hours at 75°C. After the battery was cooled sufficiently, it was discharged at 0.5C to 3V at 25°C, then charged at a constant current of 0.2C to 4.35V, then charged at a constant voltage of 4.35V until the current value reached 0.05C, and then discharged at a constant current of 0.2C to 3.0V to determine the storage capacity.

[0132] The capacity retention rate (%) was calculated based on the following formula. Capacity retention rate (%)=(storage capacity) / (initial discharge capacity)×100

[0133] <Measurement of resistance increase rate after low-temperature cycle test> At 25°C, the battery was charged to 4.2V at a constant current equivalent to 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This cycle was repeated twice to stabilize the battery. The secondary battery produced above was then charged to 4.2V at a constant current of 0.2C in an environment of -10°C, then charged at a constant voltage of 4.2V until the current value reached 0.05C, and then discharged to 3.0V at a constant current of 0.2C to determine the initial discharge capacity. Charge and discharge were repeated in the same manner, and a 200-cycle test was performed.

[0134] The resistance of the battery stabilized as described above when calculating the initial discharge capacity and the resistance after the cycle test were measured. The measurement temperature was −20° C. The resistance increase rate after the low-temperature cycle test was calculated based on the following formula. Resistance increase rate (%) = Resistance after 200 cycles (Ω) / Resistance after calculating initial discharge capacity (Ω) × 100

[0135] The results are shown in Table 2.

[0136] [Table 2]

Claims

1. An electrode comprising an electrode active material layer and a polymer layer formed on the electrode active material layer, wherein the polymer layer contains a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit and inorganic particles, the fluoromonomer being an olefin having a fluorine atom bonded to an sp 2 hybridized carbon atom, and the amide bond-containing monomer having a lactam ring.

2. 2. The electrode according to claim 1, wherein the fluoromonomer is at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and 2,3,3,3-tetrafluoropropene.

3. 3. The electrode according to claim 1, wherein the amide bond-containing monomer is N-vinyl-2-pyrrolidone.

4. 3. The electrode according to claim 1, wherein the content of the fluoromonomer units in the copolymer is 75 to 7 mol % based on the total monomer units, and the content of the amide bond-containing monomer units in the copolymer is 25 to 93 mol % based on the total monomer units.

5. 3. The electrode according to claim 1, wherein the inorganic particles contain at least one element selected from the group consisting of Mg, Al, Si, Ti, Zr, and Ba.

6. 3. The electrode according to claim 1, wherein the content ratio of the copolymer to the inorganic particles [(copolymer) / (inorganic particles)] is 0.1 / 99.9 to 49.9 / 50.1 by mass.

7. 3. The electrode according to claim 1, wherein the electrode active material layer contains an electrode active material and a binder, and the binder contains a polymer (excluding a copolymer containing a fluoromonomer unit and an amide bond-containing monomer unit).

8. The electrode according to claim 7 , wherein the electrode active material is a positive electrode active material.

9. 9. The electrode according to claim 8, wherein the positive electrode active material contains at least one alkali metal selected from the group consisting of Li, Na, and K.

10. 9. The electrode according to claim 8, wherein the positive electrode active material contains at least one alkali metal selected from the group consisting of Li, Na, and K, and at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge.

11. The electrode according to claim 8 , wherein the electrode active material layer further contains a conductive material.

12. When the mass of the electrode active material layer is 100% by mass, The content of the positive electrode active material is 80.0 to 99.8 mass %, The content of the conductive material is 0.1 to 10.0 mass %, The binder content is 0.1 to 10.0 mass %.

12. The electrode of claim 11.

13. 8. The electrode according to claim 7, wherein the electrode active material is a negative electrode active material.

14. 14. The electrode according to claim 13, wherein the negative electrode active material is a negative electrode active material containing a carbonaceous material or a negative electrode active material containing a compound containing at least one element selected from the group consisting of Si, Sn, V, Nb, and Ti.

15. When the mass of the electrode active material layer is 100% by mass, The content of the negative electrode active material is 99.9 to 80.0 mass %, The binder content is 0.1 to 20.0 mass %.

14. The electrode of claim 13.

16. 3. The electrode according to claim 1, which is used in an electrochemical device.

17. A secondary battery comprising the electrode according to claim 1 or 2.

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