Electrode for all-solid-state secondary battery, all-solid-state secondary battery, and method for manufacturing all-solid-state secondary battery

Abstract

To provide an electrode for an all-solid-state secondary battery that can provide a practical all-solid-state secondary battery even when an electrode active material layer does not contain an electrolyte, which has been an essential component in a conventional electrode for an all-solid-state secondary battery, and a practical all-solid-state secondary battery that uses an electrode in which an electrode active material layer does not contain an electrolyte.SOLUTION: The present invention relates to an electrode for an all-solid-state secondary battery including an electrode active material layer containing an electrode active material and a binder resin on a current collector, the binder resin including a polyimide-based resin, and the electrode active material layer including no electrolyte, and an all-solid-state secondary battery having this electrode as a positive electrode or a negative electrode.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electrode for an all-solid-state secondary battery and an all-solid-state secondary battery. [Background technology]

[0002] Lithium-ion secondary batteries have high energy density and capacity, and are therefore widely used as power sources for mobile information terminals, etc. In recent years, their use in industrial applications, such as in electric and hybrid vehicles that require large capacity, has also been expanding, and research is being conducted to further increase capacity and improve performance.

[0003] While there is a demand for higher energy density of lithium ion secondary batteries, in order to ensure and improve the safety of batteries, all-solid-state secondary batteries using non-flammable inorganic solid electrolytes instead of non-aqueous electrolytes in which electrolyte salts such as lithium salts are dissolved in organic solvents are being studied. All-solid-state secondary batteries include a positive electrode and a negative electrode, and a solid electrolyte layer disposed between them. From the viewpoint of performance, a solid electrolyte is generally added to each electrode (specifically, the positive electrode active material layer and the negative electrode active material layer).

[0004] For example, Patent Document 1 discloses an all-solid-state secondary battery having a positive electrode active material layer, an inorganic solid electrolyte layer, and a negative electrode active material layer in this order, the positive electrode active material layer, the inorganic solid electrolyte layer, and the negative electrode active material layer containing a specific polymer and an inorganic solid electrolyte. Patent Document 2 discloses an electrode for a solid electrolyte battery in which a mixture of a powdered active material, a solid electrolyte, and a conductive assistant is bound by a specific binder, and an active material layer is formed in a film shape on a current collector, and a solid electrolyte battery in which the electrode for a solid electrolyte battery is used for at least one of the positive electrode and the negative electrode. Furthermore, Patent Document 3 discloses an all-solid-state secondary battery having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, in which the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer are layers containing an inorganic solid electrolyte having ion conductivity of a metal element belonging to Group 1 or Group 2 of the periodic table, and an ion-conductive material, specifically, binder particles containing an inorganic solid electrolyte or a liquid electrolyte.

[0005] Patent Document 4 also discloses a solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer made of a solid electrolyte provided between the positive electrode and the negative electrode, the negative electrode having a negative electrode active material, a first binder that is bound to the solid electrolyte and is inactive against the solid electrolyte, and a second binder that has better binding properties to a negative electrode current collector than the first binder, the second binder containing a highly elastic resin. Patent Document 4 describes that the negative electrode does not contain a solid electrolyte, but in the examples, an electrolyte layer coating liquid is applied to the negative electrode structure and then dried to form an electrolyte layer on the negative electrode structure. In this method, during the manufacture of the solid-state battery, that is, when the electrolyte layer coating liquid is applied to the negative electrode, the solid electrolyte swells (permeates) from the electrolyte layer into the negative electrode layer, so that the formed negative electrode layer contains the solid electrolyte.

[0006] Patent Document 5 discloses an all-solid-state secondary battery having a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer in this order, in which the content of inorganic solid electrolyte in at least one of the positive electrode active material layer and the negative electrode active material layer is 0 to 10 mass% relative to the total solid content constituting each layer, the solid electrolyte layer contains a sulfide-based solid electrolyte, at least one of the positive electrode active material layer and the negative electrode active material layer contains a binder, and the negative electrode active material layer contains a specific negative electrode active material. However, in the examples of Patent Document 5, a solid electrolyte composition is applied onto the positive electrode active material layer of a secondary battery positive electrode sheet, heated to form a solid electrolyte layer, and then a composition for secondary battery negative electrode is applied onto the dried solid electrolyte layer and heated to form a negative electrode active material layer. In this method, as in the method described in Patent Document 4, the solid electrolyte permeates the positive electrode active material layer and the negative electrode active material layer, so that the formed positive electrode active material layer and negative electrode active material layer contain the solid electrolyte.

[0007] In addition, all-solid-state secondary batteries using organic solid electrolytes, i.e., polymer solid electrolytes, instead of inorganic solid electrolytes, have also been studied, but in that case, in general, solid electrolytes are added to each electrode (specifically, the positive electrode active material layer and the negative electrode active material layer) from the viewpoint of performance. For example, Patent Document 6 discloses a polymer solid electrolyte lithium battery that includes a positive electrode using a compound mainly composed of a transition metal oxide as a positive electrode active material, a negative electrode using lithium metal, lithium alloy, or a material capable of absorbing and releasing lithium ions as a negative electrode active material, and an electrolyte, and is characterized in that a specific polymer solid electrolyte is used for the electrolyte. In the examples, a composite positive electrode containing an electrolyte is formed by impregnating a precursor of the polymer solid electrolyte on the formed positive electrode active material layer and curing it by electron beam irradiation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 125716 [Patent Document 2] JP 2013-45683 A [Patent Document 3] International Publication No. 2017 / 099248 [Patent Document 4] JP 2014-116154 A [Patent Document 5] JP 2016-212990 A [Patent Document 6] JP 2003-92138 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide an electrode for an all-solid-state secondary battery that can provide a practical all-solid-state secondary battery even if the electrode active material layer does not contain an electrolyte, which was an essential component in conventional electrodes for all-solid-state secondary batteries, and to provide a practical all-solid-state secondary battery using an electrode in which the electrode active material layer does not contain an electrolyte. [Means for solving the problem]

[0010] The present invention relates to the following items: [1] An electrode having an electrode active material layer containing an electrode active material and a binder resin on a current collector, The binder resin includes a polyimide resin, The electrode for an all-solid-state secondary battery, wherein the electrode active material layer does not contain an electrolyte. [2] The electrode according to item [1], wherein the electrode active material layer further contains a conductive assistant. [3] An all-solid-state secondary battery having a positive electrode, a solid electrolyte layer, and a negative electrode, Item [1] or [2] above, wherein the positive electrode and / or the negative electrode is the electrode. [4] A step of applying an electrode mixture paste containing an electrode active material, a polyimide resin or a precursor thereof as a binder resin, and a solvent, but not containing an electrolyte, onto a current collector; A step of drying or heat-treating the applied electrode mixture paste to form an electrode active material layer. A method for producing an electrode for an all-solid-state secondary battery, comprising: [5] preparing an electrode sheet having an electrode active material layer on a current collector, the electrode active material layer including an electrode active material and a polyimide-based resin as a binder resin, and no electrolyte; a step of laminating and integrating the electrode sheet, a solid electrolyte-containing sheet containing a solid electrolyte, and a counter electrode sheet; A method for producing an all-solid-state secondary battery comprising the steps of: [6] The step of preparing an electrode sheet comprises: A step of applying an electrode mixture paste containing an electrode active material, a polyimide resin or a precursor thereof as a binder resin, and a solvent, but not containing an electrolyte, onto a current collector; A step of drying or heat-treating the applied electrode mixture paste to form an electrode active material layer. The method for producing an all-solid-state secondary battery according to item [5], [7] The method for producing an all-solid-state secondary battery according to item [5] or [6], wherein the counter electrode sheet includes an electrode active material and a polyimide resin as a binder resin, and has an electrode active material layer that does not include an electrolyte on a current collector. [8] The method for producing the all-solid-state secondary battery according to any one of the above items [5] to [7], characterized in that the electrode sheet, the solid electrolyte-containing sheet, and the counter electrode sheet are laminated by a dry method. Effect of the Invention

[0011] According to the present invention, it is possible to provide an electrode for an all-solid-state secondary battery that can obtain a practical all-solid-state secondary battery even if the electrode active material layer does not contain an electrolyte, which was an essential component in conventional electrodes for all-solid-state secondary batteries, and a practical all-solid-state secondary battery that uses an electrode in which the electrode active material layer does not contain an electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The electrode for an all-solid-state secondary battery of the present invention includes an electrode active material and a binder resin, and has an electrode active material layer on a current collector that does not contain an electrolyte (liquid electrolyte and solid electrolyte), and the binder resin contained in the electrode active material layer contains a polyimide-based resin. The all-solid-state secondary battery of the present invention has a positive electrode, a solid electrolyte layer, and a negative electrode, and the positive electrode and / or the negative electrode is the electrode for an all-solid-state secondary battery of the present invention. That is, the all-solid-state secondary battery of the present invention has a positive electrode, a solid electrolyte layer, and a negative electrode, and the positive electrode includes a positive electrode active material and a polyimide-based resin as a positive electrode binder resin, and has a positive electrode active material layer on a positive electrode current collector that does not contain an electrolyte, or the negative electrode includes a negative electrode active material and a polyimide-based resin as a negative electrode binder resin, and has a negative electrode active material layer on a negative electrode current collector that does not contain an electrolyte.

[0013] In addition, when the electrode is a positive electrode, the electrode active material and binder resin contained therein are referred to as a positive electrode active material and a positive electrode binder resin, respectively, and the electrode active material layer and the current collector are referred to as a positive electrode active material layer and a positive electrode current collector, respectively. When the electrode is a negative electrode, the electrode active material and binder resin contained therein are referred to as a negative electrode active material and a negative electrode binder resin, respectively, and the electrode active material layer and the current collector are referred to as a negative electrode active material layer and a negative electrode current collector, respectively. In addition, one of the positive electrode and the negative electrode may be referred to as an electrode and the other as a counter electrode. For example, when the positive electrode is the electrode for the all-solid-state secondary battery of the present invention, the positive electrode may be referred to as an electrode and the negative electrode as a counter electrode, and when the negative electrode is the electrode for the all-solid-state secondary battery of the present invention, the negative electrode may be referred to as an electrode and the positive electrode as a counter electrode. However, in either case, the counter electrode may also be the electrode for the all-solid-state secondary battery of the present invention.

[0014] Hereinafter, the electrode for an all-solid-state secondary battery and the all-solid-state secondary battery of the present invention will be described in detail for each component.

[0015] <Electrode> The electrode for an all-solid-state secondary battery of the present invention includes an electrode active material (positive electrode active material or negative electrode active material) and a polyimide resin as a binder resin, and has an electrode active material layer (positive electrode active material layer or negative electrode active material layer) that does not contain an electrolyte on a current collector (positive electrode current collector or negative electrode current collector). The electrode active material layer may further include a conductive assistant or other additives.

[0016] It is generally known that polyimide resins have almost no ion conductivity. However, despite the almost no ion conductivity, by using polyimide resins as binder resins, it is possible to obtain a practical all-solid-state secondary battery without adding an electrolyte, which was an essential component in conventional all-solid-state secondary battery electrodes, to the electrode active material layer. In the present invention, the "electrolyte" not included in the electrode active material layer refers to a material that serves as a source of ions that release cations (Li ions), as well as commonly known and used inorganic solid electrolytes and polymer solid electrolytes, and liquid electrolytes that do not themselves release cations (Li ions) but exhibit an ion transport function and function as an electrolyte. The electrode active material layer of the all-solid-state secondary battery electrode of the present invention may contain an electrode active material containing lithium.

[0017] <<Binder resin>> In the present invention, a polyimide resin is used as the binder resin. Here, the polyimide resin means a polymer or oligomer containing at least one repeating unit having an imide structure derived from a tetracarboxylic acid component (the tetracarboxylic acid component includes tetracarboxylic acid derivatives such as tetracarboxylic acid dianhydrides and tetracarboxylic acid esters in addition to tetracarboxylic acids, and is preferably tetracarboxylic acid dianhydrides) and a diamine component (the diamine component includes diisocyanates in addition to diamines, and is preferably diamines), and includes, for example, polyamideimide, polyetherimide, polyesterimide, etc. Also, the polyimide resin used in the present invention may be a partially imidized polyamic acid having an imidization rate of less than 100%.

[0018] The polyimide resin used as the binder resin in the present invention is preferably, for example, a polyimide resin comprising a repeating unit represented by the following chemical formula (1).

[0019] [ka] In chemical formula (1), A is one or more tetravalent groups obtained by removing a carboxyl group from a tetracarboxylic acid, and is preferably one or more tetravalent groups represented by any of the following chemical formulas (A-1) to (A-7), and particularly preferably 10 to 100 mol %, preferably 15 to 70 mol %, more preferably 20 to 60 mol %, and particularly preferably 20 to 50 mol % of A is a tetravalent group represented by the following chemical formula (A-1), and 90 to 0 mol %, preferably 85 to 30 mol %, more preferably 80 to 40 mol %, and particularly preferably 80 to 50 mol % of A is a tetravalent group represented by the following chemical formula (A-2) and / or the following chemical formula (A-3), B is at least one kind of divalent group obtained by removing an amino group from a diamine, preferably at least one kind of divalent group having 1 to 4 aromatic rings, more preferably at least one kind of divalent group represented by any one of the following chemical formulas (B-1) to (B-5), and particularly preferably at least one kind of divalent group represented by any one of the following chemical formulas (B-1) to (B-3).

[0020] [ka]

[0021] [ka] In the chemical formula (B-3), X represents a direct bond, an oxygen atom, a sulfur atom, a methylene group, a carbonyl group, a sulfoxyl group, a sulfonyl group, a 1,1'-ethylidene group, a 1,2-ethylidene group, a 2,2'-isopropylidene group, a 2,2'-hexafluoroisopropylidene group, a cyclohexylidene group, a phenylene group, a 1,3-phenylenedimethylene group, a 1,4-phenylenedimethylene group, a 1,3-phenylenediethylidene group, a 1,4- It is any one of a phenylenediethylidene group, a 1,3-phenylenedipropylidene group, a 1,4-phenylenedipropylidene group, a 1,3-phenylenedioxy group, a 1,4-phenylenedioxy group, a biphenylenedioxy group, a methylenediphenoxy group, an ethylidene diphenoxy group, a propylidenediphenoxy group, a hexafluoropropylidenediphenoxy group, an oxydiphenoxy group, a thiodiphenoxy group, and a sulfonediphenoxy group.

[0022] Examples of tetracarboxylic acid components that can be suitably used to obtain a polyimide resin consisting of a repeating unit represented by the chemical formula (1) include 4,4'-oxydiphthalic acids [tetracarboxylic acid components that provide a tetravalent group represented by the chemical formula (A-1)], 3,3',4,4'-biphenyltetracarboxylic acids [tetracarboxylic acid components that provide a tetravalent group represented by the chemical formula (A-2)], pyromellitic acids [tetracarboxylic acid components that provide a tetravalent group represented by the chemical formula (A-3)], 3,3',4,4'-diphenylsulfonetetracarboxylic acids [tetracarboxylic acid components that provide a tetravalent group represented by the chemical formula (A-4)], and the like. -4)], 3,3',4,4'-benzophenonetetracarboxylic acids [tetracarboxylic acid components which provide a tetravalent group represented by the above chemical formula (A-5)], 2,3,3',4'-biphenyltetracarboxylic acids [tetracarboxylic acid components which provide a tetravalent group represented by the above chemical formula (A-6)], 2,2',3,3'-biphenyltetracarboxylic acids [tetracarboxylic acid components which provide a tetravalent group represented by the above chemical formula (A-7)], p-terphenyltetracarboxylic acids, m-terphenyltetracarboxylic acids, and the like.

[0023] Examples of diamine components that can be suitably used to obtain a polyimide resin consisting of a repeating unit represented by the chemical formula (1) include aromatic diamines having one aromatic ring, such as p-phenylenediamine [a diamine component that provides a divalent group represented by the chemical formula (B-2)], m-phenylenediamine, 2,4-diaminotoluene, 2,4-bis(β-amino-tert-butyl)toluene, bis-p-(1,1-dimethyl-5-amino-pentyl)benzene, 1-isopropyl-2,4-m-phenylenediamine, m-xylylenediamine, and p-xylylenediamine. Diamine, 4,4'-diaminodiphenyl ether [diamine component that provides a divalent group represented by the above chemical formula (B-1)], 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-biphenyldiamine, benzidine, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 4,4'-diamino Aromatic diamines having two aromatic rings, such as diphenyl sulfone, 4,4'-diaminodiphenylpropane, bis(4-amino-3-carboxyphenyl)methane, and bis(p-β-amino-tert-butylphenyl)ether; and aromatic diamines having three aromatic rings, such as 1,3-bis(4-aminophenoxy)benzene [diamine component that provides the divalent group represented by the above chemical formula (B-5)], 1,4-bis(4-aminophenoxy)benzene [diamine component that provides the divalent group represented by the above chemical formula (B-4)], and bis(p-β-methyl-6-aminophenyl)benzene. Examples of aromatic diamines include aromatic diamines having four aromatic rings, such as 2,2-bis[4-(4-aminophenoxy)phenyl]propane [a diamine component which provides a divalent group represented by the above chemical formula (B-3) in which X is a 2,2'-isopropylidene group], bis[4-(4-aminophenoxy)phenyl]sulfone [a diamine component which provides a divalent group represented by the above chemical formula (B-3) in which X is a sulfonyl group], and 4,4'-bis(4-aminophenoxy)biphenyl [a diamine component which provides a divalent group represented by the above chemical formula (B-3) in which X is a direct bond].

[0024] As the polyimide-based resin used as the binder resin in the present invention, for example, at least one of a tetracarboxylic acid component or a diamine component, more preferably either one of a tetracarboxylic acid component or a diamine component, is preferably a polyimide-based resin containing 50 mol % or more, more preferably 80 mol % or more, of an aliphatic compound. For example, a polyimide-based resin consisting of a repeating unit represented by the above chemical formula (1) in which A is one or more tetravalent groups having one or two aromatic rings, and B is one or more divalent alkylene groups having 1 to 20 carbon atoms is particularly preferred. In this polyimide-based resin, A is preferably one or more tetravalent groups represented by any of the above chemical formulas (A-1) to (A-3) and (A-6), and B is preferably one or more alkylene groups having 3 to 16 carbon atoms, more preferably one or more alkylene groups having 3 to 14 carbon atoms. B may be a straight-chain alkylene group or a branched alkylene group.

[0025] Examples of tetracarboxylic acid components that can be suitably used to obtain this polyimide resin include aromatic tetracarboxylic acids such as 3,3',4,4'-biphenyltetracarboxylic acids, 2,3,3',4'-biphenyltetracarboxylic acids, 2,2',3,3'-biphenyltetracarboxylic acids, pyromellitic acids, benzophenonetetracarboxylic acids, 4,4'-oxydiphthalic acids, diphenylsulfonetetracarboxylic acids, p-terphenyltetracarboxylic acids, and m-terphenyltetracarboxylic acids, and also include aliphatic tetracarboxylic acids such as butane-1,2,3,4-tetracarboxylic acids.

[0026] Examples of diamine components that can be suitably used to obtain this polyimide resin include aliphatic diamines such as 1,2-propanediamine, 1,3-diaminopropane, 2-methyl-1,3-propanediamine, 1,4-diaminobutane, 1,3-diaminopentane, 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, 1,6-diaminohexane (hexamethylenediamine), 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, and 1,12-diaminododecane. Also, examples of diamine components that can be suitably used to obtain this polyimide resin include aliphatic diamines such as p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, m-xylylenediamine, p-xylylenediamine, 4, Examples of aromatic diamines include 4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl methane, 3,3'-diaminodiphenyl methane, 3,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, bis(4-amino-3-carboxyphenyl)methane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, and 4,4'-bis(4-aminophenoxy)biphenyl.

[0027] As the polyimide resin used as the binder resin, commercially available products can be used, and for example, Upia-LB-1001, Upia-LB-2001, Upia-AT (U-Varnish-A), Upia-ST (U-Varnish-S), etc. manufactured by Ube Industries, Ltd. can be suitably used.

[0028] The polyimide resin as the binder resin may be used alone or in combination of two or more kinds.

[0029] Furthermore, one or more other binder resins that are generally used as binder resins for electrodes can be used in combination, preferably in an amount of less than 50 mass %, more preferably less than 30 mass %, and particularly preferably less than 10 mass %, within a range that does not impair the characteristics of the present invention. However, it is preferable not to use binder resins other than polyimide-based resins.

[0030] <<Electrode active material>> The electrode active material (positive electrode active material) used in the positive electrode of the all-solid-state secondary battery of the present invention is not particularly limited, and any known positive electrode active material may be used as long as it can reversibly insert and release lithium ions. The positive electrode active material may be used alone or in combination of two or more kinds.

[0031] Examples of the positive electrode active material include transition metal oxides that contain lithium and one or more transition metal elements selected from Co, Ni, Fe, Mn, Cu, and V. In addition, those in which some of these transition metal elements are substituted with elements of Group 1 (Ia) or Group 2 (IIa) of the periodic table of metals other than lithium, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, and the like can also be used.

[0032] More specifically, examples of the positive electrode active material include (1) transition metal oxides having a layered rock-salt structure, (2) transition metal oxides having a spinel structure, (3) lithium-containing transition metal phosphate compounds, (4) lithium-containing transition metal halide phosphate compounds, (5) lithium-containing transition metal silicate compounds, etc. Among these, (1) transition metal oxides having a layered rock-salt structure are preferred as the positive electrode active material.

[0033] (1) Examples of transition metal oxides having a layered rock-salt structure include LiCoO2 (lithium cobalt oxide [LCO]), LiNi2O2 (lithium nickel oxide), LiNi 0.85 Co 0.10 Al 0.05 O2 (Lithium Nickel Cobalt Aluminum Oxide [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 (Lithium Nickel Manganese Cobalt Oxide [NMC]), LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide), etc.

[0034] (2) Examples of transition metal oxides having a spinel structure include LiMn2O4 (LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, and Li2CrMn3O 8、 Li2NiMn3O8, etc.

[0035] (3) Examples of lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic Nasicon-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate).

[0036] (4) Examples of lithium-containing transition metal halophosphate compounds include iron fluorophosphates such as Li2FePO4F, manganese fluorophosphates such as Li2MnPO4F, and cobalt fluorophosphates such as Li2CoPO4F.

[0037] (5) Examples of lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4.

[0038] The average particle size of the positive electrode active material is not particularly limited, but is usually preferably 0.1 μm to 50 μm.

[0039] The electrode active material (negative electrode active material) used in the negative electrode of the all-solid-state secondary battery of the present invention is not particularly limited, and any known negative electrode active material may be used as long as it can reversibly insert and release lithium ions. The negative electrode active material may be used alone or in combination of two or more kinds.

[0040] Examples of the negative electrode active material include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alone, lithium alloys such as lithium-aluminum alloys, and metals capable of forming alloys with lithium such as Sn and Si. Among them, the negative electrode active material is preferably a carbonaceous material or a lithium composite oxide. In addition, the metal composite oxide is not particularly limited, but preferably contains titanium and / or lithium.

[0041] The carbonaceous material used as the negative electrode active material is a material that is substantially made of carbon. For example, carbon black such as petroleum pitch and acetylene black (AB), natural graphite, artificial graphite such as vapor-grown graphite, and carbonaceous materials obtained by baking various synthetic resins such as PAN (polyacrylonitrile)-based resins and furfuryl alcohol resins can be mentioned. In addition, various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers can also be mentioned, as well as mesophase microspheres, graphite whiskers, and tabular graphite.

[0042] As the metal oxide and metal composite oxide used as the negative electrode active material, particularly amorphous oxides are preferred, and chalcogenides which are reaction products between metal elements and elements of Group 16 of the periodic table are also preferred. Among the compound group consisting of amorphous oxides and chalcogenides, amorphous oxides and chalcogenides of semimetal elements are preferred, and oxides and chalcogenides consisting of one of elements of Groups 13 (IIIB) to 15 (VB) of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi, or a combination of two or more of them, are more preferred. Preferable amorphous oxides and chalcogenides include, for example, Ga2O3, SiO, GeO, SnO, SnO2, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O5, Bi2O3, Bi2O4, SnSiO3, GeS, SnS, SnS2, PbS, PbS2, Sb2S3, Sb2S5, SnSiS3, etc. These may also be composite oxides with lithium oxide, for example, Li2SnO2.

[0043] The negative electrode active material is preferably one containing titanium atoms. Examples of the negative electrode active material containing titanium atoms include Li4Ti5O 12 (Lithium titanate [LTO]) and others.

[0044] It is also preferable to use a negative electrode active material containing Si element. Generally, a negative electrode using a negative electrode active material containing Si element can absorb more Li ions and increase the battery capacity compared to a negative electrode using conventional carbon (graphite, acetylene black, etc.) as a negative electrode active material.

[0045] The average particle size of the negative electrode active material is not particularly limited, but is usually preferably 0.1 μm to 60 μm.

[0046] <<Electrode active material layer>> The electrode active material layer of the electrode for an all-solid-state secondary battery of the present invention contains a binder resin containing the polyimide-based resin as described above, and an electrode active material.

[0047] When the electrode is a positive electrode, the content of the positive electrode active material in the electrode active material layer is not particularly limited, but is usually preferably 10 to 95 mass %, more preferably 55 to 80 mass %, and the content of the binder resin in the electrode active material layer is not particularly limited, but is preferably 5 to 90 mass %, more preferably 20 to 45 mass %.

[0048] When the electrode is a negative electrode, the content of the negative electrode active material in the electrode active material layer is not particularly limited, but is usually preferably 10 to 80 mass %, more preferably 20 to 70 mass %, and the content of the binder resin in the electrode active material layer is not particularly limited, but is preferably 20 to 90 mass %, more preferably 30 to 80 mass %.

[0049] The electrode active material layer may further contain a conductive assistant as necessary. The conductive assistant aids the conductivity of electrons. The conductive assistant is not particularly limited, and any of those generally used in all-solid-state secondary batteries may be used.

[0050] Examples of the conductive assistant include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, and furnace black, amorphous carbon such as needle coke, carbon fibers such as vapor-grown carbon fibers and carbon nanotubes, carbonaceous materials such as graphene and fullerene, metal powders such as copper and nickel, metal fibers, and conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives. The conductive assistant may be used alone or in combination of two or more.

[0051] The content of the conductive assistant in the electrode active material layer is not particularly limited, but is usually preferably 5 mass % or less.

[0052] If necessary, additives such as a surfactant for improving coatability can also be added to the electrode active material layer.

[0053] The thickness of the electrode active material layer is not particularly limited, but in both the positive electrode and the negative electrode, it is usually preferably 1 to 1000 μm, more preferably 3 to 500 μm.

[0054] Unit area of ​​the positive electrode active material layer (cm 2 The mass (mg) (weight per unit area) of the positive electrode active material per unit area (cm 2 The mass (mg) (weight per unit area) of the negative electrode active material per unit area is not particularly limited and can be appropriately selected depending on the desired battery capacity.

[0055] <<Current collector>> The current collector used in the electrode of the all-solid-state secondary battery of the present invention is preferably an electronic conductor that does not undergo chemical change.

[0056] Examples of materials for forming the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, titanium, etc. Aluminum, aluminum alloys, and stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. (thin films formed thereon) can also be used. Among these, aluminum and aluminum alloys are preferred as the positive electrode current collector.

[0057] Examples of materials for forming the negative electrode current collector include aluminum, copper, copper alloys, stainless steel, nickel, titanium, etc. Aluminum, copper, copper alloys, and stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. (thin films formed thereon) can also be used. Among these, aluminum, copper, copper alloys, and stainless steel are preferred as the negative electrode current collector.

[0058] The current collector is usually in the form of a foil (film sheet), but it may also be in the form of a net, a punched material, a porous material, a molded body of a fiber group, etc. The current collector may also have a surface irregularity formed by a surface treatment.

[0059] The thickness of the current collector is not particularly limited, but is usually preferably 1 μm to 500 μm.

[0060] <<Electrode manufacturing method>> The electrode for an all-solid-state secondary battery of the present invention can be manufactured by preparing an electrode mixture paste that contains an electrode active material, a polyimide resin or a precursor thereof as a binder resin, and a solvent, but does not contain an electrolyte, applying the paste onto a current collector, and then drying or heat treating the paste to form an electrode active material layer. The electrode mixture paste can be prepared by mixing the electrode active material, the binder resin or a precursor thereof, and a solvent to form a slurry.

[0061] An example of a method for manufacturing an electrode using a polyimide resin as a binder resin is shown briefly below. (1) A method for producing an electrode by adding an electrode active material and a conductive assistant to a polyimide precursor (particularly a polyamic acid) solution, and further adding an imidization catalyst, an organic phosphorus-containing compound, a dehydrating agent, etc., as necessary, to form a polyimide precursor solution composition (electrode mixture paste) on a current collector, and then heating to perform cyclization and desolvation to convert the polyimide precursor into a polyimide, thereby forming an electrode active material layer on the current collector (thermal imidization); (2) A method in which an electrode active material, a conductive assistant, etc. are added to a polyimide precursor (particularly a polyamic acid) solution, and a cyclization catalyst and a dehydrating agent are further added to form a polyimide precursor solution composition (electrode mixture paste) on a current collector, which is then chemically dehydrated and cyclized, and the resulting mixture is heated to remove the solvent and imidize, thereby converting the polyimide precursor into a polyimide, and an electrode active material layer is formed on the current collector, thereby producing an electrode (chemical imidization); (3) When polyimide is soluble in an organic solvent, a polyimide solution composition (electrode mixture paste) obtained by adding an electrode active material and a conductive assistant to a polyimide solution is cast onto a current collector, and the solvent is removed by heating or the like to form an electrode active material layer on the current collector, thereby producing an electrode. etc.

[0062] First, the production of a polyimide precursor solution and a polyimide solution will be described. A polyimide precursor solution or a polyimide solution can be obtained by polymerizing approximately equimolar amounts of a tetracarboxylic acid component and a diamine component in an organic solvent or in water. The reaction method is preferably a method in which a tetracarboxylic acid component is added all at once or in multiple stages to a solution in which a diamine component is dissolved in a solvent (organic solvent or water), and the mixture is heated to polymerize.

[0063] The molar ratio of the tetracarboxylic acid component to the diamine component [tetracarboxylic acid component / diamine component] is preferably approximately equimolar, specifically 0.95 to 1.05, and more preferably 0.97 to 1.03.

[0064] Alternatively, two or more kinds of polyimide precursors each having an excess of one of the components may be synthesized in advance, and the respective polyimide precursor solutions may be combined and then mixed under reaction conditions.

[0065] The organic solvent is not particularly limited, but examples thereof include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and N-vinyl-2-pyrrolidone; cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonate and propylene carbonate; glycol-based solvents such as triethylene glycol; phenol-based solvents such as phenol, o-cresol, m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, and dimethyl sulfoxide. Further, for example, alcohol solvents such as methanol and ethanol, ester solvents such as butyl acetate, ethyl acetate, isobutyl acetate, ethyl propionate, ethyl butyrate, butyl butyrate, butyl benzoate, ethyl benzoate, and methyl benzoate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexane ... Other common organic solvents include hexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, N-methylcaprolactam, hexamethylphosphorotriamide, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, diphenyl sulfone, tetramethylurea, anisole, turpentine, mineral spirits, petroleum naphtha solvents, biodegradable methyl lactate, ethyl lactate, butyl lactate, and other common organic solvents. The organic solvent used may be one type or two or more types.

[0066] When water is used as a solvent, it is preferable to add an imidazole such as 1,2-dimethylimidazole or a base such as triethylamine, preferably in an amount of 0.8 or more equivalents relative to the carboxyl groups of the polyamic acid (polyimide precursor) to be produced.

[0067] When carrying out the polymerization reaction to obtain the polyimide precursor solution and the polyimide solution, respectively, the concentration of the total monomers in the organic solvent (substantially equal to the solids concentration of the polyimide precursor solution or the polyimide solution) may be appropriately selected depending on the type of monomer used. The solids concentration of the obtained polyimide precursor solution or the polyimide solution is not particularly limited, but is preferably 3% by mass to 45% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 7% by mass to 30% by mass, based on the total amount of the polyimide precursor or the polyimide and the solvent. If the solids concentration is lower than 3% by mass, the productivity and handling during use may be deteriorated, and if it is higher than 45% by mass, the solution loses fluidity, making it difficult to apply it uniformly on the current collector.

[0068] The solution viscosity of the polyimide precursor solution or polyimide solution at 30°C is not particularly limited, but is preferably 1000 Pa·s or less, more preferably 0.1 to 500 Pa·s, even more preferably 0.1 to 300 Pa·s, and particularly preferably 0.1 to 200 Pa·s for ease of handling. If the solution viscosity exceeds 1000 Pa·s, the solution loses fluidity and may be difficult to apply uniformly onto the current collector, while if it is lower than 0.1 Pa·s, dripping or repelling may occur during application onto the current collector, and it may be difficult to obtain an electrode active material layer and an electrode with high characteristics.

[0069] As an example of a method for producing a polyimide precursor solution, a polymerization reaction between a tetracarboxylic acid component and a diamine component is carried out by, for example, mixing substantially equimolar amounts of each component or a slight excess of either component (acid component or diamine component), and reacting for about 0.2 to 60 hours at a reaction temperature of 100° C. or lower, preferably 80° C. or lower, to obtain a polyimide precursor solution.

[0070] As an example of a method for producing a polyimide solution, a polymerization reaction between a tetracarboxylic acid component and a diamine component is carried out, for example, by mixing substantially equimolar amounts of each component or a slight excess of either component (acid component or diamine component) and reacting them by a known method, for example, at a reaction temperature of 120°C or higher, preferably 140°C or higher, and more preferably 160°C or higher (preferably 250°C or lower, and more preferably 230°C or lower) for about 0.5 to 60 hours to obtain a polyimide solution.

[0071] Although the polymerization reaction can be carried out in an air atmosphere, it is usually carried out in an inert gas atmosphere (for example, an argon gas atmosphere, a helium gas atmosphere, or a nitrogen gas atmosphere), preferably in a nitrogen gas atmosphere.

[0072] The polyimide precursor solution or polyimide solution thus obtained can be used as it is, or after removing the solvent or adding fresh solvent if necessary, for forming an electrode active material layer or for producing an electrode.

[0073] In the case of thermal imidization [method (1)], an imidization catalyst, an organic phosphorus-containing compound, etc. may be added to the polyimide precursor solution as needed. In the case of chemical imidization [method (2)], a cyclization catalyst, a dehydrating agent, etc. may be added to the polyimide precursor solution as needed.

[0074] Examples of the imidization catalyst include substituted or unsubstituted nitrogen-containing heterocyclic compounds, N-oxide compounds of the nitrogen-containing heterocyclic compounds, substituted or unsubstituted amino acid compounds, aromatic hydrocarbon compounds or aromatic heterocyclic compounds having a hydroxyl group, and in particular, lower alkyl imidazoles such as 1,2-dimethylimidazole, N-methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 5-methylbenzimidazole, benzimidazoles such as N-benzyl-2-methylimidazole, isoquinoline, and substituted pyridines such as 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, and 4-n-propylpyridine. The amount of the imidization catalyst used is preferably 0.01 to 2 times equivalent, particularly 0.02 to 1 times equivalent, relative to the amic acid unit of the polyamic acid.

[0075] Examples of the organic phosphorus-containing compound include phosphates such as monocaproyl phosphate, monooctyl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, monophosphate of triethylene glycol monotridecyl ether, monophosphate of tetraethylene glycol monolauryl ether, monophosphate of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, dicetyl phosphate, distearyl phosphate, diphosphate of tetraethylene glycol mononeopentyl ether, diphosphate of triethylene glycol monotridecyl ether, diphosphate of tetraethylene glycol monolauryl ether, and diphosphate of diethylene glycol monostearyl ether, as well as amine salts of these phosphates. Examples of the amine include ammonia, monomethylamine, monoethylamine, monopropylamine, monobutylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, and triethanolamine.

[0076] Examples of the cyclization catalyst include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as isoquinoline, pyridine, α-picoline, and β-picoline.

[0077] Examples of the dehydrating agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride.

[0078] In the manufacture of an electrode, an electrode active material is added to the polyimide precursor solution or polyimide solution obtained in this manner, and further, if necessary, a conductive assistant and other additives are added and mixed to prepare an electrode mixture paste. The prepared electrode mixture paste is cast or applied onto a current collector, and a heat treatment is preferably performed under pressure to effect imidization and removal of the solvent (mainly removal of the solvent in the case of a polyimide solution), thereby forming an electrode active material layer on the current collector, and an electrode can be manufactured.

[0079] The method for casting the electrode mixture paste onto the current collector is not particularly limited, but examples thereof include conventionally known methods such as spin coating, screen printing, bar coating, and electrodeposition.

[0080] The heat treatment conditions when a polyimide precursor solution is used are not particularly limited, but it is preferable to dry the solution in a temperature range of 50° C. to 150° C., and then heat treat the solution at a maximum heating temperature of, for example, 150° C. to 600° C., preferably 200° C. to 550° C., and more preferably 250° C. to 500° C. The heat treatment conditions when a polyimide solution is used are not particularly limited, but it is preferable to heat treat the solution at a maximum heating temperature of, for example, 100° C. to 600° C., preferably 150° C. to 500° C., and more preferably 200° C. to 450° C.

[0081] Although the heat treatment can be carried out in an air atmosphere, it is usually carried out in an inert gas atmosphere (for example, an argon gas atmosphere, a helium gas atmosphere, or a nitrogen gas atmosphere), preferably in a nitrogen gas atmosphere.

[0082] <All-solid-state secondary battery> The all-solid-state secondary battery of the present invention has a positive electrode and a negative electrode, and a solid electrolyte layer disposed between them, and the positive electrode and / or the negative electrode is the electrode for the all-solid-state secondary battery of the present invention as described above. More specifically, the all-solid-state secondary battery of the present invention has a negative electrode current collector, a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order, and the negative electrode active material layer and / or the positive electrode active material layer does not contain an electrolyte. In addition, as described later, if the positive electrode is the electrode for the all-solid-state secondary battery of the present invention, the negative electrode does not have to be the electrode for the all-solid-state secondary battery of the present invention. For example, the negative electrode may be a sheet of a carbonaceous material or a metal foil, and in that case, the all-solid-state secondary battery of the present invention can have a negative electrode, a solid electrolyte layer, a positive electrode active material layer not containing an electrolyte, and a positive electrode current collector in this order. If the negative electrode is the electrode for an all-solid-state secondary battery of the present invention, the positive electrode does not have to be the electrode for an all-solid-state secondary battery of the present invention. For example, the positive electrode may be a metal foil such as a lithium foil. In that case, the all-solid-state secondary battery of the present invention can have a negative electrode current collector, a negative electrode active material layer not containing an electrolyte, a solid electrolyte layer, and a positive electrode in this order.

[0083] In the all-solid-state secondary battery of the present invention, functional layers or members may be appropriately provided in addition to the negative electrode (negative electrode current collector and negative electrode active material layer), the solid electrolyte layer, and the positive electrode (positive electrode active material layer and positive electrode current collector). Each layer may be composed of a single layer or multiple layers. For example, to make it into a dry cell, the negative electrode (negative electrode current collector and negative electrode active material layer), the solid electrolyte layer, and the positive electrode (positive electrode active material layer and positive electrode current collector), which are the basic structure of the all-solid-state secondary battery, are enclosed in a suitable case. The case may be made of metal such as aluminum alloy or stainless steel, or may be made of resin (plastic). It is preferable that the metallic case is divided into a positive electrode side case and a negative electrode side case, and electrically connected to the positive electrode current collector and the negative electrode current collector, respectively. It is preferable that the positive electrode side case and the negative electrode side case are joined and integrated via a gasket for preventing short circuit.

[0084] <<Solid electrolyte layer>> The solid electrolyte layer of the all-solid-state secondary battery of the present invention is a layer containing a solid electrolyte.

[0085] The solid electrolyte layer is preferably a layer made of a polymer solid electrolyte (an intrinsic polymer solid electrolyte made of only solid polymers). The polymer solid electrolyte is not particularly limited, and any known polymer solid electrolyte can be used, such as polyethylene oxide polymers, polypropylene oxide polymers, perfluorocarbon sulfonic acid polymers, sulfonated polyether ether ketones, sulfonated polyether sulfones, and other aromatic hydrocarbon polymer electrolytes having ionic groups.

[0086] In addition, for example, as described in JP 2015-165461 A, a composite electrolyte membrane in which a crosslinked aromatic polymer electrolyte formed by linking aromatic polymer electrolytes having ionic groups at sites other than the ionic groups via at least one or more types of crosslinking components is filled into the pores of a porous substrate can also be suitably used as the solid electrolyte layer.

[0087] The solid electrolyte layer of the all-solid-state secondary battery of the present invention is also preferably an inorganic solid electrolyte layer containing an inorganic solid electrolyte and a binder resin (solid electrolyte layer binder resin). The inorganic solid electrolyte layer will be described below.

[0088] <<Inorganic solid electrolyte layer>> The content of the inorganic solid electrolyte in the solid electrolyte layer is not particularly limited, but is usually preferably 80 mass % to 99.9 mass %, more preferably 90 mass % to 99.7 mass %, and even more preferably 95 mass % to 99.5 mass %.

[0089] The content of the binder resin in the solid electrolyte layer is not particularly limited, but is usually preferably 0.1% by mass to 20% by mass, more preferably 0.3% by mass to 10% by mass, and particularly preferably 0.5% by mass to 5% by mass.

[0090] The solid electrolyte layer may further contain one or more kinds of lithium salts as necessary. The lithium salt is not particularly limited, and any of the known lithium salts generally used in all-solid-state secondary batteries may be used, for example, inorganic lithium salts such as inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, LiSbF6, perhalogen salts such as LiClO4, LiBrO4, LiIO4, inorganic chloride salts such as LiAlCl4, perfluoroalkanesulfonates such as LiCF3SO3, perfluoroalkanesulfonates such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2, LiN(CF3SO2)(C4F9SO2). fluorine-containing organic lithium salts such as fluoroalkyl fluorophosphates such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], and Li[PF3(CF2CF2CF2CF3)3]; and oxalatoborate salts such as lithium bis(oxalato)borate and lithium difluorooxalatoborate.

[0091] The content of the lithium salt in the solid electrolyte layer is not particularly limited, but is usually preferably more than 0 parts by mass per 100 parts by mass of the inorganic solid electrolyte, and usually more preferably 0.1 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the inorganic solid electrolyte.

[0092] The thickness of the solid electrolyte layer is not particularly limited, but is usually preferably 1 to 1000 μm, more preferably 3 to 500 μm.

[0093] <<<Inorganic solid electrolyte>>> The inorganic solid electrolyte used in the present invention is not particularly limited, and may be any known inorganic solid electrolyte used in all-solid-state secondary batteries as long as it contains a metal (preferably lithium) belonging to Group 1 or Group 2 of the periodic table and has conductivity of the ions of this metal (preferably lithium ions). One type of inorganic solid electrolyte may be used alone, or two or more types may be used in combination.

[0094] Examples of inorganic solid electrolytes include (1) sulfide-based inorganic solid electrolytes and (2) oxide-based inorganic solid electrolytes.

[0095] (1) The sulfide-based inorganic solid electrolyte preferably contains a sulfur atom (S), a metal belonging to Group 1 or 2 of the periodic table, has ionic conductivity, and has electronic insulation. Examples of the sulfide-based inorganic solid electrolyte include those represented by the following formula: Li a M b P c S d (In the formula, M is an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al and Ge, and a to d represent the composition ratio of each element, where a:b:c:d=1-12:0-1:1:2-9, preferably a:b:c:d=1-9:0:1:3-7, and more preferably a:b:c:d=1.5-4:0:1:3.25-4.5.)

[0096] The ratio of Li2S to P2S5 in a Li-PS solid electrolyte containing Li, P and S is preferably Li2S:P2S5=60:40 to 90:10 (molar ratio), and more preferably Li2S:P2S5=68:32 to 78:22.

[0097] The sulfide-based inorganic solid electrolyte may be amorphous or crystallized, or may be only partially crystallized.

[0098] Examples of sulfide-based inorganic solid electrolytes include those made of a raw material composition containing Li2S and a sulfide of an element of groups 13 to 15. More specifically, the raw material combinations include Li2S-P2S5, Li2S-GeS2, Li2S-GeS2-ZnS, Li2S-Ga2S3, Li2S-GeS2-Ga2S3, Li2S-GeS2-P2S5, Li2S-GeS2-Sb2S5, Li2S-GeS2-Al2S3, Li2S-SiS2, Li2S-Al2S3, Li2S-SiS2-Al2S3, Li2S-SiS2-P2S5, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 The mixing ratio of each raw material can be appropriately selected. Examples of a method for synthesizing a sulfide-based inorganic solid electrolyte using such a raw material composition include amorphization methods such as mechanical milling and melt quenching.

[0099] The sulfide-based inorganic solid electrolyte can be synthesized by referring to, for example, Journal of Power Sources, 233, (2013), pp. 231-235, and Chem. Lett., (2001), pp. 872-873, and the like.

[0100] (2) The oxide-based inorganic solid electrolyte preferably contains an oxygen atom (O), contains a metal belonging to Group 1 or 2 of the periodic table, has ionic conductivity, and has electronic insulation properties.

[0101] Examples of oxide-based inorganic solid electrolytes include Li x La y TiO3 (wherein x = 0.3-0.7, y = 0.3-0.7) (LLT), Li7La3Zr2O 12 (LLZ, lithium lanthanum zirconate), a Li with LISICON type crystal structure 3.5 Zinc 0.25 GeO4, LiTi2P3O with NASICON type crystal structure 12 , Li 1+m+n (Al,Ga) m(Ti,Ge) 2-m S n P 3-n O 12 (wherein 0≦m≦1, 0≦n≦1), Li7La3Zr2O having a garnet-type crystal structure 12 etc.

[0102] Examples of oxide-based inorganic solid electrolytes include phosphorus compounds containing Li, P, and O. More specifically, examples include lithium phosphate (Li3PO4), LiPON in which some of the oxygen atoms of lithium phosphate are replaced with nitrogen atoms, LiPOD (D represents at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), etc. Examples of oxide-based inorganic solid electrolytes include LiAON (A represents at least one selected from Si, B, Ge, Al, C, Ga, etc.), etc.

[0103] The average particle size of the inorganic solid electrolyte is not particularly limited, but is usually preferably 0.01 μm to 100 μm, and more preferably 0.1 μm to 50 μm.

[0104] <<<Binder resin for solid electrolyte layer>>> The binder resin of the solid electrolyte layer used in the present invention is not particularly limited, and any binder resin generally used in all-solid-state secondary batteries can be used. The binder resin of the solid electrolyte layer may be used alone or in combination of two or more kinds.

[0105] Examples of the binder resin of the solid electrolyte layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylene difluoride (PVdF), and copolymers of polyvinylene difluoride and hexafluoropropylene (PVdF-HFP); hydrocarbon thermoplastic resins such as polyethylene, polypropylene, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber (HSBR), butylene rubber, acrylonitrile butadiene rubber, polybutadiene, and polyisoprene; acrylic resins, for example, copolymers of (meth)acrylic acid and (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, copolymers of methyl (meth)acrylate and styrene, copolymers of methyl (meth)acrylate and acrylonitrile, copolymers of butyl (meth)acrylate, acrylonitrile and styrene, and further, polyurethane resins, polyurea resins, polyamide resins, polyimide resins, polyester resins, polyether resins, polycarbonate resins, and cellulose derivative resins.

[0106] <<Electrodes other than the electrode for the all-solid-state secondary battery of the present invention>> In the all-solid-state secondary battery of the present invention, if the positive electrode is the electrode for the all-solid-state secondary battery of the present invention in which the electrode active material layer does not contain an electrolyte, the negative electrode may be one having an electrode active material layer containing an electrolyte on a current collector, or a sheet of a carbonaceous material, a metal (including an alloy), a metal oxide, etc. Also, if the negative electrode is the electrode for the all-solid-state secondary battery of the present invention in which the electrode active material layer does not contain an electrolyte, the positive electrode may be one having an electrode active material layer containing an electrolyte on a current collector, or a sheet of a metal (including an alloy), a metal oxide, etc.

[0107] The electrode having an electrode active material layer containing an electrolyte on a current collector is an electrode having an electrode active material layer containing an electrode active material, a binder resin, and a solid electrolyte, preferably an inorganic solid electrolyte, on a current collector, and is similar to the electrode for an all-solid-state secondary battery of the present invention described above, except that the electrode active material layer contains an electrolyte and the binder resin does not have to be a polyimide-based resin.

[0108] The content of the inorganic solid electrolyte in the electrode active material layer (positive electrode active material layer and negative electrode active material layer) is not particularly limited, but is usually preferably 10 to 40 mass %, more preferably 20 to 30 mass %. The inorganic solid electrolyte contained in the electrode active material layer is not particularly limited, but may be, for example, the same as the inorganic solid electrolyte used in the solid electrolyte layer described above, and one type may be used alone, or two or more types may be used in combination.

[0109] The binder resin used in the electrode active material layer containing the electrolyte is not particularly limited, and any of the conventionally known positive electrode binder resins and negative electrode binder resins can be used. Examples of the binder resin include fluorine-based resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymers (PVdF-HFP), polyethylene, polypropylene, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber (HSBR), butylene rubber, acrylonitrile butadiene rubber, polybutadiene, and hydrocarbon resins such as polyisoprene, acrylic resins, styrene resins, amide resins, acrylamide resins, imide resins, urethane resins, urea resins, polyester resins, polyether resins, phenol resins, epoxy resins, polycarbonate resins, and silicone resins. Further, examples of the anionic polymer include polyacrylic acid, polymethacrylic acid, polysulfonic acid, and salts thereof, and also include celluloses such as carboxyalkyl cellulose and hydroxyalkyl cellulose, polyvinyl alcohol, polyalkylene glycol, polyvinylpyrrolidone, alginic acid, and salts thereof. In addition, the above-mentioned polyimide resin can be used as the binder resin used in the electrode active material layer containing the electrolyte. In the electrode active material layer containing the electrolyte, the binder resin may be used alone or in combination of two or more.

[0110] The electrode is not limited to one having an electrode active material layer on a current collector, and for example, a sheet made of an electrode active material material, or only a current collector on which an electrode active material layer is not formed can be used as an electrode. Specifically, a sheet of a carbonaceous material, a sheet of a metal (including an alloy) or a metal oxide, etc. can be used as the negative electrode, and among them, a sheet of a carbonaceous material can be preferably used. In addition, a sheet of a metal (including an alloy) or a metal oxide, etc. can be used as the positive electrode, and among them, a sheet of a lithium-containing compound such as a lithium foil or a lithium-containing transition metal oxide, particularly preferably a lithium foil, can be preferably used.

[0111] <<Manufacturing method for all-solid-state secondary batteries>> The all-solid-state secondary battery of the present invention can be manufactured by preparing the positive electrode sheet and the negative electrode sheet, which are the electrodes for the all-solid-state secondary battery of the present invention, as described above, separately preparing a solid electrolyte-containing sheet containing the solid electrolyte as described above, and laminating and integrating the positive electrode sheet, the solid electrolyte-containing sheet, and the negative electrode sheet by a dry method. In the case of using an electrode other than the electrode for the all-solid-state secondary battery of the present invention, that is, an electrode having an electrode active material layer containing an electrolyte on a current collector, or a sheet of a carbonaceous material, a metal (including alloys), or a metal oxide, etc., similarly, a positive electrode sheet and a negative electrode sheet are prepared respectively (when a sheet of a carbonaceous material, a metal (including alloys), or a metal oxide, etc. is used, a sheet is prepared), separately preparing a solid electrolyte-containing sheet, and then laminating and integrating the positive electrode sheet, the solid electrolyte-containing sheet, and the negative electrode sheet, thereby manufacturing the all-solid-state secondary battery of the present invention.

[0112] <<<Preparation of solid electrolyte-containing sheet>>> The solid electrolyte-containing sheet can be produced by mixing the above-mentioned solid electrolyte, a binder resin for the solid electrolyte layer, and a solvent to form a slurry to prepare a solid electrolyte-containing paste, applying the paste onto a substrate and drying the paste to form a solid electrolyte layer on the substrate, and peeling off the formed solid electrolyte layer from the substrate.

[0113] The mixing conditions for preparing the solid electrolyte-containing paste are not particularly limited and can be appropriately selected. When the lithium salt and other additives are to be contained in the solid electrolyte layer, they may be added to the solvent and mixed together with the solid electrolyte and the binder resin, or may be added separately and mixed.

[0114] The solvent for the solid electrolyte-containing paste is not particularly limited, and any commonly used solvent can be used. Examples of the solvent include alcohol solvents such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 2-butanol, ethylene glycol, propylene glycol, glycerin, 1,6-hexanediol, cyclohexanediol, sorbitol, xylitol, 2-methyl-2,4-pentanediol, 1,3-butanediol, and 1,4-butanediol; alkylene glycol alkyl ethers (ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol, dipropylene glycol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol); , polyethylene glycol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether, etc.), dimethyl ether, diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, dimethoxyethane, 1,4-dioxane and other ether solvents, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, formamide, N-methylformamide, acetamide, N-methylacetamide, N,Examples of the solvent include amide-based solvents such as N-dimethylacetamide, N-methylpropionamide, and hexamethylphosphoric triamide; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, diisopropyl ketone, diisobutyl ketone, and cyclohexanone; aromatic hydrocarbon-based solvents such as benzene, toluene, xylene, chlorobenzene, and dichlorobenzene; aliphatic hydrocarbon-based solvents such as hexane, heptane, octane, decane, and dodecane; alicyclic hydrocarbon-based solvents such as cyclohexane, cycloheptane, cyclooctane, and cyclononane; ester-based solvents such as ethyl acetate, propyl acetate, butyl acetate, ethyl butyrate, butyl butyrate, butyl valerate, γ-butyrolactone, and heptane; carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and propylene carbonate; and nitrile-based solvents such as acetonitrile, propionitrile, butyronitrile, isobutyronitrile, and benzonitrile. The solvent may be used alone or in combination of two or more.

[0115] The content of the solvent in the solid electrolyte-containing paste is not particularly limited, but is usually preferably 20 to 99 mass %, more preferably 25 to 90 mass %, and particularly preferably 30 to 80 mass %.

[0116] In the solid electrolyte-containing paste, the binder resin may be either soluble or insoluble in the solvent.

[0117] The substrate to which the solid electrolyte-containing paste is applied is not particularly limited as long as it is capable of forming a solid electrolyte layer on the substrate, and for example, a sheet of an organic material or an inorganic material can be used. Examples of the organic material of the substrate include various polymers such as polyethylene terephthalate, polypropylene, polyethylene, and cellulose. Examples of the inorganic material include glass and ceramics.

[0118] The method for applying the solid electrolyte-containing paste to the substrate is not particularly limited and can be appropriately selected. Examples of the application method include spray application, spin coating, dip coating, slit coating, stripe coating, and bar coating.

[0119] The conditions for drying the solid electrolyte-containing paste applied to the substrate are not particularly limited and can be appropriately selected. The drying temperature is not particularly limited, but is usually preferably 30°C to 300°C, more preferably 60°C to 250°C, and even more preferably 80°C to 200°C. Drying may be performed in a vacuum, in the atmosphere, in dry air, or in an inert gas (e.g., in argon gas, helium gas, or nitrogen gas).

[0120] The solid electrolyte layer thus formed can be peeled off from the substrate to obtain a solid electrolyte-containing sheet.

[0121] <<<Preparation of electrode sheets other than the electrodes for the all-solid-state secondary battery of the present invention>>> An electrode having an electrode active material layer containing an electrolyte on a current collector can be manufactured by mixing the above-mentioned electrode active material and solid electrolyte, preferably an inorganic solid electrolyte, and a binder resin for the electrode active material layer and a solvent to form a slurry, preparing an electrode active material and solid electrolyte-containing paste (electrode mixture paste), applying this on a current collector, and then drying to form an electrode active material layer on the current collector. The formation of this electrode active material layer can be performed in the same manner as the formation of the solid electrolyte layer of the above-mentioned solid electrolyte-containing sheet, except for adding the electrode active material.

[0122] <<<Lamination of positive electrode sheet, solid electrolyte-containing sheet and negative electrode sheet>>> The positive electrode sheet and the negative electrode sheet (the electrode sheet of the present invention) prepared as described above and the solid electrolyte-containing sheet are laminated in the order of the positive electrode sheet, the solid electrolyte-containing sheet, and the negative electrode sheet, and integrated to produce an all-solid-state secondary battery. After laminating the positive electrode sheet and the solid electrolyte-containing sheet, the obtained laminate and the negative electrode sheet may be laminated, or the order may be reversed, that is, after laminating the negative electrode sheet and the solid electrolyte-containing sheet, the obtained laminate and the positive electrode sheet may be laminated.

[0123] The laminate of the positive electrode sheet, the solid electrolyte-containing sheet, and the negative electrode sheet may be pressurized to be integrated. The method of pressurizing the laminate is not particularly limited and can be selected appropriately, and examples thereof include a method using a hydraulic cylinder press machine or the like. The pressure applied to the laminate is not particularly limited, but is usually preferably in the range of 50 to 1500 MPa. The atmosphere during pressurization is not particularly limited, and pressurization can be performed, for example, in air, dry air, or in an inert gas (for example, in argon gas, helium gas, nitrogen gas), etc. The pressurization time is also not particularly limited and can be selected appropriately. For example, high pressure may be applied for a short time (for example, within a few hours), or moderate pressure may be applied for a long time (for example, one day or more).

[0124] The laminate of the positive electrode sheet, the solid electrolyte-containing sheet, and the negative electrode sheet may be heated at the same time as it is pressed. The heating temperature is not particularly limited, but is usually in the range of 30 to 300°C.

[0125] The pressure applied may be uniform or may vary across the sheet surface, and the magnitude of the pressure applied may be changed during application.

[0126] The all-solid-state secondary battery thus obtained can be enclosed in a case for use, if necessary.

[0127] The all-solid-state secondary battery of the present invention is excellent in safety and has a high capacity, and therefore can be suitably used for various applications. For example, the all-solid-state secondary battery of the present invention can be suitably used for automobiles (electric automobiles, etc.). It can also be suitably used for mobile phones, smartphones, tablets, small unmanned aerial vehicles (drones, etc.), etc. EXAMPLES

[0128] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0129] Example 1 Silicon was used as the negative electrode active material, UPIA-LB-1001 [polyimide precursor varnish manufactured by Ube Industries] was used as the binder resin composition for electrodes, and acetylene black was used as the conductive assistant in a ratio of 73:25:2 (mass ratio; UPIA-LB-1001 is the amount of solids (polyimide precursor)), and NMP (N-methyl-2-pyrrolidone) was added so that the slurry concentration was about 60 mass%, to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied onto a nickel-plated steel foil (thickness 10 μm) as a current collector, and placed in a vacuum dryer and heated at 350 ° C for 1 hour to prepare an electrode (negative electrode) on which an electrolyte-free electrode active material layer having a thickness of 3 μm was formed. The prepared negative electrode was cut into a size of 3 cm x 5 cm. A polyethylene oxide-based polymer electrolyte membrane (thickness: 80 μm) was used as the solid electrolyte layer, and lithium foil (thickness: 500 μm) was used as the counter electrode (cathode). The prepared negative electrode, solid electrolyte layer, and counter electrode were laminated in this order, and the negative electrode current collector and positive electrode were connected to prepare an all-solid-state battery. The fabricated battery was charged and discharged for 30 cycles at a constant current of 0.56 mA in a battery voltage range of 1 mV to 1 V in an environment of 60° C. The discharge capacity at the first cycle was taken as the initial capacity, and the value obtained by dividing the discharge capacity at the 30th cycle by the initial capacity was calculated, and this value was taken as the capacity retention rate (%) after 30 cycles. The initial capacity of the battery was 1800mAh / g, and the capacity density of the negative electrode material was 1.7mAh / cm 2The capacity retention rate after 30 cycles was 95%.

[0130] Example 2 Silicon-titanium alloy as a negative electrode active material, UPIA-LB-1001 [polyimide precursor varnish manufactured by Ube Industries] as a binder resin composition for electrodes, and acetylene black as a conductive assistant were mixed to a ratio of 80:18:2 (mass ratio; UPIA-LB-1001 is the amount of solids (polyimide precursor)), and NMP (N-methyl-2-pyrrolidone) was added so that the slurry concentration was about 60 mass%, to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied onto a nickel-plated steel foil (thickness 10 μm) as a current collector, placed in a vacuum dryer, and heat-treated at 350 ° C for 1 hour to prepare an electrode (negative electrode) with a 3 μm-thick electrode active material layer not containing electrolyte. The prepared negative electrode was cut into a size of 3 cm x 5 cm. A polyethylene oxide-based polymer electrolyte membrane (thickness: 80 μm) was used as the solid electrolyte layer, and lithium foil (thickness: 500 μm) was used as the counter electrode (cathode). The prepared negative electrode, solid electrolyte layer, and counter electrode were laminated in this order, and the negative electrode current collector and positive electrode were connected to prepare an all-solid-state battery. The fabricated battery was charged and discharged for 30 cycles at a constant current of 0.59 mA in a battery voltage range of 1 mV to 1 V in an environment of 45° C. The discharge capacity at the first cycle was taken as the initial capacity, and the discharge capacity at the 30th cycle was divided by the initial capacity to calculate the capacity retention rate (%) after 30 cycles. The initial capacity of the battery was 1300mAh / g, and the capacity density of the negative electrode material was 1.8mAh / cm 2 The capacity retention rate after 30 cycles was 97%. [Industrial Applicability]

[0131] According to the present invention, even if the electrode active material layer does not contain an electrolyte, which was an essential component in conventional electrodes for all-solid-state secondary batteries, a practical all-solid-state secondary battery can be obtained.

Claims

1. An electrode having an electrode active material layer containing an electrode active material and a binder resin on a current collector, the binder resin contains 50% by mass or more of a polyimide-based resin composed of a repeating unit represented by the following chemical formula (1), in which A is one or more tetravalent groups obtained by removing a carboxyl group from a tetracarboxylic acid and contains 10 mol% or more of the tetravalent group represented by the following chemical formula (A-1), and B is one or more divalent groups obtained by removing an amino group from a diamine, the electrode active material layer contains a conductive additive, When the electrode is a negative electrode, the content of the negative electrode active material in the negative electrode active material layer is 10 to 80 mass %, and the content of the binder resin in the electrode active material layer is 18 to 90 mass %; and when the electrode is a positive electrode, the content of the positive electrode active material in the electrode active material layer is 10 to 95 mass %, and the content of the binder resin in the electrode active material layer is 20 to 90 mass %. 【Chemical 1】 【Chemistry 2】

2. An all-solid-state secondary battery having a positive electrode, a solid electrolyte layer, and a negative electrode, An all-solid-state secondary battery, wherein the positive electrode and / or the negative electrode is the electrode according to claim 1.

3. a step of applying an electrode mixture paste containing an electrode active material, a polyimide resin or a precursor thereof as a binder resin, and a solvent, but not containing an electrolyte, onto a current collector; a step of drying or heat-treating the applied electrode mixture paste to form an electrode active material layer; 3. The method for producing an electrode for an all-solid-state secondary battery according to claim 1, further comprising:

4. preparing an electrode sheet having an electrode active material layer on a current collector, the electrode active material layer including an electrode active material and a polyimide-based resin as a binder resin, and not including an electrolyte; a step of laminating and integrating the electrode sheet, a solid electrolyte-containing sheet containing a solid electrolyte, and a counter electrode sheet; The method for producing an all-solid-state secondary battery according to claim 3, further comprising the steps of:

5. The step of preparing an electrode sheet includes: a step of applying an electrode mixture paste containing an electrode active material, a polyimide resin or a precursor thereof as a binder resin, and a solvent, but not containing an electrolyte, onto a current collector; a step of drying or heat-treating the applied electrode mixture paste to form an electrode active material layer; The method for producing an all-solid-state secondary battery according to claim 4, further comprising the steps of:

6. 6. The method for producing an all-solid-state secondary battery according to claim 5, wherein the counter electrode sheet contains an electrode active material and a polyimide-based resin as a binder resin, and has an electrode active material layer containing no electrolyte on a current collector.

7. 7. The method for producing an all-solid-state secondary battery according to claim 5, wherein the electrode sheet, the solid electrolyte-containing sheet, and the counter electrode sheet are laminated by a dry method.

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