Positive electrode active material layer, electrode, and solid-state battery

Abstract

Provided are: a positive electrode active material layer capable of forming a positive electrode in which interface resistance between a current collector and an electrode active material is suppressed; an electrode provided with said positive electrode active material layer; and a semi-solid-state battery or an all-solid-state battery provided with said electrode.　The present invention uses a positive electrode active material layer which contains a positive electrode active material (A), a solid electrolyte (B), and a binder (C). The binder (C) is a polymer (C-a) or a polymer (C-b).　Polymer (C-a): A homopolymer of vinylidene fluoride, and having an intrinsic viscosity of 3.5 dL / g or less.　Polymer (C-b): A vinylidene fluoride copolymer that includes a constituent unit derived from vinylidene fluoride and a constituent unit derived from hexafluoropropylene, that has an intrinsic viscosity of 1.3-4.0 dl / g, and in which the constituent unit derived from hexafluoropropylene is contained in an amount of 8.0 mass% or less with respect to 100.0 mass% of the total constituent units of the vinylidene fluoride copolymer.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material layer, an electrode, and a solid-state battery. [Background technology]

[0002] Conventional secondary batteries containing electrolytes have a high risk of ignition if an abnormality such as an internal short circuit occurs in the cell, causing the cell temperature to rise. Therefore, in order to improve cell safety, semi-solid or all-solid-state batteries in which most or all of the electrolyte is replaced with a solid electrolyte are being studied. Semi-solid or all-solid-state batteries contain only a small amount or no electrolyte containing flammable organic solvents, which is thought to simplify safety devices and be superior in terms of manufacturing cost and productivity.

[0003] The active material layer of an electrode in a semi-solid or all-solid-state battery is expected to contain a solid electrolyte in addition to the active material, conductive additive, and binder that constitute the electrode active material layer of a conventional secondary battery. However, compared to when an electrolytic solution is used as the electrolyte, the movement of lithium ions and electrons becomes more difficult, resulting in a problem of increased interfacial resistance between the current collector and the electrode active material layer.

[0004] In response to this, for example, Patent Document 1 discloses a positive electrode material for a lithium-sulfur solid state battery that contains sulfur, a conductive material, a binder, and an ionic liquid or solvated ions, with the aim of suppressing the interfacial resistance between the solid electrolyte and the electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-168435 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the use of ionic liquids can cause corrosion of the metal contained in the electrode current collector, making it difficult to achieve good charge-discharge efficiency. Therefore, there is a need for a technology that can reduce the interfacial resistance between the current collector and the electrode active material layer without using ionic liquids.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a positive electrode active material layer capable of forming a positive electrode in which the interfacial resistance between a current collector and an electrode active material is reduced, an electrode including the positive electrode active material layer, and a semi-solid battery or all-solid battery including the electrode. [Means for solving the problem]

[0008] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by incorporating a vinylidene fluoride homopolymer or copolymer having a specific intrinsic viscosity as a binder in a positive electrode active material layer containing a positive electrode active material and a solid electrolyte, and have thus completed the present invention.

[0009] An embodiment of the present invention relates to the following positive electrode active material layer, electrode, and semi-solid battery or all-solid battery, each containing a positive electrode active material (A), a solid electrolyte (B), and a binder (C).

[0010] [1] A positive electrode active material layer containing a positive electrode active material (A), a solid electrolyte (B), and a binder (C), The positive electrode active material layer, wherein the binder (C) is the following polymer (Ca) or polymer (Cb): Polymer (Ca): A homopolymer of vinylidene fluoride having an intrinsic viscosity of 3.5 dL / g or less. Polymer (Cb): A vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from hexafluoropropylene, having an intrinsic viscosity of 1.3 dL / g or more and 4.0 dL / g or less, and containing 8.0 mass% or less of structural units derived from hexafluoropropylene when the total structural units of the vinylidene fluoride copolymer are taken as 100.0 mass%.

[0011] [2] The positive electrode active material layer according to [1], wherein the intrinsic viscosity of the polymer (Ca) or the polymer (Cb) is less than 3.0 dL / g. [3] The positive electrode active material layer according to [1] or [2], wherein the solid electrolyte (B) is an oxide-based solid electrolyte. [4] The solid electrolyte (B) is represented by the following formula (1): Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 ···(1) (In formula (1), x and y satisfy 0≦x≦1 and 0≦y≦1.) The positive electrode active material layer according to [3], comprising a material represented by the formula: [5] The positive electrode active material (A) contains lithium metal phosphate, The positive electrode active material layer according to any one of [1] to [4], wherein the lithium metal phosphate is selected from the group consisting of LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. [6] An electrode comprising a current collector and the positive electrode active material layer according to any one of [1] to [5]. [7] A semi-solid or all-solid battery comprising the electrode according to [6]. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a positive electrode active material layer capable of forming a positive electrode in which the interfacial resistance between the current collector and the electrode active material is reduced, an electrode including the positive electrode active material layer, and a semi-solid battery or all-solid battery including the electrode. DETAILED DESCRIPTION OF THE INVENTION

[0013] ≪Positive electrode active material layer≫ The positive electrode active material layer contains a positive electrode active material (A), a solid electrolyte (B), and a binder (C). The binder (C) contained in the positive electrode active material layer is the following polymer (Ca) or polymer (Cb). Polymer (Ca): A homopolymer of vinylidene fluoride having an intrinsic viscosity of 3.5 dL / g or less. Polymer (Cb): A vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from hexafluoropropylene, having an intrinsic viscosity of 1.3 dL / g or more and 4.0 dL / g or less, and containing 8.0 wt% or less of structural units derived from hexafluoropropylene when the total structural units of the vinylidene fluoride copolymer are taken as 100 mass%. When the positive electrode active material layer contains the specific binder (C), an electrode can be formed in which the interfacial resistance between the current collector and the positive electrode active material layer is suppressed.

[0014] Essential and optional components contained in the positive electrode active material layer will be described below.

[0015] <Cathode active material (A)> The positive electrode active material (A) is not particularly limited, and for example, a conventionally known electrode active material for a positive electrode can be used. As the electrode active material for a positive electrode, a lithium-based electrode active material for a positive electrode containing at least lithium is preferred. As an electrode active material for a lithium-based positive electrode, for example, a positive electrode active material represented by the following formula (A-1) can be mentioned. Li x M y O z (A-1) (In formula (A-1), M is a transition metal element, x=0.02 to 2.2, y=1 to 2, and z=1.4 to 4.)

[0016] In formula (A-1), M is at least one selected from the group consisting of Co, Mn, Ni, V, Fe, and Si, and may be at least one selected from the group consisting of Co, Ni, and Mn. Specific examples of such positive electrode active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, Li2FeSiO4, Li2MnSiO4, etc.

[0017] The positive electrode active material represented by formula (A-1) is preferably a lithium metal oxide represented by the following formula (A-2), from the viewpoint of suppressing the interface resistance between the current collector and the positive electrode active material layer. LiNi x Co y Mn z O2···(A-2) (In formula (A-2), 0≦x<1, 0 <y≦1、0≦z<1である。)

[0018] In formula (A-2), the composition ratios of x, y, and z are preferably, for example, 0.3≦x≦0.8, 0.1≦y≦0.4, and 0.15≦z≦0.5, and more preferably 0.35≦x≦0.7, 0.1≦y≦0.35, and 0.2≦z≦0.45.

[0019] Examples of the lithium metal oxide represented by formula (A-2) include LiNi 0.33 Co 0.33 Mn 0.33 (NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.5 Co 0.3 Mn 0.2 O2(NCM532), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 (NCM811), LiCoO2 (LCO), etc. Among these, LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) is preferred.

[0020] Furthermore, examples of the positive electrode active material (A) other than the above formula (A-1) include lithium titanate (for example, Li4Ti5O 12), lithium metal phosphate (LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4), transition metal oxides (VO5, MoO3), TiS2, LiCoN, Si, SiO2, Li2SiO3, Li4SiO4, and lithium-storing intermetallic compounds (e.g., Mg2Sn, Mg2Ge, Mg2Sb, Cu3Sb). Of these, lithium metal phosphate is preferred from the viewpoint of suppressing the interface resistance between the current collector and the positive electrode active material layer. Of the lithium metal phosphates, LiFePO4 is more preferred.

[0021] The shape of the positive electrode active material (A) is not particularly limited, and may be, for example, particulate or thin film, and may be particulate from the viewpoint of ease of handling. When the positive electrode active material is in the form of particles, the average particle size (D50) of the particles is, for example, preferably 1 nm or more and 100 μm or less, and more preferably 10 nm or more and 30 μm or less.

[0022] A coating layer containing a Li-ion conductive oxide may be formed on the surface of the positive electrode active material (A) from the viewpoint of suppressing the reaction between the positive electrode active material and the solid electrolyte. Examples of Li-ion conductive oxides include LiNbO3 and Li4Ti5O 12 , and Li3PO4, etc. The lower limit of the thickness of the coating layer is preferably 0.1 nm or more, more preferably 1 nm or more, and the upper limit of the thickness of the coating layer is preferably 100 nm or less, more preferably 20 nm or less.

[0023] The content of the positive electrode active material (A) is not particularly limited, and is preferably 50.0 mass% or more and 98.0 mass% or less, more preferably 60.0 mass% or more and 95.0 mass% or less, and even more preferably 70.0 mass% or more and 90.0 mass% or less, relative to 100.0 mass% of the positive electrode active material layer.

[0024] <Solid electrolyte (B)> As the solid electrolyte (B), sulfide-based solid electrolytes, oxide-based solid electrolytes, etc. can be used. Among these, it is preferable to use oxide-based solid electrolytes from the viewpoint of the safety and stability of the electrolyte.

[0025] Examples of sulfide-based solid electrolytes include Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4.

[0026] Oxide-based solid electrolytes include LLTO-based compounds ((La,Li)TiO3), Li6La2CaTa2O 12 , Li6La2ANb2O 12 (A: alkaline earth metal), Li2Nd3TeSbO 12 , Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP-based compounds (Li 1+x Al x Ge 2-x (PO4)3(0≦x≦1)), LATP-based compounds such as Li2O-Al2O3-TiO2-P2O5 (Li 1+x Al x Ti 2-x (PO4)3(0≦x≦1)), Li 1+x Ti 2-x Al x Si y (PO4) 3-y (0≦x≦1, 0≦y≦1), Li 1+y Al x M 2-x (PO4)3 (M is one or more elements selected from the group consisting of Ti, Ge, Sr, Sn, Zr, and Ca, and 0≦x≦1, 0≦y≦1), LiTi x Zr 2-x (PO4)3(0≦x≦1), LISICON(Li 4-2x Zn x GeO4 (0≦x≦1)), LIPON-based compounds (Li 3+y PO 4-x N x(0≦x≦1, 0≦y≦1)), NASICON-based compounds (LiTi2(PO4)3, etc.), garnet-based compounds (Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O 12 (0≦x≦1, etc.)

[0027] Among oxide-based solid electrolytes, LATP-based compounds are preferred from the viewpoint of high lithium ion conductivity. Examples of LATP-based compounds include those represented by the following formula (1): Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 ···(1) (In formula (1), x and y satisfy 0≦x≦1 and 0≦y≦1.) It is preferable that the material contains a material represented by the formula:

[0028] Furthermore, examples of preferred oxide-based solid electrolytes other than the LATP-based compounds include Li7La3Zr2O 12 (LLZO), Li 6.75 La3Zr 1.75 Ta 0.25 O 12 (LLZTO), Li 0.33 La 0.56 TiO3(LLTO), Li 1.6 Al 0.6 Ge 1.4 (PO4)3(LAGP), etc.

[0029] The content of the solid electrolyte (B) is not particularly limited, and is preferably 1.0 mass % or more and 40.0 mass % or less, more preferably 2.0 mass % or more and 20.0 mass % or less, and even more preferably 5.0 mass % or more and 15.0 mass % or less, relative to 100.0 mass % of the positive electrode active material layer.

[0030] <Binder (C)> The binder (C) is the following polymer (Ca) or polymer (Cb). Polymer (Ca): A homopolymer of vinylidene fluoride having an intrinsic viscosity of 3.5 dL / g or less. Polymer (Cb): A vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from hexafluoropropylene, having an intrinsic viscosity of 1.3 dL / g or more and 4.0 dL / g or less, and containing 8.0 wt% or less of structural units derived from hexafluoropropylene when the total structural units of the vinylidene fluoride copolymer are taken as 100.0 mass%. The polymer (Ca) or the polymer (Cb) is used for the purpose of suppressing the interfacial resistance between the current collector and the positive electrode active material layer. In the following description, when there is no need to particularly distinguish between the polymer (Ca) and the polymer (Cb), they will simply be referred to as "binder (C)."

[0031] (Polymer (Ca)) The upper limit of the intrinsic viscosity of the polymer (Ca) is 3.5 dL / g or less, preferably less than 3.0 dL / g, and more preferably less than 2.5 dL / g, from the viewpoint of suppressing the interfacial resistance between the current collector and the positive electrode active material layer.

[0032] The lower limit of the intrinsic viscosity of the polymer (Ca) is not particularly limited, but from the viewpoint of production, it is preferably 0.3 dL / g or more, and more preferably 0.5 dL / g or more. That is, when preparing a polymer (Ca) having an intrinsic viscosity of less than 0.3 dL / g, it is necessary to dilute the monomer concentration or use an excess amount of a chain transfer agent, which will be described later. If polymerization is carried out under such conditions, the polymerization rate becomes very slow, and in the case of suspension polymerization, which will be described later, it may be difficult to maintain suspension stability.

[0033] (Polymer (Cb)) The structural units of the polymer (Cb) may contain structural units derived from other monomers than the aforementioned vinylidene fluoride (VDF) and hexafluoropropylene (HFP), as long as the effects of the present invention are not impaired. Examples of such other monomers include, for example, monomers having a hydrogen-bonding polar functional group (preferably carboxyl group-containing monomers). Examples of carboxyl group-containing monomers copolymerizable with vinylidene fluoride include unsaturated monobasic acids such as acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, and 2-carboxyethyl methacrylate; unsaturated dibasic acids such as maleic acid and citraconic acid; monoesters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester; acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, and methacryloyloxypropyl succinate.

[0034] The content of structural units derived from hexafluoropropylene (HFP) in polymer (Cb) is 8.0% by mass or less, and preferably 7.5% by mass or less, when all structural units of polymer (Cb) are taken as 100% by mass.

[0035] When polymer (Cb) contains a structural unit derived from monomethyl maleate (MMM), the content of the structural unit is not particularly limited, but is preferably 1.0% by mass or less, and more preferably 0.6% by mass or less, when all structural units of polymer (Cb) are taken as 100% by mass.

[0036] The upper limit of the intrinsic viscosity of the polymer (Cb) is 4.0 dL / g or less, preferably less than 3.0 dL / g, and more preferably less than 2.5 dL / g, from the viewpoint of suppressing the interfacial resistance between the current collector and the positive electrode active material layer.

[0037] The lower limit of the intrinsic viscosity of the polymer (Cb) is preferably 1.3 dL / g or more, more preferably 1.6 dL / g or more, from the viewpoint of suppressing the interfacial resistance between the current collector and the positive electrode active material layer.

[0038] The polymer (Ca) and the polymer (Cb) may be used either alone or in combination.

[0039] The content of the binder (C) is not particularly limited, and is preferably 1.0 mass% or more and 40.0 mass% or less, more preferably 2.0 mass% or more and 30.0 mass% or less, and even more preferably 3.0 mass% or more and 20.0 mass% or less, relative to 100.0 mass% of the positive electrode active material layer.

[0040] (Method for producing binder (C)) The method for producing the binder (C) is not particularly limited, and is usually carried out by a method such as suspension polymerization, emulsion polymerization, solution polymerization, etc. From the viewpoint of ease of post-treatment, aqueous suspension polymerization and emulsion polymerization are preferred, and aqueous suspension polymerization is more preferred.

[0041] The aqueous suspension polymerization method is not particularly limited, and examples thereof include a method in which a monomer to be used for polymerization is polymerized in an aqueous medium in the presence of a suspending agent, a polymerization initiator, a chain transfer agent, etc.

[0042] The suspending agent is not particularly limited, and examples thereof include methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, polyvinyl alcohol, polyethylene oxide, gelatin, etc. The amount of the suspending agent used is not particularly limited, and is preferably 0.005 parts by mass or more and 1.0 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.4 parts by mass or less, relative to 100 parts by mass of all monomers used in the polymerization.

[0043] The polymerization initiator is not particularly limited, and examples thereof include diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-n-heptafluoropropyl peroxydicarbonate, isobutyryl peroxide, di(chlorofluoroacyl)peroxide, di(perfluoroacyl)peroxide, t-butyl peroxypivalate, etc. The amount of the polymerization initiator used is not particularly limited, and is, for example, preferably 0.05 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.15 parts by mass or more and 2.0 parts by mass or less, relative to 100.0 parts by mass of all monomers used in the polymerization.

[0044] The chain transfer agent is not particularly limited, and examples thereof include ethyl acetate, propyl acetate, acetone, and diethyl carbonate.

[0045] The amount of monomers used in the polymerization, expressed as the mass ratio of total monomers to water, is usually 1:1 to 1:10, preferably 1:2 to 1:5. The polymerization conditions, such as polymerization temperature and polymerization time, used in suspension polymerization are not particularly limited, and known polymerization conditions may be used. The polymerization temperature T is appropriately selected depending on the 10-hour half-life temperature T10 of the polymerization initiator, and is usually selected within the range of T10 - 25°C ≦ T ≦ T10 + 25°C. For example, the T10 values ​​of t-butyl peroxypivalate and diisopropyl peroxydicarbonate are 54.6°C and 40.5°C, respectively (see NOF Corporation product catalog). Therefore, when using t-butyl peroxypivalate and diisopropyl peroxydicarbonate as polymerization initiators, the polymerization temperature T is appropriately selected within the ranges of 29.6°C ≦ T ≦ 79.6°C and 15.5°C ≦ T ≦ 65.5°C, respectively. The polymerization time is not particularly limited, but is preferably 1 to 24 hours in consideration of productivity and the like.

[0046] <Other ingredients> The positive electrode active material layer may contain components (hereinafter also referred to as "other components") other than the above-described positive electrode active material (A), solid electrolyte (B), and binder (C) as long as the effects of the present invention are not impaired. Examples of other components include any known additives, such as conductive additives, insulating inorganic fillers such as alumina, magnesia, and silica, insulating organic fillers such as polytetrafluoroethylene, polyimide, and polyacrylonitrile, plasticizers such as ethylene carbonate, propylene carbonate, and ethyl methyl carbonate, Li salts such as LiPF6, LiFSI, and LiTFSI, dispersants, flame retardants, and antifoaming agents.

[0047] Examples of the conductive additive (D) include carbon black, carbon nanotubes, etc. These may be used alone or in combination of two or more.

[0048] The content of the conductive additive (D) is not particularly limited, but is preferably 0.05% by mass or more and 15.0% by mass or less, more preferably 0.1% by mass or more and 10.0% by mass or less, and even more preferably 0.5% by mass or more and 8.0% by mass or less, relative to 100.0% by mass of the positive electrode active material layer.

[0049] ≪Electrode≫ The electrode refers to a positive electrode, which includes a current collector and the above-described positive electrode active material layer. By providing the positive electrode active material layer, the electrode has an effect of suppressing the interface resistance between the current collector and the positive electrode active material layer.

[0050] (current collector) The current collector is a terminal for extracting electricity. The material of the current collector is not particularly limited, and metal foil or metal mesh of aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc. can be used. Alternatively, the current collector may be formed by applying the above metal foil or metal mesh to the surface of another medium.

[0051] The bulk density of the electrode is not particularly limited, and is, for example, 1.5 g / cm 3More than 5.0g / cm 3 It is preferable that: The weight of the electrode is not particularly limited, and is, for example, 20 g / m 2 More than 1000g / m 2 It is preferable that:

[0052] <Electrode manufacturing method> The electrode manufacturing method may include, for example, a step of preparing a positive electrode slurry by mixing the above-mentioned positive electrode active material (A), the solid electrolyte (B), the binder (C), and optionally other components and the nonaqueous solvent (S), and a step of applying the obtained positive electrode slurry to a current collector and then drying it. That is, in the above embodiment, a positive electrode active material layer is produced and an electrode is also produced through the step of drying the positive electrode slurry.

[0053] Examples of the non-aqueous solvent (S) include N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP"), dimethylformamide, N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N,N-dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, cyclohexanone, methyl ethyl ketone, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0054] The coating method is not particularly limited, and for example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, a dip coating method, etc. can be used.

[0055] The drying temperature is, for example, preferably 80°C or higher and 300°C or lower, more preferably 90°C or higher and 200°C or lower, and even more preferably 100°C or higher and 180°C or lower. The drying time is, for example, preferably 10 seconds or more and 300 minutes or less, and more preferably 1 minute or more and 200 minutes or less. Drying may be performed multiple times at different temperatures. Pressure may be applied during drying.

[0056] ≪All-solid-state battery≫ The all-solid-state battery includes the electrode of the above-described embodiment. As the all-solid-state battery, conventionally known components other than the positive electrode, such as the negative electrode and separator, can be used.

[0057] ≪Semi-solid battery≫ The semi-solid battery includes the electrode of the above-described embodiment. For the semi-solid battery, conventionally known components other than the positive electrode, such as the negative electrode and separator, can be used. The amount of electrolyte contained in the semi-solid battery is preferably 1.0 to 95.0%, more preferably 1.0 to 90.0%, and even more preferably 1.0 to 80.0%, when the volume of the electrolyte contained in a conventional secondary battery containing an electrolyte is taken as 100.0%. [Example]

[0058] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0059] [Examples 1 to 10 and Comparative Examples 1 to 5] <Materials used> In the examples and comparative examples, the following A1 and A2 were used as the positive electrode active material (A). A1: LiFePO4 A2:NCM523

[0060] In the examples and comparative examples, the following B1 was used as the solid electrolyte (B). B1:Li 1+x+y Al x Ti 2x Si y P 3y O 12 (LATP) (Ohara Corporation, "LICGC TM PW-01 (particle size 1μm)

[0061] In the examples and comparative examples, the following binders C1 to C12 were prepared and used as binders (C). The intrinsic viscosity of each prepared binder was measured according to the following method.

[0062] (Measurement of intrinsic viscosity) 80 mg of each binder was dissolved in 20 ml of N,N-dimethylformamide to prepare a binder-containing solution. The viscosity η1 of the binder-containing solution was measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. Similarly, the viscosity η0 of N,N-dimethylformamide was measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. The intrinsic viscosity η was then calculated based on the following formula: Intrinsic viscosity η=(1 / C)·ln(η1 / η0)

[0063] (Example of producing binder C1 (PVDF)) A 2-liter autoclave was charged with 253.0 parts by weight of ion-exchanged water, 0.05 parts by weight of methyl cellulose, 100 parts by weight of vinylidene fluoride (VDF), 0.6 parts by weight of di-n-propyl peroxydicarbonate, 0.6 parts by weight of methanol, and 1.4 parts by weight of ethyl acetate, and polymerization was initiated at 26°C. The temperature was then raised to 40°C, and suspension polymerization was carried out for 12 hours. After polymerization was completed, the resulting polymer slurry was heat-treated at 95°C for 30 minutes, dehydrated, washed with water, and further dried at 80°C for 20 hours to obtain binder C1. Binder C1 contained 100.0% by weight of VDF relative to all structural units. The intrinsic viscosity (η) of binder C1 was 1.1 dL / g.

[0064] (Example of binder C2 (PVDF) production) A 2-liter autoclave was charged with 231.8 parts by weight of ion-exchanged water, 0.05 parts by weight of methyl cellulose, 100 parts by weight of VDF, 0.7 parts by weight of di-i-propyl dioxydicarbonate (IPP), and 0.7 parts by weight of ethyl acetate. VDF was polymerized in the same manner as in the preparation example of binder C1 to obtain binder C2. Binder C2 contained 100.0% by weight of VDF based on all structural units. The intrinsic viscosity (η) of binder C2 was 2.1 dL / g.

[0065] (Example of producing binder C3 (PVDF)) VDF was polymerized in the same manner as in the preparation example of binder C2, except that the amounts of ion-exchanged water, IPP, and ethyl acetate were changed to 213.8 parts by mass, 0.3 parts by mass, and 0.42 parts by mass of ethyl acetate, to obtain binder C3. Binder C3 contained 100.0% by mass of VDF based on all structural units. The intrinsic viscosity (η) of binder C3 was 3.1 dL / g.

[0066] (Example of producing binder C4 (PVDF)) VDF was polymerized in the same manner as in the preparation example of binder C1, except that the amounts of ion-exchanged water were changed to 312.5 parts by mass, diethyl carbonate 3.5 parts by mass, VDF 100 parts by mass, t-butyl peroxypivalate 0.13 parts by mass, and ethyl acetate 0.1 parts by mass, to obtain binder C4. Binder C4 contained 100.0% by mass of VDF based on all structural units. The intrinsic viscosity (η) of binder C4 was 0.3 dL / g.

[0067] (Example of binder C5 (VDF / HFP) production) A 2L autoclave was charged with 290 parts by weight of ion-exchanged water, 0.15 parts by weight of methylcellulose, 57.9 parts by weight of vinylidene fluoride (VDF), 7.8 parts by weight of hexafluoropropylene (HFP), and 0.9 parts by weight of diisopropyl peroxydicarbonate, and polymerized at 45°C. 34.3 parts by weight of VDF was added as an aftercharge to obtain a copolymer. The resulting copolymer was heat-treated at 95°C for 60 minutes, dehydrated, washed with water, and further dried at 80°C for 20 hours to obtain Binder C5. Binder C5 contained 94.3% by weight of VDF and 5.7% by weight of HFP based on the total amount of constituent units. The intrinsic viscosity (η) of Binder C5 was 1.5 dL / g.

[0068] (Example of binder C6 (VDF / HFP) production) VDF and HFP were polymerized in the same manner as in the preparation example of binder C1, except that 253.0 parts by mass of ion-exchanged water, 0.05 parts by mass of methyl cellulose, 90.0 parts by mass of VDF, 10.0 parts by mass of HFP, 0.4 parts by mass of IPP, and 1.0 part by mass of ethyl acetate were used, to obtain binder C6. Binder C6 contained 93.0% by mass of VDF and 7.0% by mass of HFP based on the total structural units. The intrinsic viscosity (η) of binder C6 was 1.9 dL / g.

[0069] (Example of binder C7 (VDF / HFP / MMM)) VDF, HFP, and MMM were polymerized in the same manner as in the preparation example of binder C1, except that 240.2 parts by mass of ion-exchanged water, 0.2 parts by mass of methyl cellulose, 96.7 parts by mass of VDF, 3.0 parts by mass of HFP, 0.3 parts by mass of monomethyl maleate (MMM), and 0.47 parts by mass of IPP were used to obtain binder C7. The amount of each monomer in binder C7 was determined by calculating the VDF / HFP ratio by F-NMR, calculating the VDF / MMM ratio by the method described below, and then calculating so that the total of VDF, HFP, and MMM was 100 mol%. The VDF / MMM ratio in the polymer (the molar ratio of the amount of structural units derived from vinylidene fluoride to the amount of structural units derived from monomethyl maleate) was calculated based on the calculation method using IR spectra and a calibration curve disclosed in WO 2009 / 084483. Binder C7 contained 97.4% by mass of VDF, 2.3% by mass of HFP, and 0.3% by mass of MMM relative to the total structural units. The intrinsic viscosity (η) of binder C7 was 3.0 dL / g.

[0070] (Example of binder C8 (VDF / CTFE) production) VDF and CTFE were polymerized in the same manner as in the preparation example of binder C1, except that 256.6 parts by mass of ion-exchanged water, 0.05 parts by mass of methyl cellulose, 96.0 parts by mass of VDF, 4.0 parts by mass of chlorotrifluoroethylene (CTFE), 0.6 parts by mass of IPP, and 0.59 parts by mass of ethyl acetate were used, to obtain binder C8. Binder C8 contained 96.0% by mass of VDF and 4.0% by mass of CTFE based on the total structural units. The intrinsic viscosity (η) of binder C8 was 2.1 dL / g.

[0071] (Example of binder C9 (VDF / HFP / MMM) production) VDF, HFP, and MMM were polymerized in the same manner as in the preparation example of binder C1, except that 259.0 parts by mass of ion-exchanged water, 0.2 parts by mass of methyl cellulose, 90 parts by mass of VDF, 10 parts by mass of HFP, 0.5 parts by mass of MMM, 2.0 parts by mass of IPP, and 0.17 parts by mass of ethyl acetate were used, to obtain binder C9. Binder C9 contained 93.3% by mass of VDF, 6.2% by mass of HFP, and 0.5% by mass of MMM based on the total structural units. The intrinsic viscosity (η) of binder C9 was 1.2 dL / g.

[0072] (Example of binder C10 (VDF / HFP / MMM) production) VDF, HFP, and MMM were polymerized in the same manner as in the preparation example of binder C1, except that 243.1 parts by mass of ion-exchanged water, 0.2 parts by mass of methyl cellulose, 86.0 parts by mass of VDF, 13.5 parts by mass of HFP, 0.5 parts by mass of MMM, and 1.77 parts by mass of IPP were used, to obtain binder C10. Binder C10 contained 89.5% by mass of VDF, 10.0% by mass of HFP, and 0.5% by mass of MMM based on the total structural units. The intrinsic viscosity (η) of binder C10 was 1.5 dL / g.

[0073] (Example of producing binder C11 (PVDF)) VDF was polymerized in the same manner as in the preparation example of binder C1, except that 217 parts by mass of ion-exchanged water, 0.05 parts by mass of methyl cellulose, 100 parts by mass of VDF, 0.09 parts by mass of IPP, and 0.25 parts by mass of ethyl acetate were used, to obtain binder C11. Binder C11 contained 100.0% by mass of VDF based on all structural units. The intrinsic viscosity (η) of binder C11 was 4.2 dL / g.

[0074] (Example of binder C12 (VDF / HFP) production) VDF and HFP were polymerized in the same manner as in the preparation example of binder C1, except that 256.0 parts by mass of ion-exchanged water, 0.05 parts by mass of methyl cellulose, 90.0 parts by mass of VDF, 10 parts by mass of HFP, 0.1 parts by mass of IPP, and 0.2 parts by mass of ethyl acetate were used, to obtain binder C12. Binder C12 contained 93.0% by mass of VDF and 7.0% by mass of HFP based on all structural units. The intrinsic viscosity (η) of binder C12 was 4.4 dL / g.

[0075] Detailed information on the obtained binders C1 to C12 is shown in Table 1.

[0076] [Table 1]

[0077] In the examples and comparative examples, the following D1 and D2 were used as the conductive additive (D). D1: Carbon nanotube (CNT) dispersion D2:SuperP

[0078] In the examples and comparative examples, the following S1 was used as the non-aqueous solvent (S). S1: N-methyl-2-pyrrolidone (NMP)

[0079] (Preparation of positive electrode slurry) Each binder (C) was dispersed in N-methyl-2-pyrrolidone (NMP) at room temperature so that the concentration of the binder (C) was adjusted to a desired concentration, and then the solution temperature was raised to 50°C to dissolve each binder (C) (hereinafter referred to as the "binder solution"). The positive electrode active material (A), solid electrolyte (B), conductive additive (D), and each of the binder solutions were mixed so that the components had the contents shown in Table 2 below, to obtain each positive electrode slurry. The solid content of the positive electrode slurry was adjusted using NMP.

[0080] (Preparation of positive electrode) Each of the obtained positive electrode slurries was applied to an Al foil (thickness 15 μm) and then dried at 120° C. Each of the obtained preliminary positive electrodes was pressed and further heat-treated at 120° C. for 3 hours. As a result, when LiFePO4 was used as the active material, the electrode bulk density was 2.3 g / cm 3 When NCM523 was used as the active material, the electrode bulk density was 3.3 g / cm 3 When any of the active materials was used, the coating weight was 200 g / m 2 Each positive electrode was obtained.

[0081] <Evaluation> The electrode resistance of each of the obtained positive electrodes was measured according to the following method.

[0082] (interface resistance) Each of the prepared positive electrodes was punched out to a diameter of 14 mm to prepare a total of three measurement samples. Five measurements were taken for each measurement sample using the electrode resistance measurement system RM2610 (Hioki E.E. Corporation). The interfacial resistance (Ω cm) was calculated from the average of a total of 15 measurement data. 2 The results are shown in Table 2.

[0083] [Table 2]

[0084] From Table 2, it can be seen that the positive electrode of Comparative Example 4, which has a positive electrode active material layer containing binder C11 (PVDF) with an intrinsic viscosity of more than 3.5 dL / g, has an interface resistance of 1.03 Ω cm2 On the other hand, in the case of a positive electrode having a positive electrode active material layer containing binders C1 to C4 (all of which are PVDF) having an intrinsic viscosity of 3.5 dL / g or less, as shown in Examples 1 to 4, the interface resistance was at most 0.50 Ω cm 2 It is clear that the interface resistance between the current collector and the electrode active material was significantly suppressed. In addition, the positive electrodes of Comparative Examples 2, 3, and 5, which have positive electrode active material layers containing binder C9 (VDF / HFP / MMM) with an intrinsic viscosity of less than 1.3 dL / g, binder C12 (VDF / HFP) with an intrinsic viscosity of more than 4.0 dL / g, and binder C10 (VDF / HFP / MMM) with more than 8% by mass of structural units derived from HFP, have a minimum interfacial resistance of 0.79 Ω cm 2 It remained there. On the other hand, in the case of a positive electrode having a positive electrode active material layer containing binders C5 to C6 (VDF / HFP) and C7 (VDF / HFP / MMM) having an intrinsic viscosity of 1.3 dL / g or more and 4.0 dL / g or less and containing 8 mass % or less of a structural unit derived from HFP, as shown in Examples 5 to 7, the interfacial resistance was at most 0.56 Ω cm 2 It is clear that the interface resistance between the current collector and the electrode active material was suppressed. On the other hand, in a positive electrode having a positive electrode active material layer containing binder C8 (VDF / CTFE) which satisfies the above intrinsic viscosity range but contains a structural unit derived from CTFE instead of HFP, the interface resistance was 0.74 Ω cm as shown in Comparative Example 1. 2 It remained there.

Claims

1. A positive electrode active material layer containing a positive electrode active material (A), a solid electrolyte (B), and a binder (C), The positive electrode active material layer, wherein the binder (C) is the following polymer (Ca) or polymer (Cb): Polymer (Ca): A homopolymer of vinylidene fluoride having an intrinsic viscosity of 3.5 dL / g or less. Polymer (C-b): A vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from hexafluoropropylene, having an intrinsic viscosity of 1.3 dL / g or more and 4.0 dL / g or less, and containing 8.0 mass% or less of structural units derived from hexafluoropropylene when the total structural units of the vinylidene fluoride copolymer are taken as 100.0 mass%.

2. 2. The positive electrode active material layer according to claim 1, wherein the intrinsic viscosity of the polymer (Ca) or the polymer (Cb) is less than 3.0 dL / g.

3. The positive electrode active material layer according to claim 1 or 2, wherein the solid electrolyte (B) is an oxide-based solid electrolyte.

4. The solid electrolyte (B) is represented by the following formula (1): Li １＋ｘ＋ｙ Al ｘ Ti ２-ｘ Si ｙ P ３-ｙ O １２ ・・・(1) (In formula (1), x and y satisfy 0≦x≦1 and 0≦y≦1.) The positive electrode active material layer according to claim 3 , comprising a material represented by the formula:

5. The positive electrode active material (A) contains lithium metal phosphate, The lithium metal phosphate is LiFePO ４ , LiMnPO ４ , LiCoPO ４ , and LiNiPO ４ The positive electrode active material layer according to claim 1 or 2, selected from the group consisting of:

6. An electrode comprising a current collector and the positive electrode active material layer according to claim 1 or 2.

7. A semi-solid or all-solid battery comprising the electrode according to claim 6.

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