Components for secondary batteries

Abstract

Provided is a composition for a secondary battery, using a polymer having a structure derived from 1,2-difluoroethylene. This composition for a secondary battery contains a fluorine-containing polymer and a solvent, and is characterized in that the fluorine-containing polymer contains a structural unit represented by general formula (1).

Description

[Technical Field]

[0001] This disclosure relates to compositions for secondary batteries. [Background technology]

[0002] Fluorine-containing polymers are polymers used in a great many fields. Well-known monomers for producing such polymers include tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene. Furthermore, the method for producing 1,2-difluoroethylene is disclosed in Patent Document 1. In addition, Non-Patent Document 1 discloses the compound and a polymer using it.

[0003] On the other hand, it is known that fluorine-containing resins such as polyvinylidene fluoride are used as binders in electrodes of secondary batteries, etc. (Patent Document 2, etc.). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2019 / 216239 [Patent Document 2] Japanese Patent Publication No. 2016-25027 [Non-patent literature]

[0005] [Non-Patent Document 1] Poly(vinylene fluoride), Synthesis and Properties WS Durrell et. al. Journal of Polymer Science: Part A Vol.3,P2975-2982 (1965) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This disclosure aims to provide a composition for secondary batteries using a polymer having a structure derived from 1,2-difluoroethylene. [Means for solving the problem]

[0007] This disclosure relates to a composition for secondary batteries containing a fluorine-containing polymer and a solvent, The composition for secondary batteries is characterized in that the fluorine-containing polymer is a polymer containing structural units represented by the following general formula (1). [ka]

[0008] The disclosure also indicates that the fluorine-containing polymer may further contain a structural unit represented by the following general formula (2). [ka] (R1 is hydrogen, fluorine, a hydrocarbon group with 5 or fewer carbon atoms that is partially or fully fluorinated, or an OR5 group (an R5 group is a hydrocarbon group with 5 or fewer carbon atoms that is partially or fully fluorinated). R2, R3, and R4 are each independently hydrogen or fluorine.)

[0009] The structural unit represented by the general formula (2) is preferably at least one structural unit selected from the group consisting of structural units represented by the following general formulas (3) to (8). [ka]

[0010] Preferably, the weight-average molecular weight of the fluorine-containing polymer is 50,000 to 5,000,000. It is preferable that the proportion of structural units represented by general formula (1) in the fluorine-containing polymer is 0.1 to 100 mol%.

[0011] Preferably, the solvent is at least one compound selected from the group consisting of ester compounds, ketone compounds, and amide compounds.

[0012] The above-mentioned secondary battery composition is preferably for use as an electrode in a secondary battery. The above-mentioned secondary battery composition is preferably for use as the positive electrode of a secondary battery. The above-mentioned secondary battery composition is preferably for use as a separator in a secondary battery.

[0013] This disclosure also relates to a method for forming a layer for a secondary battery, comprising the step of applying a slurry onto a substrate and performing heat drying, wherein the slurry contains the above-mentioned secondary battery composition.

[0014] This disclosure also relates to an electrode for a secondary battery, characterized by having a polymer containing a structural unit represented by the following general formula (1) and an active material layer containing an active material. [ka]

[0015] This disclosure also relates to a polymer containing a structural unit represented by the following general formula (1), and a solid electrolyte layer for a secondary battery containing a solid electrolyte. [ka]

[0016] This disclosure also relates to a separator for secondary batteries containing a polymer containing a structural unit represented by the following general formula (1). [ka]

[0017] This disclosure also relates to a secondary battery characterized by comprising the above-mentioned electrodes for secondary batteries and / or the above-mentioned separator for secondary batteries. [Effects of the Invention]

[0018] The secondary battery composition disclosed herein is suitable for use in electrode formation and the like, taking advantage of the fact that a polymer having a structure derived from 1,2-difluoroethylene has excellent solubility in various general-purpose solvents. [Modes for carrying out the invention]

[0019] The details of this disclosure are described below. This disclosure relates to a secondary battery composition that is preferably used for electrode formation, electrolyte layer formation, or separator formation, mainly for secondary batteries.

[0020] For example, in the formation of electrodes and electrolyte layers for sulfide-based solid-state batteries, a known method involves coating and drying a slurry containing sulfide-based solid electrolyte particles, a binder, and a solvent, followed by pressing. When forming good electrodes and electrolyte layers using such a method, the selection of the binder and solvent used in combination with the sulfide-based solid electrolyte particles is crucial. When using sulfide-based solid electrolyte particles, it is necessary to select a solvent that does not react with them, thus limiting the types of solvents that can be used. Furthermore, to prepare a slurry using such a solvent, it is necessary to select a binder that dissolves in that solvent.

[0021] Therefore, it is desirable to use a binder that has suitable solubility in the solvent. However, most known binders have low solubility in solvents. As a result, they could not be sufficiently dissolved in slurries containing sulfide-based solid electrolyte particles and could not fully exhibit their function as a binder.

[0022] Furthermore, using polyvinylidene fluoride, a relatively inexpensive and widely used polymer, as a binder can lead to gelation in the slurry. If the binder gels, a uniform slurry cannot be obtained, and therefore it cannot perform its function as a binder.

[0023] This type of gelation is particularly likely to occur in slurries using positive electrode active materials containing lithium hydroxide. Some oxide-based solid electrolytes are sensitive to moisture and are thought to react with moisture in the air to transform into lithium hydroxide, which becomes an alkaline component that causes gelation. It has been known that gelation occurs in the production of slurries, especially those used in the manufacture of electrode materials, and many attempts have been made to improve this process.

[0024] In this disclosure, a secondary battery composition suitable for battery manufacturing is obtained by using a fluorine-containing polymer having a structure derived from 1,2-difluoroethylene, which has good dissolution performance, as a binder. Furthermore, the secondary battery composition disclosed herein exhibits excellent dispersibility, stability, gelling properties, and improved solid content relative to viscosity. It can also be expected to reduce the resistance of the electrode surface. Moreover, because a low-boiling point solvent can be used, it offers advantages such as lowering the drying temperature and shortening the drying time during the manufacturing process of electrodes and other components.

[0025] The fluorine-containing polymer used in this disclosure is a polymer having a structure represented by the following general formula (1), and may be a homopolymer or a copolymer.

[0026] [ka]

[0027] The structure represented by the above general formula (1) is given by the following general formula (10)

[0028] [ka]

[0029] This structure, represented by [the given formula], is obtained by polymerization using 1,2-difluoroethylene as the monomer. While 1,2-difluoroethylene is a known compound, conventional studies have primarily focused on its use as a refrigerant, and little research has been conducted on its potential as a polymerization monomer.

[0030] Furthermore, 1,2-difluoroethylene can be copolymerized with other monomers using conventional methods. Moreover, the copolymerization ratio can be easily varied.

[0031] The above-mentioned fluorine-containing polymer is either a polymer consisting solely of the structure represented by the above general formula (1), or a copolymer having the structural unit represented by the above general formula (1).

[0032] Furthermore, 1,2-difluoroethylene exists in both trans (E) and cis (Z) isomers.

[0033] [ka]

[0034] Therefore, differences in stereochemistry occur depending on whether only the trans isomer is used as a raw material, only the cis isomer is used as a raw material, or a mixture of these is used as a raw material. The above-mentioned fluorine-containing polymer may be any of these, or a mixture of these in any proportion.

[0035] When the above-mentioned fluorine-containing polymer is used as a copolymer, it is preferable that it has structural units represented by the following general formula (2) in addition to the constituent units represented by the above general formula (1).

[0036] [ka] (R1 is hydrogen, fluorine, a hydrocarbon group with 5 or fewer carbon atoms that is partially or fully fluorinated, or an OR5 group (an R5 group is a hydrocarbon group with 5 or fewer carbon atoms that is partially or fully fluorinated). R2, R3, and R4 are each independently hydrogen or fluorine.)

[0037] Examples of structural units represented by the above general formula (2) include structures derived from ethylenic monomers in which at least one hydrogen atom may be substituted with fluorine, structural units derived from propylene monomers in which at least one hydrogen atom may be substituted with fluorine, structural units derived from butenic monomers in which at least one hydrogen atom may be substituted with fluorine, structural units derived from pentene monomers in which at least one hydrogen atom may be substituted with fluorine, and so on. The fluorine-containing polymer of this disclosure may also be a combination of two or more copolymer structural units.

[0038] Examples of structures derived from ethylenic monomers in which at least one hydrogen atom may be substituted with fluorine include vinylidene fluoride, tetrafluoroethylene (TFE), vinyl fluoride, and 1,1,2-trifluoroethylene.

[0039] Structural units derived from propylene monomers in which at least one hydrogen atom is replaced by fluorine include 1270, 1216, 1252, 1243, 1234, 1225, and 1252. Examples of structural units derived from butenoid monomers in which at least one hydrogen atom may be substituted with fluorine include 1390, 1381, 1372, 1363, 1354, 1345, 1336, 1327, and 1318. Examples of pentene monomers in which at least one hydrogen atom may be substituted with fluorine include R600, R600a, nonahydrofluoropentene, 1492, 1483, 1474, 1465, 1456, 1447, 1438, 1429, and perfluoropentene. These are all Ashley numbers.

[0040] Structural units derived from propylene monomers in which at least one hydrogen atom is substituted with fluorine include Ashley numbers 1216 (hexafluoropropylene), 1225, 1234, 1243, and 1252. Suitable examples of such structural units are those represented by the following general formulas (11) to (16).

[0041] [ka] (In the formula, Rf1 to Rf6 represent fluoromethyl groups having 1 to 3 fluorines.)

[0042] Specific examples of compounds that give the structure represented by the above general formula include 2,3,3,3-tetrafluoropropene (HFO-1234yf), (Z or E-)1,3,3,3-tetrafluoropropene (HFO-1234ze), (Z or E-)1,2,3,3,3-pentafluoropropene (HFO-1225ye), (Z or E-)1,1,3,3,3-pentafluoropropene (HFO-1225zc), and (Z or E-)3,3,3-trifluoropropene (HFO-1243zf).

[0043] The structural unit represented by general formula (2) is, [ka] (R1-R3 are selected from H and F, and Rf is a fluorine-containing alkyl group with 1-6 carbon atoms.) That's fine.

[0044] The structural unit represented by the above general formula (20) is a structural unit derived from a fluorinated vinyl ether compound. The above fluorinated vinyl ether compound is not particularly limited and can be perfluoromethyl vinyl ether (PMVE) (see general formula (7) below), perfluoroethyl vinyl ether (see general formula (8) below), perfluoropropyl vinyl ether (see general formula (9) below), etc.

[0045] [ka]

[0046] In the copolymerized polymer described above, among the structural units represented by the general formula (2) described above, those that can be used particularly suitably are the structural units represented by the following general formulas (3) to (8).

[0047] [ka]

[0048] The structure represented by the above general formula (3) is a structural unit derived from tetrafluoroethylene, and the structure represented by the general formula (4) is a structural unit derived from vinylidene fluoride. Furthermore, the structure represented by general formula (5) is a structural unit derived from hexafluoropropylene (HFP), and the structure represented by general formula (6) is a structural unit derived from CH2=CFCF3. The structure represented by general formula (7) is a structural unit derived from perfluoro(methyl vinyl ether). The structure represented by general formula (8) is a structural unit derived from perfluoro(ethyl vinyl ether).

[0049] When the fluorine-containing polymer is a copolymer, the proportion of structural units represented by the above general formula (1) is preferably 0.1 mol% or more and 99.9 mol% or less, more preferably 1 mol% or more and 99 mol% or less, and even more preferably 10 mol or more and 99 mol% or less. The composition of the above-mentioned fluorine-containing polymer can be measured using an NMR analyzer. When the fluorine-containing polymer is a copolymer, the proportion of structural units represented by the above general formula (2) is preferably 0.1 mol% or more and 99.9 mol% or less.

[0050] Furthermore, depending on the copolymer's composition, it may result in a polymer that is difficult to dissolve in general-purpose solvents. For example, this is the case when TFE is copolymerized. Therefore, it is preferable to use TFE or similar materials in an amount of 60 mol% or less.

[0051] The fluorine-containing polymer may have structural units derived from copolymer components other than the structural unit represented by the general formula (2) above. The copolymer component is not particularly limited and can be chlorotrifluoroethylene, hexafluoroisobutene, ethylene, propylene, and alkyl vinyl ethers.

[0052] The amount of copolymer components other than the structural unit represented by the general formula (2) above is not particularly limited, but it is more preferably 99.9 mol% or less, even more preferably 99 mol% or less, and most preferably 97 mol% or less.

[0053] The above-mentioned fluorine-containing polymer preferably has a weight-average molecular weight of 50,000 to 5,000,000. This range is preferable in terms of thermal decomposition resistance and slurry stability. The above upper limit is more preferably 3,000,000 and even more preferably 2,000,000. The above lower limit is more preferably 80,000 and even more preferably 100,000. Furthermore, since coating properties depend on molecular weight, it is even more preferable that the weight-average molecular weight be 120,000 or more. The weight-average molecular weights in this disclosure are values ​​measured by gel permeation chromatography (GPC).

[0054] (Polymerization method) The fluorine-containing polymer relating to this disclosure is the following general formula (10)

[0055] [ka] It can be obtained by polymerizing a monomer composition comprising part or all of the monomer represented by the above general formula (10). The compound represented by the above general formula (10) is a known compound and can be produced, for example, by the method described in Patent Document 1.

[0056] The method for producing the above-mentioned fluorine-containing polymer is not particularly limited and can be carried out by any common polymerization method such as solution polymerization, emulsion polymerization, or suspension polymerization. The solvents, emulsifiers, and initiators used in these polymerizations are also not particularly limited and can be those that are commonly known.

[0057] The above-mentioned fluorine-containing polymer exhibits excellent solubility in solvents. Preferably, the secondary battery composition of this disclosure is such that the above-mentioned fluorine-containing polymer dissolves in the solvent and exhibits a slurry-like state. The above-mentioned fluorine-containing polymer is particularly preferable from a cost standpoint because it has good solubility in general-purpose solvents. Examples of general-purpose solvents that can dissolve the above-mentioned fluorine-containing polymer include N-methyl-2-pyrrolidone (NMP), acetone, methyl ethyl ketone, tetrahydrofuran, N,N-dimethylformamide, dimethylacetamide (DMAC), and butyl acetate.

[0058] The solvent used in this disclosure preferably contains at least one compound selected from the group consisting of ester compounds, ketone compounds, amide compounds, aromatic compounds, aliphatic hydrocarbon compounds, ether compounds, and carbonate compounds. Preferably, it is at least one compound selected from the group consisting of ester compounds, ketone compounds, and amide compounds. More preferably, it is at least one compound selected from the group consisting of ketone compounds and amide compounds.

[0059] Examples of ester compounds include those represented by the following general formula (21). General formula (21): [ka] (wherein, R 1 and R 2 are each independently H, a linear or branched aliphatic group having 1 to 10 carbon atoms, or an aromatic group having 6 to 10 carbon atoms.)

[0060] In the above general formula (21), R 1 and R 2 are each independently H, a linear or branched aliphatic group having 1 to 10 carbon atoms, or an aromatic group having 6 to 10 carbon atoms. Examples of the aliphatic group include an alkyl group or an alkenyl group having 1 to 10 carbon atoms. Specifically, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, vinyl group, propenyl group, butenyl group and the like can be mentioned. Among them, methyl group, ethyl group, propyl group, butyl group and the like are preferable. Examples of the aromatic group include phenyl group, naphthyl group and the like.

[0061] Specific examples of the ester compound include ethyl butyrate, butyl butyrate, propyl propionate, butyl methacrylate, ethyl acetate and the like.

[0062] Examples of the ketone compound include those represented by the following general formula (22). General formula (22):

Chemical formula

[0063] In the above general formula (22), R 3 and R 4 are each independently H, a linear or branched aliphatic group having 1 to 10A linear or branched aliphatic group, or C6~C 10 It is an aromatic group. As for aliphatic groups, C1~C 10 Alkyl groups are preferred. Specifically, examples include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, etc. Among these, methyl group or ethyl group is preferred, and methyl group is more preferred. Examples of aromatic groups include phenyl group and naphthyl group.

[0064] Examples of ketone compounds include acetone and methyl ethyl ketone.

[0065] Examples of amide compounds include those represented by the following general formulas (23) or (24). General formula (23): [ka] (In the formula, R 5 H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is an aromatic group. General formula (24): [ka] (In the formula, R 6 H, C1~C 10 Linear or branched aliphatic groups, R 7 H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is an aromatic group.

[0066] In the above general formula (23), R 5 H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is an aromatic group. The aliphatic group and aromatic group are as follows: 3 and R4 It is the same as what was explained earlier.

[0067] In the above general formula (24), R 6 H, C1~C 10 Linear or branched aliphatic groups, R 7 H, C1~C 10 A linear or branched aliphatic group, or C6~C 10 It is an aromatic group. Also, two R 7 These may be the same or different. The aliphatic group and aromatic group are as follows: 3 and R 4 It is the same as what was explained earlier.

[0068] In the above general formulas (23) and (24), R 5 ~R 7 Among the above, it is preferable that each is independently H, a methyl group, or an ethyl group.

[0069] Examples of amide compounds include N-methyl-2-pyrrolidone, dimethylformamide, and dimethylacetamide.

[0070] In this disclosure, when using a sulfide-based solid electrolyte, it is preferable to use a low-polarity solvent. Using a low-polarity solvent is preferable because it reduces the likelihood of reaction with the sulfide-based solid electrolyte particles. In this disclosure, a low-polarity solvent is defined as one with a relative permittivity of less than 20 at a frequency of 100 kHz. More preferably, it is less than 10.

[0071] The low-polarity solvents mentioned above are not particularly limited and include n-octane, n-nonane, n-decane, n-butyl ether, diisopentyl ether, ethylbenzene, ethyl acetate, ethyl butyrate, butyl butyrate, propyl propionate, butyl methacrylate, dimethyl carbonate, diethyl carbonate, methylphenyl ether, cyclopentyl methyl ether, ethylene carbonate, diphenyl ether, fluorobenzene, trifluoromethylbenzene, bistrifluoromethylbenzene, benzene, thiols, and the like.

[0072] Among these, at least one solvent selected from the group consisting of propyl propionate, butyl methacrylate, ethyl acetate, ethyl butyrate, and butyl butyrate can be used more preferably. A mixed solvent using two or more of these is also acceptable.

[0073] When the above fluorine-containing polymer is dissolved in a solvent to form a secondary battery composition, the polymer concentration may be set according to the application used, but it is preferably between 0.5% by mass and 90.0% by mass. The lower limit of the polymer concentration is more preferably 1.0% by mass, and even more preferably 2.5% by mass. The upper limit of the polymer concentration is more preferably 80.0% by mass, and even more preferably 75.0% by mass. By defining this range, it is possible to create a stable slurry of composition for secondary batteries.

[0074] In the secondary battery composition of this disclosure, the moisture content is preferably low, specifically preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 100 ppm or less.

[0075] The secondary battery composition disclosed herein can be used for electrodes in solid-state batteries as well as for electrodes in secondary batteries containing an electrolyte. It can also be used for the solid electrolyte layer in solid-state batteries. Furthermore, it can be used for separators in secondary batteries. Depending on these applications, the components constituting the electrodes, etc., may be combined as appropriate.

[0076] If the electrode is for a solid-state battery, an electrode active material and a solid electrolyte are also used. If the electrode is for a secondary battery containing an electrolyte, an electrode active material is also used. Conductive additives and other components may be used as needed.

[0077] The secondary battery composition disclosed herein can be used as a slurry for a positive electrode or a slurry for a negative electrode. Furthermore, it can be used as a slurry for forming a solid electrolyte layer. When used as an electrode slurry, it further contains active material particles. When used as an electrode slurry for a solid-state battery, it contains active material particles and a solid electrolyte. The active material particles can be a positive electrode active material or a negative electrode active material. The secondary battery composition disclosed herein can be more preferably used as a slurry for a positive electrode using a positive electrode active material.

[0078] The following details each component that makes up the electrode.

[0079] (electrode active material) When the secondary battery composition of this disclosure is used as a cathode slurry, a cathode active material is incorporated into the slurry. The cathode active material can be any cathode active material known for use in secondary batteries. In particular, it is preferable to use a cathode active material capable of intercalating and releasing lithium ions.

[0080] The positive electrode active material is not particularly limited as long as it is electrochemically capable of intercalating and releasing lithium ions. Specifically, materials containing lithium and at least one transition metal are preferred, such as lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

[0081] Preferred transition metals for lithium transition metal composite oxides include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of lithium transition metal composite oxides include lithium-cobalt composite oxides such as LiCoO2, lithium-nickel composite oxides such as LiNiO2, lithium-manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and those in which some of the transition metal atoms that make up the main body of these lithium transition metal composite oxides are substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and Si. A specific example of a substituted metal is, for example, LiNi 0.5 Mn 0.5 O2, LiLiLi0.85 Co 0.10 Al 0.05 O2, LiLiLi 0.82 Co 0.15 Al 0.03 O2, LiLiLi 0.80 Co 0.15 Al 0.05 O2, LiLiLi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiLiLi 0.80 Co 0.10 Mn 0.10 O2, LiMn 1.8 Al 0.2 O4, LiMn 1.5 Ni 0.5 O4, Li4Ti5O 12 These are some examples. In positive electrode active materials containing Ni, the higher the proportion of Ni, the higher the capacity of the positive electrode active material, and therefore, further improvements in battery capacity can be expected.

[0082] Preferred transition metals for lithium-containing transition metal phosphate compounds include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of lithium-containing transition metal phosphate compounds include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that make up the main component of these lithium-containing transition metal phosphate compounds are substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

[0083] In particular, from the viewpoint of high voltage, high energy density, or charge / discharge cycle characteristics, LiCoO2, LiNiO2, LiMn2O4, LiNi 0.82 Co 0.15 Al 0.03 O2, LiLiLi 0.80 Co 0.15 Al 0.05 O2, LiLiLi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiFePO4 are preferred.

[0084] Furthermore, it is also possible to use positive electrode active materials in which a substance with a different composition from the main component of the positive electrode active material is attached to its surface. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

[0085] These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating them into the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating it into the positive electrode active material, then reacting it by heating or other means; or adding it to the positive electrode active material precursor and simultaneously firing it.

[0086] The amount of surface-adhered material is preferably 0.1 ppm, more preferably 1 ppm, even more preferably 10 ppm, and preferably 20%, more preferably 10%, and even more preferably 5% by mass relative to the positive electrode active material. The surface-adhered material can suppress the oxidation reaction of the non-aqueous electrolyte on the surface of the positive electrode active material, thereby improving battery life. However, if the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions, potentially increasing resistance.

[0087] The positive electrode active material particles can take on various shapes, such as lumps, polyhedrons, spheres, ellipsoids, plates, needles, and columns, as has been done conventionally. However, it is preferable that the particles are formed by the aggregation of primary particles to create secondary particles, with the shape of these secondary particles being spherical or ellipsoidal. Normally, in electrochemical elements, the active material in the electrode expands and contracts with charging and discharging, making it susceptible to deterioration such as destruction of the active material or breakage of the conductive path due to this stress. Therefore, it is preferable to have an active material in which primary particles aggregate to form secondary particles rather than a single-particle active material consisting only of primary particles, as this reduces the stress of expansion and contraction and prevents deterioration. Furthermore, spherical or ellipsoidal particles are preferable to plate-shaped equiaxially oriented particles because they require less orientation during electrode molding, resulting in less expansion and contraction of the electrode during charging and discharging, and they are also easier to mix uniformly with conductive additives when creating the electrode.

[0088] The tap density of the positive electrode active material is typically 1.3 g / cm³. 3 Preferably 1.5 g / cm³ 3 More preferably 1.6 g / cm³ 3 In summary, the most preferred amount is 1.7 g / cm³. 3 The above is a summary. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, as does the amount of conductive additives and binders needed, which can restrict the packing rate of the positive electrode active material into the positive electrode active material layer and limit the battery capacity. By using metal composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the non-aqueous electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting step, which can easily degrade the load characteristics. Therefore, it is usually set at 2.5 g / cm³. 3 Preferably, 2.4 g / cm³ 3 The following applies:

[0089] The tap density of the positive electrode active material was determined by passing it through a sieve with a mesh size of 300 μm over 20 cm. 3After dropping the sample into the tapping cell to fill the cell volume, a powder density analyzer (e.g., TapDenser manufactured by Seishin Corporation) is used to perform 1000 taps with a stroke length of 10 mm. The density obtained from the volume and weight of the sample at that time is defined as the tap density.

[0090] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is typically 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most preferably 3 μm or more, and typically 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If it falls below the lower limit, it may not be possible to obtain a high bulk density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take longer, which may lead to a decrease in battery performance, or problems such as streaking may occur when preparing the positive electrode of the battery, i.e., when the positive electrode active material, conductive additives, binders, etc. are slurryed with a solvent and applied as a thin film. Here, the packing performance during positive electrode preparation can be further improved by mixing two or more positive electrode active materials with different median diameters d50.

[0091] In this disclosure, the median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with a measurement refractive index of 1.24.

[0092] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is typically 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, most preferably 0.1 μm or more, and typically 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. Exceeding the above upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the above lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals. The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a photograph at 10,000x magnification, finding the longest value of the intercept between the left and right boundaries of the primary particle relative to a horizontal line for any 50 primary particles, and taking the average value.

[0093] The BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g or more, preferably 0.3m 2 / g or more, more preferably 0.4m 2 For values ​​of / g or more, 4.0m 2 Less than or equal to / g, preferably 2.5m 2 / g or less, more preferably 1.5m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, it becomes difficult to increase the tap density, which can easily cause problems with the coating properties when forming the positive electrode active material.

[0094] The BET specific surface area is defined as the value measured by the nitrogen adsorption BET single-point method using the gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0095] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method is to dissolve or grind and disperse transition metal raw materials such as transition metal nitrates and sulfates, and raw materials of other elements as needed, in a solvent such as water, adjust the pH while stirring to create and recover spherical precursors, dry them as needed, and then add a Li source such as LiOH, Li2CO3, or LiNO3 and calcine at a high temperature to obtain the active material. Another method involves dissolving or grinding transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, and oxides, and raw materials of other elements as needed, in a solvent such as water. One method involves dispersing the material, drying and molding it with a spray dryer or the like to form a spherical or ellipsoidal precursor, adding a Li source such as LiOH, Li2CO3, or LiNO3, and firing it at a high temperature to obtain the active material. Another method involves dissolving or pulverizing and dispersing transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, or oxides, a Li source such as LiOH, Li2CO3, or LiNO3, and raw materials of other elements as needed, in a solvent such as water, drying and molding the mixture with a spray dryer or the like to form a spherical or ellipsoidal precursor, and firing it at a high temperature to obtain the active material.

[0096] Furthermore, the positive electrode active material may be used alone, or two or more materials with different compositions or different powder properties may be used in any combination and ratio.

[0097] When the secondary battery composition of this disclosure is used as a negative electrode slurry, a negative electrode active material is added to the slurry. The negative electrode active material can be any negative electrode active material known for use in secondary batteries.

[0098] The negative electrode active material is not particularly limited and includes, for example, lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbonaceous materials such as non-graphitizable carbon, silicon and silicon alloys, silicon-containing compounds, Li4Ti5O 12Examples include any of the above, or a mixture of two or more types. Among these, materials containing at least a portion of carbonaceous material, or silicon-containing compounds, can be used particularly suitably.

[0099] In this disclosure, the amount of active material particles in the electrode slurry is preferably 1 to 99.0% by mass relative to the total solid content of the slurry. The lower limit is more preferably 10% by mass, and even more preferably 20% by mass. The upper limit is more preferably 98% by weight, and even more preferably 97% by mass. By blending in the above proportions, the active material layer will contain the active material in the proportions described above.

[0100] (Conductive additive) In this disclosure, the electrode slurry may further contain a conductive additive as needed. The conductive additives used in this disclosure are not particularly limited as long as they can improve the conductivity in the target electrode, but examples include carbon black such as acetylene black and Ketjen black; carbon fibers such as multi-walled carbon nanotubes, single-walled carbon nanotubes, carbon nanofibers, and vapor-grown carbon fibers (VGCF); and metal powders such as SUS powder and aluminum powder.

[0101] When a conductive additive is used, it is typically contained in the solid content of the electrode slurry at a concentration of 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and typically 50% by mass or less, preferably 30% by mass or less, and more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0102] The slurry described above may contain materials other than those described above. However, the content of such materials is preferably 8% by mass or less, and more preferably 4% by mass or less, when the total volume of the slurry is considered as 100% by mass.

[0103] (Solid electrolyte) The solid electrolyte used in the composition for a secondary battery of the present disclosure may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, when a sulfide-based solid electrolyte is used, there is an advantage of flexibility.

[0104] Examples of the sulfide-based solid electrolyte include a lithium ion-conductive inorganic solid electrolyte satisfying the composition represented by the following formula (1). Li a1 M b1 P c1 S d1 A e1 (1) In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. A represents an element selected from I, Br, Cl, and F. a1 to e1 represent the composition ratios of the respective elements, and a1:b1:c1:d1:e1 satisfies 1 to 12:0 to 5:1:2 to 12:0 to 10. a1 is preferably 1 to 9, more preferably 1.5 to 7.5. b1 is preferably 0 to 3, more preferably 0 to 1. d1 is preferably 2.5 to 10, more preferably 3.0 to 8.5. e1 is preferably 0 to 5, more preferably 0 to 3.

[0105] In the present disclosure, the sulfide-based solid electrolyte preferably contains lithium. The sulfide-based solid electrolyte containing lithium is used in a solid battery using lithium ions as carriers, and is particularly preferable in terms of an electrochemical device having a high energy density.

[0106] The composition ratio of each element can be controlled by adjusting the blending amount of the raw material compounds when manufacturing the sulfide-based solid electrolyte as follows.

[0107] The sulfide-based solid electrolyte may be amorphous (glass) or crystalline (glass-ceramic), or partially crystalline. For example, a Li-PS glass containing Li, P, and S, or a Li-PS glass-ceramic containing Li, P, and S can be used. Sulfide-based solid electrolytes can be produced by the reaction of at least two raw materials from among lithium sulfide (Li2S), phosphorus sulfide (e.g., diphosphorus pentasulfide (P2S5)), elemental phosphorus, elemental sulfur, sodium sulfide, hydrogen sulfide, lithium halides (e.g., LiI, LiBr, LiCl), and sulfides of the element represented by M above (e.g., SiS2, SnS, GeS2).

[0108] As specific examples of sulfide-based solid electrolytes, the following are examples of raw material combinations: For example, Li2S-P2S5-LiCl, Li2S-P2S5-H2S, Li2S-P2S5-H2S-LiCl, Li2S-LiI-P2S5, Li2S-LiI-Li2O-P2S5, Li2S-LiBr-P2S5, Li2S-Li2O-P2S5, Li2S-Li3PO4-P2S5, Li2S-P2S5-P2O5, Li2S-P2S5-SiS2, Li2S-P2S5-SiS2-LiCl, Li2S-P2S5-SnS, Li2S-P2S5-Al2S3, 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-P2S5-LiI, Li2S-SiS2-LiI, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li 10 GeP2S 12 These are some examples. However, the mixing ratio of each ingredient is not specified.

[0109] The oxide-based solid electrolyte described above is preferably a compound that contains oxygen atoms (O), has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is also an electronically insulating compound.

[0110] Specific compound examples include, for example, Li xa La ya TiO3 [xa = 0.3 to 0.7, ya = 0.3 to 0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (M bb is at least one element of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, xb satisfies 5 ≤ xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ nb ≤ 20.)、Li xc B yc M cc zc O nc (M cc is at least one element of C, S, Al, Si, Ga, Ge, In, Sn, xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.)、Li xd (Al, Ga) yd (Ti, Ge) zd Si ad P md O nd (However, 1 ≤ xd ≤ 3, 0 ≤ yd ≤ 1, 0 ≤ zd ≤ 2, 0 ≤ ad ≤ 1, 1 ≤ md ≤ 7, 3 ≤ nd ≤ 13)、Li (3-2xe) M ee xe D ee O (xe represents a number from 0 to 0.1, M ee represents a divalent metal atom. D ee represents a halogen atom or a combination of two or more halogen atoms.)、Li xf Si yf O zf (1 ≤ xf ≤ 5, 0 < yf ≤ 3, 1 ≤ zf ≤ 10)、Li xg S yg O zg (1 ≤ xg ≤ 3, 0 < yg ≤ 2, 1 ≤ zg ≤ 10)、Li3BO3 - Li2SO4、Li2O - B2O3 - P2O5、Li2O - SiO2、Li6BaLa2Ta2O 12Li3PO (4-3 / 2w) N w (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xh Si yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include (LLZ). Furthermore, ceramic materials in which elemental substitution has been performed on LLZ are also known. For example, it is preferable to use materials containing at least one element selected from the group consisting of Mg, Al, Si, Ca (calcium), Ti, V (vanadium), Ga (gallium), Sr, Y (yttrium), Nb (niobium), Sn (tin), Sb (antimony), Ba (barium), Hf (hafnium), Ta (tantalum), W (tungsten), Bi (bismuth), and lanthanide elements. Even more preferable are LLZ-based ceramic materials in which at least one elemental substitution has been performed on LLZ, consisting of Mg (magnesium) and A (A being at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)). Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON and LiPOD, which are lithium phosphates in which some of the oxygen is replaced with nitrogen. 1 (D 1 Examples include at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. Also, LiA 1 ON(A 1(At least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used.

[0111] The above oxide-based solid electrolyte preferably contains lanthanum. Oxide-based solid electrolytes containing lanthanum are particularly preferred in terms of good Li-ion conductivity.

[0112] The above oxide-based solid electrolyte is preferably a garnet-type ion-conducting oxide. Selecting one with such a structure is preferable in terms of good Li ion conductivity.

[0113] The volume-average particle diameter of the above solid electrolyte is not particularly limited, but is preferably 0.01 μm or larger, and more preferably 0.03 μm or larger. The upper limit of the volume-average particle diameter is preferably 100 μm or smaller, and more preferably 50 μm or smaller. The average particle size of solid electrolyte particles is measured using the following procedure: Dilute the solid electrolyte particles in a 20 ml sample bottle with water (or heptane if the substance is unstable in water) to prepare a 1% by mass dispersion. Irradiate the diluted dispersion sample with 1 kHz ultrasound for 10 minutes and use it for testing immediately thereafter. Using this dispersion sample, acquire data 50 times using a laser diffraction / scattering particle size distribution analyzer LA-920 (HORIBA) at a temperature of 25°C with a quartz cell to obtain the volume-average particle size. For other detailed conditions, refer to JIS Z 8828:2013 "Particle size analysis - Dynamic light scattering method" as needed. Prepare five samples for each level and use their average value.

[0114] When considering the reduction of interfacial resistance and the maintenance of the reduced interfacial resistance when used in a solid-state secondary battery, the content of the solid electrolyte in the solid component of the solid electrolyte composition is preferably 3% by mass or more, more preferably 4% by mass or more, and particularly preferably 5% by mass or more, per 100% by mass of the solid component in the electrodes. From a similar viewpoint, the upper limit of the solid electrolyte content is preferably 99% by mass or less, more preferably 90% by mass or less, and particularly preferably 80% by mass or less. Furthermore, in the solid electrolyte layer placed between the positive electrode and the negative electrode, it is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. From a similar viewpoint, the upper limit of the solid electrolyte content is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, and particularly preferably 99.7% by mass or less. The above solid electrolyte may be used alone or in combination of two or more types. In this specification, "solid content" refers to components that do not volatilize or evaporate when dried at 170°C under a nitrogen atmosphere for 6 hours. Typically, this refers to components other than the dispersion medium described above.

[0115] When the total mass of the slurry is 100% by mass, the solvent content is preferably 10% by mass or more and 90% by mass or less. If the solvent content is less than 10% by mass, the solvent content is too low, and binders, active materials, etc., may not dissolve in the solvent, which may hinder the formation of the layer that forms the secondary battery. On the other hand, if the solvent content exceeds 90% by mass, the solvent content is too high, which may make it difficult to control the basis (coating) of the slurry. When the total mass of the slurry is 100% by mass, the solvent content is more preferably 20% by mass or more and 70% by mass or less, and even more preferably 25% by mass or more and 65% by mass or less.

[0116] The slurry described above preferably contains 0.1 to 9.5 parts by mass of the aforementioned fluorine-containing polymer as a binder, per 100 parts by mass of the total solid content in the slurry. If there is too little binder, the adhesion within the electrode layer and the adhesion between the negative electrode layer and the current collector will be poor when used as electrodes, which may make it difficult to handle the electrodes. If there is too much binder, the resistance of the electrodes will increase, which may prevent the acquisition of a solid-state battery with sufficient performance.

[0117] In this disclosure, the amount of solid content (electrode active material, solid electrolyte, and binder) relative to the solvent in the step of preparing the slurry is not particularly limited, but it is preferable, for example, that the solid content in the slurry be 30% by mass or more and 75% by mass or less. With such a solid content ratio, electrodes or solid electrolyte layers can be manufactured more easily. The lower limit of the solid content ratio is more preferably 50% by mass or more, and the upper limit of the solid content ratio is more preferably 70% by mass or less.

[0118] In the process of preparing the slurry described above, the components described above are mixed to form the slurry. The order in which the components are mixed is not particularly limited; each component can be added to the solvent and mixed. However, from the viewpoint of obtaining a slurry in which the binder is dissolved, it is preferable to mix them in the following manner.

[0119] In preparing the slurry, it is preferable to first prepare a binder solution by dissolving the aforementioned binder in the aforementioned solvent, and then mix it with other materials.

[0120] In this disclosure, it is preferable to prepare the slurry using the following procedure. (1) Add the above-mentioned binder to the solvent to obtain a binder solution containing the binder. (2) In the case of an electrode slurry, the binder solution obtained in (1), the separately prepared positive electrode active material or negative electrode active material, and a solid electrolyte as needed are added to the solvent and stirred to obtain an "electrode slurry" in which the active material, binder, etc. are dispersed in the solvent. Further solvent is added and dispersion treatment is performed using a stirrer or the like to prepare an "electrode slurry" of a predetermined viscosity in which the electrode active material, solid electrolyte, and binder remain highly dispersed in the solvent. A conductive additive may be added in step (2) as needed. (3) In the case of a slurry for a solid electrolyte layer, the binder solution obtained in (1) and a separately prepared solid electrolyte are added to the solvent, and dispersion treatment is performed using a stirrer or the like to obtain a "slurry for a solid electrolyte layer" in which the solid electrolyte and binder are highly dispersed in the solvent. Further solvent is added and dispersion treatment is performed using a stirrer or the like to prepare a "slurry for a solid electrolyte layer" with a predetermined viscosity while the solid electrolyte and binder remain highly dispersed in the solvent. A conductive additive may be added in step (3) as needed.

[0121] In this way, by adding the binder, electrode active material, and / or solid electrolyte in stages and performing sequential dispersion treatment, a slurry in which each component is highly dispersed in the solvent can be easily obtained. The same applies when adding other optional components (such as conductive additives); it is preferable to add them while performing sequential dispersion treatment. However, it is possible to obtain a slurry even when the binder, electrode active material, solid electrolyte, and optional components are added to the solvent at the same time and dispersed in a single process. As an example of a dispersion process, the above-mentioned agitator can be used. Other methods, such as dispersion using a homogenizer, are also possible.

[0122] In the process of preparing the slurry, the mixing ratio of the binder, electrode active material, and / or solid electrolyte can be any known mixing ratio that allows each layer to function properly when formed.

[0123] The slurry described above can be used to form electrodes for secondary batteries and / or electrolyte layers for solid-state batteries. The method for manufacturing electrodes for secondary batteries is not particularly limited, but it can be carried out by (1) preparing a substrate, (2) preparing a slurry, and (3) coating the slurry to form electrodes for secondary batteries. The following explains steps (1) to (3) in order.

[0124] Process (1) Preparation of the base material The substrate used in this disclosure is not particularly limited, as long as it has a flat surface to which a slurry can be applied. The substrate may be in the form of a plate or a sheet. The substrate may be pre-fabricated or a commercially available product.

[0125] The substrate used in this disclosure may be used in a secondary battery after forming electrodes for a secondary battery and / or an electrolyte layer for a solid battery, or it may not be a material for a secondary battery. Examples of substrates used in secondary batteries include electrode materials such as current collectors and solid electrolyte layer materials such as solid electrolyte membranes. The electrodes for a secondary battery and / or an electrolyte layer for a solid battery obtained by using the slurry of this disclosure can also be used as a substrate, and further electrodes for a secondary battery and / or an electrolyte layer for a solid battery can be formed thereon.

[0126] Examples of substrates that are not used as materials for secondary batteries include transfer substrates such as transfer sheets and transfer substrates. A secondary battery electrode and / or solid-state battery electrolyte layer formed on a transfer substrate can be bonded to the solid-state battery electrode and / or solid-state battery electrolyte layer by thermocompression bonding or the like, and then the transfer substrate can be peeled off to form a secondary battery electrode on the solid-state electrolyte layer. Alternatively, a secondary battery electrode formed on a transfer substrate can be bonded to a current collector by thermocompression bonding or the like, and then the transfer substrate can be peeled off to form a secondary battery electrode on an electrode current collector.

[0127] Step (2) Step to prepare the slurry This process can be carried out according to the slurry preparation method described above.

[0128] Step (3) Step of applying slurry to form an electrode for a secondary battery or an electrolyte layer for a solid battery. This process involves coating the slurry onto at least one surface of the substrate to form an electrode for a secondary battery or an electrolyte layer for a solid-state battery. The electrode for the secondary battery or the electrolyte layer for the solid battery may be formed on only one side of the substrate, or on both sides of the substrate.

[0129] The coating method and drying method for the slurry can be selected as appropriate. For example, coating methods include spraying, screen printing, doctor blade, bar coating, roll coating, gravure printing, and die coating. Furthermore, drying methods include, for example, vacuum drying, heat drying, and vacuum-heated drying. There are no restrictions on the specific conditions for vacuum drying and heat drying; they can be set as appropriate.

[0130] The amount of slurry to be applied varies depending on the slurry composition and the intended use of the secondary battery electrodes, but in a dry state, it is 5-30 mg / cm³. 2 It should be set to a certain extent. Furthermore, while the thickness of the electrodes for secondary batteries is not particularly limited, it should be approximately 10 to 250 μm.

[0131] This disclosure also relates to an electrode for a secondary battery, characterized by having a polymer containing a structural unit represented by general formula (1) and an active material layer containing an active material. When used as an electrode for a solid-state secondary battery, the active material layer further contains a solid electrolyte.

[0132] The above-mentioned electrode for the secondary battery may include, in addition to the active material layer, a current collector and a lead connected to the current collector.

[0133] The thickness of the active material layer used in this disclosure varies depending on the intended application of the secondary battery, but is preferably 10 to 250 μm, particularly preferably 20 to 200 μm, and most preferably 30 to 150 μm.

[0134] The current collector used in this disclosure is not particularly limited as long as it has the function of collecting current from the active material layer described above. Examples of materials for the positive electrode current collector include aluminum, stainless steel (SUS), nickel, iron, titanium, chromium, gold, platinum, and zinc, with aluminum and SUS being preferred. Examples of shapes for the positive electrode current collector include foil, plate, and mesh, with foil being preferred.

[0135] The positive electrode for secondary batteries according to this disclosure exhibits excellent adhesive strength by setting the content ratio of the binder to 0.5 to 10% by mass of the positive electrode for secondary batteries (preferably the electrode active material layer), and the secondary battery using this positive electrode exhibits high output.

[0136] The negative electrode current collector used in this disclosure is not particularly limited as long as it has the function of collecting current from the negative electrode active material layer described above. Examples of materials for the negative electrode current collector include chromium, stainless steel (SUS), nickel, iron, titanium, copper, cobalt, and zinc, with copper, iron, and SUS being preferred. Examples of shapes for the negative electrode current collector include foil, plate, and mesh, with foil being preferred.

[0137] The negative electrode for secondary batteries according to this disclosure exhibits excellent adhesive strength by setting the content ratio of the binder to 0.5 to 10% by mass of the negative electrode for secondary batteries (preferably the electrode active material layer), and a sulfide-based solid battery using this negative electrode exhibits high output.

[0138] Furthermore, this disclosure also relates to a polymer containing a structural unit represented by general formula (1) and a solid electrolyte layer containing a solid electrolyte. The solid electrolyte used may be the solid electrolyte described above.

[0139] The secondary battery composition disclosed herein can also be used as a separator slurry. Furthermore, this disclosure also relates to a separator for secondary batteries that contains a polymer containing the structural unit represented by the above general formula (1). The separator will be described in detail below.

[0140] The separator of this disclosure preferably comprises a porous substrate and a composite porous membrane formed on the porous substrate. The composite porous membrane preferably comprises the fluorine-containing polymer and at least one inorganic particle selected from the group consisting of metal oxide particles and metal hydroxide particles. The composite porous membrane preferably further comprises organic particles.

[0141] The content of the above-mentioned fluorine-containing polymer is preferably 50% by mass or less in the composite porous membrane. If the concentration exceeds 50% by mass, the porosity of the composite porous membrane may decrease too much, potentially preventing it from performing its ion-permeable function as a separator. The content of the above-mentioned fluorine-containing polymer is preferably 1% by mass or more in the composite porous membrane, as insufficient adhesion between inorganic particles may lead to a significant decrease in the mechanical properties of the composite porous membrane. The content of the above-mentioned fluorine-containing polymer in the composite porous membrane is more preferably 45% by mass or less, even more preferably 40% by mass or less, more preferably 2% by mass or more, even more preferably 3% by mass or more, and particularly preferably 4% by mass or more.

[0142] The above-mentioned composite porous membrane contains at least one inorganic particle selected from the group consisting of metal oxide particles and metal hydroxide particles. The inorganic particle content is preferably 50 to 99% by mass of the composite porous membrane. When the inorganic particle content is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder lithium ion permeability is laminated. Furthermore, a separator with high heat resistance and minimal thermal shrinkage can be realized. The content of the above inorganic particles in the composite porous membrane is more preferably 55% by mass or more, even more preferably 60% by mass or more, more preferably 98% by mass or less, even more preferably 97% by mass or less, and particularly preferably 96% by mass or less.

[0143] The inorganic particles described above preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. The lower limit of the average particle diameter is preferably 0.001 μm. The average particle size mentioned above is a value obtained by measuring it using a transmission electron microscope, a laser-type particle size distribution analyzer, or the like.

[0144] As for the metal oxide particles mentioned above, metal oxides other than alkali metals or alkaline earth metals are preferred from the viewpoint of improving the ion conductivity and shutdown effect of the separator, and at least one selected from the group consisting of aluminum oxide, silicon oxide, titanium oxide, vanadium oxide, and copper oxide is more preferred.

[0145] The above metal oxide particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. The lower limit of the above average particle diameter is preferably 0.001 μm. The average particle size mentioned above is a value obtained by measurement using a transmission electron microscope.

[0146] Particularly preferred metal oxide particles are aluminum oxide particles or silicon oxide particles with an average particle diameter of 5 μm or less, due to their excellent ionic conductivity.

[0147] The content of the above-mentioned metal oxide particles is preferably 50 to 99% by mass in the composite porous membrane. When the content of the above-mentioned metal oxide particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. Furthermore, a separator with high heat resistance and low thermal shrinkage can be realized. The content of the above metal oxide particles in the composite porous membrane is more preferably 55% by mass or more, even more preferably 60% by mass or more, more preferably 98% by mass or less, even more preferably 97% by mass or less, and particularly preferably 96% by mass or less.

[0148] As for the metal hydroxide particles mentioned above, alkali metal or alkaline earth metal hydroxides are preferred from the viewpoint of improving the ion conductivity and shutdown effect of the separator, and at least one selected from the group consisting of magnesium hydroxide, calcium hydroxide, aluminum hydroxide, chromium hydroxide, zirconium hydroxide, and nickel hydroxide is more preferred.

[0149] The above metal hydroxide particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. The lower limit of the above average particle diameter is preferably 0.001 μm. The average particle size mentioned above is a value obtained by measurement using a transmission electron microscope.

[0150] The content of the above-mentioned metal hydroxide particles is preferably 50 to 99% by mass in the composite porous membrane. When the content of the above-mentioned metal hydroxide particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. Furthermore, a separator with high heat resistance and low thermal shrinkage can be realized. The content of the above-mentioned metal hydroxide particles in the composite porous membrane is more preferably 55% by mass or more, even more preferably 60% by mass or more, more preferably 98% by mass or less, and even more preferably 97% by mass or less.

[0151] The above-mentioned composite porous membrane preferably further contains organic particles. The organic particles are preferably non-conductive crosslinked polymers, and more preferably crosslinked polystyrene, crosslinked polymethacrylate, and crosslinked acrylate.

[0152] The above organic particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. The lower limit of the above average particle diameter is preferably 0.001 μm. The average particle size mentioned above is a value obtained by measurement using a transmission electron microscope.

[0153] The content of the above-mentioned organic particles is preferably 0 to 49% by mass in the composite porous membrane. When the content of the above-mentioned organic particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. The content of the above organic particles in the composite porous membrane is more preferably 2% by mass or more, even more preferably 5% by mass or more, more preferably 37% by mass or less, and even more preferably 35% by mass or less.

[0154] The above-mentioned composite porous membrane may further contain other components in addition to the fluorine-containing polymer, inorganic particles, and organic particles described above. Examples of other components include other resins and rubbers. Preferred resins to be used in combination include, for example, one or more of the following: polyacrylate, polymethacrylate, polyacrylonitrile, polyamide-imide, polyvinylidene fluoride (PVdF), and VdF / HEP copolymer resins. Preferred rubbers to be used in combination include, for example, one or more types of VdF / HFP copolymer rubber, VdF / TFE / HFP copolymer rubber, and acrylic rubber. These rubbers may or may not be crosslinked.

[0155] Particularly preferred resins or rubbers to be used in combination include acrylic rubber from the viewpoint of improving ionic conductivity, and VdF / HFP copolymer rubber, VdF / TFE / HFP copolymer rubber, and VdF / HFP resin from the viewpoint of improving both ionic conductivity and oxidation resistance.

[0156] The VdF / HFP copolymer rubber preferably has a molar ratio of 80 / 20 to 65 / 35 in terms of VdF units to HFP units. The VdF / TFE / HFP copolymer rubber preferably has a molar ratio of 80 / 5 / 15 to 60 / 30 / 10 for VdF units, HFP units, and TFE units. The VdF / HFP resin preferably has a molar ratio of 98 / 2 to 85 / 15 in terms of VdF units / HFP units. VdF / HFP resin preferably has a melting point of 100 to 200°C.

[0157] The amount of other resins or rubbers added is preferably 400 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less, per 100 parts by mass of the fluorine-containing polymer. The lower limit varies depending on the desired effect, but is about 10 parts by mass.

[0158] The above-mentioned composite porous membrane is preferably provided on a porous substrate, and more preferably provided directly on the porous substrate. Furthermore, the composite porous membrane may be provided on only one side of the porous substrate, or on both sides. Also, the composite porous membrane may be provided so as to cover the entire porous substrate on which the composite porous membrane is provided, or so as to cover only a part of it.

[0159] The weight of the above-mentioned composite porous membrane is 0.5 to 50.0 g / m² when the composite porous membrane is formed on only one side of the porous substrate. 2 A range of 0.5 g / m² is preferred. 2 Using less than 50.0 g / m² may result in insufficient adhesion to the electrodes. 2 If the amount is too high, it tends to impede ion conduction and degrade the load characteristics of the battery, which is undesirable. When forming the above composite porous film on both the front and back surfaces of a porous substrate, the weight of the above fluorine-containing polymer should be 0.1 to 6.0 g / m². 2 It is preferable.

[0160] The porous substrates mentioned above refer to substrates that have voids or cavities inside. Examples of such substrates include microporous membranes, porous sheets made of fibrous materials such as nonwoven fabrics and laminated sheets, or composite porous membranes in which one or more other porous layers are laminated onto these microporous membranes or porous sheets. A microporous membrane refers to a membrane that has a large number of fine pores inside, in which these fine pores are interconnected, and which allows gas or liquid to pass from one side to the other.

[0161] The materials constituting the porous substrate can be either electrically insulating organic or inorganic materials. In particular, from the viewpoint of providing the substrate with a shutdown function, it is preferable to use a thermoplastic resin as the constituent material of the substrate. Here, the shutdown function refers to the function that, when the battery temperature rises, melts the thermoplastic resin and blocks the pores of the porous substrate, thereby blocking ion movement and preventing thermal runaway of the battery. Suitable thermoplastic resins have a melting point of less than 200°C, and polyolefins are particularly preferred.

[0162] As a porous substrate using polyolefin, a polyolefin microporous membrane is preferred. As the polyolefin microporous membrane, a conventional polyolefin microporous membrane used in separators for non-aqueous secondary batteries, which has sufficient mechanical properties and ion permeability, can be used. Furthermore, from the viewpoint of having the shutdown function described above, it is preferable that the polyolefin microporous membrane contains polyethylene.

[0163] Polyolefins with a weight-average molecular weight of 100,000 to 5,000,000 are preferable. If the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. Conversely, if the weight-average molecular weight is greater than 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult.

[0164] Such polyolefin microporous membranes can be manufactured by, for example, the following methods: (i) extruding molten polyolefin resin from a T-die to form a sheet, (ii) subjecting the sheet to a crystallization treatment, (iii) stretching the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane. Another method involves (i) melting polyolefin resin together with a plasticizer such as liquid paraffin, extruding it from a T-die, and cooling it to form a sheet, (ii) stretching the sheet, (iii) extracting the plasticizer from the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane.

[0165] As porous sheets made of fibrous materials, porous sheets can be made of fibrous materials made of polyester such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, heat-resistant polymers such as aromatic polyamides and polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides, or mixtures thereof.

[0166] The above-mentioned porous substrate may be a composite porous substrate in which a functional layer is further laminated. The above-mentioned composite porous substrate is preferable in that further functionality can be added by a functional layer. As a functional layer, for example, from the viewpoint of providing heat resistance, a porous layer made of a heat-resistant resin or a porous layer made of a heat-resistant resin and an inorganic filler can be used. Examples of heat-resistant resins include one or more heat-resistant polymers selected from aromatic polyamides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Suitable inorganic fillers include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. As for composite formation methods, methods include coating the porous sheet with a functional layer, joining with an adhesive, and heat-pressing.

[0167] In this disclosure, the porous substrate is preferably made of at least one resin selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, polyester, and polyacetal.

[0168] In this disclosure, the film thickness of the porous substrate is preferably in the range of 5 to 50 μm from the viewpoint of obtaining good mechanical properties and internal resistance.

[0169] The separator of this disclosure can be manufactured by laminating the composite porous membrane on the porous substrate. The lamination method is not particularly limited, and conventionally known methods may be employed. Specifically, preferred methods include roll coating a solution or dispersion obtained by dissolving or dispersing the fluorine-containing polymer, inorganic particles, and other components as needed in a solvent or water onto a porous substrate; dipping the porous substrate into the solution or dispersion; and coating the porous substrate with the solution or dispersion and then immersing it in a suitable coagulation solution.

[0170] Alternatively, a film made of the above-mentioned composite porous membrane may be prepared in advance, and the film and the porous substrate may be laminated together by a method such as lamination. An example of a method for preparing the above-mentioned composite porous membrane is to cast a solution or dispersion obtained by dissolving or dispersing the above-mentioned fluorine-containing polymer, the above-mentioned inorganic particles, and other components as needed in a solvent onto a film having a smooth surface such as a polyester film or an aluminum film, and then peel it off.

[0171] Suitable solvents include amide solvents such as dimethylacetamide (DMAC), ketone solvents such as acetone, and cyclic ether solvents such as tetrahydrofuran. Alternatively, the fluorine-containing polymer and any other components may be dispersed in water before use.

[0172] The solution or dispersion containing the above-mentioned fluorine-containing polymer and inorganic particles may, in the case of an aqueous system, be prepared by adding a viscosity-adjusting thickener (stabilizer). Examples of the thickening agents (stabilizers) mentioned above include carboxyalkylcellulose, alkylcellulose, and hydroxyalkylcellulose.

[0173] A preferred method for forming the composite porous film on the porous substrate is to apply a slurry-like coating liquid containing the fluorine-containing polymer, the inorganic particles, and water, etc., to the porous substrate by a known method and then dry it. The slurry-like coating liquid may also contain the organic particles, thickeners, etc.

[0174] The slurry coating liquid described above preferably contains 0.5 to 25% by mass of the fluorine-containing polymer, more preferably 1% by mass or more, and even more preferably 20% by mass or less. The concentration of the fluorine-containing polymer can be adjusted according to the mixing ratio of the fluorine-containing polymer, inorganic particles, and water.

[0175] The slurry-like coating liquid described above preferably contains 1 to 60% by mass of the inorganic particles, more preferably 2% by mass or more, and even more preferably 55% by mass or less. The concentration of the inorganic particles can be adjusted according to the mixing ratio of the fluorine-containing polymer, inorganic particles, and water.

[0176] If the above slurry-like coating liquid contains organic particles, it is preferable that it contains 1 to 60% by mass, more preferably 2% by mass or more, and even more preferably 55% by mass or less. The concentration of the above organic particles can be adjusted according to the mixing ratio of the fluorine-containing polymer, inorganic particles, and water.

[0177] If the above-mentioned slurry-like coating liquid contains a thickening agent, it is preferable that it contains 0.1 to 20% by mass. The concentration of the thickening agent can be adjusted according to the amount of thickening agent added to the slurry-like coating liquid.

[0178] This disclosure also relates to a secondary battery characterized by comprising the above-described electrodes and / or separator for secondary batteries. The secondary battery is preferably a lithium-ion battery. In particular, the secondary solid-state battery is a solid-state battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein the positive electrode and / or the negative electrode contain the above-mentioned fluorine-containing polymer.

[0179] The positive and negative electrodes used in the secondary battery of this disclosure are the same as those for secondary battery electrodes described above. Below, the solid electrolyte layer, separator, and battery case, which are suitably used in the secondary battery of this disclosure, will be described in detail.

[0180] The solid electrolyte layer used in the secondary battery of this disclosure is not particularly limited, but preferably contains the solid electrolyte described above. The solid electrolyte layer of this disclosure described above may be used. The solid electrolyte layer used in the secondary battery of this disclosure is preferably a layer made of a sulfide-based solid electrolyte.

[0181] The secondary battery of this disclosure may include a separator between the positive electrode and the negative electrode. Examples of the separator include the separator of this disclosure described above, porous membranes such as polyethylene and polypropylene, and nonwoven fabrics such as resin nonwoven fabrics such as polypropylene and glass fiber nonwoven fabrics.

[0182] The secondary battery of this disclosure may further include a battery case. The shape of the battery case used in this disclosure is not particularly limited as long as it can house the positive electrode, negative electrode, electrolyte layer, etc. as described above, but specific examples include cylindrical, prismatic, coin-type, laminated type, etc. The shape and configuration of the positive electrode, negative electrode, and separator may be changed and used according to the shape of each battery.

[0183] For example, a method for manufacturing a solid-state battery is a method for manufacturing a solid-state battery including a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, the method including a step of preparing the solid electrolyte layer, a step of kneading a positive electrode or negative electrode active material, a solid electrolyte, a binder, and a solvent or dispersion medium to prepare a slurry, and a step of manufacturing the solid-state battery by applying the slurry to one surface of the solid electrolyte layer to form a positive electrode and applying the negative electrode to the other surface of the solid electrolyte layer.

Example

[0184] Hereinafter, the present disclosure will be specifically described based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "mass %", respectively.

[0185] (Method for manufacturing a fluoropolymer)

[0186] (Monomer represented by general formula (10)) The E-form of 1,2-difluoroethylene used in each of the following examples had a purity of 99.9 mass% or more. The purity was confirmed by GC / MS to have no impurity peaks and was set to 99.9 mass%. A high-purity monomer was obtained by manufacturing according to the examples of Patent Document 1 and performing separation by preparative gas chromatography.

[0187] (Polymerization method) Polymers were polymerized by a polymerization method according to each of the following synthesis examples. The obtained polymers were evaluated based on the following evaluation criteria.

[0188] (Dimethylacetamide (DMAC) solubility) 0.9 g of DMAC was added to 0.1 g of the resin obtained from each synthesis example, and the mixture was stirred using a stirrer. When it was confirmed that there was no residue after 1 hour, it was considered to be dissolved.

[0189] (Composition analysis) The copolymer composition was measured by solution NMR or melt NMR. <Solution NMR method> Measurement device: Varian VNMRS400 Resonance frequency: 376.04 (Sfrq) Pulse width: 30° <Fusion NMR Method> Measurement device: Bruker Japan AVANCE300 Resonance frequency: 282.40[MHz] Pulse width: 45°

[0190] (molecular weight) [Weight average molecular weight (Mw)] Based on the results measured by the GPC method, the molecular weight was calculated using standard polystyrene as a reference. Depending on the type of polymer, the following methods were used for measurement. GPC device: TOSOH HLC-8020 Columns: 2 x Shodex GPC806M, 1 x GPC801, 1 x GPC802 Developing solvent: Tetrahydrofuran [THF] Sample concentration: 0.1% by mass Measurement temperature: 40℃

[0191] GPC equipment: TOSOH AS-8010, CO-8020, and SIMADZURID-10A Columns: GMHHR-H (3 pieces) Developing solvent: Dimethylformamide [DMF] Sample concentration: 0.05% by mass Measurement temperature: 40℃

[0192] (Melting point) The measurement can be performed using a differential scanning calorimeter in accordance with ASTM D4591. Specifically, a differential scanning calorimeter RDC220 (manufactured by Seiko Instruments) was used to measure the thermal properties of the copolymer at a heating rate of 10°C / min, and the maximum value in the resulting heat of fusion curve was defined as the melting point.

[0193] (Slurry stability test) The slurry viscosity was measured immediately after preparation of the mixture and 5 days after preparation, and the stability of the slurry was evaluated based on the following calculation formula. Slurry viscosity was measured using a Type B viscometer (Toki Sangyo Co., Ltd., TV-10M) under the conditions of 25°C, rotor No. M4, and rotation speed of 6 rpm. The value obtained 10 minutes after the start of measurement was adopted as the slurry viscosity of the mixture. Slurry stability (%) = Viscosity 3 days after mixing preparation / Viscosity immediately after mixing preparation × 100

[0194] Furthermore, the following positive electrode active material and conductive additive were used in the examples and comparative examples. NMC622: LiNi 0.6 Mn 0.2 Co 0.2 O2 AB: Acetylene Black

[0195] Polymer Synthesis Example 1 1,330 g of deionized water and 0.67 g of methylcellulose were introduced into a 1.8 liter autoclave, and the autoclave was then thoroughly purged with nitrogen under vacuum. Subsequently, the autoclave was degassed under vacuum, and 250 g of 1,2-difluoroethylene E, 1 ml of methanol, and 2 g of dinormal propyl peroxydicarbonate were added to the vacuum-sealed autoclave. The mixture was heated to 45°C over 1.5 hours, maintained at 45°C for 3 hours, and then an additional 4 g of dinormal propyl peroxydicarbonate was introduced. The temperature was then maintained at 45°C for 4 hours. The maximum pressure reached during this time was 2.7 MPaG. After that, the pressure was released back to atmospheric pressure, the reaction product was washed with water, and dried to obtain 198 g of fluororesin powder. The melting point was 198.3°C.

[0196] Polymer Synthesis Example 2 A 1.8 L stainless steel autoclave was thoroughly purged with vacuum nitrogen. Then, the autoclave was degassed under vacuum. Into the vacuum-sealed autoclave, 1000 g of HFE-347pc-f, 197 g of 1,2-difluoroethylene E, and 128 g of vinylidene fluoride (VdF) were introduced, and the autoclave was heated to 25°C. Next, 10.5 g of an 8% di(ω-hydrododecafluoroheptanoyl) peroxide (hereinafter abbreviated as "DHP") perfluorohexane solution was added to the autoclave to initiate polymerization. The starting pressure was 1.04 MPaG. To maintain polymerization pressure, a mixed gas of 1,2-difluoroethylene / VdF = 86.0 / 14.0 (mol%) was flowed through the autoclave, and the temperature inside the autoclave was maintained at 25°C for 6.3 hours. After that, the pressure was released to return to atmospheric pressure, the reaction product was washed with water, and dried to obtain 86 g of fluororesin powder. The obtained resin contained 1,2-difluoroethylene and VdF in a molar ratio of 86.1 / 13.9. The melting point was 197.9°C.

[0197] Polymer Synthesis Example 3 A 1.8 L stainless steel autoclave was thoroughly purged with vacuum nitrogen. Then, the autoclave was degassed under vacuum. Into the vacuum-sealed autoclave, 1000 g of HFE-347pc-f, 70 g of 1,2-difluoroethylene E isomer, and 250 g of VdF were introduced, and the autoclave was heated to 25°C. Next, 7.0 g of an 8% DHP perfluorohexane solution was added to the autoclave to initiate polymerization. The initial pressure was 1.40 MPaG. To maintain the polymerization pressure, a mixed gas of 1,2-difluoroethylene / VdF = 54.0 / 46.0 (mol%) was flowed, and the temperature inside the autoclave was maintained at 25°C for 6.2 hours. After that, the pressure was released back to atmospheric pressure, the reaction product was washed with water, and dried to obtain 91 g of fluororesin powder. The resulting resin contained 1,2-difluoroethylene and VdF in a molar ratio of 53.3 / 46.7. The melting point was 180.0°C.

[0198] Polymer Synthesis Example 4 The inside of a glass-lined stainless steel autoclave with an internal volume of 4.1 L was thoroughly replaced with vacuum nitrogen. Then, the inside of the autoclave was vacuum degassed, and after introducing 2300 g of HFE-347pc-f, 41 g of 1,2-difluoroethylene E-form, and 436 g of VdF into the autoclave in a vacuum state, the autoclave was heated to 25°C. Next, 14.0 g of an 8% DHP perfluorohexane solution was introduced into the autoclave to initiate polymerization. The pressure at the start was 1.11 MPaG. To maintain the polymerization pressure, a mixed gas of 1,2-difluoroethylene / VdF = 25.0 / 75.0 (mol%) was flowed, and the temperature inside the autoclave was maintained at 25°C for 3.3 hours. Then, the pressure was released to return to atmospheric pressure, and the reaction product was washed with water and dried to obtain 104 g of a fluororesin powder. The obtained resin contained 1,2-difluoroethylene and VdF in a molar ratio of 24.2 / 75.8. The melting point was 161.7°C.

[0199] Polymer Synthesis Example 5 The inside of a glass-lined stainless steel autoclave with an internal volume of 4.1 L was thoroughly replaced with vacuum nitrogen. Then, the inside of the autoclave was vacuum degassed, and after introducing 2300 g of HFE-347pc-f, 27 g of 1,2-difluoroethylene E-form, and 423 g of VdF into the autoclave in a vacuum state, the autoclave was heated to 25°C. Next, 14.0 g of an 8% DHP perfluorohexane solution was introduced into the autoclave to initiate polymerization. The pressure at the start was 1.06 MPaG. To maintain the polymerization pressure, a mixed gas of 1,2-difluoroethylene / VdF = 16.0 / 84.0 (mol%) was flowed, and the temperature inside the autoclave was maintained at 25°C for 3.4 hours. Then, the pressure was released to return to atmospheric pressure, and the reaction product was washed with water and dried to obtain 125 g of a fluororesin powder. The obtained resin contained 1,2-difluoroethylene and VdF in a molar ratio of 16.5 / 83.5. The melting point was 162.4°C.

[0200] Polymer Synthesis Example 6 The inside of a 0.5-liter autoclave was thoroughly purged with vacuum nitrogen. Then, the autoclave was degassed under vacuum. Into the vacuum-sealed autoclave, 150 g of HFE-347pc-f, 23 g of 1,2-difluoroethylene E, and 4 g of tetrafluoroethylene were introduced, and the autoclave was heated to 28°C. Next, 2.0 g of an 8% DHP perfluorohexane solution was added to the autoclave to initiate polymerization. The initial polymerization pressure was 0.5 MPaG. To maintain the polymerization pressure, a mixed gas of 1,2-difluoroethylene E / tetrafluoroethylene = 85 / 15 (mol%) was flowed, and the temperature inside the autoclave was maintained at 28°C for 5 hours and 15 minutes. After that, the pressure was released to return to atmospheric pressure, the reaction product was washed with water, and dried to obtain 12.2 g of fluororesin powder. The obtained resin contained 1,2-difluoroethylene E and tetrafluoroethylene in a molar ratio of 85.5 / 14.5. The melting point was 210.0°C.

[0201] Polymer Synthesis Example 7 The inside of a 0.5-liter autoclave was thoroughly purged with vacuum nitrogen. Then, the autoclave was degassed under vacuum. Into the vacuum-sealed autoclave, 150 g of HFE-347pc-f, 6.8 g of 1,2-difluoroethylene E, and 20 g of tetrafluoroethylene were introduced, and the autoclave was heated to 28°C. Next, 1.5 g of an 8% DHP perfluorohexane solution was added to the autoclave to initiate polymerization. The initial polymerization pressure was 0.5 MPaG. To maintain the polymerization pressure, a mixed gas of 1,2-difluoroethylene E / tetrafluoroethylene = 42 / 58 (mol%) was flowed, and the temperature inside the autoclave was maintained at 28°C for 1 hour and 50 minutes. After that, the pressure was released to return to atmospheric pressure, the reaction product was washed with water, and dried to obtain 13.1 g of fluororesin powder. The obtained resin contained 1,2-difluoroethylene E and tetrafluoroethylene in a molar ratio of 42.4 / 57.6. The melting point was 246.5°C.

[0202] Polymer Synthesis Example 8 In a 100 ml stainless steel (SUS) autoclave, 40 g of R-225 and 0.43 g of an 8% DHP perfluoroxane solution were placed. The autoclave was cooled to dry ice temperature, and after purging with nitrogen, 3.0 g of hexafluoropropylene (HFP) and 5.2 g of 1,2-difluoroethylene E were added. The mixture was shaken at 25°C for 13.0 hours using a shaker. The product was dried to obtain 2.41 g of fluororesin. The obtained resin contained 1,2-difluoroethylene E and HFP in a molar ratio of 99.2 / 0.8. The melting point was 188.5 degrees.

[0203] Polymer synthesis example 9 600 g of deionized water and 0.3 g of methylcellulose were introduced into a 1.8 liter autoclave, and the autoclave was then thoroughly purged with nitrogen under vacuum. Subsequently, the autoclave was degassed under vacuum, and 150 g of perfluorooctacyclobutane, 100 g of HFP, and 64 g of 1,2-difluoroethylene E were introduced into the vacuum-sealed autoclave, and the autoclave was heated to 35°C. Next, 1.5 g of dinormalpropyl peroxycarbonate was added to the autoclave to start polymerization. The polymerization pressure at the start was 1.16 MPaG. After maintaining the temperature inside the autoclave at 35°C for 7 hours, the pressure was released to return to atmospheric pressure, and the reaction product was washed with water and dried to obtain 17 g of fluororesin powder. The obtained resin contained 1,2-difluoroethylene E and HFP in a molar ratio of 94.9 / 5.1. The melting point was 151.2 degrees Celsius.

[0204] Polymer Synthesis Example 10 In a 100 ml stainless steel (SUS) autoclave, 40 g of R-225 and 0.43 g of 8% DHP perfluoroxane solution were charged. The autoclave was cooled to dry ice temperature, purged with nitrogen, and then 3.0 g of 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 9.1 g of 1,2-difluoroethylene E were added. The mixture was shaken at 25°C for 11.8 hours using a shaker. The product was dried to obtain 1.81 g of fluororesin. The obtained resin contained 1,2-difluoroethylene E and HFO-1234yf in a molar ratio of 96.5 / 3.5. The melting point was 205.9°C.

[0205] Polymer synthesis example 11 In a 100 ml stainless steel (SUS) autoclave, 40 g of R-225 and 0.43 g of 8% DHP perfluoroxane solution were charged. The autoclave was cooled to dry ice temperature, purged with nitrogen, and then 20.9 g of HFO-1234yf and 3.8 g of 1,2-difluoroethylene E were added. The mixture was shaken at 25°C for 13.2 hours using a shaker. The product was dried to obtain 1.23 g of fluororesin. The obtained resin contained 1,2-difluoroethylene E and HFO-1234yf in a molar ratio of 16.3 / 83.7. It did not have a melting point.

[0206] Polymer synthesis example 12 In a 100 ml stainless steel (SUS) autoclave, 40 g of R-225 and 0.42 g of an 8% DHP perfluoroxane solution were charged. The autoclave was cooled to dry ice temperature, and after purging with nitrogen, 6.0 g of perfluoromethyl vinyl ether (PMVE) and 10.2 g of 1,2-difluoroethylene E were added. The mixture was shaken at 25°C for 13.2 hours using a shaker. The product was dried to obtain 3.0 g of fluororesin. The obtained resin contained E and PMVE in a molar ratio of 95.3 / 4.5. The melting point was 173.3 degrees.

[0207] (Preparation of compositions for secondary batteries) Polymers from Synthesis Examples 1-12 were used as binders, NMC622 as the cathode active material, AB as the conductive additive, and DMAC as the solvent. The mixture was prepared by stirring to obtain a mixture with a mass ratio of active material / conductive additive / binder / solvent of 72.8 / 1.1 / 1.1 / 25. The mixture was allowed to stand at room temperature, and the slurry stability of the mixture was evaluated. The results are shown in Table 1.

[0208] (Electrode fabrication) The resulting mixture was uniformly applied to one side of a positive electrode current collector (aluminum foil with a thickness of 20 μm), and after the DMAC was completely evaporated, a positive electrode comprising a positive electrode material layer and a positive electrode current collector was fabricated by pressing with a pressure of 10 tons using a roll press machine. Table 1 shows the coating properties of the positive electrode material layer on the positive electrode current collector. The coating properties were evaluated visually based on the following criteria. ○...Electrodes with smooth surfaces were successfully fabricated without any problems. △...The electrodes were created, but the surface was rough. ×...The electrodes were created, but some parts were cracked.

[0209] [Table 1] [Industrial applicability]

[0210] The secondary battery composition disclosed herein can be suitably used for electrode formation in secondary batteries and the like, taking advantage of the fact that polymers having a structure derived from 1,2-difluoroethylene have excellent solubility in various organic solvents.

Claims

1. A composition for secondary batteries containing a fluorine-containing polymer and a solvent, The fluorine-containing polymer is a polymer consisting of structural units represented by the following general formula (1), or a polymer containing at least one structural unit selected from the group consisting of structural units represented by the following general formula (1) and structural units represented by the following general formulas (4) to (8). A composition for secondary batteries, characterized in that it is used for electrodes or solid electrolyte layers of secondary batteries. 【Chemistry 1】 【Chemistry 2】

2. The secondary battery composition according to claim 1, wherein the weight-average molecular weight of the fluorine-containing polymer is 50,000 to 5,000,000.

3. The secondary battery composition according to claim 1 or 2, wherein the proportion of structural units represented by general formula (1) in the fluorine-containing polymer is 0.1 to 100 mol%.

4. The secondary battery composition according to claim 1 or 2, wherein the solvent is at least one compound selected from the group consisting of ester compounds, ketone compounds, and amide compounds.

5. A secondary battery composition according to claim 1 or 2, which is for use as the positive electrode of a secondary battery.

6. A method for forming a layer for a secondary battery, comprising the steps of applying a slurry onto a substrate and heating and drying it, A method for forming a layer for a secondary battery, characterized in that the slurry contains the secondary battery composition described in claim 1 or 2.

7. An electrode for a secondary battery having an active material layer containing a fluorine-containing polymer and an active material, The electrode for a secondary battery is characterized in that the fluorine-containing polymer is a polymer consisting of structural units represented by the following general formula (1), or a polymer containing at least one structural unit selected from the group consisting of structural units represented by the following general formula (1) and structural units represented by the following general formulas (4) to (8). 【Transformation 3】 【Chemistry 4】

8. A solid electrolyte layer for a secondary battery containing a fluorine-containing polymer and a solid electrolyte, A solid electrolyte layer for a secondary battery, wherein the fluorine-containing polymer is a polymer consisting of structural units represented by the following general formula (1), or a polymer containing at least one structural unit selected from the group consisting of structural units represented by the following general formula (1) and structural units represented by the following general formulas (4) to (8). 【Transformation 5】 【Transformation 6】

9. A secondary battery characterized by comprising the electrode for secondary battery described in claim 7 and / or the solid electrolyte layer for secondary battery described in claim 8.

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