Composite solid electrolyte, and composite solid electrolyte secondary battery

Abstract

The present invention provides a novel composite solid electrolyte that enables solid electrolyte secondary batteries to exhibit excellent charge-discharge characteristics. The composite solid electrolyte comprises an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether.

Description

Technical Field

[0001] The present invention relates to a composite solid electrolyte and a composite solid electrolyte secondary battery.

Background Art

[0002] Conventionally, in non-aqueous electrolyte secondary batteries typified by lithium ion batteries, electrolytes in the form of solutions or pastes have been used from the viewpoint of ionic conductivity. However, since there is a risk of damage to devices due to liquid leakage, various safety measures are required, which has become an obstacle to the development of large-sized batteries.

[0003] In contrast, solid electrolytes in which electrolytes such as polymer solid electrolytes and inorganic solid electrolytes are solidified have been proposed. Polymer solid electrolytes generally have advantages such as excellent flexibility, bendability, and moldability, and a high degree of freedom in the design of applied devices. However, they have disadvantages such as poor load characteristics and low-temperature characteristics, so they are limited to battery applications that operate at high temperatures. On the other hand, although inorganic solid electrolytes have higher ionic conductivity than polymer solid electrolytes, the electrolyte is composed of crystalline or amorphous materials, and it is difficult to relieve volume changes caused by positive and negative electrode active materials during charge and discharge. Furthermore, due to the high interfacial resistance between the electrode and the electrolyte, there is a problem that the charge and discharge characteristics are insufficient.

[0004] As a method for reducing the interfacial resistance between the electrode and the electrolyte, it is known that mixing a polymer with an inorganic solid electrolyte can improve the binding property between the electrolyte and the electrode interface. For example, in Patent Document 1, a hydrogenated polymer such as hydrogenated styrene-butadiene rubber as a branched polymer is used as a binder for a sulfide-based solid electrolyte, but such a polymer does not reach the level of suppressing a decrease in ionic conductivity. In addition, in Patent Documents 2 and 3, polyethylene oxide (polyethylene glycol) having relatively high ionic conductivity is used, but polyethylene oxide has high crystallinity, a melting point of around 60°C as a polymer, and low ionic conductivity below the melting point. In addition, when heated above the melting point, it softens and cannot maintain its strength, and there is a problem that a short circuit due to fracture is likely to occur.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The main object of the present invention is to provide a novel composite solid electrolyte that exhibits excellent charge-discharge characteristics in a solid electrolyte secondary battery. Further, an object of the present invention is also to provide a composite solid electrolyte secondary battery including the composite solid electrolyte.

Means for Solving the Problems

[0007] The present inventors conducted intensive studies to solve the above problems. As a result, it was found that a composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether exhibits excellent charge-discharge characteristics in a solid electrolyte secondary battery. The present invention was completed by further studies based on such findings.

[0008] That is, the present invention provides an invention in the following aspects. Item 1. A composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether. Item 2. The composite solid electrolyte according to Item 1, wherein the branched polyether includes a structural unit formed from an ether compound having an ethylene oxide unit in a side chain. Item 3. The branched polyether-containing composite solid electrolyte according to Item 1 or 2, which contains a structural unit formed from at least one selected from the group consisting of allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate. Item 4. The branched polyether-containing composite solid electrolyte according to any one of Items 1 to 3, which is crosslinked. Item 5. The composite solid electrolyte according to any one of Items 1 to 4, wherein the inorganic solid electrolyte is an oxide-based solid electrolyte or a sulfide-based solid electrolyte. Item 6. A composite solid electrolyte secondary battery containing the composite solid electrolyte according to any one of Items 1 to 5.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a novel composite solid electrolyte that exhibits excellent charge and discharge characteristics in a solid electrolyte secondary battery. Furthermore, according to the present invention, it is also possible to provide a composite solid electrolyte secondary battery containing the composite solid electrolyte.

Modes for Carrying Out the Invention

[0010] The composite solid electrolyte of the present invention is characterized by containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether. By having such a configuration, when the composite solid electrolyte of the present invention is applied as the solid electrolyte of a solid electrolyte secondary battery, it can exhibit excellent charge and discharge characteristics in the solid electrolyte secondary battery. More specifically, since the composite solid electrolyte of the present invention contains a polymer solid electrolyte containing a branched polyether in addition to the inorganic solid electrolyte, compared with the case where the solid electrolyte is formed only by the inorganic solid electrolyte, the contact area of the interface between the electrode material layer and the solid electrolyte layer is large. As a result, it is considered that the interfacial resistance between the electrode and the electrolyte is reduced and excellent charge and discharge characteristics are exhibited. Also, in the composite solid electrolyte, it is considered that the polymer solid electrolyte reduces the resistance inside the composite solid electrolyte by adhering closely to the inorganic solid electrolyte. In addition, although a solid electrolyte secondary battery may be used in a high-temperature environment (for example, a high-temperature environment of 100°C or higher), by using the composite solid electrolyte of the present invention, excellent charge and discharge characteristics are exhibited in a high-temperature environment. Hereinafter, the composite solid electrolyte of the present invention and the solid electrolyte secondary battery using the same will be described in detail.

[0011] In this specification, numerical values connected by "~" mean a numerical range including the numerical values before and after "~" as the lower limit value and the upper limit value. When a plurality of lower limit values and a plurality of upper limit values are separately described, any lower limit value and upper limit value can be selected and connected by "~".

[0012] The composite solid electrolyte of the present invention contains at least an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether. Specifically, the composite solid electrolyte of the present invention is at least a mixture of an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether.

[0013] The branched polyether may contain a crosslinked body.

[0014] The branched polyether preferably contains a structural unit formed from an epoxy compound having an ethylene oxide unit in the side chain. That is, the branched polyether is preferably a polymer having, as at least a monomer, an epoxy compound having an ethylene oxide unit in the side chain.

[0015] Examples of the epoxy compound having an ethylene oxide unit in the side chain include a monomer represented by the following formula (2). The branched polyether using the monomer represented by the following formula (2), and optionally the monomer represented by the following formula (1) or the following formula (3), becomes a polyether (i) having an ethylene oxide unit in the side chain. Only one kind of the monomers represented by the formulas (1) to (3) may be used, or two or more kinds may be mixed and used.

[0016]

Chemical formula

[0017]

Chemical formula

[0018] [In formula (2), R is -CH2O(CH2CH2O) n R 4 and R 4 is an alkyl group having 1 to 6 carbon atoms, and n is a number from 0 to 12.]

[0019]

Chemical formula

[0020] [In formula (3), R 5 represents a group containing an ethylenically unsaturated group.]

[0021] As the monomer of formula (3), allyl glycidyl ether, 4-vinylcyclohexyl glycidyl ether, α-terpinyl glycidyl ether, cyclohexenylmethyl glycidyl ether, p-vinylbenzyl glycidyl ether, allylphenyl glycidyl ether, vinyl glycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-pentene, 4,5-epoxy-2-pentene, 1,2-epoxy-5,9-cyclododecadiene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5-cyclooctene, glycidyl acrylate, glycidyl methacrylate, glycidyl sorbate, glycidyl cinnamate, glycidyl crotonate, glycidyl-4-hexenoate are used. Preferably, allyl glycidyl ether, glycidyl acrylate ether, glycidyl methacrylate ether.

[0022] The synthesis of the polyether (i) having an ethylene oxide unit in the side chain can be carried out, for example, as follows. As a ring-opening polymerization catalyst, a coordination anion initiator such as a catalyst system mainly composed of organic aluminum, a catalyst system mainly composed of organic zinc, an organic tin-phosphate ester condensate catalyst system, or an anion initiator such as potassium alkoxide containing K + Using potassium alkoxide, diphenylmethyl potassium, potassium hydroxide and other anion initiators containing potassium, each monomer is reacted in the presence or absence of a solvent at a reaction temperature of 10 to 120 ° C with stirring to obtain polyether (i). From the viewpoints of the degree of polymerization or the properties of the obtained copolymer, a coordination anion initiator is preferred, and among them, an organic tin-phosphate ester condensate catalyst system is particularly preferred because it is easy to handle.

[0023] In the polyether (i) having an ethylene oxide unit in the side chain, the molar ratios of the repeating unit (A) derived from the monomer of formula (1), the repeating unit (B) derived from the monomer of formula (2), and the repeating unit (C) derived from the monomer of formula (3) are preferably (A) 95 to 5 mol%, (B) 5 to 95 mol%, and (C) 0 to 20 mol%, more preferably (A) 92 to 9 mol%, (B) 7 to 90 mol%, and (C) 1 to 15 mol%, and even more preferably (A) 88 to 18 mol%, (B) 10 to 80 mol%, and (C) 2 to 15 mol%. When the repeating unit (A) is 95 mol% or less, it does not cause an increase in the glass transition temperature and crystallization of the oxyethylene chain, which is preferably in terms of ionic conductivity.

[0024] Specific examples of the polyether (i) having an ethylene oxide unit in the side chain include ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl methacrylate terpolymer, ethylene oxide / diethylene glycol methyl glycidyl ether / glycidyl acrylate terpolymer, and the like.

[0025] The weight average molecular weight of the polyether (i) having an ethylene oxide unit in the side chain is not particularly limited, but may be 10,000 to 3,000,000, more preferably 50,000 to 2,500,000, and particularly preferably 100,000 to 2,000,000. The weight average molecular weight is calculated by gel permeation chromatography (GPC) using dimethylformamide (DMF) as a solvent and in terms of standard polystyrene conversion.

[0026] As a polymer solid electrolyte of a branched polyether, it is preferable to contain a lithium salt compound. As the lithium salt compound, a lithium salt compound having a wide potential window, such as those commonly used in lithium ion batteries, is suitable. Examples of the lithium salt compound include, but are not limited to, LiBF4, LiPF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2 (LiTFSI), LiN(SFO2)2 (LiFSI), LiN(C2F5SO2)2, LiN[CF3SC(C2F5SO2)3]2, etc. These may be used alone or in combination of two or more.

[0027] When the polymer solid electrolyte contains lithium chloride, the content is preferably such that the value of the number of moles of the lithium salt compound / the total number of moles of ether oxygen atoms of the branched polyether is 0.0001 to 5, and more preferably in the range of 0.001 to 0.5.

[0028] Also, as the polymer solid electrolyte of the branched polyether, a room temperature molten salt may be contained. The room temperature molten salt refers to a salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which the power supply is assumed to operate normally. The temperature range in which the power supply is assumed to operate normally has an upper limit of about 120 °C, and in some cases about 60 °C, and a lower limit of about -40 °C, and in some cases about -20 °C.

[0029] The room temperature molten salt is also called an ionic liquid, and quaternary ammonium organic cations of pyridine-based, aliphatic amine-based, and alicyclic amine-based are known. Examples of the quaternary ammonium organic cation include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions, piperidinium ions, etc. In particular, imidazolium cations are preferred.

[0030] As for tetraalkylammonium ions, examples include trimethylethylammonium ion, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, tetraamylammonium ion, triethylmethylammonium ion, etc., but are not limited thereto.

[0031] As for alkylpyridinium ions, examples include N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion, 1-ethyl-2-methylpyridinium ion, 1-butyl-4-methylpyridinium ion, 1-butyl-2,4-dimethylpyridinium ion, etc., but are not limited thereto.

[0032] As for imidazolium cations, examples include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-methyl-3-butylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, etc., but are not limited thereto.

[0033] Note that the room temperature molten salts having these cations may be used alone or in combination of two or more.

[0034] When the room temperature molten salt is contained in the polymer solid electrolyte, the content thereof is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, based on 100 parts by mass of the branched polyether.

[0035] The polymer solid electrolyte may contain a plasticizer in addition to the branched polyether. The plasticizer is not particularly limited, but dicyano compounds and branched ether compounds are preferred. When adding a plasticizer, it is preferable to crosslink the branched polyether. This crosslinking is a chemical crosslinking and can suppress the outflow of the plasticizer from the electrode.

[0036] Examples of the dicyano compound include succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, etc. Examples of the branched ether compound include the following multi-branched ether compounds.

[0037]

Chemical formula

[0038]

Chemical formula

[0039] When the polymer solid electrolyte contains a plasticizer, the content of the plasticizer is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, based on 100 parts by mass of the branched polyether.

[0040] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes. In the composite solid electrolyte of the present invention, the inorganic solid electrolyte is contained, for example, in a particulate form and has a structure in which the polymer solid electrolyte adheres between the particles of the inorganic solid electrolyte.

[0041] The oxide-based solid electrolyte is not particularly limited as long as it contains oxygen, has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electron insulation.

[0042] Specific compounds constituting the oxide-based solid electrolyte include Li xLa y TiO3 [x = 0.3 to 0.7, y = 0.3 to 0.7] (LLT), Li x La y Zr z M m O n (M is at least one or more elements of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, where x satisfies 5 ≤ x ≤ 10, y satisfies 1 ≤ y ≤ 4, z satisfies 1 ≤ z ≤ 4, m satisfies 0 ≤ m ≤ 2, and n satisfies 5 ≤ n ≤ 20.) Li x B y M z O n (In the formula, M is at least one or more elements of C, S, Al, Si, Ga, Ge, In, Sn, where x satisfies 0 ≤ x ≤ 5, y satisfies 0 ≤ y ≤ 1, z satisfies 0 ≤ z ≤ 1, and n satisfies 0 ≤ n ≤ 6.) Li x (Al, Ga) y (Ti, Ge) z Si a P m O n (However, 1 ≤ x ≤ 3, 0 ≤ y ≤ 1, 0 ≤ z ≤ 2, 0 ≤ a ≤ 1, 1 ≤ m ≤ 7, 3 ≤ n ≤ 13), Li (3-2x) M x DO (x represents a number from 0 or more to 0.1 or less, M represents a divalent metal atom. D represents a halogen atom or a combination of two or more halogen atoms.), Li x Si y O z (1 ≤ x ≤ 5, 0 < y ≤ 3, 1 ≤ z ≤ 10), Li x S y O z (1 ≤ x ≤ 3, 0 < y ≤ 2, 1 ≤ z ≤ 10), Li3BO3 - Li2SO4, Li2O - B2O3 - P2O5, Li2O - SiO2, Li6BaLa2Ta2O 12 、Li3PO (4-3 / 2w) N w (w is w < 1), Li having a LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO4, La having a perovskite type crystal structure 0.55 Li 0.35TiO3, LiTi2P3O with a NASICON (Natrium super ionic conductor) crystal structure 12 Li (1+x+y) (Al, Ga) x (Ti, Ge) (2-x) Si y P (3-y) O 12 (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), examples include Li7La3Zr2O12 with a garnet crystal structure. Also, phosphorus compounds containing Li, P, and O are desirable. For example, lithium phosphate (Li3PO4), LiPON in which part of the oxygen in lithium phosphate is replaced by nitrogen, LiPOD (D is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), etc. can be mentioned. Also, LiAON (A is at least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used.

[0043] Among them, Li x La y TiO3 [x = 0.3 to 0.7, y = 0.3 to 0.7] (LLT), Li x La y Zr z M m O n (M is at least one element of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, Sn, etc., x satisfies 5 ≦ x ≦ 10, y satisfies 1 ≦ y ≦ 4, z satisfies 1 ≦ z ≦ 4, m satisfies 0 ≦ m ≦ 2, n satisfies 5 ≦ n ≦ 20.), Li7La3Zr2O 12 (LLZ), Li3BO3, Li3BO3 - Li2SO4, Li3BO3 - Li2CO3, Li x (Al, Ga) y (Ti, Ge) z Si a P m O n (where 1 ≦ x ≦ 3, 0 ≦ y ≦ 1, 0 ≦ z ≦ 2, 0 ≦ a ≦ 1, 1 ≦ m ≦ 7, 3 ≦ n ≦ 13) are preferred. These can be used alone or in combination of two or more.

[0044] The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur, has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electron insulation. For example, a lithium-ion conductive inorganic solid electrolyte satisfying the composition represented by the following formula can be mentioned.

[0045] Li a M b P c S d A e

[0046] In the formula, M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. Among them, B, Sn, Si, Al, and Ge are preferable, and Sn, Al, and Ge are more preferable. A represents I, Br, Cl, and F, I and Br are preferable, and I is particularly preferable. a to e represent the composition ratios of the respective elements, and a:b:c:d:e satisfies 1 to 12:0 to 1:1:2 to 12:0 to 5. a is further preferably 1 to 9, and more preferably 1.5 to 4. b is preferably 0 to 0.5. d is further preferably 3 to 7, and more preferably 3.25 to 4.5. e is further preferably 0 to 3, and more preferably 0 to 2.

[0047] In the formula, the composition ratios of Li, M, P, S, and A are preferably such that b and e are 0, more preferably b = 0, e = 0, and the ratio of a, c, and d (a:c:d) is a:c:d = 1 to 9:1:3 to 7, and even more preferably b = 0, e = 0, and a:c:d = 1.5 to 4:1:3.25 to 4.5.

[0048] When the inorganic solid electrolyte is in a particulate form, examples of its particle diameter include 0.01 to 100 μm, preferably 0.1 to 20 μm.

[0049] In the composite solid electrolyte of the present invention, the mass ratio of the inorganic solid electrolyte to the polymer solid electrolyte is not particularly limited. However, from the viewpoint of more preferably exhibiting excellent charge-discharge characteristics in the solid electrolyte secondary battery, with respect to 100 parts by mass of the inorganic solid electrolyte, it is preferably 0.1 to 1000 parts by mass, more preferably 0.5 to 500 parts by mass, and even more preferably 1 to 400 parts by mass.

[0050] Since the composite solid electrolyte of the present invention contains a polymer solid electrolyte in addition to the inorganic solid electrolyte, unlike the case of using only the inorganic solid electrolyte, it can also be suitably formed into a sheet shape. The thickness when the composite solid electrolyte of the present invention is applied to a solid electrolyte secondary battery is not particularly limited, but for example, it is about 0.01 to 1 mm, preferably about 0.05 to 0.3 mm.

[0051] Method for manufacturing composite solid electrolyte The composite solid electrolyte of the present invention can be prepared by using a conventionally known method. For example, a method of preparing a composite solid electrolyte slurry by dispersing an inorganic solid electrolyte in a solvent containing a branched polyether and a lithium salt compound, and spraying and drying the slurry in hot air to obtain a composite solid electrolyte, or a method of heating and evaporating the solvent of the dispersion slurry under atmospheric pressure or reduced pressure to dry it, or a method of applying the dispersion slurry to a current collector sheet, etc. and drying it, etc. can be used for manufacturing.

[0052] As the dispersion solvent, water, an organic solvent, or a mixture of these in any ratio can be used. Even if the obtained dispersion slurry is a homogeneous solution, or if the solute that does not dissolve in the dispersion solvent is an inorganic solid electrolyte and / or a polymer solid electrolyte of a branched polyether, it can be prepared by the above general preparation method. It is desirable to remove as much as possible the remaining solvent and moisture from the composite solid electrolyte obtained by removing the dispersion solvent. For example, it can be achieved by vacuum evacuation for 1 hour to 48 hours under heating at 30°C to 200°C. Since the dried composite solid electrolyte of the present invention has ionic conductivity and binding properties, the electrolyte powder itself can be pressure-molded and used as a solid electrolyte material. Furthermore, by performing pressure heat treatment, the porosity can be reduced and the particle interface adhesion can be increased. As the organic solvent, a polar solvent is preferred. Specifically, acetonitrile, ethyl alcohol, methyl alcohol, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, dioxane, methyl ethyl ketone, methyl isobutyl ketone, etc. are used alone or in combination. When an inorganic solid electrolyte alone is pressure-molded, it has almost no binding property and becomes a thick-film electrolyte, but in the case of a composite solid electrolyte, due to the binding property of the polymer solid electrolyte, it is possible to manufacture a thinner solid electrolyte.

[0053] Crosslinking of composite solid electrolyte The composite solid electrolyte can increase the binding strength between the inorganic solid electrolyte and the polymer solid electrolyte in the composite solid electrolyte by crosslinking, and can also prevent the short circuit of the battery due to the restraint pressure and the deposition of dendrites. As the crosslinking method, it can be crosslinked by applying heat or irradiating active energy rays such as ultraviolet rays.

[0054] In the case of crosslinking by heat, a radical initiator selected from organic peroxides, azo compounds, etc. is used. As the organic peroxide, those usually used for crosslinking purposes such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxyester, etc. are used, and as the azo compound, those usually used for crosslinking purposes such as azonitrile compound, azoamide compound, azoamidine compound, etc. are used. The addition amount of the radical initiator varies depending on the type, but usually it is in the range of 0.1 to 10 parts by mass with 100 parts by mass of the branched polyether (ion conductive polymer).

[0055] As the radical initiator in the case of crosslinking by irradiating active energy rays, alkylphenone-based, benzophenone-based, acylphosphine oxide-based, titanocenes, triazines, bisimidazoles, oxime esters, etc. are used. The addition amount of these radical polymerization initiators varies depending on the type, but usually it is in the range of 0.01 to 5.0 parts by mass with 100 parts by mass of the branched polyether (ion conductive polymer).

[0056] In the present invention, a crosslinking aid may be used when crosslinking the composite solid electrolyte. As the crosslinking aid, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, triallyl isocyanurate, maleimide, phenyl maleimide, maleic anhydride, etc. can be arbitrarily used.

[0057] In the composite solid electrolyte secondary battery of the present invention, a crosslinked film of an ion conductive polymer material having ethylene oxide units in a side chain containing a lithium salt compound may be disposed between at least one of the positive electrode and the composite solid electrolyte and between the negative electrode and the composite solid electrolyte. The crosslinked film of the ion conductive polymer material is a crosslinked film of a composition containing a lithium salt compound and an ion conductive polymer. By disposing the crosslinked film, the interfacial resistance of the electrode and the composite solid electrolyte can be further reduced.

[0058] The crosslinked film is formed by crosslinking at least a composition containing a lithium salt compound and an ion conductive polymer having ethylene oxide units in a side chain. That is, the crosslinked film is a crosslinked film of a composition containing a lithium salt compound and an ion conductive polymer. The lithium salt compound and the ion conductive polymer are as described above.

[0059] The content of the ion conductive polymer contained in the crosslinked film is preferably 10 to 90 parts by mass, more preferably 20 to 80 parts by mass, based on 100 parts by mass of the entire crosslinked film.

[0060] The content of lithium chloride contained in the crosslinked film, the value of the number of moles of the lithium salt compound / the total number of moles of ether oxygen atoms of the ion conductive polymer is preferably 0.0001 to 5, and more preferably in the range of 0.001 to 0.5.

[0061] Further, the crosslinked film may contain a room temperature molten salt. The room temperature molten salt is as described above.

[0062] When the crosslinked film contains a room temperature molten salt, the content thereof is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, based on 100 parts by mass of the ion conductive polymer.

[0063] The crosslinked film may contain a plasticizer or the like. The plasticizer is as described above.

[0064] When the crosslinked film contains a plasticizer, the content of the plasticizer is preferably 10 to 1000 parts by mass, more preferably 20 to 500 parts by mass, based on 100 parts by mass of the ion conductive polymer.

[0065] A crosslinked film may be formed by blending a reaction initiator and a crosslinking aid into a composition containing a lithium salt compound and an ion conductive polymer. Examples of the reaction initiator include thermal reaction initiators and photo reaction initiators.

[0066] As the thermal reaction initiator, a radical initiator selected from organic peroxides, azo compounds, etc. is used. As the organic peroxide, those usually used for crosslinking purposes such as ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxyester, etc. are used. As the azo compound, those usually used for crosslinking purposes such as azonitrile compound, azoamide compound, azoamidine compound, etc. are used. The addition amount of the radical initiator varies depending on the type, but is usually in the range of 0.1 to 10 parts by mass based on 100 parts by mass of the ion conductive polymer.

[0067] As the photo reaction initiator, radical initiators such as alkylphenone-based, benzophenone-based, acylphosphine oxide-based, titanocenes, triazines, bisimidazoles, oxime esters, etc. are used. The addition amounts of these radical polymerization initiators vary depending on the type, but are usually in the range of 0.01 to 5.0 parts by mass based on 100 parts by mass of the ion conductive polymer.

[0068] As the crosslinking aid, ethylene glycol diacrylate, ethylene glycol dimethacrylate, oligoethylene glycol diacrylate, oligoethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, triallyl isocyanurate, maleimide, phenyl maleimide, maleic anhydride, etc. can be arbitrarily used.

[0069] The composition containing a lithium salt compound and an ion-conductive polymer may be blended with an organic solvent. Examples of the organic solvent include toluene, xylene, benzene, acetonitrile, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and THF (tetrahydrofuran).

[0070] The method for producing a crosslinked film includes, for example, mixing and dissolving an ion-conductive polymer, a reaction initiator if necessary, and a lithium salt compound in an organic solvent to form a composition, casting the composition onto a substrate (such as a PET film or a Teflon (registered trademark) plate), and after removing the solvent, producing a crosslinked film by heating or irradiating with active energy rays such as ultraviolet rays. Also, the crosslinked film can be produced by directly casting the composition onto the surface of the composite solid electrolyte.

[0071] The film thickness of the crosslinked film is preferably in the range of 0.1 μm to 200 μm, more preferably 0.5 μm to 100 μm.

[0072] Examples of the laminated structure of the composite solid electrolyte secondary battery of the present invention include the following structures. A laminated structure in which a positive electrode, an inorganic composite solid electrolyte, and a negative electrode are laminated in this order; A laminated structure in which a positive electrode, a crosslinked film, a composite solid electrolyte, a crosslinked film, and a negative electrode are laminated in this order; A laminated structure in which a positive electrode, a crosslinked film, a composite solid electrolyte, and a negative electrode are laminated in this order; A laminated structure in which a positive electrode, a composite solid electrolyte, a crosslinked film, and a negative electrode are laminated in this order.

[0073] In the composite solid electrolyte secondary battery of the present invention, it is preferable that the composite solid electrolyte is in contact with the above-mentioned crosslinked film. Since the crosslinked film is a crosslinked product of a composition containing an ion-conductive polymer containing a lithium salt compound, it has ion conductivity and high flexibility compared to inorganic materials. Therefore, the contact area between the crosslinked film and the composite solid electrolyte becomes large, and as a result, the interfacial resistance of the composite solid electrolyte is effectively reduced, and it is considered that the composite solid electrolyte secondary battery of the present invention exhibits excellent charge-discharge characteristics. In the composite solid electrolyte secondary battery of the present invention, it is also preferable that the crosslinked film is in contact with the electrode material layer of the electrode, and it is also preferable that the crosslinked film is in contact with both the electrode material layer and the composite solid electrolyte.

[0074] Composite solid electrolyte secondary battery The composite solid electrolyte secondary battery of the present invention includes at least a positive electrode, a negative electrode, and the composite solid electrolyte of the present invention. The composite solid electrolyte of the present invention is as described above. The composite solid electrolyte of the present invention is disposed between the positive electrode and the negative electrode. In particular, the composite solid electrolyte used in the composite solid electrolyte secondary battery of the present invention contains a polymer solid electrolyte containing a branched polyether in addition to the inorganic solid electrolyte as described above. Therefore, compared with the case where the solid electrolyte is formed only by the inorganic solid electrolyte, the contact area of the interface between the electrode material layer and the composite solid electrolyte layer is considered to be large, and as a result, the interfacial resistance between the electrode and the electrolyte is reduced, and it is considered that excellent charge-discharge characteristics are exhibited. Also, in the composite solid electrolyte, it is considered that the polymer solid electrolyte reduces the resistance inside the composite solid electrolyte by adhering between the particles of the inorganic solid electrolyte.

[0075] Known materials can be used for both the positive electrode and the negative electrode, and examples thereof include electrodes having an electrode material layer, that is, a positive electrode material layer or a negative electrode material layer, on a current collector.

[0076] Known current collectors can be used for the positive and negative electrodes. Specifically, for the positive electrode, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium are used as the current collector. For the negative electrode, metals such as copper, nickel, stainless steel, gold, platinum, and titanium are used as the current collector.

[0077] In addition, the positive electrode material layer and the negative electrode material layer each contain at least a positive electrode active material and a negative electrode active material, and may further contain a conductive assistant, a binder, and a thickener, and may contain the aforementioned inorganic solid electrolyte as needed.

[0078] The positive electrode active material used in the present invention is a lithium metal-containing composite oxide powder having a composition of any one of LiMO2, LiM2O4, Li2MO3, and LiMEO4. Here, M in the formula mainly consists of transition metals and includes at least one of Co, Mn, Ni, Cr, Fe, and Ti. Although M consists of transition metals, in addition to transition metals, Al, Ga, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. may be added. E includes at least one of P and Si. The particle size of the positive electrode active material is preferably 50 μm or less, more preferably 20 μm or less. These active materials have an electromotive force of 3 V (vs. Li / Li+) or more.

[0079] Specific examples of the positive electrode active material include lithium cobaltate, lithium nickelate, lithium nickel / cobalt / manganese (ternary system), spinel-type lithium manganate, lithium iron phosphate, and the like.

[0080] The negative electrode active material used in the present invention is a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (intercalation compound) capable of occluding and releasing alkali metal ions such as lithium ions, or a metal such as lithium, aluminum-based compound, tin-based compound, silicon-based compound, titanium-based compound, etc. capable of occluding and releasing alkali metal ions such as lithium ions. In the case of powder, the particle size is preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 20 μm or less. A mixed active material of a metal and a carbon material may also be used.

[0081] When using a conductive aid, known conductive aids can be used, such as conductive carbon blacks like graphite, furnace black, acetylene black, Ketjen black, carbon fibers such as carbon nanotubes, or metal powders, etc. These conductive aids may be used alone or in combination of two or more.

[0082] As the binder, for example, one or more compounds selected from fluororesins such as PVdF, fluororubbers, acrylic rubbers, modified acrylic rubbers, styrene-butadiene rubbers, acrylic polymers, vinyl polymers, and the branched polyethers described above can be used. These binders are added in an amount of preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, based on 100 parts by mass of the active material.

[0083] Specific examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose and their salts (alkali metal salts such as sodium salts, ammonium salts), polyvinyl alcohol, polyacrylate, polyethylene oxide, etc. These thickeners may be used alone or in combination of two or more. These thickeners are added in an amount of preferably 5 parts by mass or less, more preferably 3 parts by mass or less, for example, 0.01 to 2 parts by mass, based on 100 parts by mass of the active material. Also, when the viscosity of the coating liquid is low, a thickener can be used in combination.

[0084] The method for manufacturing the positive electrode and negative electrode provided with the current collector, the positive electrode material layer, and the negative electrode material layer is not particularly limited, and general methods are used. For example, a paste (coating liquid) of a positive electrode material or a negative electrode material composed of a positive electrode active material or a negative electrode active material, a conductive aid, a binder, a solvent such as water or N-methyl-2-pyrrolidone (NMP), and, if necessary, a thickener, etc. is uniformly applied to an appropriate thickness on the surface of the current collector by a doctor blade method, a silk screen method, or the like.

[0085] For example, in the doctor blade method, the negative electrode active material powder, positive electrode active material powder, conductive assistant, binder, etc. are dispersed in water to form a slurry, which is then applied to a metal electrode substrate and homogenized to an appropriate thickness by a blade having a predetermined slit width. After applying the active material, the electrode is dried, for example, with hot air at 100 °C or under reduced pressure at 80 °C to remove the excess organic solvent. The dried electrode is manufactured by press-molding with a pressing device.

[0086] When the positive electrode material layer and the negative electrode material layer are formed on the current collector, voids will be generated between the electrode materials of the positive electrode material layer and the negative electrode material, for example, between the active materials, between the active material and other electrode materials, etc. In the composite solid electrolyte secondary battery of the present invention, such voids may contain the branched polyether which is an ion-conductive polymer.

[0087] Method for manufacturing composite solid electrolyte secondary battery The manufacturing method of the composite solid electrolyte secondary battery of the present invention is not particularly limited, and it is at least composed of a positive electrode, a negative electrode, and the composite solid electrolyte of the present invention, and is manufactured by a known method. For example, in the case of a coin-type lithium-ion battery, the positive electrode, the composite solid electrolyte, and the negative electrode are inserted into an outer can. Then, they are joined by a sealing body and tab welding, etc., the sealing body is enclosed, and the battery is obtained by caulking. The shape of the battery is not limited, and examples include coin type, cylindrical type, sheet type, etc., and a structure in which two or more batteries are stacked may also be used.

Examples

[0088] The present invention will be described more specifically in the following examples, but the present invention is not limited thereto.

[0089] In this example, a coin battery was fabricated using a composite solid electrolyte, and the performance evaluation of the charge and discharge characteristics of the coin battery was conducted in the following experiment.

[0090] [Evaluation of the fabricated battery] As an evaluation of the fabricated battery, a charge and discharge test was conducted using a charge and discharge device to obtain the charge capacity and the discharge capacity.

[0091] Charge-discharge measurement After CCCV charging up to 4.2 V with a current corresponding to 0.1C (10-hour rate) (0.01C cut-off), and then discharging by CCCV down to 2.5 V with a current corresponding to 0.1C (0.01C cut-off). The test temperature was set in a 100 °C environment.

[0092] [Production Example of Positive Electrode] (1) To 100 parts by mass of NCM (lithium nickel cobalt manganese oxide = 5 / 2 / 3) as a positive electrode active material, 3 parts by mass of acetylene black, 3 parts by mass of graphite as conductive aids, and 3 parts by mass of PVdF as a binder were added. Further, it was added to an NMP solution so that the solid content concentration of the slurry became 35% by mass, and thoroughly mixed to obtain a positive electrode slurry. The obtained positive electrode slurry was applied onto an aluminum current collector with a thickness of 20 μm using a die coater, dried at 100 °C for 12 hours or more, and then pressed with a roll press to produce a precursor of a positive electrode with a thickness of 20 μm (coating weight 6.6 mg / cm 2 , positive electrode density 3.1 g / cm 3 , porosity 26%).

[0093] (2) A coating solution for positive electrode impregnation was prepared by completely dissolving 100 parts by mass of a terpolymer of ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol% (weight average molecular weight 1.5 million) as a branched polyether, 12 parts by mass of lithium borofluoride as a lithium salt compound, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking aid, and 0.3 parts by mass of benzoyl peroxide (Niper BMT, manufactured by NOF Corporation) as a radical initiator in 900 parts by mass of acetonitrile.

[0094] (3) The coating solution for positive electrode impregnation prepared in (2) was applied onto the precursor of the positive electrode in (1). Then, by standing for 2 hours, while removing the solvent, the voids in the positive electrode were impregnated with the branched polyether and the electrolyte lithium compound. Crosslinking of the impregnated branched polyether was carried out under reduced pressure at 100 °C for 2 hours to produce a positive electrode.

[0095] [Production Example of Negative Electrode] (1) As the negative electrode active material, 100 parts by mass of artificial graphite (particle size 10 μm) was added with 2 parts by mass of vapor-grown carbon fiber (VGCF) as a conductive assistant, 3 parts by mass of SBR as a binder, and 2 parts by mass of sodium carboxymethyl cellulose as a thickener. Further, water was added so that the solid content concentration of the slurry became 35% by mass, and they were sufficiently mixed to obtain a negative electrode slurry. The obtained negative electrode slurry was applied onto a copper current collector with a thickness of 16.5 μm using a die coater, and after drying at 100 °C for 12 hours or more, it was pressed with a roll press to produce a negative electrode precursor with a thickness of 22 μm (coating weight 3.1 mg / cm 2 , negative electrode density 1.2 g / cm 3 , porosity 23%).

[0096] (2) A coating solution for impregnating a negative electrode was prepared by completely dissolving 100 parts by mass of an ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol% terpolymer (weight average molecular weight 1.5 million) as a branched polyether, and as a lithium salt compound, 38 parts by mass of LiTFSI, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking assistant, and 0.3 parts by mass of benzoyl peroxide (Niper BMT, manufactured by NOF Corporation) as a radical initiator in 900 parts by mass of acetonitrile.

[0097] (3) The coating solution for impregnating an electrode of (2) was applied onto the negative electrode precursor of (1). Then, by allowing it to stand for 2 hours, while removing the solvent, the voids in the negative electrode were impregnated with the branched polyether and the electrolyte lithium compound. Crosslinking of the impregnated branched polyether was carried out at 100 °C under reduced pressure for 2 hours to produce a negative electrode.

[0098] [Example of Fabrication of Composite Solid Electrolyte] (1) Preparation of Inorganic Solid Electrolyte Dissolve 0.5 parts by mass of lithium borate in 99.5 parts by mass of ion-exchanged water to prepare a 0.5 mass% aqueous lithium borate solution. Separately, dissolve 0.5 parts by mass of lithium sulfate monohydrate in 99.5 parts by mass of ion-exchanged water, add 13 parts by mass of a 0.5 mass% aqueous lithium sulfate solution, and further add 10.5 parts by mass of an oxide-based solid electrolyte LATP (manufactured by Toyoshima Seisakusho) (composition: Li 1.3 Al 0.3 Ti 1.7 P3O 12 ; average particle size: 1 μm), and stir at room temperature. Transfer this slurry to a rotary evaporator equipped with a 60°C water bath, distill off and dry the solvent under heating, stirring, and reduced pressure to obtain a white dried product. This was vacuum dried at 150°C for 1 hour to obtain a dried product of LATP (inorganic solid electrolyte) coated with 5 mass% - lithium borate - lithium sulfate. 84 mg of the dried product (powder) was placed in a tablet molding die with a diameter of 10 mmφ and pressed at 20 kN for 5 minutes to obtain a molded product with a thickness of 500 μm. Note that when the powder was 50 mg or less, the molded product was damaged during removal and no molded product could be obtained.

[0099] (2) Preparation of a polymer solid electrolyte of a branched polyether As the branched polyether, 100 parts by mass of an ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol% terpolymer (weight average molecular weight 1.5 million), 12 parts by mass of lithium borofluoride as a lithium salt compound, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking aid, and 0.3 parts by mass of Niper BMT (manufactured by NOF Corporation) as a radical initiator were stirred in acetonitrile at room temperature for 10 hours and completely dissolved to prepare an acetonitrile solution containing a 0.5 mass% polymer solid electrolyte of a branched polyether.

[0100] (3) Preparation of a composite solid electrolyte of an inorganic solid electrolyte and a polymer solid electrolyte To 100 parts by mass of an acetonitrile solution containing 0.5% by mass of the branched polyether polymer solid electrolyte described in (2) above, 8.7 parts by mass of the dried product of the inorganic solid electrolyte described in (1) above was added, and the solvent was distilled off under heating, stirring, and reduced pressure using a rotary evaporator equipped with a water bath at 60 °C until dry. The dried product was vacuum dried at 110 °C for 2 hours to obtain a white dried product. 39 mg of the powder of the dried product was placed in a tablet molding die with a diameter of 10 mmφ and pressed at 20 kN for 5 minutes. Under these compression molding conditions, the molded products could all be taken out smoothly, and a molded product with a thickness of 230 μm was obtained.

[0101] [Comparative Preparation Example of Composite Solid Electrolyte] (1) Preparation of Polymer Solid Electrolyte of Polyethylene Oxide 100 parts by mass of polyethylene oxide (weight average molecular weight 1.1 million) and 12 parts by mass of lithium borofluoride as a lithium salt compound were stirred in acetonitrile at room temperature for 10 hours to be completely dissolved, and an acetonitrile solution containing 0.5% by mass of the polymer solid electrolyte of polyethylene oxide was prepared.

[0102] (2) Preparation of Composite Solid Electrolyte To 100 parts by mass of an acetonitrile solution containing 0.5% by mass of the polymer solid electrolyte of polyethylene oxide, 8.7 parts by mass of the dried product of the inorganic solid electrolyte obtained in the preparation of the inorganic solid electrolyte described in (1) above was added, and the solvent was distilled off under heating, stirring, and reduced pressure using a rotary evaporator equipped with a water bath at 60 °C until dry. The dried product was vacuum dried at 110 °C for 2 hours to obtain a white dried product. 45 mg of the powder of the dried product was placed in a tablet molding die with a diameter of 10 mmφ and pressed at 20 kN for 5 minutes. Under these compression molding conditions, the molded products could all be taken out smoothly, and a molded product with a thickness of 350 μm was obtained.

[0103] [Preparation of Crosslinked Film of Ion Conductive Polymer Material] As an ion-conductive polymer having an ethylene oxide unit in the side chain, 100 parts by mass of an ethylene oxide / diethylene glycol methyl glycidyl ether / allyl glycidyl ether = 80 / 17 / 3 mol% terpolymer, 38 parts by mass of LiTFSI as a lithium salt compound, 10 parts by mass of trimethylolpropane triacrylate as a crosslinking assistant, and 0.3 parts by mass of Niper BMT (manufactured by NOF Corporation) as a radical initiator were dissolved in 900 parts by mass of acetonitrile to prepare a solution. This solution was cast onto a polytetrafluoroethylene mold and dried at room temperature, and then heat-crosslinked at 100°C for 2 hours to produce a crosslinked film of an ion-conductive polymer material with a thickness of 20 μm.

[0104] Manufacturing example of battery [Example Manufacturing Example 1 of Coin Battery] In a dry room, the positive electrode obtained in the Example Manufacturing Example of the positive electrode, a molded product of the composite solid electrolyte (thickness 230 μm), the crosslinked film of the ion-conductive polymer material of the Manufacturing Example, and a metal lithium foil as the negative electrode were laminated in order, caulked, and a test 2032-type coin battery was manufactured. [Charge and Discharge Conditions] Lower limit voltage 2.5 V - upper limit voltage 4.2 V, 100°C CC-CV / CC-CV 0.1C - 0.01C charge, 0.1C - 0.01C discharge [Charge and Discharge Test Results] Charge capacity 165 mAh / g, discharge capacity 150 mAh / g

[0105] [Example Manufacturing Example 2 of Coin Battery] In a dry room, the positive electrode obtained in the Example Manufacturing Example of the positive electrode, a molded product of the composite solid electrolyte obtained in the Example Manufacturing Example of the composite solid electrolyte, and the negative electrode obtained in the Example Manufacturing Example of the negative electrode were laminated, caulked, and a test 2032-type coin battery was manufactured. [Charge and Discharge Conditions] Lower limit voltage 2.5 V - upper limit voltage 4.2 V, 100°C CC(0.1C) - CV(0.01C) charge CC(0.1C) - CV(0.01C) discharge [Charge and Discharge Test Results] Charge capacity: 151 mAh / g, Discharge capacity: 130 mAh / g

[0106] [Comparative production example 1 of coin cell] In a dry room, the positive electrode obtained in the production example of the positive electrode, the molded product of the composite solid electrolyte obtained in the comparative production example of the composite solid electrolyte using polyethylene oxide, the cross-linked film of the ion conductive polymer material of the production example, and the metal lithium foil as the negative electrode were laminated in order, caulked, and a 2032-type coin cell for testing was manufactured. <Charge and discharge conditions> Lower limit voltage: 2.5 V - Upper limit voltage: 4.2 V, 100 °C CC(0.1C) - CV(0.01C) charge CC(0.1C) - CV(0.01C) discharge <Charge and discharge test results> Charge capacity: 110 mAh / g, Discharge capacity: 90 mAh / g

[0107] From the production examples and comparative production examples, it can be seen that the composite solid electrolyte composed of an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether clearly exhibits higher charge and discharge capacities for solid electrolyte secondary batteries compared to solid electrolytes that do not contain a polymer solid electrolyte. Also, when the inorganic solid electrolyte is pressure-molded alone, it becomes a thick-film electrolyte because it has almost no flexibility and binding property, but in the composite solid electrolyte, a thinner solid electrolyte is obtained due to the flexibility and binding property of the polymer solid electrolyte.

Industrial applicability

[0108] The composite solid electrolyte of the present invention and the solid electrolyte secondary battery manufactured using the composite solid electrolyte have excellent charge and discharge characteristics and are suitably applicable to large battery applications such as in-vehicle use in electric vehicles and hybrid electric vehicles, and storage batteries for household power storage.

Claims

1. A composite solid electrolyte containing an inorganic solid electrolyte and a polymer solid electrolyte containing a branched polyether and a lithium salt compound, wherein the branched polyether contains a structural unit formed from an epoxy compound having an ethylene oxide unit in a side chain, the epoxy compound has a molar ratio of a repeating unit (A) derived from a monomer of the following formula (1), a repeating unit (B) derived from a monomer of the following formula (2), and a repeating unit (C) derived from a monomer of the following formula (3) of (A) 95 to 5 mol%, (B) 5 to 95 mol%, and (C) 0 to 20 mol%. A composite solid electrolyte. 【Chemical Formula 1】 【Chemical Formula 2】 [In formula (2), R is -CH 2 O(CH 2 CH 2 O) n R 4, R 4 is an alkyl group having 1 to 6 carbon atoms, and n is a number from 0 to 12.] [Chemical Formula 3] [In formula (3), R 5 represents a group containing an ethylenically unsaturated group.]

2. The composite solid electrolyte according to Claim 1, wherein the epoxy compound has a molar ratio of a repeating unit (A) derived from a monomer of the following formula (1), a repeating unit (B) derived from a monomer of the following formula (2), and a repeating unit (C) derived from a monomer of the following formula (3) of (A) 92 to 9 mol%, (B) 7 to 90 mol%, and (C) 1 to 15 mol%.

3. The composite solid electrolyte according to Claim 1 or 2, wherein the branched polyether contains a structural unit formed from at least one selected from the group consisting of allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate.

4. The composite solid electrolyte according to any one of Claims 1 to 3, wherein the branched polyether is crosslinked.

5. The composite solid electrolyte according to any one of Claims 1 to 4, wherein the inorganic solid electrolyte is an oxide-based solid electrolyte or a sulfide-based solid electrolyte.

6. A composite solid electrolyte secondary battery containing the composite solid electrolyte according to any one of Claims 1 to 5.

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