Composite electrolyte, production method therefor, and power storage device

Abstract

A composite electrolyte according to the present invention contains an inorganic solid electrolyte and an organic solid electrolyte. The organic solid electrolyte contains molecular crystals and a polymer. The molecular crystals contain, as constituent units, an alkali metal salt and an organic molecule having at least one atom selected from the group consisting of sulfur, oxygen, nitrogen, and phosphorous. The polymer has substantially no repeating units represented by the formula –(R1-O)- (with the caveat that R1 is an alkylene group) in the main chain thereof.

Description

Composite electrolyte, method for producing the same, and electricity storage device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Japanese Patent Application No. 2024-105386, filed on June 28, 2024, the entire contents of which are incorporated herein by reference. The present disclosure relates to a composite electrolyte and a method for producing the same, and an electricity storage device.

[0002] Various types of energy storage devices have been put to practical use, including various secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries, as well as electric double-layer capacitors. Among these, lithium-ion secondary batteries are used in a wide range of applications due to their high energy density and battery capacity. In recent years, sodium-ion secondary batteries, potassium-ion secondary batteries, and magnesium-ion secondary batteries have been attracting attention as post-lithium-ion secondary batteries that use elements that replace the rare metal lithium.

[0003] Lithium-ion secondary batteries, which are widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte, and are charged and discharged by transferring lithium ions between the electrodes via the electrolyte. Conventionally, nonaqueous electrolytes have been used primarily as the electrolyte. However, nonaqueous electrolytes contain flammable organic solvents, which raise concerns about electrolyte leakage and short-circuiting within the battery due to overcharging and overdischarging.

[0004] In response to this, non-flammable inorganic solid electrolytes using inorganic materials have been proposed as an alternative to non-aqueous electrolyte solutions. However, while inorganic solid electrolytes are excellent in safety, they have the disadvantage that, because they are produced by compacting powder, gaps are likely to form at the interfaces with the positive electrode or negative electrode or at the interfaces between particles of the inorganic solid electrolyte material, resulting in high interfacial resistance.

[0005] Therefore, in recent years, in order to achieve both improved safety and reduced interface resistance, it has been proposed to use a composite electrolyte containing an inorganic solid electrolyte and a nonaqueous electrolyte solution as the electrolyte used in lithium ion secondary batteries (see, for example, Patent Document 1). Patent Document 1 discloses that a sintered body having a dense portion and a porous portion is produced by sintering an inorganic oxide as the inorganic solid electrolyte, and the sintered body is immersed in an electrolyte solution such as an organic electrolyte solution or an ionic liquid and then evacuated, thereby filling the porous portion of the sintered body with the electrolyte solution to obtain a composite electrolyte.

[0006] Furthermore, Patent Document 2 discloses a lithium ion conductive composite material containing lithium ion conductive particles that are inorganic solid electrolytes, a polymer such as polyethylene oxide, and an alkali metal salt, and describes that this composite material has reduced interfacial resistance regarding lithium ion conductivity between the polymer and the particles.

[0007] Japanese Patent Application Laid-Open No. 2017-111890 Japanese Patent Application Laid-Open No. 2019-519885

[0008] In the production of inorganic solid electrolytes, for example, oxide-based solid electrolytes generally undergo powder compaction followed by sintering at high temperatures (e.g., temperatures exceeding 1,000°C) to improve the bonding between particles and between electrodes and the electrolyte and reduce interfacial resistance in order to achieve high ionic conductivity. However, sintering is a process that requires a lot of energy, and furthermore, industrialization requires the introduction of large-area sintering equipment. Furthermore, sulfide-based solid electrolytes generally require pressing at high pressures (e.g., pressures exceeding 10 MPa), which has the disadvantage of significant process constraints.

[0009] If the thickness of the electrolyte layer is increased to, for example, 100 μm or more in order to increase strength, there is a concern that the energy density of the manufactured electricity storage device will be reduced. Therefore, it is conceivable to make the thickness of the electrolyte layer as thin as possible in order to increase the energy density. However, if the inorganic solid electrolyte filled with the electrolytic solution is a sintered body as in Patent Document 1, there is a concern that if the electrolyte layer is thin, it will be prone to cracking when stress is applied to the electrolyte. Furthermore, the lithium ion conductive composite material of Patent Document 2 has high interface resistance, insufficient ion conductivity, and sometimes has problems with heat resistance.

[0010] The present disclosure has been made in view of the above circumstances, and has as one object to provide a composite electrolyte of an inorganic solid electrolyte and an organic solid electrolyte that exhibits high ionic conductivity and good flexibility and heat resistance while minimizing constraints on the manufacturing process, and as another object to provide an electricity storage device including the composite electrolyte.

[0011] As a result of intensive research to solve the above problems, the present inventors have found that a composite electrolyte containing specific components exhibits high ionic conductivity and has good flexibility and heat resistance without the need for a molding step such as sintering or high-pressure pressing. That is, the present disclosure provides the following composite electrolyte, a method for producing the same, and an electricity storage device.

[0012] [1] A composite electrolyte containing an inorganic solid electrolyte and an organic solid electrolyte, wherein the organic solid electrolyte contains a molecular crystal and a polymer, the molecular crystal contains an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom, and an alkali metal salt as a constituent unit, and the polymer contains a -(R １ A repeating unit represented by —O)— (where R １ [2] The composite electrolyte according to [1], wherein the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure. [3] The composite electrolyte according to [1], wherein the oxide having a NASICON-type crystal structure is a compound represented by the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ (wherein M1 contains Fe, In, Y, or Al, M2 contains Si, and M3 contains W, and x > 0, y ≥ 0, and z ≥ 0 are satisfied). [4] The composite electrolyte according to any one of [1] to [3], wherein the total number of carbon atoms per molecule of the organic molecules is 2 or more and 6 or less. [5] The composite electrolyte according to any one of [1] to [4], wherein the organic molecules are at least one selected from the group consisting of sulfones and nitriles. [6] The composite electrolyte according to any one of [1] to [5], wherein the alkali metal salt constituting the molecular crystal contains an imide-based alkali metal salt. [7] The composite electrolyte according to any one of [1] to [6], wherein the polymer is a non-crosslinked polymer. [8] The composite electrolyte according to any one of [1] to [7], further containing an alkali metal salt. [9] The composite electrolyte according to any one of [1] to [8], wherein the composite electrolyte is a thin film having a thickness of 50 μm or less.

[10] A method for producing the composite electrolyte according to any one of [1] to [9], comprising a step of mixing the inorganic solid electrolyte, the molecular crystal, and the polymer.

[11] A method for producing the composite electrolyte according to

[10] , wherein the inorganic solid electrolyte, the molecular crystal, and the polymer are mixed in the presence of a solvent.

[12] An electricity storage device comprising the composite electrolyte according to any one of [1] to [9].

[0013] According to the present disclosure, a composite electrolyte of an inorganic solid electrolyte and an organic solid electrolyte can be obtained that exhibits high ionic conductivity and has good flexibility and heat resistance, even without performing a sintering process during the production of the composite electrolyte. Furthermore, by using the composite electrolyte of the present disclosure as an electrolyte for an electricity storage device such as a secondary battery or a capacitor, an electricity storage device can be obtained that combines high ionic conductivity with the safety ensured by the solidification of the electrolyte. Furthermore, the composite electrolyte of the present disclosure is suitable for use as a thin film, and therefore, it is possible to achieve a thinner, smaller, and lighter electricity storage device while maintaining high performance.

[0014] FIG. 1 is a schematic diagram of a press die used to prepare the sample pellets.

[0015] The composite electrolyte and the electricity storage device of the present disclosure will be described in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic. "(meth)acrylo" means acrylo and / or methacrylo. "(meth)acrylate" means acrylate and / or methacrylate.

[0016] <<Composite Electrolyte>> The composite electrolyte of the present disclosure is an organic-inorganic hybrid solid electrolyte containing an inorganic solid electrolyte and an organic solid electrolyte. The organic solid electrolyte contained in the composite electrolyte of the present disclosure contains a molecular crystal and a polymer. Details of each component contained in the composite electrolyte of the present disclosure are described below. Note that, unless otherwise specified, each component may contain one type alone or two or more types in combination.

[0017] (Inorganic Solid Electrolyte) The inorganic solid electrolyte is not particularly limited as long as it is an inorganic solid that exhibits ion conductivity. Examples of inorganic solid electrolytes that can be used include oxide-based solid electrolytes, sulfide-based solid electrolytes, and chloride-based solid electrolytes. Of these, oxide-based solid electrolytes and sulfide-based solid electrolytes are preferred as inorganic solid electrolytes because of their high ion conductivity, and oxide-based solid electrolytes are more preferred because of their high safety in the atmosphere.

[0018] The crystalline structure of the inorganic solid electrolyte is not particularly limited, and examples of the crystalline structure of the inorganic solid electrolyte include a NASICON structure, a LISICON structure, a perovskite structure, and a garnet structure.

[0019] Specific examples of inorganic solid electrolytes include solid electrolytes having a NASICON structure, such as Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ (x≧0, also referred to as “LTP” or “LATP”), Li １＋ｘ Al ｘ Ge ２－ｘ (P.O.４ ) ３ (x≧0, also referred to as “LGP” or “LAGP”), LiZr ２ (P.O. ４ ) ３ (also referred to as "LZP"), and oxides in which some of the elements constituting these compounds are substituted with various elements (for example, B, Na, Al, Si, Ca, Ga, Ge, Sc, Fe, Sr, In, Ti, Hf, Sn, V, Nb, Ta, Sb, Bi, W, lanthanoid elements, etc.).

[0020] As a solid electrolyte having a LISICON structure, Li １４ ZnGe ４ O １６ Ya, Li １４ ZnGe ４ O １６ Examples of the solid electrolyte having a perovskite structure include oxides in which some of the elements constituting the solid electrolyte are substituted with the above-mentioned various elements. ０．３５ La ０．５５ TiO ３ Ya, Li ０．３５ La ０．５５ TiO ３ Examples of the solid electrolyte having a garnet structure include oxides in which some of the elements constituting the solid electrolyte are substituted with the above-mentioned various elements. ７ La ３ Zr ２ O １２ and Li ５ La ３ Nb ２ O １２ Ya, Li ７ La ３ Zr ２ O １２ or Li ５ La ３ Nb ２ O １２ and oxides in which some of the elements constituting the above-mentioned compound are substituted with the above-mentioned various elements.

[0021] One embodiment of the composite electrolyte of the present disclosure is an organic-inorganic hybrid solid electrolyte comprising an inorganic solid electrolyte having a NASICON-type crystal structure and an organic solid electrolyte. Unlike layered structures, the NASICON-type crystal structure provides a three-dimensionally expanded space for alkali metal ion migration, and zirconium (Zr) is stable even under high voltages, making it useful as a solid electrolyte for high operating voltages. In the composite electrolyte of the present disclosure, an oxide having a NASICON-type crystal structure can be preferably used as the inorganic solid electrolyte. The crystal structure of the solid electrolyte can be determined from a diffraction profile obtained by powder X-ray diffraction measurement.

[0022] When an oxide having a NASICON-type crystal structure is used as the inorganic solid electrolyte, a preferred example of the oxide is oxide (X) shown below. Oxide (X): General formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ A solid electrolyte represented by the formula (wherein M1 contains Fe, In, Y or Al, M2 contains Si, M3 contains W, and x>0, y≧0 and z≧0 are satisfied).

[0023] ・About oxide (X) Oxide (X) is LiZr ２ (P.O. ４ ) ３ In an oxide having a basic skeleton of the above, a portion of Zr is substituted with M1 (including Fe, In, Y, or Al), and a portion of P is substituted with M2 (including Si) and / or M3 (including W).

[0024] In the oxide (X), M1 may contain Fe, In, Y, or Al. That is, M1 may be Fe, In, Y, or Al, or may further contain, together with Fe, In, Y, or Al, an element other than Fe, In, Y, or Al that forms a trivalent cation. Examples of elements that form trivalent cations other than Fe, In, Y, or Al include Group 13 elements, transition elements (Groups 3 to 11 elements) that form trivalent cations, Sb, Bi, etc.

[0025] M2 may contain Si. That is, M2 may be Si, or may further contain an element other than Si that forms a tetravalent cation. Examples of elements other than Si that form a tetravalent cation include Group 14 elements other than Si, transition elements (Groups 3 to 11 elements) that form a tetravalent cation, and Te.

[0026] M3 may contain W. That is, M3 may be W, or may further contain an element other than W that becomes a hexavalent cation. Examples of elements other than W that become a hexavalent cation include transition elements (elements of Groups 3 to 11) other than W that become a hexavalent cation, and Group 16 elements.

[0027] In the general formula of the oxide (X), x, y, and z are not particularly limited as long as x > 0, y ≥ 0, and z ≥ 0 are satisfied. For example, when x > 0, y > 0, and z = 0, the oxide (X) is "Li １＋ｘ＋ｙ M1 ｘ Zr ２－ｘ M2 ｙ P ３－ｙ O １２ When x>0, y=0 and z>0, the oxide (X) is represented by "Li １＋ｘ－ｚ M1 ｘ Zr ２－ｘ M3 ｚ P ３－ｚ O １２ When x>0, y>0 and z>0, the oxide (y1) is represented by "Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ " is expressed as:

[0028] More specifically, x, y, and z in the general formula of oxide (X) preferably satisfy x≦0.3, and more preferably satisfy x≦0.25, in that an impurity phase is unlikely to be formed, thereby enabling a solid electrolyte exhibiting high ionic conductivity to be obtained. The lower limit of x preferably satisfies x≧0.01, more preferably satisfies x≧0.05, and even more preferably satisfies x≧0.10.

[0029] Regarding y, since y has a dominant effect on the formation of the α phase, thereby enabling the production of a solid electrolyte with higher ionic conductivity, it is preferable that y≦0.2, more preferably y≦0.15, and even more preferably y≦0.10. Furthermore, when y>0, the lower limit of y is preferably y≧0.01, and more preferably y≧0.03. Note that zirconium phosphate-based oxides having a NASICON-type crystal structure can have four phase structures: α phase, α' phase, β phase, and β' phase. Of these, the α phase has the highest lithium ion conductivity due to its isotropic crystal structure.

[0030] Regarding z, in order to suppress the formation of an impurity phase and obtain a solid electrolyte exhibiting higher ionic conductivity, it is preferable that z≦0.2, more preferably z≦0.15, and even more preferably z≦0.10. When z>0, the lower limit of z is preferably z≧0.01, and more preferably z≧0.03.

[0031] In the above general formula representing the oxide (X), the stoichiometric ratio of O is written as 12, but the stoichiometric ratio of O does not have to be strictly 12 as long as the charge neutrality of the oxide as a whole can be maintained. In other words, the O content in the oxide (X) may be a value less than 12 or a value greater than 12, as long as the charge neutrality of the oxide (X) as a whole can be maintained. For example, Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２±β (where 0≦β≦1 is satisfied, and M1, M2, M3, x, y, and z are the same as M1, M2, M3, x, y, and z in the above formula shown as the general formula of oxide (X)) is also included in oxide (X) as long as the charge neutrality of oxide (X) as a whole is maintained.

[0032] The method for producing the oxide (X) is not particularly limited. The oxide (X) can be produced, for example, by weighing and mixing raw materials so as to satisfy the stoichiometric ratios of the compositions represented by the above general formulas (mixing step), and then firing the resulting mixture (firing step).

[0033] As the raw material of oxide (X), a supply component corresponding to an element for obtaining the target oxide (X) can be used from among the Li supply component, M1 supply component (Fe supply component, In supply component, Y supply component, or Al supply component), M2 supply component (Si supply component), M3 supply component (W supply component), Zr supply component, and P supply component. For example, when obtaining an oxide (X) where y > 0 and z = 0, the Li supply component, M1 supply component, M2 supply component, Zr supply component, and P supply component are used as raw materials.

[0034] Examples of the Li supply component, M1 supply component (Fe supply component, In supply component, Y supply component, or Al supply component), M2 supply component, M3 supply component, Zr supply component, and P supply component for obtaining oxide (X) include carbonates, hydrogen carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, and sulfides of these metal elements. Note that one type of these supply components may be a compound containing two or more elements selected from Li, M1, M2, M3, Zr, and P.

[0035] As the P supply component, it is preferable to use a compound containing one or more elements selected from Li, M1, M2, M3, and Zr. Among these, it is preferable to use a zirconium phosphate compound as the supply component (Zr and P supply component). As the zirconium phosphate compound, Zr(HPO ４ ) ２ , Zr(HPO ４ ) ２ ・nH ２ Zirconium hydrogen phosphate such as O; Zr ３ (P.O. ４ ) ４ Zirconium phosphate such as Zr(PO ４ ) (H ２ P.O. ４ ), Zr(PO４ ) (H ２ P.O. ４ ) ２ ・nH ２ Zirconium hydrogen phosphate (n is 0≦n≦2) such as HZr ２ (P.O. ４ ) ３ , ZrP ２ O ７ , (ZrO) ２ P ２ O ７ Among these, Zr(HPO), which is called layered zirconium phosphate, is preferred because it has good handling properties as an inorganic solid electrolyte during production. ４ ) ２ ・nH ２ O can be preferably used.

[0036] When producing the oxide (X), the raw materials may be mixed by dry mixing, but it is preferable to mix them by wet mixing using a liquid. By adopting wet mixing, the density of the sintered product obtained by the firing step can be increased compared to the case of dry mixing. In addition, the ionic conductivity of the resulting solid electrolyte can be relatively improved. As the liquid used for wet mixing, water, various organic solvents, and mixtures thereof can be appropriately used.

[0037] In the firing step, the mixture obtained in the mixing step may be fired without molding, or may be molded and then fired. The firing temperature is not limited, but can be, for example, 900°C or higher, preferably 1,000°C or higher, more preferably 1,150°C or higher, and even more preferably 1,200°C or higher. The upper limit of the firing temperature can be, for example, 1,500°C or lower, preferably 1,400°C or lower, and more preferably 1,350°C or lower. During firing, the temperature may be increased stepwise from a temperature lower than the firing temperature (pre-firing), and the temperature required for firing may finally be maintained.

[0038] When pre-firing is performed, the obtained pre-firing product may be pulverized before the next firing process. When firing is performed at multiple temperature ranges, firing may be performed in three stages, for example, by performing a first pre-firing in a temperature range of 100°C or higher and lower than 800°C, a second pre-firing in a temperature range of 800°C or higher and lower than 1,200°C, and a main firing in a temperature range of 1,200°C or higher, and the pre-firing product may be pulverized each time the firing temperature range is changed. The firing time is not limited, but for example, the pre-firing may be performed for 1 hour to 40 hours and the main firing may be performed for 1 hour to 40 hours.

[0039] The oxide (X) exhibits high lithium ion conductivity and is therefore suitable as a solid electrolyte material for an electricity storage device in which the ion carrier is lithium ions.

[0040] The inorganic solid electrolyte obtained by the firing step is preferably pulverized by any method to prepare a powder for use in the production of a composite electrolyte. The pulverization treatment of the inorganic solid electrolyte may be carried out using a pulverizer such as a ball mill, a bead mill, or a blender.

[0041] The average particle size of the inorganic solid electrolyte used to produce the composite electrolyte is preferably 0.1 μm or more and 20 μm or less in volume-based median particle size measured in an aqueous medium. When the average particle size of the inorganic solid electrolyte is within the above range, it is preferable that a composite electrolyte exhibiting high ionic conductivity can be obtained while improving handleability. From the viewpoint of handleability, the average particle size of the inorganic solid electrolyte is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more, in volume-based median diameter. Furthermore, from the viewpoint of further increasing ionic conductivity, the average particle size of the inorganic solid electrolyte is more preferably 15 μm or less, and even more preferably 10 μm or less, in volume-based median diameter. The average particle size of the inorganic solid electrolyte is a value measured by laser diffraction / scattering particle size measurement. Details of the measurement method follow the method described in the Examples below.

[0042] The content of the inorganic solid electrolyte in the composite electrolyte is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, even more preferably 50% by mass or more, and even more preferably 55% by mass or more, based on the total amount of the composite electrolyte, from the viewpoint of obtaining a composite electrolyte with high ionic conductivity while utilizing the properties of the inorganic solid electrolyte (specifically, safety, heat resistance, alkali metal ion transport number, etc.). Furthermore, the upper limit of the content of the inorganic solid electrolyte is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, even more preferably 80% by mass or less, even more preferably 75% by mass or less, and even more preferably 70% by mass or less, based on the total amount of the composite electrolyte, in that the use of the inorganic solid electrolyte sufficiently reduces the resistance at the particle interface of the inorganic solid electrolyte, thereby increasing the ionic conductivity of the composite electrolyte. As the inorganic solid electrolyte, one type may be used alone, or two or more types may be used in combination.

[0043] (Organic Solid Electrolyte) The organic solid electrolyte includes a molecular crystal and a polymer. The molecular crystal is a solid in which structural units are regularly arranged in a crystal lattice. The polymer functions as a binder that binds inorganic solid electrolyte particles together and can exhibit ionic conductivity in the presence of the molecular crystal (more specifically, the molecular crystal electrolyte). The composite electrolyte of the present disclosure, which combines an inorganic solid electrolyte and an organic solid electrolyte, takes advantage of the high safety of the inorganic solid electrolyte and the high flexibility of the organic solid electrolyte, while improving the high interfacial resistance, which is a disadvantage of the inorganic solid electrolyte, by interposing the organic solid electrolyte. As a result, the composite electrolyte of the present disclosure exhibits high ionic conductivity. Below, we will first explain the molecular crystal, followed by the polymer.

[0044] Molecular Crystal The molecular crystal contained in the composite electrolyte of the present disclosure contains, as constituent units, an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom (hereinafter also referred to as "organic molecule (A)"), and an alkali metal salt. The molecular crystal containing the organic molecule (A) and the alkali metal salt as constituent units has an ion conduction path due to the regular arrangement of the constituent units, and is therefore a molecular crystal electrolyte that exhibits excellent ion conductivity.

[0045] Organic Molecule (A) The number of atoms of at least one type selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms contained in one molecule of the organic molecule (A) is not particularly limited. In the organic molecule (A), the number of atoms of at least one type selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms is preferably 1 to 8, and more preferably 2 to 6, per molecule. Of these, the organic molecule (A) preferably contains two or more, and more preferably 2 to 6, atoms of at least one type selected from sulfur atoms, oxygen atoms, and nitrogen atoms per molecule.

[0046] The molecular weight of the organic molecule (A) is, for example, 300 or less, preferably 250 or less, and more preferably 200 or less. The lower limit of the molecular weight of the organic molecule (A) is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. From the viewpoint of promoting crystallization of the mixture of the organic molecule (A) and the alkali metal salt, the total number of carbon atoms per molecule of the organic molecule (A) is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The total number of carbon atoms per molecule of the organic molecule (A) is preferably 2 or more.

[0047] Specific examples of the organic molecule (A) include organic molecules having a sulfur atom, such as sulfones, sulfides, thiols, thioesters, thiocarbonates, sulfoxides, and sulfamides. Organic molecules having a nitrogen atom include nitriles, amines, and amides. Organic molecules having a phosphorus atom include phosphines, phosphine oxides, and phosphinimines. Organic molecules having an oxygen atom include organic molecules having an oxygen atom among the examples of organic molecules having a sulfur atom, organic molecules having an oxygen atom among the examples of organic molecules having a nitrogen atom, and organic molecules having an oxygen atom among the examples of organic molecules having a phosphorus atom, as well as ethers, esters, ketones, and carbonates. The organic molecules constituting the molecular crystal may be of one type alone or two or more types.

[0048] In terms of being able to further increase the ionic conductivity of the molecular crystal, the organic molecule (A) is preferably at least one selected from the group consisting of organic molecules having a sulfur atom and an oxygen atom, organic molecules having a nitrogen atom, and organic molecules having a phosphorus atom.

[0049] (Organic molecule having sulfur atom and oxygen atom) As the organic molecule having sulfur atom and oxygen atom, sulfone can be preferably used. Preferred examples of sulfone include those represented by the following formula (1): (In formula (1), R ２ and R ３ are each independently an alkyl group or an alkoxy group, or R ２ and R ３ and represents a cyclic structure formed by bonding together, and the total number of carbon atoms in formula (1) is 2 to 16.

[0050] The molecule represented by the above formula (1) (hereinafter also referred to as "organic molecule (A1)") has a sulfonyl group (-SO ２ -) in the above formula (1). ２ and R ３When R is an alkyl group or an alkoxy group, the alkyl group and the alkoxy group may be linear or branched. ２ and R ３ The number of carbon atoms in each group of R ２ and R ３ There are no particular limitations on the number of carbon atoms, as long as the total number of carbon atoms between R and R is 2 to 16. From the viewpoint of inducing crystallization in the mixture of the supply components of the organic molecule (A1) and the alkali metal salt during the production of molecular crystals, ２ and R ３ Each of the groups preferably has 1 to 3 carbon atoms, more preferably 1 or 2.

[0051] R in the above formula (1) ２ and R ３ But, R ２ and R ３ When R represents a cyclic structure formed by bonding R to R, the cyclic structure may have a saturated ring skeleton or an unsaturated bond in the ring skeleton. ２ and R ３ The cyclic structure formed by bonding R may be a structure in which an alkyl group (e.g., a methyl group or an ethyl group) is bonded to the ring skeleton. ２ and R ３ The number of carbon atoms in the cyclic structure formed by bonding of is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5.

[0052] R in the above formula (1) is preferred because it can improve the ionic conductivity of the molecular crystal. ２ and R ３ is R ２ and R ３ and more preferably, the cyclic structure has a saturated ring skeleton.

[0053] The total number of carbon atoms in the above formula (1) is 2 to 16. From the viewpoint of promoting crystallization of a mixture of the supply components of the organic molecule (A1) and the alkali metal salt during the production of molecular crystals, the total number of carbon atoms in the above formula (1) is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 5.

[0054] Specific examples of the organic molecule (A1) include R ２ and R ３ are each an alkyl group or an alkoxy group, examples of which include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, and diethyl sulfate. ２ and R ３ But, R ２ and R ３ Examples of the cyclic structure formed by bonding include tetrahydrothiophene 1,1-dioxide, 3-methylsulfolane, 3-sulfolene, 1,3-propane sultone, 1,4-butane sultone, 1,3,2-dioxathiolane 2,2-dioxide, etc. The organic molecule (A1) constituting the molecular crystal may be one type alone or a combination of two or more types.

[0055] (Nitrogen Atom-Containing Organic Molecule) As the nitrogen atom-containing organic molecule, at least one selected from the group consisting of compounds having a nitrile group and an amide group can be preferably used.

[0056] Preferred examples of the nitrile include those represented by the following formula (2): (In formula (2), R ４ represents a hydrocarbon chain, R ５ and R ６ each independently represents a hydrogen atom, an alkyl group, or a cyano group, and the total number of carbon atoms in formula (2) is 16 or less.

[0057] The molecule represented by the above formula (2) (hereinafter also referred to as "organic molecule (A2)") is a molecule having two or more cyano groups (-CN). ４ R may be a saturated hydrocarbon chain or may have an unsaturated bond. R is a group that can be used to obtain molecular crystals with excellent ionic conductivity. ４ Preferably, R represents a saturated hydrocarbon chain. ４ has, for example, 1 to 10 carbon atoms, preferably 1 to 6, and more preferably 2 to 4 carbon atoms.

[0058] R ５or R ６ When R is an alkyl group, the alkyl group may be linear or branched. ５ or R ６ The alkyl group represented by R is preferably linear. ５ and R ６ The number of carbon atoms in each group is preferably 0 to 3, more preferably 0 or 1, from the viewpoint of causing crystallization by mixing the supply component of the organic molecule (A2) with the alkali metal salt during production of the molecular crystal.

[0059] From the viewpoint of promoting crystallization of the mixture of the supply components of the organic molecule (A2) and the alkali metal salt during the production of molecular crystals, the total number of carbon atoms in the above formula (2) is preferably 8 or less, more preferably 6 or less.

[0060] Specific examples of the organic molecule (A2) include succinonitrile, adiponitrile, 3-hexenedinitrile, 1,3,5-pentanetricarbonitrile, tert-butylmalononitrile, 1,2,2,3-propanetetracarbonitrile, etc. The organic molecule (A2) constituting the molecular crystal may be one type alone or a combination of two or more types.

[0061] The compound having an amide group preferably has two or more amide groups in one molecule in terms of high heat resistance. Specific examples of the compound having an amide group include malonamide, succinamide, glutaramide, adipamide, N,N,N',N'-tetramethylmalonamide, N,N,N',N'-tetraethylmalonamide, N,N,N',N'-tetramethylsuccinamide, and terephthalamide.

[0062] (Organic Molecule Having a Phosphorus Atom) Examples of organic molecules having a phosphorus atom include ethylenebis(dimethylphosphine), ethylenebis(diphenylphosphine), methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphine imine, and triphenylphosphine imine.

[0063] From the viewpoint of ease of production of the molecular crystal and of obtaining a composite electrolyte exhibiting an alkali metal ion transport number, the organic molecule (A) is preferably at least one selected from the group consisting of sulfones and nitriles, and more preferably at least one selected from the group consisting of organic molecules (A1) and (A2), in that a composite electrolyte excellent in ionic conductivity of the molecular crystal can be obtained.

[0064] Alkali Metal Salt The alkali metal salt is not particularly limited as long as it generates an alkali metal ion. Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt. The anion constituting the alkali metal salt may be either a monoatomic ion or a polyatomic ion, and may be either an inorganic ion or an organic ion.

[0065] Specific examples of alkali metal salts include Li ２ CO ３ , LiBr, LiCl, LiI, LiSCN, LiBF ４ , LiAsF ６ , LiClO ４ , C.H. ３ COOLi, CF ３ COOLi, LiCF ３ SO ３ , LiPF ６ , LiC(CF ３ SO ２ ) ３ and imide-based lithium salts; and salts of the anions of these lithium salts with alkali metal ions other than lithium ions (for example, sodium ions, potassium ions, etc.).

[0066] The imide-based lithium salt is a lithium salt containing an imide-based anion as a counter anion. Specific examples of the imide-based lithium salt include lithium bis(fluorosulfonyl)imide (Li ＋ (FSO ２ ) ２ N － ), lithium bis(trifluoromethanesulfonyl)imide (Li ＋ (CF ３ SO ２ ) ２ N－ ), lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide, and the like.

[0067] Of these, the alkali metal salts constituting the molecular crystal preferably include imide-based alkali metal salts, and more preferably imide-based lithium salts, in that they can provide molecular crystals with high ionic dissociation properties and higher ionic conductivity.

[0068] Among these, the imide-based lithium salt is preferably lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide, more preferably lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide, and even more preferably lithium bis(fluorosulfonyl)imide.

[0069] The molecular weight of the alkali metal salt is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. The lower limit of the molecular weight of the alkali metal salt is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. The alkali metal salt constituting the molecular crystal may be one type alone or two or more types.

[0070] The melting point of the alkali metal salt is, for example, 60° C. or higher, preferably 70° C. or higher, and more preferably 80° C. or higher. There is no particular upper limit to the melting point of the alkali metal salt, but it may be, for example, 300° C. or lower, or 250° C. or lower.

[0071] - Production of Molecular Crystals The molecular crystals contained in the composite electrolyte of the present disclosure can be produced by mixing an organic substance (hereinafter simply referred to as organic molecule (A)) that provides the organic molecule (A) with an alkali metal salt. Specifically, the molecular crystals can be produced by the first or second production method shown below. - First Production Method: A method including a step of mixing the organic molecule (A) with an alkali metal salt while applying mechanical energy (hereinafter also referred to as a "mechanical mixing step"). - Second Production Method: A method including a step of mixing the organic molecule (A) with an alkali metal salt in a solvent that can dissolve at least one of the organic molecule (A) and the alkali metal salt (hereinafter also referred to as a "solvent mixing step"), and a step of removing the solvent from a solution containing the organic molecule (A), the alkali metal salt, and the solvent (hereinafter also referred to as a "solvent removal step").

[0072] (Regarding the first manufacturing method) Mechanical mixing step In the mechanical mixing step, the organic molecule (A) and the alkali metal salt are mixed while applying mechanical energy to a substance containing the organic molecule (A) and the alkali metal salt by means of impact, shear, compression, friction, or the like. This preferably causes changes in the physicochemical properties of the organic molecule (A), the alkali metal salt, or both. In this specification, the process of mixing substances while applying mechanical energy is also referred to as "mechanical mixing."

[0073] The compounding ratio when mixing the organic molecule (A) and the alkali metal salt is not particularly limited and may be set depending on the types of the organic molecule (A) and the alkali metal salt, etc. The compounding ratio of the organic molecule (A) to the alkali metal salt may be, for example, 0.1 to 10 moles of the organic molecule (A) per mole of the alkali metal salt. The compounding ratio of the organic molecule (A) to the alkali metal salt is preferably 0.2 to 5 moles, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles of the organic molecule (A) per mole of the alkali metal salt.

[0074] In addition, when producing a molecular crystal, a substance other than the organic molecule (A) and the alkali metal salt may be further used as a constituent unit of the crystal lattice, as long as the effects of the present invention are not impaired. However, in consideration of the ionic conductivity and ease of production of the molecular crystal, it is preferable to minimize the amount of the substance other than the organic molecule (A) and the alkali metal salt used. Specifically, the amount of the substance other than the organic molecule (A) and the alkali metal salt used is preferably 0.1 mol or less, more preferably 0.05 mol or less, per mol of the total amount of the organic molecule (A) and the alkali metal salt.

[0075] The method for mixing the organic molecule (A) and the alkali metal salt while applying mechanical energy is not particularly limited. In the mechanical mixing step, the organic molecule (A) and the alkali metal salt can be mixed using various devices, such as a ball mill, a bead mill, a blender, a homogenizer, a stamp mill, a homomixer, or a disperser-type mixer. Furthermore, when producing molecular crystals on a small scale, the organic molecule (A) and the alkali metal salt can also be mechanically mixed using a mortar and pestle. The mechanical mixing of the organic molecule (A) and the alkali metal salt can be performed in a dry or wet manner. Furthermore, the mechanical mixing of the organic molecule (A) and the alkali metal salt can be performed at room temperature or at a low temperature. For example, when the melting point of the organic molecule (A) is lower than room temperature, the organic molecule (A) in a liquid state can be mechanically mixed with the alkali metal salt. Alternatively, the organic molecule (A) in a solid state can be mechanically mixed with the alkali metal salt at a temperature lower than the melting point of the organic molecule (A).

[0076] The mechanical mixing of the organic molecule (A) and the alkali metal salt may be carried out while heating. However, in order to suppress volatilization or sublimation of the organic molecule (A), the mechanical mixing step is preferably carried out at a temperature lower than the heating temperature in the subsequent heating step. Specifically, the mechanical mixing step is carried out, for example, at 50°C or lower, preferably 40°C or lower, and more preferably 35°C or lower. The time for mechanical mixing varies depending on the amount and type of the organic molecule (A) and alkali metal salt used, but may be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0077] The mixture of organic molecules (A) and an alkali metal salt obtained by mechanical mixing (hereinafter also referred to simply as "mixture") preferably has a melting point of 40°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher. The melting point of the mixture is preferably 110°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower, in order to suppress decomposition of molecular crystals accompanying volatilization or sublimation of the organic molecules (A) in the heating step after the mechanical mixing step. In this specification, the melting point of the mixture of organic molecules (A) and an alkali metal salt is a value obtained by differential scanning calorimetry (DSC). Details of the measurement method follow the method described in the Examples below.

[0078] When producing a molecular crystal by the first production method, the first production method preferably further includes a step of heating the mixture obtained by the mechanical mixing step (i.e., a mixture of organic molecules (A) and an alkali metal salt). This heating step can make the organic molecules (A) and the alkali metal salt in the mixture more uniform, thereby further increasing the ionic conductivity of the molecular crystal. In particular, a method that combines the mechanical mixing step and the heating step is thought to generate intermolecular interactions between the alkali metal ions derived from the alkali metal salt and the organic molecules (A) due to the mechanical mixing, thereby making it possible to suppress volatilization or sublimation of the organic molecules (A) during heat treatment. This has the advantage of making it easier to obtain a molecular crystal of the desired composition.

[0079] Heating Step In the heating step, after the mechanical mixing step, the mixture obtained by the mechanical mixing step is heated. The method for heating the mixture is not particularly limited. The heating temperature of the mixture can be appropriately set depending on the types of organic molecules (A) and alkali metal salt used as raw materials in the production of molecular crystals. From the viewpoint of making the organic molecules (A) and the alkali metal salt in the mixture more uniform, it is preferable to heat the mixture in this heating step at a temperature equal to or higher than the melting point of the mixture of organic molecules (A) and alkali metal salt obtained by mechanical mixing. Setting the heating temperature equal to or higher than the melting point of the mixture melts the mixture, thereby promoting uniform mixing of the organic molecules (A) and the alkali metal salt.

[0080] The temperature at which the mixture is heated is preferably higher than the melting point of the mixture, from the viewpoint of homogenizing the organic molecules (A) and the alkali metal salt in the mixture by melting the mixture. Furthermore, from the viewpoint of promoting homogenization of the organic molecules (A) and the alkali metal salt in the mixture, the heating temperature of the mixture is more preferably 5°C or higher, and even more preferably 7°C or higher, than the melting point of the mixture (unit: °C). With regard to the upper limit of the heating temperature of the mixture, from the viewpoint of suppressing volatilization or sublimation of the components contained in the mixture, when the melting point of the mixture is expressed as Mp (unit: °C), it is preferably (Mp + 20)°C or lower, and more preferably (Mp + 15)°C or lower. The heating time is not particularly limited as long as it homogenizes the organic molecules (A) and the alkali metal salt in the mixture. The heating time is, for example, 1 minute to 3 hours, preferably 15 minutes to 2 hours, and more preferably 30 minutes to 2 hours. Furthermore, the heat treatment is usually carried out under normal pressure, but may also be carried out under pressure or reduced pressure.

[0081] When the mixture is heated, it is preferable to heat the mixture while stirring it to further homogenize the organic molecule (A) and the alkali metal salt. The stirring method is not particularly limited, and examples thereof include a magnetic stirrer, a stirring rod, a stirrer with stirring blades, and external circulation stirring. Stirring may also be performed by a mechanical mixing operation that can generate a larger shear force, such as a homomixer, a disperser-type mixer, or a homogenizer.

[0082] After heating a mixture containing an organic molecule (A) and an alkali metal salt, the heated mixture can be crystallized by lowering the temperature of the heated mixture, thereby obtaining the desired molecular crystals. When lowering the temperature of the heated mixture, the mixture may be gradually cooled (e.g., slowly lowered at room temperature over 1 to 48 hours). Alternatively, the heated mixture may be rapidly cooled (e.g., the heated mixture is placed in a thermostatic bath at a temperature lower than room temperature (e.g., 15°C or lower) for a short period of time). From the viewpoint of favorable crystallization of the heated mixture, it is preferable to cool the heated mixture by gradually lowering the temperature of the mixture.

[0083] (Second Production Method) Solvent Mixing Step When the boiling point of the organic molecule (A) is high (for example, 100°C or higher), the second production method may be applied as a method for producing the molecular crystal (A). By mixing the organic molecule (A) and the alkali metal salt in a solvent, it is possible to promote homogenization of the organic molecule (A) and the alkali metal salt.

[0084] The solvent used in the solvent mixing step may be any solvent capable of dissolving at least one of the organic molecule (A) and the alkali metal salt. An organic solvent is preferably used as the solvent. The organic solvent used preferably has a moderately low boiling point (e.g., 100°C or less) and a low dielectric constant, such as dimethyl carbonate, tetrahydrofuran, or ethyl acetate. In the solvent mixing step, the order in which the organic molecule (A) and the alkali metal salt are added to the solvent is not particularly limited. For example, the organic molecule (A) and the alkali metal salt may be added to the solvent simultaneously, or one of the organic molecule (A) and the alkali metal salt may be dissolved in the solvent and then the other raw material may be added to the solvent. When mixing the organic molecule (A) and the alkali metal salt in the solvent, it is preferable to perform the mixing while stirring to homogenize the organic molecule (A) and the alkali metal salt. The stirring method is not particularly limited, and the stirring methods exemplified in the first production method may be used as appropriate.

[0085] Solvent Removal Step The method for removing the solvent from a solution containing the organic molecule (A), an alkali metal salt, and a solvent is not particularly limited as long as it can remove the solvent from the solution. As a method for removing the solvent, heat treatment is preferred because it can remove the solvent simply and efficiently. The heat treatment may be carried out under normal pressure, but may also be carried out under increased pressure or reduced pressure. When a solvent with a high boiling point is used in the solvent mixing step, it is preferable to carry out the heat treatment under reduced pressure in order to suppress decomposition of the organic molecule (A) and the alkali metal salt.

[0086] The fact that the product obtained by the above-mentioned production method contains molecular crystals having the organic molecule (A) and an alkali metal salt as structural units can be detected by powder X-ray diffraction measurement of the product. The details of the measurement method follow the method described in the Examples below.

[0087] The molecular crystal contained in the composite electrolyte of the present disclosure exhibits ionic conductivity. Specifically, the molecular crystal has an ionic conductivity of 1.0 × 10 at 25°C. －６ The ionic conductivity of the molecular crystal at 25° C. is preferably 1.0×10 S / cm or more. －６ When the ionic conductivity of the molecular crystal is 1.0×10 S / cm or more, the decrease in the interfacial resistance of the inorganic solid electrolyte can be compensated for, and a composite electrolyte having excellent ionic conductivity can be obtained. －５ S / cm or more, and －５ S / cm or more is more preferable, and 3.5×10 －５ More preferably, it is 5.0×10 S / cm or more. －５ It is more preferable that the ionic conductivity of the molecular crystal is 25 S / cm or more. The ionic conductivity of the molecular crystal is a value measured at 25°C using an AC impedance method. The details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0088] In the composite electrolyte of the present disclosure, the content of the molecular crystals is, from the viewpoint of obtaining a composite electrolyte exhibiting good ionic conductivity, preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 15% by mass or more, even more preferably 20% by mass or more, and still more preferably 25% by mass or more, relative to the total amount of the composite electrolyte. With regard to the upper limit of the content of the molecular crystals, from the viewpoint of ensuring the heat resistance of the composite electrolyte, it is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, still more preferably 45% by mass or less, and still more preferably 40% by mass or less, relative to the total amount of the composite electrolyte.

[0089] The content of the organic molecule (A) in the composite electrolyte of the present disclosure is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total amount of the composite electrolyte. From the viewpoint of ensuring the heat resistance of the composite electrolyte, the upper limit of the content of the organic molecule (A) is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the composite electrolyte. The content of the organic molecule (A) in the composite electrolyte shown here is basically equivalent to the amount of the organic molecule (A) used as a raw material when producing the molecular crystal.

[0090] Polymer The composite electrolyte of the present disclosure is a polymer １ A repeating unit represented by —O)— (where R １ The polymer (P) is blended into the composite electrolyte for the purposes of imparting flexibility to the composite electrolyte, functioning as a binder that binds inorganic solid electrolyte particles together, and exhibiting ionic conductivity in the presence of a molecular crystalline electrolyte.

[0091] Here, −(R １ The polymer having a repeating unit represented by —(R —O)— in the main chain is typically a polymer obtained by polymerization using alkylene oxides or cyclic ethers as monomers, and １ -O) ｒ- (where r is an integer of 2 or more) in the main chain. １ Generally, the number of carbon atoms is 2 or more, and may be 2 to 10. That is, the polymer (P) contained in the composite electrolyte of the present disclosure is a polymer different from polyether-based polymers such as polyalkylene oxides and polyethers.

[0092] In this specification, "-(R １ The phrase "substantially does not have a repeating unit represented by -(R —O)— in the main chain" means that the polymer (P) does not have a repeating unit represented by -(R —O)— in the main chain. １ However, the polymer (P) does not exhibit the properties derived from the repeating unit represented by -(R -O)- to the extent that the effect of the present disclosure is not impaired. １ It is permissible for the polymer (P) to have a small amount of repeating units represented by —(R —O)— in the main chain. １ The proportion of repeating units represented by -(R -O)- is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total amount of repeating units constituting the main chain of the polymer (P). １ -O) ｒ It is preferred that the main chain does not have a structure represented by - (where r is an integer of 2 or more).

[0093] A "repeating unit" is a basic unit of the chemical structure of a polymer, and the chemical formula of the polymer is expressed as an integer multiple of the repeating unit. Basically, one molecule of a monomer introduces one repeating unit having a structure corresponding to that monomer into the polymer, or introduces a structure consisting of two or more consecutive repeating units into the polymer. In the latter case, the structure consisting of two or more consecutive repeating units corresponds to one molecule of the monomer.

[0094] As the polymer (P), a polymer that exhibits higher ionic conductivity at room temperature (25° C.) in the coexistence with a molecular crystalline electrolyte than an organic electrolyte composed of a polyether polymer and a molecular crystalline electrolyte is preferably used. Examples of such polymers (P) include nitrile group-containing polymers, polyester polymers, polycarbonate polymers, fluorine-containing polymers, olefin polymers, and (meth)acrylic polymers.

[0095] Nitrile Group-Containing Polymers Examples of nitrile group-containing polymers include polymers containing structural units derived from nitrile group-containing vinyl monomers. Examples of nitrile group-containing vinyl monomers include (meth)acrylonitrile, ethacrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile, α-chloroacrylonitrile, and α-fluoroacrylonitrile. The nitrile group-containing polymer is preferably a polymer containing repeating units derived from (meth)acrylonitrile. In the nitrile group-containing polymer, the proportion of repeating units derived from (meth)acrylonitrile is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total repeating units constituting the nitrile group-containing polymer.

[0096] Polyester-Based Polymers Examples of polyester-based polymers include polymers containing a repeating unit represented by the following formula (3). (In formula (3), R ７ represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 10.

[0097] In the above formula (3), R ７ is preferably a hydrogen atom or a methyl group from the viewpoint of availability of raw materials and ease of synthesis of a polyester polymer. m is preferably 0 to 8, more preferably 0 to 6, and even more preferably 0 to 4, from the viewpoint of availability of raw materials. Furthermore, m is preferably 1 or more, more preferably 2 to 8, and even more preferably 2 to 6, in order to provide the resulting composite electrolyte with better ionic conductivity and flexibility.

[0098] Monomers used to introduce the repeating unit represented by formula (3) above into a polymer include lactones and lactides. Specific examples of these include lactones such as β-propiolactone, γ-butyrolactone, β-butyrolactone, pivalolactone, δ-valerolactone, and ε-caprolactone. Lactides include glycolide obtained by dehydration condensation of two glycolic acid molecules, dilactide obtained by dehydration condensation of two lactic acid molecules, and tetramethylglycolide. When the above lactides are used as monomers, a structure consisting of two consecutive repeating units represented by formula (3) above is introduced into the polymer per lactide molecule. That is, a structure consisting of two consecutive repeating units represented by formula (3) above corresponds to one lactide molecule.

[0099] Among the above, the monomer constituting the polyester polymer is preferably at least one selected from the group consisting of γ-butyrolactone, δ-valerolactone, ε-caprolactone, and dilactide, in that a composite electrolyte having superior ionic conductivity can be obtained.

[0100] The number of repeating units represented by formula (3) contained in the polyester polymer can be appropriately set depending on the desired molecular weight of the polyester polymer. The number of repeating units represented by formula (3) contained in the polyester polymer is, for example, 10 to 1,500, preferably 20 to 1,200, more preferably 30 to 1,000, and even more preferably 30 to 800.

[0101] The polyester polymer may further contain a repeating unit different from the repeating unit in formula (3) above, as long as the effects of the present invention are not impaired. Examples of the other repeating unit include dioxepanone, ethylene oxalate, dioxanone, γ-nonalactone, γ-decalactone, γ-undecalactone, cyclopentadecanolide, and cyclohexedecanolide.

[0102] In the polyester polymer, the proportion of the repeating units represented by the formula (3) is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more, based on the total repeating units constituting the polyester polymer. By setting the proportion of the repeating units represented by the formula (3) in the polyester polymer within the above range, a composite electrolyte with superior ionic conductivity can be obtained.

[0103] The polyester polymer may have a hydroxyl group or carboxyl group derived from the monomer at its terminal. Alternatively, the terminal of the polyester polymer may be modified by utilizing a hydroxyl group or carboxyl group present at the polymer terminal. By modifying the terminal hydroxyl group or terminal carboxyl group of the polyester polymer, it is possible to improve the heat resistance (durability) of the polyester polymer or reduce the crystallinity of the polyester polymer. When the terminal structure of the polyester polymer is an alkyl group, the alkyl group is preferably a linear or branched alkyl group having 3 to 20 carbon atoms, from the viewpoint of improving the heat resistance of the polyester polymer and promoting a reduction in crystallinity.

[0104] A preferred example of the polyester polymer is a polymer represented by the following formula (3-1). [In formula (3-1), R ７ represents a hydrogen atom or an alkyl group; X and Y are the same or different and represent a hydrogen atom, a hydroxyl group, or an alkyl group; n represents an integer of 1 or more, and m represents an integer of 0 to 10.

[0105] The method for producing the polyester polymer is not particularly limited, and the polyester polymer can be produced by any conventionally known method. In terms of being able to produce the polyester polymer simply and inexpensively, it is preferred to produce the polyester polymer by ring-opening polymerization using at least one monomer selected from the group consisting of the lactones and lactides described above.

[0106] Polycarbonate-Based Polymers Examples of polycarbonate-based polymers include polymers containing a repeating unit represented by the following formula (4). (In formula (4), R ８ represents an alkylene group.)

[0107] In the above formula (4), R ８ The carbon number of the carboxylic acid is preferably 2 to 10, more preferably 2 to 8, and even more preferably 2 to 6, in terms of the availability of raw materials and the ability to provide the resulting composite electrolyte with better ionic conductivity and flexibility.

[0108] The number of repeating units represented by the formula (4) contained in the polycarbonate polymer can be appropriately set depending on the desired molecular weight of the polycarbonate polymer. The number of repeating units represented by the formula (4) contained in the polycarbonate polymer is, for example, 10 to 1,500, preferably 20 to 1,200, more preferably 30 to 1,000, and even more preferably 30 to 800.

[0109] In the polycarbonate-based polymer, the proportion of the repeating unit represented by the above formula (4) is preferably 80 mass% or more, more preferably 85 mass% or more, even more preferably 90 mass% or more, and even more preferably 95 mass% or more, based on the total repeating units constituting the polycarbonate-based polymer. By setting the proportion of the repeating unit represented by the above formula (4) in the polycarbonate-based polymer within the above range, a composite electrolyte with superior ion conductivity can be obtained. The polycarbonate-based polymer may further have a repeating unit different from the repeating unit in the above formula (4) (for example, a repeating unit derived from bisphenol A) within a range that does not impair the effects of the present invention.

[0110] The method for producing the polycarbonate polymer is not particularly limited, and the polycarbonate polymer can be produced by any conventionally known method. For example, the polycarbonate polymer can be produced by using a dihydroxy compound as a raw material and a phosgene method or an ester exchange method.

[0111] Fluorine-containing polymer The fluorine-containing polymer may be a polymer containing a repeating unit having a fluorine atom. As the fluorine-containing polymer, a polymer containing carbon atoms in the main skeleton and having fluorine atoms bonded to the carbon atoms can be preferably used. Specifically, the fluorine-containing polymer preferably contains a repeating unit represented by the following formula (5) as the repeating unit having a fluorine atom: -[CR ９ R １０ -CFR １１ ]-(5) (In formula (5), R ９ , R １０ and R １１ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or a perfluoroalkyloxy group having 1 to 3 carbon atoms.

[0112] Specific examples of the repeating unit represented by the above formula (5) include -[CH ２ -CHF]-, -[CH ２ -CF ２ ]-,-[CHF-CF ２ ] -, -[CF ２ -CF ２ ] -, -[CF ２ -CFCF ３ ]-,-[CHF-CFCF ３ ] -, -[CF ２ -CF (OCF ３ ) )]-, -[CF ２ -CF(OC ２ F ５ ) )]-, -[CF ２ The repeating unit represented by the above formula (5) is, among these, -[CH ２ -CHF]-, -[CH ２ -CF ２ ]-,-[CHF-CF ２ ] -, -[CF ２ -CF ２ ] -, -[CF ２ -CFCF ３ ]- and -[CHF-CFCF ３ ]- is preferred.

[0113] In the fluorine-containing polymer, the proportion of the repeating units having fluorine atoms is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more, based on the total repeating units constituting the fluorine-containing polymer. The fluorine-containing polymer may have only one kind of repeating unit having a fluorine atom, or may have two or more kinds of repeating units having a fluorine atom.

[0114] The fluorine-containing polymer may be composed solely of repeating units having fluorine atoms, or may further contain repeating units not having fluorine atoms. Specific examples of monomers constituting repeating units having no fluorine atoms include olefins such as ethylene, propylene, n-butene, and isobutene; carboxyl group-containing monomers such as (meth)acrylic acid, vinylacetic acid, and pentenoic acid; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, vinyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl allyl ether, and 4-hydroxybutyl allyl ether; amide group-containing monomers such as N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, and N-vinyl-γ-valerolactam; and ester group-containing monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, phenyl (meth)acrylate, cyclohexyl (meth)acrylate, vinyl acetate, isopropenyl acetate, vinyl butyrate, vinyl isobutyrate, vinyl versatate, and vinyl benzoate.

[0115] Specific examples of the fluorine-containing polymer include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene / hexafluoropropylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene / trifluoroethylene copolymer, ethylene / chlorotrifluoroethylene copolymer, vinylidene fluoride / hexafluoropropane / (meth)acrylic acid copolymer, and vinylidene fluoride / pentafluoropropylene copolymer.

[0116] Furthermore, a fluororubber may be used as the fluorine-containing polymer. Specific examples of the fluororubber include vinylidene fluoride rubber, tetrafluoroethylene / propylene rubber, tetrafluoroethylene / propylene / vinylidene fluoride rubber, and ethylene / hexafluoropropylene rubber.

[0117] Among the above, the fluorine-containing polymer is preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, and vinylidene fluoride / tetrafluoroethylene copolymer, and more preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypentafluoropropylene, and vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP).

[0118] Olefin-Based Polymers Examples of olefin-based polymers include polymers containing structural units derived from α-olefins having 2 to 20 carbon atoms. Specific examples include homopolymers of α-olefins having 2 to 20 carbon atoms and copolymers of α-olefins having 2 to 20 carbon atoms with other monomers. Specific examples of α-olefins having 2 to 20 carbon atoms include ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 4-methyl-1-hexene, 1-octene, 4,4-dimethyl-1-hexene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene.

[0119] In the olefin polymer, the proportion of structural units derived from α-olefins having 2 to 20 carbon atoms is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on all repeating units constituting the olefin polymer. The α-olefins constituting the olefin polymer may be one type or two or more types.

[0120] The olefin polymer may contain repeating units derived from other vinyl monomers in addition to repeating units derived from α-olefins. Examples of other vinyl monomers constituting the olefin polymer include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid, and cinnamic acid; unsaturated dicarboxylic acids such as fumaric acid, maleic acid, citraconic acid, chloromaleic acid, glutaconic acid, and itaconic acid; half esters or half amides of unsaturated dicarboxylic acids; unsaturated tricarboxylic acids such as trans-aconitic acid; maleic anhydride, citraconic anhydride, chloromaleic anhydride, itaconic anhydride, Examples of suitable carboxylic acid anhydrides include 3,4,5,6-tetrahydrophthalic anhydride; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, and tert-butyl (meth)acrylate; styrenes such as styrene and methylstyrene; conjugated dienes such as 1,3-butadiene, isoprene, 1,3-pentadiene, and 1,3-hexadiene; and vinyl ethers such as vinyl acetate.

[0121] Preferred examples of olefin polymers include polypropylene, propylene / ethylene copolymer, propylene / 1-butene copolymer, propylene / ethylene / 1-butene copolymer, and propylene / ethylene / 1-octene copolymer. Furthermore, examples of olefin polymers copolymerized with other vinyl monomers include ethylene / ethyl acrylate copolymer and ethylene / vinyl acetate copolymer. When a copolymer is used, a random copolymer, a block copolymer, or a graft copolymer can be appropriately selected. Among the above, polypropylene, a propylene / ethylene copolymer, or a propylene / 1-butene copolymer is preferred as the olefin polymer.

[0122] (Meth)acrylic Polymer As the (meth)acrylic polymer, a polymer containing a repeating unit derived from a (meth)acrylic acid alkyl ester can be preferably used, since it can provide a composite electrolyte that exhibits a good balance between ionic conductivity and flexibility.

[0123] Examples of the (meth)acrylic acid alkyl ester constituting the (meth)acrylic polymer include (meth)acrylic acid alkyl esters having an alkyl group having 1 to 20 carbon atoms in the ester moiety. Specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0124] From the viewpoint of obtaining a composite electrolyte having excellent ionic conductivity while ensuring the formability and flexibility of the composite electrolyte, the (meth)acrylic acid alkyl ester constituting the (meth)acrylic polymer is preferably a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 12 carbon atoms in the ester moiety, and more preferably a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 8 carbon atoms in the ester moiety, among the above.

[0125] The (meth)acrylic polymer may contain repeating units derived from other vinyl monomers in addition to repeating units derived from (meth)acrylic acid alkyl esters. Examples of other vinyl monomers constituting the (meth)acrylic polymer include (meth)acrylic acid, aliphatic cyclic (meth)acrylic acid esters, aromatic (meth)acrylic acid esters, alkoxyalkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, polyalkylene glycol mono(meth)acrylates, (meth)acrylates having a heterocyclic structure, and zwitterionic mono(meth)acrylates.

[0126] In the (meth)acrylic polymer, the proportion of repeating units derived from a (meth)acrylic acid alkyl ester is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, and still more preferably 95% by mass or more, based on the total repeating units constituting the (meth)acrylic polymer. The method for producing the (meth)acrylic polymer is not particularly limited, and the polymer can be produced by appropriately using a conventionally known method such as radical polymerization.

[0127] The polymer (P) may be linear or branched. A specific example of a branched polymer (P) is a star polymer having a core portion and three or more branched chains (arm portions) extending from the core portion. When such a star polymer is used, it is believed that crystallization of the polymer (P) is suppressed, facilitating molecular motion of the polymer (P). The polymer (P) may be a crosslinked polymer or a non-crosslinked polymer. A non-crosslinked polymer is preferably used as the polymer (P) because it can more actively activate the molecular motion of the polymer (P), thereby facilitating the formation of ion conduction paths in the composite electrolyte.

[0128] The polymer (P) is preferably at least one selected from the group consisting of a nitrile group-containing polymer, a polyester polymer, a polycarbonate polymer, a fluorine-containing polymer, and a (meth)acrylic polymer, in that it can provide a composite electrolyte that exhibits high ionic conductivity and is excellent in formability and flexibility. Among these, at least one selected from the group consisting of a polyester polymer, a fluorine-containing polymer, and a (meth)acrylic polymer is more preferred, and a polyester polymer is even more preferred, in that it can be dissolved in a solvent having a relatively low boiling point.

[0129] From the viewpoint of imparting good flexibility to the composite electrolyte, the glass transition temperature (Tg) of the polymer (P) is preferably 65°C or lower. From the viewpoint of obtaining a composite electrolyte exhibiting even better flexibility, the glass transition temperature of the polymer (P) is preferably 50°C or lower, more preferably 20°C or lower, preferably 0°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, and even more preferably -50°C or lower. The lower limit of the glass transition temperature of the polymer (P) is not particularly limited, and is, for example, -80°C or higher. In this specification, the glass transition temperature of the polymer is a value measured by differential scanning calorimetry (DSC).

[0130] The weight-average molecular weight (Mw) of the polymer (P) is preferably 3,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and still more preferably 20,000 or more, from the viewpoints of obtaining a composite electrolyte having high strength and high ionic conductivity and of improving the formability of the composite electrolyte. The upper limit of the Mw of the polymer (P) is preferably 1,000,000 or less, more preferably 800,000 or less, and even more preferably 500,000 or less, from the viewpoints of ensuring appropriate fluidity of the polymer (P) and ensuring flexibility of the composite electrolyte.

[0131] The molecular weight distribution (Mw / Mn) of the polymer (P), which is the ratio of Mw to the number average molecular weight (Mn), is preferably 4.5 or less, more preferably 4.0 or less, and even more preferably 3.5 or less, from the viewpoint of obtaining a composite electrolyte exhibiting good ionic conductivity. In this specification, the Mw and Mn of the polymer are polystyrene-equivalent values ​​determined by gel permeation chromatography (GPC).

[0132] In the composite electrolyte of the present disclosure, the content of the polymer (P) is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and even more preferably 2% by mass or more, based on the total amount of the composite electrolyte, from the viewpoint of obtaining a composite electrolyte exhibiting good flexibility. The upper limit of the content of the polymer (P) is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, still more preferably 8% by mass or less, and even more preferably 5% by mass or less, based on the total amount of the composite electrolyte, from the viewpoint of suppressing a decrease in the alkali metal ion transport number of the composite electrolyte. The polymer (P) may be used singly or in combination of two or more types.

[0133] The composite electrolyte of the present disclosure may further contain components (other components) other than the inorganic solid electrolyte, molecular crystal, and polymer described above, as long as the effects of the present invention are not impaired. For example, to further increase the ionic conductivity of the composite electrolyte, an alkali metal salt may be further blended as another component, and the organic solid electrolyte may be composed of components including molecular crystals, a polymer, and an alkali metal salt. That is, the composite electrolyte of the present disclosure may contain an inorganic solid electrolyte, molecular crystals, a polymer, and an alkali metal salt. Examples of alkali metal salts include those similar to those used in producing molecular crystals.

[0134] When a composite electrolyte containing an alkali metal salt together with an inorganic solid electrolyte, a molecular crystal, and a polymer is obtained, the alkali metal salt as another component may be the same as or different from the alkali metal salt constituting the molecular crystal. From the viewpoint of fully obtaining the effect of increasing the ionic conductivity of the composite electrolyte, it is preferable that the alkali metal salt blended together with the inorganic solid electrolyte, the molecular crystal, and the polymer is the same as the alkali metal salt constituting the molecular crystal.

[0135] When an alkali metal salt is further blended as another component in the composite electrolyte, the content of the alkali metal salt as another component is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on the total amount of the composite electrolyte, and is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total amount of the composite electrolyte.

[0136] Furthermore, from the viewpoint of obtaining a composite electrolyte exhibiting good ionic conductivity, the content of the alkali metal salt in the composite electrolyte of the present disclosure is preferably 2 mass% or more, more preferably 5 mass% or more, even more preferably 10 mass% or more, and still more preferably 15 mass% or more, relative to the total amount of the composite electrolyte. From the viewpoint of ensuring the heat resistance of the composite electrolyte, the upper limit of the content of the alkali metal salt in the composite electrolyte is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 35 mass% or less, relative to the total amount of the composite electrolyte. The content of the alkali metal salt in the composite electrolyte referred to here is the total amount of the alkali metal salt used as a raw material in producing the molecular crystal and the alkali metal salt blended into the composite electrolyte separately from the raw materials for the molecular crystal in producing the composite electrolyte.

[0137] Examples of other components include, in addition to alkali metal salts, inorganic fillers, conductive additives, positive electrode active materials, negative electrode active materials, antioxidants, colorants, etc. However, in consideration of the ionic conductivity and ease of production of the composite electrolyte, it is preferable to use as few components as possible other than the alkali metal salts. Specifically, the content of components other than the alkali metal salts is, for example, 5% by mass or less, or may be 2% by mass or less, or may be 1% by mass or less, based on the total amount of the composite electrolyte.

[0138] <Method for Producing Composite Electrolyte> The method for producing the composite electrolyte of the present disclosure is not particularly limited as long as it can produce a composite electrolyte exhibiting desired properties. The composite electrolyte of the present disclosure can be produced by a method including a step of mixing an inorganic solid electrolyte, a molecular crystal, and a polymer (mixing step). The composite electrolyte of the present disclosure is preferable in that it can produce a solid electrolyte exhibiting high ionic conductivity without requiring a firing step during the production of the composite electrolyte, and is less subject to process constraints. Furthermore, a solid electrolyte exhibiting good ionic conductivity can be produced by a simple method in which an inorganic solid electrolyte and an organic solid electrolyte are mixed and then molded as necessary.

[0139] In the mixing step for producing a composite electrolyte, the inorganic solid electrolyte, molecular crystals, and polymer may be mixed uniformly, and the method is not particularly limited. The inorganic solid electrolyte, molecular crystals, and polymer may be charged all at once in a container, or each raw material may be charged sequentially. In the latter case, for example, the molecular crystals and polymer may first be charged and mixed in a container, and then the inorganic solid electrolyte may be charged into the container containing the mixture of molecular crystals and polymer, and further mixed. Alternatively, at least some of the raw materials among the inorganic solid electrolyte, molecular crystals, and polymer may be continuously supplied to the container. Among the above, initial lump-sum charging, in which the inorganic solid electrolyte, molecular crystals, and polymer are charged all at once, is preferred because it facilitates homogenization of the inorganic solid electrolyte, molecular crystals, and polymer and facilitates the production of a composite electrolyte with excellent flexibility and ionic conductivity. When mixing the molecular crystals, inorganic solid electrolyte, and polymer, an alkali metal salt may be added as another component to further enhance the ionic conductivity of the composite electrolyte.

[0140] When an alkali metal salt is added when mixing the inorganic solid electrolyte, the molecular crystal, and the polymer, the amount of the alkali metal salt added is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on the total amount of the composite electrolyte, and is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total amount of the composite electrolyte.

[0141] The process of mixing the inorganic solid electrolyte, molecular crystals, and polymer may be performed by dry mixing or wet mixing using a solvent. Of these, wet mixing is preferred. By using wet mixing, the components can be mixed more uniformly, which can relatively improve the ionic conductivity of the composite electrolyte.

[0142] Various organic solvents can be used as the solvent for wet mixing. From the viewpoint of increasing the uniformity of the inorganic solid electrolyte and the organic solid electrolyte and increasing the flexibility of the composite electrolyte, the solvent used for wet mixing is preferably an organic solvent capable of dissolving a polymer, and more preferably an organic solvent capable of dissolving a polymer and dissolving or dispersing molecular crystals. Such a solvent can be appropriately selected depending on the types of polymer and molecular crystal used in the production of the composite electrolyte. Examples of such solvents include ethers such as 1,2-dimethoxyethane and tetrahydrofuran; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and heptane; esters such as ethyl acetate; carbonates such as dimethyl carbonate and ethyl methyl carbonate; amides such as N-methylformamide, N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; and nitriles such as acetonitrile. The solvent used in the wet mixing may be one kind or a mixed solvent of two or more kinds.

[0143] When a solvent is used when mixing the inorganic solid electrolyte, the molecular crystals, and the polymer, the amount of solvent used may be appropriately set. From the viewpoint of achieving uniform mixing, the amount of solvent used may be, for example, 10 to 2,000 parts by mass per 100 parts by mass of the total amount of components other than the solvent used in the production of the composite electrolyte. From the viewpoint of achieving uniform mixing while simplifying the operation in the solvent removal step after the mixing step, the amount of solvent used is preferably 10 to 1,000 parts by mass, more preferably 15 to 500 parts by mass, and even more preferably 20 to 250 parts by mass per 100 parts by mass of the total amount of components other than the solvent used in the production of the composite electrolyte. The mixing of the inorganic solid electrolyte, the molecular crystals, and the polymer may be performed at room temperature, at a low temperature, or under heating.

[0144] In order to enhance the uniformity of these components, the inorganic solid electrolyte, molecular crystals, and polymer may be mixed by mechanical mixing using various devices such as a ball mill, planetary ball mill, bead mill, blender, homogenizer, stamp mill, homomixer, and disperser mixer. Furthermore, when producing a composite electrolyte on a small scale, the components may be mechanically mixed using a mortar and pestle. Furthermore, when wet mixing is performed, ultrasonic treatment or the like may be performed to enhance the dispersibility of the inorganic solid electrolyte.

[0145] The mixture obtained by mixing an inorganic solid electrolyte, a molecular crystal, and a polymer may be used as a composite electrolyte by molding or thinning. When a mixture containing an inorganic solid electrolyte, a molecular crystal, and a polymer is molded to obtain a molded body, the molding method is not particularly limited, and known molding methods can be appropriately adopted. Specific examples of molding methods include extrusion molding, transfer molding, pressure molding, slip casting, mold casting, tape casting, etc. The shape of the molded body is not particularly limited and can be appropriately set depending on the application and shape of the electricity storage device. The shape of the molded body is, for example, rectangular or circular.

[0146] By the above-described operations, a composite electrolyte having high ionic conductivity can be obtained by a relatively simple method. In particular, the present disclosure is advantageous in that a composite electrolyte exhibiting high ionic conductivity can be obtained without the need for a molding step such as a sintering treatment or a high-pressure press treatment. Furthermore, since the composite electrolyte of the present disclosure exhibits high ionic conductivity, an electricity storage device having high ionic conductivity can be obtained by using the composite electrolyte of the present disclosure as an electrolyte material for the electricity storage device.

[0147] Specifically, the ionic conductivity of a thin film of the composite electrolyte of the present disclosure having a thickness of about 35 μm (specifically, 35±10 μm) measured at 25° C. using an AC impedance method is 1.0×10 －５ From the viewpoint of obtaining an electricity storage device with excellent performance, the ionic conductivity under the same conditions is preferably 2.0 × 10 S / cm or more. －５ S / cm or more is more preferable, and 5.0×10 －５ The ionic conductivity is more preferably 25 S / cm or more. Details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0148] The ionic conductivity of the composite electrolyte can be adjusted within a desired range by adjusting the content of the inorganic solid electrolyte and the content of the molecular crystal in the composite electrolyte. Specifically, the ionic conductivity of the composite electrolyte tends to decrease as the content of the inorganic solid electrolyte in the composite electrolyte increases. Furthermore, the ionic conductivity of the composite electrolyte tends to increase by appropriately adjusting the content of the molecular crystal in the composite electrolyte.

[0149] <Electricity Storage Device> The electricity storage device of the present disclosure (hereinafter also referred to as "the device") includes the composite electrolyte of the present disclosure described above. Examples of the device include a secondary battery, a capacitor, etc. When the device is a secondary battery, one embodiment is an all-solid-state battery, and a lithium-ion secondary battery is preferred because of its excellent ionic conductivity.

[0150] The following describes an all-solid-state lithium-ion secondary battery, which is one embodiment of the device. The lithium-ion secondary battery is a laminate including an electrode layer made of a positive electrode layer and a negative electrode layer, and a solid electrolyte layer, with the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer so that the solid electrolyte layer is in contact with the electrode layer.

[0151] The materials constituting the positive electrode layer and the negative electrode layer are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium ion secondary batteries. For example, the positive electrode layer may be configured to include a positive electrode current collector and a positive electrode mixture layer. The positive electrode current collector can be a metal foil such as aluminum or stainless steel. The positive electrode mixture layer is a layer containing a positive electrode active material and is disposed on the surface of the positive electrode current collector. Examples of the positive electrode active material include metal oxides having a layered rock salt, spinel, or olivine crystal structure. The negative electrode layer may be configured to include a negative electrode current collector and a negative electrode mixture layer. The negative electrode current collector can be a metal foil such as copper foil or lithium foil. The negative electrode mixture layer is a layer containing a negative electrode active material and is disposed on the surface of the negative electrode current collector. Examples of the negative electrode active material include metallic lithium, graphite, Li ４ Ti ５ O １２ , silicon monoxide, silicon, etc.

[0152] The solid electrolyte layer is formed of a composite electrolyte containing the above-described inorganic solid electrolyte and organic solid electrolyte. The thickness of the solid electrolyte layer is not particularly limited and can be appropriately set depending on the application of the secondary battery, etc. The thickness of the solid electrolyte layer is, for example, 5 to 5,000 μm. From the viewpoint of realizing a smaller, lighter, and higher-capacity all-solid-state secondary battery by making the thickness of the solid electrolyte layer as thin as possible, the solid electrolyte layer is a thin film, and its thickness is preferably 50 μm or less, more preferably 20 μm or less. In particular, the composite electrolyte of the present disclosure is flexible and, even when made thin, has good heat resistance and ionic conductivity, making it suitable as a solid electrolyte material for realizing a smaller, lighter, and higher-capacity all-solid-state secondary battery.

[0153] The method for producing the solid electrolyte layer and the lithium-ion secondary battery is not particularly limited, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a laminate including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer may be produced by sandwiching a molded body of the composite electrolyte of the present disclosure as a solid electrolyte layer between a positive electrode layer and a negative electrode layer, and preferably performing a pressure treatment for bonding. The laminate including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is usually housed in a case and used as a secondary battery.

[0154] The device is not limited to the above-described configuration in which the carrier for ion conduction is lithium ions, but may also be a secondary battery in which other ions, such as sodium ions, are used as carriers. The device may also be a capacitor. One form of the capacitor includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, with the solid electrolyte disposed between the positive electrode layer and the negative electrode layer so that the solid electrolyte layer is in contact with each electrode layer.

[0155] The power storage device including the composite electrolyte of the present disclosure can be used in a variety of applications, specifically as a power source for various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various moving objects such as electric vehicles, hybrid vehicles, robots, and drones; and various electric and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances.

[0156] The present invention will be specifically described below based on examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0157] <<Production of Inorganic Solid Electrolyte and Physical Properties>> [Production Example 1] 1. Production of Inorganic Solid Electrolyte ISE-1 Layered zirconium phosphate (Zr(HPO)) was used as a feed component so as to achieve the molar ratio (Li:In:Zr:Si:P=1.25:0.20:1.80:0.05:2.95) shown in Production Example 1 in Table 1. ４ ) ２ ・nH ２4.000 g of Zr(HPO), 0.432 g of zirconium hydroxide, 0.415 g of lithium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 0.027 g of silicon dioxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 0.25 g of indium oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were weighed and placed in a mortar, and 25 g of pure water was added and wet-mixed to obtain a mixture (mixing step). The obtained mixture was dried at 100 ° C. for 2 hours, then transferred to an alumina crucible (capacity 30 mL), heated to 1,250 ° C. over 5.5 hours, and held for 5 hours to perform firing (firing step). Thereafter, the mixture was allowed to cool to room temperature (25 ° C.) to obtain a fired product. The obtained fired product was pulverized in a mortar to obtain an inorganic solid electrolyte ISE-1. In each production example, Zr(HPO ４ ) ２ ・nH ２ The value of n in O was set to 1.0.

[0158] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained inorganic solid electrolyte ISE-1 was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement conditions were a measurement range of 2θ = 10-80 deg, a scanning rate of 2.5 deg / min, and a step angle of 0.01 deg. As a result, it was found that the main crystalline phase of the inorganic solid electrolyte ISE-1 was monoclinic or rhombohedral LiZr ２ P ３ O １２ It was confirmed that the inorganic solid electrolyte ISE-1 has a NASICON-type crystal structure.

[0159] 3. Measurement of Volumetric Median Diameter Inorganic solid electrolyte ISE-1 was diluted with pure water in a 30 mL sample bottle to give a 1% by mass dispersion. The diluted dispersion was irradiated with 1 kHz ultrasound for 10 minutes. Using the dispersion immediately after ultrasound irradiation as a measurement sample, the volumetric median diameter (D50) of inorganic solid electrolyte ISE-1 was measured at room temperature (25°C) using a laser diffraction / scattering particle size measuring device MT-3000 (manufactured by Microtrac). Particle size measurements were performed twice, and the average value was used as the volumetric median diameter of inorganic solid electrolyte ISE-1. The volumetric median diameter of inorganic solid electrolyte ISE-1 was 1.4 μm.

[0160] 4. Measurement of Ionic Conductivity Using a press die consisting of a die set 11, an upper punch 12, and a lower punch 13 (see Figure 1), sample pellets were prepared in a dry room with a dew point of -40°C or below. First, the die set 11 containing 0.150 g of inorganic solid electrolyte ISE-1 was placed on the lower punch 13, and the upper punch 12 was placed on the die set 11. The inorganic solid electrolyte ISE-1 was compressed using a hydraulic press at a pressure of 10 MPa for 1 minute to obtain a circular sample pellet with a diameter of 1 cm and a thickness of 1000 μm. Next, the sample pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or below. The resistance value at 25°C was measured by AC impedance measurement using the all-solid-state battery evaluation cell encapsulating the sample pellet. The ionic conductivity (σ) was calculated using the obtained resistance value according to the following formula (1): σ = L / (R × S) (1) (In formula (1), σ is the ionic conductivity (unit: S / cm), R is the resistance (unit: Ω), and S is the cross-sectional area of ​​the sample pellet during measurement (unit: cm ２ ), and L represents the distance between the electrodes (unit: cm). The ionic conductivity (σ ＩＳＥ ) is 2.0 x 10 －7 S / cm.

[0161] [Production Examples 2 to 4] Inorganic solid electrolytes (referred to as inorganic solid electrolytes ISE-2 to ISE-4) were obtained by the same operation as in Production Example 1, except that the types and amounts of raw materials and the firing temperature were changed as shown in Table 1. In addition, the volume-based median diameter and ionic conductivity (σ ＩＳＥ The results are shown in Table 1. Powder X-ray diffraction measurements were carried out on the inorganic solid electrolytes ISE-2 to ISE-4 in the same manner as in Production Example 1. As a result, it was found that the main crystalline phase of the inorganic solid electrolytes ISE-2 to ISE-4 was monoclinic or rhombohedral LiZr ２ P ３ O １２ It was confirmed that the inorganic solid electrolytes ISE-2 to ISE-4 have a NASICON-type crystal structure.

[0162]

[0163] <<Molecular Crystal Production and Physical Properties>> [Production Example 5] 1. Production of molecular crystal OSE-1 In a dry room with a dew point of -40 ° C. or less, succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.1384 g (100.0 parts by mass) as an organic molecule, and lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) 0.1616 g (116.8 parts by mass) as an alkali metal salt were weighed out to the molar ratio shown in Table 2 Production Example 5 (organic molecule: alkali metal salt = 2: 1), and mechanically mixed for 5 minutes at room temperature (25 ° C.) using a mortar to obtain a mixture (mechanical mixing step). The melting point of the mixture was measured using a differential scanning calorimeter (TA Instruments, DSC250, measurement atmosphere: under a nitrogen atmosphere) at a heating rate of 10 ° C. per minute, and a large endothermic peak (melting point) was observed at 60 ° C. The mixture was transferred to a vial and stirred with a magnetic stirrer at a set temperature of 80°C for 1 hour, and it was confirmed that the mixture was dissolved uniformly (heating step). Thereafter, the resulting melt was allowed to cool to room temperature, and a white solid was obtained.

[0164] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained white solid was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement range was 2θ = 5-60 deg, the scanning speed was 2.3 deg / min, and the step angle was 0.02 deg. If an X-ray diffraction spectrum with a sharp peak at an angle within the measurement range was observed, it indicates that the measured sample (white solid) is crystalline. If an X-ray diffraction spectrum different from that of the lithium salt and organic molecules used as raw materials was obtained, it was determined that molecular crystals composed of lithium salt and organic molecules had been formed. If the organic molecules used as raw materials were liquid at room temperature, it was determined that molecular crystals composed of lithium salt and organic molecules had been formed if an X-ray diffraction spectrum different from that of lithium salt was observed. The white solid obtained as described above was subjected to powder X-ray diffraction measurement, and the X-ray diffraction spectrum showed sharp peaks in the measurement angle range that were different from those of the raw material. This confirmed that the obtained white solid was crystalline, i.e., a molecular crystal (hereinafter referred to as "molecular crystal OSE-1").

[0165] 3. Measurement of Ionic Conductivity Using the press die 10 shown in Figure 1, sample pellets were prepared in a dry room with a dew point of -40°C or below. First, a die set 11 containing 0.0200 g of white solid (molecular crystal OSE-1) was placed on the lower punch, and an upper punch 13 was placed on the die set 11. The white solid was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press, yielding a circular sample pellet with a diameter of 1 cm and a thickness of 200 μm. Next, the sample pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or below. Ionic conductivity was measured using the all-solid-state battery evaluation cell encapsulating the sample pellet. To measure ionic conductivity, the sealed cell encapsulating the sample pellet was first heat-treated in a thermostatic chamber at 40°C (corresponding to the heat treatment temperature in Table 2), while the resistance value was measured by AC impedance measurement. The heat treatment was terminated when the resistance value became constant. Next, the resistance value at 25°C was measured by AC impedance measurement. Using the obtained resistance value, the ionic conductivity (σ) was calculated by the above formula (1). The AC impedance measurement for calculating the ionic conductivity was carried out after the cell was kept at the measurement temperature in a thermostatic bath for 2 hours. The ionic conductivity (σ) of the molecular crystal OSE-1 at 25°C was ＯＳＥ ) is 3.9 x 10 －５ S / cm.

[0166] [Production Examples 6 and 7] White solids were obtained by the same procedure as in Production Example 5, except that the types and amounts of raw materials and the heating temperature of the mixture of organic molecules and alkali metal salt in the heating step were changed as shown in Table 2. Powder X-ray diffraction measurements were performed on the white solids obtained in each Production Example in the same manner as in Production Example 5. As a result, X-ray diffraction spectra with sharp peaks different from those of the raw materials were observed in the angle range of the measurement. Therefore, it was confirmed that each white solid was a molecular crystal composed of a lithium salt and an organic molecule (referred to as "molecular crystal OSE-2" and "molecular crystal OSE-3," respectively). Furthermore, the ionic conductivity (σ) at 25°C was measured using the white solids of each Production Example (molecular crystal OSE-2, molecular crystal OSE-3) at the heat treatment temperatures shown in Table 2. ОＳＥThe melting point of the mixture of organic molecules and alkali metal salts obtained by the mechanical mixing step was measured, along with the ionic conductivity (σ ОＳＥ The measurement results are shown in Table 2.

[0167]

[0168] Details of the compounds used in Table 2 are as follows: SN: succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) SL: sulfolane (manufactured by Tokyo Chemical Industry Co., Ltd.) AdN: adiponitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) LiFSI: lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.)

[0169] <<Polymer Production and Physical Properties>> [Production Example 8] 1. Synthesis of Polymer PCL 11.41 g (100 parts by mass) of ε-caprolactone, 0.0371 g (0.33 parts by mass) of 1-butanol, 0.0203 g (0.17 parts by mass) of tin(II) 2-ethylhexanoate, 11.41 g (100 parts by mass) of toluene, and a stirrer were placed in a 100 mL test tube and stirred at 95°C for 96 hours under dry air (dew point -60°C or lower). ε-Caprolactone and 1-butanol were dehydrated using molecular sieves before use. The polymer solution was poured into a large amount of isopropanol to precipitate the polymer. The precipitate was collected by vacuum filtration and dried in vacuo to obtain polymer PCL.

[0170] 2. Molecular Weight Measurement The molecular weight of polymer PCL was measured using gel permeation chromatography (hereinafter also referred to as "GPC") according to the following procedure. The molecular weight of polymer PCL was a number average molecular weight (Mn) of 18,700 and a weight average molecular weight (Mw) of 26,800. <Procedure> A sample solution was obtained by dissolving 4 mg of polymer in 4 mL of tetrahydrofuran. This sample solution was filtered through a polytetrafluoroethylene membrane filter, and 100 μL was injected into a GPC apparatus, and the weight average molecular weight (Mw) and number average molecular weight (Mn) were measured under the following conditions. Column: 4 columns of TSKgel SuperMultiporeHZ-M manufactured by Tosoh Corporation Temperature: 40°C Eluent: Tetrahydrofuran Detector: Differential refractometer Flow rate: 600 μL / min Standard: Polystyrene

[0171] 3. Glass Transition Temperature Measurement The glass transition temperature of the polymer PCL was determined using a differential scanning calorimeter (hereinafter also referred to as "DSC") according to the following procedure. The glass transition temperature of the polymer PCL was -65°C. <Procedure> 5 mg of polymer sealed in an aluminum pan was cooled to -80°C, and then swept up to 100°C at a rate of 10°C / min to obtain a heat flux curve. The glass transition temperature was determined from the intersection of the baseline of the heat flux curve and the tangent at the inflection point. Model: DSC250 manufactured by TA Instruments Measurement atmosphere: Nitrogen

[0172] [Production Example 9] A curable composition was obtained by dissolving 0.025 g (5 parts by mass) of 2-hydroxy-2-methylpropiophenone (hereinafter also referred to as "HMP") as a photopolymerization initiator in 0.5 g (100 parts by mass) of n-butyl acrylate (hereinafter also referred to as "BA") as a monomer. The BA used was dehydrated using a molecular sieve. Next, a 300 μm silicone rubber sheet with a 15 mm square opening was placed on a 20 mm square heavy-release release PET film, and the above curable composition was poured into it, followed by laminating it from above with a light-release release PET film. The curable composition sandwiched on both sides between the release PET films was exposed to ultraviolet light at a wavelength of 365 nm (illuminance 56 mW / cm) using an ultraviolet irradiation device (ultraviolet curing device manufactured by Minaga Electric Mfg. Co., Ltd., mercury xenon lamp, lamp height 10 mm). ２ ) from the light release film side and the heavy release film side, respectively, for 45 seconds each, and this was repeated twice (cumulative light amount: 10,080 mJ / cm ２ ), and polymer pBA was obtained as an active energy ray-cured product. The illuminance was measured using an ultraviolet integrating actinometer (UV Power Puck II (center wavelength of the light-receiving part: 355 nm) manufactured by EIT Corporation). The above series of operations were carried out in a dry room with a dew point of -40°C or lower. The reaction rate of BA was over 96%. The molecular weight (Mn, Mw) and glass transition temperature of the obtained pBA were measured in the same manner as in Production Example 8. The results are shown in Table 3.

[0173]

[0174] Details of the compounds used in Table 3 are as follows: CL: ε-caprolactone (manufactured by Tokyo Chemical Industry Co., Ltd.) BA: n-butyl acrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) BuOH: 2-butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) HMP: 2-hydroxy-2-methylpropiophenone (manufactured by Tokyo Chemical Industry Co., Ltd.) Sn(Oct) ２ : tin(II) 2-ethylhexanoate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Toluene: toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0175] <<Production and Evaluation of Composite Electrolyte>> [Example 1] 1. Production of Composite Electrolyte HSE-1 In a dry room with a dew point of −40° C. or less, an inorganic solid electrolyte Li １．２５ In ０．２ Zr １．８ Si ０．０５ P ２．９５ O １２ 66 parts of the inorganic solid electrolyte ISE-1 obtained in Production Example 1, molecular crystal Li(FSI)(SN) ２29 parts of the molecular crystal OSE-1 (obtained in Production Example 5), 2 parts of polycaprolactone (polymer PCL obtained in Production Example 8), and 3 parts of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) were weighed, and 43 parts of methyl isobutyl ketone was added and mechanically mixed using a mortar at room temperature (25 ° C.) to obtain a mixture. The obtained mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a composite electrolyte slurry. The obtained composite electrolyte slurry was coated on aluminum foil (thickness: 17 μm) and dried at 50 ° C. for 2 hours. Thereafter, it was vacuum dried at 50 ° C. for 24 hours and punched out with a φ10 mm hand punch (manufactured by Nogami Giken Co., Ltd.) to obtain a composite electrolyte precursor with aluminum foil. Using the press mold 10 shown in FIG. 1 , in a dry room with a dew point of −40°C or less, the obtained aluminum foil-attached composite electrolyte precursor and die set 11 were placed on a lower punch 13, and an upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press, yielding a circular thin film pellet. Next, the thin film pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) and sealed in a dry room with a dew point of −40°C or less. The all-solid-state battery evaluation cell encapsulating the thin film pellet was heat-treated in a thermostatic chamber at 55°C (corresponding to the temperature in the heating step in Table 4) (heating step), and the resistance value was measured by AC impedance measurement during the heat treatment. The heat treatment was terminated when the resistance value became constant, and the mixture was air-cooled to 25°C, yielding a composite electrolyte with aluminum foil (referred to as "composite electrolyte HSE-1"). The thickness of the portion of the obtained composite electrolyte HSE-1 excluding the aluminum foil (i.e., the composite electrolyte layer) was 35 μm.

[0176] 2. Evaluation (1) Measurement of Ion Conductivity The ionic conductivity (σ) of the aluminum foil-attached composite electrolyte HSE-1 was measured at 25°C in the same manner as in Production Example 1. ＳＥ As a result, the σ of the composite electrolyte HSE-1 was ＳＥ is 1.1 x 10 －４ The inter-electrode distance L in the above formula (1) was calculated as σ, assuming that the thickness of the layer excluding the aluminum foil was 35 μm. ＳＥwas calculated.

[0177] (2) Evaluation of Flexibility The end of the composite electrolyte HSE-1 with the aluminum foil was pinched with tweezers and bent, and the flexibility was evaluated based on the angle at which the composite electrolyte layer (i.e., the portion excluding the aluminum foil) broke when bent, based on the following criteria: ○: Does not break even when bent by 90° or more △: Can be bent, but breaks when bent by 90° ×: Cannot be bent, breaks when force is applied The flexibility of the composite electrolyte HSE-1 with the aluminum foil was evaluated as "○".

[0178] (3) Evaluation of Heat Resistance The aluminum foil was peeled off from the composite electrolyte precursor with the aluminum foil attached, and 50 mg of composite electrolyte precursor was collected. Using the press mold 10 shown in FIG. 1 , in a dry room with a dew point of −40°C or less, the obtained composite electrolyte precursor and die set 11 were placed on the lower punch 13, and the upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet. The all-solid-state battery evaluation cell containing the circular sample pellet was heat-treated in a thermostatic bath at 55°C (corresponding to the temperature in the heating step in Table 4) (heating step), and the resistance value was measured by AC impedance measurement during the heat treatment. The heat treatment was terminated when the resistance value became constant, and the cell was air-cooled to 25°C to obtain a circular pellet (thickness of composite electrolyte layer: 265 μm) made of the composite electrolyte HSE-1. The obtained pellet was placed in a drying furnace at 100°C and left for 1 hour, and then its heat resistance was evaluated based on its appearance according to the following criteria. In this evaluation, the thickness of the composite electrolyte layer was increased to 265 μm to make it easier to check the change in appearance due to the application of heat. ○: Maintains solid state. △: Partially melts, and there are parts that can no longer maintain their solid state. ×: Melts, and can no longer maintain its solid state. The heat resistance of the composite electrolyte HSE-1 was evaluated as "○".

[0179] [Examples 2 to 14] Composite electrolytes HSE-2 to HSE-12 and HSE-16 to HSE-17 with aluminum foil (thickness of composite electrolyte layer: see Table 4) and composite electrolytes HSE-2 to HSE-12 and HSE-16 to HSE-17 without aluminum foil (thickness of composite electrolyte layer: 265 μm) were obtained by the same procedure as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 4. In addition, the ionic conductivities (σ ＳＥ The results are shown in Table 4.

[0180] [Comparative Example 1] In a dry room with a dew point of -40°C or less, Li was added to obtain the amount ratio shown in Comparative Example 1 in Table 4. １．２５ In ０．２ Zr １．８ Si ０．０５ P ２．９５ O １２ 0.100 g (69 parts by mass) of the inorganic solid electrolyte ISE-1 obtained in Production Example 1 and Li(FSI)(SN) ２0.0469 g (31 parts by mass) of each of the molecular crystals OSE-1 obtained in Production Example 5 was weighed out and mechanically mixed in a mortar at room temperature (25°C) to obtain a mixture (mixing step). Using the press mold 10 shown in FIG. 1 , a sample pellet consisting of a mixture of an inorganic solid electrolyte and molecular crystals was prepared in a dry room with a dew point of −40°C or lower by the following procedure. First, a die set 11 containing 0.050 g of the mixture was placed on the lower punch 13, and an upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet having a diameter of 1 cm and a thickness of 315 μm. When an attempt was made to obtain a composite electrolyte with an aluminum foil by performing the same operation as in Example 1, the composite electrolyte did not adhere well to the aluminum foil and the composite electrolyte was hard and brittle, resulting in cracking, making it impossible to obtain a thin film. Next, the sample pellets were enclosed in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) and sealed in a dry room with a dew point of -40°C or less. The all-solid-state battery evaluation cell containing the sample pellets was heat-treated in a thermostatic chamber at 55°C (corresponding to the temperature in the heating step in Table 4) (heating step), and the resistance value was measured by AC impedance measurement during the heat treatment. When the resistance value became constant, the heat treatment was terminated and the cell was air-cooled to 25°C, thereby obtaining a composite electrolyte (referred to as composite electrolyte HSE-13). The obtained composite electrolyte HSE-13 (thickness of composite electrolyte layer: 315 μm) was subjected to ionic conductivity (σ ＳＥ The results are shown in Table 4.

[0181] Comparative Examples 2 and 3 The same operations as in Example 1 were carried out, except that the types and amounts of raw materials were changed as shown in Table 4, to obtain composite electrolytes HSE-14 to HSE-15 with aluminum foil (thickness of composite electrolyte layer: see Table 4) and composite electrolytes HSE-14 to HSE-15 peeled from the aluminum foil (thickness of composite electrolyte layer: 265 μm), respectively. In addition, the ionic conductivity (σ ＳＥ The results are shown in Table 4.

[0182]

[0183] Details of the compounds used in Table 4 are as follows: PCL: Polycaprolactone obtained in Production Example 8 pBA: Polyn-butyl acrylate obtained in Production Example 9 PVDF: Polyvinylidene fluoride, KF polymer #1300 (manufactured by Kureha Corporation) LiFSI: Lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.)

[0184] <Evaluation Results> As is clear from the results in Table 4, the composite electrolytes HSE-1 to HSE-12 and HSE-16 to HSE-17 of Examples 1 to 14, which contained molecular crystals in addition to an inorganic solid electrolyte and a polymer (P), all exhibited high ionic conductivity and good flexibility and heat resistance. Furthermore, it was shown that the composite electrolytes HSE-1 to HSE-12 and HSE-16 to HSE-17 of Examples 1 to 14 are also suitable for use in thin films.

[0185] In contrast, the composite electrolyte HSE-13 (Comparative Example 1), which did not contain the polymer (P), could not be made into a thin film, and when it was molded into a compact, the thickness of the composite electrolyte became as thick as 300 μm or more, resulting in poor flexibility. This is thought to be because the composite electrolyte HSE-13 did not contain a polymer component, and therefore the binding force connecting the particles of the inorganic solid electrolyte to each other was insufficient.

[0186] The composite electrolyte HSE-14 (Comparative Example 2) containing no molecular crystals had a higher ionic conductivity (σ ＳＥ ) was low. This is thought to be because the grain boundary resistance of the inorganic solid electrolyte in the composite electrolyte HSE-14 was high, and the ion conduction path was not sufficiently formed by blending the polymer alone. The composite electrolyte HSE-15 (Comparative Example 3), which did not contain an inorganic solid electrolyte, was inferior in heat resistance.

[0187] From the above results, it has become clear that a composite electrolyte containing an inorganic solid electrolyte and an organic solid electrolyte, in which the organic solid electrolyte contains an organic molecule (A), an alkali metal salt, and a polymer (P), and at least a part of the organic molecule (A) and at least a part of the alkali metal salt contained in the organic solid electrolyte form molecular crystals, can provide a composite electrolyte that exhibits high ionic conductivity while also being excellent in flexibility and heat resistance.

[0188] The present invention is not limited to the above-described embodiments, and encompasses various modifications and equivalent modifications within the scope of the spirit of the present invention. Therefore, in light of the above teachings, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are to be understood as falling within the scope and spirit of the present invention.

[0189] 10... Press mold

Claims

1. A composite electrolyte containing an inorganic solid electrolyte and an organic solid electrolyte, wherein the organic solid electrolyte includes a molecular crystal and a polymer, the molecular crystal includes, as structural units, an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom, and an alkali metal salt, and the polymer has a structure represented by the formula -(R １ A repeating unit represented by —O)— (where R １ is an alkylene group) in the main chain.

2. The composite electrolyte of claim 1, wherein the inorganic solid electrolyte comprises an oxide having a NASICON-type crystal structure.

3. The oxide having a NASICON-type crystal structure is represented by the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ wherein M1 comprises Fe, In, Y, or Al; M2 comprises Si; M3 comprises W; and x > 0, y ≥ 0, and z ≥ 0 are satisfied.

4. The composite electrolyte according to claim 1, wherein the total number of carbon atoms per molecule of said organic molecules is 6 or less.

5. The composite electrolyte according to claim 1, wherein the organic molecule is at least one selected from the group consisting of sulfones and nitriles.

6. The composite electrolyte according to claim 1, wherein the alkali metal salt constituting the molecular crystal includes an imide-based alkali metal salt.

7. The composite electrolyte of claim 1, wherein the polymer is a non-crosslinked polymer.

8. The composite electrolyte of claim 1, further comprising an alkali metal salt.

9. The composite electrolyte according to claim 1, which is a thin film having a thickness of 50 μm or less.

10. A method for producing a composite electrolyte according to any one of claims 1 to 9, comprising the step of mixing the inorganic solid electrolyte, the molecular crystal, and the polymer.

11. The method for producing a composite electrolyte according to claim 10, wherein the inorganic solid electrolyte, the molecular crystal, and the polymer are mixed in the presence of a solvent.

12. An electricity storage device comprising the composite electrolyte according to any one of claims 1 to 9.

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