Solid electrolyte, method for producing same, and power storage device

Abstract

This solid electrolyte includes: a film-like porous body having communication holes; and molecular crystals containing, as structural units, an alkali metal salt and organic molecules having at least one type of atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms. The molecular crystals are retained in the communication holes.

Description

Solid electrolyte and method for manufacturing the same, and energy storage device

[0001] [Cross-reference of related applications] This application claims priority under Japanese Patent Application No. 2024-211517, filed on 4 December 2024, which is incorporated herein by reference in its entirety. This disclosure relates to solid electrolytes, methods for manufacturing the same, and energy storage devices.

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

[0003] Lithium-ion secondary batteries, widely used as energy storage devices, are secondary batteries that have a negative electrode, a positive electrode, and an electrolyte, and charge and discharge by moving lithium ions between the two electrodes via the electrolyte. Conventionally, non-aqueous electrolytes have been mainly used as the electrolyte. In contrast, in recent years, as a technology to eliminate concerns about electrolyte leakage and short circuits inside the battery due to overcharging and over-discharging, solid or gel-like electrolytes using inorganic or organic materials have been proposed as an alternative to organic electrolytes.

[0004] Organic solid electrolytes have advantages such as excellent adhesion to electrodes due to the moderate flexibility and high moldability of organic materials, but they tend to have lower ionic conductivity compared to, for example, inorganic solid electrolytes. Therefore, in order to improve practicality, various studies are being conducted on the development of new materials that constitute organic solid electrolytes (see, for example, Patent Document 1 and Non-Patent Document 1).

[0005] Patent Document 1 discloses a solid electrolyte for an electrochemical device, comprising a composite of an ionic salt-doped plastic crystal matrix electrolyte and a polymer crosslinked structure having a weight-average molecular weight of 100 to 5,000 and a linear polymer having one functional group as a side chain chemically bonded. Here, the plastic crystal matrix is ​​a material in which molecules or ions exhibit rotational disorder, while the center of gravity occupies a position aligned in the crystal lattice structure, thereby exhibiting plasticity. Non-Patent Document 1 discloses the formation of a crystalline organic solid electrolyte using a soft solid crystal composed of lithium chloride and isoquinoline.

[0006] Special table 2014-504788 publication

[0007] Ionics, 2018, Vol. 24, pp. 343-349

[0008] The organic solid electrolyte described in Patent Document 1 has good ionic conductivity but poor flexibility and bendability. Furthermore, the crystalline organic solid electrolyte (i.e., molecular crystalline electrolyte) described in Non-Patent Document 1 has poor strength and bendability due to its regular crystalline structure, and its ionic conductivity is insufficient. In particular, when a solid electrolyte layer is made using a crystalline organic solid electrolyte as a raw material, for example by compaction molding, cracks are likely to occur at the crystal interface, resulting in poor handling. From the viewpoint of obtaining a high-performance energy storage device that can be easily manufactured, is less prone to damage or performance degradation when external force is applied to the energy storage device, and exhibits high ionic conductivity while possessing high strength and bendability, a solid electrolyte is required.

[0009] This disclosure has been made in view of these circumstances, and one objective is to provide a film-like solid electrolyte that exhibits high ionic conductivity while having good strength and flexibility. Another objective is to provide an energy storage device equipped with the solid electrolyte.

[0010] As a result of diligent research to solve the above problems, the present inventors have found that a solid electrolyte in which molecular crystals are held on a specific substrate exhibits high ionic conductivity while also possessing good strength and flexibility. In other words, the present disclosure provides the following solid electrolyte, a method for manufacturing the same, and an energy storage device.

[0011] [1] A solid electrolyte comprising a film-like porous body having interconnected pores, a molecular crystal comprising an organic molecule having at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms, and an alkali metal salt as constituent units, wherein the molecular crystal is held inside the interconnected pores. [2] The solid electrolyte according to [1], wherein the content of the molecular crystal is 30 to 90% by mass. [3] The solid electrolyte according to [1] or [2], wherein the film-like porous body is a resin film. [4] The solid electrolyte according to any one of [1] to [3], wherein the film-like porous body is formed from a fluorine-containing polymer. [5] The solid electrolyte according to any one of [1] to [4], wherein the film-like porous body is a hydrophilic treated substrate in which the inside of the pores of the porous film is subjected to a hydrophilic treatment. [6] The solid electrolyte according to any one of [1] to [5], wherein the organic molecule is at least one selected from the group consisting of sulfone, nitrile, amide, and urea. [7] The solid electrolyte according to any one of [1] to [6], wherein the alkali metal salt is a salt of lithium ions or sodium ions with a counter anion. [8] A method for producing a solid electrolyte according to any one of [1] to [7], comprising the steps of: contacting the inside of the pores of the film-like porous body with a molten material obtained by melting the molecular crystal or the raw material for the molecular crystal; and cooling the film-like porous body after contact with the molten material to below the melting point of the molecular crystal. [9] A method for producing a solid electrolyte according to any one of [1] to [7], comprising the steps of: contacting the inside of the pores of the film-like porous body with a solution containing the molecular crystal or the raw material for the molecular crystal and a solvent; and removing the solvent from the film-like porous body after contact with the solution.

[10] A method for producing a solid electrolyte according to any one of [1] to [7], comprising the steps of: obtaining a film-like porous body by impregnating the inside of the pores of a porous film with a surfactant and performing a hydrophilization treatment; and contacting the inside of the pores of the film-like porous body after the hydrophilization treatment with the molecular crystal or the raw material for the molecular crystal.

[11] An energy storage device comprising a solid electrolyte according to any one of [1] to [7].

[0012] According to this disclosure, a film-like solid electrolyte can be obtained that exhibits high ionic conductivity while possessing good strength and flexibility. Furthermore, by using the solid electrolyte of this disclosure as an electrolyte in energy storage devices such as secondary batteries and capacitors, it is possible to obtain an energy storage device that combines safety ensured by the solidification of the electrolyte with high ionic conductivity.

[0013] Figure 1 shows the results of powder X-ray diffraction measurement of molecular crystals obtained by manufacturing example 1. Figure 2 is a schematic diagram of the press mold used to produce the sample pellets. Figure 3 shows the strength test of Example 1. Figure 4 shows the strength test of Example 3. Figure 5 shows the strength test of Example 4.

[0014] The solid electrolyte, its manufacturing method, and energy storage device described herein will be explained in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0015] ≪Solid Electrolyte≫ The solid electrolyte of this disclosure is composed of a film-like porous material having interconnected pores and molecular crystals. The solid electrolyte uses the film-like porous material as a base material, and molecular crystals are held inside the interconnected pores of the film-like porous material. As a result, the solid electrolyte of this disclosure exhibits high ionic conductivity while exhibiting the high strength and flexibility of the film-like porous material. The components constituting the solid electrolyte of this disclosure and the method for manufacturing the solid electrolyte will be described in detail below. Unless otherwise specified, each component may be included alone or in combination of two or more types.

[0016] <Film-like porous material> The film-like porous material that constitutes the solid electrolyte of this disclosure only needs to have a large number of interconnected pores, and its form is not particularly limited. Examples of film-like porous materials include resin films, nonwoven fabrics, and woven fabrics. When a film-like porous material formed by the entanglement of fibers, such as a nonwoven fabric or a woven fabric, is used, pinholes are easily formed due to the displacement of fibers during the process of holding molecular crystals inside the interconnected pores of the film-like porous material. For this reason, when applied to the solid electrolyte layer of an energy storage device, there is a concern that penetration by dendrites is likely to occur in the solid electrolyte layer. In contrast, a resin film is a substrate in which a polymer is integrated, and even when applied to the solid electrolyte layer of an energy storage device, penetration by dendrites is less likely to occur, making it suitable as a film-like porous material to be combined with molecular crystals. Examples of such resin films include those used in applications such as battery separators, moisture-permeable waterproof films, and membrane filters.

[0017] The method for producing a porous film is not particularly limited and can be produced by known methods. For example, porous films made of resin are generally produced by dry stretching or wet stretching. Alternatively, a porous film may be obtained by dispersing a filler in a polymer solution in which the polymer constituting the porous film or its precursor (e.g., a polyimide precursor) is dissolved in a solvent, casting the solution, and then drying the resulting film from which the filler is dissolved and removed.

[0018] The type of material used to form the porous film is not particularly limited. Considering its application to solid electrolytes, electrochemically stable materials are preferable. Specific examples of materials that form the porous film include, for example, polyolefins such as polyethylene, polypropylene, polymethylpentene, propylene / ethylene copolymer, propylene / 1-butene copolymer, propylene / ethylene / 1-butene copolymer, and propylene / ethylene / 1-octene copolymer; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, and vinylidene fluoride / tetrafluoroethylene copolymer. Examples of fluorine-containing polymers include fluoroethylene copolymers, ethylene / tetrafluoroethylene copolymers, ethylene / tetrafluoroethylene / hexafluoropropylene copolymers, polychlorotrifluoroethylene, chlorotrifluoroethylene / trifluoroethylene copolymers, ethylene / chlorotrifluoroethylene copolymers, vinylidene fluoride / hexafluoropropane / (meth)acrylic acid copolymers, and vinylidene fluoride / pentafluoropropylene copolymers; high-performance resins such as polyimides, polyamides, polyamideimides, aramids, polysulfones, and polyetheretherketones; and materials combining two or more of these. In addition, porous films formed from cellulose-based polymers can be used as porous films. Examples of cellulose-based polymers include cellulose oxide, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose (CMC), carboxymethylethylcellulose, and hydroxypropylmethylcellulose. The polymer used to form the porous film may be a crosslinked polymer or a non-crosslinked polymer. Preferably, it is a non-crosslinked polymer.

[0019] Of the porous films used in combination with molecular crystals, olefin-based porous films such as polyethylene and polypropylene are manufactured by stretching and widely used as battery separators, ensuring reliability and easy availability. Moreover, olefin-based porous films have excellent strength and flexibility, and high durability. For this reason, olefin-based porous films can be preferably used as porous films in combination with molecular crystals. However, if the melting point of the molecular crystal is relatively high (for example, 90°C or higher), the application of the method of thermally melting and impregnating the molecular crystal into the interconnected pores of the porous film may be limited. Therefore, if the melting point of the molecular crystal is relatively high, it is preferable to use a polymer with high heat resistance (for example, PTFE, PVDF, polyimide, polyamide-imide, etc.) as the porous film.

[0020] As for the porous film, in order to obtain a solid electrolyte exhibiting excellent ionic conductivity when combined with molecular crystals, at least one selected from the group consisting of polyolefins and fluorine-containing polymers is preferred, and fluorine-containing polymers are more preferred. Furthermore, considering availability, polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) are particularly preferred.

[0021] The porous film has a structure in which the pores are connected to each other (i.e., interconnected pores), and therefore has many pores that penetrate the porous film in the vertical direction. The average pore diameter of the interconnected pores is preferably 10 μm or less, and more preferably within the range of 0.01 to 5.0 μm. When the average pore diameter of the interconnected pores is 0.01 μm or more, it is easier to retain molecular crystals inside the interconnected pores, and it is easier to obtain a solid electrolyte with high ionic conductivity. Furthermore, when the average pore diameter of the interconnected pores is 10 μm or less, it is easier to maintain high strength in the solid electrolyte and it is easier to suppress penetration of the electrolyte layer by dendrites. From these viewpoints, the average pore diameter of the interconnected pores is more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. Furthermore, the average pore diameter of the interconnected pores is more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. The average pore diameter of the interconnected pores can be measured by scanning electron microscope (SEM).

[0022] The porosity of the porous film is preferably 30 to 90%. When the porosity of the porous film is 30% or more, a sufficient amount of molecular crystals can be retained within the porous film, and a solid electrolyte with sufficiently high ionic conductivity can be obtained. Furthermore, when the porosity of the porous film is 90% or less, sufficient strength of the solid electrolyte can be ensured. From these viewpoints, the porosity of the porous film is more preferably 40% or more, even more preferably 45% or more, even more preferably 50% or more, and particularly preferably 60% or more. Furthermore, the porosity of the porous film is more preferably 85% or less, and even more preferably 80% or less. The porosity of the porous film represents the ratio (%) of the volume of pores to the total volume of the porous film.

[0023] From the viewpoint of obtaining a solid electrolyte with a good balance between strength and flexibility, the thickness of the porous film is preferably 5 to 200 μm. From the viewpoint of obtaining a solid electrolyte with higher strength, the thickness of the porous film is more preferably 10 μm or more. Furthermore, from the viewpoint of minimizing the internal resistance of the solid electrolyte to improve ionic conductivity and obtaining a solid electrolyte with excellent flexibility, the thickness of the porous film is more preferably 180 μm or less, and even more preferably 150 μm or less.

[0024] As the porous film to be combined with molecular crystals, a porous film such as a resin film manufactured by a stretching method may be used as is (i.e., without surface treatment), but it is preferable to use a hydrophilic treated substrate in which the inside of the pores of the porous film has been hydrophilized. By using a hydrophilic treated substrate as the porous film, molecular crystals are more easily retained inside the interconnected pores of the hydrophilic surface, and a solid electrolyte with superior ionic conductivity can be obtained. The hydrophilic treated substrate only needs to have hydrophilic treatment applied to at least the pores (i.e., the surface inside the pores) of the porous film, and other parts, such as the outer surface of the porous film, may also be hydrophilic treated. For ease of hydrophilization treatment, it is preferable that the entire surface of the porous film, including the inside of the pores, be hydrophilic treated. A resin film is preferred as the porous film used for hydrophilization treatment.

[0025] The method of hydrophilization treatment is not particularly limited, and known hydrophilization treatments applied to resin films can be used as appropriate. Examples of such treatment methods include coating with hydrophilic substances (e.g., polyvinyl alcohol or surfactants); surface modification by plasma treatment, corona treatment, deep UV treatment, etc.; and plasma polymerization utilizing functional groups derived from hydrophilic monomers on the substrate surface. Of these, coating treatment with hydrophilic substances is preferred because it can achieve surface hydrophilization of porous films with relatively simple operations and offers high productivity and performance stability.

[0026] <Molecular Crystals> The molecular crystals contained in the solid electrolytes of this disclosure are organic solid electrolytes comprising an organic molecule (hereinafter also referred to as "organic molecule (A)") having at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms, and an alkali metal salt as constituent units. A molecular crystal is a solid in which the constituent units in the crystal lattice are arranged regularly. A molecular crystal containing organic molecule (A) and an alkali metal salt has ion conduction paths due to the regular arrangement of constituent units, and is a molecular crystal electrolyte that exhibits excellent ionic conductivity.

[0027] The molecular crystal structure of a substance containing organic molecules and alkali metal salts can be evaluated by analysis of its X-ray diffraction spectrum. Specifically, if a sharp peak is observed in the measurement range angle (2θ = 5–60 deg) and a different X-ray diffraction spectrum is obtained from that of the raw materials, it can be determined that a molecular crystal containing organic molecules and alkali metal salts has been formed. In this case, if both the organic molecules and alkali metal salts used as raw materials are solids at room temperature, different X-ray diffraction spectra will be obtained from each of the raw materials. Also, if the organic molecules used as raw materials are liquids at room temperature, a different X-ray diffraction spectrum will be obtained from that of the alkali metal salt.

[0028] Furthermore, according to Timmermans' empirical rule, the melting entropy is 20 JK. －１ mol －１ If the value is smaller than 20 JK, the substance has a viscous crystalline phase and can be evaluated as a viscous crystal. On the other hand, if the fusion entropy of a substance containing organic molecules and alkali metal salts is 20 JK －１ mol －１ If the above conditions are met, it can be determined that the substance does not have a viscous crystalline phase and is not a viscous crystal. That is, while viscous crystals transition from the crystalline phase to the liquid phase via a viscous crystalline phase during melting, molecular crystals have the property of directly transitioning from the crystalline phase to the liquid phase during melting, and the two are different substances. The molecular crystal contained in the solid electrolyte of this disclosure has a melting entropy of 20 JK －１ mol －１ Based on the above, it can be concluded that it is not a viscous crystal. The fusion entropy of the material can be obtained by differential scanning calorimetry (DSC).

[0029] ○Organic molecule (A) The number of at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms in organic molecule (A) is not particularly limited. In organic molecule (A), the number of at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms is preferably 1 to 8 per molecule, and more preferably 2 to 6. Of these, organic molecule (A) preferably has 2 or more of at least one atom selected from sulfur atoms, oxygen atoms, and nitrogen atoms in one molecule, and more preferably 2 to 6.

[0030] The molecular weight of 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 organic molecule (A) is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. Furthermore, from the viewpoint of promoting the crystallization of the mixture of organic molecule (A) and alkali metal salt, the total number of carbon atoms per molecule of organic molecule (A) is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Furthermore, the total number of carbon atoms per molecule of organic molecule (A) is preferably 2 or more.

[0031] Specific examples of organic molecules (A) include organic molecules containing a sulfur atom such as sulfones, sulfides, thiols, thioesters, thiocarbonates, sulfoxides, and sulfamides. Examples of organic molecules containing a nitrogen atom include nitriles, amines, amides, and ureas. Examples of organic molecules containing a phosphorus atom include phosphines, phosphine oxides, and phosphineimines. Examples of organic molecules containing an oxygen atom include organic molecules containing an oxygen atom among the examples of organic molecules containing a sulfur atom, organic molecules containing an oxygen atom among the examples of organic molecules containing a nitrogen atom, and organic molecules containing an oxygen atom among the examples of organic molecules containing a phosphorus atom, as well as ethers, esters, ketones, and carbonates. Note that the organic molecules constituting the molecular crystal may be one type or two or more types.

[0032] 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 an organic molecule having a sulfur atom and an oxygen atom, an organic molecule having a nitrogen atom, and an organic molecule having a phosphorus atom among the above.

[0033] (Organic molecule having a sulfur atom and an oxygen atom) As the organic molecule having a sulfur atom and an oxygen atom, sulfone can be preferably used. Preferred examples of sulfone include the following formula (1): (In formula (1), R １ and R ２ are each independently an alkyl group or an alkoxy group, or R １ and R ２ represent a cyclic structure formed by bonding, provided that the total number of carbon atoms in formula (1) is 2 to 16), and the molecules represented thereby are exemplified.

[0034] The molecule represented by the above formula (1) (hereinafter, also referred to as "organic molecule (A1)") is a chain-like or cyclic molecule having a sulfonyl group (-SO ２ -). When R １ and R ２ in the above formula (1) are an alkyl group or an alkoxy group, the alkyl group and alkoxy group of R １ , R ２ may be linear or branched. Also, the number of carbon atoms of each of the alkyl group and alkoxy group (that is, the number of carbon atoms in each group of R １ and R ２ ) is not particularly limited as long as the total number of carbon atoms of R １ and R ２ is 2 to 16. From the viewpoint of causing crystallization in the mixture of the organic molecule (A1) and the alkali metal salt during the production of the molecular crystal, R １ and R ２ are each preferably 1 to 3 carbon atoms, and more preferably 1 or 2 carbon atoms.

[0035] In the above formula (1), R １ and R ２ are such that R １ and R ２When representing a cyclic structure formed by the bonding of and , the cyclic structure may have a saturated ring skeleton, or it may have unsaturated bonds within the ring skeleton. Also, R １ and R ２ The cyclic structure formed by the bonding of these elements may also be a structure in which an alkyl group (for example, a methyl group or an ethyl group) is bonded to the cyclic skeleton. １ and R ２ The number of carbon atoms in the cyclic structure formed by the bonding of these atoms is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5.

[0036] In terms of being able to improve the ionic conductivity of molecular crystals, R in formula (1) above １ and R ２ R １ and R ２ It is preferable that the combination of these elements forms a cyclic structure, and it is more preferable that the cyclic structure has a saturated ring skeleton.

[0037] The total number of carbon atoms in formula (1) above is 2 to 16. From the viewpoint of promoting the crystallization of the mixture of organic molecule (A1) and alkali metal salt during the production of molecular crystals, the total number of carbon atoms in formula (1) above is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 5.

[0038] A specific example of the organic molecule (A1) is R in formula (1) above. １ and R ２ Examples of cases where each is an alkyl group or an alkoxy group include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, diethyl sulfate, etc. In formula (1) above, R １ and R ２ However, R １ and R ２ Examples of cases representing a cyclic structure formed by the bonding of these molecules include tetrahydrothiophene 1,1-dioxide, 3-methylsulfolane, 3-sulfolene, 1,3-propanesultone, 1,4-butanesultone, and 1,3,2-dioxathiolane 2,2-dioxide. The organic molecule (A1) constituting the molecular crystal may be a single type or a combination of two or more types.

[0039] (Organic molecules having nitrogen atoms) As organic molecules having nitrogen atoms, at least one selected from the group consisting of nitriles, compounds having amide groups, and compounds having urea groups can preferably be used.

[0040] A preferred example of a nitrile is the following formula (2): (In formula (2), R ３ represents a hydrocarbon chain, R ４ and R ５ Examples of molecules represented by formula (2) are those in which each independently represents a hydrogen atom, an alkyl group, or a cyano group, provided that the total number of carbon atoms in formula (2) is 16 or less.

[0041] The molecule represented by formula (2) above (hereinafter also referred to as "organic molecule (A2)") is a molecule having two or more cyano groups (-CN). ３ R may be a saturated hydrocarbon chain or may have unsaturated bonds. In terms of obtaining molecular crystals with excellent ionic conductivity, ３ R preferably represents a saturated hydrocarbon chain. ３ The number of carbon atoms is, for example, 1 to 10, preferably 1 to 6, and more preferably 2 to 4.

[0042] R ４ or R ５ If the alkyl group is an alkyl group, it may be linear or branched. It is preferably linear. ４ and R ５ The number of carbon atoms in each group is preferably 0 to 3, and more preferably 0 or 1, from the viewpoint of mixing the organic molecule (A2) and the alkali metal salt to produce crystallization during the production of molecular crystals.

[0043] From the viewpoint of promoting the crystallization of a mixture of organic molecules (A2) and alkali metal salts during the production of molecular crystals, the total number of carbon atoms in formula (2) above is preferably 8 or less, and more preferably 6 or less.

[0044] Specific examples of organic molecules (A2) include succinonitrile, adiponitrile, 3-hexendinitrile, 1,3,5-pentanetricarbonitride, tert-butylmalononitrile, and 1,2,2,3-propanetetracarbonitride. The organic molecules (A2) constituting the molecular crystal may be a single type or a combination of two or more types.

[0045] Compounds containing amide groups are preferable to have two or more amide groups in a single molecule due to their high heat resistance. Specific examples of compounds containing amide groups include malonamide, succinamide, glutaramide, adipoamide, N,N,N',N'-tetramethylmalonamide, N,N,N',N'-tetraethylmalonamide, N,N,N',N'-tetramethylsuccinamide, and terephthalamide.

[0046] Compounds containing a urea group may be linear or cyclic. Specific examples of compounds containing a urea group include N,N'-dimethylethylene urea, N,N'-dimethylpropylene urea, and tetramethyl urea.

[0047] (Organic molecules containing a phosphorus atom) Examples of organic molecules containing a phosphorus atom include ethylenebis(dimethylphosphine), ethylenebis(diphenylphosphine), methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphineimine, and triphenylphosphineimine.

[0048] From the viewpoint of ease of manufacturing molecular crystals, organic molecule (A) is preferably at least one selected from the group consisting of sulfone, nitrile, amide, and urea, and more preferably at least one selected from the group consisting of sulfone, nitrile, and amide, as it provides a greater effect in improving ionic conductivity by combining it with a film-like porous body. Furthermore, organic molecule (A2) is more preferred in that it is possible to obtain a solid electrolyte with superior ionic conductivity while improving the flexibility of the solid electrolyte by combining a non-crosslinked polymer and molecular crystals, and R in formula (2) above is more preferred. ３ It is preferable that this represents a saturated hydrocarbon chain.

[0049] ○ Alkali metal salts: Alkali metal salts can be any salt that produces alkali metal ions and are not particularly limited. Examples of alkali metal salts include lithium salts, sodium salts, potassium salts, etc. Furthermore, the anions constituting the alkali metal salt may be monatomic or polyatomic ions, and may be inorganic or organic ions.

[0050] A specific example of an alkali metal salt is, for example, Li ２ CO ３ , LiBr, LiCl, LiI, LiSCN, LiBF ４ , lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), LiAsF ６ LiClO ４ ,CH ３ COOLi, CF ３ COOLi, LiCF ３ SO ３ LiPF ６ LiC (CF ３ SO ２ ) ３ Examples include various lithium salts such as imide-based lithium salts; and salts of these lithium salt anions with alkali metal ions other than lithium ions (for example, sodium ions and potassium ions).

[0051] Lithium imide salts are lithium salts that contain an imide anion as a counter anion. A specific example of a lithium imide salt is lithium bis(fluorosulfonyl)imide (Li ＋ (FSO ２ ) ２ N － ), lithium bis(trifluoromethanesulfonyl)imide (Li ＋ (CF ３ SO ２ ) ２ N － Examples include lithium (fluorosulfonyl) (trifluoromethanesulfonyl)imide.

[0052] In terms of higher ionic dissociation, the counter anions that make up alkali metal salts are (FSO ２ )２ N － (CF ３ SO ２ ) ２ N － (FSO ２ ) (CF ３ SO ２ ) N － , PF ６ － BF ４ － It is preferable that the alkali metal salt constituting the molecular crystal is a salt of lithium ion or sodium ion with a counter anion (i.e., lithium salt or sodium salt), and more preferably lithium salt, in order to obtain molecular crystals with high ion dissociation and higher ionic conductivity. ６ LiBF ４ Lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) are particularly preferred because they have high ion dissociation properties and allow for the production of molecular crystals with excellent ionic conductivity.

[0053] Among the imide-based lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide are particularly preferred, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide are more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0054] 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 a single type or two or more types.

[0055] 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, and may also be 250°C or lower.

[0056] ○ Manufacturing of Molecular Crystals The molecular crystals constituting the solid electrolyte of this disclosure can be manufactured using an organic substance that provides organic molecules (A) (hereinafter simply referred to as organic molecule (A)) and an alkali metal salt. Molecular crystals are preferably manufactured by mixing organic molecule (A) and alkali metal salt, and then heating as necessary. Specifically, molecular crystals can be manufactured by the following manufacturing methods (1) or (2). ・Manufacturing method (1) A method including a step of mixing organic molecule (A) and alkali metal salt while applying mechanical energy (hereinafter also referred to as the "mechanical mixing step") ・Manufacturing method (2) A method including a step of mixing organic molecule (A) and alkali metal salt in a solvent capable of dissolving at least one of organic molecule (A) and alkali metal salt (hereinafter also referred to as the "solvent mixing step") and a step of removing the solvent from a solution containing organic molecule (A), alkali metal salt, and solvent (hereinafter also referred to as the "solvent removal step")

[0057] (Regarding manufacturing method (1)) - Mechanical mixing process In the mechanical mixing process, the organic molecule (A) and the alkali metal salt are mixed while mechanical energy is applied to the substance containing the organic molecule (A) and the alkali metal salt by means of impact, shear, compression, friction, etc. It is preferable that this causes a change 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".

[0058] The mixing ratio of organic molecule (A) to alkali metal salt is not particularly limited and can be set according to the types of organic molecule (A) and alkali metal salt. For example, the mixing ratio of organic molecule (A) to alkali metal salt may be 0.1 to 10 moles of organic molecule (A) per mole of alkali metal salt. Preferably, the mixing ratio of organic molecule (A) to alkali metal salt is 0.2 to 5 moles, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles.

[0059] Furthermore, in the production of molecular crystals, to the extent that the effects of the present invention are not impaired, substances other than organic molecule (A) and alkali metal salts (for example, sulfur-containing organic molecules other than organic molecule (A)) may be used as constituent units of the crystal lattice. However, considering the ionic conductivity and ease of production of the molecular crystals, it is preferable to minimize the amount of substances other than organic molecule (A) and alkali metal salts used. Specifically, the amount of substances other than organic molecule (A) and alkali metal salts used is preferably 0.1 moles or less, and more preferably 0.05 moles or less, per 1 mole of the total amount of organic molecule (A) and alkali metal salts.

[0060] The method for mixing an organic molecule (A) and an alkali metal salt while applying mechanical energy is not particularly limited. In the mechanical mixing process, the mixing of the organic molecule (A) and the alkali metal salt can be carried out using various equipment such as a ball mill, bead mill, blender, homogenizer, stamp mill, homomixer, or disper mixer. Furthermore, when manufacturing molecular crystals on a small scale, the mechanical mixing of the organic molecule (A) and the alkali metal salt can also be carried out using a mortar and pestle. The mechanical mixing of the organic molecule (A) and the alkali metal salt may be carried out dry or wet. In addition, the mechanical mixing of the organic molecule (A) and the alkali metal salt may be carried out at room temperature or at low temperatures. For example, if the melting point of the organic molecule (A) is lower than room temperature, the liquid organic molecule (A) may be mechanically mixed with the alkali metal salt. Alternatively, the solid organic molecule (A) may be mechanically mixed with the alkali metal salt at a temperature lower than the melting point of the organic molecule (A).

[0061] The mechanical mixing of the organic molecule (A) and the alkali metal salt may be carried out while heating. However, in order to suppress the volatilization and sublimation of the organic molecule (A), the mechanical mixing step should be carried out at a lower temperature than the heating temperature in the subsequent heating step. Specifically, the mechanical mixing step should be carried out at, for example, 50°C or lower, preferably 40°C or lower, and more preferably 35°C or lower. The time for mechanical mixing depends on the amount and type of organic molecule (A) and alkali metal salt used, but may be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0062] The mixture of organic molecule (A) and alkali metal salt obtained by mechanical mixing (hereinafter also simply referred to as "the 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. Furthermore, 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 the decomposition of molecular crystals due to the volatilization or sublimation of organic molecule (A) during the heating step after the mechanical mixing step. In this specification, the melting point of the mixture of organic molecule (A) and alkali metal salt is the value obtained by differential scanning calorimetry (DSC). Details of the measurement method are as described in the examples below.

[0063] When manufacturing molecular crystals by method (1), it is preferable that method (1) further includes a step of heating the mixture obtained by the mechanical mixing step (i.e., a mixture of organic molecules (A) and alkali metal salts). This heating step makes the organic molecules (A) and alkali metal salts in the mixture more uniform, and further enhances the ionic conductivity of the molecular crystals. In particular, by combining the mechanical mixing step and the heating step, it is thought that intermolecular interactions occur between the alkali metal ions derived from the alkali metal salt and the organic molecules (A) due to the mechanical mixing, and as a result, it is possible to suppress the volatilization and sublimation of organic molecules (A) during the heat treatment. This has the advantage of making it easier to obtain molecular crystals with a desired composition.

[0064] • Heating step: In the heating step, after the mechanical mixing step described above is performed, the mixture obtained in the mechanical mixing step is heated. The method of heating the mixture is not particularly limited. The heating temperature of the mixture can be appropriately set depending on the type of organic molecule (A) and alkali metal salt used as raw materials in the production of molecular crystals. From the viewpoint of making the organic molecule (A) and alkali metal salt in the mixture more uniform, it is preferable to heat the mixture in this heating step at a temperature above the melting point of the mixture of organic molecule (A) and alkali metal salt obtained by mechanical mixing. By setting the heating temperature above the melting point of the mixture, the mixture melts, which promotes uniform mixing of the organic molecule (A) and alkali metal salt.

[0065] Regarding the heating temperature of the mixture, it is preferable to set the temperature higher than the melting point of the mixture, from the viewpoint of homogenizing the organic molecules (A) and alkali metal salts in the mixture by melting it. Furthermore, from the viewpoint of promoting homogenization of the organic molecules (A) and alkali metal salts in the mixture, it is more preferable to set the heating temperature of the mixture to be 5°C or more higher than the melting point of the mixture (unit: °C), and even more preferable to set it to be 7°C or more higher. Regarding the upper limit of the heating temperature of the mixture, from the viewpoint of suppressing the volatilization and sublimation of components contained in the mixture, it is preferable to set it to (Mp + 20)°C or less, and more preferably to (Mp + 15)°C or less, when the melting point of the mixture is expressed as Mp (unit: °C). The heating time is not particularly limited, as long as it is sufficient to homogenize the organic molecules (A) and alkali metal salts 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. In addition, the heat treatment can usually be carried out under normal pressure, but it may also be carried out under pressure or reduced pressure.

[0066] When heating the mixture, it is preferable to stir the mixture while heating to further homogenize the organic molecules (A) and the alkali metal salt. The method of stirring is not particularly limited and examples include a magnetic stirrer, stirring rod, stirrer with stirring blades, and external circulation stirring. Stirring may also be performed by mechanical mixing operations that can obtain a greater shear force, such as a homomixer, disper mixer, or homogenizer.

[0067] By heating a mixture containing an organic molecule (A) and an alkali metal salt, and then lowering the temperature of the heated mixture, the heated mixture can crystallize, and the desired molecular crystal can be obtained. When lowering the temperature of the heated mixture, the mixture may be cooled gradually (for example, slowly lowering the temperature at room temperature over 1 to 48 hours). Alternatively, the heated mixture may be cooled rapidly (for example, placing the heated mixture in a constant temperature bath at a temperature lower than room temperature (e.g., 15°C or below) for a short period of time). From the viewpoint of suitably crystallizing the heated mixture, it is preferable to cool the heated mixture by gradually lowering its temperature.

[0068] (Regarding manufacturing method (2)) - Solvent mixing step When the boiling point of organic molecule (A) is high (for example, 100°C or higher), manufacturing method (2) is applicable as a method for producing molecular crystal (A). By mixing organic molecule (A) and alkali metal salt in a solvent, it is possible to promote homogenization of organic molecule (A) and alkali metal salt.

[0069] The solvent used in the solvent mixing step can be any solvent capable of dissolving at least one of the organic molecule (A) and the alkali metal salt. Organic solvents are preferably used as the solvent. The organic solvent used should preferably have a moderately low boiling point (e.g., 100°C or below) and a low dielectric constant; examples include dimethyl carbonate, tetrahydrofuran, and ethyl acetate. The order in which the organic molecule (A) and the alkali metal salt are added to the solvent in the solvent mixing step 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) or the alkali metal salt may be dissolved in the solvent before adding the other raw material. When mixing the organic molecule (A) and the alkali metal salt in the solvent, it is preferable to stir while mixing to ensure homogenization of the organic molecule (A) and the alkali metal salt. The stirring method is not particularly limited, but for example, the stirring method exemplified in manufacturing method (1) can be used as appropriate.

[0070] - Solvent removal step The method for removing the solvent from a solution containing an organic molecule (A), an alkali metal salt, and a solvent is not particularly limited as long as the solvent can be removed from the solution. As a method for removing the solvent, heat treatment is preferable in terms of being able to simply and efficiently remove the solvent. The heat treatment may be performed under normal pressure, or may be performed under pressure or under reduced pressure. When a solvent having a high boiling point is used in the solvent mixing step, it is preferable to perform the heat treatment under reduced pressure in order to suppress the decomposition of the organic molecule (A) and the alkali metal salt.

[0071] It can be detected by performing powder X-ray diffraction measurement of the product that the product obtained by the above production method is a molecular crystal containing an organic molecule (A) and an alkali metal salt as constituent units. Details of the measurement method follow the method described in the examples below.

[0072] The molecular crystal contained in the solid electrolyte of the present disclosure exhibits ion conductivity. Specifically, the ion conductivity of the molecular crystal at 25 °C is preferably 1.0×10 －５ S / cm or more. When the ion conductivity of the molecular crystal at 25 °C is 1.0×10 －５ S / cm or more, a solid electrolyte with better ion conductivity can be obtained. From the viewpoint of obtaining a solid electrolyte exhibiting excellent ion conductivity, the ion conductivity of the molecular crystal at 25 °C is preferably 1.5×10 －５ S / cm or more, more preferably 2.0×10 －５ S / cm or more, and even more preferably 3.0×10 －５ S / cm or more. The ion conductivity of the molecular crystal is a value measured at 25 °C using the alternating current impedance method. Details of the measurement method of the ion conductivity follow the method described in the examples below.

[0073] In the solid electrolyte of this disclosure, the molecular crystal content (F value) is preferably 30 to 90% by mass of the total amount of the solid electrolyte, from the viewpoint of obtaining a solid electrolyte that exhibits good ionic conductivity. When the molecular crystal content in the solid electrolyte is within the above range, the strength, ionic conductivity, and flexibility of the solid electrolyte can be improved in a well-balanced manner. From the viewpoint of making the ionic conductivity of the solid electrolyte excellent, the molecular crystal content in the solid electrolyte is more preferably 40% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, from the viewpoint of ensuring the strength and flexibility of the solid electrolyte, the molecular crystal content in the solid electrolyte is more preferably 85% by mass or less.

[0074] In energy storage devices, it is desirable to increase the thickness of the solid electrolyte layer to address issues such as penetration of the solid electrolyte layer by lithium dendrites and accelerated dendrite growth due to cracking of the solid electrolyte layer. However, currently, simply increasing the thickness of the solid electrolyte layer is not sufficient to suppress dendrite growth. Furthermore, although molecular crystals are normally solid at room temperature, some have melting points relatively close to the operating temperature of energy storage devices, and depending on the usage environment and method, temporary melting of the molecular crystal may occur due to a rise in the temperature of the energy storage device. In this case, there is a concern that the positive and negative electrodes may come into direct contact due to the melting of the molecular crystal, so it is considered necessary to increase the thickness of the layer when fabricating a solid electrolyte layer using molecular crystals. Looking at the solid electrolyte of this disclosure in which the molecular crystal electrolyte is held inside the pores of a film-like porous material, it is thought that the ionic conductivity tends to decrease due to the inclusion of a film-like porous material that does not have ionic conductivity. However, because the solid electrolyte exhibits high strength due to the inclusion of a film-like porous material, the thickness of the solid electrolyte layer can be reduced compared to when molecular crystals are used alone. This reduces the internal resistance of the solid electrolyte layer, and as a result, the solid electrolyte of this disclosure, in which the molecular crystalline electrolyte is held within the pores of a film-like porous material, is thought to exhibit high strength and flexibility while achieving ionic conductivity equivalent to or better than that of a solid electrolyte made of molecular crystals alone. However, the above inference does not limit the present invention.

[0075] <Other Components> The solid electrolyte of this disclosure may further contain components other than the film-like porous material and molecular crystals (other components), to the extent that they do not impair the effects of the present invention. For example, alkali metal salts may be further added to the solid electrolyte of this disclosure in order to adjust the ionic conductivity of the solid electrolyte. Examples of alkali metal salts include those used in the production of molecular crystals. The alkali metal salt added to the solid electrolyte may be the same as or different from the alkali metal salt that constitutes the molecular crystal. From the viewpoint of sufficiently obtaining the effect of increasing the ionic conductivity of the solid electrolyte, it is preferable that the alkali metal salt added together with the molecular crystal is the same as the alkali metal salt that constitutes the molecular crystal.

[0076] Other components include alkali metal salts, as well as, for example, inorganic fillers, conductive additives, positive electrode active materials, negative electrode active materials, antioxidants, and colorants. However, considering the ease of manufacturing the solid electrolyte and its ionic conductivity, it is preferable to use as few other components as possible. Specifically, the content of other components is, for example, 5% by mass or less, 2% by mass or less, or 1% by mass or less, relative to the total amount of the solid electrolyte.

[0077] <Method for Manufacturing Solid Electrolytes> The method for manufacturing the solid electrolyte of this disclosure is not particularly limited, as long as it can produce a solid electrolyte exhibiting desired properties. The solid electrolyte of this disclosure can be manufactured by a method that includes a contact step of bringing the interior of a film-like porous body into contact with a molecular crystal or a raw material for a molecular crystal. Specifically, the following first and second manufacturing methods are mentioned. ・First manufacturing method: A method in which the contact step is a step of bringing a molten material obtained by melting a molecular crystal or a raw material for a molecular crystal into contact with the interior of a film-like porous body, and further includes a cooling step of cooling the film-like porous body after contact with the molten material to below the melting point of the molecular crystal. ・Second manufacturing method: A method in which the contact step is a step of bringing a film-like porous body into contact with a solution containing a molecular crystal or a raw material for a molecular crystal and a solvent, and further includes a desolvation step of removing the solvent from the film-like porous body after contact with the solution.

[0078] (Regarding the first manufacturing method) ○ Contact step In the first manufacturing method, a molten material obtained by melting molecular crystals or molecular crystal raw materials is brought into contact with the inside of the pores of a film-like porous material. The method of bringing the molten material into contact with the inside of the pores of the film-like porous material is not particularly limited and can be carried out by treatments such as immersion, impregnation, coating, and spraying. Of these, impregnation is preferred because it allows the molten material to be uniformly brought into contact with the inside of the pores of the film-like porous material using as little molecular crystal as possible. When bringing the molten material into contact with the inside of the pores of the film-like porous material by impregnation, for example, the molten material can be placed on a support, and then the film-like porous material can be placed on top of the molten material on the support, allowing the molten material to permeate into the interior of the film-like porous material. Alternatively, after placing the film-like porous material on a support, molecular crystals or molecular crystal raw materials can be placed on top of the film-like porous material on the support, and the molecular crystals or molecular crystal raw materials can be heated and melted to allow the molten material to permeate into the interior of the film-like porous material.

[0079] The molten material can be obtained by heating molecular crystals or molecular crystal raw materials at a temperature above the melting point of the molecular crystals. The heating method is not particularly limited, but can be carried out using, for example, a hot plate, heater, or hot air blower. From the viewpoint of sufficiently melting the molecular crystals or molecular crystal raw materials, the heating temperature is preferably higher than the melting point of the molecular crystals. For example, it may be heated at a temperature 2°C or more higher than the melting point of the molecular crystals, or at a temperature 5°C or more higher. The heating time is sufficient to melt the molecular crystals or molecular crystal raw materials, for example, 1 to 30 minutes. The heat treatment can usually be carried out under atmospheric pressure, but it may also be carried out under pressurized or reduced pressure.

[0080] The raw material for the molecular crystal corresponds to a mixture of an organic molecule (A) and an alkali metal salt. Preferably, the raw material for the molecular crystal used here is a mixture obtained by mechanically mixing an organic molecule (A) and an alkali metal salt. In the contact step, the process for obtaining a solid electrolyte can be simplified by bringing the molten material of the molecular crystal raw material into contact with the inside of the pores of the film-like porous material. ○ Cooling step After the contact step, the film-like porous material that has been in contact with the molten material is cooled to below the melting point of the molecular crystal. This causes the molten molecular crystal to crystallize, and the molecular crystal can be supported inside the pores of the film-like porous material. When lowering the temperature of the film-like porous material after contact with the molten material, the film-like porous material may be cooled gradually over, for example, 1 to 24 hours, or it may be cooled rapidly using a constant temperature oven or the like. From the viewpoint of suitably allowing the molecular crystal to crystallize on the film-like porous material, it is preferable to gradually lower the temperature of the film-like porous material to room temperature after contact with the molten material.

[0081] (Regarding the second manufacturing method) ○ Contact step In the second manufacturing method, a solution containing molecular crystals or raw materials for molecular crystals and a solvent (hereinafter also referred to as "molecular crystal solution") is prepared, and the prepared molecular crystal solution is brought into contact with the inside of the pores of a film-like porous body. The solvent used in the contact step is preferably an organic solvent capable of dissolving or dispersing molecular crystals. Such organic solvents can be appropriately set depending on the type of molecular crystal used in the production of solid electrolytes, but examples 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 ethylmethyl carbonate; amides such as N-methylformamide, N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidone; nitriles such as acetonitrile; and so on.

[0082] When preparing the molecular crystal solution, the amount of solvent used can be set as appropriate. From the viewpoint of uniformly and sufficiently depositing molecular crystals inside the pores of the porous film, the amount of solvent used is preferably such that the molecular crystal concentration is 5 to 60% by mass, and more preferably 10 to 50% by mass. When preparing the molecular crystal solution, it may be done at room temperature, at low temperature, or under heating. The method of bringing the molecular crystal solution into contact with the inside of the pores of the porous film is not particularly limited and can be done by treatments such as immersion, impregnation, coating, or spraying. Of these, impregnation is preferred because it allows for uniform contact of the molecular crystal solution with the inside of the pores of the porous film using as little molecular crystal as possible. When bringing the molecular crystal solution into contact with the inside of the pores of the porous film, the method of using the molecular crystal solution instead of the molten material in the embodiment exemplified in the first manufacturing method can be used as appropriate.

[0083] ○Solvent Removal Process After the contact process, the solvent is removed from the porous film after contact with the molecular crystal solution. This allows the molecular crystals in the molecular crystal solution to crystallize, and the molecular crystals to be supported inside the pores of the porous film. The method for removing the solvent from the molecular crystal solution in the porous film is not particularly limited, as long as the solvent can be removed from the molecular crystal solution. As a method for removing the solvent, heat treatment is preferred because it is simple and efficient to remove the solvent. When removing the solvent by heating, the heating temperature can be appropriately set according to the type of solvent, but for example it can be 30 to 120°C, and preferably 35 to 100°C. The heating time is, for example, 1 to 30 minutes. The heat treatment may be carried out under atmospheric pressure or under reduced pressure. From the viewpoint of removing the solvent in the mixture at the lowest possible temperature, it is preferable to carry out the solvent removal treatment under reduced pressure and with a heating temperature of 80°C or lower.

[0084] (Other steps) ○ Hydrophilization treatment step The manufacturing method of the present disclosure may further include, in addition to the contact step, a hydrophilization treatment step in which a surfactant is impregnated into the pores of the porous film to obtain a porous film, as a pretreatment when contacting the molecular crystal or the raw material for the molecular crystal with the porous film. By further including the hydrophilization step in the manufacturing method of the present disclosure, a solid electrolyte with superior ionic conductivity can be obtained while maintaining high strength and flexibility.

[0085] The surfactant used in the hydrophilization treatment is not particularly limited. Examples of surfactants include anionic surfactants, nonionic surfactants, and cationic surfactants. In addition, fluorine-based surfactants, silicone-based surfactants, and acetylene glycol-based surfactants may also be used.

[0086] Specific examples of fluorinated surfactants include fluoroalkyl (C2-C10) carboxylic acids, disodium N-perfluorooctanesulfonyl glutamate, sodium 3-[fluoroalkyl (C6-C11) oxy]-1-alkyl (C3-C4) sulfonate, sodium 3-[ω-fluoroalkanoyl (C6-C8)-N-ethylamino]-1-propanesulfonate, sodium N-[3-(perfluorooctanesulfonamide)propyl]-N,N-dimethyl-N-carboxymethyleneammonium betaine, and fluoroalkyl (C11-C20) carboxylate. Examples include acids, perfluoroalkyl carboxylic acids (C7-C13), perfluorooctanesulfonic acid diethanolamide, perfluoroalkyl (C4-C12) sulfonates (Li, K, Na), N-propyl-N-(2-hydroxyethyl) perfluorooctanesulfonamide, perfluoroalkyl (C6-C10) alphonamidopropyltrimethylammonium salt, perfluoroalkyl (C6-C10)-N-ethylsulfonylglycine salt (K), bis(N-perfluorooctylsulfonyl-N-ethylaminoethyl) phosphate, monoperfluoroalkyl (C6-C16) ethyl phosphate ester, perfluoroalkenyl quaternary ammonium salt, perfluoroalkenyl polyoxyethylene ether, and sodium perfluoroalkenylsulfonate salt.

[0087] Specific examples of silicone-based surfactants include silicones that have been hydrophilically modified with polyethylene oxide, polypropylene oxide, etc. Using fluorine-based surfactants is preferable because it is possible to improve the wettability of the surface of a film-like porous material with a small amount of surfactant, thereby reducing the influence of impurities.

[0088] Specific examples of acetylene glycol-based surfactants include compounds in which a polyethylene oxide structure is bonded to an acetylene glycol skeleton, such as Surfinol and Dynol, manufactured by Nisshin Chemical Industry Co., Ltd. Acetylene glycol-based surfactants are preferable because they have antifoaming properties, which reduces foaming of the surfactant treatment solution and minimizes treatment defects due to bubble adhesion.

[0089] In the process of impregnating the pores of a porous film with a surfactant, a suspension of the surfactant is preferable. Such a suspension can be prepared by mixing the surfactant with an aqueous solvent. Water or a mixture of water and alcohol is preferably used as the aqueous solvent. The amount of water in the aqueous solvent is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. When preparing the surfactant suspension, the surfactant may be suspended while applying ultrasonic vibration to the liquid. In the surfactant suspension, the concentration of the surfactant is preferably 0.001 to 5% by mass, and more preferably 0.01 to 5% by mass.

[0090] The method for impregnating the porous film with a surfactant is not particularly limited. For example, it can be done by immersing the porous film in a surfactant suspension, or by impregnating, coating, or spraying the porous film with a surfactant suspension. The hydrophilization treatment may also be performed under atmospheric pressure, or under pressurized or reduced pressure. After the surfactant suspension has been brought into contact with the pores of the porous film, it is preferable to perform a drying treatment by heating, hot air drying, or natural drying.

[0091] In the first and second manufacturing methods described above, a hydrophilic treated substrate, which has been treated with a surfactant to make it hydrophilic as described above, can preferably be used as the film-like porous body used in the contact step. The presence of a surfactant on the inner surface of the interconnected pores of the film-like porous body can be confirmed by dropping a water droplet onto the inner surface of the interconnected pores and observing that the water does not repel but seeps into the film-like porous body.

[0092] Through the above operations, a high-strength, flexible solid electrolyte can be obtained by a relatively simple method. The solid electrolyte obtained in this way exhibits excellent ionic conductivity. Therefore, by using the solid electrolyte of this disclosure as an electrolyte material for an energy storage device, an energy storage device with excellent ionic conductivity can be obtained.

[0093] Specifically, for the solid electrolyte of the present disclosure, the ionic conductivity measured at 25°C using the alternating current impedance method is preferably 1.0×10 －５ S / cm or more. From the viewpoint of obtaining a power storage device with excellent performance, the ionic conductivity under the same conditions is more preferably 1.5×10 －５ S / cm or more, still more preferably 2.0×10 －５ S / cm or more, and even more preferably 5.0×10 －５ S / cm or more. The details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0094] <<Power storage device>> The power storage device of the present disclosure (hereinafter also referred to as "this device") includes the solid electrolyte of the present disclosure described above. Examples of this device include secondary batteries and capacitors. When this device is a secondary battery, one aspect thereof is an all-solid-state battery, and a lithium-ion secondary battery is preferable in terms of excellent ionic conductivity.

[0095] An all-solid-state lithium-ion secondary battery, which is one aspect of this device, will be described. A lithium-ion secondary battery is a laminate including an electrode layer composed of a positive electrode layer and a negative electrode layer, and a solid electrolyte layer, and the solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer so as to be in contact with the electrode layer.

[0096] The materials constituting the positive electrode layer and the negative electrode layer are not particularly limited, and can be appropriately selected from known materials as electrode materials for lithium-ion secondary batteries. For example, the positive electrode layer may have a configuration including a positive electrode current collector and a positive electrode mixture layer. As the positive electrode current collector, a metal foil such as aluminum or stainless steel can be used. 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 type, spinel type, or olivine type crystal structure. The negative electrode layer may have a configuration including a negative electrode current collector and a negative electrode mixture layer. As the negative electrode current collector, a metal foil such as a copper foil or a lithium foil can be used. 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 and graphite.

[0097] The solid electrolyte layer is formed of a solid electrolyte in which molecular crystals are held within the pores of the aforementioned film-like porous material. The thickness of the solid electrolyte layer is not particularly limited and can be set appropriately depending on the application of the secondary battery. For example, the thickness of the solid electrolyte layer is 5 to 5,000 μm. From the viewpoint of miniaturizing, reducing weight, and increasing capacity of all-solid-state secondary batteries by making the thickness of the solid electrolyte layer as thin as possible, the thickness of the solid electrolyte layer is preferably 50 μm or less, and more preferably 20 μm or less. The solid electrolyte layer formed by the solid electrolyte of this disclosure has high strength despite being in the form of a film, is easy to handle even when the thickness is 20 μm or less, and can fully perform its function as an electrolyte layer.

[0098] The method for manufacturing 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 comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer may be manufactured by sandwiching the film-like solid electrolyte of this disclosure, which serves as the solid electrolyte layer, between a positive electrode layer and a negative electrode layer, and performing a pressurizing treatment for bonding as necessary. The laminate comprising the positive electrode layer, a solid electrolyte layer, and a negative electrode layer is usually housed in a case and used as a secondary battery.

[0099] This device is not limited to the above configuration in which lithium ions are the ion carriers, but may also be a secondary battery that uses other ions, such as sodium ions, as carriers. Furthermore, this device may be a capacitor. One embodiment of a capacitor includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer, with the solid electrolyte disposed between the positive and negative electrode layers such that the solid electrolyte layer is in contact with each electrode layer.

[0100] The energy storage device comprising the solid electrolyte of this disclosure can be applied to a variety of uses. Specifically, it can be used as a power source in various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various mobile devices such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances.

[0101] The present invention will be described in detail below based on the following 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.

[0102] ≪Production and Structural Confirmation of Molecular Crystal Electrolytes≫ [Production Example 1] 1. Production of Molecular Crystals In a dry room where the dew point was maintained below -40°C, 0.5387 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt and 0.4613 g of succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule were weighed out in a molar ratio of 1:2 and mechanically mixed in an agate mortar at room temperature (25°C) for 5 minutes 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: nitrogen atmosphere) at a heating rate of 10°C per minute, and a large endothermic peak (melting point) was observed at 60°C. Although succinonitrile before mixing showed plasticity, the mixture did not. The mixture was transferred to a vial and stirred for 1 hour using a magnetic stirrer at a set temperature of 70°C to confirm that it had dissolved uniformly (heating step). The resulting molten material was then allowed to cool to room temperature to obtain a white solid.

[0103] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Powder X-ray diffraction was performed on the obtained white solid using an X-ray diffractometer (Bruker AXS, D8 ADVANCE). CuKα was used as the X-ray source, with an applied voltage of 40 kV and a current of 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 sharp peaks within the measurement range angle was observed, it indicates that the sample (solid) is crystalline. Therefore, if sharp peaks were observed within the measurement range angle, and different X-ray diffraction spectra were obtained for the organic molecules and alkali metal salts used as raw materials, it was determined that molecular crystals composed of alkali metal salts and organic molecules had been formed. Figure 1 shows the results of powder X-ray diffraction measurement on the white solid obtained as described above. Sharp peaks were observed within the measurement range angle, and different X-ray diffraction spectra were observed for the raw materials. From this, it can be concluded that the obtained white solid is crystalline, that is, a molecular crystal composed of alkali metal salts and organic molecules (referred to as "Li(FSI)(SN)"). ２ It was confirmed that this was the case (to be written as "). Furthermore, in the composition formula of the molecular crystal in Production Example 1, bis(fluorosulfonyl)imide anion is abbreviated as FSI, and succinonitrile as SN.

[0104] 3. Confirmation of the crystalline phase by differential scanning calorimetry (DSC measurement) The obtained molecular crystals were subjected to DSC measurements using a differential scanning calorimetry meter (TA Instruments, DSC250, measurement atmosphere: nitrogen atmosphere) in the range of -80°C to 100°C at a heating rate of 10°C per minute. According to Timmermans' empirical rule, the entropy of melting is 20 JK. －１ mol －１ If the value is smaller than this, the substance has a viscous crystalline phase and can be said to be a plastic crystal. (Reference: J.W. Timmermans, J.Phys.Chem.Solids, 18 (1961) 1.) DSC measurement revealed an endothermic peak (melting point) with a peak at 63°C (this was visually confirmed to be the melting point). The melting entropy was calculated to be 110.97 JK. －１ mol－１ Therefore, Li(FSI)(SN) ２ It was confirmed that it does not have a viscous crystalline phase and is not a plastic crystal.

[0105] 4. Measurement of Ionic Conductivity: Using the press mold 10 shown in Figure 2, sample pellets were prepared in a dry room with a dew point of -40°C or lower. First, molecular crystal (Li(FSI)(SN) ２ A die set 11 containing 0.0200 g of the sample was placed on the lower punch 12, and the upper punch 13 was placed on the die set 11. The molecular crystal was compressed for 1 minute under pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet with a diameter of 1 cm and a thickness of 200 μm. Next, the sample pellet was sealed in an all-solid-state battery evaluation cell (Hosen Co., Ltd., KP-SolidCell) in a dry room with a dew point of -40°C or lower. The ionic conductivity was measured using the all-solid-state battery evaluation cell containing the sample pellet. In measuring the ionic conductivity, first, the sealed cell containing the sample pellet was heat-treated in a constant temperature bath at 40°C (corresponding to the heat treatment temperature in Table 1), and 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 using the following formula (1). The AC impedance measurement for calculating ionic conductivity was performed after holding the cell at the measurement temperature for 2 hours in a constant temperature bath. σ = L / (R × S) (1) (In formula (1), σ is ionic conductivity (unit: S / cm), R is resistance (unit: Ω), and S is the cross-sectional area of ​​the sample pellet at the time of measurement (unit: cm) ２ ), L represents the distance between electrodes (unit: cm). ) Li(FSI)(SN) of Manufacturing Example 1 ２ The ionic conductivity at 25°C is 1.2 × 10⁻⁶. －４ The value was S / cm.

[0106] [Manufacturing Examples 2-4] Except for changing the type and amount of raw materials and the heating temperature in the heating process as shown in Table 1, the same procedure as in Manufacturing Example 1 was performed, with molecular crystal Li(FSI)(SL) produced in Manufacturing Example 2 and Li(FSI)(AdN) produced in Manufacturing Example 3. ２ In manufacturing example 4, Li(TFSI)４ (DMPU) ３ The following were obtained. For the mixtures after the mechanical mixing step, large endothermic peaks (melting points) were observed at 73°C in Production Example 2, 90°C in Production Example 3, and 105°C in Production Example 4. In addition, the compositional formulas of the molecular crystals in Production Examples 2 to 4 were abbreviated as follows: bis(fluorosulfonyl)imide anion was abbreviated as FSI, bis(trifluoromethanesulfonyl)imide anion as TFSI, tetrahydrothiophene 1,1-dioxide as SL, adiponitrile as AdN, and N,N'-dimethylpropyleneurea as DMPU. DSC measurements were performed on the obtained molecular crystals in the same manner as in Production Example 1, and Li(FSI)(SL), Li(FSI)(AdN) ２ and Li (TFSI) ４ (DMPU) ３ It was confirmed that it does not have a viscous crystalline phase and is not a plastic crystal. The temperature of the endothermic peak indicating the melting point was 74°C for Li(FSI)(SL) and Li(FSI)(AdN) ２ 92℃, Li(TFSI) ４ (DMPU) ３ The temperature was 105°C.

[0107]

[0108] The details of the compounds used in Table 1 are shown below: • LiFSI: Lithium bis(fluorosulfonyl)imide [Kanto Chemical Co., Ltd.] • LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide [Kanto Chemical Co., Ltd.] • SN: Succinonitrile [Tokyo Chemical Industries, Ltd.] • SL: Tetrahydrothiophene 1,1-dioxide [Tokyo Chemical Industries, Ltd.] • AdN: Adiponitrile [Fujifilm Wako Pure Chemical Industries, Ltd.] • DMPU: N,N'-dimethylpropyleneurea [Tokyo Chemical Industries, Ltd.]

[0109] ≪Manufacturing and Evaluation of Solid Electrolytes≫ [Example 1] (Hydrophilic Treatment Process) A polyethylene (PE) battery separator (Shenzhen Senior Technology Material, SW320) with a thickness of 20 μm and a porosity of 48 volume% was cut to 5 cm x 5 cm as a porous film. Since the inner and outer surfaces of this porous material are hydrophobic, the porous material surface was made hydrophilic by impregnation treatment with a surfactant using the following method. The porous film was immersed in a 1% aqueous solution of surfactant (DIC Corporation, Megafac F-444). After the surfactant aqueous solution penetrated into the pores of the porous film and the entire film became semi-transparent, it was held for another 5 minutes. Then the porous film was removed from the surfactant aqueous solution, spread on a laboratory cloth (Nippon Paper Crecia Co., Ltd., Kimwipe), and left overnight to air dry. Next, it was left overnight in a dry room with a dew point of -40°C or lower to dry, and a hydrophilic film-like porous material was obtained. This porous film is referred to as "F-444 treated PE". F-444 treated PE was used in the following contact process.

[0110] (Contact process) A PET film with one side treated for release was spread on a hot plate heated to 70°C, with the release-treated side facing upwards. On this PET film, the molecular crystal Li(FSI)(SN) obtained in Production Example 1 was placed ２An appropriate amount was placed on top and melted. Next, F-444 treated PE was placed on top of the molten molecular crystals, and the molten material penetrated into the pores of the film-like porous material (F-444 treated PE), making the penetrated areas semi-transparent. Furthermore, a PET film with one side treated for release was placed on top, with the release side facing the film-like porous material, and the molten material was scraped from the back side of the release side of the PET film with a plastic spatula until it spread across the entire surface of the film-like porous material. After confirming that the molten material had penetrated the film-like porous material and that the entire material was semi-transparent, the excess molten material was scraped off the outside of the film-like porous material with a plastic spatula. After that, when the whole thing was removed from the hot plate, molecular crystals began to form inside and on the outer surface of the film-like porous material, which had appeared semi-transparent, within a few seconds. The transparency decreased in the areas where crystals had formed, and it was visually confirmed that the entire material had crystallized in about 10 seconds (cooling process). After the film-like porous material cooled to room temperature, the two PET films were peeled off and removed to obtain a film-like solid electrolyte in which molecular crystals were retained within the film-like porous material. Hereafter, this solid electrolyte will be referred to as "Molecular Crystal Impregnated F-444 Treated PE". When the Molecular Crystal Impregnated F-444 Treated PE was placed on a 70°C hot plate, the molecular crystals inside and on the outer surface of the film-like porous material melted, increasing its transparency again. When it returned to room temperature, the formation of crystals throughout the entire film-like porous material was repeatedly observed. This confirmed that molecular crystals were retained inside the pores of the film. Here, the mass of the film-like porous material is [W ０ (g)] and the mass [W] of a film-like porous material (i.e., a solid electrolyte) impregnated with molecular crystals. １ The amount (g) was weighed, and the content of molecular crystals in the solid electrolyte (F value) was determined by the following formula (2). F value (%) = {([W １ -W ０ ) ÷ W １} × 100 (2) In Example 1, the W of F-444 treated PE ０ This is 0.0346 g of molecular crystal impregnated F-444 treated PE W １ Since the g was 0.1012 g, the F value was calculated to be 66%.

[0111] (Measurement of Ionic Conductivity) In a dry room where the dew point was maintained below -40°C, four layers of molecular crystal impregnated F-444 treated PE were stacked and punched out using a hole punch and hammer to obtain a sample for ionic conductivity measurement with a diameter of 10 mm. Next, the sample was sealed in an all-solid-state battery evaluation cell (Hosen Co., Ltd., KP-SolidCell). The ionic conductivity was measured using the all-solid-state battery evaluation cell containing the sample. In measuring the ionic conductivity, first, the resistance value was measured by AC impedance measurement while the all-solid-state battery evaluation cell containing the sample was heat-treated in a constant temperature bath at 50°C (corresponding to the heat treatment temperature in Table 2). The resistance value decreased with the heat treatment time, and the heat treatment was terminated when it became constant. Next, the resistance value at 25°C was measured by AC impedance measurement. Using the obtained resistance value, the ionic conductivity (S / cm) was calculated using the above formula (1). Furthermore, the AC impedance measurement for calculating ionic conductivity was performed after holding the cell at the measurement temperature for 2 hours in a constant temperature bath. The ionic conductivity of molecular crystal-impregnated F-444 treated PE at 25°C was 2.5 × 10⁻⁶. －５ The value was S / cm.

[0112] (Evaluation of Flexibility) In a dry room where the dew point was maintained at -40°C or below, molecular crystal impregnated F-444 treated PE was punched out using a hole punch and hammer to obtain circular sample pellets with a diameter of 10 mm for evaluation of flexibility. The sample pellets were wrapped around a polyethylene rod with a diameter of 20 mm, and the appearance of the curved sample pellets was observed to evaluate their flexibility according to the following criteria. ○: No abnormalities in appearance were observed in the sample pellet. △: Fine cracks were observed in the sample pellet. ×: Clear cracks were observed in the sample pellet, or a part of the sample pellet peeled off. As a result, the molecular crystal impregnated F-444 treated PE showed no abnormalities in appearance even when the sample pellet was bent, and was judged to be "○". From this, it was confirmed that the solid electrolyte of Example 1 has flexibility. Furthermore, the molecular crystal impregnated F-444 treated PE did not break even when bent at a 90-degree angle, and the solid electrolyte of Example 1 showed excellent flexibility.

[0113] (Strength Evaluation) In a dry room where the dew point was maintained at -40°C or below, molecular crystal impregnated F-444 treated PE was cut to 10 mm x 50 mm to obtain a sample for strength evaluation. Polyimide tape was attached to the end of the sample to prevent slipping, and the part with the polyimide tape was used as the part to be gripped with a clip, and a 200 g weight was attached via the clip. The molecular crystal impregnated F-444 treated PE was lifted by grasping the end with the weight attached and the opposite end, and the strength was evaluated according to the following criteria. Figure 3 shows the strength test of Example 1. ○: The sample did not break. △: The sample did not break but stretched significantly. ×: The sample broke. As a result, as shown in Figure 3, the molecular crystal impregnated F-444 treated PE was judged to be "○" because the sample did not break and hardly stretched. From this result, it was confirmed that the solid electrolyte of Example 1 has high strength.

[0114] [Examples 2-7, 9] Except for changing the type of raw material and the heat treatment temperature for ionic conductivity measurement as shown in Table 2, the same procedure as in Example 1 was performed to obtain a film-like solid electrolyte in which molecular crystals were held in a film-like porous material. The ionic conductivity at 25°C was measured using the film-like solid electrolyte of each example in the same manner as in Example 1. In the ionic conductivity measurement, the film-like solid electrolytes using porous materials made of PE and polytetrafluoroethylene (PTFE) were thin, with thicknesses of 20 μm and 35 μm respectively, and their resistance was too low to measure accurately, so four layers were used for measurement. On the other hand, in the example using porous materials made of polyvinylidene fluoride (PVDF), the thickness was 125 μm, which was a sufficiently measurable thickness, so one layer was used for measurement. The results of the ionic conductivity measurement are shown in Table 2. In addition, a flexibility evaluation test was performed using the film-like solid electrolyte of each example in the same manner as in Example 1. The results are shown in Table 2. In all of the examples, similar to Example 1, the material did not break even when bent at a 90-degree angle, demonstrating excellent flexibility. Figures 4 and 5 show the strength tests conducted in Examples 3 and 4, respectively.

[0115] [Example 8] The molecular crystals obtained in Production Example 1 were dissolved in acetone to prepare a 30% solution. A few drops of this solution were placed on a PET film, and a hydrophobic PE porous material (Shenzhen Senior Technology Material, SW320) that had not undergone hydrophilization treatment was placed on top of the droplets. The acetone solution of the molecular crystals was absorbed into the pores of the film-like porous material (PE porous material) (contact step). Next, the PE porous material that had absorbed the acetone solution of the molecular crystals was peeled off the PET film and dried in the air. After repeating this operation five times, it was placed on a PET film and left on a hot plate heated to 70°C for about 5 minutes to remove the acetone and obtain molecular crystal-impregnated PE (desolvation step). Ionic conductivity measurement, flexibility evaluation test, and strength test were performed in the same manner as in Example 1. The results are shown in Table 2. This molecular crystal-impregnated PE also did not break even when bent at 90 degrees, similar to Example 1, and showed excellent flexibility.

[0116] [Comparative Examples 1-4] The molecular crystals produced in Production Examples 1-4 were molded into pellets with a diameter of 10 mm and a thickness of approximately 200 μm using the same method as the ionic conductivity measurement in Production Example 1, and used for various measurements. The measurement results are shown in Table 2. Note that the molecular crystals themselves were too brittle to obtain a molded body of 10 mm x 50 mm, so a strength test was attempted using compression-molded pellets with a diameter of 10 mm and a thickness of approximately 0.2 mm. However, the molded body of the molecular crystals themselves easily broke when clamped with a clip for attaching a weight, so the flexibility and strength were rated as "×".

[0117]

[0118] The compounds and porous films used in Table 2 are detailed below. (Compounds) ・F-444: Fluorine-based surfactant [DIC Corporation, Megafac F-444] ・D604: Acetylene glycol-based wetting agent [Nisshin Chemical Industry Co., Ltd., Dynol 604] (Porous films) ・PE: Polyethylene separator for batteries, 20 μm thick, 48 vol% porosity [Shenzhen Senior Technology Material, SW320] ・PVDF: Polyvinylidene fluoride membrane filter, 125 μm thick, average pore size 0.45 μm, 70 vol% porosity [AS ONE Corporation, MODEL 047045MFPVDF] - F-444 treated PE: A porous material hydrophilically treated in Example 1. - D604 treated PE: A porous material hydrophilically treated in the same manner as in Example 1, except that F-444 is replaced with D604. - F-444 treated PVDF: A porous material hydrophilically treated in the same manner as in Example 1, except that PE is replaced with PVDF. - Hydrophilized PTFE: Polytetrafluoroethylene membrane filter, hydrophilic type, 35 μm thickness, 83% vol. porosity, average pore size 1 μm [Manufactured by Advantec Toyo Co., Ltd., H100A047A]

[0119] <<Evaluation Results>> As is clear from the results of Examples 1 to 9, the solid electrolyte in which the molecular crystalline electrolyte is held inside the pores of a film-like porous material exhibited high ionic conductivity, high strength, and flexibility. This is thought to be because the molecular crystalline electrolyte is held inside the numerous interconnected pores of the film-like porous material, resulting in high ionic conductivity while the film-like porous material is given high strength and flexibility. In contrast, while molecular crystalline electrolyte alone can be obtained, its strength and flexibility were inferior (Comparative Examples 1 to 4).

[0120] Among Examples 1 to 9, Examples 3, 4, 6, and 7, which used a porous film made of a fluorine-containing polymer that had been hydrophilized, showed higher ionic conductivity and better ionic conductivity compared to the case of molecular crystals alone (Comparative Examples 1 to 3). In particular, Example 7, in which the fluorine-containing polymer was polyvinylidene fluoride (PVDF), showed higher ionic conductivity than Comparative Example 3, in which the solid electrolyte was made from the same molecular crystal. This is presumed to be because when molecular crystals are held inside PVDF, which has a high dielectric constant, some kind of action occurs at the interface between PVDF and molecular crystals, resulting in the formation of higher ion conduction paths.

[0121] From the above results, it has become clear that the solid electrolyte obtained by holding molecular crystals inside the interconnected pores of a film-like porous material exhibits high ionic conductivity while possessing high strength and flexibility. By using the solid electrolyte of this disclosure, which has such properties, as the electrolyte material for energy storage devices, handling during the manufacture of energy storage devices becomes easier, and the device can follow bending forces even when bending forces are applied to it. Therefore, by using the solid electrolyte of this disclosure in the manufacture of energy storage devices, it is possible to obtain energy storage devices that are less prone to damage or performance degradation even when external forces are applied to them, and that are highly safe.

[0122] The present invention is not limited to the embodiments described above, and encompasses various modifications and variations within the scope of equivalents, without departing from the spirit of the invention. Therefore, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of these elements, should be understood to fall within the scope and conceptual range of the present invention in light of the above teachings.

[0123] 10... Press molds

Claims

1. A solid electrolyte comprising a film-like porous body having interconnected pores, and a molecular crystal comprising an organic molecule having at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms, and an alkali metal salt as constituent units, wherein the molecular crystal is held inside the interconnected pores.

2. The solid electrolyte according to claim 1, wherein the content of the molecular crystals is 30 to 90% by mass.

3. The solid electrolyte according to claim 1, wherein the porous film is a resin film.

4. The solid electrolyte according to claim 1, wherein the film-like porous body is formed of a fluorine-containing polymer.

5. The solid electrolyte according to claim 1, wherein the film-like porous body is a hydrophilic treated substrate in which the inside of the pores of the porous film has been subjected to a hydrophilic treatment.

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

7. The solid electrolyte according to claim 1, wherein the alkali metal salt is a salt of lithium ions or sodium ions with a counter anion.

8. A method for producing a solid electrolyte according to any one of claims 1 to 7, comprising the steps of: bringing into contact with the interior of the pores of the film-like porous body a molten material obtained by melting the molecular crystal or the raw material for the molecular crystal; and cooling the film-like porous body after contact with the molten material to below the melting point of the molecular crystal.

9. A method for producing a solid electrolyte according to any one of claims 1 to 7, comprising the steps of: bringing a solution containing the molecular crystal or the raw material for the molecular crystal and a solvent into contact with the interior of the pores of the porous film; and removing the solvent from the porous film after contact with the solution.

10. A method for producing a solid electrolyte according to any one of claims 1 to 7, comprising the steps of: obtaining a film-like porous body by impregnating the inside of the pores of a porous film with a surfactant and performing a hydrophilization treatment; and contacting the inside of the pores of the film-like porous body after the hydrophilization treatment with the molecular crystal or the raw material for the molecular crystal.

11. An energy storage device comprising a solid electrolyte according to any one of claims 1 to 7.

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