Solid electrolyte and power storage device

Abstract

A solid electrolyte containing a molecular crystal and a fluorine-containing polymer, the molecular crystal including an organic molecule having at least one kind of atom selected from a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom, and an alkali metal salt, the solid electrolyte having a diffraction spectrum derived from the molecular crystal in X-ray diffraction.

Description

Technical Field

[0001] [Cross-reference to related applications] This application claims priority based on Japanese Patent Application No. 2023-202027, filed on November 29, 2023, the entirety of which is incorporated herein by reference.

[0002] This disclosure relates to solid electrolytes and energy storage devices. Background Technology

[0003] As energy storage devices, various rechargeable batteries, such as nickel-metal hydride batteries and lithium-ion batteries, as well as double-layer capacitors, have been put into practical use. Among them, lithium-ion batteries are widely used due to their high energy density and high battery capacity. In addition, in recent years, sodium-ion batteries, potassium-ion batteries, and magnesium-ion batteries, which use lithium as a substitute for lithium, a rare metal, have attracted attention as alternatives to lithium-ion batteries.

[0004] Lithium-ion secondary batteries, widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte. They are charged and discharged by allowing lithium ions to move between the two electrodes via the electrolyte. Previously, organic electrolytes were primarily used. However, in recent years, to eliminate concerns about internal short circuits caused by electrolyte leakage, overcharging, and over-discharging, technologies have been proposed to use solid or gel-like electrolytes made of inorganic or organic materials instead of organic electrolytes.

[0005] Organic solid electrolytes have the advantage of excellent adhesion to electrodes due to the moderate softness and high formability of organic materials. On the other hand, they tend to have lower ionic conductivity compared to inorganic solid electrolytes. Therefore, in order to improve practicality, various studies have been conducted on the development of new materials constituting organic solid electrolytes (see, for example, Patent Document 1 and Non-Patent Document 1).

[0006] Patent Document 1 discloses a solid electrolyte for electrochemical devices, comprising a composite of a plastic crystalline matrix electrolyte doped with an ionic salt and a polymer cross-linked structure, wherein linear polymers with a weight-average molecular weight of 100-5000 and having one functional group are chemically bonded as side chains in the polymer cross-linked structure. Here, a plastic crystalline matrix refers to a substance in which molecules or ions exhibit rotational irregularity, but whose centers of mass occupy positions arranged in a lattice structure, thus exhibiting plasticity. Non-Patent Document 1 discloses the formation of a crystalline organic solid electrolyte using a soft solid crystal containing lithium chloride and isoquinoline.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Publication No. 2014-504788 Non-patent literature Non-patent literature 1: Ionics, 2018, Vol. 24, pp. 343-349 Summary of the Invention The technical problem that the invention aims to solve While the organic solid electrolyte described in Patent Document 1 exhibits good ionic conductivity, it lacks flexibility and has poor bendability. Furthermore, the crystalline organic solid electrolyte (i.e., molecular crystal electrolyte) described in Non-Patent Document 1, due to its regular crystal structure, suffers from poor bendability and insufficient ionic conductivity at room temperature; furthermore, its ionic conductivity decreases significantly below room temperature. From the viewpoint of obtaining a high-performance energy storage device that is not easily damaged or degraded even when subjected to external force, a solid electrolyte exhibiting high ionic conductivity and good bendability at both room temperature and below is required.

[0008] This disclosure was made in view of the above circumstances, and one of its objectives is to provide a solid electrolyte that exhibits high ionic conductivity and good flexibility at room temperature and below. Another objective is to provide an energy storage device incorporating this solid electrolyte.

[0009] Technical solutions for solving technical problems To solve the aforementioned technical problems, the inventors conducted in-depth research and discovered that the following solid electrolyte exhibits high ionic conductivity at room temperature and below, while also possessing good flexibility: This solid electrolyte contains molecular crystals and specific polymers, wherein the molecular crystals comprise specific organic molecules and alkali metal salts as building blocks in the crystal lattice, and the solid electrolyte exhibits characteristic spectra in X-ray diffraction. According to this disclosure, the following solid electrolyte and energy storage device are provided.

[0010] [1] A solid electrolyte comprising a molecular crystal and a fluoropolymer, said molecular crystal comprising an organic molecule having at least one atom selected from sulfur, oxygen, nitrogen and phosphorus, and an alkali metal salt, said solid electrolyte having a diffraction pattern derived from said molecular crystal in X-ray diffraction.

[0011] [2] According to the solid electrolyte of [1], wherein when the total amount of the molecular crystal and the fluoropolymer is set to 100, the mass ratio of the molecular crystal to the fluoropolymer (molecular crystal / fluoropolymer) is 99 / 1 to 50 / 50.

[0012] [3] A solid electrolyte according to [1] or [2], wherein the fluoropolymer contains carbon atoms in the main framework and has fluorine atoms bonded to the carbon atoms.

[0013] [4] A solid electrolyte according to any one of [1] to [3], wherein the organic molecule is selected from at least one of nitrile compounds and sulfone compounds.

[0014] [5] A solid electrolyte according to any one of [1] to [4], wherein the counter anion constituting the alkali metal salt is (FSO2)2N. - (CF3SO2)2N - (FSO2)(CF3SO2)N - PF6 - Or BF4 - .

[0015] [6] A solid electrolyte according to any one of [1] to [5], wherein the solid electrolyte further contains an inorganic filler.

[0016] [7] The solid electrolyte according to [6], wherein the inorganic filler comprises an inorganic oxide.

[0017] [8] An energy storage device having a solid electrolyte of any one of [1] to [7].

[0018] Invention Effects According to this disclosure, a solid electrolyte exhibiting high ionic conductivity and good flexibility at room temperature and below can be obtained. Furthermore, by using the solid electrolyte of this disclosure as the electrolyte for energy storage devices such as secondary batteries and capacitors, energy storage devices that balance the safety guarantees and ionic conductivity resulting from solidification of the electrolyte can be obtained. Attached Figure Description

[0019] Figure 1 This is a diagram showing the X-ray diffraction patterns of the solid electrolytes of Examples 1 and 2 and Comparative Examples 2 and 5, as well as the PVDF-HFP monomer.

[0020] Figure 2 This is a simplified diagram of the molding die used in the preparation of sample particles. Detailed Implementation

[0021] The solid electrolyte and energy storage device disclosed herein will now be described in detail. It should be noted that "(meth)acrylic acid" in this specification refers to acrylic acid and / or methacrylic acid.

[0022] Solid Electrolytes The solid electrolyte disclosed herein contains the following components (X) and (Y).

[0023] Component (X): A molecular crystal containing an organic molecule having at least one atom selected from sulfur, oxygen, nitrogen, and phosphorus, and an alkali metal salt. Composition (Y): Fluoropolymer The solid electrolyte of this disclosure exhibits a diffraction pattern in X-ray diffraction originating from the molecular crystals (i.e., component (X)) contained within the solid electrolyte. This indicates that the solid electrolyte of this disclosure maintains the crystal structure of the molecular crystals while containing a fluoropolymer. Here, the molecular crystals, as component (X), are crystalline organic compounds in which the building blocks of the crystal lattice are regularly arranged, i.e., organic molecules and alkali metal salts. It should be noted that molecular crystals are known to form crystals when the organic molecules and alkali metal salts have a specific molecular weight ratio. The molecular crystals (X) possess ion conduction pathways through the regular arrangement of their building blocks, thereby exhibiting excellent ion conductivity. Therefore, the appearance of diffraction patterns originating from the molecular crystals in the X-ray diffraction measurements of the solid electrolyte of this disclosure suggests the existence of ion conduction pathways originating from the molecular crystals in the solid electrolyte of this disclosure, which contains both molecular crystals and fluoropolymers. Thus, the solid electrolyte of this disclosure is considered to exhibit high ion conductivity.

[0024] It should be noted that diffraction patterns in X-ray diffraction can be obtained using X-ray diffraction measurements with CuKα rays as the source. Regarding whether a solid electrolyte possesses diffraction patterns originating from molecular crystals contained within it, as determined by X-ray diffraction measurements of the solid electrolyte, this can be determined by comparing the diffraction patterns obtained from X-ray diffraction measurements of the solid electrolyte with those obtained from X-ray diffraction measurements of molecular crystal monomers. When comparing diffraction patterns, given the tendency in X-ray diffraction measurements that a larger diffraction angle (2θ) corresponds to lower reliability, the determination can be based on the presence or absence of diffraction patterns within a relatively small diffraction angle range. For example, if a diffraction pattern appears at the same position as the diffraction pattern with the smallest diffraction angle observed in X-ray diffraction measurements of molecular crystal monomers in the solid electrolyte, it can be determined that the solid electrolyte possesses diffraction patterns originating from molecular crystals contained within it.

[0025] Next, the molecular crystals and fluoropolymers contained in the solid electrolyte of this disclosure will be described in detail.

[0026] <Component (X): Molecular Crystal> The solid electrolyte disclosed herein contains a molecular crystal (hereinafter also referred to as "molecular crystal (X)"), in which the constituent units of the crystal include an organic molecule (hereinafter also referred to as "organic molecule (M)") having at least one type of atom selected from sulfur, oxygen, nitrogen, and phosphorus atoms, and an alkali metal salt. It is believed that the molecular crystal (X) possesses ion conduction pathways through the regular arrangement of its constituent units, and that Li... + It exhibits excellent ionic conductivity due to hopping conduction.

[0027] The ratio of organic molecules (M) to alkali metal salt in the molecular crystal (X) is not particularly limited. Regarding the ratio of organic molecules (M) to alkali metal salt in the molecular crystal, the amount of organic molecules (M) can be 0.1 to 10 moles relative to 1 mole of alkali metal salt. From the viewpoint of improving ionic conductivity, the ratio of organic molecules (M) to alkali metal salt in the molecular crystal is preferably 0.2 to 5 moles relative to 1 mole of alkali metal salt, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles.

[0028] (Organic molecule (M)) The number of at least one atom selected from sulfur, oxygen, nitrogen, and phosphorus atoms in the organic molecule (M) is not particularly limited. Preferably, there are 1 to 8 atoms selected from sulfur, oxygen, nitrogen, and phosphorus atoms per molecule of the organic molecule (M), more preferably 2 to 6. Among these, the organic molecule (M) preferably has a total of 2 or more atoms selected from sulfur, oxygen, and nitrogen atoms per molecule, more preferably 2 to 6.

[0029] The molecular weight of the organic molecule (M) is, for example, 300 or less, preferably 250 or less, and more preferably 200 or less. Regarding the lower limit of the molecular weight of the organic molecule (M), it 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 the organic molecule (M) and the alkali metal salt, the total number of carbon atoms per molecule of the organic molecule (M) is preferably 16 or less, more preferably 10 or less, further preferably 8 or less, and even more preferably 6 or less.

[0030] Specific examples of organic molecules (M) that have sulfur atoms include sulfone compounds, thioether compounds, thiols, thioesters, thiocarbonates, sulfoxides, and sulfonamides.

[0031] Examples of organic molecules containing nitrogen atoms include nitrile compounds, amine compounds, and amide compounds.

[0032] Examples of organic molecules containing phosphorus atoms include phosphine compounds, phosphine oxide compounds, and phosphine imine compounds.

[0033] As organic molecules containing oxygen atoms, examples of organic molecules containing oxygen atoms include those containing sulfur atoms, those containing nitrogen atoms, and those containing phosphorus atoms, as well as ether compounds, ester compounds, ketone compounds, and carbonate compounds.

[0034] From the viewpoint of further improving the ionic conductivity of the molecular crystal (X), the organic molecule (M) is preferably selected from at least one of organic molecules having sulfur and oxygen atoms, organic molecules having nitrogen atoms, and organic molecules having phosphorus atoms.

[0035] Organic molecules containing sulfur and oxygen atoms Sulfones are preferred as organic molecules having sulfur and oxygen atoms. A preferred example of a sulfone is the molecule shown in formula (1) below.

[0036] [Chemistry 1] (In equation (1), R) 1 and R 2 Each is independently alkyl or alkoxy, or represents R. 1 With R 2 The ring structure formed by bonding, wherein the total number of carbon atoms in formula (1) is 2 to 16).

[0037] The molecule shown in formula (1) above (hereinafter also referred to as "molecule (M-1)") is a chain or cyclic molecule having a sulfonyl group (-SO2-). In formula (1) above, R... 1 and R 2 In the case of alkyl or alkoxy groups, the alkyl and alkoxy groups can be straight-chain or branched. Additionally, the number of carbon atoms in each alkyl and alkoxy group (i.e., R...) 1 and R 2 The number of carbon atoms in each group (as long as it is R) 1 and R 2 The total number of carbon atoms is 2 to 16, without any particular limitation. From the viewpoint of crystallizing mixtures of organic molecules (M) and alkali metal salts, R... 1 and R 2 The number of carbon atoms in each is preferably 1 to 3, more preferably 1 or 2.

[0038] In the above equation (1), R 1 and R 2 R represents1 With R 2 In the case of a bonded ring structure, the ring structure can have a saturated ring skeleton or unsaturated bonds in the ring skeleton. R 1 With R 2 The number of carbon atoms in the bonded ring structure is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5. Additionally, in R... 1 With R 2 Alkyl groups (such as methyl and ethyl groups) can be bonded to the ring backbone of the bonded ring structure.

[0039] From the perspective of improving the ionic conductivity of the molecular crystal (X), R in the above equation (1) 1 and R 2 Preferred representation of R 1 With R 2 The bonded ring structure is more preferably a ring structure with a saturated ring skeleton.

[0040] The total number of carbon atoms in the above formula (1) is 2 to 16. From the viewpoint of promoting the crystallization of the mixture of molecule (M-1) and alkali metal salt, the total number of carbon atoms in the above formula (1) is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 5.

[0041] As a specific example of molecule (M-1), R in the above equation (1) 1 and R 2 Examples of compounds that are alkyl or alkoxy groups include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, and diethyl sulfate. As R in the above formula (1)... 1 and R 2 R represents 1 With R 2 Examples of cyclic structures formed by bonding include tetrahydrothiophene-1,1-dioxide, 3-methylcyclobutane sulfone, 3-cyclobutene sulfone, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3,2-dioxazolthiophene-2,2-dioxide. As a molecule (M-1), one type can be used alone, or two or more types can be used in combination.

[0042] Organic molecules containing nitrogen atoms Nitrile compounds are preferred as organic molecules having nitrogen atoms. A preferred example of a nitrile compound is the molecule shown in formula (2) below.

[0043] [Chemistry 2] (In equation (2), R) 3 R represents a hydrocarbon chain. 4 and R5 Each of the following groups independently represents a hydrogen atom, an alkyl group, or a cyano group, wherein the total number of carbon atoms in formula (2) is 16 or less.

[0044] The molecule shown in formula (2) above (hereinafter also referred to as "molecule (M-2)") is a molecule having two or more cyano groups (-CN). R in formula (2) above... 3 It can be a saturated hydrocarbon chain or it can contain unsaturated bonds. From the perspective of obtaining molecular crystals with superior ionic conductivity, R... 3 Preferably, it represents a saturated hydrocarbon chain. R 3 The number of carbon atoms is, for example, 1 to 10, preferably 1 to 6, and more preferably 2 to 4.

[0045] In R 4 Or R 5 When the alkyl group is alkyl, it can be either linear or branched. Linearity is preferred. From the viewpoint of crystallizing an organic molecule (M) by mixing it with an alkali metal salt, R... 4 and R 5 The number of carbon atoms in each group is preferably 0 to 3, more preferably 0 or 1.

[0046] The total number of carbon atoms in the above formula (2) should be 16 or less. From the viewpoint of promoting the crystallization of the mixture of molecule (M-2) and alkali metal salt, the total number of carbon atoms in the above formula (2) is preferably 8 or less, and more preferably 6 or less.

[0047] Specific examples of molecules (M-2) include succinic anionyl nitrile, adiponitrile, 3-hexenedionitrile, 1,3,5-pentanetricarbonyl nitrile, tert-butylmalonium nitrile, and 1,2,2,3-propanetetracarbonyl nitrile. A single molecule (M-2) can be used, or two or more can be used in combination.

[0048] Organic molecules containing phosphorus atoms Examples of organic molecules containing phosphorus atoms include 1,2-bis(dimethylphosphine)ethane, 1,2-bis(diphenylphosphine)ethane, methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphine imine, and triphenylphosphine imine.

[0049] From the viewpoint of ease of manufacturing molecular crystals, the organic molecule (M) is preferably selected from at least one of nitrile compounds and sulfone compounds. Furthermore, considering the superior ionic conductivity of the molecular crystal, it is more preferable to select at least one of molecules (M-1) and (M-2), and even more preferably to select R from the above formula (1). 1 With R 2 This represents a molecule with a bonded ring structure and R in the above formula (2). 3It represents at least one of the molecules with saturated hydrocarbon chains. It should be noted that as an organic molecule (M), one type can be used alone or in combination of two or more types.

[0050] (alkali metal salts) Alkali metal salts are any salts that produce alkali metal ions; there are no particular limitations. Examples of alkali metal salts include lithium salts, sodium salts, and potassium salts. Furthermore, the anions constituting alkali metal salts can be either monatomic or polyatomic ions, or either inorganic or organic ions.

[0051] Specific examples of alkali metal salts include Li₂CO₃, LiBr, LiCl, LiI, LiSCN, LiBF₄, LiAsF₆, LiClO₄, CH₃COOLi, CF₃COOLi, LiCF₃SO₃, LiPF₆, LiC(CF₃SO₂)₃, and lithium bis(fluorosulfonyl)imide (Li + (FSO2)2N - ), Lithium bis(trifluoromethanesulfonyl)imide (Li + (CF3SO2)2N - Lithium salts such as (fluorosulfonyl) (trifluoromethanesulfonyl)imide lithium; and salts of these lithium salts with anions of alkali metals other than lithium (e.g., sodium, potassium, etc.). Considering high ionic dissociation and the ability to further improve the ionic conductivity of the molecular crystal (X), lithium salts or sodium salts are preferred, and lithium salts are more preferred.

[0052] Furthermore, considering the higher dissociation of ions, the counter anion constituting the alkali metal salt is preferably (FSO2)2N. - (CF3SO2)2N - (FSO2)(CF3SO2)N - PF6 - Or BF4 - .

[0053] From the perspective of further improving the ionic conductivity of the molecular crystal (X), the alkali metal salt constituting the molecular crystal (X) preferably includes an imide-based alkali metal salt. From the perspective of high ionic dissociation, the imide-based alkali metal salt is preferably an imide-based lithium salt, and 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. Regarding the lower limit of the molecular weight of the alkali metal salt, it is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. One type of alkali metal salt can be used alone, or two or more types can be used in combination.

[0055] The melting point of alkali metal salts at atmospheric pressure 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 alkali metal salts; for example, it can be below 300°C or below 250°C.

[0056] It should be noted that the molecular crystal (X) may further comprise constituent units different from those of the organic molecule (M) and the alkali metal salt, without impairing the effects of this disclosure. However, considering the ionic conductivity and ease of manufacture of the molecular crystal (X), it is preferable that the molecular crystal (X) is composed of an organic molecule (M) and an alkali metal salt.

[0057] In the solid electrolyte of this disclosure, from the viewpoint of exhibiting good ionic conductivity, the content of molecular crystals (X) relative to the total amount of solid electrolyte is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 75% by mass or more. Regarding the upper limit of the content of molecular crystals (X), from the viewpoint of ensuring flexibility, it is preferably 99% by mass or less relative to the total amount of solid electrolyte, more preferably 95% by mass or less.

[0058] (Methods for manufacturing molecular crystals) Molecular crystals (X) can be manufactured using organic molecules (M) and alkali metal salts as raw materials. The method for manufacturing molecular crystals (X) is not particularly limited. Molecular crystals (X) can be manufactured, for example, by methods including: a process of mixing organic molecules (M) with alkali metal salts while applying mechanical energy (hereinafter also referred to as a "mechanical mixing process") (hereinafter also referred to as a "first manufacturing method"); a method including a process of dissolving organic molecules (M) and alkali metal salts in a solvent (hereinafter also referred to as a "dissolution process"), and a process of removing the solvent from the solution formed by dissolving organic molecules (M) and alkali metal salts in the solvent (hereinafter also referred to as a "solvent removal process") (hereinafter also referred to as a "second manufacturing method").

[0059] ○First Manufacturing Method Mechanical mixing process In a mechanical mixing process, organic molecules (M) and alkali metal salts are mixed simultaneously by applying mechanical energy to the substance through means such as impact, shearing, compression, and friction (hereinafter also referred to as "mechanical mixing"). This preferably induces changes in the physicochemical properties of the organic molecules (M), the alkali metal salt, or both.

[0060] The ratio of organic molecule (M) to alkali metal salt can be set according to the types of organic molecule (M) and alkali metal salt, and is not particularly limited. For example, the ratio of organic molecule (M) to alkali metal salt can be set to 0.1 to 10 moles relative to 1 mole of alkali metal salt. From the viewpoint of obtaining molecular crystals exhibiting excellent ionic conductivity, the ratio of organic molecule (M) to alkali metal salt is preferably set to 0.2 to 5 moles relative to 1 mole of alkali metal salt, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles.

[0061] There are no particular limitations on the method for mixing organic molecules (M) with alkali metal salts while applying mechanical energy. In the mechanical mixing process, the mixing of organic molecules (M) with alkali metal salts can be performed using various equipment such as ball mills, bead mills, mixers, homogenizers, pulverizers, homogenizing mixers, and disperser-type mixers. Furthermore, in the case of small-scale manufacturing of molecular crystals, the mechanical mixing of organic molecules (M) with alkali metal salts can also be performed using a mortar and pestle. The mechanical mixing of organic molecules (M) with alkali metal salts can be performed dry or wet. Moreover, the mechanical mixing of organic molecules (M) with alkali metal salts can be performed at room temperature or at low temperature. For example, when the melting point of the organic molecule (M) is below room temperature, the liquid organic molecule can be mechanically mixed with the alkali metal salt. Alternatively, the solid organic molecule can be mechanically mixed with the alkali metal salt at a temperature below the melting point of the organic molecule (M).

[0062] It should be noted that the mechanical mixing of organic molecules (M) and alkali metal salts can be carried out while heating is present. However, in order to suppress the volatilization and sublimation of organic molecules (M), the heating in the mechanical mixing process can be carried out at a temperature lower than the heating temperature in any subsequent heating process. Specifically, the mechanical mixing of organic molecules (M) and alkali metal salts is carried out, for example, at a temperature below 50°C. The temperature at which organic molecules (M) and alkali metal salts are mechanically mixed is preferably below 40°C, more preferably below 35°C. The time for mechanical mixing depends on the amount and type of organic molecules (M) and alkali metal salts used, and may be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0063] In the case of manufacturing molecular crystals using the first manufacturing method, the first manufacturing method preferably further includes a step of heating the mixture obtained by the mechanical mixing step (i.e., a mixture of organic molecules (M) and alkali metal salts) (hereinafter also referred to as the "heating step"). This heating step enables the organic molecules (M) and alkali metal salts in the mixture to become more homogeneous, further improving the ionic conductivity of the molecular crystal (X). In particular, it can be considered that by combining the mechanical mixing step with the heating step, intermolecular interactions are generated between the alkali metal ions derived from the alkali metal salt and the organic molecules (M) through mechanical mixing, thereby suppressing the volatilization and sublimation of the organic molecules (M) during heat treatment. This provides the advantage of easily obtaining molecular crystals with the desired composition.

[0064] Heating process In the heating process, there are no particular limitations on the temperature and method of heating the mixture. The heating temperature of the mixture can be appropriately set according to the type of organic molecules (M) and alkali metal salt used in the raw materials. From the viewpoint of making the organic molecules (M) and alkali metal salt in the mixture more homogeneous, in the heating process of the first manufacturing method, it is preferable to heat the mixture at a temperature above the melting point of the mixture of organic molecules (M) and alkali metal salt obtained by mechanical mixing. By setting the heating temperature above the melting point of the mixture, the mixture melts, thereby promoting the homogeneous mixing of organic molecules (M) and alkali metal salt.

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

[0066] When heating the mixture, it is preferable to further homogenize the organic molecules (M) and the alkali metal salt by heating while stirring the mixture. The stirring method is not particularly limited; examples include magnetic stirrers, stirring rods, mixers with stirring blades, and external circulation mixers. Alternatively, mechanical operations that can generate greater shear forces, such as homogenizers, disperser mixers, and homogenizers, can also be used for stirring.

[0067] After heating a mixture containing an organic molecule (M) and an alkali metal salt, the heated mixture crystallizes by lowering its temperature, yielding the target molecular crystal. When lowering the temperature of the heated mixture, it can be cooled slowly (e.g., slowly lowering the temperature at room temperature over 1 to 48 hours). Alternatively, the heated mixture can be rapidly cooled (e.g., briefly placing the heated mixture in a thermostat at a temperature lower than room temperature (e.g., below 15°C)). From the viewpoint of ensuring proper crystallization of the heated mixture, it is preferable to lower the temperature slowly. The fact that the product obtained by this manufacturing method is a molecular crystal containing an organic molecule (M) and an alkali metal salt can be detected by performing powder X-ray diffraction analysis of the product.

[0068] ○Second manufacturing method Dissolving process When the boiling point of the organic molecule (M) is high (e.g., above 100°C), a second manufacturing method can be applied as a method for manufacturing the molecular crystal (X). An organic solvent is preferably used as the solvent for dissolving the organic molecule (M) and the alkali metal salt. This organic solvent is preferably one that can dissolve both the organic molecule (M) and the alkali metal salt, has a moderately low boiling point (e.g., below 100°C), and a low dielectric constant. Examples of such organic solvents include dimethyl carbonate, tetrahydrofuran, and ethyl acetate. When dissolving the organic molecule (M) and the alkali metal salt in the solvent, it is preferable to carry out the process while stirring, thereby achieving homogenization of the organic molecule (M) and the alkali metal salt. The stirring method is not particularly limited; for example, the stirring method exemplified in the first manufacturing method can be appropriately used.

[0069] Solvent removal process Regarding methods for removing solvent from solutions containing organic molecules (M) and alkali metal salts dissolved in a solvent, there are no particular limitations as long as the solvent can be removed from the solution. From the perspective of simple and efficient solvent removal, heat treatment is preferred. The heat treatment can be carried out at atmospheric pressure, or under pressure or reduced pressure. When a solvent with a high boiling point is used in the dissolution process, heat treatment under reduced pressure is preferred to suppress the decomposition of the organic molecules (M) and alkali metal salts.

[0070] It should be noted that the method for manufacturing molecular crystal (X) is not limited to the methods described above. For example, in the first manufacturing method described above, molecular crystal (X) can also be manufactured by heating and mixing organic molecules (M) and alkali metal salts without mechanical mixing.

[0071] <Composition (Y): Fluoropolymer> Fluoropolymers are not particularly limited to any polymer that contains structural units having fluorine atoms. As fluoropolymers, polymers containing carbon atoms in the main backbone and having fluorine atoms bonded to those carbon atoms are preferred. Specifically, fluoropolymers preferably contain structural units with fluorine atoms as shown in formula (3).

[0072] -[CR 6 R 7 -CFR 8 ]- (3) (In equation (3), R) 6 R 7 and R 8 Each of these atoms is independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or a perfluoroalkoxy group having 1 to 3 carbon atoms. Specific examples of the structural unit shown in formula (3) above include -[CH2-CHF]-, -[CH2-CF2]-, -[CHF-CF2]-, -[CF2-CF2]-, -[CF2-CFCF3]-, -[CHF-CFCF3]-, -[CF2-CF(OCF3)]-, -[CF2-CF(OC2F5)]-, and -[CF2-CFCl]-. Among these, the structural unit shown in formula (3) above is preferably -[CH2-CHF]-, -[CH2-CF2]-, -[CHF-CF2]-, -[CF2-CF2]-, -[CF2-CFCF3]-, and -[CHF-CFCF3]-. It should be noted that the fluoropolymer may have only one structural unit shown in formula (3) above, or it may have two or more structural units.

[0073] In fluoropolymers, the proportion of structural units having fluorine atoms is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to all structural units constituting the fluoropolymer. The fluoropolymer may have only one type of structural unit having fluorine atoms, or it may have two or more types.

[0074] Fluoropolymers may consist solely of structural units having fluorine atoms, or may further include structural units without fluorine atoms (hereinafter also referred to as "other structural units"). Specific examples of monomers constituting other structural units include: olefins such as ethylene, propylene, n-butene, and isobutene; carboxyl-containing monomers such as (meth)acrylic acid, vinylacetic acid, and pentenoic acid; hydroxyl-containing monomers such as (meth)acrylic acid-2-hydroxyethyl ester, vinyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl allyl ether, and 4-hydroxybutyl allyl ether; and N-vinyl-2-pyrrolidone, N-vinyl-2-piperidinone, and N-vinyl- γ -Amide-containing monomers such as valproamide; ester-containing monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, vinyl acetate, isopropylene acetate, vinyl butyrate, isovinyl butyrate, vinyl tert-carbonate, and vinyl benzoate. Fluoropolymers may possess only one or more other structural units.

[0075] From the viewpoint of maintaining the ion conduction pathway originating from the molecular crystal, thereby obtaining a solid electrolyte exhibiting good ion conductivity, non-crosslinked polymers are preferred as fluoropolymers. Therefore, when a fluoropolymer contains other structural units, those other structural units preferably do not have crosslinking groups.

[0076] Specific examples of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene / hexafluoropropylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene / trifluoroethylene copolymer, ethylene / chlorotrifluoroethylene copolymer, vinylidene fluoride / hexafluoropropane / (meth)acrylic acid copolymer, and vinylidene fluoride / pentafluoropropylene copolymer.

[0077] In addition, fluororubber can also be used as a fluoropolymer. Specific examples of fluororubber include vinylidene fluoride-based rubber, tetrafluoroethylene / propylene-based rubber, tetrafluoroethylene / propylene / vinylidene fluoride-based rubber, and ethylene / hexafluoropropylene-based rubber. When manufacturing solid electrolytes, only one type of fluoropolymer can be used, or two or more types can be used.

[0078] In the above, the fluoropolymer is preferably selected from at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, polyvinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer and polyvinylidene fluoride / tetrafluoroethylene copolymer, more preferably selected from at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and polypentafluoropropylene, polyvinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP).

[0079] The weight-average molecular weight (Mw) of the fluoropolymer is preferably 3,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and still more preferably 15,000 or more. Furthermore, the upper limit of the Mw of the fluoropolymer is preferably 500,000 or less, more preferably 300,000 or less. It should be noted that the Mw of the fluoropolymer is a polystyrene conversion value determined by gel permeation chromatography (GPC).

[0080] In the solid electrolyte of this disclosure, from the viewpoint of exhibiting good flexibility, the content of the fluoropolymer is preferably 1% by mass or more, more preferably 5% by mass or more, relative to the total amount of the solid electrolyte. Regarding the upper limit of the fluoropolymer content, from the viewpoint of exhibiting good ionic conductivity, it is preferably 60% by mass or less, more preferably 50% by mass or less, further preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to the total amount of the solid electrolyte.

[0081] In the solid electrolyte of this disclosure, the mass ratio of molecular crystal (X) to fluoropolymer, expressed as "molecular crystal / fluoropolymer," is preferably 99 / 1 to 40 / 60. When the mass ratio of molecular crystal (X) to fluoropolymer is within the above range, a solid electrolyte with a well-improved balance between ionic conductivity and tortuosity can be obtained. From the viewpoint of balancing the ionic conductivity and tortuosity of the solid electrolyte, the mass ratio of molecular crystal (X) to fluoropolymer is more preferably 99 / 1 to 50 / 50, further preferably 99 / 1 to 60 / 40, even more preferably 99 / 1 to 70 / 30, and even more preferably 95 / 5 to 70 / 30. It should be noted that the above mass ratio, expressed as "molecular crystal / fluoropolymer," is the ratio of each component when the total amount of molecular crystal (X) and fluoropolymer is set to 100.

[0082] <Other Ingredients> The solid electrolyte disclosed herein may further contain components different from the aforementioned molecular crystal (X) and fluoropolymer (hereinafter also referred to as "other components"). Examples of other components include, for example, inorganic fillers, inorganic electrolytes (e.g., ceramic electrolytes, glass electrolytes, etc.), binders, conductive additives, positive electrode active materials, negative electrode active materials, etc.

[0083] Inorganic fillers are used to improve the strength and ionic conductivity of solid electrolytes. Examples of inorganic fillers include oxides, nitrides, and carbides. Specific examples of oxides include zinc oxide, silicon suboxide, silicon dioxide, aluminum oxide, magnesium oxide, titanium oxide, and iron oxide.

[0084] Examples of nitrides include silicon nitride, boron nitride, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, and magnesium nitride.

[0085] Examples of carbides include silicon carbide, boron carbide, aluminum carbide, titanium carbide, and tungsten carbide. It should be noted that the solid electrolyte disclosed herein may contain only one type of inorganic filler, or it may contain two or more types.

[0086] In the case where the solid electrolyte of this disclosure contains inorganic fillers, from the viewpoint of obtaining a solid electrolyte exhibiting good ion conductivity, the solid electrolyte preferably contains oxides (i.e., inorganic oxides) as inorganic fillers, and particularly preferably contains silicon dioxide.

[0087] When the solid electrolyte of this disclosure contains inorganic fillers, the content of inorganic fillers in the solid electrolyte is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, relative to the total amount of solid electrolyte.

[0088] Furthermore, when the solid electrolyte of this disclosure contains molecular crystals (X) and fluoropolymers, and includes inorganic fillers as an optional component, the mass ratio of the content of molecular crystals (X) to the total content of fluoropolymers and inorganic fillers, expressed as "molecular crystals / fluoropolymers and inorganic fillers," is preferably 99 / 1 to 40 / 60. From the viewpoint of improving the ionic conductivity of the solid electrolyte, the mass ratio of the content of molecular crystals (X) to the total content of fluoropolymers and inorganic fillers is more preferably 99 / 1 to 50 / 50, further preferably 99 / 1 to 60 / 40, and even more preferably 99 / 1 to 70 / 30. It should be noted that the above-mentioned mass ratio expressed as "molecular crystals / fluoropolymers and inorganic fillers" is the ratio of the content of molecular crystals (X) to the total amount of fluoropolymers and inorganic fillers when the total amount of molecular crystals (X) and fluoropolymers and inorganic fillers is set to 100.

[0089] <Methods for Manufacturing Solid Electrolytes> The solid electrolyte of this disclosure can be manufactured by mixing a molecular crystal (X) with a fluoropolymer. That is, as one method of manufacturing the solid electrolyte of this disclosure, a method including a step of mixing the molecular crystal (X) with the fluoropolymer (hereinafter also referred to as the "mixing step") can be described.

[0090] • Mixing process In the mixing process during the manufacture of solid electrolytes, any method is acceptable as long as it ensures uniform mixing of the molecular crystal (X) and the fluoropolymer. The mixing of the molecular crystal (X) and the fluoropolymer can be either dry or wet. Dry mixing is preferred for ease of operation, while wet mixing is preferred for more uniform mixing of the molecular crystal (X) and the fluoropolymer.

[0091] When mixing the molecular crystal (X) and the fluoropolymer in a dry manner, it is preferable to homogenize them by mechanically mixing the molecular crystal (X) and the fluoropolymer. As a specific method of mechanical mixing, the same method illustrated in the description of the first manufacturing method of the molecular crystal (X) can be cited.

[0092] When mixing the molecular crystal (X) and the fluoropolymer using a wet process, it is preferable to dissolve the molecular crystal (X) and the fluoropolymer in a solvent and mix them in the mixing step, and then remove the solvent from the solution formed by dissolving the molecular crystal (X) and the fluoropolymer in the solvent. It should be noted that the step of removing the solvent from the solution formed by dissolving the molecular crystal (X) and the fluoropolymer in the solvent will also be referred to below as the "solvent removal step".

[0093] Organic solvents are preferably used as solvents to dissolve the molecular crystal (X) and the fluoropolymer. The organic solvent is not particularly limited as long as it can dissolve both the molecular crystal (X) and the fluoropolymer. Examples of organic solvents include N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl carbonate, tetrahydrofuran, ethyl acetate, acetone, and methyl ethyl ketone. When dissolving the molecular crystal (X) and the fluoropolymer in the solvent, it is preferable to achieve homogenization of the molecular crystal (X) and the fluoropolymer by stirring. The stirring method is not particularly limited; for example, the stirring method exemplified in the first manufacturing method can be used appropriately.

[0094] Solvent removal process Regarding the method for removing the solvent from the solution formed by dissolving the molecular crystal (X) and the fluoropolymer in a solvent, there are no particular limitations as long as the solvent can be removed from the solution. As a method for solvent removal, heat treatment is preferred for its simplicity and efficiency. The heat treatment can be carried out at atmospheric pressure, under pressure, or under reduced pressure. Alternatively, two or more heat treatments can be combined. When a solvent with a high boiling point (e.g., a polar solvent such as N,N-dimethylacetamide) is used in the dissolution process, heat treatment under reduced pressure is preferred to suppress the decomposition of the molecular crystal (X).

[0095] Regarding the mixing ratio of the molecular crystal (X) and the fluoropolymer, it is set such that a diffraction pattern originating from the molecular crystal (X) appears during X-ray diffraction measurements of the solid electrolyte. From the viewpoint of achieving a good balance in improving ionic conductivity and flexibility, the mass ratio of the molecular crystal (X) to the fluoropolymer, expressed as "molecular crystal / fluoropolymer," is preferably set to 99 / 1 to 40 / 60. Considering the improvement of the ionic conductivity of the solid electrolyte, the mixing ratio of the molecular crystal (X) to the fluoropolymer, expressed as a mass ratio, is more preferably 99 / 1 to 50 / 50, further preferably 99 / 1 to 60 / 40, even more preferably 99 / 1 to 70 / 30, and still more preferably 95 / 5 to 70 / 30. It should be noted that the above-mentioned mixing ratio, expressed as "molecular crystal / fluoropolymer," is the ratio of each component when the total amount of the molecular crystal (X) and the fluoropolymer is set to 100.

[0096] The solid electrolyte disclosed herein is typically used in the form of a molded article containing molecular crystals (X) and a fluoropolymer, formed into a desired shape. The molding method is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, casting, die casting, and tape casting can be employed. Among these methods, from the perspective of minimizing the porosity of the resulting solid electrolyte and facilitating the formation of ion conduction pathways, pressure molding, die casting, or tape casting is preferred. The shape of the molded article is not particularly limited and can be appropriately set according to the shape of the energy storage device to which it is applied. The shape of the molded article may be, for example, rectangular or circular.

[0097] It should be noted that when the final solid electrolyte is a molded body, this molded body can be directly used as the solid electrolyte layer of a storage device. Alternatively, multiple molded bodies can be stacked to form the solid electrolyte layer of a storage device. When the solid electrolyte of this disclosure is obtained as a molded body, the thickness of the molded body is, for example, 5 to 5000 mm. μ m, preferably 5 to 3500 μ m, more preferably 10 to 3000 μ m.

[0098] The solid electrolyte obtained as described above exhibits high ionic conductivity not only at room temperature (25°C) but also at temperatures below room temperature (e.g., below -20°C). Therefore, by using the solid electrolyte of this disclosure as the electrolyte material for energy storage devices, energy storage devices with high ionic conductivity can be obtained. Specifically, for a thickness of 130... μ Approximately m (specifically, 130±10 m) μ For a solid electrolyte (m), the preferred ionic conductivity, measured by AC impedance spectroscopy at 25°C, is 1.0 × 10⁻⁶. -6 S / cm or higher. From the viewpoint of obtaining a high-performance energy storage device, an ionic conductivity of 5.0 × 10⁻⁶ is more preferable under the same conditions. -6 S / cm or higher, more preferably 1.0×10 -5 S / cm or higher.

[0099] Additionally, for a thickness of 130 μ Approximately m (specifically, 130±10 m) μ The ionic conductivity of the solid electrolyte (m) measured by AC impedance spectroscopy at -20°C is preferably 1.0 × 10⁻⁶. -8 S / cm or higher, more preferably 5.0 × 10 -8 S / cm or higher, more preferably 1.0×10 -7 S / cm or higher. It should be noted that the details of the method for determining ionic conductivity are as described in the examples below.

[0100] Energy Storage Equipment The energy storage device disclosed herein (hereinafter also referred to as "the device") incorporates the solid electrolyte of the present disclosure. Specific embodiments of the device include secondary batteries and capacitors. In the case of the device being a secondary battery, one embodiment is an all-solid-state battery; from the perspective of excellent ion conductivity, a lithium-ion secondary battery is preferred.

[0101] An all-solid-state lithium-ion secondary battery, which is one embodiment of this device, will be described. A lithium-ion secondary battery is a laminate comprising electrodes including a positive electrode and a negative electrode, and a solid electrolyte, wherein the solid electrolyte is disposed between the positive and negative electrodes in such a way that the solid electrolyte is in contact with the electrodes. The materials constituting the positive and negative electrodes are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium-ion secondary batteries. For example, as the positive electrode current collector, metal foils such as aluminum or stainless steel can be used. As the negative electrode current collector, metal foils such as copper foil or lithium foil can be used.

[0102] In the lithium-ion secondary battery disclosed herein, the solid electrolyte is formed using a molecular crystalline electrolyte comprising an organic molecule (M) and an alkali metal salt, along with a fluoropolymer. The thickness of the solid electrolyte is not particularly limited and can be appropriately set according to the application of the secondary battery. For example, the thickness of the solid electrolyte is 5 mm. μ m~500 μ m.

[0103] There are no particular limitations on the method for manufacturing lithium-ion secondary batteries, and known methods can be appropriately adopted depending on the battery structure. For example, a molded body formed using a molecular crystalline electrolyte and a fluoropolymer can be annealed, and the resulting solid electrolyte can be sandwiched between a positive electrode and a negative electrode to manufacture a laminate having a positive electrode, a solid electrolyte, and a negative electrode. Alternatively, an electrolyte material containing a molecular crystalline electrolyte and a fluoropolymer can be housed in a container by sandwiching positive and negative electrodes, and the container can be annealed to manufacture a laminate having a positive electrode, a solid electrolyte, and a negative electrode. The laminate having a positive electrode, a solid electrolyte, and a negative electrode is usually housed in a casing and used as a secondary battery.

[0104] It should be noted that this device is not limited to the above-described configuration where the charge carriers for ion conduction are lithium ions. For example, it could also be a secondary battery using other ions such as sodium ions as charge carriers. Furthermore, this device could also be a capacitor. One example of a capacitor configuration is as follows: it comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte, with the solid electrolyte disposed between the positive and negative electrode layers in a manner that connects the solid electrolyte to each electrode layer.

[0105] Energy storage devices incorporating this solid electrolyte can be used for a wide variety of applications. Specifically, they can be used as power sources 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, camcorders, music players, power tools, and home appliances.

[0106] Example The present disclosure will now be described in detail based on the embodiments. It should be noted that the present disclosure is not limited to these embodiments. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0107] Fabrication and Structural Confirmation of Molecular Crystal Electrolytes [Manufacturing Example 1] 1. Manufacturing of molecular crystals In a dry chamber where the dew point was maintained below -40°C, 0.2156 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt and 0.1846 g of succinate (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule were weighed at a molar ratio of 1:2. The mixture was mechanically mixed in a mortar at room temperature (25°C) for 5 minutes to obtain a mixture (mechanical mixing process). The melting point of the mixture was determined using a differential scanning calorimeter (TA Instruments, DSC250, measurement atmosphere: nitrogen atmosphere) at a heating rate of 10°C per minute. A large endothermic peak (melting point) was observed at 60°C. It should be noted that the succinate before mixing exhibited plasticity, but the mixture did not.

[0108] Transfer the mixture to a tubular flask and stir with a magnetic stirrer set to 70°C for 1 hour until homogeneous dissolution is achieved (heating step). Then, cool the resulting melt to room temperature to obtain a white solid.

[0109] 2. Confirmation of crystallinity using powder X-ray diffraction. The obtained white solid was subjected to powder X-ray diffraction analysis using an X-ray diffraction apparatus (Bruker AXS, D8 ADVANCE). It should be noted that 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 set to 2θ = 5–60°, the scan rate to 2.3° / min, and the step angle to 0.02°. The observation of a large X-ray diffraction pattern within the measurement range indicates that the sample (white solid) is crystalline.

[0110] Powder X-ray diffraction was performed on the white solid obtained above, and a large diffraction pattern was observed within the measured angle range. This confirmed that the obtained white solid is crystalline, i.e., a molecular crystal (referred to as "Li(FSI)(SN)2"). It should be noted that, for the composition of the molecular crystal of Manufacturing Example 1, the bis(fluorosulfonyl)imide anion is abbreviated as FSI, and the succinate is abbreviated as SN.

[0111] 3. Identification of the crystalline phase using differential scanning calorimetry (DSC) The obtained white solid was measured using a differential scanning calorimeter (TA Instruments, DSC 250, measurement atmosphere: nitrogen atmosphere) at a heating rate of 10°C per minute within the range of -80°C to 100°C. According to Timmermans' rule of thumb, the melting entropy should be less than 20 JK. -1 mol -1In this case, it can be said that the substance has a flexible crystalline phase and is a plastic crystal.

[0112] DSC measurements revealed an endothermic peak (melting point) around 60℃ (visually confirmed as the melting point). The fusion entropy was calculated to be 110.97 JK. -1 mol -1 Therefore, it is confirmed that Li(FSI)(SN)2 does not have a flexible crystalline phase and is not a plastic crystal.

[0113] [Manufacturing Example 2] The types and amounts of raw materials, as well as the heating temperature in the heating process, were changed as described in Table 1. Otherwise, the same operation as in Manufacturing Example 1 was performed to obtain molecular crystals (Li(FSI)(SL)). It should be noted that for the composition of the molecular crystals in Manufacturing Example 2, the bis(fluorosulfonyl)imide anion is abbreviated as FSI, and the tetrahydrothiophene 1,1-dioxide is abbreviated as SL.

[0114] The obtained molecular crystal was subjected to DSC analysis in the same manner as in Manufacturing Example 1, confirming that Li(FSI)(SL) does not have a viscous crystalline phase and is not a plastic crystal.

[0115] [Manufacturing Example 3] In a drying chamber maintained at a dew point below -40°C, 0.4307 g of lithium hexafluorophosphate (manufactured by Fujifilm and Kohsen Pure Chemical Industries Co., Ltd.) as an alkali metal salt and 0.6129 g of adiponitrile (manufactured by Fujifilm and Kohsen Pure Chemical Industries Co., Ltd.) as an organic molecule were measured in a molar ratio of 1:2 and transferred to a tubular flask. 8 g of dimethyl carbonate (manufactured by Fujifilm and Kohsen Pure Chemical Industries Co., Ltd.) was added, and the mixture was stirred for 1 hour using a magnetic stirrer set at 25°C until homogeneous dissolution was confirmed. The resulting solution was poured onto a PTFE (polytetrafluoroethylene) petri dish. To remove the solvent, the solution was dried on a hot plate at 60°C for 5 hours, followed by vacuum drying at 60°C for at least 12 hours. A white solid was thus obtained.

[0116] Powder X-ray diffraction was performed on the white solid obtained above. The results showed sharp peaks within the measured angle range and a diffraction pattern different from that of the raw material. This confirmed that the obtained white solid is a crystalline molecular crystal composed of an alkali metal salt and organic molecules (referred to as "Li(PF6)(AdN)2"). It should be noted that adiponitrile is abbreviated as AdN for the composition of the molecular crystal of Manufacturing Example 3. Furthermore, using the molecular crystal (Li(PF6)(AdN)2) of Manufacturing Example 3, the heat treatment temperature was set to 165°C, and the ionic conductivity at 25°C was measured. The measurement results are shown in Table 1.

[0117] [Table 1] Manufacturing and Evaluation of Solid Electrolytes [Example 1] Li(FSI)(SN)2 (manufactured in Example 1 above), a molecular crystal, and KF polymer W#8500 (manufactured by KUREHA Co., Ltd., poly(vinylidene fluoride-co-hexafluoropropylene)) were weighed into a tubular bottle at a mass ratio of 70:30. 2.0 g of acetone (super-dehydrated, manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.) was added as a solvent to obtain a mixture. The mixture was then stirred for 2 hours using a magnetic stirrer at a set temperature of 60°C to obtain a homogeneous solution (mixing step).

[0118] The obtained solution was poured onto polyethylene release paper. To remove the solvent, it was dried on a hot plate at 60°C for 5 hours, and then vacuum dried in a vacuum dryer at 60°C for more than 12 hours (solvent removal process). This yielded a soft solid electrolyte.

[0119] (Evaluation of the presence or absence of structural features of molecular crystals using X-ray diffraction) The obtained solid electrolyte was subjected to X-ray diffraction (XRD) measurements using an X-ray diffraction apparatus (Bruker AXS, D8 ADVANCE). It should be noted that 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 set to 2θ = 5–60°, the scan rate to 2.3° / min, and the step angle to 0.02°. If diffraction patterns originating from molecular crystals, which are the building blocks of the solid electrolyte, are observed within the measurement range, the sample (solid electrolyte) can be said to possess the structural characteristics of a molecular crystal. Here, the presence or absence of a peak near 2θ = 10° is used to determine whether the sample possesses the structural characteristics of a molecular crystal; if a peak is observed near 2θ = 10°, the sample is considered to possess the structural characteristics of a molecular crystal.

[0120] XRD measurements were performed on the solid electrolyte of Example 1, and the results showed that diffraction patterns originating from Li(FSI)(SN)2 were observed within the measurement range, including an angle approximately 2θ = 10° (refer to...). Figure 1 Based on this result, it was confirmed that the solid electrolyte of Example 1 has the structural characteristics of a molecular crystal.

[0121] (Determination of ionic conductivity) Sample particles for ionic conductivity determination were prepared in a drying chamber with a dew point maintained below -40°C. The solid electrolyte was punched using a punching machine and hammer to obtain particles with a diameter of 10 mm and a thickness of 131 mm. μ The sample particles were spherical in shape. Next, the sample particles were encapsulated into an all-solid-state battery evaluation cell (manufactured by Hosen Co., Ltd., KP-SolidCell).

[0122] Ionic conductivity was measured using an all-solid-state battery evaluation unit containing sample particles. In the ionic conductivity measurement, the all-solid-state battery evaluation unit containing sample particles was first heat-treated in a constant-temperature bath at 40°C (corresponding to the heat treatment temperature in Table 2), while the resistance value was measured by AC impedance spectroscopy. The resistance value decreased with heat treatment time, and the heat treatment was stopped when it reached a stable point. Next, the resistance values ​​at 25°C and -20°C were measured by AC impedance spectroscopy. The ionic conductivity (σ) was calculated using the obtained resistance values ​​by the following mathematical formula (1). It should be noted that the AC impedance spectroscopy used to calculate the ionic conductivity was performed after the unit was held at the measurement temperature in a constant-temperature bath for 2 hours.

[0123] σ=L / (R×S) (1) (In mathematical formula (1), σ represents ionic conductivity (unit: S / cm), R represents resistance (unit: Ω), and S represents the cross-sectional area of ​​the composite electrolyte during measurement (unit: cm²). 2 L represents the distance between electrodes (unit: cm). The solid electrolyte of Example 1 exhibited ionic conductivity of 1.1 × 10⁻⁶ at 25°C and -20°C, respectively. -7 S / cm, 3.5×10 -10 S / cm.

[0124] (Evaluation of flexibility) Sample particles for evaluating the tortuosity of the solid electrolyte were prepared in a drying chamber with a dew point maintained below -40°C. The solid electrolyte was punched using a punching machine and hammer to obtain particles with a diameter of 10 mm and a thickness of 131 mm. μ A circular sample particle of size m was used. The sample particle was wound around a polyethylene rod with a diameter of 20 mm, and the bending of the sample particle was observed. The bendability was evaluated according to the following criteria. The result showed that the solid electrolyte of Example 1 exhibited no visual abnormalities even when the sample particle was bent, and was therefore judged as "○". Thus, it was confirmed that the solid electrolyte of Example 1 possesses bendability.

[0125] ○: No abnormal appearance was found in the sample particles.

[0126] △: Fine cracks were confirmed in the sample particles.

[0127] ×: Clear cracks were observed in the sample particles, or a portion of the sample particles peeled off.

[0128] [Examples 2 and 3] The types and amounts of raw materials were changed as described in Table 2, and the same operation as in Example 1 was performed to obtain a solid electrolyte.

[0129] Using the solid electrolytes of each embodiment, the procedures were performed in the same manner as in Example 1. The presence or absence of structural features of the molecular crystals was evaluated using XRD, and ionic conductivity and bendability were measured at 25°C and -20°C. The results are shown in Table 2. It should be noted that, for Example 2, the X-ray diffraction patterns obtained by XRD are also shown in Table 2. Figure 1 .in addition, Figure 1 The X-ray diffraction pattern of the PVDF-HFP monomer is also shown in the image.

[0130] [Example 4] Li(PF6)(AdN)2 (manufactured in Example 3 above), a molecular crystal, and KF polymer W#8500 (manufactured by KUREHA Co., Ltd., poly(vinylidene fluoride-co-hexafluoropropylene)) were weighed into a tubular bottle at a mass ratio of 70:30. 1.1667 g of Li(PF6)(AdN)2 and 0.5000 g of KF polymer W#8500 were added to the bottle. 3.8877 g of N,N-dimethylacetamide (super-dehydrating, manufactured by Fujifilm and Koujun Pharmaceutical Co., Ltd.) was added as a solvent to obtain a mixture. The mixture was then mixed using a rotary mixer (THINKY Co., Ltd.) to obtain a homogeneous solution (mixing step). The mixing method was as follows: mixing at 2000 rpm for 7 minutes in MIX mode, followed by mixing at 2200 rpm for 30 seconds in DEFORM mode.

[0131] The obtained solution was cast onto a biaxially stretched polypropylene film using a Baker-type coater. To remove the solvent, it was dried on a hot plate at 80°C for 5 hours, followed by vacuum drying in a vacuum dryer at 60°C for at least 12 hours (solvent removal process). This yielded a soft, solid electrolyte formed on the biaxially stretched polypropylene.

[0132] Using the obtained solid electrolyte, the same procedures as in Example 1 were performed. The presence or absence of structural features of the molecular crystals was evaluated by XRD determination, and ionic conductivity and bendability were measured at 25°C and -20°C. The results are shown in Table 2.

[0133] [Example 5] Li(FSI)(SN)2 (manufacturing example 1 above), which is a molecular crystal, and silica (manufactured by AEROSIL Co., Ltd. of Japan, AEROSIL 300), which is an inorganic filler, were weighed in a mass ratio of 4:1. 0.4064 g of Li(FSI)(SN)2 and 0.1016 g of silica were mechanically mixed in a mortar and pestle at room temperature for 20 minutes to obtain a mixture.

[0134] Next, 0.0270 g of PTFE (manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd., Teflon (registered trademark) 6-J) as a polymer was added to the above mixture in a mass ratio of PTFE = 95:5. The mixture was mechanically mixed in a mortar and pestle at room temperature for 20 minutes to obtain a white solid as a solid electrolyte.

[0135] The obtained white solid was processed in the same manner as in Example 1, with XRD used to evaluate the presence or absence of structural features of the molecular crystal, and ionic conductivity and bendability were measured at 25°C and -20°C. The results are shown in Table 2.

[0136] [Example 6] Li(FSI)(SN)2 (manufacturing example 1 above), which is a molecular crystal, and PTFE (manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd., Teflon 6-J), which is a polymer, were weighed in a mass ratio of 99:1. The mixtures were mechanically mixed in a mortar for 20 minutes at room temperature to obtain a white solid as a solid electrolyte.

[0137] The obtained white solid was processed in the same manner as in Example 1, with XRD used to evaluate the presence or absence of structural features of the molecular crystal, and ionic conductivity and bendability were measured at 25°C and -20°C. The results are shown in Table 2.

[0138] [Comparative Example 1] In a dry chamber where the dew point is maintained below -40°C, 0.4119 g of poly(ethylene oxide) (manufactured by Thermo Scientific) as the polymer was measured into a tubular flask, and 2.0 g of acetonitrile (super-dehydrated) (manufactured by Fujifilm and Kojun Chemical Co., Ltd.) was added. The tubular flask was stirred for 60 hours using a mixing rotor to dissolve the poly(ethylene oxide).

[0139] With Li +0.0879 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.), an alkali metal salt, was measured in a molar ratio of 1:20 to the ethylene oxide units in poly(ethylene oxide) and added to a tubular flask. The mixture was stirred at room temperature for 1 hour using a magnetic stirrer to obtain a homogeneous solution of lithium bis(fluorosulfonyl)imide. The mixture was poured onto a Teflon petri dish, heated on a hot plate at 90°C for 5 hours, and then vacuum-dried at 90°C for 24 hours to obtain a soft solid electrolyte.

[0140] The obtained solid electrolyte was processed in the same manner as in Example 1, with XRD used to evaluate the presence or absence of structural features of the molecular crystals, and ionic conductivity and bendability were measured at 25°C and -20°C. The results are shown in Table 2.

[0141] [Comparative Example 2] A die 10 comprising module 11, upper punch 12, and lower punch 13 is used (see reference). Figure 2 Sample particles were prepared using Li(FSI)(SN)2 (Manufacturing Example 1 above) as the raw material. First, a module 11 containing 0.0600 g of solid Li(FSI)(SN)2 was placed on the lower punch 13, and an upper punch 12 was placed on the module. The raw material was compressed for 1 minute using a hydraulic press at a pressure of 10 MPa to obtain a sample with a diameter of 10 mm and a thickness of 498 mm. μ m-shaped spherical sample particles.

[0142] The obtained sample particles were subjected to XRD measurements in the same manner as in Example 1 to confirm the presence or absence of structural features of the molecular crystal. As a result, within the measurement range, diffraction patterns originating from Li(FSI)(SN)₂ were observed (refer to...). Figure 1 ).

[0143] In addition, for Li(FSI)(SN)2, the ionic conductivity at 25°C and -20°C and the bending performance evaluation tests were performed in the same manner as in Example 1. The results are shown in Table 2.

[0144] [Comparative Example 3] Li(FSI)(SL) (Preparation Example 2 above) was used instead of Li(FSI)(SN)2 as the raw material. Otherwise, the sample particles were prepared in the same manner as in Comparative Example 2, and XRD measurements were performed in the same manner as in Example 1 to confirm the presence or absence of structural features of the molecular crystal. The results are shown in Table 2.

[0145] In addition, for Li(FSI)(SL), the ionic conductivity at 25°C and -20°C and the bending performance evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.

[0146] [Comparative Example 4] Li(PF6)(AdN)2 (manufacturing example 3 above) was used instead of Li(FSI)(SN)2 as the raw material. Otherwise, sample particles were prepared in the same manner as in Comparative Example 2, and XRD measurements were performed in the same manner as in Example 1 to confirm the presence or absence of structural features of the molecular crystal. The results are shown in Table 2.

[0147] In addition, for Li(PF6)(AdN)2, the ionic conductivity at 25°C and -20°C and the bending performance evaluation tests were performed in the same manner as in Example 1. The results are shown in Table 2.

[0148] [Comparative Example 5] The types and amounts of raw materials were changed as described in Table 2, and the same procedures as in Example 1 were performed to obtain a solid electrolyte. Using the obtained solid electrolyte, XRD measurements were performed in the same manner as in Example 1 to confirm the presence or absence of molecular crystal structural features. However, in the solid electrolyte of Comparative Example 5, no diffraction pattern originating from Li(FSI)(SN)2 was observed within the measurement range (see reference). Figure 1 ).

[0149] In addition, for the solid electrolyte of Comparative Example 5, the ionic conductivity at 25°C and -20°C and the bendability evaluation test were performed in the same manner as in Example 1. The results are shown in Table 2.

[0150] [Table 2] Details of the compounds in Tables 1 and 2 are shown below.

[0151] • LiFSI: Lithium bis(fluorosulfonyl)imide [Manufactured by Kanto Chemical Co., Ltd.] • LiPF6: Lithium hexafluorophosphate (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) •SN: Butadionitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) •SL: Tetrahydrothiophene-1,1-dioxide [Manufactured by Tokyo Chemical Industry Co., Ltd.] ·PVDF-HFP[1]: Poly(vinylidene fluoride-co-hexafluoropropylene), KF polymer W#8500 [manufactured by KUREHA Corporation] ·PVDF-HFP[2]: Poly(vinylidene fluoride-co-hexafluoropropylene) [manufactured by Sigma-Aldrich Corporation] • PTFE: Teflon 6-J [Manufactured by Chemours-Mitsui Fluoroproducts Co., Ltd.] • PEO: Poly(ethylene oxide) [manufactured by Thermo Scientific] • Silica: AEROSIL 300 [Manufactured by AEROSIL Corporation, Japan] • DMC: Dimethyl carbonate (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) DMAc: N,N-Dimethylacetamide (superhydration) [Manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.] • AcN: Acetonitrile (super-dehydrated) [Manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.] <<Evaluation Results>> The results from Examples 1-6 show that the solid electrolytes containing molecular crystals and fluoropolymers exhibit high ionic conductivity at both room temperature (25°C) and low temperature (-20°C). In the solid electrolytes of Examples 1-6, diffraction patterns originating from the molecular crystals were observed by X-ray diffraction, indicating that the solid electrolytes of Examples 1-6 maintain the crystal structure of the molecular crystals and possess ion conduction pathways, thus exhibiting high ionic conductivity. Furthermore, the solid electrolytes of Examples 1-6 exhibit good flexibility.

[0152] In contrast, the solid electrolyte of Comparative Example 1, which used poly(ethylene oxide) that interacts with lithium ions as a polymer component, and the solid electrolyte of Comparative Example 5, for which no diffraction pattern from the molecular crystal was observed by X-ray diffraction, exhibited good flexibility, but their ionic conductivity was worse than that of Examples 1-8 at both room temperature (25°C) and low temperature (-20°C). It should be noted that the results for Comparative Example 5 suggest that the crystal structure of the molecular crystal in the solid electrolyte of Comparative Example 4 collapsed, disrupting the ion conduction pathway, thus resulting in low ionic conductivity. Furthermore, the solid electrolytes of Comparative Examples 2, 3, and 4, which consisted solely of molecular crystals, exhibited poor flexibility.

[0153] The above results show that the solid electrolyte, which contains molecular crystals (X) and fluoropolymers and exhibits a diffraction pattern derived from the molecular crystals in X-ray diffraction, displays high ionic conductivity and high flexibility at both room and low temperatures. By using the solid electrolyte of this disclosure, which possesses these properties, as the electrolyte material for energy storage devices, processing during device manufacturing becomes easier, and it can also follow the bending force applied to the energy storage device. Therefore, by using the solid electrolyte of this disclosure, even when external forces are applied to the energy storage device, it is less prone to breakage and performance degradation, resulting in a highly safe energy storage device.

[0154] This invention is not limited to the embodiments described above, and includes various modifications and variations within the same scope without departing from the spirit of the invention. Therefore, it should be understood that, in accordance with the above teachings, various combinations, forms, and other combinations and forms including only one element, its superordinate concept, or its subordinate concept also fall within the scope and spirit of this invention.

[0155] Explanation of reference numerals in the attached figures 10… Press mold.

Claims

1. A solid electrolyte, characterized in that, It contains molecular crystals and fluoropolymers, wherein the molecular crystals comprise organic molecules having at least one type of atom selected from sulfur, oxygen, nitrogen, and phosphorus, and alkali metal salts. The solid electrolyte exhibits a diffraction pattern derived from the molecular crystal in X-ray diffraction.

2. The solid electrolyte according to claim 1, wherein, When the total amount of the molecular crystal and the fluoropolymer is set to 100, the mass ratio of the molecular crystal to the fluoropolymer, i.e., molecular crystal / fluoropolymer, is 99 / 1 to 50 / 50.

3. The solid electrolyte according to claim 1, wherein, The fluoropolymer contains carbon atoms in its main backbone and has fluorine atoms bonded to the carbon atoms.

4. The solid electrolyte according to claim 1, wherein, The organic molecule is selected from at least one of nitrile compounds and sulfone compounds.

5. The solid electrolyte according to claim 1, wherein, The counter anion constituting the alkali metal salt is (FSO2)2N. - (CF3SO2)2N - (FSO2)(CF3SO2)N - PF6 - Or BF4 - .

6. The solid electrolyte according to claim 1, wherein, The solid electrolyte further contains inorganic fillers.

7. The solid electrolyte according to claim 6, wherein, The inorganic filler contains inorganic oxides.

8. An energy storage device, characterized in that, The solid electrolyte comprising any one of claims 1 to 7.

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