Solid electrolyte and power storage device

Abstract

This solid electrolyte contains: a molecular crystal that contains an alkali metal salt and an organic molecule which has at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms; and a fluorine-containing polymer. The solid electrolyte has a diffraction spectrum derived from the molecular crystal in X-ray diffraction.

Description

Solid electrolytes and energy storage devices

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to Japanese Patent Application No. 2023-202027, filed on November 29, 2023, the entire contents of which are incorporated herein by reference. The present disclosure relates to solid electrolytes and electricity storage devices.

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

[0003] Lithium-ion secondary batteries, which are widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte, and are charged and discharged by transferring lithium ions between the electrodes via the electrolyte. Organic electrolyte solutions have traditionally been used primarily as electrolytes. In recent years, solid or gel electrolytes using inorganic or organic materials have been proposed as a way to eliminate concerns about electrolyte leakage and short circuits within batteries due to overcharge and overdischarge.

[0004] While organic solid electrolytes have the advantage of excellent adhesion to electrodes due to the moderate flexibility and high formability of organic materials, they tend to have lower ionic conductivity than, for example, inorganic solid electrolytes. Therefore, in order to improve their practicality, various studies have been conducted on the development of new materials for constituting organic solid electrolytes (see, for example, Patent Document 1 and Non-Patent Document 1).

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

[0006] Special Publication No. 2014-504788

[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 bendability due to its regular crystalline structure, insufficient ionic conductivity at room temperature, and even at temperatures lower than room temperature, the ionic conductivity significantly decreases. From the perspective of obtaining a high-performance electricity storage device that is resistant to damage and performance degradation even when an external force is applied to the device, a solid electrolyte that exhibits high ionic conductivity at room temperature and temperatures lower than room temperature while also having good bendability is required.

[0009] The present disclosure has been made in view of the above circumstances, and has as one object to provide a solid electrolyte that exhibits high ionic conductivity at room temperature and temperatures lower than room temperature while also having good flexibility, and another object to provide an electricity storage device including the solid electrolyte.

[0010] The present inventors have conducted extensive research to solve the above problems and have found that a solid electrolyte containing a molecular crystal, which contains a specific organic molecule and an alkali metal salt as structural units in a crystal lattice, and a specific polymer, and which has a characteristic spectrum in X-ray diffraction, exhibits high ionic conductivity at room temperature and temperatures lower than room temperature, while also having good flexibility.The present disclosure provides the following solid electrolyte and electricity storage device.

[0011] [1] A solid electrolyte comprising a molecular crystal containing an alkali metal salt and an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom, and a fluoropolymer, and having a diffraction spectrum derived from the molecular crystal in X-ray diffraction. [2] The solid electrolyte of [1], wherein the mass ratio of the molecular crystal to the fluoropolymer (molecular crystal / fluoropolymer) is 99 / 1 to 50 / 50, where the total amount of the molecular crystal and the fluoropolymer is taken as 100. [3] The solid electrolyte of [1] or [2], wherein the fluoropolymer contains a carbon atom in its main skeleton and has a fluorine atom bonded to the carbon atom. [4] The solid electrolyte of any of [1] to [3], wherein the organic molecule is at least one selected from the group consisting of nitrile compounds and sulfone compounds. [5] The solid electrolyte of any of [1] to [3], wherein the counter anion constituting the alkali metal salt is (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) (CF ３ SO ２ ) N － , P.F. ６ － or BF ４ － [6] The solid electrolyte of any one of [1] to [4], further comprising an inorganic filler. [7] The solid electrolyte of [6], wherein the inorganic filler comprises an inorganic oxide. [8] An electricity storage device comprising the solid electrolyte of any one of [1] to [7].

[0012] According to the present disclosure, a solid electrolyte having good flexibility while exhibiting high ionic conductivity at room temperature and temperatures lower than room temperature can be obtained. Furthermore, by using the solid electrolyte of the present disclosure as the electrolyte for an electricity storage device such as a secondary battery or a capacitor, it is possible to obtain an electricity storage device that combines ionic conductivity with the safety ensured by the solidification of the electrolyte.

[0013] Fig. 1 shows X-ray diffraction spectra of the solid electrolytes of Examples 1 and 2 and Comparative Examples 2 and 5, and of PVDF-HFP alone. Fig. 2 is a schematic diagram of the press die used to prepare the sample pellets.

[0014] The solid electrolyte and the electricity storage device of the present disclosure will be described in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0015] <<Solid Electrolyte>> The solid electrolyte of the present disclosure contains the following component (X) and component (Y): Component (X): a molecular crystal containing an organic molecule having at least one atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom, and an alkali metal salt; and Component (Y): a fluorine-containing polymer.

[0016] The solid electrolyte of the present disclosure has, in X-ray diffraction, a diffraction spectrum derived from the molecular crystals (i.e., component (X)) contained in the solid electrolyte. This indicates that the solid electrolyte of the present disclosure maintains the crystalline structure of the molecular crystals while containing a fluoropolymer. Here, the molecular crystal, which is component (X), is a crystalline organic material in which organic molecules and alkali metal salts, which are structural units in a crystal lattice, are regularly arranged. It is known that molecular crystals are formed when the organic molecules and alkali metal salts have a specific molecular weight ratio. The molecular crystal (X) has ion conduction paths due to the regular arrangement of structural units, and thus exhibits excellent ion conductivity. Therefore, the appearance of a diffraction spectrum derived from the molecular crystals in X-ray diffraction measurement of the solid electrolyte of the present disclosure suggests the presence of ion conduction paths derived from the molecular crystals in the solid electrolyte of the present disclosure, which contains the molecular crystals and the fluoropolymer. This suggests that the solid electrolyte of the present disclosure exhibits high ion conductivity.

[0017] The diffraction spectrum in X-ray diffraction can be obtained by X-ray diffraction measurement using CuKα radiation as a radiation source. Whether or not the diffraction spectrum obtained by X-ray diffraction measurement of a solid electrolyte has a diffraction spectrum derived from molecular crystals contained in the solid electrolyte can be determined by comparing the diffraction spectrum obtained by X-ray diffraction measurement of the solid electrolyte with the diffraction spectrum obtained by X-ray diffraction measurement of the molecular crystal alone. When comparing diffraction spectra, it is advisable to determine based on the presence or absence of a diffraction spectrum in a relatively small diffraction angle range, in view of the fact that the reliability of X-ray diffraction measurement tends to decrease as the diffraction angle (2θ) increases. For example, if a diffraction spectrum appears in the diffraction spectrum obtained by X-ray diffraction measurement of a solid electrolyte at a position equivalent to the diffraction spectrum with the smallest diffraction angle among the diffraction spectra appearing in X-ray diffraction measurement of the molecular crystal alone, it can be determined that the solid electrolyte has a diffraction spectrum derived from molecular crystals contained in the solid electrolyte.

[0018] Next, the molecular crystals and fluorine-containing polymer contained in the solid electrolyte of the present disclosure will be described in detail.

[0019] <Component (X): Molecular Crystal> The molecular crystal (hereinafter also referred to as "molecular crystal (X)") contained in the solid electrolyte of the present disclosure includes, as a structural unit of the crystal, an organic molecule (hereinafter also referred to as "organic molecule (M)") 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. The molecular crystal (X) has ion conduction paths due to the regular arrangement of the structural units, and Li ions are transported through the ion conduction paths. ＋ It is believed that hopping conduction provides excellent ionic conductivity.

[0020] The ratio of the organic molecule (M) to the alkali metal salt contained in the molecular crystal (X) is not particularly limited. The ratio of the organic molecule (M) to the alkali metal salt in the molecular crystal may be 0.1 to 10 moles of the organic molecule (M) per mole of the alkali metal salt. From the viewpoint of increasing ionic conductivity, the ratio of the organic molecule (M) to the alkali metal salt in the molecular crystal is preferably 0.2 to 5 moles, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles, of the organic molecule (M) per mole of the alkali metal salt.

[0021] (Organic Molecule (M)) The number of at least one atom selected from the group consisting of sulfur atoms, oxygen atoms, nitrogen atoms, and phosphorus atoms contained in the organic molecule (M) is not particularly limited. In the organic molecule (M), 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, and more preferably 2 to 6, per molecule. Of these, the organic molecule (M) preferably contains a total of two or more, and more preferably two to six, of at least one atom selected from sulfur atoms, oxygen atoms, and nitrogen atoms per molecule.

[0022] The molecular weight of the organic molecule (M) is, for example, 300 or less, preferably 250 or less, and more preferably 200 or less. The lower limit of the molecular weight of the organic molecule (M) is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. From the viewpoint of promoting crystallization of the mixture of the organic molecule (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, even more preferably 8 or less, and even more preferably 6 or less.

[0023] Specific examples of the organic molecule (M) include organic molecules having a sulfur atom, such as sulfone compounds, sulfide compounds, thiol compounds, thioester compounds, thiocarbonate compounds, sulfoxide compounds, and sulfamide compounds. Examples of organic molecules having a nitrogen atom include nitrile compounds, amine compounds, and amide compounds. Examples of organic molecules having a phosphorus atom include phosphine compounds, phosphine oxide compounds, and phosphinimine compounds. Examples of organic molecules having an oxygen atom include organic molecules having an oxygen atom among the examples of organic molecules having a sulfur atom, organic molecules having an oxygen atom among the examples of organic molecules having a nitrogen atom, and organic molecules having an oxygen atom among the examples of organic molecules having a phosphorus atom, as well as ether compounds, ester compounds, ketone compounds, and carbonate compounds.

[0024] In terms of being able to further increase the ionic conductivity of the molecular crystal (X), the organic molecule (M) 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.

[0025] Organic molecules having sulfur atoms and oxygen atoms As the organic molecules having sulfur atoms and oxygen atoms, sulfones can be preferably used. Preferred examples of sulfones include those represented by 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 R２ and represents a cyclic structure formed by bonding together, and the total number of carbon atoms in formula (1) is 2 to 16.

[0026] The molecule represented by the above formula (1) (hereinafter also referred to as "molecule (M-1)") has a sulfonyl group (-SO ２ -) in the above formula (1). １ and R ２ When R is an alkyl group or an alkoxy group, the alkyl group and the alkoxy group may be linear or branched. １ and R ２ The number of carbon atoms in each group of R １ and R ２ There are no particular limitations on the number of carbon atoms in R as long as the total number of carbon atoms in R is 2 to 16. From the viewpoint of inducing crystallization in the mixture of the organic molecule (M) and the alkali metal salt, １ and R ２ Each of the groups preferably has 1 to 3 carbon atoms, more preferably 1 or 2.

[0027] R in the above formula (1) １ and R ２ But, R １ and R ２ When R represents a cyclic structure formed by bonding R and R, the cyclic structure may have a saturated ring skeleton or an unsaturated bond in the ring skeleton. １ and R ２ The number of carbon atoms in the cyclic structure formed by bonding R is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5. １ and R ２ The ring skeleton of the cyclic structure formed by bonding the above may have an alkyl group (for example, a methyl group or an ethyl group) bonded thereto.

[0028] The R in the above formula (1) is preferable in that it can make the ionic conductivity of the molecular crystal (X) more excellent. １ and R ２ is R １ and R ２and more preferably, the cyclic structure has a saturated ring skeleton.

[0029] The total number of carbon atoms in the above formula (1) is 2 to 16. From the viewpoint of promoting crystallization of the mixture of the molecule (M-1) and the 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.

[0030] Specific examples of the molecule (M-1) include R １ and R ２ are each an alkyl group or an alkoxy group, examples of which include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, and diethyl sulfate. １ and R ２ But, R １ and R ２ Examples of the ring structure formed by bonding include tetrahydrothiophene 1,1-dioxide, 3-methylsulfolane, 3-sulfolene, 1,3-propane sultone, 1,4-butane sultone, 1,3,2-dioxathiolane 2,2-dioxide, etc. As the molecule (M-1), one type may be used alone, or two or more types may be used in combination.

[0031] Nitrogen-containing organic molecules Nitrogen-containing organic molecules include nitrile compounds. Preferred examples of nitrile compounds include those represented by the following formula (2): (In formula (2), R ３ represents a hydrocarbon chain, R ４ and R ５ each independently represents a hydrogen atom, an alkyl group, or a cyano group, and the total number of carbon atoms in formula (2) is 16 or less.

[0032] The molecule represented by the above formula (2) (hereinafter also referred to as "molecule (M-2)") is a molecule having two or more cyano groups (-CN). ３R may be a saturated hydrocarbon chain or may have an unsaturated bond. R is a suitable ionic conductive material for obtaining a molecular crystal having excellent ionic conductivity. ３ Preferably, R represents a saturated hydrocarbon chain. ３ has, for example, 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms.

[0033] R ４ or R ５ When R is an alkyl group, the alkyl group 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, more preferably 0 or 1, from the viewpoint of causing crystallization by mixing the organic molecule (M) with the alkali metal salt.

[0034] The total number of carbon atoms in the above formula (2) may be 16 or less. From the viewpoint of promoting crystallization of the mixture of molecule (M-2) and an alkali metal salt, the total number of carbon atoms in the above formula (2) is preferably 8 or less, more preferably 6 or less.

[0035] Specific examples of the molecule (M-2) include succinonitrile, adiponitrile, 3-hexenedinitrile, 1,3,5-pentanetricarbonitrile, tert-butylmalononitrile, 1,2,2,3-propanetetracarbonitrile, etc. As the molecule (M-2), one type may be used alone, or two or more types may be used in combination.

[0036] Organic Molecules Having a Phosphorus Atom Examples of organic molecules having a phosphorus atom include ethylenebis(dimethylphosphine), ethylenebis(diphenylphosphine), methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphine imine, and triphenylphosphine imine.

[0037] From the viewpoint of ease of production of the molecular crystal, the organic molecule (M) is preferably at least one selected from the group consisting of nitrile compounds and sulfone compounds. In addition, in terms of more excellent ionic conductivity of the molecular crystal, at least one selected from the group consisting of molecules (M-1) and molecules (M-2) is more preferable, and R １ and R ２ and a molecule representing a cyclic structure formed by bonding R ３ It is more preferable that the organic molecule (M) is at least one selected from the group consisting of molecules in which M represents a saturated hydrocarbon chain. As the organic molecule (M), one type may be used alone, or two or more types may be used in combination.

[0038] (Alkali Metal Salt) The alkali metal salt is not particularly limited as long as it generates an alkali metal ion. Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt. The anion constituting the alkali metal salt may be either a monoatomic ion or a polyatomic ion, and may be either an inorganic ion or an organic ion.

[0039] Specific examples of alkali metal salts include Li ２ CO ３ , LiBr, LiCl, LiI, LiSCN, LiBF ４ , LiAsF ６ , LiClO ４ , C.H. ３ COOLi, CF ３ COOLi, LiCF ３ SO ３ , LiPF ６ , LiC(CF ３ SO ２ ) ３ , lithium bis(fluorosulfonyl)imide (Li ＋ (FSO ２ ) ２ N － ), lithium bis(trifluoromethanesulfonyl)imide (Li ＋ (CF ３ SO ２ ) ２ N －and salts of the anions of these lithium salts with alkali metals other than lithium (for example, sodium, potassium, etc.). Among these, lithium salts or sodium salts are preferred, and lithium salts are more preferred, in that they have high ionic dissociation properties and can further increase the ionic conductivity of the molecular crystal (X).

[0040] In addition, the counter anion constituting the alkali metal salt is preferably (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) (CF ３ SO ２ ) N － , P.F. ６ － or BF ４ － is preferred.

[0041] In terms of being able to further increase the ionic conductivity of the molecular crystal (X), the alkali metal salt constituting the molecular crystal (X) preferably contains an imide-based alkali metal salt. In terms 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 is particularly preferred, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide is more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0042] 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. One type of alkali metal salt may be used alone, or two or more types may be used in combination.

[0043] The melting point of the alkali metal salt under 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 the alkali metal salt, but it may be, for example, 300° C. or lower, or 250° C. or lower.

[0044] The molecular crystal (X) may further contain a structural unit different from the organic molecule (M) and the alkali metal salt, provided that the effect of the present disclosure is not impaired. However, in consideration of the ionic conductivity and ease of production of the molecular crystal (X), the molecular crystal (X) is preferably a molecular crystal composed of the organic molecule (M) and the alkali metal salt.

[0045] In the solid electrolyte of the present disclosure, the content of the molecular crystal (X) 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, based on the total amount of the solid electrolyte, from the viewpoint of exhibiting good ionic conductivity. The upper limit of the content of the molecular crystal (X) is preferably 99% by mass or less, more preferably 95% by mass or less, based on the total amount of the solid electrolyte, from the viewpoint of ensuring flexibility.

[0046] (Method for Producing Molecular Crystal) The molecular crystal (X) can be produced using an organic molecule (M) and an alkali metal salt as raw materials. The method for producing the molecular crystal (X) is not particularly limited. The molecular crystal (X) can be produced, for example, by a method (hereinafter also referred to as a "first production method") including a step of mixing the organic molecule (M) and an alkali metal salt while applying mechanical energy (hereinafter also referred to as a "mechanical mixing step"); a method (hereinafter also referred to as a "second production method") including a step of dissolving the organic molecule (M) and the alkali metal salt in a solvent (hereinafter also referred to as a "dissolving step") and a step of removing the solvent from the solution in which the organic molecule (M) and the alkali metal salt are dissolved in the solvent (hereinafter also referred to as a "solvent removing step"); or the like.

[0047] First Production Method Mechanical Mixing Step In the mechanical mixing step, the organic molecules (M) and the alkali metal salt are mixed while applying mechanical energy to a substance containing the organic molecules (M) and the alkali metal salt by means of impact, shear, compression, friction, etc. (hereinafter also referred to as "mechanical mixing") This preferably causes changes in the physicochemical properties of the organic molecules (M), the alkali metal salt, or both.

[0048] The compounding ratio of the organic molecule (M) to the alkali metal salt is not particularly limited and may be set depending on the types of the organic molecule (M) and the alkali metal salt. The compounding ratio of the organic molecule (M) to the alkali metal salt may be, for example, 0.1 to 10 moles of the organic molecule (M) per mole of the alkali metal salt. The compounding ratio of the organic molecule (M) to the alkali metal salt is preferably 0.2 to 5 moles, more preferably 0.25 to 4 moles, and even more preferably 0.5 to 2 moles, of the organic molecule (M) per mole of the alkali metal salt, in order to obtain a molecular crystal exhibiting excellent ionic conductivity.

[0049] The method for mixing the organic molecule (M) and the alkali metal salt while applying mechanical energy is not particularly limited. In the mechanical mixing step, the organic molecule (M) and the alkali metal salt can be mixed using various devices, such as a ball mill, a bead mill, a blender, a homogenizer, a stamp mill, a homomixer, or a disperser-type mixer. Furthermore, when producing molecular crystals on a small scale, the organic molecule (M) and the alkali metal salt can also be mechanically mixed using a mortar and pestle. The mechanical mixing of the organic molecule (M) and the alkali metal salt can be performed in a dry or wet manner. Furthermore, the mechanical mixing of the organic molecule (M) and the alkali metal salt can be performed at room temperature or at a low temperature. For example, when the melting point of the organic molecule (M) is lower than room temperature, the organic molecule in a liquid state can be mechanically mixed with the alkali metal salt. Furthermore, the organic molecule in a solid state can be mechanically mixed with the alkali metal salt at a temperature lower than the melting point of the organic molecule (M).

[0050] The organic molecules (M) and the alkali metal salt may be mechanically mixed while being heated. However, in order to suppress volatilization or sublimation of the organic molecules (M), the heating in the mechanical mixing step is preferably carried out at a temperature lower than the heating temperature in the heating step optionally carried out after the mechanical mixing step. Specifically, in the mechanical mixing step, the organic molecules (M) and the alkali metal salt are mechanically mixed at, for example, 50°C or lower. The temperature when mechanically mixing the organic molecules (M) and the alkali metal salt is preferably 40°C or lower, more preferably 35°C or lower. The time for mechanical mixing varies depending on the amount and type of the organic molecules (M) and the alkali metal salt used, but may be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0051] When producing a molecular crystal by the first production method, the first production method preferably further includes a step of heating the mixture obtained by the mechanical mixing step (i.e., a mixture of organic molecules (M) and an alkali metal salt) (hereinafter also referred to as the "heating step"). This heating step can make the organic molecules (M) and the alkali metal salt in the mixture more uniform, thereby further increasing the ionic conductivity of the molecular crystal (X). In particular, a method that combines the mechanical mixing step and the heating step is thought to generate intermolecular interactions between the alkali metal ions derived from the alkali metal salt and the organic molecules (M) due to the mechanical mixing, thereby making it possible to suppress volatilization or sublimation of the organic molecules (M) during heat treatment. This has the advantage of making it easier to obtain a molecular crystal of the desired composition.

[0052] Heating Step In the heating step, the temperature and method for heating the mixture are not particularly limited. The heating temperature of the mixture may be set appropriately depending on the types of organic molecules (M) and alkali metal salt used as raw materials. From the viewpoint of making the organic molecules (M) and alkali metal salt in the mixture more uniform, it is preferable that in the heating step of the first production method, the mixture is heated at a temperature equal to or higher than the melting point of the mixture of organic molecules (M) and alkali metal salt obtained by mechanical mixing. Setting the heating temperature equal to or higher than the melting point of the mixture melts the mixture, thereby promoting uniform mixing of the organic molecules (M) and alkali metal salt.

[0053] The temperature at which the mixture is heated is preferably higher than the melting point of the mixture, from the viewpoint of homogenizing the organic molecules (M) and the alkali metal salt in the mixture by melting the mixture. Furthermore, from the viewpoint of promoting homogenization of the organic molecules (M) and the alkali metal salt in the mixture, the heating temperature of the mixture is more preferably 5°C or higher, and even more preferably 7°C or higher, than the melting point of the mixture (unit: °C). With regard to the upper limit of the heating temperature of the mixture, from the viewpoint of suppressing volatilization or sublimation of the components contained in the mixture, when the melting point of the mixture is expressed as Mp (unit: °C), it is preferably (Mp + 20)°C or lower, and more preferably (Mp + 15)°C or lower. The heating time is not particularly limited as long as it homogenizes the organic molecules (M) and the alkali metal salt in the mixture. The heating time is, for example, 1 minute to 3 hours, preferably 15 minutes to 2 hours, and more preferably 30 minutes to 2 hours. Furthermore, the heat treatment is usually carried out under normal pressure, but may also be carried out under pressure or reduced pressure.

[0054] When the mixture is heated, it is preferable to heat the mixture while stirring it, thereby further homogenizing the organic molecule (M) and the alkali metal salt. The stirring method is not particularly limited, and examples thereof include a magnetic stirrer, a stirring rod, a stirrer with stirring blades, and external circulation stirring. Stirring may also be performed using a mechanical operation that can generate a larger shear force, such as a homomixer, a disperser-type mixer, or a homogenizer.

[0055] After heating a mixture containing an organic molecule (M) and an alkali metal salt, the heated mixture can be crystallized by lowering the temperature of the heated mixture, thereby obtaining the desired molecular crystal. The temperature of the heated mixture can be lowered by gradually cooling the mixture (e.g., slowly lowering the temperature at room temperature over 1 to 48 hours). Alternatively, the heated mixture can be rapidly cooled (e.g., placing the heated mixture in a thermostatic bath at a temperature lower than room temperature (e.g., 15°C or lower) for a short period of time). From the viewpoint of favorable crystallization of the heated mixture, gradually lowering the temperature of the mixture is preferable. The fact that the product obtained by this production method is a molecular crystal containing an organic molecule (M) and an alkali metal salt can be detected by powder X-ray diffraction measurement of the product.

[0056] Second Manufacturing Method - Dissolution Step When the boiling point of the organic molecule (M) is high (e.g., 100°C or higher), the second manufacturing method may be used to manufacture the molecular crystal (X). An organic solvent can be preferably used as the solvent for dissolving the organic molecule (M) and the alkali metal salt. The organic solvent is preferably a solvent that can dissolve the organic molecule (M) and the alkali metal salt, has a moderately low boiling point (e.g., 100°C or lower), 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 stir the mixture to homogenize the organic molecule (M) and the alkali metal salt. The stirring method is not particularly limited, and the stirring methods exemplified in the first manufacturing method can be used as appropriate.

[0057] Solvent Removal Step The method for removing the solvent from the solution in which the organic molecule (M) and the alkali metal salt are dissolved is not particularly limited as long as it can remove the solvent from the solution. As a method for removing the solvent, heat treatment is preferred because it can remove the solvent simply and efficiently. The heat treatment may be carried out under normal pressure, but may also be carried out under increased pressure or reduced pressure. When a solvent with a high boiling point is used in the dissolving step, it is preferable to carry out the heat treatment under reduced pressure in order to suppress decomposition of the organic molecule (M) and the alkali metal salt.

[0058] The method for producing the molecular crystal (X) is not limited to the above. For example, the molecular crystal (X) may be produced by the method of heating and mixing the organic molecule (M) and the alkali metal salt without performing mechanical mixing in the first production method described above.

[0059] <Component (Y): Fluorine-Containing Polymer> The fluorine-containing polymer is not particularly limited as long as it is a polymer containing a structural unit having a fluorine atom. As the fluorine-containing polymer, a polymer containing a carbon atom in the main skeleton and having a fluorine atom bonded to the carbon atom can be preferably used. Specifically, the fluorine-containing polymer preferably contains a structural unit represented by the following formula (3) as a structural unit having a fluorine atom: -[CR ６ R ７ -CFR ８ ]- (3) (In formula (3), R ６ , R ７ and R ８ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 3 carbon atoms, a perfluoroalkyl group having 1 to 3 carbon atoms, or a perfluoroalkyloxy group having 1 to 3 carbon atoms.

[0060] Specific examples of the structural unit represented by the above formula (3) include -[CH ２ -CHF]-, -[CH ２ -CF ２ ]-,-[CHF-CF ２ ] -, -[CF ２ -CF ２ ] -, -[CF ２ -CFCF ３ ]-,-[CHF-CFCF３ ] -, -[CF ２ -CF (OCF ３ ) )]-, -[CF ２ -CF(OC ２ F ５ ) )]-, -[CF ２ Of these, the structural unit represented by the formula (3) is -[CH ２ -CHF]-, -[CH ２ -CF ２ ]-,-[CHF-CF ２ ] -, -[CF ２ -CF ２ ] -, -[CF ２ -CFCF ３ ]- and -[CHF-CFCF ３ The fluorine-containing polymer may have only one type of structural unit represented by the above formula (3), or may have two or more types.

[0061] In the fluoropolymer, the proportion of structural units having fluorine atoms is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on all structural units constituting the fluoropolymer. The fluoropolymer may have only one type of structural unit having a fluorine atom, or may have two or more types.

[0062] The fluorine-containing polymer may be composed solely of structural units having fluorine atoms, but may also contain structural units not having 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 group-containing monomers such as (meth)acrylic acid, vinylacetic acid, and pentenoic acid; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, vinyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 2-hydroxyethyl allyl ether, and 4-hydroxybutyl allyl ether; amide group-containing monomers such as N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, and N-vinyl-γ-valerolactam; and ester group-containing monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, phenyl (meth)acrylate, cyclohexyl (meth)acrylate, vinyl acetate, isopropenyl acetate, vinyl butyrate, vinyl isobutyrate, vinyl versatate, and vinyl benzoate. The fluoropolymer may have one or more types of other structural units.

[0063] From the viewpoint of maintaining the ion conduction paths derived from the molecular crystals and thereby obtaining a solid electrolyte exhibiting good ion conductivity, a non-crosslinked polymer is preferably used as the fluorine-containing polymer. Therefore, when the fluorine-containing polymer contains other structural units, it is preferable that the other structural units do not have a crosslinkable group.

[0064] Specific examples of the fluorine-containing polymer include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, vinylidene fluoride / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / tetrafluoroethylene / hexafluoropropylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene / trifluoroethylene copolymer, ethylene / chlorotrifluoroethylene copolymer, vinylidene fluoride / hexafluoropropane / (meth)acrylic acid copolymer, and vinylidene fluoride / pentafluoropropylene copolymer.

[0065] Furthermore, a fluororubber may be used as the fluoropolymer. Specific examples of the fluororubber include vinylidene fluoride rubber, tetrafluoroethylene / propylene rubber, tetrafluoroethylene / propylene / vinylidene fluoride rubber, ethylene / hexafluoropropylene rubber, etc. When producing the solid electrolyte, only one type of fluoropolymer may be used, or two or more types may be used.

[0066] Among the above, the fluorine-containing polymer is preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polypentafluoropropylene, vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), tetrafluoroethylene / hexafluoropropylene copolymer, and vinylidene fluoride / tetrafluoroethylene copolymer, and more preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polypentafluoropropylene, and vinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP).

[0067] 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 even more preferably 15,000 or more. The upper limit of Mw of the fluoropolymer is preferably 500,000 or less, more preferably 300,000 or less. The Mw of the fluoropolymer is a polystyrene-equivalent value determined by gel permeation chromatography (GPC).

[0068] In the solid electrolyte of the present disclosure, the content of the fluoropolymer is preferably 1% by mass or more, and more preferably 5% by mass or more, based on the total amount of the solid electrolyte, from the viewpoint of exhibiting good flexibility. The upper limit of the content of the fluoropolymer is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total amount of the solid electrolyte, from the viewpoint of exhibiting good ionic conductivity.

[0069] In the solid electrolyte of the present disclosure, the mass ratio of the molecular crystal (X) to the fluoropolymer, when expressed as "molecular crystal / fluoropolymer," is preferably 99 / 1 to 40 / 60. When the mass ratio of the molecular crystal (X) to the fluoropolymer is within the above range, a solid electrolyte can be obtained that has a well-balanced improvement in ionic conductivity and flexibility. In terms of achieving both ionic conductivity and flexibility of the solid electrolyte, the mass ratio of the molecular crystal (X) to the fluoropolymer is more preferably 99 / 1 to 50 / 50, even more preferably 99 / 1 to 60 / 40, even more preferably 99 / 1 to 70 / 30, and even more preferably 95 / 5 to 70 / 30. The mass 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 taken as 100.

[0070] <Other Components> The solid electrolyte of the present disclosure may further contain components (hereinafter also referred to as "other components") other than the above-described molecular crystal (X) and fluoropolymer. Examples of the other components include inorganic fillers, inorganic electrolytes (e.g., ceramic electrolytes, glass electrolytes, etc.), binders, conductive additives, positive electrode active materials, and negative electrode active materials.

[0071] The inorganic filler can be used for purposes such as improving the strength and ionic conductivity of the solid electrolyte. Examples of inorganic fillers include oxides, nitrides, and carbides. Specific examples of these include oxides such as zinc oxide, silicon monoxide, silicon dioxide (silica), aluminum oxide (alumina), magnesium oxide, titanium oxide, and iron oxide. Nitrides include silicon nitride, boron nitride, aluminum nitride, gallium nitride, chromium nitride, tungsten nitride, and magnesium nitride. Carbides include silicon carbide, boron carbide, aluminum carbide, titanium carbide, and tungsten carbide. The solid electrolyte of the present disclosure may contain only one type of inorganic filler, or may contain two or more types.

[0072] When the solid electrolyte of the present disclosure contains an inorganic filler, from the viewpoint of obtaining a solid electrolyte that exhibits good ion conductivity, the solid electrolyte preferably contains an oxide (i.e., an inorganic oxide) as the inorganic filler, and particularly preferably contains silica.

[0073] When the solid electrolyte of the present disclosure contains an inorganic filler, the content of the inorganic filler in the solid electrolyte is preferably 30 mass % or less, more preferably 25 mass % or less, and still more preferably 20 mass % or less, relative to the total amount of the solid electrolyte.

[0074] Furthermore, when the solid electrolyte of the present disclosure contains a molecular crystal (X) and a fluoropolymer and optionally contains an inorganic filler, the mass ratio of the content of the molecular crystal (X) to the total content of the fluoropolymer and inorganic filler, expressed as "molecular crystal / fluoropolymer and inorganic filler", is preferably 99 / 1 to 40 / 60. From the viewpoint of enhancing the ionic conductivity of the solid electrolyte, the mass ratio of the content of the molecular crystal (X) to the total content of the fluoropolymer and inorganic filler is more preferably 99 / 1 to 50 / 50, even more preferably 99 / 1 to 60 / 40, and even more preferably 99 / 1 to 70 / 30. The mass ratio expressed as "molecular crystal / fluoropolymer and inorganic filler" is the ratio of the content of the molecular crystal (X) to the total amount of the fluoropolymer and inorganic filler when the total amount of the molecular crystal (X), the fluoropolymer, and the inorganic filler is taken as 100.

[0075] <Method for Producing Solid Electrolyte> The solid electrolyte of the present disclosure can be produced by mixing the molecular crystal (X) with a fluoropolymer. That is, one embodiment of the method for producing the solid electrolyte of the present disclosure includes a method including a step of mixing the molecular crystal (X) with a fluoropolymer (hereinafter also referred to as a "mixing step").

[0076] - Mixing Step In the mixing step for producing a solid electrolyte, the method is not particularly limited as long as the molecular crystal (X) and the fluoropolymer are mixed uniformly. The molecular crystal (X) and the fluoropolymer may be mixed by a dry method or a wet method. Dry mixing is preferred in terms of ease of operation, and wet mixing is preferred in terms of enabling more uniform mixing of the molecular crystal (X) and the fluoropolymer.

[0077] When the molecular crystal (X) and the fluoropolymer are mixed by a dry method, it is preferable to homogenize the molecular crystal (X) and the fluoropolymer by mechanical mixing. Specific embodiments of the mechanical mixing include the same embodiments as those exemplified in the description of the first production method of the molecular crystal (X).

[0078] When the molecular crystal (X) and the fluoropolymer are mixed by a wet method, it is preferable that in the mixing step, the molecular crystal (X) and the fluoropolymer are dissolved in a solvent and mixed, and then the solvent is removed from the solution in which the molecular crystal (X) and the fluoropolymer are dissolved in the solvent. Hereinafter, the step of removing the solvent from the solution in which the molecular crystal (X) and the fluoropolymer are dissolved in the solvent is also referred to as the "solvent removal step".

[0079] As the solvent for dissolving the molecular crystal (X) and the fluoropolymer, an organic solvent can be preferably used. The organic solvent is not particularly limited as long as it can dissolve the molecular crystal (X) and the fluoropolymer. Examples of the organic solvent 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 carry out the dissolution with stirring to homogenize the molecular crystal (X) and the fluoropolymer. The stirring method is not particularly limited, and for example, the stirring methods exemplified in the first production method can be used appropriately.

[0080] Solvent Removal Step The method for removing the solvent from the solution in which the molecular crystal (X) and the fluoropolymer are dissolved in the solvent is not particularly limited as long as it can remove the solvent from the solution. As a method for removing the solvent, heat treatment is preferred because it can remove the solvent simply and efficiently. The heat treatment may be carried out under normal pressure, but may also be carried out under increased pressure or under reduced pressure. Furthermore, two or more types of heat treatment may be carried out in combination. When a solvent with a relatively high boiling point (for example, a polar solvent such as N,N-dimethylacetamide) is used in the dissolving step, it is preferable to carry out the heat treatment under reduced pressure in order to suppress decomposition of the molecular crystal (X).

[0081] The blending ratio of the molecular crystal (X) and the fluoropolymer when mixed may be set so that a diffraction spectrum derived from the molecular crystal (X) appears when X-ray diffraction measurement of the solid electrolyte is performed. From the viewpoint of improving ionic conductivity and flexibility in a well-balanced manner, the mass ratio of the molecular crystal (X) to the fluoropolymer, expressed as "molecular crystal / fluoropolymer", is preferably 99 / 1 to 40 / 60. In terms of being able to enhance the ionic conductivity of the solid electrolyte, the blending ratio of the molecular crystal (X) to the fluoropolymer is more preferably 99 / 1 to 50 / 50 by mass, even more preferably 99 / 1 to 60 / 40, even more preferably 99 / 1 to 70 / 30, and even more preferably 95 / 5 to 70 / 30. The blending 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 taken as 100.

[0082] The solid electrolyte of the present disclosure is usually used as a molded body obtained by molding an electrolyte material containing a molecular crystal (X) and a fluorine-containing polymer into a desired shape. The molding method is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, slip casting, mold casting, and tape casting can be used. Among these, it is preferable to obtain a molded body by pressure molding, mold casting, or tape casting, since this method minimizes the porosity of the resulting solid electrolyte and facilitates the formation of ion conduction paths. The shape of the molded body is not particularly limited and can be appropriately set depending on the shape of the applied electricity storage device. The shape of the molded body is, for example, rectangular or circular.

[0083] When the solid electrolyte finally obtained is a compact, the compact may be used as is as the solid electrolyte layer of the electricity storage device. Alternatively, a plurality of compacts may be stacked to form the solid electrolyte layer of the electricity storage device. When the solid electrolyte of the present disclosure is obtained as a compact, the thickness of the compact is, for example, 5 to 5,000 μm, preferably 5 to 3,500 μm, and more preferably 10 to 3,000 μm.

[0084] The solid electrolyte obtained as described above exhibits high ionic conductivity not only at room temperature (25°C) but also at temperatures lower than room temperature (for example, -20°C or lower). Therefore, by using the solid electrolyte of the present disclosure as an electrolyte material for an electricity storage device, an electricity storage device with high ionic conductivity can be obtained. Specifically, for a solid electrolyte having a thickness of about 130 μm (specifically, 130±10 μm), the ionic conductivity measured at 25°C using an AC impedance method is 1.0×10 －６ From the viewpoint of obtaining an electricity storage device with excellent performance, the ionic conductivity under the same conditions is preferably 5.0 × 10 S / cm or more. －６ S / cm or more, and more preferably 1.0×10 －５ It is more preferable that the viscosity is 25 S / cm or more.

[0085] In addition, the ionic conductivity of a solid electrolyte having a thickness of about 130 μm (specifically, 130±10 μm) measured at −20° C. using an AC impedance method is 1.0×10 －８ S / cm or more, and preferably 5.0×10 －８ S / cm or more, and more preferably 1.0×10 －７ The ionic conductivity is more preferably 25 S / cm or more. Details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0086] <Electricity Storage Device> The electricity storage device of the present disclosure (hereinafter also referred to as "the device") includes the solid electrolyte of the present disclosure. Specific embodiments of the device include a secondary battery, a capacitor, and the like. When the device is a secondary battery, one embodiment is an all-solid-state battery, and a lithium-ion secondary battery is preferred in terms of excellent ionic conductivity.

[0087] An all-solid-state lithium-ion secondary battery, which is one embodiment of the device, will now be described. A lithium-ion secondary battery is a laminate comprising electrodes consisting of a positive electrode and a negative electrode, and a solid electrolyte, with the solid electrolyte being disposed between the positive electrode and the negative electrode so that the solid electrolyte is in contact with the electrode. The materials constituting the positive electrode and the negative electrode are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium-ion secondary batteries. For example, a metal foil such as aluminum or stainless steel can be used as the positive electrode current collector. A metal foil such as copper foil or lithium foil can be used as the negative electrode current collector.

[0088] In the lithium-ion secondary battery of the present disclosure, the solid electrolyte is formed using a molecular crystalline electrolyte containing an organic molecule (M) and an alkali metal salt, and a fluorine-containing polymer. The thickness of the solid electrolyte is not particularly limited and can be appropriately set depending on the application of the secondary battery, etc. The thickness of the solid electrolyte is, for example, 5 to 500 μm.

[0089] The method for producing a lithium-ion secondary battery is not particularly limited, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a laminate including a positive electrode, a solid electrolyte, and a negative electrode may be produced by annealing a molded body formed using a molecular crystalline electrolyte and a fluorine-containing polymer, and sandwiching the resulting solid electrolyte between a positive electrode and a negative electrode. Alternatively, a laminate including a positive electrode, a solid electrolyte, and a negative electrode may be produced by placing an electrolyte material including a molecular crystalline electrolyte and a fluorine-containing polymer between a positive electrode and a negative electrode in a container, and then annealing the container. A laminate including a positive electrode, a solid electrolyte, and a negative electrode is usually housed in a case and used as a secondary battery.

[0090] The device is not limited to the above-described configuration in which the carrier for ion conduction is lithium ions, but may also be a secondary battery in which other ions, such as sodium ions, are used as carriers. The device may also be a capacitor. One form of the capacitor includes a positive electrode layer, a negative electrode layer, and a solid electrolyte, with the solid electrolyte disposed between the positive electrode layer and the negative electrode layer so that the solid electrolyte is in contact with each electrode layer.

[0091] The power storage device including the solid electrolyte can be used for a variety of purposes, specifically as a power source for various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various moving objects such as electric vehicles, hybrid vehicles, robots, and drones; and various electric and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances.

[0092] The present disclosure will be specifically described below based on examples. However, the present disclosure is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0093] <<Production and structural confirmation of molecular crystal electrolyte>> [Production Example 1] 1. Production of molecular crystals In a dry room where the dew point was maintained below -40 ° C., lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt and succinonitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule were weighed out in a molar ratio of 1: 2, and 0.2156 g of lithium bis(fluorosulfonyl)imide and 0.1846 g of succinonitrile were mechanically mixed for 5 minutes at room temperature (25 ° C.) using a mortar to obtain a mixture (mechanical mixing step). The melting point of the mixture was measured using a differential scanning calorimeter (TA Instruments, DSC250, measurement atmosphere: nitrogen atmosphere) at a heating rate of 10 ° C. per minute, and a large endothermic peak (melting point) was observed at 60 ° C. Note that although succinonitrile before mixing exhibited plasticity, the mixture did not exhibit plasticity. The mixture was transferred to a vial and stirred with a magnetic stirrer at a set temperature of 70°C for 1 hour, and it was confirmed that the mixture was dissolved uniformly (heating step). Thereafter, the resulting melt was allowed to cool to room temperature, and a white solid was obtained.

[0094] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained white solid was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement range was 2θ = 5-60 deg, the scanning speed was 2.3 deg / min, and the step angle was 0.02 deg. If a large X-ray diffraction spectrum is observed at an angle within the measurement range, this indicates that the measured sample (white solid) has crystallinity. As a result of powder X-ray diffraction measurement of the white solid obtained as described above, a large diffraction spectrum was observed at an angle within the measurement range. This indicates that the obtained white solid has crystallinity, that is, it is a molecular crystal (this is referred to as "Li(FSI)(SN) ２ In the composition formula of the molecular crystal of Production Example 1, bis(fluorosulfonyl)imide anion is abbreviated as FSI, and succinonitrile is abbreviated as SN.

[0095] 3. Confirmation of Crystalline Phase by Differential Scanning Calorimetry (DSC Measurement) The obtained white solid was subjected to DSC measurement using a differential scanning calorimeter (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 fusion is 20 JK. －１ mol －１ If the melting point is smaller than 100°C, the substance has a plastic crystalline phase and can be said to be a plastic crystal. As a result of DSC measurement, an endothermic peak (melting point) was observed around 60°C (confirmed by visual observation). The melting entropy was calculated to be 110.97 JK －１ mol －１ Therefore, Li(FSI)(SN) ２ It was confirmed that the material does not have a plastic crystal phase and is not a plastic crystal.

[0096] [Production Example 2] A molecular crystal (Li(FSI)(SL)) was obtained by the same procedure as in Production Example 1, except that the types and amounts of raw materials and the heating temperature in the heating step were changed as shown in Table 1. In the composition formula of the molecular crystal of Production Example 2, bis(fluorosulfonyl)imide anion is abbreviated as FSI and tetrahydrothiophene 1,1-dioxide is abbreviated as SL. The obtained molecular crystal was subjected to DSC measurement in the same manner as in Production Example 1, and it was confirmed that Li(FSI)(SL) did not have a plastic crystal phase and was not a plastic crystal.

[0097] [Production Example 3] In a dry room maintained at a dew point of -40°C or below, 0.4307 g of lithium hexafluorophosphate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as an alkali metal salt and 0.6129 g of adiponitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as an organic molecule were weighed out to a molar ratio of 1:2 and transferred to a vial. 8 g of dimethyl carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added and stirred for 1 hour using a magnetic stirrer set at 25°C, and uniform dissolution was confirmed. The resulting solution was cast onto a PTFE (polytetrafluoroethylene) Petri dish and dried for 5 hours on a hot plate at 60°C to remove the solvent, followed by vacuum drying for 12 hours or more in a vacuum dryer at 60°C. This resulted in a white solid. Powder X-ray diffraction measurement of the white solid obtained above revealed a diffraction spectrum with a sharp peak at the angle within the measurement range and different from that of the raw material. From this, it can be concluded that the obtained white solid has crystallinity, that is, a molecular crystal composed of an alkali metal salt and an organic molecule (this is called "Li(PF ６ ) (AdN) ２ It was confirmed that the molecular crystal of Production Example 3 was adiponitrile, abbreviated as AdN. ６ ) (AdN) ２ The ionic conductivity was measured at 25° C. using a heat treatment temperature of 165° C. The measurement results are shown in Table 1.

[0098]

[0099] <<Production and Evaluation of Solid Electrolyte>> [Example 1] Li(FSI)(SN) as molecular crystal ２ (Production Example 1 above), KF Polymer W#8500 (Kureha Corporation, poly(vinylidene fluoride-co-hexafluoropropylene)) was used as the polymer, and Li(FSI)(SN) was used in a mass ratio of 70:30. ２ 0.3502 g of the above and 0.1507 g of KF polymer W#8500 were weighed into a vial, and 2.0 g of acetone (ultra-dehydrated, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a solvent to obtain a mixture. Next, the mixture was stirred for 2 hours using a magnetic stirrer set at 60 ° C., obtaining a solution in which the mixture was uniformly dissolved (mixing step). The obtained solution was cast onto polyethylene release paper, and 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 12 hours or more (solvent removal step). This resulted in a flexible solid electrolyte.

[0100] (Evaluation of the Presence or Absence of Structural Characteristics of Molecular Crystals by X-ray Diffraction Measurement) X-ray diffraction measurement (XRD measurement) was performed on the obtained solid electrolyte using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement range was 2θ = 5-60 deg, the scanning speed was 2.3 deg / min, and the step angle was 0.02 deg. If a diffraction spectrum derived from molecular crystals, which are the structural units of the solid electrolyte, is observed at angles within the measurement range, it can be said that the measured sample (solid electrolyte) has structural characteristics of molecular crystals. Here, whether or not the measured sample has structural characteristics of molecular crystals was determined based on the presence or absence of a peak near 2θ = 10 deg, and if a peak was observed near 2θ = 10 deg, the measured sample was evaluated to have structural characteristics of molecular crystals. As a result of XRD measurement of the solid electrolyte of Example 1, it was found that Li(FSI)(SN) ２ A diffraction spectrum resulting from the above was observed (see FIG. 1). From this result, it was confirmed that the solid electrolyte of Example 1 has structural characteristics of a molecular crystal.

[0101] (Measurement of Ionic Conductivity) Sample pellets for ionic conductivity measurement were prepared in a dry room maintained at a dew point of -40°C or below. The solid electrolyte was punched out using a punch and hammer to obtain circular sample pellets with a diameter of 10 mm and a thickness of 131 μm. The sample pellets were then encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.). Ionic conductivity measurements were performed using the all-solid-state battery evaluation cell encapsulating the sample pellets. To measure ionic conductivity, first, the resistance value was measured by AC impedance measurement while the all-solid-state battery evaluation cell encapsulating the sample pellets was heat-treated in a thermostatic chamber at 40°C (corresponding to the heat treatment temperature in Table 2). The resistance value decreased with heat treatment time, and the heat treatment was terminated when it became constant. Next, resistance values ​​at 25°C and -20°C were measured by AC impedance measurement. Using the obtained resistance values, ionic conductivity (σ) was calculated using the following formula (1): The AC impedance measurement for calculating the ionic conductivity was carried out after the cell was kept at the measurement temperature in a thermostatic bath for 2 hours. σ = L / (R × S) (1) (In formula (1), σ is the ionic conductivity (unit: S / cm), R is the resistance (unit: Ω), and S is the cross-sectional area of ​​the composite electrolyte at the time of measurement (unit: cm ２ ), and L represents the distance between the electrodes (unit: cm). The ionic conductivities of the solid electrolyte of Example 1 at 25°C and -20°C were 1.1 × 10 －７ S / cm, 3.5×10 －１０ The viscosity was S / cm.

[0102] (Evaluation of Flexibility) Sample pellets for evaluating the flexibility of the solid electrolyte were prepared in a dry room where the dew point was maintained at -40°C or below. The solid electrolyte was punched using a punch and a hammer to obtain circular sample pellets with a diameter of 10 mm and a thickness of 131 μm. The sample pellets were wrapped around a polyethylene rod with a diameter of 20 mm, and the state of the bent sample pellets was observed. The flexibility was evaluated according to the following criteria. As a result, the solid electrolyte of Example 1 showed no abnormalities in appearance even when bent, and was rated as "Good." This confirmed that the solid electrolyte of Example 1 had flexibility. Good: No abnormalities in appearance were observed in the sample pellets. Fair: Fine cracks were observed in the sample pellets. Bad: Clear cracks were observed in the sample pellets, or parts of the sample pellets peeled off.

[0103] [Examples 2 and 3] Solid electrolytes were obtained by the same procedure as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 2. Using the solid electrolytes of each example, the presence or absence of structural characteristics of molecular crystals was evaluated by XRD measurement in the same manner as in Example 1, and ionic conductivity measurements at 25°C and -20°C and a flexibility evaluation test were also performed. The results are shown in Table 2. Note that for Example 2, the X-ray diffraction spectrum obtained by XRD measurement is also shown in Figure 1. Figure 1 also shows the X-ray diffraction spectrum of PVDF-HFP alone.

[0104] [Example 4] Li(PF) as molecular crystal ６ ) (AdN) ２ (Production Example 3) and KF Polymer W#8500 (Kureha Corporation, poly(vinylidene fluoride-co-hexafluoropropylene)) as the polymer were mixed in a mass ratio of 70:30 with Li(PF ６ ) (AdN) ２1.1667 g of the above and 0.5000 g of KF polymer W#8500 were weighed into a vial, and 3.8877 g of N,N-dimethylacetamide (ultra-dehydrated, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a solvent to obtain a mixture. Next, the mixture was mixed using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro) to obtain a solution in which the mixture was uniformly dissolved (mixing process). The mixing method was mixed in MIX mode at 2000 rpm for 7 minutes, followed by mixing in DEFORM mode at 2200 rpm for 30 seconds. The obtained solution was cast onto a biaxially oriented polypropylene film using a Baker-type applicator, and then dried on a hot plate at 80 °C for 5 hours to remove the solvent, and then vacuum dried in a vacuum dryer at 60 °C for 12 hours or more (solvent removal process). This resulted in a flexible solid electrolyte formed on the biaxially oriented polypropylene. Using the obtained solid electrolyte, the presence or absence of structural characteristics of molecular crystals was evaluated by XRD measurement, and the ionic conductivity was measured at 25° C. and −20° C., and a flexibility evaluation test was also carried out in the same manner as in Example 1. The results are shown in Table 2.

[0105] [Example 5] Li(FSI)(SN) as molecular crystal ２ (Production Example 1) and silica (Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) as an inorganic filler were mixed in a mass ratio of 4:1 with Li(FSI)(SN) ２ 0.4064 g of POLYMER and 0.1016 g of silica were weighed out and mechanically mixed in a mortar at room temperature for 20 minutes to obtain a mixture. Next, 0.0270 g of PTFE (Teflon (registered trademark) 6-J, manufactured by Mitsui Chemours Fluoroproducts) was added to the mixture as a polymer so that the mass ratio of the mixture to PTFE was 95:5, and the mixture was mechanically mixed in a mortar at room temperature for 20 minutes to obtain a white solid as a solid electrolyte. The obtained white solid was evaluated for the presence or absence of structural characteristics of molecular crystals by XRD measurement in the same manner as in Example 1, and ionic conductivity measurements at 25°C and -20°C and a flexibility evaluation test were also performed. The results are shown in Table 2.

[0106] [Example 6] Li(FSI)(SN) as molecular crystal ２(Production Example 1) and PTFE (Teflon 6-J, manufactured by Mitsui Chemours Fluoroproducts) as a polymer were mixed in a mass ratio of 99:1 with Li(FSI)(SN) ２ 0.2970 g of the above and 0.0031 g of PTFE were weighed out and mechanically mixed in a mortar at room temperature for 20 minutes to obtain a white solid as a solid electrolyte. The obtained white solid was evaluated for the presence or absence of structural characteristics of molecular crystals by XRD measurement, and its ionic conductivity was measured at 25°C and -20°C, and its flexibility was evaluated, in the same manner as in Example 1. The results are shown in Table 2.

[0107] Comparative Example 1 In a dry room where the dew point was maintained at -40°C or less, 0.4119 g of poly(ethylene oxide) (manufactured by Thermo Scientific) was weighed into a vial as a polymer, and 2.0 g of acetonitrile (ultra-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added thereto. The vial was stirred for 60 hours using a mix rotor to dissolve the poly(ethylene oxide). 0.0879 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) was added as an alkali metal salt, and 0.0879 g of Lithium bis(fluorosulfonyl)imide was added thereto. ＋ A mixture of lithium bis(fluorosulfonyl)imide and poly(ethylene oxide) was weighed out so that the molar ratio of ethylene oxide units in the poly(ethylene oxide) and lithium bis(fluorosulfonyl)imide was 1:20. The mixture was added to a vial and stirred at room temperature for 1 hour using a magnetic stirrer, yielding a mixture in which lithium bis(fluorosulfonyl)imide was uniformly dissolved. The mixture was cast onto a Teflon petri dish, heated on a hot plate at 90°C for 5 hours, and then vacuum-dried in a vacuum oven at 90°C for 24 hours to obtain a flexible solid electrolyte. The resulting solid electrolyte was evaluated for the presence or absence of molecular crystal structural characteristics by XRD measurement, and its ionic conductivity was measured at 25°C and -20°C, as well as its flexibility, in the same manner as in Example 1. The results are shown in Table 2.

[0108] Comparative Example 2 Using a press die 10 consisting of a die set 11, an upper punch 12, and a lower punch 13 (see FIG. 2), Li(FSI)(SN) ２ Sample pellets were prepared using the above-mentioned Preparation Example 1 as a raw material. First, solid Li(FSI)(SN) ２A die set 11 containing 0.0600 g of Li(FSI)(SN) was placed on the lower punch 13, and the upper punch 12 was placed on the die set. The raw material was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet having a diameter of 10 mm and a thickness of 498 μm. XRD measurement was performed using the obtained sample pellet in the same manner as in Example 1 to confirm the presence or absence of structural characteristics of molecular crystals. As a result, within the angle measurement range, Li(FSI)(SN) ２ The diffraction spectrum derived from Li(FSI)(SN) was observed (see Figure 1). ２ The ionic conductivity of each sample was measured at 25° C. and −20° C., and a flexibility evaluation test was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0109] [Comparative Example 3] Li(FSI)(SN) as raw material ２ A sample pellet was prepared in the same manner as in Comparative Example 2, except that Li(FSI)(SL) (Preparation Example 2) was used instead of Li(FSI)(SL), and XRD measurement was carried out in the same manner as in Example 1 to confirm the presence or absence of structural characteristics of molecular crystals. The results are shown in Table 2. Furthermore, for Li(FSI)(SL), measurement of ionic conductivity at 25°C and -20°C and an evaluation test of flexibility were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0110] [Comparative Example 4] Li(FSI)(SN) as raw material ２ Instead of Li(PF ６ ) (AdN) ２ Sample pellets were prepared in the same manner as in Comparative Example 2, except that Li(PF) (previously mentioned in Production Example 3) was used. XRD measurements were carried out in the same manner as in Example 1 to confirm the presence or absence of structural characteristics of molecular crystals. The results are shown in Table 2. ６ ) (AdN) ２ The ionic conductivity of each sample was measured at 25° C. and −20° C., and a flexibility evaluation test was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0111] [Comparative Example 5] A solid electrolyte was obtained by the same operation as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 2. The obtained solid electrolyte was subjected to XRD measurement in the same manner as in Example 1 to confirm the presence or absence of structural characteristics of molecular crystals. However, in the solid electrolyte of Comparative Example 5, the Li(FSI)(SN) ２ No diffraction spectrum due to the above was observed (see FIG. 1). Furthermore, for the solid electrolyte of Comparative Example 5, the ionic conductivity was measured at 25° C. and −20° C., and a flexibility evaluation test was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0112]

[0113] The details of the compounds in Tables 1 and 2 are as follows: LiFSI: lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) LiPF ６ : Lithium hexafluorophosphate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] SN: Succinonitrile [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] PTFE: Teflon 6-J [manufactured by Mitsui-Chemours Fluoroproducts] PEO: Poly(ethylene oxide) [manufactured by Thermo Scientific] Silica: Aerosil 300 [manufactured by Nippon Aerosil Co., Ltd.] DMC: Dimethyl carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) DMAc: N,N-dimethylacetamide (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) AcN: Acetonitrile (super dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0114] <Evaluation Results> As is clear from the results of Examples 1 to 6, the solid electrolytes containing molecular crystals and fluorine-containing polymers exhibited high ionic conductivity at both room temperature (25°C) and low temperature (-20°C). For the solid electrolytes of Examples 1 to 6, diffraction spectra derived from the molecular crystals were observed by X-ray diffraction measurement. Therefore, it is believed that the solid electrolytes of Examples 1 to 6 maintained the crystalline structure of the molecular crystals and had ion conduction paths, thereby exhibiting high ionic conductivity. Furthermore, the solid electrolytes of Examples 1 to 6 exhibited good flexibility.

[0115] In contrast, the solid electrolyte of Comparative Example 1, which used poly(ethylene oxide) that interacts with lithium ions as the polymer component, and the solid electrolyte of Comparative Example 5, in which no diffraction spectrum derived from molecular crystals was observed by X-ray diffraction measurement, had good flexibility but were inferior in ionic conductivity to Examples 1 to 8 at both room temperature (25°C) and low temperature (-20°C). The results of Comparative Example 5 are thought to be due to the fact that the crystalline structure of the molecular crystals in the solid electrolyte of Comparative Example 4 had collapsed, resulting in the ion conduction paths being cut, resulting in low ionic conductivity. Furthermore, the solid electrolytes of Comparative Examples 2, 3, and 4, which consisted only of molecular crystals, were inferior in flexibility.

[0116] From the above results, it has become clear that a solid electrolyte containing a molecular crystal (X) and a fluorine-containing polymer and having a diffraction spectrum derived from the molecular crystal in X-ray diffraction exhibits high ionic conductivity at both room temperature and low temperatures, while also having high flexibility. By using the solid electrolyte of the present disclosure having such properties as an electrolyte material for an electricity storage device, the electricity storage device can be easily handled during production, and can also follow bending when a bending force is applied to the electricity storage device. Therefore, by using the solid electrolyte of the present disclosure, it is possible to obtain an electricity storage device that is less likely to be damaged or its performance to be reduced even when an external force is applied to the electricity storage device, and that is highly safe.

[0117] The present invention is not limited to the above-described embodiments, and encompasses various modifications and equivalent modifications within the scope of the spirit of the present invention. Therefore, in light of the above teachings, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are to be understood as falling within the scope and spirit of the present invention.

[0118] 10... Press mold

Claims

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

2. The solid electrolyte according to claim 1, wherein a mass ratio of the molecular crystals to the fluoropolymer (molecular crystals / fluoropolymer) is 99 / 1 to 50 / 50, where the total amount of the molecular crystals and the fluoropolymer is taken as 100.

3. The solid electrolyte according to claim 1, wherein the fluorine-containing polymer contains carbon atoms in its main skeleton and has fluorine atoms bonded to the carbon atoms.

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

5. The counter anion constituting the alkali metal salt is (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) (CF ３ SO ２ ) N － , P.F. ６ － or BF ４ － The solid electrolyte according to claim 1 , 6. The solid electrolyte according to claim 1, further comprising an inorganic filler.

7. The solid electrolyte of claim 6, wherein the inorganic filler comprises an inorganic oxide.

8. An electricity storage device comprising the solid electrolyte according to any one of claims 1 to 7.

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