Ion conductor, solid electrolyte, electrode, power storage device, and secondary battery

Abstract

Provided is a novel ion conductor containing an ionic soft crystal. An ion conductor according to one embodiment of the present invention contains an ionic soft crystal and a zwitterionic compound. An ion conductor according to another embodiment of the present invention contains an ionic soft crystal and a metal salt.

Description

Ion conductors, solid electrolytes, electrodes, power storage devices, secondary batteries

[0001] The present invention relates to an ion conductor, a solid electrolyte, an electrode, an electricity storage device, and a secondary battery. This application claims priority based on Japanese Patent Application No. 2024-050482 filed on March 26, 2024, and Japanese Patent Application No. 2024-050448 filed on March 26, 2024, the contents of which are incorporated herein by reference.

[0002] A plastic crystal phase, which is an intermediate phase between a solid phase and a liquid phase, is flexible while remaining in a crystalline state. In a compound that exhibits a plastic crystal phase (hereinafter also referred to as a plastic crystal), the center of gravity of its constituent molecules is regular, but the orientation of the constituent molecules is irregular. Ionic plastic crystals, which are a type of plastic crystal, have excellent heat resistance and electrochemical stability, and are therefore attracting attention as solid electrolyte materials for all-solid-state batteries, which repeatedly expand and contract with heat generation (for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 2017-091813

[0004] However, according to the investigations of the present inventors, there is room for improvement in the solid electrolyte containing ionic plastic crystals.

[0005] An object of the present invention is to provide a novel ionic conductor containing ionic plastic crystals.

[0006] The present invention has the following aspects. [A1] An ionic conductor containing an ionic plastic crystal and a zwitterionic compound. [A2] The ionic conductor according to [A1], wherein the temperature range in which the ionic plastic crystal contained in the ionic conductor exhibits a plastic crystal phase is 60 to 100, where the temperature range in which the ionic plastic crystal contained in the ionic conductor exhibits a plastic crystal phase is 100. [A3] The ionic conductor according to [A1] or [A2], wherein the ionic conductivity at 30°C is higher than the ionic conductivity of the ionic plastic crystal at 30°C. [A4] The steric hindrance %V of the cation contained in the ionic plastic crystal ｂｕｒ % V of the steric hindrance of the cation contained in the zwitterionic compound relative to ｂｕｒ The ratio r ｃThe ionic conductor according to any one of [A1] to [A3], wherein the steric hindrance % V is 0.5 to 2.0. ｂｕｒ is calculated using a structure in which energy is minimized by quantum chemical calculation at the functional ωB97XD / basis set def2TZVP level and the Python library morpheus. ｃ [A6] The ionic conductor according to [A4], wherein the steric hindrance %V of the anion contained in the ionic plastic crystal is 0.7 to 1.3. ｂｕｒ % V of the steric hindrance of the anion contained in the zwitterionic compound relative to ｂｕｒ The ratio r ａ The ionic conductor according to any one of [A1] to [A5], wherein the steric hindrance % V is 0.5 to 2.0. ｂｕｒ is calculated using a structure in which energy is minimized by quantum chemical calculation at the functional ωB97XD / basis set def2TZVP level and the Python library morpheus. ａ [A8] The ionic conductor according to [A6], wherein the molecular volume V of the anion contained in the ionic plastic crystal is 0.7 to 1.3. ＰＣ The partial volume V of the anion contained in the zwitterionic compound relative to ｐ ＺＷ The ratio r ｐ Ａ [A9] The ionic conductor according to any one of [A1] to [A7], wherein the ratio r is 0.5 or more. ｐ Ａ [A10] The ionic conductor according to [A8], wherein the molecular volume V of the anion contained in the ionic plastic crystal is 0.7 or more. ＰＣ The fragment volume V of the anion contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ａ [A11] The ionic conductor according to any one of [A1] to [A9], wherein the ratio r is 2.0 or less. ｆ Ａ [A12] The ionic conductor according to [A10], wherein the molecular volume V of the cation contained in the ionic plastic crystal is 1.5 or less. ＰＣthe partial volume V of the cations contained in the zwitterionic compound relative to ｐ ＺＷ The ratio r ｐ Ｃ [A13] The ionic conductor according to any one of [A1] to [A11], wherein the ratio r is 0.5 or more. ｐ Ｃ [A14] The ionic conductor according to [A12], wherein the molecular volume V of the cation contained in the ionic plastic crystal is 0.7 or more. ＰＣ The fragment volume V of the cation contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ｃ [A15] The ionic conductor according to [A13], wherein the ratio r is 2.0 or less. ｆ Ｃ The ionic conductor according to [A14], wherein the ionic conductor has a molecular weight of 1.5 or less. [A16] A solid electrolyte containing the ionic conductor according to any one of [A1] to [A15]. [A17] An electrode having the ionic conductor according to any one of [A1] to [A15]. [A18] An electricity storage device having the ionic conductor according to any one of [A1] to [A15]. [A19] A secondary battery having the ionic conductor according to any one of [A1] to [A15].

[0007] Another aspect of the present invention is as follows: [B1] An ionic conductor containing an ionic plastic crystal and a metal salt. Or, the ionic conductor according to any one of [A1] to [A15] further containing a metal salt. [B2] The metal salt has a steric hindrance %V ｂｕｒ The ionic conductor according to [B1], comprising a metal salt having a steric hindrance %V of 68% or more. ｂｕｒis calculated by the Python library morpheus for a structure in which energy has been minimized by quantum chemical calculation using ωB97XD as the functional and def2TZVP as the basis function. [B3] The ionic conductor according to [B1] or [B2], wherein the ratio of the volume of the anion contained in the metal salt to the molecular volume of the anion contained in the ionic plastic crystal is 1.3 or more. [B4] The ionic conductor according to any one of [B1] to [B3], wherein the ionic conductivity at 30°C is higher than the ionic conductivity of the ionic plastic crystal at 30°C. [B5] The ionic conductor according to any one of [B1] to [B4], wherein the relationship of the following formula (BI) is satisfied: (Ionic conductivity of ionic conductor at 30°C) / (ionic conductivity of the ionic plastic crystal at 30°C)>1...formula (BI). [B6] An ionic conductor according to any one of [B1] to [B5], wherein the frequency factor is higher than that of the ionic plastic crystal. [B7] An ionic conductor according to any one of [B1] to [B6], wherein the relationship of the following formula (BII) is satisfied: (Frequency factor of ionic conductor) / (Frequency factor of the ionic plastic crystal)>1...formula (BII). [B8] An ionic conductor according to any one of [B1] to [B7], wherein the metal salt comprises at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. [B9] An ionic conductor according to any one of [B1] to [B8], wherein the metal salt comprises at least one selected from the group consisting of lithium salts, sodium salts, potassium salts, calcium salts, and magnesium salts. [B10] The ionic conductor according to any one of [B1] to [B9], wherein the anion of the metal salt includes an anion represented by the following formula (B1): [(R ｎ M) ｊ L ｊ－１ ] ｃ－(B1) In formula (B1), R each independently represents a halogen atom or a hydrocarbon group which may have a heteroatom, M represents B, Al, P, C, N, As, Sb, or Te, L represents an imidazole ring which may be substituted with a halogen atom or a hydrocarbon group which may have a heteroatom, and R may be bonded to each other. n represents an integer of 6 or less, c represents an integer of 1 or more, and j represents 1 or 2. However, when j is 2, M represents B, Al, P, As, Sb, or Te. [B11] The ionic conductor according to any one of [B1] to [B10], wherein the anion of the metal salt is an anion represented by the following formula (B2) or (B3):

[0008]

[0009] In formula (B2), each Z is independently a halogen atom or a hydrocarbon group which may have a heteroatom, M is B, Al, P, C, N, As, Sb, or Te, and each W is independently a halogen atom or a hydrocarbon group which may have a heteroatom. p is an integer of 0 to 3, q ​​is an integer of 0 to 6, and satisfies 3≦2p+q≦6. c is an integer of 1 or greater.

[0010]

[0011] In formula (B3), M １ , M ２ are each independently B, Al, P, As, Sb or Te, W １ , W ２ each independently represents a hydrocarbon group which may have a halogen atom or a heteroatom; Z １ , Z ２are each independently a halogen atom or a hydrocarbon group which may have a heteroatom, L is an indazole ring which may be substituted with a halogen atom or a hydrocarbon group which may have a heteroatom, p1 is an integer of 0 to 3, q1 is an integer of 0 to 6 and satisfies 3≦2p1+q1≦5, p2 is an integer of 0 to 3, q2 is an integer of 0 to 6 and satisfies 3≦2p2+q2≦5, and c is an integer of 1 or greater. [B12] The ionic conductor according to any one of [B1] to [B11], wherein the anion of the metal salt comprises at least one anion selected from the group consisting of anions represented by the following formula (BA1), anions represented by the following formula (BA2), anions represented by the following formula (BA3), anions represented by the following formula (BA4), anions represented by the following formula (BA5), anions represented by the following formula (BA6), anions represented by the following formula (BA7), anions represented by the following formula (BA8), anions represented by the following formula (BA9), anions represented by the following formula (BA10), and anions represented by the following formula (BA11).

[0012]

[0013] [B13] A solid electrolyte containing the ionic conductor according to any one of [B1] to [B12]. [B14] An electrode having the ionic conductor according to any one of [B1] to [B12]. [B15] An electricity storage device having the ionic conductor according to any one of [B1] to [B12]. [B16] A secondary battery having the ionic conductor according to any one of [B1] to [B12].

[0014] According to the present invention, a novel ionic conductor containing ionic plastic crystals can be provided.

[0015] Fig. 1 shows a schematic diagram of the introduction of zwitterions into an ionic plastic crystal, and Fig. 2 shows the Raman spectra of the ionic conductors of Experimental Examples 1-7 and 2-1.

[0016] The following terms used in this specification have the following meanings. The term "to" indicating a numerical range means that the numerical values ​​before and after it are inclusive of the upper and lower limits. For example, "X to Y" means X or more and Y or less. The upper and lower limits of the numerical ranges "X to Y," "X or more," and "Y or less" disclosed in this specification can be arbitrarily selected to create new numerical ranges. "X or more" means "greater than X and / or X," and also discloses a numerical range "greater than X." Similarly, "Y or more" means "smaller than Y and / or Y," and also discloses a numerical range "smaller than Y." A "heteroatom" refers to an atom other than carbon, hydrogen, and halogen atoms. A "hydrocarbon group" refers to an aliphatic hydrocarbon group or an aromatic hydrocarbon group. A "hydrocarbon group optionally having a heteroatom" refers to one or more carbon atoms of the hydrocarbon group that may be substituted with a heteroatom, one or more carbon atoms of the aliphatic hydrocarbon group that may have a heteroatom such as an oxo group (═O) as a substituent, or one or more hydrogen atoms of the aliphatic hydrocarbon group that may be substituted with a monovalent substituent containing a heteroatom such as an alkoxy group. The heteroatom is preferably a nitrogen atom or an oxygen atom, more preferably an oxygen atom. Examples of the substituent having a heteroatom include a cyano group, an isocyanato group, an alkoxy group, an acyl group, an acyloxy group, an alkoxycarbonyl group, and an alkoxycarbonyloxy group.

[0017] The ionic conductivity of ionic plastic crystals preferably follows the Arrhenius process characteristic of solid conductors. The Arrhenius process follows the equation σ=A×exp(−E / RT), where σ is the ionic conductivity, A is the frequency factor, E is the activation energy, R is the gas constant, and T is the absolute temperature. Therefore, the experimentally measured conductivity follows the first-order linear form: lnσ=−E / R×(T －１ ) + lnA, the inverse temperature T －１ is in a linear relationship with

[0018] Since the conductivity follows the Arrhenius equation, it is assumed that the conduction in ionic plastic crystals is caused by lattice defects. Therefore, the inventors conceived the idea that the conductivity could be improved by intentionally introducing defects that partially destroy the crystal structure of ionic plastic crystals. As shown schematically in Figure 1, the inventors succeeded in improving the conductivity by introducing zwitterions into ionic plastic crystals, which distorts the structure and generates defects while preventing the crystal from collapsing.

[0019] As mentioned above, the experimentally measured conductivity is expressed by the linear equation: lnσ = -E / R × (T －１ ) + lnA, the inverse temperature T －１ The present inventors came up with the idea of ​​improving the ionic conductivity σ by controlling the intercept lnA and the slope -E / R in this first-order linear equation. For example, the frequency factor A can be increased by intentionally introducing defects that partially destroy the crystal structure of the ionic plastic crystal. The present inventors discovered that by employing a metal salt as a defect-introducing factor for partially destroying the crystal structure of the ionic plastic crystal, the frequency factor A can be increased and the ionic conductivity improved.

[0020] Hereinafter, several embodiments of the present invention will be described, but the following description is for typical examples and the present invention is not limited to the following description.

[0021] [Ionic Conductor According to First Aspect] The ionic conductor according to the first aspect of the present invention contains an ionic plastic crystal and a zwitterionic compound. In a preferred embodiment, the temperature range (1) in which the ionic conductor can exist as a plastic crystal is at least 10°C or higher. The lower limit of the temperature range (1) is preferably 30°C, more preferably 50°C, even more preferably 70°C, particularly preferably 90°C, and particularly preferably 110°C. The upper limit of the temperature range (1) is preferably 200°C, more preferably 180°C, even more preferably 160°C, and particularly preferably 140°C. In another preferred embodiment, when the temperature range (2) in which the ionic plastic crystal contained in the ionic conductor exhibits a plastic crystal phase is taken as 100, the temperature range (3) in which the ionic conductor exhibits a plastic crystal phase is preferably 60 to 100. The lower limit of the temperature range (3) is more preferably 65°C, even more preferably 70°C, even more preferably 75°C, particularly preferably 80°C, and most preferably 90°C. The upper limit of the temperature range (3) is more preferably 99°C, even more preferably 98°C, especially preferably 95°C, and particularly preferably 90°C. When measuring the temperature ranges (1) to (3), the temperature range where the mesophase appears can be confirmed using the method described below. The measurement sample may be prepared by mixing 100 mol% of the ionic plastic crystals contained in the target ionic conductor with 100 mol% of the zwitterionic compound contained in the target ionic conductor using the method disclosed in the Examples. For compounds without a melting point, the temperature range is calculated from the difference between the solid-solid phase transition point and the 5% weight loss temperature measured by TG-DTA (thermogravimetric differential thermal analysis) in a nitrogen atmosphere. Furthermore, the ionic conductor of the present invention is preferably a solid ionic conductor. Whether or not a material is a solid ionic conductor is determined by whether or not the temperature dependence of ionic conductivity follows the Arrhenius process. The ionic conductor according to the first aspect of the present invention will be described below.

[0022] [Ionic plastic crystal] Ionic plastic crystal has one or more cations and one or more anions. The appearance of the mesophase can be confirmed by the fact that an endothermic peak is observed during temperature rise in differential scanning calorimetry (DSC). Furthermore, whether the mesophase is a plastic crystal phase can be confirmed by the fact that a diffraction peak is observed in the region of 2θ≦30° in X-ray diffraction (XRD) measurement above the endothermic peak temperature.

[0023] Ionic plastic crystals exhibit characteristic X-ray diffraction patterns at temperatures above the solid-meso phase transition point. That is, ionic plastic crystals are compounds in which ions exhibit rotational disorder while the centers of mass occupy aligned positions in the crystal lattice structure. Ionic plastic crystals can be either protic or aprotic, and either can be used.

[0024] In addition to ionic plastic crystals, there are also plastic molecular crystals made of neutral molecules and plastic zwitterionic crystals made of zwitterions. However, plastic molecular crystals and plastic zwitterionic crystals are clearly distinguished from ionic plastic crystals made of non-neutral molecules.

[0025] The ionic plastic crystal is preferably an organic substance, that is, it preferably contains at least the elements carbon (C) and hydrogen (H) in its chemical structure. Furthermore, it is more preferable that it contains any of oxygen (O), nitrogen (N), and sulfur (S). The ionic plastic crystal preferably contains a chemical structure in which cations and anions form ionic bonds. This makes it easier to control the physical properties by the chemical structure. The combination of cations and anions of the ionic plastic crystal is not particularly limited as long as it can produce an ionic plastic crystal. Examples of combinations of cations and anions of ionic plastic crystals include those described in Chem. Soc. Rev., 2020, 49, 8878-8896, Chem. Soc. Rev. , 2020, 49, 8878-8896, Trends in Chemistry, 2019, 1, 126-140, Advanced Materials, 2001, 13, 957-966, Phys. Chem. Chem. Phys. , 2013, 15, 1339-1351, Energy Adv. , 2023, 2, 748-764 and the like.

[0026] The cation of the ionic plastic crystal preferably includes a nitrogen-containing cation. From the viewpoint of thermal stability, the nitrogen-containing cation more preferably includes a cyclic structure. From the viewpoint of solubility, the nitrogen-containing cation more preferably includes a chain structure. The anion of the ionic plastic crystal preferably includes a nitrogen-containing anion, more preferably includes a sulfonimide anion, and even more preferably includes a bissulfonimide anion. The molecular weight of the ionic plastic crystal is preferably 50 to 1,000, more preferably 50 to 800, even more preferably 50 to 600, and especially preferably 50 to 400. Within this molecular weight range, thermal properties are easily controlled. The temperature at which the ionic plastic crystal transitions from a mesophase to a liquid phase (hereinafter also referred to as the melting point) is preferably 25 to 200°C, more preferably 25 to 180°C, even more preferably 25 to 160°C, and especially preferably 40 to 160°C. Having a melting point within this range facilitates the formation of a conductor with appropriate thermal stability.

[0027] (Method for producing ionic plastic crystals) Ionic plastic crystals can be synthesized by conventionally known synthesis methods, and the synthesis method is not particularly limited. Examples of the synthesis method include a method in which a halide compound of an onium salt and an alkali metal or alkaline earth metal salt of an organic anion are mixed in a solvent and subjected to a salt exchange reaction.

[0028] The solvent generally used is a polar solvent that easily dissolves the substrate and product, and examples of such solvents include protic solvents such as water, methanol, ethanol, and propanol, and aprotic polar solvents such as acetonitrile, DMF, and N-methyl-2-pyrrolidone. It is preferable to select a solvent that takes into consideration the removal of by-product alkali metal halide salts. Typically, after a salt exchange reaction in an aqueous solvent, the ionic plastic crystals are extracted with dichloromethane or the like, and then washed with water to remove the alkali metal halide salts, thereby obtaining high-purity ionic plastic crystals.

[0029] In the case of anions that decompose in water, ionic plastic crystals can be obtained by dissolving a halide compound of an onium salt and an alkali metal or alkaline earth metal salt of an organic anion in a halide solvent such as dichloromethane, precipitating and removing the by-product alkali metal halide salt.

[0030] [Zwitterionic Compounds] Zwitterionic compounds are compounds in which one or more cations and one or more anions are covalently bonded. The overall charge of a zwitterionic compound does not need to be neutral; it may be positively or negatively charged overall. In addition, multiple cations or multiple anions may be bonded together, and zwitterionic compounds may have a ring structure.

[0031] The zwitterionic compound is preferably a compound in which any of the following cations and anions are connected via a covalent linker, and the overall charge is neutral. The linker is not particularly limited, but is preferably a single bond or a hydrocarbon group having 1 to 10 carbon atoms and optionally having a heteroatom.

[0032] Suitable partial structures of the cation of the zwitterionic compound include, for example, the following: The cation of the ionic plastic crystal preferably contains a nitrogen-containing cation. From the viewpoint of thermal stability, the nitrogen-containing cation more preferably contains a cyclic structure. From the viewpoint of solubility, the nitrogen-containing cation more preferably contains a chain structure.

[0033]

[0034] Suitable anionic partial structures of zwitterionic compounds include, for example, the following: The partial structure below preferably contains a nitrogen-containing anion, more preferably contains a sulfonimide anion, and even more preferably contains a bissulfonimide anion.

[0035]

[0036] (Method for Producing Zwitterionic Compounds) Zwitterionic compounds can be synthesized by conventionally known synthesis methods, and the synthesis method is not particularly limited. Typical synthesis methods include a method of mixing an alkyl halide compound having an anionic structure such as 1,1,1-trifluoro-N-(methanesulfonyl)sulfonamide, sulfonate, carbonate, or phosphate with a tertiary amine, heterocyclic amine, tertiary phosphine, or secondary sulfide in a solvent or without a solvent, and carrying out a quaternary salt reaction; and a method of mixing a tertiary amine having an anionic structure such as 1,1,1-trifluoro-N-(methanesulfonyl)sulfonamide, sulfonate, carbonate, or phosphate with an alkyl halide in a solvent, and carrying out a quaternary salt reaction.

[0037] The reaction temperature may be room temperature or may be heated. The solvent is preferably a polar solvent that easily dissolves the substrate and product, such as protic solvents such as water, methanol, ethanol, and propanol, or aprotic polar solvents such as acetonitrile, DMF, and N-methyl-2-pyrrolidone. After the reaction, the zwitterion can be obtained by recrystallization in a general-purpose solvent.

[0038] [Metal Salt] The ionic conductor according to the first aspect of the present invention may further contain a metal salt in addition to the ionic plastic crystal and the zwitterionic compound.

[0039] The metal salt may be the same as the metal salt described later in the description of the conductor according to the second embodiment of the present invention.

[0040] [Other Components] The ionic conductor according to the embodiment may further contain other components in addition to the ionic plastic crystal, the zwitterionic compound, and the metal salt.

[0041] Examples of other components include inorganic fillers and binders (organic fillers). However, the other components are not limited to these examples. One type of other component may be used alone, or two or more types may be used in combination.

[0042] Examples of inorganic fillers include active fillers such as garnet-type oxides, NASICON-type oxides, perovskite-type oxides, LGPS-type sulfides, argyrodite-type sulfides, glass-type oxides, and glass sulfides, as well as other passive fillers. However, the inorganic fillers are not limited to these examples. One type of inorganic filler may be used alone, or two or more types may be used in combination.

[0043] Examples of binders include thermoplastic polymers, fluororesins, and epoxy resins. However, the binder is not limited to these examples. One type of binder may be used alone, or two or more types may be used in combination.

[0044] [Composition] The molar ratio of the zwitterionic compound to the ionic plastic crystal (zwitterionic compound / ionic plastic crystal) is not particularly limited and can be changed appropriately depending on the ionic species of each component, but is preferably, for example, 5 to 20. When the molar ratio (zwitterionic compound / ionic plastic crystal) is within the above numerical range, an ionic conductor with improved conductivity is likely to be obtained.

[0045] In one example, when the ionic conductor according to the first aspect of the present invention contains a metal salt, the content of the metal salt is preferably 50 mass % or less, more preferably 1 to 20 mass %, of the total amount of the ionic conductor. When the content of the metal salt is within the above range, an ionic conductor with improved conductivity is likely to be obtained.

[0046] When the ionic conductor-type component according to the first aspect of the present invention is contained, the content of the other components is 60 mol % or less of the total amount including the ionic plastic crystal, the zwitterionic compound, and, when the ionic conductor according to the first aspect of the present invention contains a metal salt, the metal salt. In one example, the content of the other components is preferably 60 mol % or less of the total amount of the ionic conductor.

[0047] [Characteristics] The ionic conductor according to the first aspect of the present invention preferably has an ionic conductivity at 30° C. higher than the ionic conductivity of the ionic plastic crystal alone at 30° C. That is, the ionic conductor of the present invention preferably satisfies the relationship of the following formula (AI):

[0048] (ionic conductivity of ionic conductor at 30°C) / (ionic conductivity of ionic plastic crystal at 30°C)>1... Formula (AI)

[0049] The ionic conductivity is calculated by measuring impedance by an AC impedance method (measurement frequency: 4 Hz to 8 MHz, applied voltage: 100 mV) using an LCR meter (product of Hioki E.E. Corporation: IM3536). Details of the conditions for the calculation are as described in the Examples.

[0050] [Suitable Combinations of Ionic Plastic Crystals and Zwitterionic Compounds] The combination of an ionic plastic crystal and a zwitterionic compound can be optimized by quantum chemical calculations. For example, the steric hindrance % V of the cations contained in the ionic plastic crystal can be optimized by the quantum chemical calculations. ｂｕｒ % V of steric hindrance of cations contained in zwitterionic compounds relative to ｂｕｒ The ratio r ｃ The ratio r is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.7 to 1.3. ｃWhen the ratio r is equal to or greater than the lower limit of the above-mentioned range, an ionic conductor with improved conductivity is easily obtained. ｃ When is equal to or less than the upper limit of the above-mentioned range, an ionic conductor with improved conductivity is likely to be obtained.

[0051] Steric hindrance %V of anions contained in ionic plastic crystals ｂｕｒ % V of the steric hindrance of the anion contained in the zwitterionic compound relative to ｂｕｒ The ratio r ａ The ratio r is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, and even more preferably 0.7 to 1.3. ａ When the ratio r is equal to or greater than the lower limit of the above-mentioned range, an ionic conductor having improved conductivity is likely to be obtained. ａ When is equal to or less than the upper limit of the above-mentioned range, an ionic conductor with improved conductivity is likely to be obtained.

[0052] Molecular volume V of an anion contained in an ionic plastic crystal ＰＣ The partial volume V of the anion contained in the zwitterionic compound ｐ ＺＷ The ratio r ｐ Ａ is preferably 0.5 or more, and more preferably 0.7 or more. ｐ Ａ When the value is equal to or less than the upper limit, an ionic conductor with improved conductivity is easily obtained.

[0053] Molecular volume V of an anion contained in an ionic plastic crystal ＰＣ The fragment volume V of the anion contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ａ is preferably 2.0 or less, and more preferably 1.5 or less. ｆ Ａ When is equal to or greater than the lower limit, an ion conductor with improved conductivity is likely to be obtained.

[0054] Molecular volume V of the cation contained in the ionic plastic crystal ＰＣ The partial volume V of the cations contained in the zwitterionic compound ｐ ＺＷThe ratio r ｐ Ｃ is preferably 0.5 or more, and more preferably 0.7 or more. ｐ Ｃ When is equal to or greater than the lower limit, an ion conductor with improved conductivity is likely to be obtained.

[0055] Molecular volume V of the cation contained in the ionic plastic crystal ＰＣ The fragment volume V of the cation contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ｃ is preferably 2.0 or less, and more preferably 1.5 or less. ｆ Ｃ When the value is equal to or less than the upper limit, an ionic conductor with improved conductivity is easily obtained.

[0056] [Method for calculating structural parameters of compounds] (Method for calculating molecular volume) The case of ionic plastic crystals will be described. The volume of an ionic plastic crystal is calculated using structural information obtained by structural optimization, the programming language Python 3.9.13, and the Python library morpheus 0.7.2. Specifically, SMILES of the anions and cations constituting the ionic plastic crystal are prepared, and these are loaded into the Python library RdKit 2022.03.5 to generate 1,000 conformations. These are structurally optimized using a classical force field, and structures with the same energy are deleted, and up to 20 conformations are extracted in ascending order of energy. Next, energy-minimized structures are obtained by performing quantum chemical calculations on these structures using ωB97XD as the functional and def2TZVP as the basis function. The lowest-energy structure is extracted from the resulting structures, and the volume is calculated by passing coordinates and element information to the Python library morpheus. More specifically, SASA is imported from morpheus, and the element type and coordinate information are passed as arguments, and the volume is stored in the volume variable. For details on how to use the Python library morpheus 0.7.2, please refer to the following URL: https: / / digital-chemistry-laboratory.github.io / morfeus / sasa.html (accessed March 14, 2024).

[0057] The case of zwitterionic compounds will be explained. A method for obtaining an energy-minimized structure for a zwitterionic compound will be explained. SMILES is prepared and loaded into the Python library RdKit 2022.03.5 to generate 1,000 conformations. These are then structurally optimized using a classical force field, structures with the same energy are deleted, and up to 20 structures with the lowest energy are extracted. Next, energy-minimized structures are obtained by performing quantum chemical calculations on these structures using ωB97XD as the functional and def2TZVP as the basis function. Regarding volume calculations, partial volumes V are used to clearly separate the anion and cation portions.ｐ ＺＷ and the fragment volume V ｆ ＺＷ The volume is calculated by defining the target structure from the energy-optimized structure and then extracting it. Specifically, the coordinate information of the extracted structure is passed to the Python library morpheus.

[0058] Partial volume: Partial volume refers to the volume introduced to compare the volume of the ionic molecules that make up an ionic plastic crystal with the volume of the cation or anion portion of a zwitterionic compound. A specific explanation will be given below using cations as an example. For cationic molecules that make up an ionic plastic crystal, the molecules bonded to the ionic center are assigned numbers 1 for the nearest atom, 2 for the atom bonded to the nearest atom, and so on up to the terminal atom. However, only one number can be assigned to the same atom, and hydrogen atoms are not considered. The maximum number assigned is n_(b,max)^PC.

[0059]

[0060] For the cationic moiety contained in a zwitterionic compound, the bonding coordination sphere from the cation center to the n_(b,max)^PC position is extracted, and the volume of the extracted site structure is called the partial volume V ｐ ＺＷ Here, the volume of the cation molecules that make up the ionic plastic crystal is defined as V ＰＣ Below is an example of a cation with n_(b,max)^PC=2.

[0061]

[0062] Fragment volume: The fragment volume is a volume introduced to compare the volume of the cation or anion part of an ionic molecule that constitutes an ionic plastic crystal with that of a zwitterionic compound. For multiple ionic centers contained in a zwitterionic compound, a fragment containing only one ionic center is created by breaking the bond at a point where the number of covalent bonds between the ionic centers becomes the same. The fragment volume at this time is called V ｆ ＺＷHowever, if a zwitterionic compound contains multiple ionic centers, the cleavage begins with the site with the smallest number of covalent bonds.

[0063]

[0064] (Steric Hindrance) In the first embodiment of the present invention, the steric hindrance of the ion center is calculated based on the fragment structure information used for the fragment volume and the Percent Buried Volume (%V) calculated using the programming language Python 3.9.13 and the Python library morpheus 0.7.2. ｂｕｒ More specifically, when expressed in SMILES, a three-dimensional sphere with a radius of 3.5 Å is drawn around an atom (ionic center) with a positive or negative charge, and the degree to which the sphere is occupied by surrounding molecules is quantified in percentage. Here, %V ｂｕｒ does not contain an ionic center (e.g., [Br － ]%V ｂｕｒ is zero. ), and the influence of hydrogen atoms is not taken into account. The remaining calculation conditions are set to the default values ​​of the library. The default values ​​are as follows: radii = None, radii_type = 'bondi', radii_scale = 1.17, density = 0.001, z_axis_atoms = None, xz_plane_atoms = None.

[0065] For example, the SMILES of [C2epyr] is expressed as [N+]1(CC)(CC)CCCC1, so [N+] is the central atom of the steric hindrance. However, if Python 3.9.13 and RdKit 2022.03.5 are unable to read the SMILES and generate the structure, the ionic center cannot be determined. When dealing with such ions, the steric hindrance is calculated by specially placing a pseudomolecule at the center of mass. Examples of ions for which the ionic center cannot be determined include carborane anions.

[0066] How to determine the ionic center: There are various ways to determine the ionic center atom, so it is determined according to the following procedure. For positively or negatively charged resonance structures, first, the following elements are defined as the ionic center, starting from the left. However, for elements not listed, priority is given to elements with a larger group and period in the element table. For anions: B, Al, P, As, Sb, Te, N, C, S, O For cations: Fe, Sn, Mo, N, P, S

[0067] Next, when there are two or more atoms that can be ionic centers in a resonance structure such as imidazole, the ionic centers are determined so that the number of covalent bonds between the ionic centers is minimized. For example, the following example is given:

[0068]

[0069] Finally, after expressing it in SMILES, load SMILES using the Python library RdKit and confirm that the structure can be generated. In the case of a non-covalent bond such as metallocene, it is expressed as, for example, [Fe+]. C1=CC=CC1.1C1=CC=CC1. For molecules such as carborane whose structure cannot be generated from SMILES, a dummy atom with zero volume / mass is placed at the coordinate center of gravity to make it the ion center.

[0070] [Method for Producing Ionic Conductor] The ionic conductor according to the first aspect of the present invention can be produced, for example, by dissolving and mixing an ionic plastic crystal, a zwitterionic compound, and, if necessary, a metal salt or other components in a dehydrated solvent, and then removing the solvent. The solvent is preferably a good solvent for each component, non-reactive, and volatile, so that it can be easily removed. One type of solvent may be used alone, or two or more types may be used in combination.

[0071] Another manufacturing method involves mixing and dissolving a zwitterionic compound, and optionally a metal salt or other components, into molten ionic plastic crystals. When using this method, the temperature for mixing and melting the crystals should be below the thermal decomposition temperature of each component, and can be appropriately selected or set by those skilled in the art. In either method, moisture absorption can impair the electrolyte's performance, so all operations must be performed in a low-humidity environment, such as a dry room or glove box.

[0072] [Ionic Conductor According to Second Aspect] The ionic conductor according to the second aspect of the present invention contains an ionic plastic crystal and a metal salt. The metal salt is used to partially destroy the crystal structure of the ionic plastic crystal. It is believed that at least a portion of the crystal structure originally possessed by the ionic plastic crystal is replaced by the metal salt or its cations or anions. Furthermore, the ionic conductor of the present invention is preferably a solid ionic conductor. Whether or not a material is a solid ionic conductor is determined by whether or not the temperature dependence of ionic conductivity follows the Arrhenius process. The ionic conductor according to the second aspect of the present invention will be described below.

[0073] [Ionic Plastic Crystal] In the ionic conductor according to the second aspect of the present invention, an ionic plastic crystal similar to the ionic plastic crystal described in the description of the conductor according to the first aspect of the present invention can be used.

[0074] [Metal Salt] The metal salt is a component for improving the ionic conductivity of an ionic conductor containing ionic plastic crystals. From the viewpoint of intentionally introducing defects that partially destroy the crystal structure of the ionic plastic crystals, the metal salt preferably satisfies the following two independent parameters:

[0075] (Steric hindrance) A metal salt suitable for partially destroying the crystal structure of an ionic plastic crystal is one having a steric hindrance %V ｂｕｒ For example, the steric hindrance % V of the metal salt is preferably high. ｂｕｒThe higher the steric hindrance %V of the metal salt, the more likely the crystal structure of the ionic plastic crystal is to be partially destroyed by the presence of the metal salt. Therefore, due to defects in the crystal structure of the ionic plastic crystal, the frequency factor is likely to increase and the ionic conductivity is likely to improve. ｂｕｒ The lower limit of the steric hindrance %V of the metal salt is not particularly limited, but may be 60% or more, 65% or more, 68% or more, 80% or more, or 90% or more. ｂｕｒ The upper limit of is not particularly limited, but may be 100% or less. The above upper and lower limits can be combined arbitrarily. For example, it may be 60 to 100%, 65 to 100%, 68 to 100%, 80 to 100%, or 90 to 100%.

[0076] In the second aspect of the present invention, the steric hindrance %V ｂｕｒ is calculated by the Python library morpheus for a structure that has been energy-minimized by quantum chemistry calculations using ωB97XD as the functional and def2TZVP as the basis set. The energy-minimized structure is calculated as the lowest energy structure using the quantum chemistry calculation package Gaussian16, using ωB97XD as the functional and def2TZVP as the basis set.

[0077] Steric hindrance %V ｂｕｒ is calculated based on the ion center as follows: ｂｕｒ The structural information obtained by the structural optimization and the Percent Buried Volume (%V) were calculated using the programming language Python 3.9.13 and the Python library morpheus 0.7.2. ｂｕｒ ) is calculated as

[0078] More specifically, when the energy-minimized structure is expressed in SMILES, a three-dimensional sphere with a radius of 2.5 Å is drawn around an atom with a positive or negative charge (ionic center). The steric hindrance %V is an index that quantifies, in percentage, the degree to which the three-dimensional sphere is occupied by the van der Waals radii of the surrounding molecules.ｂｕｒ is.

[0079] Steric hindrance %V ｂｕｒ does not include ionic centers, but the influence of hydrogen atoms is not taken into account. For example, [Br － ] steric hindrance % V ｂｕｒ is zero. The remaining calculation conditions are set to the default values ​​of the library. The default values ​​are as follows: radii = None, radii_type = 'bondi', radii_scale = 1.17, density = 0.001, z_axis_atoms = None, xz_plane_atoms = None.

[0080] As an example, the calculation details are shown for [C2epyr] having the following chemical structure.

[0081]

[0082] The SMILES of [C2epyr] is expressed as [N+]1(CC)(CC)CCCC1. Therefore, [N+] is the central atom of the steric hindrance. However, if Python 3.9.13 and RdKit 2022.03.5 cannot read the SMILES or generate the structure, the ionic center cannot be determined. When dealing with such ions, steric hindrance is calculated by specially placing a pseudomolecule at the center of mass. Examples of ions for which the ionic center cannot be determined include carborane anions.

[0083] (Molecular Volume) Metal salts suitable for partially destroying the crystal structure of ionic plastic crystals preferably have a large volume. For example, the ratio of the volume of the anions of the ionic plastic crystal to the volume of the anions of the metal salt (volume of anions of ionic plastic crystals / volume of anions of metal salt) is preferably 1.3 to 4.8, more preferably 1.3 to 3.5, and even more preferably 1.5 to 3.0. The larger the volume of the anions of the metal salt is compared to the volume of the anions of the ionic plastic crystals, the more likely it is that the crystal structure of the ionic plastic crystals will be partially destroyed by the presence of the metal salt. Therefore, defects in the crystal structure of the ionic plastic crystals tend to increase the frequency factor and improve ionic conductivity.

[0084] The molecular volumes of the ionic plastic crystal and the metal salt can be calculated in the same manner as in the calculation of the molecular volume in the explanation of the conductor of the first embodiment of the present invention.

[0085] [Metal Salt] In the conductor according to the second embodiment of the present invention, the metal salt preferably includes at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts, more preferably at least one selected from the group consisting of lithium salts, sodium salts, potassium salts, calcium salts and magnesium salts, and even more preferably at least one selected from lithium salts, sodium salts and magnesium salts.

[0086] Examples of lithium salts include lithium bis(fluoromethanesulfonyl)amide (LiN(SO ２ CH ２ F) ２ ), lithium bis(trifluoromethanesulfonyl)amide (LiN(SO ２ CF ３ ) ２ ), lithium bis(2,2,2-trifluoroethanesulfonyl)amide (LiN(SO ２ C ２ H ２ F ３ ) ２ ), lithium bis(pentafluoroethanesulfonyl)amide (LiN(SO ２ C ２ F ５ ) ２ ), lithium bis(fluorosulfonyl)amide (LiN(SO ２ F) ２ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(SO ２ CF ３ ) ３ ), lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium bis(oxalato)borate (LiB(C) ２ O４ ) ２ ), lithium perchlorate (LiClO ４ ), lithium hexafluoroarsenate (LiAsF ６ However, the lithium salt is not limited to these examples. One type of lithium salt may be used alone, or two or more types may be used in combination.

[0087] Examples of sodium salts include sodium bis(fluorosulfonyl)amide (NaN(SO ２ F) ２ ), sodium bis(trifluoromethanesulfonyl)amide (NaN(SO ２ CF ３ ) ２ However, the sodium salt is not limited to these examples. One type of sodium salt may be used alone, or two or more types may be used in combination.

[0088] Examples of magnesium salts include bis(fluorosulfonyl)imide magnesium (Mg[N(SO ２ F) ２ ]), magnesium bis(trifluoromethanesulfonyl)imide (Mg[N(SO ２ CF ３ ) ２ However, the magnesium salt is not limited to these examples. One type of magnesium salt may be used alone, or two or more types may be used in combination.

[0089] The anion of the metal salt preferably contains an anion represented by the following formula (B5): ｎ ...Formula (B5)

[0090] In formula (B5), M is a boron atom or an aluminum atom, R is each independently a halogen atom or a halogenated hydrocarbon group which may have a heteroatom, and n is an integer of 4 or less.

[0091] When R is a halogen atom, the anion represented by formula (B5) is not particularly limited, but examples thereof include haloborate and haloaluminate.

[0092] Examples of haloborates include tetrafluoroborate anions (BF ４ － However, the haloborates are not limited to these examples.

[0093] Examples of haloaluminates include tetrafluoroaluminate anions (AlF ４ － However, the haloaluminates are not limited to these examples.

[0094] When R is a halogenated hydrocarbon group, the anion represented by formula (B5) is not particularly limited, and examples thereof include haloalkylborate, haloarylborate, haloalkylaluminate, and haloarylaluminate.

[0095] Examples of haloalkylborates include tetrakis(pentafluoroethyl)borate anions ((C ２ F ５ ) ４ B － However, the haloalkyl borate is not limited to these examples.

[0096] Examples of haloarylborates include tetrakis(pentafluorophenyl)borate ((C ６ F ５ ) ４ B － ), tetrakis(bistrifluoromethylphenyl)borate anion ((C ８ F ６ H ３ ) ４ B － However, the haloaryl borate is not limited to these examples.

[0097] Examples of haloalkylaluminates include tetrakis(pentafluoroethyl)aluminate anions ((C ２ F ５ ) ４ Al － However, the haloalkylaluminates are not limited to these examples.

[0098] Examples of haloaryl aluminates include tetrakis(pentafluorophenyl)aluminate ((C ６ F ５ ) ４ Al － However, the haloaryl aluminates are not limited to these examples.

[0099] When R is a halogenated hydrocarbon group having a hetero atom, the anion represented by formula (B5) is not particularly limited, and examples thereof include haloalkoxyborate, haloaryloxyborate, haloalkoxyaluminate, and haloaryloxyaluminate.

[0100] Examples of haloalkoxyborates include tetrakis(hexafluoroisopropoxy)borate anions ((C ３ F ６ H.O.) ４ B － ), tetrakis(trifluoroethoxy)borate anion ((C ２ F ３ H ２ O) ４ B － ), bis(dodecafluoropinacolato)borate anion ((C ６ F １２ O ２ ) ２ B － However, the haloalkoxyborates are not limited to these examples.

[0101] Examples of haloaryloxyborates include bis(hexafluorobiphenolato)borate anions ((C １２ F ６ H ２ O ２ ) ２ B － However, the haloaryloxyborate is not limited to these examples.

[0102] Examples of haloalkoxyaluminates include tetrakis(hexafluoroisopropoxy)aluminate anions ((C３ F ６ H.O.) ４ Al － ), tetrakis(trifluoroethoxy)aluminate anion ((C ２ F ３ H ２ O) ４ Al － ), bis(dodecafluoropinacolato)aluminate anion ((C ６ F １２ O ２ ) ２ Al － ), tetrakis(nonafluorot-butoxy)aluminate anion ((C ４ F ９ O) ４ Al － However, the haloalkoxyaluminate is not limited to these examples.

[0103] Examples of haloaryloxyaluminates include bis(hexafluorobiphenolato)aluminate anions ((C １２ F ６ H ２ O ２ ) ２ Al － However, the haloaryloxyaluminates are not limited to these examples.

[0104] The anion of the metal salt is not particularly limited, but preferably contains an anion represented by the following formula (B1).

[0105] [(R ｎ M) ｊ L ｊ－１ ] ｃ－ (B1)

[0106] In formula (B1), each R is independently a halogen atom or a hydrocarbon group which may have a heteroatom, M is B, Al, P, C, N, As, Sb, or Te, L is an imidazole ring which may be substituted with a halogen atom or a hydrocarbon group which may have a heteroatom, and R may be bonded to each other. n is an integer of 6 or less, c is an integer of 1 or more, and j is 1 or 2. However, when j is 2, M is B, Al, P, As, Sb, or Te.

[0107] When j in the formula (B1) is 1, the anion of the metal salt is preferably an anion represented by the following formula (B2).

[0108]

[0109] In formula (B2), each Z is independently a halogen atom or a hydrocarbon group which may have a heteroatom, M is B, Al, P, C, N, As, Sb, or Te, and each W is independently a halogen atom or a hydrocarbon group which may have a heteroatom. p is an integer of 0 to 3, q ​​is an integer of 0 to 6, and satisfies 3≦2p+q≦6. c is an integer of 1 or greater.

[0110] When j in the formula (B1) is 2, the anion of the metal salt is preferably an anion represented by the following formula (B3).

[0111]

[0112] In formula (B3), M １ , M ２ are each independently B, Al, P, As, Sb or Te, and W １ , W ２ are each independently a hydrocarbon group which may have a halogen atom or a heteroatom, and Z １ , Z ２ are each independently a halogen atom or a hydrocarbon group which may have a heteroatom, and L is an imidazole ring which may be substituted with a halogen atom or a hydrocarbon group which may have a heteroatom.

[0113] In formula (B3), p1 is an integer of 0 to 3, q1 is an integer of 0 to 6, and satisfies 3≦2p1+q1≦5. p2 is an integer of 0 to 3, q2 is an integer of 0 to 6, and satisfies 3≦2p2+q2≦5. c is an integer of 1 or more.

[0114] Among these, at least one selected from the group consisting of anions represented by the following formula (BA1), anions represented by the following formula (BA2), anions represented by the following formula (BA3), anions represented by the following formula (BA4), anions represented by the following formula (BA5), anions represented by the following formula (BA6), anions represented by the following formula (BA7), anions represented by the following formula (BA8), anions represented by the following formula (BA9), anions represented by the following formula (BA10), and anions represented by the following formula (BA11) are preferred.

[0115]

[0116] The metal salt may be prepared by preparation or may be purchased commercially.

[0117] [Other Components] The ionic conductor according to the second aspect of the present invention may further contain other components in addition to the ionic plastic crystals and the metal salt.

[0118] As the other components, the same types of other components as those described in the description of the conductor according to the first embodiment of the present invention can be used.

[0119] [Composition] As already explained, the metal salt is used to partially destroy the crystal structure of the ionic plastic crystal. It is believed that at least a part of the crystal structure originally possessed by the ionic plastic crystal is replaced by the cation or anion of the metal salt. Like the metal salt, other components may also be incorporated into part of the crystal structure originally possessed by the ionic plastic crystal, but are not necessarily limited to such a crystal structure.

[0120] The molar ratio of metal salt to ionic plastic crystal (metal salt / ionic plastic crystal) is not particularly limited, as it can be changed appropriately depending on the ionic species of each component, but for example, 0.1 to 24 mol% is preferable, 2 to 12 mol% is more preferable, and 4 to 6 mol% is even more preferable. If the molar ratio (metal salt / ionic plastic crystal) is equal to or greater than the lower limit of the above-mentioned numerical range, an ionic conductor with improved conductivity is likely to be obtained. If the molar ratio (metal salt / ionic plastic crystal) is equal to or less than the upper limit of the above-mentioned numerical range, an ionic conductor with improved conductivity is likely to be obtained.

[0121] [Characteristics] The ionic conductor according to the second aspect of the present invention preferably has an ionic conductivity at 30° C. higher than the ionic conductivity of the ionic plastic crystal alone at 30° C. That is, the ionic conductor of the present invention preferably satisfies the relationship of the following formula (BI):

[0122] (ionic conductivity of ionic conductor at 30°C) / (ionic conductivity of ionic plastic crystal at 30°C)>1... Formula (BI)

[0123] The ionic conductivity is calculated by measuring impedance by an AC impedance method (measurement frequency: 4 Hz to 8 MHz, applied voltage: 100 mV) using an LCR meter (product of Hioki E.E. Corporation: IM3536). Details of the conditions for the calculation are as described in the Examples.

[0124] The ionic conductor of the present invention preferably has a frequency factor higher than that of the ionic plastic crystal alone. That is, the ionic conductor of the present invention preferably satisfies the relationship of the following formula (BII): (frequency factor of ionic conductor) / (frequency factor of ionic plastic crystal)>1 ... formula (BII)

[0125] The frequency factor is calculated by measuring impedance by an AC impedance method (measurement frequency: 4 Hz to 8 MHz, applied voltage: 100 mV) using an LCR meter (product of Hioki E.E. Corporation: IM3536). Details of the conditions for calculation are as described in the Examples.

[0126] [Preferable Combination of Ionic Plastic Crystal and Metal Salt] As already explained, the metal salt is used to partially destroy the crystal structure of the ionic plastic crystal. In one example, it is considered that at least a part of the crystal structure originally possessed by the ionic plastic crystal has its anion replaced by the anion of the metal salt. Therefore, it is preferable that the anion of the metal salt is bulkier than the anion of the ionic plastic crystal.

[0127] [Method for producing ionic conductor] The ionic conductor can be produced, for example, by dissolving and mixing the ionic plastic crystal, metal salt, and, if necessary, other components in a dehydrated solvent, and then removing the solvent. The solvent is preferably a good solvent for each component, non-reactive, and volatile, so that it can be easily removed. One solvent may be used alone, or two or more solvents may be used in combination.

[0128] Another production method involves mixing and dissolving a metal salt and, if necessary, other components into molten ionic plastic crystals. When using this method, the temperature for mixing and melting may be selected or set appropriately by those skilled in the art as long as it is below the thermal decomposition temperature of each component. In either method, moisture absorption impairs the electrolyte's performance, so all operations must be performed in a low-humidity environment such as a dry room or glove box.

[0129] The ionic conductor of the present invention (which collectively refers to the ionic conductor according to the first aspect of the present invention and the ionic conductor according to the second aspect of the present invention) can be suitably used as a solid electrolyte. In particular, the ionic conductor of the present invention is suitable as an electrode or electrolyte material for a high ionic conductivity electricity storage device or a secondary battery.

[0130] The secondary battery has a positive electrode, a negative electrode, and the ionic conductor of the present invention. The ionic conductor in the secondary battery functions as a solid electrolyte. In a typical secondary battery, the ionic conductor is located between the positive electrode and the negative electrode and is responsible for ionic conduction.

[0131] The positive electrode usually has a positive electrode current collector and a positive electrode active material layer.

[0132] The positive electrode current collector supports the positive electrode active material layer and transfers electrons to and from the positive electrode active material. The material of the positive electrode current collector is not particularly limited. Examples of the material include metal materials such as aluminum, nickel, iron, stainless steel, titanium, and copper, and conductive polymers.

[0133] The positive electrode active material layer is a layer formed on the surface of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material include LiMn ２ O ４ , LiCoO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２ (e.g., LiNi １／３ Mn １／３ Co １／３ O ２ ), and inorganic active materials in which part of these transition metals is substituted with other elements.

[0134] The positive electrode active material layer may further contain an additive in addition to the positive electrode active material. Examples of the additive for the positive electrode active material layer include binders such as polyvinylidene fluoride, synthetic rubber binders, and epoxy resins; conductive additives such as carbon black, graphite, and vapor-grown carbon fiber; and ion-conductive polymers such as polyethylene oxide (PEO)-based polymers, polypropylene oxide (PPO)-based polymers, polyethylene carbonate (PEC)-based polymers, and polypropylene carbonate (PPC)-based polymers.

[0135] The negative electrode usually has a negative electrode current collector and a negative electrode active material layer. However, the negative electrode may be composed of only the negative electrode active material layer. That is, the negative electrode active material layer may also function as the negative electrode current collector. The negative electrode current collector supports the negative electrode active material layer and is responsible for transferring electrons to and from the negative electrode active material. Examples of materials for the negative electrode current collector include the same materials as those listed as materials for the positive electrode current collector.

[0136] The negative electrode active material layer is a layer formed on the surface of the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon; Li ４ Ti ５ O１２ lithium metal; lithium-metal alloys such as lithium-tin or lithium-silicon alloys; tin materials and other elements, alloys and compounds; sodium, potassium, magnesium and other elements, alloys and compounds of metals in Group 1 or 2 of the periodic table; sulfur or composite materials using these materials in combination.

[0137] The negative electrode active material layer may further contain an additive in addition to the negative electrode active material. Examples of the additive for the negative electrode active material layer include the same additives as those shown as additives for the positive electrode active material layer.

[0138] The secondary battery may have a separator between the positive electrode and the negative electrode. The separator prevents short circuits by electronically insulating the positive electrode and the negative electrode, allowing only ion movement. Examples of materials for the separator include porous bodies formed from insulating plastics such as polyethylene, polypropylene, and polyimide, and inorganic fine particles such as silica gel. The method for manufacturing the secondary battery is not particularly limited, and it can be manufactured according to a conventionally known method.

[0139] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[0140] 1. Experimental Example 1 [Material] (Ionic plastic crystal)

[0141]

[0142] [C2epyr] ＋ [FSI] － (Compound A1) was synthesized according to the literature: Electrochim. Acta 2019, 303, 293. The NMR spectrum was consistent with the literature.

[0143] (Zwitterionic Compounds)

[0144] (Synthesis Example 1)

[0145]

[0146] Compound 2 (22.9 mmol, 8.52 g) synthesized according to the literature Polymer Chemistry (2017), 8 (37), 5660-5665 was weighed into a 100 mL four-neck flask, 1-ethylimidazole (Tokyo Chemical Industry Co., Ltd.) (20.8 mmol, 2.0 g) and the literature Polymer Chemistry (2017), 8 (37), 5660-5665. 20 mL of acetonitrile was added and stirred at 80 ° C. for 10 hours. The reaction solution was cooled to room temperature, the precipitate was removed by filtration, and the filtrate was concentrated under reduced pressure to obtain a pale orange oil. 20 mL of methanol was added to the oil and stirred at room temperature for 1 hour. The precipitated crystals were collected by filtration and dried under reduced pressure at 80 ° C. to obtain 6.38 g of the target white crystals (ZA0: yield 89%, compound A2).

[0147] m. p. :137-140℃. １ H-NMR (400MHz, DMSO-d ６ ) δ: 9.18 (s, 1H), 7.81 (s, 1H), 7.79 (s, 1H), 4.29 (t, 2H, J = 7.0), 4.19 (q, 2 H, J = 10.0), 3.01 (t, 2H, J = 10.0), 2.25-2.18 (m, 2H), 1.42 (t, 3H, J = 7.0), １９ F-NMR (DMSO-d ６ ) δ: -77.52 (3F, CF ３ ); ESI-MS: m / z (+) 350.0 [M+1] ＋

[0148] (Synthesis Example 2)

[0149]

[0150] Into a 100 mL four-neck flask, 1-methylpyrrolidine (Tokyo Chemical Industry Co., Ltd.) (94.0 mmol, 8.0 g) and compound 2 (23.5 mmol, 8.75 g) synthesized according to the literature Polymer Chemistry (2017), 8 (37), 5660-5665 were weighed and stirred at 60 ° C. for 10 hours. The reaction solution was cooled to room temperature, the precipitate was removed by filtration, and the filtrate was concentrated under reduced pressure. Next, 80 mL of tert-butyl methyl ether was added and the precipitated crystals were filtered off, and the filtrate was concentrated under reduced pressure to obtain an orange oil. 60 mL of ethyl acetate and 10 mL of methanol were added to the oil, and the crystals were suspended and washed. The precipitated crystals were collected by filtration, and then 20 mL of acetonitrile was added and recrystallized. The precipitated crystals were collected by filtration and dried under reduced pressure at 80 ° C. to obtain 25.6 g of the desired white crystals (ZA7: yield 80.2%, compound A3).

[0151] m. p. :103-104, 171-175℃. １ H-NMR (400MHz, DMSO-d ６ ) δ: 3.507-3.34 (m, 6H), 3.08 (t, 2H, J = 10.0), 3.00 (s, 3H), 2.15-2.08 (m, 6H), １９ F-NMR (DMSO-d ６ ) δ: -77.52 (3F, CF ３ ); ESI-MS: m / z (+) 339.0 [M+1] ＋

[0152] (metal salts)

[0153]

[0154] Lithium bis(fluorosulfonyl)imide (LiFSI) was a reagent manufactured by Tokyo Chemical Industry Co., Ltd.

[0155] [Measurement Method] (Raman Scattering Spectroscopy) Raman scattering spectroscopy was performed using a palmtop Raman spectrophotometer PR-1w manufactured by JASCO Corporation. Measurements were performed outdoors in a dry atmosphere at temperatures below -40°C. 20 mg of sample was placed on a SUS sample holder using a spoon, and the instrument was placed on top of the sample, and the spectrum of the scattered light obtained was analyzed. The signal of the SNS vibration of the FSA anion was observed at 650 to 800 cm －１The state of the anion differs depending on the wave number of the peak. －１ , and if paired with one Li cation, 732 cm －１ , and 746 cm if it forms aggregates with two or more Li cations. －１ It is described that a peak appears in this wavelength range. The spectrum obtained by measurement was normalized within this wavelength range, and the wave numbers of the peaks that appear were compared.

[0156] (DSC Measurement Method) DSC measurements were performed using a DSC600 (manufactured by Hitachi High-Technologies Corporation). Approximately 10 mg of a sample was sealed in an SUS high-pressure sealed container, and measurements were performed under a nitrogen gas flow rate of 30 mL / min, at a temperature range of −120 to 150° C., and at a temperature increase / decrease rate of 5° C. / min.

[0157] (Method for measuring the plastic crystal temperature range) The plastic crystal temperature range was measured by measuring the solid phase transition temperature and melting point by DSC (differential scanning calorimetry). The DSC measurement was performed using a DSC600 (manufactured by Hitachi High-Tech Corporation). Approximately 10 mg of the sample was sealed in an SUS high-pressure sealed container, and measurement was performed under a nitrogen gas flow rate of 30 mL / min, at a temperature range of -120 to 150°C, and at a temperature increase / decrease rate of 5°C / min, and the plastic crystal temperature range was determined from the solid phase transition temperature and melting point in the second heating.

[0158] (Ionic Conductivity) To avoid the effects of moisture absorption, an impedance measurement cell was prepared in a dry room with a dew point of -50°C or below. The detailed procedure is described below. First, a cell was prepared by sandwiching the ionic conductor obtained in each example between two sheets of ITO-coated glass (50 mm x 50 mm, 0.7 mm thick). During cell preparation, polyimide tape (0.15 mm thick) was used as a spacer to adjust the thickness of the ionic conductor to 0.19 to 0.25 mm. Next, the impedance measurement cell was connected to an LCR meter (HIOKI EE Corporation product: IM3536). The resistance value of the ionic conductor was determined by AC impedance measurement (measurement frequency: 4 Hz to 8 MHz, applied voltage: 100 mV). The ionic conductivity at 30°C was calculated from the resistance value of the ionic conductor and the thickness and area of ​​the ionic conductor in the impedance measurement cell. Impedance measurements were also performed in a dry room with a dew point of -50°C or below to avoid the effects of moisture absorption. In Experimental Example 1, the ionic conductivity of Experimental Example 1-7 is expressed as a relative value, with Experimental Example 2's ionic conductivity of Experimental Example 2-1 being 100, and in Experimental Example 3's ionic conductivity of Comparative Example 3-1 being 100. Furthermore, the activation energy is expressed as a relative value, with Experimental Example 1's activation energy of Experimental Example 1-7 being 100, and Experimental Example 2's activation energy of Experimental Example 2-1 being 100.

[0159] (Ratio of steric hindrance and molecular volume of compound A2 to compound A1) For compound A1, the SMILES of [C2epyr] was determined to be [N+]1(CC)(CC)CCCC1, the SMILES of [FSI] was determined to be [N-](S(=O)(=O)CF)S(=O)(=O)CF, and the molecular volume and the steric hindrance around the ion center and molecular volume were calculated based on the calculation method described above. The SMILES of compound A2 was determined to be O=S([N-]S(=O)(CCC[N+]1=CN(CC)C=C1)=O)(C(F)(F)F)=O based on the rules described above, and the partial structures and fragment structures of the cation and anion were extracted based on the calculation method described above, and the steric hindrance, partial volume, and fragment volume were calculated. From the above results, the steric hindrance ratio r of compound A2 to compound A1 was calculated. ａ and rｃ , the ratio r of the partial volume of compound A2 to the molecular volume of compound A1 ｐ Ａ and r ｐ Ｃ , the ratio r of the fragment volume of compound A2 to the molecular volume of compound A1 ｆ Ａ and r ｆ Ｃ The results are shown in Table 1.

[0160] (Ratio of steric hindrance and molecular volume of compound A3 to compound A1) The same applies to compound A1. The SMILES of compound A3 was determined to be O=S([N-]S(=O)(CCC[N+]1(CCCC1)C)=O)(C(F)(F)F)=O based on the above rules, and the partial structures and fragment structures of the cation and anion were extracted based on the above calculation method, and the steric hindrance, partial volume, and fragment volume were calculated. From the above results, the ratio r of steric hindrance of compound A3 to compound A1 was calculated. ａ and r ｃ , the ratio r of the partial volume of compound A3 to the molecular volume of compound A1 ｐ Ａ and r ｐ Ｃ , the ratio r of the fragment volume of compound A3 to the molecular volume of compound A1 ｆ Ａ and r ｆ Ｃ The results are shown in Table 1.

[0161] [Experimental Example 1-7] [C2 epiry] ＋ [FSI] － 1.168 g of (Compound A1) was dissolved in 22.128 g of a solvent (acetonitrile), and then the solution was stirred for 2 hours using an ultrasonic cleaner, dried overnight in dry air, and then vacuum dried at 80°C for 1 day using a vacuum dryer to remove the solvent, thereby producing an ionic conductor of Experimental Example 1-7.

[0162] [Experimental Examples 1-1 to 1-6] [C2 epiry] ＋ [FSI] －Solution A1 was prepared by dissolving 0.699 g of (compound A1) in 13.288 g of solvent (acetonitrile). Solution A2 was prepared by dissolving 0.027 g of LiFSI in 0.481 g of solvent (acetonitrile). Solution A3 was prepared by dissolving 1.317 g of compound A2 in 25.028 g of solvent (acetonitrile). Solutions A1, A2, and A3 were mixed, stirred using a mixer rotor for 1 hour, then using an ultrasonic cleaner for 2 hours, and aerated and dried overnight in dry air. The mixture was then vacuum-dried at 80°C for 1 day in a vacuum dryer to remove the solvent, thereby preparing the ionic conductor of Experimental Example 1-3. In Experimental Examples 1-4 to 1-6, the ionic conductors of each example were prepared under the same conditions as Experimental Example 1-3, except that the composition was changed as shown in Table 1. In Experimental Examples 1-1 and 1-2, ionic conductors were prepared without using metal salts.

[0163]

[0164] The ionic conductivities of the ionic conductors of Experimental Examples 1-1 to 1-6, which contained a zwitterionic compound, were improved compared to the ionic conductor of Experimental Example 1-7, which did not contain a zwitterionic compound. In particular, the ionic conductivities of the ionic conductors of Experimental Examples 1-3 to 1-6, which further contained a metal salt in addition to a zwitterionic compound, were even improved compared to the ionic conductors of Experimental Examples 1-1 and 1-2.

[0165] From this, it is expected that the presence of zwitterions distorts the crystal structure of the ionic plastic crystal, increasing its conductivity. Although Experimental Examples 1-3 and 1-4 have similar molecular structures, their slight differences reveal that they achieve improved conductivity through different design concepts.

[0166] FIG. 2 shows the Raman spectra for Experimental Example 1-7 and the following Experimental Example 2-1. －１The peak around 1000 Hz corresponds to the case where [Li] and [FSA] are not dissociated. On the other hand, the ionic plastic crystal [C2epyr][FSI] and the ionic plastic crystal obtained by adding [Li][FSI] to [C2epyr][FSI] exhibit a peak at lower frequencies, suggesting that the [FSI] ion is close to being completely dissociated. Therefore, unlike polymer electrolytes, the improvement in conductivity is not related to the dissociation of ions, but is assumed to originate from the disruption of the crystal structure by zwitterions.

[0167] 2. Experimental Example 2 (Synthesis Example 3) (ZA1: Compound A4) was obtained in the same manner as in Synthesis Example 1, except that 1-methylpiperidine was used instead of 1-ethylimidazole.

[0168]

[0169] Synthesis Example 4 (ZA3: Compound A5) was obtained in the same manner as in Synthesis Example 1, except that 1-methylimidazole was used instead of 1-ethylimidazole.

[0170]

[0171] Synthesis Example 5 (ZA8: Compound A6) was obtained in the same manner as in Synthesis Example 1, except that 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene was used instead of 1-ethylimidazole.

[0172]

[0173] [Experimental Example 2-1] [C2 epiry] ＋ [FSI] － 1.168 g of (Compound A1) was dissolved in 22.128 g of a solvent (acetonitrile). Subsequently, 0.052 g of LiFSI was dissolved in 0.951 g of a solvent (acetonitrile). 19.417 g of the former and 0.590 g of the latter were mixed, stirred for 1 hour using a mix rotor, then stirred for 2 hours using an ultrasonic cleaner, and dried overnight in dry air. After that, the solvent was removed by vacuum drying at 80°C for 1 day in a vacuum dryer, thereby producing an ionic conductor of Experimental Example 2-1.

[0174] [Experimental Examples 2-2 to 2-5] [C2epyr] ＋ [FSI] － 0.699 g of (compound A1) was dissolved in 13.288 g of solvent (acetonitrile) to prepare solution A1. 0.027 g of LiFSI was dissolved in 0.481 g of solvent (acetonitrile) to prepare solution A2. 1.317 g of compound A2 was dissolved in 25.028 g of solvent (acetonitrile) to prepare solution A3. Solutions A1, A2, and A3 were mixed, stirred using a mixer rotor for 1 hour, then using an ultrasonic cleaner for 2 hours, and aerated and dried overnight in dry air. The mixture was then vacuum dried at 80°C for 1 day in a vacuum dryer to remove the solvent, thereby preparing the ionic conductor of Experimental Example 2-2. In Experimental Examples 2-3 to 2-5, the ionic conductors of each example were prepared under the same conditions as Experimental Example 1-3, except that the composition was changed as shown in Table 1.

[0175]

[0176] The zwitterions contained in the ionic conductor were changed to measure the thermal properties and conductivity. By controlling the distortion of the crystal structure due to the presence of zwitterions, an ionic conductor with a high melting point and excellent thermal stability could be produced. Furthermore, the ionic conductor was able to improve ionic conductivity while reducing activation energy. In particular, in Experimental Example 2-2, the temperature range in which the plastic crystal phase was expressed was wide. This suggests that the zwitterions distorted the crystal structure and became compatible with the plastic crystal, significantly reducing the activation energy. Meanwhile, comparing Experimental Example 2-1 with Experimental Examples 2-2 to 2-5, it was found that the melting point remained almost unchanged despite the addition of zwitterions to the plastic crystal. This suggests that the conductivity of ionic plastic crystals can be improved while reducing the destruction of the crystal structure.

[0177] 3. Experimental Example 3 [Material] (Ionic plastic crystal)

[0178]

[0179] The compound A1 used in Experimental Example 1 was used as the compound B1 in Experimental Example 3.

[0180] (metal salts)

[0181]

[0182]

[0183] [Measurement Method] (Ionic Conductivity) Ionic conductivity was measured in the same manner as in Experimental Example 1.

[0184] [Example 3-1] [C2 epir] ＋ [FSI] － 0.999 g of (Compound B1) was dissolved in 18.997 g of acetonitrile (lithium battery grade, manufactured by Kishida Chemical Co., Ltd.), and LiB(HFIP) ４ 0.044 g of the ammonium hydroxide solution was dissolved in 0.813 g of acetonitrile to prepare a standard solution. 5.238 g of the former and 0.771 g of the latter were mixed for 1 hour using a mix rotor, and then stirred for 2 hours using an ultrasonic cleaner. The mixture was then aerated and dried overnight in dry air, and then dried at 80 °C for one day using a vacuum dryer to remove the solvent, thereby producing the ionic conductor of Example 3-1.

[0185] [Example 3-2, Comparative Example 3-1] Ion conductors of each example were produced under the same conditions as in Example 3-1, except that the composition was changed as shown in Table 3. In Comparative Example 3-1, the ion conductor was produced without using any metal salt.

[0186]

[0187] The ionic conductors of Examples 3-1 and 3-2 containing a metal salt had improved ionic conductivity compared to the ionic conductor (ionic plastic crystal) of Comparative Example 3-1 containing no metal salt.

[0188] The ionic conductivity of ionic plastic crystals follows the Arrhenius equation, which is σ = A × exp(-E / RT), where σ is the ionic conductivity, A is the frequency factor, E is the activation energy, R is the gas constant, and T is the absolute temperature.

[0189] In Example 3-1, [C2 epir] ＋ [FSI] － The crystal structure of LiB(HFIP) ４It is considered that the substantial carrier concentration increased as a result of defects occurring in the crystal structure due to partial destruction by the ions. It is presumed that the ionic conductivity improved compared to Comparative Example 3-1 due to the increase in the frequency factor.

[0190] In Example 3-2, [C2 epir] ＋ [FSI] － It is considered that the crystal structure of the above-mentioned compound was partially destroyed by LiFEA, causing defects in the crystal structure, resulting in an increase in the substantial carrier concentration. It is presumed that the increase in the frequency factor resulted in an improvement in ionic conductivity compared to Comparative Example 3-1.

[0191] While the present invention has been described above with reference to specific embodiments, these embodiments are presented as examples and do not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways within the scope of the effects of the invention, and can be combined with features described in other embodiments within the scope of feasibility.

[0192] According to the present invention, a novel ionic conductor containing ionic plastic crystals can be provided.

Claims

1. An ionic conductor comprising an ionic plastic crystal and a zwitterionic compound.

2. The ionic conductor according to claim 1, wherein the temperature range in which the ionic plastic crystal contained in the ionic conductor exhibits a plastic crystal phase is 60 to 100, where the temperature range in which the ionic plastic crystal contained in the ionic conductor exhibits a plastic crystal phase is 100.

3. The ionic conductor according to claim 1, wherein the ionic conductivity at 30°C is higher than the ionic conductivity at 30°C of said ionic plastic crystal.

4. The steric hindrance %V of the cations contained in the ionic plastic crystal ｂｕｒ % V of the steric hindrance of the cation contained in the zwitterionic compound relative to ｂｕｒ The ratio r ｃ The ionic conductor according to claim 1, wherein the steric hindrance % V is 0.5 to 2.

0. ｂｕｒ is calculated using a structure in which energy has been minimized by quantum chemical calculation at the functional ωB97XD / basis set def2TZVP level and the Python library morpheus.

5. The ratio r ｃ 5. The ionic conductor according to claim 4, wherein is 0.7 to 1.

3.

6. The steric hindrance %V of the anions contained in the ionic plastic crystal ｂｕｒ % V of the steric hindrance of the anion contained in the zwitterionic compound relative to ｂｕｒ The ratio r ａ The ionic conductor according to claim 1, wherein the steric hindrance % V is 0.5 to 2.

0. ｂｕｒ is calculated using a structure in which energy has been minimized by quantum chemical calculation at the functional ωB97XD / basis set def2TZVP level and the Python library morpheus.

7. The ratio r ａ 7. The ionic conductor according to claim 6, wherein the ionic conductor is 0.7 to 1.

3.

8. The molecular volume V of the anion contained in the ionic plastic crystal ＰＣ The partial volume V of the anion contained in the zwitterionic compound relative to ｐ ＺＷ The ratio r ｐ Ａ 2. The ionic conductor according to claim 1, wherein the ionic conductor has a ρ of 0.5 or more.

9. The ratio r ｐ Ａ The ionic conductor according to claim 8, wherein is 0.7 or more.

10. Molecular volume V of the anion contained in the ionic plastic crystal ＰＣ The fragment volume V of the anion contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ａ The ionic conductor according to claim 1 , wherein is 2.0 or less.

11. The ratio r ｆ Ａ The ionic conductor according to claim 10, wherein is 1.5 or less.

12. Molecular volume V of the cation contained in the ionic plastic crystal ＰＣ the partial volume V of the cations contained in the zwitterionic compound relative to ｐ ＺＷ The ratio r ｐ Ｃ 2. The ionic conductor according to claim 1, wherein the ionic conductor has a ρ of 0.5 or more.

13. The ratio r ｐ Ｃ The ionic conductor according to claim 12, wherein is 0.7 or more.

14. Molecular volume V of the cation contained in the ionic plastic crystal ＰＣ The fragment volume V of the cation contained in the zwitterionic compound, ｆ ＺＷ The ratio r ｆ Ｃ The ionic conductor according to claim 13, wherein the ionic conductor has a ρ of 2.0 or less.

15. The ratio r ｆ Ｃ 15. The ionic conductor according to claim 14, wherein is 1.5 or less.

16. A solid electrolyte containing the ionic conductor according to any one of claims 1 to 15.

17. An electrode comprising the ionic conductor according to any one of claims 1 to 15.

18. An electricity storage device comprising the ionic conductor according to any one of claims 1 to 15.

19. A secondary battery comprising the ionic conductor according to any one of claims 1 to 15.

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