Method for producing molecular crystal and method for producing solid electrolyte

Abstract

A molecular crystal is produced by a method comprising: a step for obtaining a mixture by mixing an organic molecule having at least one type of atom selected from the group consisting of a sulfur atom, an oxygen atom, a nitrogen atom and a phosphorus atom with an alkali metal salt while applying mechanical energy; and a step for heating the mixture.

Description

Technical Field

[0001] [Cross-reference to related applications] This application claims priority based on Japanese Patent Application No. 2023-88980, filed on May 30, 2023, the entirety of which is incorporated herein by reference.

[0002] This invention relates to methods for manufacturing molecular crystals and solid electrolytes. Background Technology

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

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

[0005] Organic solid electrolytes have the advantage of excellent adhesion to electrodes due to the moderate softness and high formability of organic materials. On the other hand, they tend to have lower ionic conductivity compared to inorganic solid electrolytes. Therefore, in order to improve practicality, various studies have been conducted on the development of new materials constituting organic solid electrolytes (see, for example, Non-Patent Document 1). In Non-Patent Document 1, a method for forming a crystalline organic solid electrolyte by means of a soft solid crystal containing lithium chloride and isoquinoline is disclosed.

[0006] Existing technical documents Non-patent literature Non-patent literature 1: Ionics, 2018, Vol. 24, pp. 343-349 Summary of the Invention The technical problem that the invention aims to solve Previous organic solid electrolytes had the following problems: insufficient ionic conductivity at room temperature, and consequently, a significant decrease in ionic conductivity when the temperature was below room temperature.

[0007] This invention was made in view of the following circumstances, and one of its objectives is to provide a method for manufacturing molecular crystals that exhibit high ionic conductivity at room temperature and below. Another objective is to provide a method for manufacturing solid electrolytes that exhibit high ionic conductivity at room temperature and below.

[0008] Technical solutions for solving technical problems In order to solve the above-mentioned technical problems, the inventors conducted in-depth research and discovered that molecular crystals manufactured by a specific manufacturing method exhibit high ionic conductivity at room temperature and temperatures lower than room temperature. According to the present invention, methods for manufacturing molecular crystals and solid electrolytes can be provided.

[0009] [Means 1] A method for manufacturing a molecular crystal, comprising: a step of mixing an organic molecule having at least one type of atom selected from sulfur, oxygen, nitrogen and phosphorus with an alkali metal salt while applying mechanical energy to obtain a mixture; a step of obtaining the mixture; and a step of heating the mixture.

[0010] [Method 2] According to the method for manufacturing molecular crystals of [Method 1], the mixture is heated at a temperature above the melting point of the mixture.

[0011] [Method 3] The method for manufacturing molecular crystals according to [Method 1] or [Method 2], wherein the total number of carbon atoms in each molecule of the organic molecule is 6 or less.

[0012] [Method 4] A method for manufacturing a molecular crystal according to any one of [Method 1] to [Method 3], wherein the organic molecule is at least one selected from sulfone, nitrile and amide.

[0013] [Method 5] A method for manufacturing a molecular crystal according to any one of [Method 1] to [Method 4], wherein the alkali metal salt comprises an imide-based alkali metal salt.

[0014] [Method 6] A method for manufacturing a solid electrolyte, wherein the solid electrolyte is manufactured using a molecular crystal obtained by any one of the manufacturing methods of [Method 1] to [Method 5].

[0015] Invention Effects According to the present invention, molecular crystals exhibiting high ionic conductivity at room temperature and below can be obtained. Furthermore, by using the molecular crystals obtained by the manufacturing method of the present invention, solid electrolytes exhibiting excellent ionic conductivity at room temperature and below can be obtained. By using such solid electrolytes as electrolytes in energy storage devices such as secondary batteries and capacitors, energy storage devices that combine the safety of electrolyte-based solidification with excellent ionic conductivity can be obtained. Attached Figure Description

[0016] Figure 1 This is a simplified diagram of the stamping die used in the preparation of sample particles. Detailed Implementation

[0017] The following describes in detail the method for manufacturing the molecular crystal of the present invention, as well as the solid electrolyte and energy storage device manufactured using the molecular crystal obtained by the method.

[0018] Methods for Manufacturing Molecular Crystals Molecular crystals are solids in which structural units are regularly arranged in a crystal lattice. The method for manufacturing molecular crystals of the present invention (hereinafter also referred to as "the manufacturing method") uses an organic molecule (hereinafter also referred to as "(A) organic molecule") having at least one type of atom selected from sulfur atom, oxygen atom, nitrogen atom and phosphorus atom and an alkali metal salt to manufacture molecular crystals, including the following mechanical mixing step and heating step.

[0019] Mechanical mixing process: A process in which organic molecules (A) and alkali metal salts are mixed while mechanical energy is applied to obtain a mixture. Heating process: The process of heating the mixture obtained through mechanical mixing. The following is a detailed description of each step in this manufacturing method.

[0020] <Mechanical Mixing Process> In the mechanical mixing process, the organic molecules (A) and the alkali metal salt are mixed (hereinafter also referred to as "mechanical mixing") while mechanical energy is applied to the substance containing the organic molecules (A) and the alkali metal salt through means such as impact, shearing, compression, and friction. As a result, changes in the physicochemical properties of the organic molecules (A), the alkali metal salt, or both are preferably caused.

[0021] (A) Organic molecules (A) The number of at least one atom selected from sulfur, oxygen, nitrogen, and phosphorus atoms in an organic molecule is not particularly limited. (A) In an organic molecule, the number of at least one atom selected from sulfur, oxygen, nitrogen, and phosphorus atoms per molecule is preferably 1 to 8, more preferably 2 to 6. Among these, (A) the organic molecule preferably has 2 or more atoms selected from sulfur, oxygen, and nitrogen atoms, more preferably 2 to 6.

[0022] (A) The molecular weight of the organic molecule is, for example, 300 or less, preferably 250 or less, and more preferably 200 or less. Regarding the lower limit of the molecular weight of the (A) organic molecule, it is, for example, 20 or more, preferably 40 or more, and more preferably 50 or more. Furthermore, from the viewpoint of promoting the crystallization of the mixture of (A) organic molecule and alkali metal salt, the total number of carbon atoms per molecule of (A) organic molecule is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less.

[0023] As specific examples of (A) organic molecules, organic molecules having sulfur atoms include sulfones, thioethers, thiols, thioesters, thiocarbonates, sulfoxides, and sulfonamides.

[0024] Examples of organic molecules containing nitrogen atoms include nitriles, amines, and amides.

[0025] Examples of organic molecules containing phosphorus atoms include phosphine, phosphine oxide, and phosphine imine.

[0026] In addition to examples of organic molecules with oxygen atoms, such as those with sulfur atoms, those with nitrogen atoms, and those with phosphorus atoms, examples of organic molecules with oxygen atoms can also be given, including ethers, esters, ketones, and carbonates.

[0027] From the perspective of further improving the ionic conductivity of the molecular crystal, (A) the organic molecule is preferably selected from at least one of the following: organic molecules having sulfur and oxygen atoms, organic molecules having nitrogen atoms, and organic molecules having phosphorus atoms.

[0028] (Organic molecules containing sulfur and oxygen atoms) Sulfones are preferred as organic molecules having sulfur and oxygen atoms. A preferred example of a sulfone is the molecule shown in the following formula (1).

[0029] [Chemistry 1] (In equation (1), R) 1 and R 2 Each is independently alkyl or alkoxy, or represents R. 1 With R 2 The ring structure formed by bonding, wherein the total number of carbon atoms in formula (1) is 2 to 16. The molecule shown in formula (1) above (hereinafter also referred to as "(A-1) molecule") is a chain or cyclic molecule having a sulfonyl group (-SO2-). In formula (1) above, R... 1 and R 2In the case of alkyl or alkoxy groups, the alkyl and alkoxy groups can be straight-chain or branched. Additionally, the number of carbon atoms in each alkyl and alkoxy group (i.e., R...) 1 and R 2 The number of carbon atoms in each group) as long as R 1 and R 2 The total number of carbon atoms is 2 to 16, without any particular limitation. From the viewpoint of crystallizing a mixture of (A) organic molecules and alkali metal salts, R... 1 and R 2 The number of carbon atoms in each is preferably 1 to 3, more preferably 1 or 2.

[0030] In the above equation (1), R 1 and R 2 R represents 1 With R 2 In the case of a bonded ring structure, the ring structure can have a saturated ring framework or unsaturated bonds within the ring framework. Additionally, R 1 With R 2 The resulting cyclic structure can be a structure in which alkyl groups (such as methyl or ethyl groups) are bonded to the cyclic backbone. 1 With R 2 The number of carbon atoms in the bonded ring structure is preferably 2 to 8, more preferably 2 to 6, and even more preferably 3 to 5.

[0031] From the perspective of improving the ionic conductivity of the molecular crystal, R in the above formula (1) 1 and R 2 Preferred representation of R 1 With R 2 The bonded ring structure is more preferably a ring structure with a saturated ring skeleton.

[0032] The total number of carbon atoms in the above formula (1) is 2 to 16. From the viewpoint of promoting the crystallization of the mixture of (A-1) molecule and alkali metal salt, the total number of carbon atoms in the above formula (1) is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 5.

[0033] As a specific example of the (A-1) molecule, R in the above formula (1) is... 1 and R 2 Examples of compounds that are alkyl or alkoxy groups include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, dimethyl sulfate, and diethyl sulfate. As R in the above formula (1)... 1 and R 2 R represents 1 With R 2Examples of cyclic structures formed by bonding include tetrahydrothiophene-1,1-dioxide, 3-methylcyclobutane sulfone, 3-cyclobutene sulfone, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3,2-dioxazothiophene-2,2-dioxide. As (A-1) molecules, one type can be used alone, or two or more types can be used in combination.

[0034] (Organic molecules containing nitrogen atoms) Nitriles are preferred as organic molecules having nitrogen atoms. A preferred example of a nitrile is the molecule shown in formula (2) below.

[0035] [Chemistry 2] (In equation (2), R) 3 R represents a hydrocarbon chain. 4 and R 5 Each group independently represents a hydrogen atom, an alkyl group, or a cyano group, wherein the total number of carbon atoms in formula (2) is 16 or less. The molecule shown in formula (2) above (hereinafter also referred to as the "(A-2) molecule") is a molecule having two or more cyano groups (-CN). R in formula (2) above... 3 It can be a saturated hydrocarbon chain or it can contain unsaturated bonds. From the perspective of obtaining molecular crystals with superior ionic conductivity, R... 3 Preferably, it represents a saturated hydrocarbon chain. R 3 The number of carbon atoms is, for example, 1 to 10, preferably 1 to 6, and more preferably 2 to 4.

[0036] In R 4 Or R 5 When the alkyl group is alkyl, it can be either linear or branched. Linearity is preferred. From the viewpoint of crystallizing an organic molecule (A) by mixing it with an alkali metal salt, R... 4 and R 5 The number of carbon atoms in each group is preferably 0 to 3, more preferably 0 or 1.

[0037] The total number of carbon atoms in the above formula (2) should be 16 or less. From the viewpoint of promoting the crystallization of the mixture of (A-2) molecule and alkali metal salt, the total number of carbon atoms in the above formula (2) is preferably 8 or less, and more preferably 6 or less.

[0038] Specific examples of (A-2) molecules include succinic acid, adiponitrile, 3-hexenedionitrile, 1,3,5-pentanetricarbonylate, tert-butylmalononitrile, and 1,2,2,3-propanetetracarbonylate. One type of (A-2) molecule can be used alone, or two or more types can be used in combination.

[0039] (Organic molecules containing nitrogen atoms) As organic molecules containing nitrogen atoms, compounds with amide groups are preferred. From the perspective of high heat resistance, compounds with amide groups are preferably molecules having two or more amide groups per molecule. Specific examples of compounds with amide groups include malonamide, succinamide, glutaramide, adipamide, N,N,N',N'-tetramethylmalonamide, N,N,N',N'-tetraethylmalonamide, N,N,N',N'-tetramethylsuccinamide, and terephthalamide.

[0040] (Organic molecules containing phosphorus atoms) Examples of organic molecules containing phosphorus atoms include ethylidene bis(dimethylphosphine), ethylidene bis(diphenylphosphine), methyl(diphenyl)phosphine oxide, triphenylphosphine oxide, methyl(diphenyl)phosphine imine, and triphenylphosphine imine.

[0041] From the viewpoint of ease of manufacturing molecular crystals, as the organic molecule (A), it is preferable to select at least one of sulfone, nitrile, and amide. Furthermore, considering the superior ionic conductivity of the molecular crystal, it is more preferable to be a molecule (A-1), and even more preferable to be R representing the above formula (1). 1 With R 2 The cyclic structure formed by bonding is preferably a saturated ring skeleton. It should be noted that, as (A) organic molecule, one type can be used alone, or two or more types can be used in combination.

[0042] Alkali metal salts Alkali metal salts are any salts that produce alkali metal ions; there are no particular limitations. Examples of alkali metal salts include lithium salts, sodium salts, and potassium salts.

[0043] Specific examples of alkali metal salts include Li₂CO₃, LiBr, LiCl, LiI, LiSCN, LiBF₄, LiAsF₆, LiClO₄, CH₃COOLi, CF₃COOLi, LiCF₃SO₃, LiPF₆, LiC(CF₃SO₂)₃, and lithium bis(fluorosulfonyl)imide (Li + (FSO2)2N - ), Lithium bis(trifluoromethanesulfonyl)imide (Li + (CF3SO2)2N - Lithium salts such as (fluorosulfonyl) and (trifluoromethanesulfonyl)imide lithium; and salts of the anions of these lithium salts with alkali metals other than lithium (e.g., sodium, potassium, etc.). Considering the high ion dissociation and the ability to obtain molecular crystals with higher ion conductivity, lithium salts or sodium salts are preferred, and lithium salts are more preferred.

[0044] From the perspective of further improving the ionic conductivity of molecular crystals, the alkali metal salts used in the manufacture of molecular crystals preferably include imide-based alkali metal salts. Among these, from the perspective of high ionic dissociation, imide-based lithium salts are preferred. Among imide-based lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide are particularly preferred, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide are more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0045] The molecular weight of the alkali metal salt is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. Regarding the lower limit of the molecular weight of the alkali metal salt, it is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. One type of alkali metal salt can be used alone, or two or more types can be used in combination.

[0046] The melting point of alkali metal salts is, for example, 60°C or higher, preferably 70°C or higher, and more preferably 80°C or higher. There is no particular upper limit to the melting point of alkali metal salts; for example, it can be 300°C or lower, or even 250°C or lower.

[0047] It should be noted that, when manufacturing molecular crystals using this method, without impairing the effects of the present invention, substances different from the organic molecule and alkali metal salt (e.g., sulfur-containing organic molecules different from the organic molecule) can be used as structural units in the crystal lattice. However, considering the ionic conductivity and ease of manufacture of the molecular crystal, it is preferable to minimize the amount of the substance different from the organic molecule and alkali metal salt used. Specifically, relative to 1 mole of the total amount of the organic molecule and alkali metal salt, the amount of the substance different from the organic molecule and alkali metal salt used is preferably 0.1 moles or less, more preferably 0.05 moles or less.

[0048] The ratio of (A) organic molecules to alkali metal salts can be set according to the types of (A) organic molecules and alkali metal salts, and is not particularly limited. Regarding the ratio of (A) organic molecules to alkali metal salts, for example, relative to 1 mole of alkali metal salt, the ratio of (A) organic molecules can be set to 0.1 to 10 moles. Regarding the ratio of (A) organic molecules to alkali metal salts, relative to 1 mole of alkali metal salt, it is preferable to set the ratio of (A) organic molecules to 0.2 to 5 moles, more preferably to 0.25 to 4 moles, and even more preferably to 0.5 to 2 moles.

[0049] There are no particular limitations on the method for mixing (A) organic molecules with alkali metal salts while applying mechanical energy. In the mechanical mixing process, the mixing of (A) organic molecules with alkali metal salts can be performed using various equipment such as ball mills, bead mills, mixers, homogenizers, crushers, homogenizing mixers, and disperser-type mixers. Furthermore, in the case of small-scale manufacturing of molecular crystals, the mechanical mixing of (A) organic molecules with alkali metal salts can also be performed using a mortar and pestle. The mechanical mixing of (A) organic molecules with alkali metal salts can be performed dry or wet. Moreover, the mechanical mixing of (A) organic molecules with alkali metal salts can be performed at room temperature or at low temperature. For example, when the melting point of (A) organic molecules is below room temperature, liquid (A) organic molecules can be mechanically mixed with alkali metal salts. Alternatively, solid (A) organic molecules can be mechanically mixed with alkali metal salts at a temperature below the melting point of (A) organic molecules.

[0050] It should be noted that the mechanical mixing of (A) organic molecules and alkali metal salt can be carried out simultaneously with heating. In this case, in order to suppress the volatilization and sublimation of (A) organic molecules, the mechanical mixing process can be carried out at a lower temperature than the heating process performed after the mechanical mixing process. Specifically, the mechanical mixing process is carried out, for example, at a temperature below 50°C, preferably at a temperature below 40°C, and more preferably at a temperature below 35°C. The time for mechanical mixing depends on the amount and type of (A) organic molecules and alkali metal salt used, and can be, for example, 1 to 60 minutes, or 1 to 30 minutes.

[0051] The melting point of the mixture of (A) organic molecules and alkali metal salt (hereinafter also simply referred to as "the mixture") obtained by mechanical mixing is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 55°C or higher. Furthermore, from the viewpoint of suppressing the decomposition of molecular crystals accompanying the volatilization or sublimation of (A) organic molecules during the heating process after the mechanical mixing step, the melting point of the mixture is preferably 110°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower. In this specification, the melting point of the mixture of (A) organic molecules and alkali metal salt is a value obtained by differential scanning calorimetry (DSC). Details of the measurement method are as described in the examples below.

[0052] <Heating Process> In the heating process, after the aforementioned mechanical mixing process, the mixture obtained through the mechanical mixing process is heated. The method of heating the mixture is not particularly limited. The heating temperature of the mixture can be appropriately set according to the type of (A) organic molecules and alkali metal salt used in the raw materials. From the viewpoint of making the (A) organic molecules and alkali metal salt in the mixture more homogeneous, in the heating process of this manufacturing method, it is preferable to heat the mixture at a temperature above the melting point of the mixture of (A) organic molecules and alkali metal salt obtained through mechanical mixing. By setting the heating temperature above the melting point of the mixture, the mixture melts, thereby promoting the homogeneous mixing of (A) organic molecules and alkali metal salt.

[0053] Regarding the temperature for heating the mixture, from the viewpoint of achieving homogenization of the (A) organic molecules and alkali metal salt in the mixture by melting the mixture, it is preferable to set a temperature higher than the melting point of the mixture. Furthermore, from the viewpoint of promoting homogenization of the (A) organic molecules and alkali metal salt in the mixture, the heating temperature of the mixture is more preferably set to a temperature at least 5°C higher than the melting point (in °C), and even more preferably at least 7°C higher. Regarding the upper limit of the heating temperature of the mixture, from the viewpoint of suppressing the volatilization and sublimation of the components contained in the mixture, when the melting point of the mixture is expressed as Mp (in °C), it is preferably set to (Mp+20)°C or lower, and more preferably to (Mp+15)°C or lower. The heating time is not particularly limited as long as it is sufficient to homogenize the (A) organic molecules and 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 can generally be carried out under normal pressure, but it can also be carried out under pressure or depressurization.

[0054] When heating the mixture, it is preferable to further homogenize (A) the organic molecules and the alkali metal salt by stirring the mixture simultaneously. The stirring method is not particularly limited; examples include magnetic stirrers, stirring rods, mixers with stirring blades, and external circulation mixers. Alternatively, mechanical operations that generate greater shear forces, such as homogenizers, disperser mixers, and homogenizers, can also be used for stirring.

[0055] After heating a mixture containing (A) organic molecules and an alkali metal salt, the heated mixture crystallizes by lowering its temperature, thus obtaining the target molecular crystal. When lowering the temperature of the heated mixture, it can be cooled slowly (e.g., slowly lowering the temperature at room temperature over 1 to 48 hours). Alternatively, the heated mixture can be rapidly cooled (e.g., briefly placing the heated mixture in a thermostat at a temperature lower than room temperature (e.g., below 15°C)). From the viewpoint of suitably crystallizing the heated mixture, it is preferable to lower the temperature of the mixture slowly. The product obtained by this manufacturing method is a molecular crystal containing (A) organic molecules and an alkali metal salt, which can be detected by powder X-ray diffraction analysis of the product. Details of the analysis method are as described in the examples below.

[0056] Here, when manufacturing molecular crystals using only the mechanical mixing step within the heating step, the volatilization and sublimation of (A) organic molecules can be suppressed during manufacturing. However, sometimes it is impossible to uniformly mix (A) organic molecules with alkali metal salts, resulting in insufficient ionic conductivity of the obtained molecular crystals. Furthermore, when manufacturing molecular crystals using only the heating step within the mechanical mixing step, the volatilization and sublimation of (A) organic molecules can easily occur due to heating, making it difficult to obtain molecular crystals with the desired composition.

[0057] In contrast, it is believed that in this manufacturing method, which includes the above-mentioned mechanical mixing and heating processes, the organic molecules (A) and the alkali metal salt are mechanically mixed in advance, and then the mixture containing the organic molecules (A) and the alkali metal salt is heated. This allows the organic molecules (A) and the alkali metal salt to be uniformly mixed while suppressing the volatilization and sublimation of the organic molecules (A). As a result, a molecular crystal with excellent ion conductivity can be obtained.

[0058] It should be noted that, according to this manufacturing method, which includes a mechanical mixing process and a heating process, it is believed that during the manufacture of molecular crystals, intermolecular interactions are generated between alkali metal ions from alkali metal salts and (A) organic molecules through mechanical mixing prior to heat treatment. Therefore, it is believed that in this manufacturing method, where heat treatment is performed after mechanical mixing, the sublimation and volatilization of (A) organic molecules are suppressed during heat treatment, thereby suppressing the inhomogeneity of the molecular crystal composition. Furthermore, it is believed that by suppressing the inhomogeneity of the molecular crystal composition and forming a uniform ion conduction pathway, it is possible to manufacture molecular crystals exhibiting excellent ion conductivity.

[0059] Solid Electrolytes The molecular crystal obtained by the above-described manufacturing method is a crystalline organic compound comprising (A) organic molecules and alkali metal salts as structural units. This molecular crystal possesses ion conduction pathways through the regular arrangement of structural units comprising (A) organic molecules and alkali metal salts, thereby exhibiting excellent ion conductivity. Therefore, the molecular crystal obtained by this manufacturing method is suitable as a material for solid electrolytes. That is, by using the molecular crystal obtained by this manufacturing method, a solid electrolyte exhibiting excellent ion conductivity can be obtained.

[0060] The solid electrolyte of the present invention can be obtained by molding an electrode material comprising molecular crystals obtained by the above-described manufacturing method into a desired shape. The molding method is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, casting, die casting, and tape casting can be used. Among these methods, from the perspective of minimizing the porosity of the obtained solid electrolyte and facilitating the formation of ion conduction pathways, pressure molding is preferred. The shape of the molded body is not particularly limited and can be appropriately set according to the shape of the energy storage device to which it is applied. For example, the shape of the molded body can be rectangular or circular.

[0061] Without impairing the effects of the present invention, the solid electrolyte of the present invention may further comprise other components besides the molecular crystal of the present invention. Examples of other components include molecular crystals different from the molecular crystal of the present invention, polymeric solid electrolytes, polymeric gel electrolytes, inorganic electrolytes (e.g., ceramic electrolytes, glass electrolytes, etc.), binders, etc.

[0062] In particular, from the viewpoint of ensuring ion conductivity under low-temperature conditions, the content of the molecular crystals of the present invention in the solid electrolyte is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total amount of the solid electrolyte.

[0063] The solid electrolyte obtained as described above exhibits high ionic conductivity at room temperature and below. Specifically, for a solid electrolyte with a thickness of approximately 200 μm (more specifically, 200 ± 20 μm), the ionic conductivity measured by AC impedance spectroscopy at 25 °C is preferably 1 × 10⁻⁶. -6 S / cm or higher. From the viewpoint of obtaining a high-performance energy storage device, an ionic conductivity of 2 × 10⁻⁶ is more preferable under the same conditions. -6 S / cm or higher, more preferably 5×10 -6 S / cm or higher.

[0064] Furthermore, for solid electrolytes with a thickness of approximately 200 μm (specifically, 200 ± 20 μm), the preferred ionic conductivity, measured using AC impedance spectroscopy at -20 °C, is 2 × 10⁻⁶.-8 S / cm or higher, preferably 5×10 -8 S / cm or higher, more preferably 1×10 -7 S / cm or higher. Details of the method for determining ionic conductivity are as described in the examples below.

[0065] The solid electrolyte of this invention exhibits high ionic conductivity not only at room temperature but also at low temperatures below 0°C. Therefore, by using the solid electrolyte of this invention as the electrolyte in an energy storage device, an energy storage device with high ionic conductivity can be obtained.

[0066] Energy Storage Equipment The energy storage device of the present invention (hereinafter also referred to as "the device") includes the solid electrolyte of the present invention. Examples of the device include secondary batteries and capacitors. In the case of the device being a secondary battery, one approach is an all-solid-state battery; from the perspective of excellent ion conductivity, a lithium-ion secondary battery is preferred.

[0067] A solid-state lithium-ion secondary battery, which is one embodiment of this device, will be described. A lithium-ion secondary battery is a laminate comprising electrodes including a positive electrode and a negative electrode, and a solid electrolyte, wherein the solid electrolyte is disposed between the positive and negative electrodes in such a way that it is in contact with the electrodes. The materials constituting the positive and negative electrodes are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium-ion secondary batteries. For example, aluminum or stainless steel foil can be used as the positive electrode current collector. Copper foil or lithium foil can be used as the negative electrode current collector.

[0068] In the lithium-ion secondary battery of the present invention, the solid electrolyte is formed using a molecular crystal comprising (A) organic molecules and an alkali metal salt. The thickness of the solid electrolyte is not particularly limited and can be appropriately set according to the application of the secondary battery, etc. For example, the thickness of the solid electrolyte is 5 to 500 μm.

[0069] There are no particular limitations on the method for manufacturing lithium-ion secondary batteries, and known methods can be appropriately adopted depending on the battery structure. For example, a molded body formed using molecular crystals can be annealed, and a solid electrolyte obtained therefrom can be sandwiched between a positive electrode and a negative electrode to create a laminate having a positive electrode, a solid electrolyte, and a negative electrode. Alternatively, an electrolyte material containing molecular crystals can be housed in a container by sandwiching positive and negative electrodes, and the container can be annealed to create a laminate having a positive electrode, a solid electrolyte, and a negative electrode. The laminate having a positive electrode, a solid electrolyte, and a negative electrode is usually housed in a casing and used as a secondary battery.

[0070] It should be noted that this device is not limited to the structure described above where lithium ions are used as charge carriers for ion conduction. For example, it could also be a secondary battery using other ions such as sodium ions as charge carriers. Additionally, this device could also be a capacitor. One example of a capacitor is a configuration comprising a positive electrode, a negative electrode, and a solid electrolyte, with the solid electrolyte disposed between the positive and negative electrodes in connection with the electrodes.

[0071] Energy storage devices incorporating this solid electrolyte can be used for a wide variety of applications. Specifically, they can be used as power sources for various mobile devices such as portable telephones, personal computers, smartphones, game consoles, and wearable devices; various mobile devices such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, camcorders, music players, power tools, and home appliances.

[0072] Example The present invention will now be described in detail based on embodiments. It should be noted that the present invention is not limited to these embodiments. Unless otherwise specified, "parts" and "%" refer to "parts by mass" and "% by mass," respectively.

[0073] Fabrication and Evaluation of Molecular Crystals [Example 1] 1. Manufacturing of molecular crystals In a glove box under an argon atmosphere, 0.1379 g of succinate (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1624 g of lithium tetrafluoroborate (manufactured by Fujifilm and Kohden Chemical Co., Ltd.) as an alkali metal salt were measured in a 1:1 molar ratio and mechanically mixed for 5 minutes at room temperature (25°C) using a mortar to obtain a mixture (referred to as mixture M) (mechanical mixing process). The melting point of mixture M was determined using a differential scanning calorimeter (manufactured by TA Instruments, DSC250, measurement atmosphere: nitrogen atmosphere) at a heating rate of 10°C per minute. A large endothermic peak (melting point) was observed at 77°C.

[0074] Transfer mixture M to a tubular flask and stir with a magnetic stirrer set to 90°C for 1 hour to ensure uniform dissolution (heating step). Then, cool the resulting melt to room temperature to obtain a white solid.

[0075] 2. Evaluation (Confirmation of crystallinity based on powder X-ray diffraction) The obtained white solid was subjected to powder X-ray diffraction analysis using an X-ray diffraction apparatus (Bruker AXS, D8 ADVANCE). It should be noted that CuK was used. αAs an X-ray source, the applied voltage was set to 40 kV and the current to 40 mA. The measurement range was set to 2. i =5-60 degrees, scan speed set to 2.3 degrees / min, step angle set to 0.02 degrees. The presence of sharp peaks in the X-ray diffraction spectrum within the measurement range indicates that the sample (solid) is crystalline. Therefore, if an X-ray diffraction spectrum with sharp peaks within the measurement range, distinct from both the organic molecules and alkali metal salts used as raw materials, is obtained, it is determined that a molecular crystal composed of organic molecules and alkali metal salts has been formed. It should be noted that if the organic molecules used as raw materials are liquid at room temperature, and an X-ray diffraction spectrum with sharp peaks within the measurement range, distinct from the alkali metal salts, is observed, it is determined that a molecular crystal composed of organic molecules and alkali metal salts has been formed.

[0076] The white solid obtained by the above method was subjected to powder X-ray diffraction analysis. The results showed that it had sharp peaks within the measurement range and its X-ray diffraction spectrum differed from that of the raw material. This confirms that the obtained white solid is crystalline, that is, it is a molecular crystal composed of organic molecules and alkali metal salts.

[0077] (Determination of ionic conductivity) A stamping die 10 including module 11, upper punch 12 and lower punch 13 (see reference) Figure 1 Sample particles were prepared in a glove box under an argon atmosphere. First, a module 11 containing 0.0200 g of white solid (molecular crystal) was placed on the lower punch 13, and the upper punch 12 was placed on the module 11. The white solid was compressed for 1 minute using a hydraulic press at a pressure of 10 MPa to obtain spherical sample particles with a diameter of 1 cm and a thickness of 200 μm. Then, the sample particles were sealed into an all-solid-state battery evaluation cell (manufactured by Baoquan Corporation, KP-SolidCell) in a glove box under an argon atmosphere.

[0078] The ionic conductivity of an all-solid-state battery evaluation unit containing sample particles was measured under atmospheric conditions. In the ionic conductivity measurement, the sealed unit 20 containing the sample particles was first heat-treated in a constant temperature bath at 50°C (corresponding to the heat treatment temperature in Table 1), while the resistance value was measured by AC impedance spectroscopy. The heat treatment was terminated when the resistance value reached a certain point. Next, the resistance values ​​at 25°C and -20°C were measured by AC impedance spectroscopy. Using the obtained resistance values, the ionic conductivity was calculated using the following mathematical formula (1). s It should be noted that the AC impedance measurement used to calculate ionic conductivity was performed after the unit was kept at the measurement temperature for 2 hours in a constant temperature bath.

[0079] s =L / (R×S) (1) (In mathematical expression (1), s R represents ionic conductivity (unit: S / cm), R represents electrical resistance (unit: Ω), and S represents the cross-sectional area of ​​the molecular crystal during measurement (unit: cm²). 2 L represents the distance between electrodes (unit: cm). The obtained molecular crystals exhibited ionic conductivity of 6.6 × 10⁻⁶ at 25 °C and -20 °C, respectively. -5 S / cm, 2.7×10 - 8 S / cm.

[0080] [Examples 2-7] The types and amounts of raw materials, the heating temperature of mixture M in the heating process, and the heat treatment temperature for measuring ionic conductivity were changed as described in Table 1. Otherwise, the mechanical mixing and heating processes were performed in the same manner as in Example 1 to obtain a white solid.

[0081] For the white solids obtained in each embodiment, powder X-ray diffraction was performed in the same manner as in Example 1. The results showed sharp peaks within the measurement range and X-ray diffraction spectra different from those of the raw materials, thus confirming that each white solid was a molecular crystal composed of organic molecules and alkali metal salts. Furthermore, using the white solids (molecular crystals) of each embodiment, the ionic conductivity at 25°C and -20°C was measured in the same manner as in Example 1. The results of the melting point measurement and ionic conductivity measurement of the mixture M obtained through the mechanical mixing process are shown in Table 1.

[0082] [Comparative Example 1] In a glove box under an argon atmosphere, 0.1397 g of succinate (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1624 g of lithium tetrafluoroborate (manufactured by Fujifilm and Kohden Chemical Co., Ltd.) as an alkali metal salt were measured in a 1:1 molar ratio and gently mixed with a spatula at room temperature (25°C) without mechanical operation. The mixture was then transferred to a tubular flask and stirred for 1 hour with a magnetic stirrer set at 90°C to ensure uniform dissolution (heating step). The resulting melt was then cooled to room temperature to obtain a white solid (molecular crystal). For the obtained molecular crystal, the ionic conductivity was measured at 25°C and -20°C, with a heat treatment temperature of 50°C, in the same manner as in Example 1. The results of the ionic conductivity measurements are shown in Table 1.

[0083] [Comparative Example 2] In a glove box under an argon atmosphere, 0.1391 g of succinate (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1621 g of lithium tetrafluoroborate (manufactured by Fujifilm and Kohden Chemical Co., Ltd.) as an alkali metal salt were measured in a 1:1 molar ratio and mechanically mixed at room temperature (25°C) using a mortar and pestle to obtain a white solid (molecular crystal). The melting point of the molecular crystal obtained by mechanical mixing of the raw materials was determined by DSC in the same manner as in Example 1, and the result was 77°C.

[0084] For the molecular crystals obtained by mechanical mixing of the raw materials, the heat treatment temperature was set to 50°C, and the ionic conductivity was measured at 25°C and -20°C in the same manner as in Example 1. The results of the ionic conductivity measurements are shown in Table 1. It should be noted that in Comparative Example 2, the resistance value of the sample was significantly high in the Nyquist plot at -20°C, so the resistance value could not be read and the ionic conductivity could not be calculated. Therefore, in Table 1, the column for the ionic conductivity measurement results at -20°C is marked as "unreadable" (the same applies to Comparative Example 3).

[0085] [Comparative Example 3] In a glove box under an argon atmosphere, 0.1149 g of succinamide (manufactured by Tokyo Chemical Industry Co., Ltd.) as an organic molecule and 0.1851 g of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Ltd.) as an alkali metal salt were measured in a 1:1 molar ratio and mechanically mixed in a mortar at room temperature (25°C) for 5 minutes (mechanical mixing process) to obtain a white solid (molecular crystal). The melting point of the molecular crystal obtained by mechanical mixing of the raw materials was determined by DSC in the same manner as in Example 1, and the result was 97°C.

[0086] For the molecular crystals obtained by mechanical mixing of the raw materials, the heat treatment temperature was set to 80°C, and the ionic conductivity was measured at 25°C and -20°C in the same manner as in Example 1. The results of the ionic conductivity measurements are shown in Table 1. It should be noted that in Comparative Example 3, the resistance value of the sample was significantly high in the Nyquist plot at -20°C, so the resistance value could not be read and the ionic conductivity could not be calculated.

[0087] [Table 1] The details of the compounds used in Table 1 are shown below.

[0088] •SN: Butadionitrile (manufactured by Tokyo Chemical Industry Co., Ltd.) ·SL: Tetrahydrothiophene-1,1-dioxide [Manufactured by Tokyo Chemical Industry Co., Ltd.] • DMS: Dimethyl sulfone (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) ·3SL: 3-Cyclobutene sulfone [Manufactured by Tokyo Chemical Industry Co., Ltd.] • AdN: Adiponitrile (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • LiBF4: Lithium tetrafluoroborate (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • LiFSI: Lithium bis(fluorosulfonyl)imide [Manufactured by Kanto Chemical Co., Ltd.] SA: Succinamide (manufactured by Tokyo Chemical Industry Co., Ltd.) Evaluation Results As can be seen from the results of Examples 1 to 7, the molecular crystals obtained by this manufacturing method, which includes a mechanical mixing process and a heating process, exhibit high ionic conductivity at both room temperature (25°C) and low temperature (-20°C). Among them, Examples 2 to 7, which used an imide-based alkali metal salt as the alkali metal salt, showed higher ionic conductivity compared to Example 1, which used LiBF4. In addition, Examples 2 to 4 and Example 7, which used the molecule shown in Formula (1) above or succinamide as the organic molecule (A), showed higher ionic conductivity compared to Examples 1, 5, and 6, which used the molecule shown in Formula (2) above.

[0089] In contrast, the results of Comparative Example 1, which uses (A) organic molecules and alkali metal salts as structural units but does not perform mechanical mixing but only heating, and Comparative Examples 2 and 3, which do not perform heating after mechanical mixing, show that the ionic conductivity at 25°C and -20°C is lower than that of Examples 1 to 7.

[0090] The results above show that in the manufacturing method of molecular crystals with organic molecules and alkali metal salts as structural units (A), by setting the method to include mechanical mixing and heating processes, the obtained molecular crystals exhibit high ionic conductivity at room temperature, and the ionic conductivity is not easily reduced even at low temperatures.

[0091] This invention is not limited to the embodiments described above, and includes various modifications and variations within the same scope without departing from the spirit of the invention. Therefore, it should be understood that, in accordance with the above teachings, various combinations, forms, and other combinations and forms including only one element, more than one element, or less than one element also fall within the scope and spirit of this invention.

[0092] Explanation of reference numerals in the attached figures 10… Stamping dies.

Claims

1. A method for producing a molecular crystal, characterized by, comprising: a step of mixing an organic molecule having at least one atom selected from a sulfur atom, an oxygen atom, a nitrogen atom, and a phosphorus atom with an alkali metal salt while applying mechanical energy to obtain a mixture; and a step of heating the mixture. The mixture is heated at a temperature higher than a melting point of the mixture.

2. The method of manufacturing a molecular crystal according to claim 1, wherein The number of carbon atoms per 1 molecule of the organic molecule is 6 or less.

3. The method of manufacturing a molecular crystal according to claim 1, wherein The organic molecule is at least one selected from a sulfone, a nitrile, and an amide.

4. The method of manufacturing a molecular crystal according to claim 1, wherein The alkali metal salt contains an imide-based alkali metal salt.

5. The method of manufacturing a molecular crystal according to claim 1, wherein A solid electrolyte is manufactured using a molecular crystal obtained by the manufacturing method according to any one of claims 1 to 5.

6. A method for producing a solid electrolyte, characterized by ​

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