Electrolytes, methods for manufacturing the same, and energy storage devices

Abstract

To provide an electrolyte that exhibits high ionic conductivity at room temperature, and further exhibits high ionic conductivity even under weak confinement pressure. [Solution] The electrolyte contains a charge transfer complex formed from an electron-donating compound and an electron-accepting compound, an alkali metal-containing compound, and an organic molecule different from the charge transfer complex and the alkali metal-containing compound. The electron-donating compound has a phenylene skeleton. The organic molecule is a molecule that can dissolve the alkali metal-containing compound when 100 g of the organic molecule is mixed with 0.1 moles of the alkali metal-containing compound at 25°C.

Description

[Technical Field]

[0001] This invention relates to an electrolyte, a method for producing the same, and an energy storage device. [Background technology]

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

[0003] Lithium-ion secondary batteries, widely used as energy storage devices, are secondary batteries that have a negative electrode, a positive electrode, and an electrolyte, and charge and discharge by moving lithium ions between the two electrodes via the electrolyte. Conventionally, non-aqueous electrolytes have been mainly used as the electrolyte. However, since non-aqueous electrolytes contain flammable organic solvents, there are concerns about electrolyte leakage and short circuits inside the battery due to overcharging and over-discharging.

[0004] In response to this, in recent years, various solid electrolytes using inorganic or organic materials have been proposed as alternatives to organic electrolytes to eliminate concerns about electrolyte leakage and short circuits inside batteries due to overcharging and over-discharging (see, for example, Patent Document 1). Patent Document 1 discloses a composite of a charge transfer complex obtained by doping polyphenylene sulfide, a crystalline polymer, with an oxidizing agent, and a compound having an ion source that can act as a carrier for ion conduction (an ionic compound) as a solid electrolyte. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0005356 [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors have found that while the solid electrolyte disclosed in Patent Document 1 exhibits relatively high ionic conductivity at room temperature, it is necessary to increase the force used to hold the electrolyte in place by a restraining jig (hereinafter also referred to as "restraining pressure") in order to achieve high ionic conductivity. However, incorporating an electrolyte requiring strong restraining pressure into a practical battery requires a relatively large restraining jig. This raises concerns that the volume of wasted parts other than the battery in the packed system will increase, leading to a decrease in the overall energy density of the battery system. Furthermore, if the restraining pressure of the electrolyte is weakened to avoid increasing the size of the restraining jig, there are concerns that the ionic conductivity of the electrolyte will decrease significantly.

[0007] This invention has been made in view of these circumstances, and its main objective is to provide an electrolyte that exhibits high ionic conductivity at room temperature and further exhibits high ionic conductivity even under weak confinement pressure. [Means for solving the problem]

[0008] The inventors of the present invention hypothesized that the solid electrolyte described in Patent Document 1 is a hard powder, and that in order to achieve high ionic conductivity, it is necessary to maintain interfacial contact between the solid electrolyte powders by applying high confinement pressure. Based on this observation, the inventors found that the above problem can be solved by using a compound having a phenylene skeleton as the electron-donating compound constituting the charge transfer complex in an electrolyte utilizing a charge transfer complex, and by including a specific organic molecule in the electrolyte. According to the present invention, the following electrolyte, a method for producing the same, and an energy storage device are provided.

[0009] [1] A charge transfer complex formed by an electron-donating compound and an electron-accepting compound, an alkali metal-containing compound, and an organic molecule different from the charge transfer complex and the alkali metal-containing compound, wherein the electron-donating compound has a phenylene skeleton, and the organic molecule is a molecule capable of dissolving the alkali metal-containing compound when 0.1 mol of the alkali metal-containing compound is mixed with 100 g of the organic molecule at 25°C. [2] The electrolyte according to [1], wherein the organic molecule has at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, and a sulfur atom. [3] The electrolyte according to [1] or [2], wherein the organic molecule is at least one selected from the group consisting of a carbonate ester compound, a nitrile compound, a sulfone compound, an amide compound, and a ketone compound. [4] The electrolyte according to any one of [1] to [3], wherein the molecular weight of the organic molecule is 500 or less. [5] The ratio of the molar amount of the alkali metal-containing compound to the mass of the organic molecule is 1.0×10 -3 mol / g or more and 5.0×10 -3 mol / g or less. The electrolyte according to any one of [1] to [4]. [6] The electrolyte according to any one of [1] to [5], wherein the electron-donating compound is a (poly)phenylene oxide compound. [7] The ratio of the molar amount of the alkali metal-containing compound to the total amount of the molar amount of the electron-donating compound (wherein, when the electron-donating compound is a polymer, in terms of monomer) and the molar amount of the electron-accepting compound in the charge transfer complex is 0.03 or more and 1.0 or less. The electrolyte according to any one of [1] to [6]. [8] The electrolyte according to any one of [1] to [7], wherein the electron-accepting compound contains at least one selected from the group consisting of 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), o-benzoquinone, m-benzoquinone, and p-benzoquinone. 〔9〕 The electrolyte according to any one of 〔1〕 to 〔8〕, wherein the alkali metal-containing compound contains an alkali metal salt. 〔10〕 The electrolyte according to any one of 〔1〕 to 〔9〕, wherein the alkali metal-containing compound contains a lithium-containing compound. 〔11〕 A power storage device comprising the electrolyte according to any one of 〔1〕 to 〔10〕. 〔12〕 A method for producing an electrolyte according to any one of 〔1〕 to 〔10〕, the method comprising a step of mixing the charge transfer complex, the alkali metal-containing compound, and the organic molecule.

Advantages of the Invention

[0010] According to the present invention, an electrolyte that exhibits high ionic conductivity at room temperature and further exhibits high ionic conductivity even under a weak confinement pressure can be obtained. By using such an electrolyte of the present invention as an electrolyte of a power storage device such as a secondary battery or a capacitor, the energy density of the entire power storage device system can be increased. Further, a power storage device that combines safety assurance of the electrolyte and good battery performance can be obtained.

Brief Description of the Drawings

[0011] [Figure 1] IR spectrum. The thin line is the IR spectrum of diethyl carbonate (DEC), the broken line is the IR spectrum of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the thick line is the IR spectrum of a mixture of DEC and LiTFSI.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present disclosure will be described in detail.

[0013] ≪Electrolyte≫ The electrolyte of the present invention (hereinafter also referred to as "the present electrolyte") is an electrolyte using a charge transfer complex and is a complex containing a charge transfer complex, an alkali metal-containing compound, and an organic molecule. Hereinafter, each component contained in the present electrolyte will be described in detail.

[0014] <Charge transfer complex> The charge transfer complex contained in this electrolyte is a molecular compound formed from an electron-donating compound having a phenylene skeleton and an electron-accepting compound.

[0015] (Electron-donating compounds) The structure of an electron-donating compound is not particularly limited, as long as it has a phenylene skeleton. The electron-donating compound may be a relatively low-molecular-weight compound (i.e., a nonpolymer) that does not have a molecular weight distribution, or it may be a polymer containing a benzene ring in its main chain. The benzene ring in the phenylene skeleton may have substituents (e.g., alkyl groups, alkoxy groups, halogen atoms). From the viewpoint of obtaining an electrolyte that exhibits good ionic conductivity, it is preferable that the electron-donating compound constituting the charge transfer complex has a benzene ring and a heteroatom in its main chain.

[0016] As electron-donating compounds, compounds having a phenylene oxide structure (hereinafter also referred to as "(poly)phenylene oxide compounds") can be preferably used because they readily form ion conduction paths in the electrolyte, allowing for the production of electrolytes exhibiting high ionic conductivity. (Poly)phenylene oxide compounds are not particularly limited, as long as they have a benzene ring and an oxygen atom in their main chain; for example, a compound with the general formula: -(C6R4-O) n Examples include compounds having a structure represented by - (wherein R is the same or different hydrogen atom or alkyl group, and n is an integer of 1 or more) in the molecule. When R is an alkyl group, the number of carbon atoms in the alkyl group is preferably 1 or 2, and more preferably 1. n is, for example, 1 to 600. (Poly)phenylene oxide compounds include both low molecular weight compounds (i.e., nonpolymers) and polymers.

[0017] Specific examples of (poly)phenylene oxide compounds include 2,6-dimethyl-1,4-phenylene oxide and 2,5-dimethyl-1,4-phenylene oxide, where n is 1 in the general formula above. Compounds where n is 2 or more (hereinafter also referred to as "polyphenylene oxide compounds") include those with the general formula: -(C6R4-O) n Examples include polymers having the structure shown by - as a repeating unit. Among these, polyphenylene oxide compounds are preferred because they can increase the ionic conductivity of the electrolyte and provide an electrolyte with excellent mechanical strength, durability, and heat resistance, and polymers having the repeating unit represented by the following formula (1) are particularly preferred. [ka] (In formula (1), R 1 and R 2 (These are either the same or different hydrogen atoms or alkyl groups.)

[0018] R in equation (1) above 1 and R 2 From the viewpoint of ease of material availability, it is preferable that the group be a methyl group or an ethyl group, and more preferably a methyl group.

[0019] The number-average molecular weight of the polyphenylene oxide compound is, for example, 500 to 30,000. Preferably, the number-average molecular weight of the polyphenylene oxide compound is 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more. Furthermore, the upper limit of the number-average molecular weight of the polyphenylene oxide compound is preferably 25,000 or less, and more preferably 20,000 or less.

[0020] The preferred range for the number-average molecular weight of the polyphenylene oxide compound can be determined by combining the preferred upper and lower limits mentioned above. Specifically, the number-average molecular weight of the polyphenylene oxide compound is preferably 1,000 to 30,000, more preferably 5,000 to 30,000, even more preferably 10,000 to 30,000, and even more preferably 10,000 to 20,000. Polyphenylene oxide compounds are commercially available from companies such as Sigma-Aldrich. One electron-donating compound may be used alone, or two or more may be used in combination.

[0021] (Electron-accepting compounds) The electron-accepting compound can be any compound capable of forming a charge-transfer complex with an electron-donating compound having a phenylene skeleton. Specific examples of electron-accepting compounds include quinone compounds, cyanide compounds, oxygen, ozone, iodine, sulfur trioxide, and transition metal oxides (e.g., manganese dioxide). Among these, specific examples of quinone compounds include 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), o-benzoquinone, m-benzoquinone, and p-benzoquinone. Examples of cyanide compounds include 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE). Note that one electron-accepting compound may be used alone, or two or more may be used in combination.

[0022] In order to readily form charge transfer complexes with electron-donating compounds having a phenylene skeleton and to obtain electrolytes with high ionic conductivity, it is preferable that the electron-accepting compound contains at least one selected from the group consisting of quinone compounds and cyanide compounds. In particular, it is preferable that the electron-accepting compound contains at least one selected from the group consisting of 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), o-benzoquinone, m-benzoquinone, and p-benzoquinone.

[0023] The method for producing the charge transfer complex is not particularly limited and can be carried out according to known methods. For example, a charge transfer complex can be produced by mixing an electron-accepting compound and an electron-donating compound, and preferably by grinding and / or heating the resulting mixture. When producing the charge transfer complex, if the mixture of the electron-accepting compound and the electron-donating compound is ground and then heated, the heat treatment may be performed after mixing and grinding the electron-accepting compound and the electron-donating compound. Alternatively, the grinding treatment may be performed after heating the mixture. From the viewpoint of uniformly mixing the electron-accepting compound and the electron-donating compound so that the charge transfer complex is sufficiently formed, it is preferable to perform the heat treatment after grinding.

[0024] The method for grinding a mixture of an electron-accepting compound and an electron-donating compound is not particularly limited and can be carried out by dry grinding, wet grinding, low-temperature grinding, etc. Furthermore, it is preferable to use a grinding machine such as a ball mill, bead mill, or blender for the grinding process. The temperature when heating the mixture is usually 120 to 320°C, preferably 150 to 300°C. The heating time is, for example, 15 to 360 minutes. The heat treatment to obtain the charge-transfer complex may be performed only once or multiple times. When the heat treatment is performed multiple times, the heating temperature and heating time in each step may be the same or different. The heat treatment to obtain the charge-transfer complex is usually carried out under normal pressure, but it may also be carried out under pressure or under reduced pressure.

[0025] The amounts of electron-donating compound and electron-accepting compound in the charge transfer complex are preferably such that the ratio of the molar amount of the electron-accepting compound to the molar amount of the electron-donating compound (however, if the electron-donating compound is a polymer, this is calculated on a monomer basis) (= molar amount of electron-accepting compound / molar amount of electron-donating compound, hereinafter also referred to as "Q2 / Q1") is between 0.1 and 1.0. By setting Q2 / Q1 within the above range, an electrolyte with superior ionic conductivity can be obtained. From this viewpoint, Q2 / Q1 is more preferably 0.15 or higher, even more preferably 0.2 or higher, and even more preferably 0.25 or higher. For the upper limit of Q2 / Q1, it is more preferably 0.9 or lower, and even more preferably 0.8 or lower. A more preferable range for Q2 / Q1 can be determined by appropriately combining the upper and lower limits mentioned above. Specifically, Q2 / Q1 is more preferably 0.15 or higher and 0.9 or lower, even more preferably 0.2 or higher and 0.8 or lower, and even more preferably 0.25 or higher and 0.8 or lower.

[0026] <Alkali metal-containing compounds> The alkali metal-containing compound can be any compound that generates alkali metal ions and is not particularly limited. Specific examples of alkali metal-containing compounds include lithium-containing compounds, sodium-containing compounds, potassium-containing compounds, and the like. Of these, lithium-containing compounds or sodium-containing compounds are preferred, and lithium-containing compounds are more preferred, in that they can improve the ionic conductivity of the electrolyte.

[0027] Examples of the alkali metal-containing compound include alkali metal oxides, alkali metal hydroxides, alkali metal salts, etc. Specific examples thereof include, as the alkali metal oxide, lithium oxide, sodium oxide, potassium oxide, etc. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the alkali metal salt include, for example, Li2CO3, LiBr, LiCl, LiI, LiSCN, LiBF4, LiAsF6, LiClO4, CH3COOLi, CF3COOLi, LiCF3SO3, LiPF6, LiC(CF3SO2)3, lithium bis(fluorosulfonyl)imide (Li + (FSO2)2N - ), lithium bis(trifluoromethanesulfonyl)imide (Li + (CF3SO2)2N - ), lithium salts such as lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide; salts of anions of these lithium salts and alkali metals other than lithium (for example, sodium, potassium, etc.).

[0028] Among the above, the alkali metal salt is preferable, the lithium salt or sodium salt is more preferable, and the lithium salt is even more preferable in that an electrolyte having higher ionic conductivity can be obtained by a simple method. Further, among the lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide is preferable in that the dissociation property of ions is high.

[0029] As the alkali metal-containing compound, a compound that is solid at room temperature (25 ° C) can be preferably used. The melting point of the alkali metal-containing compound is preferably 70 ° C or higher, more preferably 80 ° C or higher, still more preferably 90 ° C or higher, and even more preferably 95 ° C or higher. The upper limit of the melting point of the alkali metal-containing compound is, for example, 350 ° C or lower.

[0030] The molecular weight of the alkali metal-containing compound is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, even more preferably 300 or less, and even more preferably 250 or less. The lower limit of the molecular weight of the alkali metal-containing compound is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. The preferred range for the molecular weight of the alkali metal-containing compound is 20 to 500, more preferably 50 to 400, and even more preferably 100 to 400. By setting the molecular weight of the alkali metal-containing compound within the above range, an electrolyte exhibiting better ionic conductivity can be obtained.

[0031] In this electrolyte, the amount of alkali metal-containing compound is preferably such that the ratio of the molar amount of alkali metal-containing compound to the total molar amount of electron-donating compound (however, if the electron-donating compound is a polymer, it is calculated on a monomer basis) and electron-accepting compound in the charge transfer complex (= molar amount of alkali metal-containing compound / (molar amount of electron-accepting compound + molar amount of electron-donating compound), hereinafter also referred to as "Q3 / (Q1+Q2)") is 0.03 or more and 1.0 or less. By having Q3 / (Q1+Q2) within the above range, an electrolyte exhibiting better ionic conductivity can be obtained. From this viewpoint, Q3 / (Q1+Q2) is more preferably 0.05 or more, even more preferably 0.1 or more, and even more preferably 0.2 or more. The upper limit of Q3 / (Q1+Q2) is more preferably 0.9 or less, even more preferably 0.8 or less, even more preferably 0.7 or less, and even more preferably 0.6 or less. A more preferred range for Q3 / (Q1+Q2) is 0.05 to 0.9, more preferably 0.1 to 0.8, and even more preferably 0.2 to 0.7. Note that the alkali metal-containing compound may be used individually or in combination of two or more.

[0032] <Organic molecules> The organic molecules contained in this electrolyte are molecules capable of dissolving alkali metal-containing compounds when 100 g of the organic molecules are mixed with 0.1 moles of alkali metal-containing compounds at 25°C (hereinafter also referred to as "organic molecule (A)"). By containing organic molecule (A) with such properties together with a predetermined charge transfer complex and alkali metal-containing compound, this electrolyte exhibits high ionic conductivity equivalent to or better than conventional electrolytes under similar confinement pressures (e.g., around 80-100 MPa), even under relatively weak confinement pressures (e.g., 30 MPa or less). Note that organic molecule (A) is a different component from the charge transfer complex and alkali metal-containing compound. Furthermore, it is preferable that organic molecule (A) is a compound different from both the electron-donating compound and the electron-accepting compound constituting the charge transfer complex.

[0033] Before being mixed with 0.1 moles of alkali metal-containing compound, organic molecule (A) may be solid or liquid at 25°C, as long as it can dissolve the alkali metal-containing compound when 100g of organic molecule (A) is mixed with 0.1 moles of alkali metal-containing compound. On the other hand, when 100g of organic molecule (A) and 0.1 moles of alkali metal-containing compound are mixed, the mixture of organic molecule (A) and alkali metal-containing compound is a liquid composition at 25°C in which the alkali metal-containing compound is dissolved in organic molecule (A). Therefore, if organic molecule (A) is solid at 25°C, then, upon mixing with the alkali metal-containing compound, the mixture of organic molecule (A) and alkali metal-containing compound becomes liquid at 25°C.

[0034] When the organic molecule used in the production of this electrolyte is denoted as organic molecule (α) and the alkali metal-containing compound is denoted as alkali metal-containing compound (β), whether or not organic molecule (α) can dissolve alkali metal-containing compound (β) when 100 g of organic molecule (α) and 0.1 mole of alkali metal-containing compound (β) are mixed at 25°C can be evaluated by placing 100 g of organic molecule (α) and 0.1 mole of alkali metal-containing compound (β) in a container and stirring for a sufficient time (e.g., 12 hours) at 25°C, and then checking whether or not any residue of alkali metal-containing compound (β) is present. At this time, if no residue of alkali metal-containing compound (β) is found by visual inspection, it can be evaluated that organic molecule (α) can dissolve alkali metal-containing compound (β), and if residue of alkali metal-containing compound (β) is present, it can be evaluated that organic molecule (α) cannot dissolve alkali metal-containing compound (β). Details of the evaluation method are as described in the examples below.

[0035] The amount of alkali metal-containing compound soluble at 25°C per 100g of organic molecule (A) should be 0.1 moles or more. Preferably, the amount of alkali metal-containing compound soluble at 25°C in organic molecule (A) is 0.15 moles or more, more preferably 0.2 moles or more, even more preferably 0.25 moles or more, and even more preferably 0.3 moles or more per 100g of organic molecule (A).

[0036] Although this invention is not limited to the present invention, an electrolyte containing a predetermined charge transfer complex, an alkali metal-containing compound, and an organic molecule (A) can be made flexible by utilizing the unique properties of the mixture of the organic molecule (A) and the alkali metal-containing compound, while maintaining good ionic conductivity mainly exhibited by the predetermined charge transfer complex and the alkali metal-containing compound. This makes it possible to obtain an electrolyte that exhibits high ionic conductivity at room temperature and also exhibits high ionic conductivity under weak confinement pressure.

[0037] The organic molecule (A) may be a relatively low molecular weight compound (nonpolymer) that does not have a molecular weight distribution, or it may be a polymer. The molecular weight of the organic molecule (A) is, for example, 1000 or less. From the viewpoint of suppressing a decrease in the ionic conductivity of the electrolyte, the molecular weight of the organic molecule (A) is preferably 500 or less, more preferably 450 or less, even more preferably 400 or less, even more preferably 350 or less, even more preferably 300 or less, and even more preferably 250 or less. Regarding the lower limit of the molecular weight of the organic molecule (A), from the viewpoint of suppressing leakage from the electrolyte and showing high ionic conductivity under low confinement pressure, it is preferably 20 or more, more preferably 40 or more, and even more preferably 50 or more. The molecular weight range of the organic molecule (A) is preferably 20 to 500, more preferably 40 to 450, and even more preferably 50 to 400.

[0038] The organic molecule (A) preferably has at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms. Having one or more atoms from among oxygen atoms, nitrogen atoms, and sulfur atoms in the organic molecule (A) makes it possible to obtain an electrolyte with high ionic conductivity while enabling the flexibility of the electrolyte. In the following, the at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms will also be referred to as a "specific atom."

[0039] The number of specific atoms in an organic molecule (A) is not particularly limited. When the organic molecule (A) is a nonpolymer, the number of specific atoms in the organic molecule (A) is preferably 1 to 8 per molecule, and more preferably 2 to 6.

[0040] Preferred specific examples of the organic molecule (A) include at least one selected from the group consisting of carbonate ester compounds, nitrile compounds, sulfone compounds, amide compounds, ketone compounds, and carboxylic acid ester compounds. Specific examples of these include carbonate ester compounds such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, ethylene carbonate, and propylene carbonate. Examples of nitrile compounds include succinonitrile, adiponitrile, 3-hexendinitrile, 1,3,5-pentanetricarbonitride, tert-butylmalononitrile, and 1,2,2,3-propanetetracarbonitride. Examples of sulfone compounds include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dioctyl sulfone, tetrahydrothiophene 1,1-dioxide, 3-methylsulfolane, and 3-sulfolene. Examples of amide compounds include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, malonamide, succinamide, glutaramide, adipoamide, N,N,N′,N′-tetramethylmalonamide, N,N,N′,N′-tetraethylmalonamide, N,N,N′,N′-tetramethylsuccinamide, and terephthalamide. Examples of ketone compounds include acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclohexanone, acetophenone, and benzophenone. Examples of carboxylic acid ester compounds include ethyl acetate, propyl acetate, butyl acetate, dimethyl succinate, dimethyl adipate, dibutyl phthalate, and poly(1,4-butylene adipate).

[0041] Organic molecule (A) can preferably be at least one selected from the group consisting of carbonate ester compounds, nitrile compounds, sulfone compounds, amide compounds, and ketone compounds. Organic molecule (A) may be used alone or in combination of two or more types.

[0042] In this electrolyte, the content of organic molecule (A) is such that the ratio of the molar amount of alkali metal-containing compound to the mass of organic molecule (A) is 1.0 × 10⁻⁶. -3 5.0 × 10⁻⁶ moles / g or more -3It is preferable that the amount be less than or equal to moles / g. The ratio of the molar amount of the alkali metal-containing compound to the mass of organic molecule (A) is 1.2 × 10⁻⁶, from the viewpoint of suppressing the decrease in ionic conductivity caused by an excess amount of organic molecule (A). -3 More preferably 1.5 × 10⁻⁶ moles / g or higher. -3 A ratio of 4.5 × 10⁻⁶ moles / g or higher is even more preferable. Furthermore, the ratio of the molar amount of the alkali metal-containing compound to the mass of the organic molecule (A) should be 4.5 × 10⁻⁶ from the viewpoint of obtaining an electrolyte that exhibits high ionic conductivity even under low confinement pressure. -3 More preferably 3.5 × 10⁻⁶ moles / g or less. -3 A value of 100% or less per mole / g is even more preferable.

[0043] A more preferred range for the ratio of the molar amount of the alkali metal-containing compound to the mass of the organic molecule (A) is 1.2 × 10⁻⁶ -3 4.5 x 10⁻⁶ moles / g or more -3 It is less than or equal to moles / g, and 1.5 × 10⁻⁶ -3 3.5 x 10⁻³ moles / g or more -3 A value of mol / g or less is more preferable.

[0044] <Other ingredients> This electrolyte may further contain components other than the charge transfer complex, alkali metal-containing compound, and organic molecule described above (hereinafter also referred to as "other components"), to the extent that they do not impair the effects of the present invention. Examples of other components include solvents (e.g., organic solvents, water, or mixtures of organic solvents and water), binders, and the like.

[0045] <Method for producing electrolytes> This electrolyte can be produced using a charge transfer complex, an alkali metal-containing compound, and an organic molecule (A) as raw materials. The method for producing this electrolyte is not particularly limited. For example, this electrolyte can be produced by a method that includes a step of mixing the charge transfer complex, the alkali metal-containing compound, and the organic molecule (A) (mixing step).

[0046] The method for mixing the charge transfer complex, alkali metal-containing compound, and organic molecule (A) is not particularly limited. For example, the charge transfer complex, alkali metal-containing compound, and organic molecule (A) may be added to a container all at once or in separate portions. The mixing of the charge transfer complex, alkali metal-containing compound, and organic molecule (A) is preferably carried out while grinding. The grinding method may be the same as the method described in the method for producing the charge transfer complex.

[0047] When producing this electrolyte, a heating treatment may be performed on a mixture of the pulverized charge transfer complex, alkali metal-containing compound, and organic molecule (A). The heating temperature of the mixture is usually 100 to 320°C, and the heating time is, for example, 15 to 360 minutes. The heating treatment to obtain this electrolyte may be performed only once or multiple times. If the heating treatment is performed multiple times, the heating temperature and heating time in each treatment may be the same or different. The heating treatment to obtain this electrolyte is usually performed under normal pressure, but it may also be performed under pressure or under reduced pressure.

[0048] When manufacturing this electrolyte, it is possible to obtain an electrolyte exhibiting high ionic conductivity without performing heat treatment at high temperatures, such as 100°C or higher, as described above. Therefore, the manufacturing process for electrolytes can be simplified.

[0049] A mixture of a charge transfer complex, an alkali metal-containing compound, and an organic molecule (A) (preferably a powdered mixture after pulverization) may be molded into a desired shape. The molding method of the mixture is not particularly limited, and known methods such as extrusion molding, injection molding, pressure molding, casting, mold casting, and tape molding can be employed. Of these, it is preferable to obtain a molded body by pressure molding of the mixture in order to minimize the porosity of the resulting electrolyte. The pressure during pressure molding is, for example, 100 MPa or less, and preferably 50 MPa or less. In this electrolyte, even when the pressure during pressure molding is more preferably 30 MPa or less, even more preferably 20 MPa or less, and even more preferably 15 MPa or less, an electrolyte molded body exhibiting high ionic conductivity can be obtained, which is preferable. 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. The shape of the molded body can be, for example, rectangular or circular.

[0050] Furthermore, this electrolyte, produced using a charge transfer complex, an alkali metal-containing compound, and an organic molecule (A), is preferable from the viewpoint of simplifying the manufacturing process because it can obtain an electrolyte that exhibits high ionic conductivity without requiring heat treatment (annealing) at high temperatures (e.g., 100°C or higher) after molding.

[0051] The degree of crystallinity of the alkali metal-containing compound in the electrolyte is, for example, 50% or less, preferably 40% or less, and more preferably 30% or less. The degree of crystallinity of the alkali metal-containing compound in the electrolyte can be calculated using the following formula by measuring the heat of fusion H1 per unit mass of the perfectly crystalline alkali metal-containing compound and the heat of fusion H2 per unit mass of the alkali metal-containing compound in the electrolyte using a differential scanning calorimeter. Crystallinity=(H2 / H1)×100 (%)

[0052] <Electrolyte properties> (Ionic conductivity) This electrolyte exhibits high ionic conductivity at room temperature (25°C). Specifically, the ionic conductivity measured at 25°C using the AC impedance method is 1 × 10⁻⁶.-7 S·cm -1 Preferably, the above conditions are met. From the viewpoint of obtaining an energy storage device with excellent performance, the ionic conductivity under the same conditions should be 5 × 10 -7 S·cm -1 More preferably, 10 × 10 -7 S·cm -1 The above is even more preferable. Details of the method for measuring ionic conductivity are as described in the examples below.

[0053] This electrolyte exhibits high ionic conductivity at room temperature. Therefore, by using this electrolyte as the electrolyte in an energy storage device, it is possible to obtain an energy storage device with stable quality.

[0054] Energy storage devices The energy storage device of the present invention (hereinafter also referred to as "this device") comprises this electrolyte. Examples of this device include secondary batteries and capacitors. When this device is a secondary battery, one embodiment is a solid-state battery, and a lithium-ion secondary battery is preferred due to its excellent ion conductivity.

[0055] A lithium-ion secondary battery, which is one embodiment of this device, will be described. The lithium-ion secondary battery is a laminate comprising electrodes consisting of a positive electrode and a negative electrode, and an electrolyte layer, with the electrolyte layer positioned between the positive electrode and the negative electrode so as to be in contact with the electrolyte layer. The materials constituting the positive electrode and the negative electrode are not particularly limited and can be appropriately selected and used from materials known as electrode materials for lithium-ion secondary batteries. For example, metal foil such as aluminum or stainless steel can be used as the positive electrode current collector. Metal foil such as copper foil or lithium foil can be used as the negative electrode current collector.

[0056] In the lithium-ion secondary battery of this disclosure, the electrolyte layer comprises the charge transfer complex, alkali metal-containing compound, and organic molecule (A) described above. The thickness of the electrolyte layer is not particularly limited and can be set as appropriate depending on the application of the secondary battery. The thickness of the electrolyte layer is, for example, 5 to 500 μm. A thickness of 5 to 300 μm is preferred, 5 to 200 μm is more preferred, and 5 to 100 μm is even more preferred, as this allows for obtaining an electrolyte layer with a sufficiently small porosity and further increasing the energy density of the energy storage device.

[0057] The method for manufacturing a lithium-ion secondary battery is not particularly limited, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a laminate comprising a positive electrode, an electrolyte layer, and a negative electrode may be manufactured by molding a powdery mixture (powdered composition) containing a charge transfer complex, an alkali metal-containing compound, and an organic molecule (A), and sandwiching the electrolyte obtained between a positive electrode and a negative electrode. The laminate comprising the positive electrode, electrolyte layer, and negative electrode is usually housed in a case and used as a secondary battery.

[0058] Furthermore, this device is not limited to the above configuration in which lithium ions are the ion carriers, but may also be a secondary battery that uses other ions, such as sodium ions, as carriers. This device may also be a capacitor. One embodiment of a capacitor includes an anode, a cathode, and an electrolyte layer, with the electrolyte layer positioned between the anode and the cathode so that the electrolyte layer is in contact with the electrodes.

[0059] Energy storage devices equipped with this electrolyte can be applied to a variety of uses. Specifically, they can be used as a power source in various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various mobile devices such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances. [Examples]

[0060] The present invention will be described in detail below based on the following examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass," respectively, unless otherwise specified.

[0061] Manufacturing of charge transfer complexes [Manufacturing Example 1] 43 parts of poly(2,6-dimethyl-1,4-phenylene oxide) (manufactured by Sigma-Aldrich) and 57 parts of chloranil were coarsely mixed in a mortar and pestle and ground for 30 minutes at a frequency of 40 Hz using a ball mill (FRITSCH Mini Mill PULVERISETTE 23; hereinafter simply referred to as "ball mill"). The obtained pulverized material was placed in a petri dish, covered with aluminum foil, and heated for 60 minutes on a hot plate (AS ONE CHP-170DF; hereinafter simply referred to as "hot plate") set to 200°C, followed by heating for 30 minutes on a hot plate set to 280°C. This yielded the charge transfer complex as a black powder.

[0062] ≪Manufacturing and Evaluation of Electrolytes≫ Electrolyte powders were prepared in each example and comparative example. Furthermore, for the examples and comparative examples in which organic molecules and alkali metal-containing compounds were used as raw materials for preparing the electrolyte powders, the solubility of the alkali metal-containing compounds in relation to the organic molecules was tested. Details of the test method are as follows. (Test of the solubility of alkali metal-containing compounds in organic molecules) In each example and comparative example, 100 g of organic molecules and 0.1 moles of alkali metal-containing compound were placed in a 200 mL container, and the mixture was stirred for 12 hours at 25°C and 30 rpm using a mix rotor (VMRC-5, manufactured by AS ONE Corporation). Solubility was then evaluated based on the following criteria. ○: Soluble (No residue of alkali metal-containing compounds was visually detected, and the entire mixture was liquid.) ×: Not soluble (residue of alkali metal-containing compounds can be visually confirmed.)

[0063] When alkali metal-containing compounds dissolve in organic molecules, the dissolution occurs through solvation of the alkali metal-containing compound by the organic molecules. Therefore, whether or not an alkali metal-containing compound is dissolved in an organic molecule can be confirmed by using a Fourier transform infrared spectrophotometer (FT-IR) to analyze the organic molecule, the alkali metal-containing compound, and the mixture of the alkali metal-containing compound and the organic molecule, respectively, and then observing the peak shift in the IR spectrum attributed to the coordinating functional group in the organic molecule that supports the alkali metal-containing compound.

[0064] [Example 1] (1) Manufacturing of electrolyte powder EL-1 To 47 parts of the charge transfer complex prepared in Production Example 1, 19 parts of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Kanto Chemical Co., Ltd., hereinafter also referred to as "LiTFSI") and 34 parts of diethyl carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., hereinafter also referred to as "DEC") were added, the mixture was roughly mixed in a mortar, and then ground using a ball mill at 25°C and 40Hz for 60 minutes to obtain electrolyte powder EL-1.

[0065] (2) Test of the solubility of alkali metal-containing compounds in organic molecules The solubility of 0.1 moles of LiTFSI (alkali metal-containing compound) per 100 g of DEC (organic molecule) was evaluated using the method described above. No residue of the alkali metal-containing compound was visually observed, and the entire mixture was liquid, resulting in a positive rating (○).

[0066] Furthermore, the FT-IR analysis results are shown in Figure 1. In Figure 1, the thin line is the IR spectrum of DEC, the dotted line is the IR spectrum of LiTFSI, and the thick line is the IR spectrum of a mixture of DEC and LiTFSI. From the IR spectrum results in Figure 1, for DEC alone, the peak at 1750 cm is due to the C=O stretching vibration of DEC. -1 Although observed in the vicinity, the mixture of DEC and LiTFSI yielded 1720 cm³. -1A peak shift was observed in the vicinity. This peak shift is thought to be due to the solvation of DEC with LiTFSI, and this result confirmed that LiTFSI was dissolved in DEC. The IR spectrum was measured using a Fourier transform infrared spectrophotometer (Thermo Fisher Scientific, Nicolet iS50) by Diamond-ATR infrared absorption spectroscopy.

[0067] (3) Manufacturing and evaluation of molded products Two sets of all-solid-state battery evaluation cells (KP-SolidCell, manufactured by Hosen Co., Ltd.) were prepared, and 30 mg of electrolyte powder EL-1 was packed into each. One of the two sets of all-solid-state battery evaluation cells was sealed with a torque of 2 N·m (restraining pressure of 9 MPa), and the other was sealed with a torque of 20 N·m (restraining pressure of 90 MPa). A disc made of SKD steel (1 cm in diameter) was used to sandwich the electrolyte powder. The confinement pressure of the all-solid-state battery evaluation cell was determined by placing a pressure measurement film (Prescale, manufactured by Fujifilm Corporation), cut to a diameter of 1 cm, into the all-solid-state battery evaluation cell and measuring the pressure when sealed with torques of 2 N·m and 20 N·m. Furthermore, using molded bodies of electrolyte powder EL-1, the ionic conductivity was measured and the variation in ionic conductivity due to confinement pressure was evaluated using the following method.

[0068] (Measurement of ionic conductivity) For the measurement, the AC impedance method was used, which involves applying an alternating current (applied voltage of 100mV) between electrodes to measure the resistance component. Ionic conductivity was calculated from the real impedance intercept of the resulting Cole-Cole plot. An impedance analyzer (Biologic SP-300) was used for the measurement, and the measurements were taken at 25°C. All of the above operations were performed in a dry room with a dew point of -60°C. The ionic conductivity (σ) was calculated using the following formula (1), and the result was 9 × 10 at a confinement pressure of 9 MPa. -5 S·cm -1 At a restraining pressure of 90 MPa, 5 × 10 -5 S·cm -1 That was the case. σ = H / (R × S) (1) (In formula (1), σ is ionic conductivity (unit: S·cm) -1 ), R is resistance (unit: Ω), S is the cross-sectional area of ​​the solid electrolyte membrane at the time of measurement (unit: cm 2 ), H indicates the distance between electrodes (unit: cm).

[0069] (Evaluation of ionic conductivity variations due to confinement pressure) Based on the measured ionic conductivity at confinement pressures of 9 MPa and 90 MPa, the variation in ionic conductivity due to confinement pressure was evaluated according to the following criteria using the value obtained by the following formula (2). As a result, the electrolyte in Example 1 was judged to be "A". Of the following criteria A to C, A and B indicate that the ionic conductivity under weak confinement pressure does not decrease significantly compared to the ionic conductivity under strong confinement pressure, and that the variation in ionic conductivity due to confinement pressure is small and acceptable. C means that the variation in ionic conductivity due to confinement pressure is too large to be acceptable. s = σ(90) / σ(9) (2) (In formula (2), σ(90) is the ionic conductivity at a confinement pressure of 90 MPa (unit: S·cm) -1 ), σ(9) is the ionic conductivity at a confinement pressure of 9 MPa (unit: S·cm). -1 ) indicates. ) A:s is less than 100 B:s is between 100 and 1,000 C:s is 1,000 or more

[0070] [Examples 2-14, Comparative Examples 1-3] Except for changing the types and quantities of raw materials as shown in Tables 1 and 2, the same procedure as in Example 1 was performed to obtain electrolyte powders EL-2 to EL-17. Furthermore, using the obtained electrolyte powders EL-2 to EL-17, molded bodies of the electrolyte powders were manufactured in the same manner as in Example 1, and the ionic conductivity was measured and the variation in ionic conductivity due to confinement pressure was evaluated. Tables 1 and 2 show the results of the evaluation of the solubility of alkali metal-containing compounds in organic molecules used in each example and comparative example, along with the results of the ionic conductivity measurement and the evaluation of the variation in ionic conductivity due to confinement pressure. In Table 2, the notation "<10^-13" indicates that the measured ionic conductivity is 1 × 10⁻¹⁶. -13 S·cm -1 This means smaller. Tables 1 and 2 also show the ratio (Q3 / (Q1+Q2)) of the molar amount of alkali metal-containing compounds to the total molar amount of electron-donating compounds (monomer equivalent) and electron-accepting compounds in the charge-transfer complex.

[0071] [Table 1]

[0072] [Table 2]

[0073] The details of the alkali metal-containing compounds and organic molecules used in Tables 1 and 2 are shown below. <Alkali metal-containing compounds> • LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide [manufactured by Kanto Chemical Co., Ltd.], Molecular weight: 287.12 • LiFSI: Lithium bis(fluorosulfonyl)imide [manufactured by Kanto Chemical Co., Ltd.], Molecular weight: 187.07 • LiFTFSI: Lithium (fluorosulfonyl) (trifluoromethanesulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; trade name: (fluorosulfonyl) (trifluoromethanesulfonyl)imide = lithium, molecular weight: 237.08) • LiPF6: Lithium hexafluorophosphate [manufactured by Kanto Chemical Co., Ltd.], Molecular weight: 151.91 <Organic molecules> • DEC: Diethyl carbonate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 118.13 • EC: Ethylene carbonate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 88.06 • SN: Sucinonitrile [manufactured by Tokyo Chemical Industry Co., Ltd.], Molecular weight: 80.09 • AdN: Adiponitrile [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 108.14 • SL: Tetrahydrothiophene 1,1-dioxide [manufactured by Tokyo Chemical Industry Co., Ltd.], Molecular weight: 120.17 • DBP: Dibutyl phthalate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 278.34 • PN7160: ADEKA Sizer PN-7160 [Manufactured by ADEKA Corporation], Molecular weight: 800 • NMP: N-methylpyrrolidone [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 99.13 • DMA: N,N-dimethylacetamide [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 87.12 Hex: Hexane [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 86.18 • Tol: Toluene [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.], Molecular weight: 92.14

[0074] <<Evaluation Results>> As is clear from the results of Examples 1 to 14, charge transfer complexes of electron-accepting compounds having a phenylene skeleton and electron-donating compounds, alkali metal-containing compounds, and electrolytes containing organic molecules (A) exhibited high ionic conductivity at room temperature and also under weak confinement pressure. Among these, Examples 1 to 10, 13, and 14 showed particularly good ionic conductivity compared to Examples 11 and 12.

[0075] In contrast, Comparative Example 1, which consisted only of a charge transfer complex and an alkali metal-containing compound and did not contain organic molecules (A), showed high ionic conductivity under strong confinement pressure, but significantly decreased ionic conductivity under weak confinement pressure. Furthermore, Comparative Examples 2 and 3, which contained organic molecules that could not dissolve the alkali metal-containing compound, showed low ionic conductivity under weak confinement pressure.

Claims

1. A charge transfer complex formed by an electron-donating compound and an electron-accepting compound, Alkali metal-containing compounds, A different organic molecule from the charge transfer complex and the alkali metal-containing compound, It contains, The electron-donating compound has a phenylene skeleton, The aforementioned organic molecule is an electrolyte that, when 100 g of the organic molecule is mixed with 0.1 moles of the alkali metal-containing compound at 25°C, is capable of dissolving the alkali metal-containing compound.

2. The electrolyte according to claim 1, wherein the organic molecule has at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, and sulfur atoms.

3. The electrolyte according to claim 1, wherein the organic molecule is at least one selected from the group consisting of carbonate ester compounds, nitrile compounds, sulfone compounds, amide compounds, and ketone compounds.

4. The electrolyte according to claim 1, wherein the molecular weight of the organic molecule is 500 or less.

5. The ratio of the molar amount of the alkali metal-containing compound to the mass of the organic molecule is 1.0 × 10 －３ 5.0 x 10⁻⁶ moles / g or more －３ The electrolyte according to claim 1, wherein the concentration is mol / g or less.

6. The electrolyte according to claim 1, wherein the electron-donating compound is a (poly)phenylene oxide compound.

7. The electrolyte according to claim 1, wherein the ratio of the molar amount of the alkali metal-containing compound to the total amount of the molar amount of the electron-donating compound (however, if the electron-donating compound is a polymer, the ratio is calculated on a monomer basis) and the molar amount of the electron-accepting compound in the charge-transfer complex is 0.03 or more and 1.0 or less.

8. The electrolyte according to claim 1, wherein the electron-accepting compound comprises at least one selected from the group consisting of 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), o-benzoquinone, m-benzoquinone, and p-benzoquinone.

9. The electrolyte according to claim 1, wherein the alkali metal-containing compound comprises an alkali metal salt.

10. The electrolyte according to claim 1, wherein the alkali metal-containing compound includes a lithium-containing compound.

11. An energy storage device comprising the electrolyte described in any one of claims 1 to 10.

12. A method for producing an electrolyte according to any one of claims 1 to 10, A method for producing an electrolyte, comprising the step of mixing the charge transfer complex, the alkali metal-containing compound, and the organic molecule.

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