Solid electrolyte, power storage device, and method for producing solid electrolyte

Abstract

The present invention provides: a plastic-crystal solid electrolyte that has high ionic conductivity; and an electricity storage device which uses this solid electrolyte. This solid electrolyte contains a plastic crystal that is doped with an electrolyte. The plastic crystal contains cations of two or more kinds, at least one kind of which is selected from the group consisting of various imidazoliums and various quaternary ammoniums.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte containing plastic crystals, an electricity storage device using this solid electrolyte, and a method for producing this solid electrolyte. [Background technology]

[0002] Secondary batteries, electric double layer capacitors, fuel cells, solar cells, and other power storage devices are generally configured with positive and negative electrodes facing each other with an electrolyte layer sandwiched between them. Lithium ion secondary batteries have a Faraday reaction electrode and charge and discharge electrical energy by reversibly inserting and desorbing lithium ions in the electrolyte layer into and from the electrode. Electric double layer capacitors have polarizable electrodes at one or both of their electrodes and are charged and discharged by utilizing the charge storage effect of the electric double layer formed at the interface between the polarizable electrode and the electrolyte layer.

[0003] A solid electrolyte layer can be selected as the electrolyte layer for an energy storage device. With a solid electrolyte layer, the area where chemical reactions with the electrodes, such as hydration degradation, occur is limited to the vicinity of the electrodes. Therefore, compared to a liquid electrolyte, leakage current is lower and self-discharge is suppressed. Furthermore, compared to a liquid electrolyte, the amount of gas generated due to chemical reactions with the electrodes is lower, and the risk of valve opening and liquid leakage is reduced.

[0004] Solid electrolytes include sulfide-based solid electrolytes such as Li2S·P2S5, Li7La3Zr2O 12 Known examples of suitable solid electrolytes include oxide-based solid electrolytes such as those described above, plastic crystal-based solid electrolytes with N-ethyl-N-methylpyrrolidinium (P12) as the cation and bis(fluorosulfonyl)amide (FSA) as the anion, and polymer-based solid electrolytes such as polyethylene glycol. For secondary batteries, lithium ions are doped as electrolytes into a selected host phase as needed, and for electric double layer capacitors, TEMABF4, for example, is doped as electrolytes into a selected host phase as needed.

[0005] Plastic crystals are soluble in organic solvents. On the other hand, sulfide-based and oxide-based solid electrolytes are insoluble. Therefore, when using plastic crystals as a solid electrolyte or the parent phase of a solid electrolyte, a manufacturing method can be used in which the anion and cation components of the plastic crystal, or salts of these, are dissolved in a solvent and cast onto an electrode. Therefore, compared to sulfide-based and oxide-based solid electrolytes, plastic crystal-based solid electrolytes have the advantage of improved adhesion to electrodes and, if the active material phase of the electrode has a porous structure, they can easily penetrate into the structure. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2014-504788 [Patent Document 2] Japanese Patent Application Publication No. 2017-91813 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it has been pointed out that the ionic conductivity of plastic crystal-based solid electrolytes is two to three orders of magnitude lower than that of sulfide-based and oxide-based solid electrolytes. For example, a solid electrolyte containing a plastic crystal composed of N,N-diethylpyrrolidinium cation and bis(fluorosulfonyl)amide anion has an ionic conductivity of 1×10 -5 It has been reported that the ionic conductivity is on the order of S / cm. In addition, a solid electrolyte containing a plastic crystal consisting of N,N-dimethylpyrrolidinium cation and bis(trifluoromethanesulfonyl)amide anion has an ionic conductivity of 1×10 -8 It has been reported that the ionic conductivity is on the order of S / cm.

[0008] In contrast, for example, the ionic conductivity of a solid electrolyte such as Li2S·P2S5 is 1×10 -2 It has been reported that the s / cm order is 12 When the solid electrolyte is-3 It has been reported to be on the order of S / cm.

[0009] The present invention has been proposed to solve the above-mentioned problems, and an object of the present invention is to provide a plastic crystal solid electrolyte having high ionic conductivity and an electricity storage device using the solid electrolyte. [Means for solving the problem]

[0010] As a result of intensive research by the inventors, it was found that when a mixture of two cations, each of which is a specific cation capable of forming a plastic crystal, is used, the ionic conductivity of the solid electrolyte is improved compared to when a single cation is used. It was also found that when one of the two cations is an imidazolium-based cation, the degree of improvement in the ionic conductivity of the solid electrolyte is greater, and it was also found that when two anions capable of forming a plastic crystal are used in combination, the ionic conductivity of the solid electrolyte is improved compared to when a single anion is used.

[0011] The present invention was made based on this finding, and in order to solve the above-mentioned problems, the solid electrolyte of the present invention comprises a plastic crystal doped with an electrolyte, and the plastic crystal contains a total of two or more cations, at least one of which is selected from the group consisting of various imidazoliums and various quaternary ammoniums.

[0012] The present invention has been made based on this finding, and the plastic crystal may contain two or more types of anions, for example, various amide anions in which two hydrogen atoms of the NH anion are substituted with perfluoroalkylsulfonyl groups, fluorosulfonyl groups, or both, and tris(trifluoromethanesulfonyl)methanide anion.

[0013] Furthermore, the present invention has been made based on this finding, and the plastic crystal may contain two types of cations selected from the group of various quaternary ammoniums, or two types of cations selected from the group of various imidazoliums, or one type of cation selected from each of the group of various imidazoliums and the group of various quaternary ammoniums, or one type of cation selected from the group of various imidazoliums and various quaternary ammoniums and one type of cation other than the various imidazoliums and the various quaternary ammoniums.

[0014] The one cation selected from the group of various imidazoliums is preferably a 1,3-dimethylimidazolium cation, a 1-ethyl-3-methylimidazolium cation, a 1-methyl-3-propylimidazolium cation, or an imidazolium having a methyl group substituted at the 2-position of any of these cations, and the plastic crystal preferably contains an N,N-hexafluoro-1,3-disulfonylamide anion as the anion for the one cation selected from the group of various imidazoliums.

[0015] Furthermore, it is preferable that the one cation selected from the group of various imidazoliums is 1,3-dimethylimidazolium or 1-ethyl-3-methylimidazolium, and the plastic crystal contains, as an anion for the one cation selected from the group of various imidazoliums, a perfluoroalkylsulfonate anion in which the hydrocarbon group extending from the sulfonic acid skeleton is substituted with a perfluoroalkyl group.

[0016] By combining these anions with imidazolium, plastic crystals can be easily synthesized and the ionic conductivity of the plastic crystals can be improved to a greater extent.

[0017] An electricity storage device using this solid electrolyte is also one embodiment of the present invention.

[0018] Furthermore, the method for producing a solid electrolyte according to the present invention has been made based on this finding, and is characterized in that it comprises a step of producing a plastic crystal containing two types of cations selected from the group consisting of various pyrrolidiniums, various imidazoliums, various quaternary ammoniums, and various phosphoniums, in order to solve the above-mentioned problems. [Effects of the Invention]

[0019] According to the present invention, the ionic conductivity of a solid electrolyte using a plastic crystal is improved. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0021] (solid electrolyte) A solid electrolyte is interposed between the positive and negative electrodes of an electricity storage device and mainly conducts ions. An electricity storage device is a passive element that charges and discharges electrical energy, such as a lithium-ion secondary battery or an electric double-layer capacitor. A lithium-ion secondary battery has a Faraday reaction electrode and charges and discharges electrical energy by reversibly inserting and desorbing lithium ions in the solid electrolyte into and from the electrode. An electric double-layer capacitor has polarizable electrodes at one or both of its electrodes, and charges and discharges by utilizing the electrical storage effect of the electric double layer formed at the interface between the electrode and the solid electrolyte.

[0022] This solid electrolyte has a parent phase made of a plastic crystal that serves as an ion-conducting medium, and contains an ionic salt doped into the plastic crystal as an electrolyte. Plastic crystals, also known as plastic crystals, have an ordered arrangement and a disordered orientation. That is, plastic crystals have a three-dimensional crystal lattice structure in which anions and cations are regularly arranged, but these anions and cations have rotational disorder. Within plastic crystals, cations and cations generated by dissociation of the electrolyte hop through the voids in the crystal lattice due to the rotation of the anions and cations.

[0023] (plastic crystalline cation) The plastic crystal is composed of at least two types of cations. At least one cation of the plastic crystal is selected from the group consisting of various imidazoliums and various quaternary ammoniums. That is, the plastic crystal contains two different types of imidazoliums, two different types of quaternary ammoniums, one type of imidazolium and one type of quaternary ammonium, one type of imidazolium and another cation, or one type of quaternary ammonium and another cation. Examples of the other cation include various phosphoniums.

[0024] Imidazolium is composed of a five-membered ring containing nitrogen atoms at the 1st and 3rd positions. The five-membered ring is a cyclic conjugated system, and the π electrons are delocalized, reducing the surface charge density and the apparent charge q. This reduces the Coulomb force with the cations that make up the plastic crystal. In addition, this imidazolium is substituted with alkyl groups at the 1st and 3rd positions. These alkyl groups create a distance from the anion, reducing the Coulomb force between this imidazolium and the anion.

[0025] These compounds are preferably selected because they are expected to particularly improve ionic conductivity since the interaction between the imidazolium and the anion is reduced and the degree of rotational freedom between the imidazolium and the anion is increased.

[0026] These various imidazoliums are 1,3-dialkylimidazoliums or 1,2,3-trialkylimidazoliums represented by the following chemical formula (A). [ka] In the formula, n and m are integers of 1 to 3, and p is 0 or 1.

[0027] In the chemical formula (A), when p is 0, n and m are 1, the compound is 1,3-dimethylimidazolium (DMI) represented by the following chemical formula (A1). The 2-position of this DMI may be substituted with a methyl group. [ka]

[0028] In the chemical formula (A), when p is 0, n is 1, and m is 2, the compound is 1-ethyl-3-methylimidazolium (EMI) represented by the following chemical formula (A2). The 2-position of this EMI may be substituted with a methyl group. [ka]

[0029] In the chemical formula (A), when p is 0, n is 1, and m is 3, it is 1-methyl-3-propylimidazolium (MPI) represented by the following chemical formula (A3). The 2-position of this MPI may be substituted with a methyl group. [ka]

[0030] The quaternary ammonium is represented by the following chemical formula (B), and includes tetraalkylammonium substituted with a linear alkyl group, regardless of the number of carbon atoms. In the following chemical formula (B), when a, b, and c are 2 and d is 1, it is triethylmethylammonium (TEMA). [ka] In the formula, a, b, c, and d are integers of 1 or more, and the number of carbon atoms may be any number.

[0031] Furthermore, examples of quaternary ammonium include pyrrolidinium, which is represented by the following chemical formula (C) and has a five-membered ring to which a methyl group, an ethyl group, or an isopropyl group is bonded. [ka] In the formula, R1 and R2 are a methyl group, an ethyl group, or an isopropyl group.

[0032] Specific examples of the five-membered ring pyrrolidinium generalized by the above chemical formula (C) include N-ethyl-N-methylpyrrolidinium (P12) represented by the following chemical formula (C1), N-isopropyl-N-methylpyrrolidinium (P13iso) represented by the following chemical formula (C2), and N,N-diethylpyrrolidinium (P22) represented by the following chemical formula (C3).

[0033] [ka]

[0034] [ka]

[0035] [ka]

[0036] Furthermore, examples of quaternary ammonium include spiropyrrolidinium (SBP) represented by the following chemical formula (D). [ka]

[0037] Other examples of cations include various phosphoniums, such as tetraalkylphosphoniums substituted with a linear alkyl group (regardless of the number of carbon atoms) represented by the following chemical formula (E): An example of a tetraalkylphosphonium is the tetraethylphosphonium cation (TEP). [ka] In the formula, e, f, g, and h are integers of 1 or more, and the number of carbon atoms may be any.

[0038] Although not limited to this mechanism, it is speculated that, taking a plastic crystal containing one type of cation as a standard, the crystal structure changes when the two types are mixed, and this change facilitates hopping of cations and anions in the electrolyte, resulting in an improvement in the ionic conductivity of the solid electrolyte.

[0039] However, rather than simply mixing two types, the ionic conductivity of the solid electrolyte is improved when the crystal structure of the plastic crystal composed of various imidazolium elements represented by chemical formula (A) changes due to the inclusion of other cations. Also, the ionic conductivity of the solid electrolyte is improved when the crystal structure of the plastic crystal composed of quaternary ammonium elements represented by chemical formula (B) changes due to the inclusion of other cations.

[0040] The ionic conductivity of the solid electrolyte is significantly improved when the molar ratio of the two species is within the range of 10:90 to 90:10, i.e., when one species accounts for 10 mol% to 90 mol% of the total number of moles of cations constituting the plastic crystal. In particular, the ionic conductivity of the solid electrolyte is significantly improved when the molar ratio of the two species is within the range of 20:80 to 80:20, i.e., when one species accounts for 20 mol% to 80 mol% of the total number of moles of cations constituting the plastic crystal.

[0041] The anion constituting the plastic crystal may be any known anion as long as it can maintain a solid state within the temperature range in which the power storage device is used without becoming an ionic liquid and can form a plastic crystal, and two or more types of anions may be selected. Imidazolium is a cation that forms an ionic liquid within a temperature range including room temperature, and when this imidazolium is selected, a specific type of anion is selected to form the plastic crystal.

[0042] (plastic crystalline anion) Examples of anions include various amide anions, tris(trifluoromethanesulfonyl)methanide anion, hexafluorophosphate anion (PF6 anion), various perfluoroalkylphosphate anions in which some of the fluorine atoms in PF6 have been substituted with fluoroalkyl groups, various perfluoroalkylborate anions in which some of the fluorine atoms in BF4 anion have been substituted with fluoroalkyl groups, and various perfluoroalkylsulfonate anions (NFS anions) in which the hydrocarbon group extending from the sulfonic acid skeleton has been substituted with a perfluoroalkyl group.

[0043] In the various amide anions, two hydrogen atoms of the NH anion are replaced by perfluoroalkylsulfonyl groups, fluorosulfonyl groups, or both. The various amide anions include, for example, linear anions, such as various bis(perfluoroalkylsulfonyl)amide anions, bis(fluorosulfonyl)amide anions, and various N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)amide anions represented by the following chemical formula (F).

[0044] [ka] In the chemical formula (F), n and m are integers of 0 or more, and the number of carbon atoms may be any number.

[0045] In the chemical formula (F), if n and m are 1 or more, the anion is a bis(perfluoroalkylsulfonyl)amide anion. Specific examples of the bis(perfluoroalkylsulfonyl)amide anion include the bis(trifluoromethanesulfonyl)amide anion (TFSA anion) represented by the following chemical formula (F1) and the bis(pentafluoroethylsulfonyl)amide anion (BETA anion) represented by the following chemical formula (F2).

[0046] [ka]

[0047] [ka]

[0048] In the chemical formula (F), a group having 0 carbon atoms is a fluorosulfonyl group, and when n and m are 0, the anion is a bis(fluorosulfonyl)amide anion (FSA anion) represented by the following chemical formula (F3).

[0049] [ka]

[0050] In the chemical formula (F), when n is 0 and m is 1 or more, it is an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)amide anion represented by the following chemical formula (F4).

[0051] [ka]

[0052] Furthermore, various amide anions include, for example, five-membered and six-membered heterocyclic rings, such as N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion) represented by the following chemical formula (G) and N,N-pentafluoro-1,3-disulfonylamide represented by the following chemical formula (H).

[0053] [ka]

[0054] [ka]

[0055] The tris(trifluoromethanesulfonyl)methanide anion (TFSM anion) is represented by the following chemical formula (I): [ka]

[0056] Examples of various perfluoroalkylphosphate anions in which some of the fluorine atoms of PF6 have been substituted with fluoroalkyl groups include tris(fluoroalkyl)trifluorophosphate anions represented by the following chemical formula (J). [ka] In the chemical formula (J), q is an integer of 1 or more, and the number of carbon atoms may be any number.

[0057] Specifically, tris(pentafluoroethyl)trifluorophosphate anion (FAP anion) represented by the following chemical formula (J1) can be mentioned. [ka]

[0058] The various perfluoroalkylborate anions include mono(fluoroalkyl)trifluoroborate anions and bis(fluoroalkyl)fluoroborate anions represented by the following chemical formula (K). [ka] In the formula, s is an integer of 0 or more, t is an integer of 1 or more, and the number of carbon atoms may be any number.

[0059] In the chemical formula (K), when s is 0 and t is 1 or more, the anion is a mono(fluoroalkyl)trifluoroborate anion represented by the following chemical formula (K1). A specific example is a mono(trifluoromethyl)trifluoroborate anion represented by the following chemical formula (K2).

[0060] [ka] In the formula, t is an integer of 1 or more, and the number of carbon atoms may be any number.

[0061] [ka]

[0062] Various perfluoroalkylsulfonate anions (NFS anions) are represented by the following chemical formula (L). [ka] In the chemical formula (L), r is an integer of 1 or more and 4 or less.

[0063] Specifically, the various perfluoroalkylsulfonate anions are preferably a trifluoromethanesulfonate anion in which r is 1 in the following chemical formula (L), a pentafluoroethylsulfonate anion in which r is 2 in the following chemical formula (L), a heptafluoropropanesulfonate anion in which r is 3 in the following chemical formula (L), and a nonafluorobutanesulfonate anion in which r is 4 in the following chemical formula (L).

[0064] When imidazolium is selected as the cation of the plastic crystal, the anion that constitutes the plastic crystal together with this imidazolium is preferably N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion) represented by the above chemical formula (G), or a perfluoroalkylsulfonate anion (NFS anion) represented by the above chemical formula (L) in which the hydrocarbon group extending from the sulfonic acid skeleton is substituted with a perfluoroalkyl group.

[0065] Imidazolium is known as a cation that forms an ionic liquid with a melting point of -3°C, composed of a bis(trifluoromethanesulfonyl)amide anion, also known as the TFSA anion. The apparent charge q and the presence of alkyl groups are sensitive to the increase or decrease in Coulomb force.

[0066] On the other hand, when the CFSA anion or NFS anion is combined with, for example, N-ethyl-N-methylpyrrolidinium, also known as the P12 cation, to form P12CFSA, it forms a plastic crystal with a melting point of 302°C. In other words, it is believed that the melting points of plastic crystals containing these anions are higher. Therefore, it is believed that these anions act to raise the melting points of salts with cations that have low melting points and are likely to form ionic liquids. Furthermore, it is believed that by adjusting the chain length of the alkyl group of the cation to 3 or less carbon atoms or 2 or less depending on the anion, it is possible to achieve a balance between the ability to form plastic crystals and the degree of improvement in ionic conductivity.

[0067] As a result, imidazolium in combination with these anions forms plastic crystals that exhibit even higher ionic conductivity.

[0068] The anion is not limited to one type, and two types may be combined. The use of two types of anions improves ionic conductivity. While not limited to this mechanism, it is speculated that, based on a plastic crystal containing one type of anion, the crystal structure changes when two types are mixed. This change facilitates hopping of anions and cations in the electrolyte, improving the ionic conductivity of the solid electrolyte. Therefore, as long as the crystal structure changes compared to the single anions, the mixing ratio of the two types may be any.

[0069] However, when the mixing ratio of the two types is within the range of 10:90 to 90:10 in terms of molar ratio, in other words, when the mixing ratio of the two types is within the range of 10 mol% to 90 mol% of one of the anions relative to the total number of moles of the anions constituting the plastic crystal, the ionic conductivity of the solid electrolyte is significantly improved. In particular, when the mixing ratio of the two types is within the range of 20:80 to 80:20 in terms of molar ratio, in other words, when the mixing ratio of the two types is within the range of 20 mol% to 80 mol% of one of the anions relative to the total number of moles of the anions constituting the plastic crystal, the ionic conductivity of the solid electrolyte is further significantly improved.

[0070] (electrolyte) The ionic salt to be doped into the plastic crystal to become the electrolyte may be selected depending on the type of electricity storage device. Examples of ionic salts for lithium ion secondary batteries include Li(CF3SO2)2N (commonly known as LiTFSA), Li(FSO2)2N (commonly known as LiFSA), Li(C2F5SO2)2N, LiPF6, LiBF4, LiAsF6, LiTaF6, LiClO4, and LiCF3SO3, which may be used alone or in combination of two or more. Examples of ionic salts for electric double layer capacitors include salts of organic acids, salts of inorganic acids, and salts of complex compounds of organic and inorganic acids, which may be used alone or in combination of two or more.

[0071] Examples of organic acids include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid including tetrafluoroborate, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic and inorganic acids include borodisalicylic acid, borodioxalic acid, and borodiglycolic acid.

[0072] Examples of the salts of these organic acids, inorganic acids, and at least one salt of a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of the quaternary ammonium ion of the quaternary ammonium salt include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of the quaternized amidinium include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of the amine of the amine salt include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine. Furthermore, examples of ionic salts for electric double layer capacitors include salts containing cation components of the above chemical formulas (N), (P), (Q), and (R) that form plastic crystals.

[0073] (Manufacturing method) An example of a method for manufacturing a solid electrolyte containing such plastic crystals is as follows: An alkali metal salt of a first type of anion that constitutes the plastic crystals and a halogenated cation are each dissolved in a solvent. Examples of alkali metals include Na, K, Li, and Cs. Examples of halogenated cations include F, Cl, Br, and I. Water is a preferred solvent. An ion exchange reaction is carried out by gradually adding a solution of the metal salt of the anion dropwise to the solution of the halogenated cation. An equimolar amount of the solution of the metal salt of the anion is added to the solution of the halogenated cation and stirred.

[0074] At this time, ion exchange produces plastic crystals containing the first type of anion, as well as an alkali metal halide. Because the plastic crystals are hydrophobic and the alkali metal halide is hydrophilic, the plastic crystals exist in a solid state in the aqueous solution, and the alkali metal halide is dissolved in the aqueous solution. An organic solvent such as dichloromethane is mixed with the aqueous solution containing the plastic crystals in a solid state. When the organic solvent such as dichloromethane is mixed and allowed to stand, the mixture separates into an aqueous layer and an organic solvent layer.

[0075] The alkali metal halide is removed by removing the aqueous layer from the separated solution. This operation can be repeated multiple times, such as five times. After removing the alkali metal halide, the organic solvent, such as dichloromethane, is evaporated to obtain plastic crystals containing the first anion. Furthermore, if the mixture is allowed to stand without adding the organic solvent, such as dichloromethane, a precipitate of plastic crystals containing the first anion is obtained. This precipitate can be collected by filtration, washed with water, and then vacuum dried.

[0076] Plastic crystals containing the second anion can be obtained by the same method as for the first anion: an alkali metal salt of the second anion and a halogenated cation are dissolved in a solvent, and the solution is subjected to an ion exchange reaction by dropwise addition. An organic solvent such as dichloromethane is then added, and the aqueous layer is removed.

[0077] After the plastic crystals containing the first and second anions are purified, they are added to a vial in a 1:1 molar ratio, and an ionic salt serving as an electrolyte is then added to the vial. The ionic salt is preferably 0.1 to 50 mol% of the total amount of plastic crystals. An organic solvent, such as acetonitrile or acetonitrile, in which the plastic crystals and the electrolyte are soluble is then added to the vial to prepare an organic solvent solution containing both the plastic crystals and the electrolyte.

[0078] This organic solvent solution is cast onto the target object, such as the active material layer of the electrode to which the solid electrolyte is to be attached, the separator, or both. After casting, the solution is left to dry in a temperature environment at which the organic solvent volatilizes, such as at 80°C, to volatilize the solvent, and then further left in a temperature environment at 150°C, etc., to volatilize any remaining moisture. This forms a solid electrolyte on the target object.

[0079] The method for producing a solid electrolyte containing plastic crystals is not limited to this, and various methods can be used. For example, powdered plastic crystals and an electrolyte may be dissolved separately in an organic solvent to prepare respective solutions, and then these solutions may be mixed. Two types of plastic crystals may be dissolved separately in an organic solvent, or two types of plastic crystals may be dissolved simultaneously in an organic solvent. Alternatively, powdered plastic crystals may be dissolved in an organic solvent, and then the electrolyte may be added to the organic solvent. Alternatively, the electrolyte may be dissolved in an organic solvent, and then the powdered plastic crystals may be added to the organic solvent. Then, the organic solvent may be cast onto the target object.

[0080] (Electricity storage device) An electricity storage device is composed of positive and negative electrodes facing each other with a solid electrolyte sandwiched between them. A separator is placed between the positive and negative electrodes to prevent contact between the electrodes and to maintain the shape of the solid electrolyte. However, if the solid electrolyte is thick enough to prevent contact between the positive and negative electrodes and has hardness that allows it to maintain its shape independently, it may be a separatorless device.

[0081] The positive and negative electrodes of an electric double layer capacitor are formed by forming an active material layer on a current collector. The current collector can be made of a valve metal such as aluminum foil, platinum, gold, nickel, titanium, steel, or carbon. The current collector can have any shape, such as a film, foil, plate, mesh, expanded metal, or cylinder. The surface of the current collector can be textured by etching or other treatment, or it can be plain. Furthermore, surface treatment can be performed to deposit phosphorus on the surface of the current collector.

[0082] At least one of the positive electrode or the negative electrode is a polarizable electrode. The active material layer of the polarizable electrode contains a porous carbon material having electric double layer capacity. A solid electrolyte using this plastic crystal is particularly suitable for an electric double layer capacitor having a porous active material layer. Because the plastic crystal is soluble, it easily penetrates into the porous structure, increasing the filling rate of the active material layer. On the other hand, sulfide-based and oxide-based solid electrolytes have low filling properties into the porous structure. Therefore, an electric double layer capacitor using this plastic crystal can combine good filling properties into the porous structure with high ionic conductivity, resulting in high capacity and high output. Note that the other of the positive electrode or negative electrode may be formed with an active material layer containing metal compound particles or carbon material that cause a Faraday reaction.

[0083] The carbon material in the polarizable electrode is mixed with a conductive additive and a binder and applied to a current collector by a doctor blade method or the like. The mixture of the carbon material, conductive additive, and binder may be formed into a sheet and then pressed onto the current collector. Here, the porous structure is formed by gaps between primary particles and secondary particles when the carbon material has a particulate shape, or by gaps between fibers when the carbon material is fibrous.

[0084] Examples of carbon materials for the active material layer in the polarizable electrode include natural plant tissues such as coconut husks, synthetic resins such as phenols, activated carbons derived from fossil fuels such as coal, coke, and pitch, carbon blacks such as ketjen black, acetylene black, and channel black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, carbon nanotubes, and carbon nanofibers. The specific surface area of ​​these carbon materials may be improved by activation treatment such as steam activation, alkali activation, zinc chloride activation, or electric field activation, as well as by aperture treatment.

[0085] Examples of binders include rubbers such as fluorine-based rubber, diene-based rubber, and styrene-based rubber, fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, celluloses such as carboxymethyl cellulose and nitrocellulose, and also polyolefin resins, polyimide resins, acrylic resins, nitrile resins, polyester resins, phenolic resins, polyvinyl acetate resins, polyvinyl alcohol resins, and epoxy resins. These binders may be used alone or in combination of two or more.

[0086] Examples of conductive additives that can be used include ketjen black, acetylene black, natural / artificial graphite, and fibrous carbon, and examples of fibrous carbon include carbon nanotubes and carbon nanofibers (hereinafter referred to as CNF). Carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) with a single graphene sheet, or multi-walled carbon nanotubes (MWCNTs) with two or more graphene sheets rolled coaxially to form multiple tube walls, or a mixture of these.

[0087] A carbon coating layer containing a conductive agent such as graphite may be provided between the current collector and the active material layer. The carbon coating layer can be formed by applying a slurry containing a conductive agent such as graphite, a binder, etc. to the surface of the current collector and drying the slurry.

[0088] The positive and negative electrodes of a lithium-ion secondary battery are formed by forming active material layers on current collectors. Examples of current collectors that can be used include metals such as aluminum foil, platinum, gold, nickel, titanium, and steel; conductive polymer materials such as carbon, polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole; and resins made by filling non-conductive polymer materials with conductive fillers. The current collectors can be in any shape, including film, foil, plate, mesh, expanded metal, and cylinder.

[0089] The active material is mixed with a binder and applied to the current collector by a doctor blade method or the like. The mixture of the carbon material and binder may be formed into a sheet and then pressed onto the current collector. Conductive carbon such as carbon black, acetylene black, ketjen black, or graphite may be added to the active material layer as a conductive additive. The active material and binder may be added, kneaded, and then applied or pressed onto the current collector.

[0090] Positive electrode active materials include metal compound particles capable of absorbing and releasing lithium ions, such as layered rock salt LiMO2, layered Li2MnO3-LiMO2 solid solution, and spinel LiMO4 (where M represents Mn, Fe, Co, Ni, or a combination thereof). Specific examples of these include LiCoO2, LiNiO2, and LiNi 4 / 5 Co1 / 5 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 1 / 2 Mn 1 / 2 O2, LiFeO2, LiMnO2, Li2MnO3-LiCoO2, Li2MnO3-LiNiO2, Li2MnO3-LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li2MnO3-LiNi 1 / 2 Mn 1 / 2 O2, Li2MnO3-LiNi 1 / 2 Mn 1 / 2 O2-LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, LiMn 3 / 2 Ni 1 / 2 O4. Metal compound particles include sulfur and Li2S, TiS2, MoS2, FeS2, VS2, Cr 1 / 2 V 1 / 2 Sulfides such as S2, selenides such as NbSe3, VSe2, NbSe3, Cr2O5, Cr3O8, VO2, V3O8, V2O5, V6O 13 In addition to oxides such as LiNi 0.8 Co 0.15 A l0.05O2, LiVOPO4, LiV3O5, LiV3O8, MoV2O8, Li2FeSiO4, Li2MnSiO4, LiFePO4, LiFe 1 / 2 Mn 1 / 2 Examples include complex oxides such as PO4, LiMnPO4, and Li3V2(PO4)3.

[0091] Examples of the active material for the negative electrode include metal compound particles capable of absorbing and releasing lithium ions, such as oxides such as FeO, Fe2O3, Fe3O4, MnO, MnO2, Mn2O3, Mn3O4, CoO, Co3O4, NiO, Ni2O3, TiO, TiO2, TiO2(B), CuO, NiO, SnO, SnO2, SiO2, RuO2, WO, WO2, WO3, MoO3, and ZnO; metals such as Sn, Si, Al, and Zn; and LiVO2, Li3VO4, and Li4Ti5O. 12 , Sc2TiO5, Fe2TiO5 and other composite oxides, Li 2.6 Co 0.4 Nitrides such as N, Ge3N4, Zn3N2, and Cu3N, Y2Ti2O5S2, and MoS2.

[0092] When a separator is used in an electricity storage device, examples of the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, and acrylic resins; and these resins can be used alone or in combination.

[0093] In such an electricity storage device, the plastic crystals and ionic salt are dissolved in a solvent such as acetonitrile and cast onto an active material layer and a separator. After casting, the mixture is left to dry in a temperature environment such as 80°C to volatilize the solvent, and the positive and negative electrode active material layers are placed opposite each other via a separator. The remaining moisture is then volatilized in a temperature environment such as 150°C. Lead electrode terminals are then connected to the positive and negative electrode current collectors, and the device is sealed in an exterior case to produce an electricity storage device. [Example]

[0094] (Examples 1 to 5) Using plastic crystals containing two types of quaternary ammonium as cations, solid electrolytes for electric double layer capacitors were prepared in Examples 1 to 5. The ionic conductivities of the solid electrolytes in Examples 1 to 5 were then measured.

[0095] The solid electrolyte of Example 1 contains a five-membered ring pyrrolidinium, N-ethyl-N-methylpyrrolidinium (P12), as the first quaternary ammonium. The solid electrolyte of Example 1 also contains a spiropyrrolidinium (SBP) as the second quaternary ammonium. The P12 cation and the SBP cation are contained in the plastic crystal in a 1:1 molar ratio.

[0096] The solid electrolyte of Example 2 contains a five-membered pyrrolidinium compound, N-isopropyl-N-methylpyrrolidinium (P13iso), as the first quaternary ammonium. The solid electrolyte of Example 1 contains a spiropyrrolidinium compound (SBP) as the second quaternary ammonium. The P13iso cation and SBP cation are contained in the plastic crystal in a 1:1 molar ratio.

[0097] The solid electrolyte of Example 3 contains a five-membered pyrrolidinium compound, N,N-diethylpyrrolidinium (P22), as the first quaternary ammonium compound. The solid electrolyte of Example 1 contains a spiropyrrolidinium compound (SBP) as the second quaternary ammonium compound. The P22 cation and the SBP cation are contained in the plastic crystal in a 1:1 molar ratio.

[0098] The solid electrolyte of Example 4 contains a five-membered ring pyrrolidinium, N-ethyl-N-methylpyrrolidinium (P12), as the first quaternary ammonium. The solid electrolyte of Example 1 contains a five-membered ring pyrrolidinium, N,N-diethylpyrrolidinium (P22), as the second quaternary ammonium. The P12 cation and P22 cation are contained in the plastic crystal in a 1:1 molar ratio.

[0099] The solid electrolyte of Example 5 contains a tetraalkylammonium triethylmethylammonium (TEMA) as the first quaternary ammonium. The solid electrolyte of Example 1 contains a five-membered pyrrolidinium N,N-diethylpyrrolidinium (P22) as the second quaternary ammonium. The TEMA cation and P22 cation are contained in the plastic crystal in a 1:1 molar ratio.

[0100] The solid electrolytes in each example were manufactured using the following common method. First, the anion constituting the plastic crystals in each example was N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion). That is, plastic crystals composed of a first type of anion and a CFSA cation and plastic crystals composed of a second type of anion and a CFSA cation were added to a vial in a 1:1 molar ratio.

[0101] The P12CFSA plastic crystals containing the P12 cation and CFSA anion were prepared as follows. First, an aqueous solution of a halide was prepared by halogenating the P12 cation with bromine Br. An aqueous solution of an alkali metal salt of the CFSA anion and lithium Li was also prepared. The aqueous solution of the alkali metal salt was added dropwise to the halide solution to carry out an ion exchange reaction. After the ion exchange reaction, dichloromethane was added, and the solution separated into an aqueous layer and an organic solvent layer. The organic solvent layer was extracted, activated carbon was added, and the mixture was stirred overnight. The precipitate was then collected by filtration and dried to obtain plastic crystals.

[0102] SBPCFSA plastic crystals containing SBP cations and CFSA anions were prepared as follows. First, an aqueous solution of halide was prepared by halogenating the SBP cation with chlorine (Cl). An aqueous solution of an alkali metal salt of the CFSA anion and lithium (Li) was also prepared. An ion exchange reaction was carried out by gradually adding the aqueous solution of the alkali metal salt to the halide solution. After the ion exchange reaction, dichloromethane was added, and the solution separated into an aqueous layer and an organic solvent layer. The organic solvent layer was extracted, activated carbon was added, and the mixture was stirred overnight. The precipitate was then collected by filtration and dried to obtain plastic crystals.

[0103] P13isoCFSA plastic crystals containing the P13iso cation and CFSA anion were prepared as follows. First, an aqueous solution of the halide was prepared by halogenating the P13iso cation with iodine I. An aqueous solution of an alkali metal salt of the CFSA anion and lithium Li was also prepared. An ion exchange reaction was carried out by gradually adding the aqueous solution of the alkali metal salt to the halide solution. After the ion exchange reaction, dichloromethane was added, and the solution separated into an aqueous layer and an organic solvent layer. The organic solvent layer was extracted, activated carbon was added, and the mixture was stirred overnight. The precipitate was then collected by filtration and dried to obtain plastic crystals.

[0104] P22CFSA plastic crystals containing the P22 cation and CFSA anion were prepared as follows. First, an aqueous solution of halide was prepared by halogenating the P22 cation with iodine I. An aqueous solution of an alkali metal salt of the CFSA anion and lithium Li was also prepared. An ion exchange reaction was carried out by gradually adding the aqueous solution of the alkali metal salt to the halide solution. After the ion exchange reaction, dichloromethane was added, and the solution separated into an aqueous layer and an organic solvent layer. The organic solvent layer was extracted, activated carbon was added, and the mixture was stirred overnight. The precipitate was then collected by filtration and dried to obtain plastic crystals.

[0105] TEMACFSA plastic crystals containing TEMA cations and CFSA anions were prepared as follows. First, an aqueous solution of a halide was prepared by halogenating the TEMA cation with chlorine (Cl). An aqueous solution of an alkali metal salt of the CFSA anion and lithium (Li) was also prepared. An ion exchange reaction was carried out by gradually adding the aqueous solution of the alkali metal salt to the halide solution. After the ion exchange reaction, dichloromethane was added, and the solution separated into an aqueous layer and an organic solvent layer. The organic solvent layer was extracted, activated carbon was added, and the mixture was stirred overnight. The precipitate was then collected by filtration and dried to obtain plastic crystals.

[0106] The vial was further charged with SBPBF4 (spirobipyrrolidinium tetrafluoroborate, manufactured by Tokyo Chemical Industry Co., Ltd.) as an electrolyte, so that the total concentration of the plastic crystals was 30 mol %, and acetonitrile (Wako Pure Chemical Industries, Ltd.) was added so that the total solids concentration of the plastic crystals and electrolyte was 10 wt %. This acetonitrile solution was dropped onto a glass separator, and the acetonitrile was evaporated by drying at 80 °C. This evaporation process was repeated three times. The glass separator impregnated with the solid electrolyte by this evaporation process was dried in a vacuum environment at 80 °C for 12 hours, further dried in a vacuum environment at 120 °C for 3 hours, and further dried in a vacuum environment at 150 °C for 2 hours, thereby removing moisture and obtaining the solid electrolyte of each example.

[0107] The ionic conductivity of each example was then measured. A two-electrode sealed cell (manufactured by Toyo Systems) was assembled by sandwiching a glass separator impregnated with a solid electrolyte between two platinum electrodes and placing them opposite each other with an electrode presser. Impedance measurements were then performed, and the ionic conductivity was calculated from the impedance measurement results and the thickness of the glass separator impregnated with the solid electrolyte. The ionic conductivity measurement results are shown in Table 1 below.

[0108] [Table 1]

[0109] Table 1 also lists the ionic conductivities of solid electrolytes using various types of plastic crystals alone. These comparative solid electrolytes were prepared under the same conditions as the solid electrolytes of each example, except that they were composed of one type of plastic crystal.

[0110] As shown in Table 1, the ionic conductivity of the solid electrolyte for electric double layer capacitors in each example was confirmed to be at least 10 times, and at most 300 times, higher than that of a solid electrolyte using one type of plastic crystal. This confirmed that solid electrolytes using plastic crystals containing two types of cations selected from the group consisting of various quaternary ammonium compounds have improved ionic conductivity.

[0111] Example 6 A solid electrolyte for an electric double layer capacitor of Example 6 was prepared using a plastic crystal containing two types of imidazolium as cations. The ionic conductivity of the solid electrolyte of Example 6 was then measured. The solid electrolyte of Example 6 contains 1-ethyl-3-methylimidazolium (EMI) as the first type of imidazolium. The solid electrolyte of Example 6 also contains 1,3-dimethylimidazolium (DMI) as the second type of imidazolium. The EMI cation and DMI cation are contained in the plastic crystal at a molar ratio of 1:1.

[0112] The anion constituting the plastic crystals in Example 6 was N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion). The solid electrolyte of Example 6 was produced under the same conditions and by the same method as in Examples 1 to 5, and the first type of plastic crystals and the second type of plastic crystals were added to a vial in a molar ratio of 1:1.

[0113] The ionic conductivity of the solid electrolyte of Example 6 was then measured. The results are shown in Table 2 below. The methods for measuring and calculating ionic conductivity were the same as those used in Examples 1 to 5. Table 2 also lists the ionic conductivity of solid electrolytes that used various types of plastic crystals alone. These comparative solid electrolytes were prepared under the same conditions as the solid electrolytes of each Example, except that they were composed of one type of plastic crystal.

[0114] [Table 2]

[0115] As shown in Table 2, it can be confirmed that the ionic conductivity of the solid electrolyte for electric double layer capacitors of Example 6 is at least 10 times higher than that of a solid electrolyte using one type of plastic crystal. This confirms that a solid electrolyte using a plastic crystal containing two types of cations selected from the group consisting of various imidazoliums has improved ionic conductivity.

[0116] Examples 7 to 11 The solid electrolytes for electric double layer capacitors of Examples 7 to 11 were prepared using plastic crystals containing two types of cations: one type selected from imidazolium and one type selected from quaternary ammonium. The ionic conductivity of the solid electrolytes of Examples 7 to 11 was then measured.

[0117] The solid electrolyte of Example 7 contains 1-ethyl-3-methylimidazolium (EMI) as the first imidazolium and triethylmethylammonium (TEMA) as the second quaternary ammonium. The EMI cation and TEMA cation are contained in the plastic crystal in a 1:1 molar ratio.

[0118] The solid electrolyte of Example 8 contains 1-ethyl-3-methylimidazolium (EMI) as the first imidazolium and N-ethyl-N-methylpyrrolidinium (P12) as the second quaternary ammonium. The EMI cation and P12 cation are contained in the plastic crystal in a 1:1 molar ratio.

[0119] The solid electrolyte of Example 9 contains 1-ethyl-3-methylimidazolium (EMI) as the first imidazolium and spiropyrrolidinium (SBP) as the second quaternary ammonium. The EMI cation and SBP cation are contained in the plastic crystal in a 1:1 molar ratio.

[0120] The solid electrolyte of Example 10 contains 1,3-dimethylimidazolium (DMI) as the first cation and spiropyrrolidinium (SBP) as the second quaternary ammonium cation. The DMI cation and SBP cation are contained in the plastic crystal in a molar ratio of 1:1.

[0121] The solid electrolyte of Example 11 contains 1-methyl-3-propylimidazolium (MPI) as the first imidazolium and spiropyrrolidinium (SBP) as the second quaternary ammonium. The MPI cation and SBP cation are contained in the plastic crystal in a 1:1 molar ratio.

[0122] The ionic conductivity of the solid electrolytes of Examples 7 to 11 was then measured. The results are shown in Table 3 below. The methods for measuring and calculating ionic conductivity were the same as those of Examples 1 to 5. Table 3 also lists the ionic conductivity of solid electrolytes using various types of plastic crystals alone. These comparative solid electrolytes were prepared under the same conditions as the solid electrolytes of each Example, except that they were composed of one type of plastic crystal.

[0123] [Table 3]

[0124] As shown in Table 3, the ionic conductivity of the solid electrolyte for electric double layer capacitors of each example was at least equivalent to that of the solid electrolyte using one type of plastic crystal, as in Example 7, and was up to about four orders of magnitude higher than that of the solid electrolyte using one type of plastic crystal. This confirmed that the ionic conductivity of solid electrolytes using plastic crystals containing one type of cation selected from the group of various imidazoliums and the group of various quaternary ammoniums was improved.

[0125] Example 12 A solid electrolyte for an electric double layer capacitor of Example 12 was prepared using a plastic crystal containing two types of cations, imidazolium and another type of cation. The ionic conductivity of the solid electrolyte of Example 12 was then measured. The solid electrolyte of Example 12 contains 1-ethyl-3-methylimidazolium (EMI) as the first type of imidazolium. The solid electrolyte of Example 12 also contains tetraethylphosphonium cation (TEP), which is a phosphonium, as the second type of cation. The EMI cation and TEP cation are contained in the plastic crystal at a molar ratio of 1:1.

[0126] The anion constituting the plastic crystal of Example 12 was N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion). The solid electrolyte of Example 12 was produced under the same conditions and by the same method as in Examples 1 to 5, and the first type of plastic crystal and the second type of plastic crystal were added to a vial in a molar ratio of 1:1.

[0127] The ionic conductivity of the solid electrolyte of Example 12 was then measured. The results are shown in Table 2 below. The methods for measuring and calculating ionic conductivity were the same as those used in Examples 1 to 5. Table 4 also lists the ionic conductivity of solid electrolytes using various types of plastic crystals alone. This comparative solid electrolyte was prepared under the same conditions as the solid electrolytes of each Example, except that it was composed of one type of plastic crystal.

[0128] [Table 4]

[0129] As shown in Table 4, the ionic conductivity of the solid electrolyte for electric double layer capacitors of Example 6 was confirmed to be at least 30 times higher than that of a solid electrolyte using one type of plastic crystal. This confirmed that the ionic conductivity of a solid electrolyte can be improved even if other cations are added.

[0130] As described above, it was confirmed that a solid electrolyte using a plastic crystal containing a total of two or more cations, at least one of which is selected from the group consisting of various imidazoliums and various quaternary ammoniums, has improved ionic conductivity.

[0131] Example 13 Two types of cations and two types of anions were combined to form two types of plastic crystals in a 1:1 molar ratio, and these plastic crystals were used to prepare a solid electrolyte for an electric double layer capacitor in Example 13. The ionic conductivity of the solid electrolyte in Example 13 was then measured. The solid electrolyte in Example 13 contained a spiropyrrolidinium (SBP) quaternary ammonium cation as the first type, and this cation was combined with N,N-hexafluoro-1,3-disulfonylamide (CFSA) to form a first type of plastic crystal. The solid electrolyte in Example 13 also contained a quaternary ammonium cation, N-ethyl-N-methylpyrrolidinium (P12) as the second type of cation, and this cation was combined with bis(trifluoromethanesulfonyl)amide (TFSA) to form a second type of plastic crystal.

[0132] The ionic conductivity of the solid electrolyte of Example 13 was then measured. The results are shown in Table 5 below. The methods for measuring and calculating ionic conductivity were the same as those used in Examples 1 to 5. Table 5 also lists the ionic conductivity of solid electrolytes using various types of plastic crystals alone. These comparative solid electrolytes were prepared under the same conditions as the solid electrolytes of each Example, except that they were composed of a single type of plastic crystal. Furthermore, the ionic conductivity of the solid electrolyte of Example 1 is also listed for comparison.

[0133] [Table 5]

[0134] As shown in Table 5, the ionic conductivity of the solid electrolyte for electric double layer capacitors of Example 13 is at least about 100 times higher than that of the solid electrolyte using one type of plastic crystal, and is at most more than 20,000 times higher. Moreover, compared to the ionic conductivity of the solid electrolyte of Example 1, which uses two types of quaternary ammonium as cations but only one type of anion, Example 13, which uses two types of cations and two types of anions in combination, has an ionic conductivity that is nearly 100 times higher.

[0135] (Examples 14 to 16) Separately from Example 13, two types of cations and two types of anions were combined to form two types of plastic crystals in a 1:1 molar ratio, and these plastic crystals were used to prepare a solid electrolyte for an electric double layer capacitor in Example 14. The solid electrolyte in Example 14 contained a spiropyrrolidinium (SBP) quaternary ammonium as the first cation, and a first type of plastic crystal was used in which this cation was combined with N,N-hexafluoro-1,3-disulfonylamide (CFSA). The solid electrolyte in Example 14 also contained a tetraalkylammonium triethylmethylammonium (TEMA) quaternary ammonium as the second cation, and a second type of plastic crystal was used in which this cation was combined with bis(trifluoromethanesulfonyl)amide (TFSA).

[0136] A mixture containing TEMA cations and TFSA anions was prepared as follows, and plastic crystals were obtained by adjusting the amounts added. Specifically, first, an aqueous solution of the halide was prepared by halogenating the TEMA cation with chlorine (Cl). An aqueous solution of an alkali metal salt of the TFSA anion and lithium (Li) was also prepared. An equal volume of the alkali metal salt solution was gradually added dropwise to the halide solution to perform an ion exchange reaction. After the ion exchange reaction, 60 wt% of dichloromethane was added to the total solution. The aqueous and organic solvent layers separated, and the organic solvent layer was extracted, added with activated carbon, and stirred overnight. The precipitate was then collected by filtration and dried. TEMATFSA plastic crystals were obtained. TEMATFSA plastic crystals possess plastic properties when they contain 30% or more TEMATFSA plastic crystals relative to the total mol% of the plastic crystals and electrolyte.

[0137] In addition, a solid electrolyte for an electric double layer capacitor of Example 15 was prepared for comparison with Example 14. The solid electrolyte of Example 15 was composed of two types of plastic crystals, combining two types of cations and one type of anion in a 1:1 molar ratio. The solid electrolyte of Example 15 contained spiropyrrolidinium (SBP), a quaternary ammonium, as the first cation, and a first type of plastic crystal was used, combining this cation with N,N-hexafluoro-1,3-disulfonylamide (CFSA). The solid electrolyte of Example 15 also contained triethylmethylammonium (TEMA), a tetraalkylammonium, as the second cation, and a second type of plastic crystal was used, combining this cation with N,N-hexafluoro-1,3-disulfonylamide (CFSA).

[0138] Furthermore, two types of cations and two types of anions were combined to form two types of plastic crystals in a 1:1 molar ratio, and these plastic crystals were used to prepare the solid electrolyte for electric double layer capacitors of Example 16. The solid electrolyte of Example 16 contained a spiropyrrolidinium (SBP) quaternary ammonium as the first cation, and this cation was combined with N,N-hexafluoro-1,3-disulfonylamide (CFSA) to form the first type of plastic crystal. The solid electrolyte of Example 14 contained a five-membered pyrrolidinium cation, N-ethyl-N-methylpyrrolidinium (P12) as the second quaternary ammonium as the second cation, and this cation was combined with tris(trifluoromethanesulfonyl)methanide anion (TFSM) to form the second type of plastic crystal.

[0139] Furthermore, a solid electrolyte for an electric double layer capacitor of Example 1 was prepared for comparison with Example 16. The solid electrolyte of Example 1 was composed of two types of plastic crystals in a molar ratio of 1:1, combining two types of cations and one type of anion.

[0140] The ionic conductivities of the solid electrolytes of Examples 14 to 16 and Example 1 were then measured. The results are shown in Table 6 below. The methods for measuring and calculating ionic conductivities were the same as those of Examples 1 to 5. Table 6 also lists the ionic conductivities of solid electrolytes using various types of plastic crystals alone. These comparative solid electrolytes were prepared under the same conditions as the solid electrolytes of each Example, except that they were composed of a single type of plastic crystal.

[0141] [Table 6]

[0142] As shown in Table 6, the ionic conductivity of the solid electrolyte for electric double layer capacitors of Example 14 was confirmed to be at least 10,000 times higher than that of the solid electrolyte using one type of plastic crystal. Moreover, compared to the ionic conductivity of the solid electrolyte of Example 15, which used two types of quaternary ammonium as cations but only one type of anion, Example 14, which used a combination of two types of cations and two types of anions, had an ionic conductivity that was more than 1,000 times higher.

[0143] It was also confirmed that the ionic conductivity of the solid electrolyte for electric double layer capacitors of Example 16 was improved by at least about 76 times compared to the solid electrolyte using one type of plastic crystal. Moreover, compared to the ionic conductivity of the solid electrolyte of Example 1, which used two types of quaternary ammonium as cations but only one type of anion, Example 16, which used a combination of two types of cations and two types of anions, had an ionic conductivity that was more than 16 times higher.

[0144] As shown by the comparison between Example 14 and Example 15 and the comparison between Example 16 and Example 17, it was confirmed that the ionic conductivity of a solid electrolyte using a plastic crystal in which two types of anions are used in combination, such as two or more types of anions selected from the group consisting of various amide anions in which two hydrogen atoms of the NH anion are substituted with perfluoroalkylsulfonyl groups, fluorosulfonyl groups, or both, and tris(trifluoromethanesulfonyl)methanide anion, is further improved.

[0145] Example 17 Three types of plastic crystals were used to prepare a solid electrolyte for a lithium-ion secondary battery of Example 17. The ionic conductivity of the solid electrolyte of Example 17 was then measured. The solid electrolyte of Example 17 contained N-ethyl-N-methylpyrrolidinium (P12), a pyrrolidinium that is a five-membered ring quaternary ammonium, as the first type of cation, and this cation was combined with bis(fluorosulfonyl)amide anion (FSA anion), which is an amide anion, to form the first type of P12FSA plastic crystal.

[0146] In addition, the solid electrolyte of Example 17 contained a second type of cation, triethylmethylammonium (TEMA), a tetraalkylammonium, as a quaternary ammonium, and combined this cation with bis(fluorosulfonyl)amide anion (FSA anion), which is an amide anion, to form the second type of TEMAFSA plastic crystal.

[0147] Furthermore, the solid electrolyte of Example 17 contains N-ethyl-N-methylpyrrolidinium (P12), a pyrrolidinium that is a five-membered ring quaternary ammonium, in combination with bis(trifluoromethanesulfonyl)amide (TFSA), an amide anion, as the second anion, and uses P12TFSA plastic crystals as the third anion.

[0148] In addition to these three types of plastic crystals, the vial also contained the electrolyte LiTFSA (lithium bis(trifluoromethanesulfonyl)amide, manufactured by Kishida Chemical Co., Ltd.) at 10 mol% of the total plastic crystals, and acetonitrile (Wako Pure Chemical Industries, Ltd.) at a total solids concentration of 10 wt% for the plastic crystals and electrolyte. P12FSA plastic crystals (A), TEMAFSA plastic crystals (B), and P12TFSA plastic crystals (C) were added to the vial in a ratio of A:B:C = 4:4:2.

[0149] This acetonitrile solution was dropped onto a glass separator and dried at 80°C to evaporate the acetonitrile. This evaporation process was repeated three times. The glass separator impregnated with the solid electrolyte by this evaporation process was dried in a vacuum environment at 80°C for 12 hours, further dried in a vacuum environment at 120°C for 3 hours, and further dried in a vacuum environment at 150°C for 2 hours, thereby removing moisture and obtaining a solid electrolyte of Example 16.

[0150] The ionic conductivity of the solid electrolyte of Example 17 was then measured. The results are shown in Table 7 below. The methods for measuring and calculating ionic conductivity were the same as those used in Examples 1 to 5. Table 7 also lists the ionic conductivity of solid electrolytes using various types of plastic crystals alone. This comparative solid electrolyte was prepared under the same conditions as the solid electrolyte of Example 17, except that it was composed of one type of plastic crystal.

[0151] [Table 7]

[0152] As shown in Table 7, it can be confirmed that the ionic conductivity of the solid electrolyte for lithium ion secondary batteries of Example 17 is at least about 2 times, and at most 600 times, higher than that of the solid electrolyte using one type of plastic crystal. This confirms that the ionic conductivity can be improved even for solid electrolytes for lithium ion secondary batteries.

Claims

1. A composite material comprising a plastic crystal as a matrix phase, The plastic crystal is composed of two or more cations in total, at least one of which is selected from the group consisting of various imidazoliums and various quaternary ammoniums; the plastic crystal is doped with an electrolyte; A solid electrolyte characterized by:

2. The plastic crystal is composed of two types of cations selected from the group of various quaternary ammonium salts; The solid electrolyte according to claim 1,

3. the plastic crystal is composed of two types of cations selected from the group of various imidazoliums; The solid electrolyte according to claim 1,

4. the plastic crystal is composed of a cation selected from each of the various imidazolium groups and the various quaternary ammonium groups; The solid electrolyte according to claim 1,

5. The plastic crystal is one cation selected from the group consisting of various imidazoliums and various quaternary ammoniums; One other cation other than the various imidazoliums and the various quaternary ammoniums; It consists of The solid electrolyte according to claim 1,

6. The various imidazoliums are 1,3-dialkylimidazoliums or 1,2,3-trialkylimidazoliums represented by the following chemical formula (A):

6. The solid electrolyte according to claim 1, wherein 【Chemical 1】 In the formula, n and m are integers of 1 to 3, and p is 0 or 1.

7. The various quaternary ammonium compounds include tetraalkylammonium compounds represented by the following chemical formula (B) and substituted with a linear alkyl group having any number of carbon atoms.

7. The solid electrolyte according to claim 1, wherein: 【Chemistry 2】 In the formula, a, b, c, and d are integers of 1 or more, and the number of carbon atoms may be any number.

8. The various quaternary ammonium compounds include a five-membered ring ammonium pyrrolidinium compound represented by the following chemical formula (C) and a spiro-type pyrrolidinium compound represented by the following chemical formula (D): The solid electrolyte according to any one of claims 1 to 7, characterized in that 【Chemistry 3】 In the formula, R1 and R2 are a methyl group, an ethyl group, or an isopropyl group. 【Chemistry 4】

9. The other one kind of cation is one kind of various phosphoniums represented by the following chemical formula (E): The solid electrolyte according to claim 5, 【Chemistry 5】 In the formula, e, f, g, and h are integers of 1 or more, and the number of carbon atoms may be any.

10. The plastic crystal is composed of two or more kinds of anions; The solid electrolyte according to any one of claims 1 to 9, characterized in that

11. A solid electrolyte according to any one of claims 1 to 10; two electrodes facing each other with the solid electrolyte therebetween; To have An electricity storage device characterized by:

12. one or both of the electrodes is a polarizable electrode having an active material layer made of a porous material and a current collector; an electric double layer is formed at the interface between the polarizable electrode and the solid electrolyte; The electricity storage device according to claim 11,

13. A step of preparing plastic crystals containing two or more cations in total, at least one of which is selected from the group consisting of various imidazoliums and various quaternary ammoniums; doping the plastic crystal as a parent phase with an electrolyte; containing, A method for producing a solid electrolyte, characterized by:

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