electric double layer capacitor

Abstract

The present invention provides an electric double layer capacitor which has an electrolyte layer that achieves a good balance between suppression of leakage current and high ionic conductivity. This electric double layer capacitor comprises a pair of electrode bodies and an electrolyte layer. The electrode bodies comprise a polarizable electrode. The electrolyte layer contains an ionic liquid and a plastic crystal.

Description

[Technical Field]

[0001] The present invention relates to an electric double layer capacitor. [Background technology]

[0002] An electric double layer capacitor is generally composed of positive and negative electrode bodies facing each other with an electrolyte layer between them. The positive and negative electrode bodies have polarizable electrodes such as activated carbon, and the electric double layer capacitor charges and discharges by utilizing the charge-storing action of the electric double layer formed at the interface between the polarizable electrodes and the electrolyte layer. Electric double layer capacitors have attracted attention as a storage power source because they have a long lifespan because no chemical reaction occurs during charging and discharging, as well as high cycle characteristics, high power density, and a wide operating temperature range.

[0003] A solid electrolyte layer can be selected as the electrolyte layer. 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 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. Electric double layer capacitors are constructed by doping a selected host phase with an electrolyte such as TEMABF4 as needed.

[0005] Plastic crystals are soluble in organic solvents. 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 crystals, or salts of these, are dissolved in a solvent and cast onto an electrode. Therefore, compared to other types of 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 problems, and an object of the present invention is to provide an electric double layer capacitor having an electrolyte layer that achieves both suppression of leakage current and high ionic conductivity. [Means for solving the problem]

[0010] To solve the above problems, the electric double layer capacitor of the present invention is characterized by comprising a pair of electrode bodies having polarizable electrodes and an electrolyte layer containing an ionic liquid and a plastic crystal. The electrolyte layer, in which leakage current is suppressed by the presence of the plastic crystal, also has increased ionic conductivity due to the use of an ionic liquid with relatively high ionic conductivity.

[0011] The plastic crystal and the ionic liquid may have the same type of anion component. By adding an ionic liquid with higher ionic conductivity than the plastic crystal to the electrolyte layer, an electrolyte layer with high ionic conductivity can be obtained. On the other hand, increasing the amount of ionic liquid added increases leakage current. As a result of intensive research by the inventors, it was discovered that the ionic conductivity of the electrolyte layer is higher when the anion components constituting the ionic liquid and the plastic crystal are the same type. Therefore, high ionic conductivity can be obtained even when the amount of ionic liquid added is limited, and leakage current can be suppressed because the amount of ionic liquid added can be limited.

[0012] The plastic crystal may be contained in the electrolyte layer at a ratio of 60 mol % to 90 mol % of the total of the ionic liquid and the plastic crystal, where 90 mol % or less improves the ionic conductivity of the electrolyte layer.

[0013] The plastic crystals may be contained in the electrolyte layer at a ratio of 60 mol% to 80 mol% of the total of the ionic liquid and the plastic crystals. By having the same anion components as the plastic crystals and the ionic liquid, high ionic conductivity can be achieved while the plastic crystal content can be set to 60 mol% to 80 mol%. Furthermore, when the plastic crystal content is set to 60 mol% to 80 mol%, leakage current in the electrolyte layer can be suppressed and ionic conductivity can be further increased.

[0014] The electrolyte layer may further contain other types of plastic crystals.

[0015] The electrolyte layer may further contain, in addition to the plastic crystals having the same anion component as the ionic liquid, other types of plastic crystals having anion components different from those of the ionic liquid. Assuming that the plastic crystals having the same anion component as the ionic liquid are contained in the electrolyte layer, if other types of plastic crystals having anion components different from those of the ionic liquid are further contained in the electrolyte layer, the effect of the low ionic conductivity of the plastic crystals on the electrolyte layer will be further reduced, and the ionic conductivity of the electrolyte layer will be closer to that of the ionic liquid.

[0016] The other type of plastic crystal may have a cation component different from that of the plastic crystal, which has the same type of anion component as the ionic liquid.

[0017] The molar ratio of the plastic crystals having the same type of anion component as the ionic liquid to the other type of plastic crystals having a different type of anion component from the ionic liquid may be in the range of 40:60 or more and 60:40 or less.

[0018] The electrolyte layer may contain two types of plastic crystals having different cation components as the plastic crystals having the same anion component as the ionic liquid. When these two types of plastic crystals are contained in the electrolyte layer, the influence of the low ionic conductivity of the plastic crystals on the electrolyte layer is further reduced, and the ionic conductivity of the electrolyte layer approaches that of the ionic liquid.

[0019] The plastic crystals contained in the electrolyte layer may be those containing pyrrolidinium-based cations, ammonium-based cations, piperidinium-based cations, or phosphonium-based cations. For example, the plastic crystals may contain spiro-type pyrrolidinium cations, N-ethyl-N-methylpyrrolidinium cations, triethylmethylammonium cations, or phosphonium-based cations. Although not limited thereto, the inclusion of plastic crystals containing at least pyrrolidinium-based cations, ammonium-based cations, piperidinium-based cations, or phosphonium-based cations in the electrolyte layer further reduces the effect of the low ionic conductivity of the plastic crystals on the electrolyte layer, bringing the ionic conductivity of the electrolyte layer closer to that of the ionic liquid.

[0020] The cations of the plastic crystals contained in the electrolyte layer may not contain lithium ions, for example, the cations of the plastic crystals contained in the electrolyte layer may be selected from spiropyrrolidinium cations, N-ethyl-N-methylpyrrolidinium cations, triethylmethylammonium cations, and phosphonium cations.

[0021] The electrolyte layer may further contain a carbonate-based polymer, which further improves the ionic conductivity of the electrolyte layer. [Effects of the Invention]

[0022] According to the present invention, the electrolyte layer of the electric double layer capacitor has both high ionic conductivity and suppressed leakage current. [Brief explanation of the drawings]

[0023] [Figure 1] 10 is a graph showing the measurement results of the ionic conductivity and leakage current of the electrolyte of Example 10. [Figure 2] 1 is a graph showing the measurement results of the ionic conductivity and leakage current of the electrolyte of Example 11. [Figure 3] 10 is a graph showing the measurement results of ionic conductivity for each blend ratio of plastic crystals in the electrolyte of Example 17. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0025] (Overall composition) The electric double layer capacitor of this embodiment has positive and negative electrode bodies with polarizable electrodes facing each other with a separator sandwiched between them. An electrolyte layer is filled between the positive and negative electrode bodies. This electric double layer capacitor is charged and discharged by utilizing the charge storage action of the electric double layer formed at the interface between the polarizable electrode and the electrolyte layer. For example, the electric double layer capacitor is of a wound type, having strip-shaped electrode bodies and a separator, and is formed by overlapping the positive electrode body and the negative electrode body with the separator interposed between them and winding them in a spiral shape.

[0026] When an electric double layer capacitor is charged, vacancies on the polarizable electrode side and anions in the electrolyte layer pair up across an extremely short distance at the interface between the polarizable electrode on the positive electrode side and the electrolyte layer. This creates a potential barrier at the positive electrode. When an electric double layer capacitor is charged, electrons on the polarizable electrode side and cations in the electrolyte layer pair up across an extremely short distance at the interface between the polarizable electrode on the negative electrode side and the electrolyte layer. This creates a potential barrier at the negative electrode. The electrolyte layer supplies these anions and cations.

[0027] (electrolyte layer) This electrolyte layer is made by adding an ionic liquid and a plastic crystal. An ionic liquid is a salt that exists in a liquid state at temperatures including room temperature, and is a liquid consisting only of ions. This ionic liquid has relatively high ionic conductivity and is non-flammable or flame-retardant. 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, while these anions and cations have rotational disorder.

[0028] The plastic crystals have poor fluidity due to their ordered arrangement, and the area where the electrode undergoes chemical reaction is limited to the vicinity of the electrode, suppressing leakage current in the electrolyte layer. Therefore, the electrolyte layer in which leakage current is suppressed by the presence of the plastic crystals also has good ionic conductivity due to the inclusion of an ionic liquid with relatively high ionic conductivity. However, this electrolyte layer has no fluidity when visually observed, and the entire system is solid.

[0029] The types of anion and cation components constituting the plastic crystal are not particularly limited, but it is preferable that the plastic crystal have the same type of anion component as the ionic liquid. When an electrolyte layer is prepared by adding an ionic liquid and plastic crystals composed of the same type of anion components, even if the blending ratio of the plastic crystals in the electrolyte layer is high, the ionic conductivity of the electrolyte layer does not decrease significantly compared to the ionic conductivity of the ionic liquid. Therefore, by increasing the blending ratio of the plastic crystals, it is possible to achieve both high ionic conductivity and suppression of leakage current.

[0030] When the ionic liquid and the plastic crystal have the same type of anion component, the molar concentration of the plastic crystal in the electrolyte layer is preferably 60 mol% or more and 80 mol% or less relative to the total of the ionic liquid and the plastic crystal. When the blending ratio of the plastic crystal is 60 mol% or more, the leakage current of the electrolyte layer can be kept low. When the plastic crystal contains the same type of anion component as the ionic liquid, the blending ratio of the plastic crystal can be 60 mol% or more without significantly reducing the ionic conductivity, thereby achieving both high ionic conductivity and low leakage current. On the other hand, when the blending ratio of the plastic crystal having the same type of anion component as the ionic liquid exceeds 80 mol%, the effect of the low ionic conductivity of the plastic crystal on the electrolyte layer becomes significantly large, and the ionic conductivity of the electrolyte layer drops sharply.

[0031] Furthermore, if the molar concentration of the plastic crystals in the electrolyte layer is 60 mol% or more and 90 mol% or less relative to the total of the ionic liquid and the plastic crystals, the ionic conductivity of the electrolyte layer can be increased compared to when the electrolyte layer is formed only from plastic crystals, regardless of whether the anion components contained in the ionic liquid and the plastic crystals are the same or different.

[0032] The same type of anion component possessed by the ionic liquid and the plastic crystal is not particularly limited as long as it is an anion component capable of constituting the ionic liquid and the plastic crystal, and is, for example, selected from the group consisting of BF4 anion, TFSA anion, FSA anion, and BF3CF3 anion.

[0033] The BF4 anion is a tetrafluoroborate anion represented by the following chemical formula (1). [ka]

[0034] The TFSA anion is a bis(trifluoromethanesulfonyl)amide anion represented by the following chemical formula (2). [ka]

[0035] The FSA anion is a bis(fluorosulfonyl)amide anion represented by the following chemical formula (3): [ka]

[0036] The BF3CF3 anion is a mono(fluoroalkyl)trifluoroborate anion represented by the following chemical formula (4). [ka]

[0037] The electrolyte layer may contain two or more types of plastic crystals, but it is preferable that the electrolyte layer further contains plastic crystals composed of an anion component different from that of the ionic liquid (hereinafter also referred to as anion-same-type plastic crystals), provided that the electrolyte layer contains plastic crystals composed of the same anion component as the ionic liquid (hereinafter also referred to as anion-different plastic crystals). For example, if the anion component of the ionic liquid is BF4 anion, the electrolyte layer may contain plastic crystals composed of BF4 anion and plastic crystals composed of, for example, TFSA anion.

[0038] If anionic homoplastic crystals are contained in the electrolyte layer, and if heteroplastic crystals are also contained in the electrolyte layer, the effect of the low ionic conductivity of the plastic crystals on the electrolyte layer will be further reduced, and the ionic conductivity of the electrolyte layer will be closer to that of the ionic liquid. There are no particular limitations on the ratio of the anionic homoplastic crystals and the heteroplastic crystals added, but for example, it is preferable to contain equimolar amounts of the anionic homoplastic crystals and the anionic heteroplastic crystals in the electrolyte.

[0039] In addition, when the plastic crystal is formed using an anion component other than the ionic liquid, examples of the anion component include PF6 anion, tris(pentafluoroethyl)trifluorophosphate anion (FAP anion), N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion), bis(pentafluoroethylsulfonyl)amide anion (BETA anion), and various perfluoroalkylsulfonate anions.

[0040] Various perfluoroalkylsulfonate anions are represented by the following chemical formula (5): Specific examples of the various perfluoroalkylsulfonate anions include a trifluoromethanesulfonate anion in which r is 1 in the chemical formula (5), a pentafluoroethanesulfonate anion in which r is 2 in the following chemical formula (5), a heptafluoropropanesulfonate anion in which r is 3 in the following chemical formula (5), and an NFS anion, i.e., a nonafluorobutanesulfonate anion in which r is 4 in the following chemical formula (5). Specific examples of the various perfluoroalkylsulfonate anions include a trifluoromethanesulfonate anion in which r is 1 in the chemical formula (5), a pentafluoroethanesulfonate anion in which r is 2 in the following chemical formula (5), a heptafluoropropanesulfonate anion in which r is 3 in the following chemical formula (5), and an NFS anion in which r is 4 in the following chemical formula (5), i.e., a nonafluorobutanesulfonate anion. [ka] In chemical formula (5), r is an integer of 1 or more, and the number of carbon atoms may be any number.

[0041] The cationic component of the ionic liquid is not particularly limited as long as it is a cationic component that can constitute an ionic liquid, and examples thereof include EMI cations, BMI cations, MPI cations, DEME cations, MEMP cations, P13 cations, pyridinium-based cations, piperidinium-based cations, and phosphonium-based cations.

[0042] The EMI cation is a 1-ethyl-3-methylimidazolium cation represented by the following chemical formula (6). [ka]

[0043] The BMI cation is a 1-butyl-3-methylimidazolium cation represented by the following chemical formula (7). [ka] In chemical formula (7), the butyl group is an n-butyl group.

[0044] The MPI cation is a 1-methyl-3-propylimidazolium cation represented by the following chemical formula (8). [ka]

[0045] The DEME cation is N,N-diethyl-N-methyl-(2-methoxyethyl)ammonium cation, as shown in the following chemical formula (9). [ka]

[0046] The MEMP cation is an N-(2-methoxyethyl)-N-methylpyrrolidium cation represented by the following chemical formula (10): [ka]

[0047] The P13 cation is an N-propyl-N-methylpyrrolidinium cation represented by the following chemical formula (11). [ka]

[0048] It should be noted that any cation having a pyrrolidinium skeleton can be used, not limited to the MEMP cation and the P13 cation. Examples of cations having a pyrrolidinium skeleton include a 1-ethyl-1-methylpyrrolidinium cation, a 1-propyl-1-methylpyrrolidinium cation, a 1-butyl-1-methylpyrrolidinium cation, a 1-ethyl-1-ethylpyrrolidinium cation, a 1-propyl-1-ethylpyrrolidinium cation, and a 1-butyl-1-ethylpyrrolidinium cation.

[0049] Examples of pyridinium cations include a pyridinium cation substituted with a methyl group at the 2-position, as shown in the following chemical formula (12), a pyridinium cation substituted with a methyl group at the 3-position, as shown in chemical formula (13), and a pyridinium cation substituted with a methyl group at the 4-position, as shown in chemical formula (14).

[0050] [ka] In chemical formula (12), n is an integer of 1 or more, and the number of carbon atoms may be any number.

[0051] Examples of the pyridinium cation substituted with a methyl group at the 2-position, as represented by chemical formula (12), include a 1-ethyl-2-methylpyridinium cation, a 1-propyl-2-methylpyridinium cation, and a 1-butyl-2-methylpyridinium cation.

[0052] [ka] In chemical formula (13), n is an integer of 1 or more, and the number of carbon atoms may be any number.

[0053] Examples of the pyridinium cation substituted with a methyl group at the 3-position, as represented by chemical formula (13), include a 1-ethyl-3-methylpyridinium cation, a 1-propyl-3-methylpyridinium cation, and a 1-butyl-3-methylpyridinium cation.

[0054] [ka] In chemical formula (14), n is an integer of 1 or more, and the number of carbon atoms may be any number.

[0055] Examples of the pyridinium cation substituted with a methyl group at the 4-position, as represented by chemical formula (14), include a 1-ethyl-4-methylpyridinium cation, a 1-propyl-4-methylpyridinium cation, and a 1-butyl-4-methylpyridinium cation.

[0056] Examples of piperidinium-based cations include 1-alkyl-1-methylpiperidinium cations or 1-alkyl-1-ethylpiperidinium cations represented by the following chemical formula (15), or 1-methoxyethyl-1-methylpiperidinium cations represented by the following chemical formula (16).

[0057] [ka] In chemical formula (15), n is an integer of 1 or more, the number of carbon atoms may be any number, and m is an integer of 1 or 2.

[0058] Examples of the 1-alkyl-1-methylpiperidinium cation represented by chemical formula (15) include the 1-ethyl-1-methylpiperidinium cation, the 1-propyl-1-methylpiperidinium cation, and the 1-butyl-1-methylpiperidinium cation. Examples of the 1-alkyl-1-ethylpiperidinium cation represented by chemical formula (15) include the 1-ethyl-1-ethylpiperidinium cation, the 1-propyl-1-ethylpiperidinium cation, and the 1-butyl-1-ethylpiperidinium cation.

[0059] [ka]

[0060] The phosphonium cation is a tetraalkylphosphonium cation substituted with a linear alkyl group, regardless of the number of carbon atoms, as shown in the following chemical formula (17): An example of a tetraalkylphosphonium cation is the tetraethylphosphonium cation (TEP cation). [ka] In chemical formula (17), e, f, g, and h are integers of 1 or more, and the number of carbon atoms may be any number.

[0061] The cationic component of the plastic crystal is not particularly limited as long as it is a cationic component that can constitute a plastic crystal, but pyrrolidinium-based cations, ammonium-based cations, piperidinium-based cations shown in chemical formula (15), and phosphonium-based cations shown in chemical formula (17) are particularly preferred. When an electrolyte layer is prepared using the same type of anionic component as the ionic liquid and a plastic crystal composed of these cationic components, the impact of the low ionic conductivity of the plastic crystal on the electrolyte layer is reduced, and even if the proportion of plastic crystal added is increased, the ionic conductivity of the electrolyte layer approaches that of the ionic liquid.

[0062] Pyrrolidinium cations are cations having a pyrrolidinium skeleton, including SBP cation, P12 cation, P11 cation, P13iso cation, and P22 cation. Among these pyrrolidinium cations, SBP cation and P12 cation are particularly preferred from the viewpoint of improving ionic conductivity. The SBP cation is a spiro-pyrrolidinium represented by the following chemical formula (18). [ka]

[0063] The P12 cation is an N-ethyl-N-methylpyrrolidinium cation represented by the following chemical formula (19). [ka]

[0064] The P11 cation is a 1-methyl-1-methylpyrrolidinium cation represented by the following chemical formula (20). [ka]

[0065] The P13iso cation is a 1-isopropyl-1-methylpyrrolidinium cation represented by the following chemical formula (21). [ka]

[0066] The P22 cation is a 1-ethyl-1-ethylpyrrolidinium cation represented by the following chemical formula (22). [ka]

[0067] Tetraalkylammonium, an ammonium cation, is a quaternary ammonium substituted with a linear alkyl group, regardless of the number of carbon atoms, as shown in the following chemical formula (23). [ka] In the chemical formula (23), a, b, c, and d are integers of 1 or more, and the number of carbon atoms may be any number.

[0068] The ammonium-based cation includes, for example, triethylmethylammonium cation (TEMA cation) represented by the following chemical formula (24), and among the ammonium-based cations, the TEMA cation is particularly preferable from the viewpoint of improving ionic conductivity. [ka]

[0069] Furthermore, the ammonium-based cation includes, for example, the tetraethylammonium cation (TEA cation) represented by the following chemical formula (25). [ka]

[0070] The piperidinium cations used in plastic crystals include the 1-methyl-1-methylpiperidinium cation represented by the following chemical formula (26): [ka]

[0071] Furthermore, the piperidinium-based cations used for plastic crystals include the 1-isopropyl-1-methylpiperidinium cation represented by the following chemical formula (27). [ka]

[0072] Furthermore, the piperidinium-based cations used in plastic crystals include the 1-methyl-1-ethylpiperidinium cation represented by the following chemical formula (28). [ka]

[0073] Furthermore, the piperidinium-based cations used in plastic crystals include the 1-ethyl-1-ethylpiperidinium cation represented by the following chemical formula (29). [ka]

[0074] The anion is preferably anion isoplastic crystals, and the electrolyte layer preferably contains two types of anion isoplastic crystals having different cations. When the electrolyte layer contains two types of anion isoplastic crystals having different cations, the influence of the low ionic conductivity of the anion isoplastic crystals on the electrolyte layer is further reduced, and the ionic conductivity of the electrolyte layer is closer to that of the ionic liquid.

[0075] The cationic components of the heteroplastic anionic crystals and the homoplastic anionic crystals are preferably different from each other. In this case, if the homoplastic anionic crystals are contained in a molar concentration of at least 30 mol% or more relative to the total of the homoplastic anionic crystals and the heteroplastic anionic crystals, the ionic conductivity of the electrolyte layer will be higher than when the plastic crystals in the electrolyte layer are solely composed of homoplastic anionic crystals.

[0076] Furthermore, when the molar ratio of the anionic homoplastic crystals to the anionic heteroplastic crystals is 40:60 or more and 60:40 or less, the ionic conductivity of the electrolyte layer is further increased, and particularly when the anionic homoplastic crystals and the anionic heteroplastic crystals are in equal amounts, the ionic conductivity of the electrolyte layer becomes quite close to the ionic conductivity of the ionic liquid.

[0077] The electrolyte layer may be prepared by further adding a polymer. Examples of the polymer include polyethylene oxide (PEO), polypropylene oxide, polyester, and carbonate-based polymers. Examples of the carbonate-based polymer include polyethylene carbonate (PEC), PEC derivatives, polypropylene carbonate, polytrimethylene carbonate, and copolymers of polytrimethylene carbonate and polycarbonate. One of these polymers may be used alone, or two or more may be combined. Of these polymers, the carbonate-based polymer is merely an example, and any aliphatic polycarbonate may be used. When two or more polymers are used in combination, the various polymers may be in the form of a homopolymer or may exist as a copolymer of two or more monomers. There are no limitations on the molecular weight of the polymer, but the molecular weight of the polymer is preferably 1000 kJ or more, and the molecular weight of polyethylene oxide (PEO) is preferably 1000 kJ or more.

[0078] The addition of these polymers can improve the mechanical strength of the electrolyte layer. The amount of polymer added is preferably 15 wt% or less of the total electrolyte layer. If the amount exceeds 15 wt%, the polymer will affect the ionic conductivity of the electrolyte layer. However, when a carbonate-based polymer is added to the electrolyte layer, the amount of carbonate-based polymer added can be in the range of 10 wt% to 150 wt% of the total amount of plastic crystals constituting the electrolyte layer, more preferably in the range of 20 wt% to 100 wt%, and even more preferably in the range of around 50 wt%. When the carbonate-based polymer is in the range of 20 wt% to 100 wt%, the ionic conductivity of the electrolyte layer is improved, and when it is in the range of around 50 wt%, the ionic conductivity of the electrolyte layer is further improved.

[0079] An example of a method for manufacturing an electrolyte layer containing such plastic crystals and an ionic liquid is as follows. Note that the method for manufacturing a solid electrolyte containing plastic crystals is not limited to the following, and various methods can be used.

[0080] For plastic crystals and ionic liquids, alkali metal salts of the anion components that make up the plastic crystals and ionic liquid and halogenated cation components are dissolved in a solvent. Examples of alkali metals include Na, K, Li, and Cs. Examples of halogens include F, Cl, Br, and I. Water is the preferred solvent. An ion exchange reaction is carried out by gradually adding a solution of the anion metal salt to the solution of the halogenated cation. An equimolar amount of the anion metal salt solution is added to the solution of the halogenated cation and stirred.

[0081] During this process, ion exchange produces plastic crystals and an ionic liquid, as well as an alkali metal halide. When an organic solvent such as dichloromethane is mixed and allowed to stand, the mixture separates into an aqueous layer and an organic solvent layer. The alkali metal halide is removed by removing the aqueous layer. This process can be repeated multiple times, such as five times. After removing the alkali metal halide, the organic solvent such as dichloromethane is evaporated, yielding plastic crystals and an ionic liquid.

[0082] The plastic crystals and ionic liquid are added to a vial. If two types of plastic crystals are to be included in the electrolyte layer, each is purified and added to the vial in a 1:1 molar ratio. If a polymer is to be added, it is added to the vial at this time. An organic solvent is also added to the vial. The organic solvent is one in which the plastic crystals and electrolyte are soluble and in which the ionic liquid does not undergo phase separation, such as acetonitrile.

[0083] The solution in the vial is then cast onto the target object, such as the active material layer of the electrode to which the electrolyte layer 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 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 an electrolyte layer on the target object.

[0084] The plastic crystal may be doped with an ionic salt that serves as an electrolyte. The ionic salt may be a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, and may be used alone or in combination of two or more.

[0085] 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.

[0086] 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 ions of the quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of the quaternized amidiniums include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of the amines of the amine salts 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.

[0087] (electrode body) The positive and negative electrodes are formed by forming polarizable electrodes on current collectors. The current collectors can be made of valve metals such as aluminum foil, platinum, gold, nickel, titanium, steel, and carbon. The current collectors can be in any shape, including film, foil, plate, mesh, expanded metal, and cylinder. The surface of the current collector can be textured by etching or other processes, or it can be plain. Furthermore, surface treatment can be performed to deposit phosphorus on the surface of the current collector.

[0088] For polarizable electrodes, porous carbon materials with electric double layer capacitance are preferred. Porous carbon materials are particularly suitable for this electrolyte layer. Because plastic crystals are soluble, they easily penetrate into the porous structure, increasing the filling rate of the polarizable electrode. On the other hand, sulfide-based and oxide-based solid electrolytes have low filling properties in porous structures. Therefore, electric double layer capacitors using this plastic crystal can combine good filling properties in the porous structure with high ionic conductivity, resulting in high capacity and high output. Note that either the positive electrode or the negative electrode may be formed with an active material layer containing metal compound particles or carbon material that cause a Faraday reaction.

[0089] 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.

[0090] Examples of carbon materials for polarizable electrodes 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] (separator) The separator is provided to prevent contact between the positive and negative electrodes and to maintain the shape of the electrolyte layer. Therefore, if the electrolyte layer has a thickness sufficient to prevent contact between the positive and negative electrodes and is hard enough to maintain its shape independently, the battery may be so-called separatorless.

[0095] When a separator is used in an electric double layer capacitor, examples of the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixtures 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. [Example]

[0096] (Examples 1 to 3) Electrolyte layers for electric double layer capacitors of Examples 1 to 3 were prepared, and the ionic conductivity of the electrolyte layer of each Example was measured.

[0097] The electrolyte layer of Example 1 was prepared using plastic crystals containing SBP cations and CFSA anions in a molar ratio of 1:1. The electrolyte layer of Example 1 was also prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and BF anions in a molar ratio of 1:1. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 77:23.

[0098] Acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added so that the total of the plastic crystals and the ionic liquid was 10 wt %. 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 on which the electrolyte layer had been formed 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 electrolyte layer of Example 1. The electrolyte layer of Example 1 had no fluidity when visually observed, and the entire system was solid.

[0099] The electrolyte layer of Example 2 was prepared using plastic crystals containing SBP cations and NFS anions in a 1:1 molar ratio. The electrolyte layer of Example 2 was also prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and BF4 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 77:23. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0100] The electrolyte layer of Example 3 was prepared using plastic crystals containing P12 cations and BF3CF3 anions in a 1:1 molar ratio. The electrolyte layer of Example 2 was prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and BF4 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 77:23. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0101] The ionic conductivity of the electrolyte layers of Examples 1 to 3 was measured. A two-electrode sealed cell (manufactured by Toyo Systems) was assembled by sandwiching the glass separator on which the electrolyte layer of each of Examples 1 to 3 was formed between two platinum electrodes and opposing them with an electrode press, and impedance measurements were performed. The ionic conductivity was calculated from the impedance measurement results and the thickness of the glass separator impregnated with the electrolyte layer. The ionic conductivity measurement results are shown in Table 1 below.

[0102] [Table 1]

[0103] In addition, Table 1 also lists the ionic conductivity of the electrolyte layer in which only the plastic crystals provided in each Example were used, omitting the ionic liquid. This comparative electrolyte layer was prepared under the same conditions as the electrolyte layer in each Example, except that the electrolyte layer was composed of only plastic crystals. In addition, Table 1 also lists the ionic conductivity of the electrolyte layer in which only the ionic liquid provided in each Example was used, omitting the plastic crystals. This comparative electrolyte layer was prepared under the same conditions as the electrolyte layer in each Example, except that the electrolyte layer was composed of only ionic liquid.

[0104] As shown in Table 1, the ionic conductivity of the electrolyte layer for the electric double layer capacitor of Example 1 is approximately 5,000 times higher than that of an electrolyte layer made only of plastic crystals. The ionic conductivity of the electrolyte layer of Example 2 is approximately 1,500 times higher than that of an electrolyte layer made only of plastic crystals. The ionic conductivity of the electrolyte layer of Example 3 is approximately 50 times higher than that of an electrolyte layer made only of plastic crystals.

[0105] This confirmed that an electrolyte layer for an electric double layer capacitor containing an ionic liquid and a plastic crystal has improved ionic conductivity compared to an electrolyte layer containing only plastic crystals. Therefore, an electrolyte layer containing an ionic liquid and a plastic crystal can suppress leakage current by using the plastic crystal, while overcoming the low ionic conductivity of the plastic crystal, thereby providing high ionic conductivity.

[0106] Examples 4 to 9 Electrolyte layers for electric double layer capacitors were prepared in Examples 4 to 9, and the ionic conductivity of the electrolyte layers in each Example was measured. The electrolyte layers in Examples 4 to 9 differ from Examples 1 to 3 in that the ionic liquid and the plastic crystal contain the same type of anion component.

[0107] The electrolyte layer of Example 4 was prepared using plastic crystals containing SBP cations and BF4 anions in a 1:1 molar ratio. The electrolyte layer of Example 4 was also prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and BF4 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 80:20. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0108] The electrolyte layer of Example 5 was prepared using plastic crystals containing P12 cations and BF3CF3 anions in a 1:1 molar ratio. The electrolyte layer of Example 5 was also prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and BF3CF3 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 77:23. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0109] The electrolyte layer of Example 6 was prepared using plastic crystals containing SBP cations and TFSA anions in a 1:1 molar ratio. The electrolyte layer of Example 6 was also prepared using an ionic liquid (manufactured by Tokyo Chemical Industry Co., Ltd.) containing EMI cations and TFSA anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 66.7:33.3. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0110] The electrolyte layer of Example 7 was prepared using plastic crystals containing SBP cations and TFSA anions in a 1:1 molar ratio. The electrolyte layer of Example 7 was also prepared using an ionic liquid (manufactured by Nisshinbo Holdings Inc.) containing MEMP cations and TFSA anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 66.7:33.3. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0111] The electrolyte layer of Example 8 was prepared using plastic crystals containing SBP cations and TFSA anions in a 1:1 molar ratio. The electrolyte layer of Example 8 was also prepared using an ionic liquid (manufactured by Nisshinbo Holdings Inc.) containing DEME cations and TFSA anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 66.7:33.3. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0112] The electrolyte layer of Example 9 was prepared using plastic crystals containing SBP cations and BF4 anions in a 1:1 molar ratio. The electrolyte layer of Example 9 was also prepared using an ionic liquid (manufactured by Nisshinbo Holdings Inc.) containing MEMP cations and BF4 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 66.7:33.3. After adding the plastic crystals and ionic liquid to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0113] The ionic conductivity of the electrolyte layers of Examples 4 to 9 was measured. The method and conditions for measuring ionic conductivity were the same as those of Examples 1 to 3. The results of the ionic conductivity measurements are shown in Table 2 below. Table 2 also lists the ionic conductivity of the electrolyte layer using only the plastic crystals provided in each Example, and the ionic conductivity of the electrolyte layer using only the ionic liquid provided in each Example. These comparative electrolyte layers were prepared under the same conditions as the electrolyte layers of each Example, except that the electrolyte layer was composed only of ionic liquid.

[0114] [Table 2]

[0115] Table 2 lists Example 1 and Example 2 compared to Example 4, and Example 3 compared to Example 5. Examples 1 and 2 have the same ionic liquid as Example 4, but differ from Example 4 in the anion components of the plastic crystals and the ionic liquid. Example 3 has the same plastic crystals as Example 5, but differs from Example 5 in the anion components of the plastic crystals and the ionic liquid.

[0116] As shown in Table 2, the ionic conductivity of the electrolyte layer for the electric double layer capacitor in Example 4 is approximately 7,200 times higher than that of an electrolyte layer composed only of plastic crystals. Even compared to Example 1, in which the anion components of the plastic crystals and the ionic liquid are different, the ionic conductivity of Example 4, in which the anion components of the plastic crystals and the ionic liquid are the same, is approximately 4.1 times higher. Furthermore, even compared to Example 2, in which the anion components of the plastic crystals and the ionic liquid are different, the ionic conductivity of Example 4 is approximately 67 times higher. Note that the amount of ionic liquid in Example 4 is smaller than in Examples 1 and 2.

[0117] Furthermore, the ionic conductivity of the electrolyte layer in Example 5 is approximately 200 times higher than that of an electrolyte layer composed only of plastic crystals. Even compared to Example 3, in which the anion components of the plastic crystals and the ionic liquid are different, the ionic conductivity of Example 5, in which the anion components of the plastic crystals and the ionic liquid are the same, is approximately four times higher.

[0118] The results of Examples 4 and 5 confirmed that the ionic conductivity of the electrolyte layer was further improved when the anion components of the ionic liquid and the plastic crystal were the same type.

[0119] As shown in Table 2, the electrolyte layers of Examples 6 to 9 also contain ionic liquids having the same type of anion components and plastic crystals, but it can be confirmed that Example 6 has an ionic conductivity that is approximately 1,000 times that of an electrolyte layer containing only plastic crystals, Example 7 has an ionic conductivity that is approximately 300 times that of an electrolyte layer containing only plastic crystals, Example 8 has an ionic conductivity that is approximately 275 times that of an electrolyte layer containing only plastic crystals, and Example 9 has an ionic conductivity that is approximately 1,000 times that of an electrolyte layer containing only plastic crystals.

[0120] Examples 10 and 11 Various electrolyte layers of Example 10 were prepared with different compounding ratios of ionic liquid and plastic crystals, and the ionic conductivity and leakage current were measured. The electrolyte layer of Example 10 was prepared using the same manufacturing method and manufacturing conditions as the electrolyte of Example 4, except that the compounding ratio of ionic liquid and plastic crystals was different. In addition, various electrolyte layers of Example 11 were prepared with different compounding ratios (molar ratios) of ionic liquid and plastic crystals, and the ionic conductivity and leakage current were measured. The electrolyte layer of Example 11 was prepared using the same manufacturing method and manufacturing conditions as the electrolyte of Example 5, except that the compounding ratio of ionic liquid and plastic crystals was different.

[0121] The separators impregnated with the electrolyte layers of Examples 10 and 11 were placed between two activated carbon electrodes (electrode area 2.1 cm) impregnated with the same electrolyte. 2 The battery was sandwiched between two sheets of aluminum foil and sealed with a laminate to produce a cell. The laminated cell was then aged at 2.6 V for 12 hours. After aging, the cell was connected to a 100 Ω resistor and a voltage of 2.3 V was applied, and constant-voltage charging was performed. During this constant-voltage charging, the voltage applied to the resistor was measured with a data logger to calculate the leakage current. In this case, the leakage current value after 50 hours of constant-voltage charging was used.

[0122] The measurement results of the ionic conductivity and leakage current of the electrolyte of Example 10 for each blending ratio of ionic liquid and plastic crystal are shown in Table 3. The results of Table 3 are also summarized in the graph of Figure 1. In the graph of Figure 1, the horizontal axis represents the molar concentration of the plastic crystal relative to the total of the plastic crystal and ionic liquid, and the vertical axis represents the ionic conductivity, with the value of leakage current (μA) added near each plot.

[0123] [Table 3]

[0124] Next, the measurement results of the ionic conductivity and leakage current of the electrolyte of Example 11 for each blending ratio of ionic liquid and plastic crystal are shown in Table 4. The results of Table 4 are also summarized in the graph of Figure 2. In the graph of Figure 2, the horizontal axis represents the molar concentration of the plastic crystal relative to the total of the plastic crystal and ionic liquid, and the vertical axis represents the ionic conductivity, with the value of leakage current (μA) added near each plot.

[0125] [Table 4]

[0126] As shown in Table 3 and Figure 1, it was confirmed that the electrolyte layer of Example 10 exhibits higher ionic conductivity than an electrolyte layer containing only plastic crystals until the blending ratio of the plastic crystals reaches 90 mol% or less relative to the total of the plastic crystals and the ionic liquid. Also, as shown in Table 4 and Figure 2, it was confirmed that the electrolyte layer of Example 11 exhibits higher ionic conductivity than an electrolyte layer containing only plastic crystals until the blending ratio of the plastic crystals reaches 90 mol% or less relative to the total of the plastic crystals and the ionic liquid.

[0127] Furthermore, as shown in Table 3 and Figure 1, the electrolyte layer of Example 10, which is composed of plastic crystals and ionic liquids having the same anionic component, exhibits approximately 40% of the ionic conductivity of an electrolyte layer composed of only ionic liquid until the blending ratio of the plastic crystals reaches 80 mol% or less relative to the total of the plastic crystals and ionic liquid. Also, as shown in Table 4 and Figure 2, the electrolyte layer of Example 11, which is composed of plastic crystals and ionic liquids having the same anionic component, exhibits approximately 30% of the ionic conductivity of an electrolyte layer composed of only ionic liquid until the blending ratio of the plastic crystals reaches 80 mol% or less relative to the total of the plastic crystals and ionic liquid.

[0128] Here, as shown in Table 3 and Figure 1, the electrolyte layer of Example 10, which is made of a plastic crystal and an ionic liquid having the same anionic component, was confirmed to have a leakage current of about half of that of 55 mol% or less when the blending ratio of the plastic crystal was 60 mol% or more and 80 mol% or less relative to the total of the plastic crystal and the ionic liquid. Also, as shown in Table 4 and Figure 2, the electrolyte layer of Example 11, which is made of a plastic crystal and an ionic liquid having the same anionic component, was confirmed to have a leakage current of about 43% of that of 55 mol% or less when the blending ratio of the plastic crystal was 60 mol% or more and 80 mol% or less relative to the total of the plastic crystal and the ionic liquid.

[0129] The electrolyte layers of Examples 10 and 11 consist of plastic crystals and an ionic liquid having the same anionic component. That is, it was confirmed that if the electrolyte layers consist of plastic crystals and an ionic liquid having the same anionic component and the blending ratio of the plastic crystals is 60 mol% to 80 mol% of the total of the plastic crystals and the ionic liquid, the ionic conductivity of the electrolyte layer can be made close to that of the ionic liquid while maintaining good suppression of leakage current.

[0130] Examples 12 to 16 Electrolyte layers for electric double layer capacitors of Examples 12 to 16 were prepared, and the ionic conductivity of each electrolyte layer was measured.

[0131] The electrolyte layer of Example 12 was prepared using plastic crystals containing P12 cations and BF3CF3 anions in a 1:1 molar ratio. The electrolyte layer of Example 12 was also prepared using an ionic liquid containing EMI cations and BF4 anions in a 1:1 molar ratio. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 2:1. That is, the electrolyte layer of Example 12 contained ionic liquid and plastic crystals, but the anion components of the ionic liquid and plastic crystals were different.

[0132] Polyethylene oxide (PEO) with a molecular weight of 2500 kJ was also added to the vial as a polymer. PEO was added so that the concentration was 5 wt% of the total amount of plastic crystals that constituted the electrolyte layer. After adding the plastic crystals, ionic liquid, and polymer to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all methods and conditions.

[0133] The electrolyte layer of Example 13 was prepared using a plastic crystal containing SBP cations and BF4 anions in a molar ratio of 1:1. The electrolyte layer of Example 13 was also prepared using an ionic liquid containing EMI cations and BF4 anions in a molar ratio of 1:1. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 2:1. That is, the electrolyte layer of Example 13 contained an ionic liquid and plastic crystals, but the anion components of the ionic liquid and plastic crystals were the same, and the electrolyte layer contained one type of plastic crystal.

[0134] The electrolyte layer of Example 14 was prepared using two types of plastic crystals. The first type of plastic crystal contained SBP cations and BF4 anions in a 1:1 molar ratio. The second type of plastic crystal contained P12 cations and BF4 anions in a 1:1 molar ratio. Both plastic crystals were added to the vial in equimolar amounts. The electrolyte layer of Example 14 was also prepared using an ionic liquid containing EMI cations and BF4 anions in a 1:1 molar ratio. The sum of both plastic crystals (A) and ionic liquid (B) were added to the vial in a molar ratio of A:B = 77:23. That is, the electrolyte layer of Example 14 contained an ionic liquid and plastic crystals, and the electrolyte layer contained two types of plastic crystals. The first type of plastic crystal had the same anion component as the ionic liquid, and both plastic crystals had the same anion component as the ionic liquid. However, the cationic components of both plastic crystals are different from each other.

[0135] The electrolyte layer of Example 15 was prepared using two types of plastic crystals. The first type of plastic crystal contained P12 cations and BF4 anions in a 1:1 molar ratio. The second type of plastic crystal contained P12 cations and BF3CF3 anions in a 1:1 molar ratio. Both plastic crystals were added to the vial in equimolar amounts. The electrolyte layer of Example 15 was also prepared using an ionic liquid containing EMI cations and BF4 anions in a 1:1 molar ratio. The sum of both plastic crystals (A) and the ionic liquid (B) were added to the vial in a molar ratio of A:B = 2:1. That is, the electrolyte layer of Example 15 contains an ionic liquid and plastic crystals, and the electrolyte layer contains two types of plastic crystals, the first type of plastic crystal having the same type of anion component as the ionic liquid, and the second type of plastic crystal having a different type of anion component from the ionic liquid, and both plastic crystals having the same type of cation component.

[0136] The electrolyte layer of Example 16 was prepared using two types of plastic crystals. The first type of plastic crystal contained SBP cations and BF4 anions in a 1:1 molar ratio. The second type of plastic crystal contained P12 cations and BF3CF3 anions in a 1:1 molar ratio. Both plastic crystals were added to the vial in equimolar amounts. The electrolyte layer of Example 16 was also prepared using an ionic liquid containing EMI cations and BF4 anions in a 1:1 molar ratio. The sum of both plastic crystals (A) and the ionic liquid (B) were added to the vial in a molar ratio of A:B = 2:1. That is, the electrolyte layer of Example 16 contains an ionic liquid and plastic crystals, and the electrolyte layer contains two types of plastic crystals, the first type of plastic crystal having the same type of anion component as the ionic liquid, and the second type of plastic crystal having a different type of anion component from the ionic liquid, and both plastic crystals have different types of cation components.

[0137] In addition, in Examples 13 to 16, polyethylene oxide (PEO) with a molecular weight of 2500 kJ was added as a polymer, and PEO was added so as to have a concentration of 5 wt% relative to the total amount of plastic crystals constituting the electrolyte layer, which are the same as in Example 12. In addition, in Examples 13 to 16, after the plastic crystals, ionic liquid, and polymer were added to the vial, the process of adding an organic solvent and drying until the electrolyte layer was obtained was the same as in Example 1 in all of the methods and conditions.

[0138] The ionic conductivities of the electrolyte layers of Examples 12 to 16 were measured, and the results are shown in Table 5. [Table 5]

[0139] As shown in Table 5, it was confirmed that the ionic conductivity of the electrolyte layer of Example 13 was higher than that of the electrolyte layer of Example 12, the ionic conductivity of the electrolyte layer of Example 14 was higher than that of the electrolyte layer of Example 13, the ionic conductivity of the electrolyte layer of Example 15 was higher than that of the electrolyte layer of Example 14, and the ionic conductivity of the electrolyte layer of Example 16 was higher than that of the electrolyte layer of Example 15.

[0140] That is, an electrolyte layer containing an ionic liquid and plastic crystals has improved ionic conductivity compared to an electrolyte layer containing only plastic crystals. When the anion components of the ionic liquid and plastic crystals are the same type, the ionic conductivity of the electrolyte layer is further improved. When the electrolyte layer contains two types of plastic crystals having the same type of anion component as the ionic liquid, the ionic conductivity of the electrolyte layer is further improved. When plastic crystals having an anion component different from that of the ionic liquid are further included, the ionic conductivity of the electrolyte layer is further improved. Furthermore, when the cation components of the plastic crystals having the same type of anion component as the ionic liquid and the plastic crystals having an anion component different from that of the ionic liquid are different from each other, the ionic conductivity of the electrolyte layer is further improved. The above was confirmed.

[0141] Example 17 Various electrolyte layers of Example 17 were prepared with different blending ratios of the two types of plastic crystals, and the ionic conductivity was measured. The electrolyte layers of Example 17 were prepared using the same manufacturing method and conditions as the electrolyte of Example 16, except for the different blending ratios of the two types of plastic crystals. The measurement results of ionic conductivity are shown in Table 6. The results of Table 6 are also summarized in the graph of Figure 3. In the graph of Figure 3, the horizontal axis represents the molar concentration of the second type of plastic crystal, consisting of SBP cations and BF4 anions, relative to the total of both plastic crystals, and the vertical axis represents ionic conductivity.

[0142] [Table 6]

[0143] As shown in Table 6 and Figure 3, it was confirmed that the ionic conductivity of the electrolyte layer of Example 17 improved as the amount of the two plastic crystals approached equimolar amounts. It was also confirmed that the ionic conductivity was higher when the molar ratio of the two plastic crystals was in the range of 40:60 to 60:40, and that the ionic conductivity was significantly improved when the amount of the two plastic crystals was equimolar.

[0144] Example 18 The electrolyte layer of Example 18 was a modification of Example 17, and the second type of plastic crystal was a P12TFSA plastic crystal containing P12 cations and TFSA anions in a 1:1 molar ratio. Other than that, it was produced using the same manufacturing method and conditions as the electrolyte of Example 17. The blending molar ratio of the two plastic crystals was in the range of 40:60 to 60:40. The measurement results of the ionic conductivity of Example 18 are shown in Table 7.

[0145] [Table 7]

[0146] As shown in Table 7, the electrolyte layer of Example 18 has higher ionic conductivity when the molar ratio of the two plastic crystals is in the range of 40:60 to 60:40, and the ionic conductivity is significantly improved when the two plastic crystals are in equimolar amounts. That is, Examples 17 and 18 confirmed that when the molar ratio of the first type of plastic crystal having the same anion component as the ionic liquid and the second type of plastic crystal having a different anion component from the ionic liquid is in the range of 40:60 to 60:40, the ionic conductivity is higher regardless of the type of plastic crystal, and when the two plastic crystals are in equimolar amounts, the ionic conductivity is significantly improved.

[0147] Examples 19 and 20 Electrolyte layers for electric double layer capacitors were prepared in Examples 19 and 20. The electrolyte layers in Examples 19 and 20 were prepared using two types of plastic crystals and an ionic liquid. The first type of plastic crystal contained SBP cations and BF4 anions in a 1:1 molar ratio. The second type of plastic crystal contained P12 cations and BF4 anions in a 1:1 molar ratio. Both plastic crystals were contained in equimolar amounts in the electrolyte layer. The electrolyte layers in Examples 19 and 20 were also prepared using an ionic liquid containing DEME cations and BF4 anions in a 1:1 molar ratio. The contents of the ionic liquid differ between Examples 19 and 20. No polymer was added to the electrolyte layers in Examples 19 and 20.

[0148] The ionic conductivity of the electrolyte layers of Examples 19 and 20 was measured, and the results are shown in Table 8. [Table 8]

[0149] As shown in Table 8, the ionic conductivity of the electrolyte layer of Example 19 is approximately 100 to 1000 times higher than that of an electrolyte layer composed only of plastic crystals. Also, the ionic conductivity of the electrolyte layer of Example 20 is approximately 460 to 4400 times higher than that of an electrolyte layer composed only of plastic crystals. In Examples 19 and 20, the total amount of plastic crystals is 66.6 to 77 mol%.

[0150] (Examples 21 to 25) As shown in Table 9, electrolyte layers of Examples 21 to 25 were prepared and the ionic conductivity was measured.

[0151] [Table 9]

[0152] As shown in Table 9, the electrolyte layers of Examples 21 to 23 and 25 contain a first type of plastic crystal composed of a 1:1 SBP cation and a BF4 anion. The electrolyte layers of Examples 21 to 23 and 25 also contain a second type of plastic crystal composed of a 1:1 P12 cation and a BF3CF3 anion. The electrolyte layers of Examples 21 to 23 and 25 also contain an ionic liquid composed of a 1:1 DEME cation and a BF4 anion. The electrolyte layers of Examples 21 to 23 and 25 have in common the fact that they contain equal amounts of both plastic crystals, but the blending ratios of the plastic crystals and the ionic liquid are different.

[0153] The electrolyte layer of Example 24 also includes a first type of plastic crystal composed of SBP cations and BF4 anions in a 1:1 ratio, a second type of plastic crystal composed of P12 cations and TFSA anions in a 1:1 ratio, and an ionic liquid composed of DEME cations and BF4 anions in a 1:1 ratio.

[0154] To the electrolyte layers of Examples 21 to 25, polyethylene oxide (PEO) having a molecular weight of 2500 kJ was added as a polymer at a concentration of 5 wt % or 10 wt % relative to the total amount of plastic crystals.

[0155] As shown in Table 9, the ionic conductivity of the electrolyte layers of Examples 21 to 23 and 25 is approximately 100 to 8,800 times higher than that of an electrolyte layer composed only of plastic crystals. Furthermore, the ionic conductivity of the electrolyte layer of Example 24 is approximately 6,800 to 390,000 times higher than that of an electrolyte layer composed only of plastic crystals. In Examples 21 to 25, the total amount of plastic crystals is 66.6 to 91 mol%. In Example 21, the ionic conductivity is at least 100 times higher, even though the ionic liquid accounts for only 9 mol% of the total.

[0156] (Comparative Example 1 and Example 26) Electrolyte layers for electric double layer capacitors were prepared in Comparative Example 1 and Example 26. Comparative Example 1 and Example 26 have in common that they were prepared using an ionic liquid containing EMI cations and TFSA anions in a 1:1 molar ratio. However, while the electrolyte layer of Example 26 contains plastic crystals composed of SBP cations and TFSA anions in a 1:1 molar ratio, the electrolyte layer of Comparative Example 1 contains lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and does not contain plastic crystals. Although lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) has a composition similar to plastic crystals, its state of matter is solid, not plastic crystals.

[0157] The ionic conductivity and resistance values of Comparative Example 1 and Example 26 were measured and are shown in Table 10 below. The separator impregnated with each electrolyte layer was connected to two activated carbon electrodes (electrode area 2.1 cm) impregnated with the same electrolyte. 2The battery was sandwiched between two sheets of plastic and sealed with a laminate to produce a cell. This cell was charged to 2.5 V at a constant current of 0.1 mA, and after the voltage reached 2.5 V, it was opened for 1 second and the voltage drop during the open period was measured. The resistance was calculated by dividing this voltage drop by the charging current value of 0.1 mA.

[0158] [Table 10]

[0159] As shown in Table 10, the ionic conductivity of Comparative Example 1 was only about 4 / 1000 of that of Example 26. This confirmed that even if an electrolyte layer was prepared by mixing a compound that is not a plastic crystal, such as LiTFSA, with an ionic liquid, the ionic conductivity was not improved, but that mixing a plastic crystal with an ionic liquid improved the ionic conductivity. Furthermore, it was confirmed that the resistance value of the electrolyte layer of Example 26 was reduced to about 7 / 1000 compared to Comparative Example 1 due to the improved ionic conductivity.

[0160] Examples 27 to 36 Electrolyte layers for the electric double layer capacitors of Examples 27 to 36 were prepared, and the ionic conductivity of each electrolyte layer was measured.

[0161] The electrolyte layers of Examples 27 to 36 have the following in common: they were prepared using an ionic liquid containing DEME cations and BF anions in a molar ratio of 1:1. Plastic crystals (A) and ionic liquid (B) were added to a vial in a molar ratio of A:B = 66.7:33.3.

[0162] The electrolyte layers of Examples 27 to 29 were fabricated using one type of plastic crystal. The plastic crystal used in the electrolyte layer of Example 27 contained SBP cations and BF anions in a 1:1 molar ratio. The plastic crystal used in the electrolyte layer of Example 28 contained P cations and BF CF anions in a 1:1 molar ratio. The plastic crystal used in the electrolyte layer of Example 29 contained P cations and BF anions in a 1:1 molar ratio.

[0163] On the other hand, the electrolyte layers of Examples 30 to 36 contain two types of plastic crystals in a 1:1 molar ratio. The electrolyte layers of Examples 30 to 33 contain plastic crystals containing SBP cations and BF4 anions in a 1:1 molar ratio and plastic crystals containing P12 cations and BF3CF3 anions in a 1:1 molar ratio. The electrolyte layer of Example 34 contains plastic crystals containing SBP cations and BF4 anions in a 1:1 molar ratio and plastic crystals containing P12 cations and BF4 anions in a 1:1 molar ratio. The electrolyte layer of Example 35 contains plastic crystals containing P12 cations and BF4 anions in a 1:1 molar ratio and plastic crystals containing P12 cations and BF3CF3 anions in a 1:1 molar ratio.

[0164] The electrolyte layers of Examples 27 to 36 have in common the addition of polyethylene carbonate (PEC) as a polymer. For the electrolyte layers of Examples 27 to 29 and Examples 35 and 36, polyethylene carbonate was added to the vials at a concentration of 50 wt % relative to the total amount of plastic crystals.

[0165] The electrolyte layers of Examples 30 to 34 had the same composition of plastic crystals and ionic liquid, but different amounts of polyethylene carbonate added. That is, in Example 30, polyethylene carbonate was added to a concentration of 10 wt% relative to the total amount of plastic crystals, in Example 31, polyethylene carbonate was added to a concentration of 20 wt% relative to the total amount of plastic crystals, in Example 32, polyethylene carbonate was added to a concentration of 50 wt% relative to the total amount of plastic crystals, in Example 33, polyethylene carbonate was added to a concentration of 100 wt% relative to the total amount of plastic crystals, and in Example 34, polyethylene carbonate was added to a concentration of 150 wt% relative to the total amount of plastic crystals.

[0166] The measurement results of the ionic conductivity of the electrolyte layers of Examples 27 to 36 are shown in Table 11. [Table 11]

[0167] As shown in Table 11, comparing the electrolyte layers of Examples 30 to 34, the ionic conductivity of the electrolyte layers of Examples 31 to 33 was higher. The electrolyte layers of Examples 31 to 33 contained polyethylene carbonate (PEC) at a concentration of 20 wt% to 100 wt% based on the total amount of plastic crystals. The electrolyte layer of Example 32 had the highest ionic conductivity. The electrolyte layer of Example 32 contained polyethylene carbonate (PEC) at a concentration of 50 wt% based on the total amount of plastic crystals. Furthermore, the electrolyte layers of Examples 27 to 29 and Examples 35 and 36 also contained polyethylene carbonate (PEC) at a concentration of 50 wt% based on the total amount of plastic crystals, and the electrolyte layers of Examples 27 to 29 and Examples 35 and 36 also had high ionic conductivity.

[0168] Thus, when the electrolyte layer contains a carbonate-based polymer, the ionic conductivity is further improved when the carbonate-based polymer is in the range of 20 wt% or more and 100 wt% or less, and it was confirmed that the ionic conductivity of the electrolyte layer is particularly significantly improved when the carbonate-based polymer is around 50 wt% of the total amount of plastic crystals.

Claims

1. a pair of electrode bodies having polarizable electrodes; an electrolyte layer containing an ionic liquid and a plastic crystal; Equipped with the plastic crystal and the ionic liquid have the same anion component; An electric double layer capacitor characterized by:

2. the plastic crystal is contained in the electrolyte layer at a ratio of 60 mol % to 90 mol % of the total of the ionic liquid and the plastic crystal; 2. The electric double layer capacitor according to claim 1,

3. the plastic crystal is contained in the electrolyte layer at a ratio of 60 mol % to 80 mol % of the total of the ionic liquid and the plastic crystal; 2. The electric double layer capacitor according to claim 1,

4. The electrolyte layer further contains other types of plastic crystals; 4. The electric double layer capacitor according to claim 1, wherein:

5. the electrolyte layer further contains, in addition to the plastic crystals having the same type of anion component as the ionic liquid, the other type of plastic crystals having a different type of anion component from the ionic liquid; 5. The electric double layer capacitor according to claim 4,

6. the other type of plastic crystal has a cation component different from that of the plastic crystal, which has the same type of anion component as the ionic liquid; 6. The electric double layer capacitor according to claim 5,

7. the blending molar ratio of the plastic crystals having the same type of anion component as the ionic liquid to the other type of plastic crystals having a type of anion component different from that of the ionic liquid is in the range of 40:60 or more and 60:40 or less; 7. The electric double layer capacitor according to claim 5 or 6,

8. the electrolyte layer contains two types of plastic crystals having different cation components as the plastic crystals having the same anion component as the ionic liquid; 8. The electric double layer capacitor according to claim 1, wherein:

9. the plastic crystal contained in the electrolyte layer has a pyrrolidinium-based cation, an ammonium-based cation, a piperidinium-based cation, or a phosphonium-based cation; 9. The electric double layer capacitor according to claim 1, wherein:

10. the cations of the plastic crystals contained in the electrolyte layer do not contain lithium ions; 10. The electric double layer capacitor according to claim 1, wherein:

11. the electrolyte layer further contains a carbonate-based polymer; 11. The electric double layer capacitor according to claim 1, wherein:

Images