Electrochemical capacitor

Abstract

An electrochemical capacitor includes a positive electrode, a negative electrode, and an electrolyte solution. The electrolyte solution contains a lactone compound and an additive. The additive is at least one selected from the group consisting of siloxane compounds and fluorinated silyl compounds.

Description

Technical Field

[0001] The present disclosure relates to electrochemical capacitors. Background Art

[0002] An electrochemical capacitor comprises a pair of electrodes and an electrolyte, at least one of which contains an active material that can adsorb and desorb ions. An electric double layer capacitor, which is an example of an electrochemical capacitor, has a longer lifespan than a secondary battery, can be quickly charged, has excellent output characteristics, and is widely used in backup power supplies, etc.

[0003] Patent Document 1 discloses a non-aqueous electrolyte for an electric double layer capacitor as follows: N-ethyl-N-methylpyrrolidinium tetrafluoroborate as a quaternary ammonium salt is dissolved, and 28.3 ppm of K is contained as an alkali metal cation. + and 0.4 ppm Na + (Example 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2016 / 092664 Summary of the invention

[0007] Problems to be solved by the invention

[0008] The performance of electrochemical capacitors tends to degrade under floating charge and further improvements are needed.

[0009] Means used to solve problems

[0010] In view of the above, one aspect of the present disclosure relates to an electrochemical capacitor including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte contains a lactone compound and an additive, wherein the additive is at least one selected from the group consisting of siloxane compounds and fluorinated silyl compounds.

[0011] Effects of the Invention

[0012] According to the present disclosure, it is possible to suppress a decrease in the floating charge characteristics of an electrochemical capacitor.

[0013] The novel features of the present invention are described in the appended claims, but the present invention relates to both the structure and the content, and together with other objects and features of the present invention, will be further fully understood through the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a perspective view of an electrochemical capacitor according to one embodiment of the present disclosure with a portion cut away. DETAILED DESCRIPTION

[0015] Hereinafter, the embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. The following description sometimes illustrates specific numerical values ​​and materials, but other numerical values ​​and materials can be applied as long as the effects of the present disclosure can be obtained. In this specification, the description of "numerical value A to numerical value B" includes numerical value A and numerical value B, which can be replaced by "above A and below B". In the following description, when the lower limit and upper limit are illustrated for numerical values ​​of specific physical properties, conditions, etc., as long as the lower limit does not reach above the upper limit, any of the illustrated lower limits can be arbitrarily combined with any of the illustrated upper limits. When multiple materials are illustrated, one can be selected from them and used alone, or two or more can be used in combination.

[0016] In addition, the present disclosure includes a combination of matters recorded in two or more claims arbitrarily selected from the plurality of claims recorded in the appendix. That is, as long as no technical contradiction occurs, matters recorded in two or more claims arbitrarily selected from the plurality of claims recorded in the appendix may be combined.

[0017] The electrochemical capacitor of the embodiment of the present disclosure comprises a positive electrode, a negative electrode and an electrolyte. The electrolyte contains a lactone compound and an additive. The additive is at least one selected from the group consisting of a siloxane compound and a fluorinated silyl compound.

[0018] It should be noted that the floating charge characteristic refers to an indicator of the degree of deterioration of an electrochemical device when a floating charge is performed using an external DC power supply to maintain a certain voltage. It can be said that the smaller the capacity reduction during floating charge and the smaller the increase in internal resistance, the better the floating charge characteristic. The above-mentioned capacity reduction and increase in internal resistance are caused by the decomposition of the electrolyte during floating charge. It can be said that the smaller the amount of gas generated accompanying the decomposition of the electrolyte, the better the floating charge characteristic.

[0019] The present disclosure can suppress decomposition of the electrolyte and improve the floating charge characteristics even when the rated voltage of the electrochemical capacitor (electric double layer capacitor) is greater than 2.5 V (or 2.7 V or more).

[0020] Lactone compounds are used as solvents for electrolytes in electrochemical capacitors because they have low viscosity at low temperatures. Examples of lactone compounds include β-propiolactone, γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Among them, γ-butyrolactone (GBL) is most preferred because of its low viscosity at low temperatures, high boiling point, and low gas release due to side reactions.

[0021] However, lactone compounds are in a highly oxidizing environment when the potential of the positive electrode is high. In a strongly acidic environment, lactone compounds sometimes undergo oxidative decomposition due to the influence of the surface functional groups of the positive electrode active material. During floating charge, since a high voltage is applied to the electrochemical capacitor for a long time, the potential of the positive electrode is high for a long time, and the lactone compound is easily oxidized and decomposed. It is believed that as a result, gas is generated, and thus the floating charge characteristics are reduced.

[0022] In contrast, according to an electrochemical capacitor of one embodiment of the present disclosure, by including an additive (siloxane compound and / or fluorinated silyl compound) in the electrolyte containing the lactone compound, the oxidative decomposition of the lactone compound can be suppressed, gas generation can be suppressed, and the reduction of the floating charge characteristics can be suppressed. It is speculated that this is because the additive reacts with the surface functional groups (carboxyl groups, etc.) of the positive electrode active material (porous carbon particles), the surface of the positive electrode active material is protected by the components (groups) derived from the additive, and the reaction sites between the surface of the positive electrode active material and the electrolyte components are reduced. It is speculated that by silylating the surface functional groups of the positive electrode active material with the additive, the oxidative decomposition of the lactone compound can be suppressed. For example, the carboxyl group (COOH) on the surface of the positive electrode active material reacts with the silyl group (SiR3) derived from the additive (the decomposition product of the additive produced during the aging treatment described later) to form COOSiR3. SiR3 is, for example, a trialkylsilyl group.

[0023] When the additive is used, the generation of gas during float charge can be significantly suppressed, and the reduction in float charge characteristics can be significantly suppressed. This is an effect specific to the case where the solvent of the electrolyte contains a lactone compound.

[0024] Assuming that the solvent of the electrolyte is propylene carbonate, even if the above-mentioned additives are used, the amount of gas generated during float charge increases. During charging, the interface between the negative electrode and the electrolyte is in an alkaline environment, and the interface between the positive electrode and the electrolyte is in an acidic environment, thereby causing a hydrolysis reaction of propylene carbonate to occur in the positive and negative electrodes, and gas is easily generated. In addition, siloxane compounds contain water, and are easily acidic or alkaline due to water, which promotes the hydrolysis of propylene carbonate. It is speculated that this is why the amount of gas generated increases. In contrast, lactone compounds such as GBL have excellent stability, are not easily decomposed in alkaline or acidic environments, and can suppress the generation of gas.

[0025] From the perspective of further suppressing gas generation (bulging) during float charge, the electrolyte preferably contains a chain ester compound together with the lactone compound. The chain ester compound is preferably a condensate of an aliphatic monocarboxylic acid and a primary alcohol. As such a chain ester compound, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, etc. can be listed. Among them, from the perspective of boiling point, flash point, viscosity and solubility, propyl acetate, methyl propionate, ethyl propionate, and methyl butyrate are particularly preferred.

[0026] (Siloxane compound)

[0027] The siloxane compound is a compound having a siloxane bond (Si—O—Si), and examples thereof include compounds represented by the following general formula (1).

[0028] [Chemical formula 1]

[0029]

[0030] In the general formula (1), R1 to R6 may each independently be a hydrocarbon group. A portion of R1 to R6 may be a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkoxy group, or an ester group. From the perspective of viscosity and solubility in the electrolyte, n may be an integer of 1 to 10, preferably an integer of 1 to 5. The carbon number of the hydrocarbon group may be, for example, 1 to 6, or 1 to 4. At least a portion of the hydrogen atoms of the hydrocarbon group may be optionally substituted by a halogen atom. The hydrocarbon group may be linear, branched, or cyclic. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group.

[0031] Examples of the hydrocarbon group include alkyl, cycloalkyl, aryl, alkenyl, and alkynyl. Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl. Examples of the cycloalkyl group include cyclopropyl and cyclobutyl. Examples of the aryl group include phenyl. Examples of the alkenyl group include vinyl, 1-propenyl, 2-propenyl, isopropenyl, 1-butenyl, and 2-butenyl. Examples of the alkynyl group include ethynyl.

[0032] Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, etc. At least a part of the hydrogen atoms of the alkoxy group may be substituted with a halogen atom.

[0033] Examples of the siloxane compound include 1,1,3,3-tetramethyldisiloxane, hexamethyldisiloxane (HMDSi), 1,3-divinyltetramethyldisiloxane, octamethyltrisiloxane (OMTSi), and decamethyltetrasiloxane.

[0034] (Fluorinated silyl compounds)

[0035] The fluorinated silyl compound is a compound having a fluorinated silyl group, and examples thereof include compounds represented by the following general formula (2).

[0036] [Chemical formula 2]

[0037]

[0038] n is 1 or 2. The compound represented by the general formula (2) is a compound having n fluorinated silyl groups.

[0039] In the general formula (2), when n=2, R7 and R8 may each independently be a hydrocarbon group. Examples of the hydrocarbon group include those exemplified in the general formula (1). At least a portion of the hydrogen atoms of the hydrocarbon group may be substituted by a halogen atom. R7 or R8 may be a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkoxy group, or an ester group. Examples of the halogen atom and the alkoxy group include the atoms and groups exemplified in the general formula (1). At least a portion of the hydrogen atoms of the alkoxy group may be substituted by a halogen atom.

[0040] Z may be a divalent hydrocarbon group or a sulfur bond (-S-). Examples of divalent hydrocarbon groups include alkylene, alkenylene, alkynylene, and cycloalkylene. Examples of alkylene groups include methylene and ethylene. Examples of alkenylene groups include vinylene. Examples of alkynylene groups include ethynylene. Examples of cycloalkylene groups include cyclopropylene and cyclobutylene.

[0041] In the general formula (2), when n=1, Z and R7 to R8 may each independently be a hydrocarbon group. Examples of the hydrocarbon group include the groups exemplified in the general formula (1). A portion of Z and R7 to R8 may be a hydrogen atom, a halogen atom, a hydroxyl group, a carboxyl group, an amino group, an alkoxy group, or an ester group. Examples of the halogen atom and the alkoxy group include the atoms and groups exemplified in the general formula (1). At least a portion of the hydrogen atoms of the alkoxy group may be substituted with a halogen atom.

[0042] As fluorinated silyl compounds, for example, there can be listed: monofluorosilane compounds such as trimethylfluorosilane ((CH3)3SiF), triethylfluorosilane, tripropylfluorosilane, phenyldimethylfluorosilane, triphenylfluorosilane, vinyldimethylfluorosilane, vinyldiethylfluorosilane, vinyldiphenylfluorosilane, trimethoxyfluorosilane, and triethoxyfluorosilane; difluorosilane compounds such as dimethyldifluorosilane, diethyldifluorosilane, divinyldifluorosilane, and ethylvinyldifluorosilane; and trifluorosilane compounds such as methyltrifluorosilane and ethyltrifluorosilane.

[0043] The siloxane compound added to the electrolyte may be decomposed by cutting the Si-O bond of the siloxane bond during the aging treatment of the electrochemical capacitor. In the case of multiple siloxane bonds, a siloxane compound and / or a fluorinated silyl compound with a smaller number of siloxane bonds will be generated as a decomposition product. In the case of one siloxane bond, a fluorinated silyl compound will be generated as a decomposition product. The fluorine atoms contained in the fluorinated silyl compound may be derived from the fluorine atoms contained in the anions of the electrolyte. After the aging treatment of the electrochemical capacitor, a portion of the siloxane compound added when preparing the electrolyte may remain without being decomposed.

[0044] The additive added to the electrolyte can be a siloxane compound having multiple siloxane bonds, more preferably octamethyltrisiloxane (OMTSi). In the case of adding OMTSi to the electrolyte, during the aging treatment of the electrochemical capacitor, OMTSi can form hexamethyldisiloxane (HMDSi) as a siloxane compound, and trimethylfluorosilane ((CH3)3SiF) as a fluorinated silyl compound. On the other hand, the decomposition product of the siloxane compound or the separately prepared siloxane compound and the fluorinated silyl compound can be directly added to the electrolyte only in the required amount on the basis of the aforementioned decomposition product. In this case, it is possible to achieve an improvement in the floating charge characteristics.

[0045] When preparing the electrolyte (before aging treatment), the content of the additive in the electrolyte is, for example, 0.01 mass % or more and 5 mass % or less relative to the electrolyte as a whole, and may be 0.1 mass % or more and 1 mass % or less. In an electrochemical capacitor, a portion of the additive may be consumed by reaction with the surface functional groups of the positive electrode active material. Therefore, after aging treatment or after charging, the additive contained in the electrolyte may be a trace amount (for example, 0.01 mass % or more).

[0046] As component analysis of the electrolyte solution, for example, gas chromatography-mass spectrometry (GC / MS), ion chromatography (IC), nuclear magnetic resonance spectroscopy (NMR), etc. can be used.

[0047] As the cation contained in the electrolyte, NR4 is preferred in terms of high voltage resistance and high solubility in aprotic solvents. + (R is an alkyl group) is a quaternary alkylammonium ion. The four alkyl groups R bonded to N may be different from the others or any one of them may be the same as the others. The four alkyl groups R may be independently C1 to C4 alkyl groups. The alkyl groups R are preferably straight-chain alkyl groups without branches, and the two alkyl groups R are bonded to each other without forming a ring structure. Among them, OH is easily generated by decomposition with a small amount of water. -In terms of reaction and easy maintenance of the pH of the electrolyte, diethyldimethylammonium ion (N(C2H5)2(CH3)2 + ).

[0048] The quaternary alkylammonium ion is added to the electrolyte in the form of a salt with an anion. The anion is preferably a fluorine-containing anion. Anions containing fluorine-containing acids are preferred. Examples of fluorine-containing anions include BF4 - PF6 - wait.

[0049] Here, the capacity of the positive electrode refers to the maximum capacity that can be exhibited at the positive electrode, which is a theoretical capacity determined by the amount of the positive electrode active material, etc. Similarly, the capacity of the negative electrode refers to the maximum capacity that can be exhibited at the negative electrode, which is a theoretical capacity determined by the amount of the negative electrode active material, etc. The capacity of the positive electrode is roughly expressed in terms of the relative area (cm2) between the positive electrode and the negative electrode. 2 ) multiplied by the amount of positive electrode active material per unit area (g / cm 2 ) and the capacity per unit weight of the positive electrode active material (F / g). The capacity of the negative electrode is roughly calculated by the relative area between the positive and negative electrodes (cm 2 ) multiplied by the amount of negative electrode active material per unit area (g / cm 2 The capacity (F) of the positive electrode active material and the negative electrode active material is obtained from the charge amount when 3V is applied.

[0050] In an electrochemical capacitor, as the capacity of the positive electrode increases relative to the capacity of the negative electrode, the potential of the positive electrode and the negative electrode decreases, and as the capacity of the negative electrode increases relative to the capacity of the positive electrode, the potential of the positive electrode and the negative electrode increases.

[0051] The electrochemical capacitor of one embodiment of the present disclosure can make the capacity of the positive electrode larger than that of the negative electrode. This can reduce the potential of the positive electrode during charging and suppress the oxidative decomposition of the lactone compound that causes the reduction of floating charge characteristics.

[0052] The larger the capacity of the positive electrode relative to the capacity of the negative electrode, the greater the effect of inhibiting the oxidative decomposition of the lactone compound and the greater the effect of inhibiting the decrease in floating charge characteristics. In order to inhibit the decrease in floating charge characteristics, the capacity ratio of the positive electrode to the negative electrode is preferably 1.1 or more.

[0053] On the other hand, the larger the capacity of the positive electrode is relative to the capacity of the negative electrode, the more the portion of the capacity of the positive electrode that does not contribute to the capacity of the electrical capacitor increases, and the capacity of the electrochemical capacitor decreases. In addition, since the potential of the negative electrode decreases, the reducibility on the negative electrode side is further increased. In terms of suppressing the reduction in the capacity of the electrochemical capacitor and suppressing the side reaction (gas generation associated with the side reaction) caused by the reductive decomposition of the lactone compound at the negative electrode, the capacity ratio of the positive electrode to the negative electrode is preferably set to 1.6 or less.

[0054] From the viewpoint of further suppressing the reduction in floating charge characteristics due to gas generation, the capacity ratio of the positive electrode to the negative electrode is more preferably 1.3 to 1.6, and even more preferably 1.3 to 1.5.

[0055] Both the positive electrode and the negative electrode are polarizable electrodes. The polarizable electrode may contain an active material that can adsorb and desorb ions. Capacitance is exhibited by the adsorption of ions on the active material. When ions are desorbed from the active material, a non-Faraday current flows. An electrochemical capacitor is an electric double layer capacitor (EDLC) that forms an electric double layer by adsorbing ions on the active material.

[0056] The polarizable electrode, for example, comprises a current collector and a polarizable electrode layer carried by the current collector. When both the positive electrode and the negative electrode are polarizable electrodes, the positive electrode, for example, comprises a positive electrode current collector and a polarizable electrode layer carried by the positive electrode current collector. The negative electrode, for example, comprises a negative electrode current collector and a polarizable electrode layer carried by the negative electrode current collector. The capacity of the positive electrode and the negative electrode depends on the amount of active material contained in the polarizable electrode layer, respectively. In addition, when the capacity is expressed by ion adsorption on the active material, it also depends on the specific surface area of ​​the active material, etc. However, by making the thickness of the polarizable electrode layer of the positive electrode thicker than the thickness of the polarizable electrode layer of the negative electrode, the capacity of the positive electrode can be easily made greater than that of the negative electrode.

[0057] In addition, by compressing the polarizable electrode layer of the positive electrode and increasing the loading density of the active material per unit area of ​​the polarizable electrode layer supported on the positive electrode collector, the capacity of the positive electrode can be made greater than that of the negative electrode while making the thickness of the positive electrode and the negative electrode approximately the same.

[0058] The thickness of the positive electrode polarizable electrode layer is preferably greater than the thickness of the negative electrode polarizable electrode layer. The thickness ratio of the positive electrode polarizable electrode layer to the negative electrode polarizable electrode layer is more preferably 1.1 or more and 1.6 or less.

[0059] When a 3V voltage is applied between the positive and negative electrodes of an electrochemical capacitor to charge, the potential of the positive electrode is expressed as Ag / Ag +It is preferable that the potential is within the range of +0.96 V to +1.0 V (the potential of the negative electrode is within the range of -2.04 V to -2.0 V) as a reference. In this case, an electrochemical capacitor can be realized in which the decrease in floating charge characteristics is significantly suppressed.

[0060] It should be noted that the potential of the positive electrode (negative electrode) is obtained as follows: the positive electrode and the negative electrode charged at 3V are immersed in a non-aqueous solution having the same composition as the electrolyte in a manner such that the active material layers (polarizable electrode layers) are opposite to each other, and the potential is measured when the negative electrode (positive electrode) is used as a counter electrode and the Ag electrode is used as a reference electrode. In the case where the positive electrode and the negative electrode have active material layers (polarizable electrode layers) on both sides, in order to avoid forming a non-opposite portion, one side of the active material layer (polarizable electrode layer) is removed. The Ag electrode can be used as follows: a solvent (GBL) is added to the electrolyte in a manner such that the salt concentration reaches 0.1 mol / L, and further Ag is added. + An electrode was prepared by filling a glass tube with an internal solution for a reference electrode obtained by adding AgBF4 so that the ion concentration becomes 0.1 mol / L, and then immersing a silver wire in the internal solution for a reference electrode.

[0061] Hereinafter, each component of the electrochemical capacitor according to the embodiment of the present invention will be described in more detail.

[0062] (positive and negative)

[0063] As the positive electrode and negative electrode of the electrochemical capacitor, for example, an electrode having an active layer (polarizable electrode layer) containing an active material and a current collector supporting the active layer is used as a polarizable electrode. The active material, for example, contains porous carbon particles. The active layer contains porous carbon particles that are the active material as an essential component, and may contain a binder, a conductive agent, etc. as optional components.

[0064] The porous carbon particles can be produced, for example, by heat-treating the raw material to carbonize it and activating the obtained carbide to make it porous. The carbide can be crushed and granulated before the activation treatment. The porous carbon particles obtained in the activation treatment can be pulverized. After the pulverization treatment, classification treatment can be performed. As activation treatment, for example, gas activation using a gas such as water vapor and chemical activation using an alkali such as potassium hydroxide can be listed.

[0065] Examples of the raw material include wood, coconut shells, pulp waste liquid, coal-based asphalt obtained by thermal decomposition of coal or coal-based asphalt obtained by thermal decomposition of heavy oil or petroleum-based asphalt obtained by thermal decomposition of heavy oil or coal-based asphalt, phenolic resin, petroleum-based coke, coal-based coke, etc. Among them, petroleum-based coke and coal-based coke are preferred raw materials.

[0066] After the petroleum coke or coal coke is heat-treated and the obtained carbide is activated, the porous carbon particles can be pulverized. The pulverization process uses, for example, a ball mill, a jet mill, etc. Through the above-mentioned pulverization process, fine porous carbon particles are obtained, and the average particle size (D50) thereof is, for example, greater than 1 μm and less than 4 μm. It should be noted that in this specification, the average particle size (D50) refers to the particle size (median particle size) at which the volume cumulative value reaches 50% in the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0067] The pore distribution and particle size distribution of the porous carbon particles can be adjusted by the raw material, heat treatment temperature, activation temperature in gas activation, degree of pulverization, etc. In addition, the pore distribution and particle size distribution of the porous carbon particles can be adjusted by mixing two kinds of porous carbon particles with different raw materials.

[0068] The average particle size and particle size distribution of the porous carbon particles are measured by a laser diffraction / scattering method. As a measuring device, for example, a laser diffraction / scattering particle size distribution measuring device "MT3300EXII" manufactured by MICROTRAC Corporation is used.

[0069] As the binder, for example, a resin material such as polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), or styrene-butadiene rubber (SBR) is used, and as the conductive agent, for example, carbon black such as acetylene black is used.

[0070] The electrode is obtained by, for example, applying a slurry containing porous carbon particles, a binder and / or a conductive agent, and a dispersion medium to the surface of a current collector, drying the coating, and rolling the coating to form an active layer. The current collector is, for example, a metal foil such as aluminum foil.

[0071] (Electrolyte)

[0072] The electrolyte solution includes a solvent (non-aqueous solvent), an ionic substance, and an additive. The ionic substance is dissolved in the solvent and includes cations and anions. The ionic substance may include, for example, a low melting point compound (ionic liquid) that can exist in the form of a liquid at near room temperature. The concentration of the ionic substance in the electrolyte solution is, for example, 0.5 mol / L or more and 2.0 mol / L.

[0073] If solvent is high boiling point, it is preferred.Solvent comprises lactone compound, and other solvents (such as chain ester compound) can be further comprised as required.As other solvents, except chain ester compound, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, polyols such as ethylene glycol, propylene glycol, cyclic sulfones such as sulfolane, amides such as N-methylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, formaldehyde etc. can also be used.

[0074] Ionic substances include, for example, organic salts. Organic salts refer to salts in which at least one of anions and cations contains an organic substance. As an organic salt in which the cation contains an organic substance, for example, quaternary ammonium salts can be cited. As an organic salt in which the anion (or two ions) contains an organic substance, for example, trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, 1,2,3,4-tetramethylimidazolinium phthalate, 1,3-dimethyl-2-ethylimidazolinium phthalate, etc. can be cited.

[0075] From the viewpoint of improving the withstand voltage characteristics, the anion preferably contains an anion of a fluorine-containing acid. Examples of the anion of a fluorine-containing acid include BF4 - and / or PF6 - The organic salt preferably contains, for example, a quaternary alkylammonium cation and a fluorine-containing acid anion. Specifically, diethyldimethylammonium tetrafluoroborate (DEDMABF4), triethylmethylammonium tetrafluoroborate (TEMABF4), and the like can be cited.

[0076] (Isolated Body)

[0077] A separator is usually sandwiched between the positive electrode and the negative electrode. The separator has ion permeability and has the function of physically separating the positive electrode from the negative electrode to prevent short circuit. As the separator, a non-woven fabric made of cellulose fiber, a non-woven fabric made of glass fiber, a microporous membrane made of polyolefin, a woven fabric or a non-woven fabric, etc. can be used. The thickness of the separator is, for example, 8 to 300 μm, preferably 8 to 40 μm.

[0078] Figure 1 This is a perspective view in which a portion of the electrochemical capacitor according to the embodiment of the present disclosure is cut away.

[0079] Figure 1The electrochemical capacitor 10 is a double-layer capacitor, and has a wound capacitor element 1. The capacitor element 1 is composed of a sheet-like first electrode (positive electrode) 2 and a second electrode (negative electrode) 3 wound with a separator 4. The first electrode 2 and the second electrode 3 respectively have a first metal collector, a second collector, and a first active layer and a second active layer supported on the surface thereof, and exhibit capacity by adsorbing and desorbing ions. The first active layer and the second active layer contain, for example, porous carbon particles.

[0080] The collector is, for example, aluminum foil. The surface of the collector can be roughened by etching or other methods. The separator 4 is, for example, a non-woven fabric with cellulose as the main component. The first lead 5a and the second lead 5b are connected to the first electrode 2 and the second electrode 3, respectively, as lead-out members. The capacitor element 1 is contained in a cylindrical housing 6 together with an electrolyte (not shown). The material of the housing 6 can be, for example, aluminum, stainless steel, copper, iron, brass or other metal. The opening of the housing 6 is sealed by a sealing member 7. The leads 5a and 5b are led out to the outside by passing through the sealing member 7. The sealing member 7 is made of, for example, a rubber material such as butyl rubber.

[0081] In the above embodiment, a winding type capacitor is described, but the application scope of the present disclosure is not limited to the above, and can also be applied to capacitors of other structures, such as stacked type or coin type capacitors.

[0082] Postscript

[0083] The following techniques are disclosed through the description of the above embodiments.

[0084] (Technology 1)

[0085] An electrochemical capacitor having a positive electrode, a negative electrode and an electrolyte,

[0086] The electrolyte comprises a lactone compound and an additive,

[0087] The additive is at least one selected from the group consisting of siloxane compounds and fluorinated silyl compounds.

[0088] (Technique 2)

[0089] The electrochemical capacitor according to technology 1, wherein the additive includes hexamethyldisiloxane as the siloxane compound and fluorotrimethylsilane as the fluorinated silyl compound.

[0090] (Technique 3)

[0091] The electrochemical capacitor according to technology 1 or 2, wherein a capacity ratio of the positive electrode to the negative electrode is 1.1 or more and 1.6 or less.

[0092] (Technique 4)

[0093] The electrochemical capacitor according to any one of techniques 1 to 3, wherein the positive electrode and the negative electrode each have a polarizable electrode layer,

[0094] The thickness of the polarizable electrode layer of the positive electrode is greater than the thickness of the polarizable electrode layer of the negative electrode.

[0095] (Technique 5)

[0096] The electrochemical capacitor according to any one of techniques 1 to 4, wherein the electrolyte solution contains a chain ester compound.

[0097] (Technique 6)

[0098] The electrochemical capacitor according to technology 5, wherein the chain ester compound includes at least one selected from the group consisting of propyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.

[0099] (Technique 7)

[0100] The electrochemical capacitor according to any one of techniques 1 to 6, wherein the electrolyte solution contains quaternary alkylammonium ions.

[0101] (Technology 8)

[0102] The electrochemical capacitor according to technology 7, wherein the quaternary alkylammonium ions include diethyldimethylammonium ions.

[0103] (Technique 9)

[0104] The electrochemical capacitor according to any one of techniques 1 to 8, wherein the lactone compound includes γ-butyrolactone.

[0105] Hereinafter, the present disclosure will be described in more detail based on examples, but the present disclosure is not limited to the examples.

[0106] 《Capacitors A1~A8, B1~B6》

[0107] As an electrochemical capacitor, a wound electric double layer capacitor (diameter Φ: 18 mm, length L: 70 mm) was produced. A specific method for producing the electrochemical capacitor will be described below.

[0108] (Electrode Preparation)

[0109] 88 parts by mass of porous carbon particles as active material, 6 parts by mass of polytetrafluoroethylene (PTFE) as a binder, and 6 parts by mass of acetylene black as a conductive agent were dispersed in water to prepare a slurry. The obtained slurry was applied to Al foil (thickness 30 μm), and the coating was hot-air dried at 110°C, rolled, and an active layer (polarizable electrode layer) was formed to obtain a positive electrode and a negative electrode. At this time, the thickness of the active layer of the positive electrode and the negative electrode was set to the values ​​shown in Table 1. Thus, the capacity ratio of the positive electrode to the negative electrode was set to the values ​​shown in Table 1.

[0110] (Preparation of Electrolyte)

[0111] Dissolve diethyldimethylammonium tetrafluoroborate (DEDMABF4) in a non-aqueous solvent, and add octamethyltrisiloxane (OMTSi) as needed to prepare an electrolyte. The non-aqueous solvent uses the compounds shown in Table 1. In Table 1, GBL is γ-butyrolactone, PC is propylene carbonate, and MP is methyl propionate. In Table 1, the capacitors A3 and A5 use a mixed solvent containing GBL and MP in a volume ratio of GBL:MP=60:40. The concentration of DEDMABF4 in the electrolyte is 1.0 mol / L. The content of OMTSi in the electrolyte is 0.5 mass%.

[0112] (Fabrication of Electrochemical Capacitors)

[0113] Leads are connected to the positive and negative electrodes respectively, and the separator (thickness 35μm) is wound to obtain a capacitor element. A cellulose non-woven fabric is used as the separator. The capacitor element and the electrolyte are contained in a specified housing, sealed with a sealing member, and an electrochemical capacitor (double-layer capacitor) is completed. Then, while applying the rated voltage, a aging treatment is performed at 60°C for 16 hours. It should be noted that for an electrochemical capacitor using an electrolyte containing OMTSi, the electrolyte is taken after the aging treatment and analyzed by GC / MS, and hexamethyldisiloxane (HMDSi) and fluorotrimethylsilane are detected.

[0114] In Table 1, A1 to A8 are examples, and B1 to B6 are comparative examples.

[0115] The following evaluations were performed on each of the electrochemical capacitors obtained above.

[0116] [Evaluation of floating charge characteristics]

[0117] The electrochemical capacitor after aging was discharged at a constant current of 1.35 A at 60°C until the voltage reached 0 V. The height H1 (mm) of the electrochemical capacitor at this time was measured using a vernier caliper. The height of the electrochemical capacitor is Figure 1 The main body of the cylindrical electrochemical capacitor 10 shown has a maximum axial dimension H.

[0118] In an environment of 60°C, a constant current charge is performed at a current of 1.5A until the voltage reaches 2.8V, and the voltage of 2.8V is maintained for 750 hours. In this way, the electrochemical capacitor is stored in a state where a voltage of 2.8V is applied (floating test). Then, in an environment of 60°C, a constant current discharge is performed at a current of 1.35A until the voltage reaches 0V. The height H2 (mm) of the electrochemical capacitor at this time is measured using a vernier caliper.

[0119] The value of H2 minus H1 is determined as the swelling (mm) of the electrochemical capacitor. When the swelling is small, it means that gas generation during float charge is suppressed and the float charge characteristics are good.

[0120] Table 1 shows the evaluation results.

[0121] Table 1

[0122]

[0123] The capacity ratio of the positive electrode to the negative electrode is 1. When comparing B1 and B5 without OMTSi addition, B1, in which the electrolyte solvent is PC, has a larger bulge than B5, in which the electrolyte solvent is GBL. It is believed that in the case of PC, the hydrolysis reaction of PC occurs by forming an acidic or alkaline atmosphere, and gas generation becomes easy. In the case of GBL, even if an acidic or alkaline atmosphere is formed, GBL is not easily decomposed, and gas generation is suppressed.

[0124] A1 to A8 had smaller swelling than B1 to B6. When the capacity ratio of the positive electrode to the negative electrode was 1.1 or more and 1.6 or less in A2 to A7, swelling was further reduced. Swelling was further reduced in A4 and A6 using electrolytes further containing MP.

[0125] A1 with OMTSi added suppressed the oxidative decomposition of GBL at the positive electrode, reduced the amount of gas generated, and reduced the bulge. In addition, A8 with OMTSi added also suppressed the reductive decomposition of GBL at the negative electrode, reduced the amount of gas generated, and reduced the bulge.

[0126] Comparing B5, A1, and A3 using an electrolyte containing GBL, A1 has a smaller bulge than B5, and A3 has a further smaller bulge than A1. B5 does not add OMTSi to the electrolyte containing GBL, and the capacity ratio of the positive electrode to the negative electrode is 1. A1 adds OMTSi to the electrolyte containing GBL, but the capacity ratio of the positive electrode to the negative electrode is 1. A3 adds OMTSi to the electrolyte containing GBL, and the capacity ratio of the positive electrode to the negative electrode is 1.3.

[0127] On the other hand, when comparing B1 and B2, which use an electrolyte solution containing PC, B2, which adds OMTSi, has a larger bulge than B1, which does not add OMTSi. The detailed reason is unknown, but it is believed that in the case of PC, even if OMTSi is added, PC is hydrolyzed in an acidic or alkaline atmosphere, and the amount of gas generated increases.

[0128] In addition, when comparing B2 and B3, B3, in which the capacity ratio of the positive electrode to the negative electrode is 1.3, has a larger bulge than B2, in which the capacity ratio is 1. It is considered that in the case of a capacity ratio of 1.3, an alkaline atmosphere is further formed compared to the case of a capacity ratio of 1, making it easier for the hydrolysis reaction of PC to occur, and the amount of gas generated increases.

[0129] As described above, the effect of improving the floating charge characteristics by adding OMTSi to the electrolyte solution and adjusting the capacity ratio of the positive electrode to the negative electrode to 1.1 to 1.6 is a unique effect when using an electrolyte solution containing a lactone compound (GBL).

[0130] Industrial Applicability

[0131] The electrochemical device disclosed herein can be suitably used for applications requiring large capacity and excellent floating charge characteristics.

[0132] The present invention has been described in terms of the presently preferred embodiments, but this disclosure should not be construed as limiting. Various modifications and changes will undoubtedly become apparent to those skilled in the art of the art to which the present invention pertains by reading the above disclosure. Therefore, the appended claims should be interpreted as including all modifications and changes that do not depart from the true spirit and scope of the present invention.

[0133] Explanation of symbols

[0134] 1: capacitor element, 2: first electrode, 3: second electrode, 4: separator, 5a: first lead, 5b: second lead, 6: case, 7: sealing member, 10: electrochemical capacitor

Claims

1. An electrochemical capacitor comprising a positive electrode, a negative electrode and an electrolyte, The electrolyte comprises a lactone compound and an additive, The additive is at least one selected from the group consisting of siloxane compounds and fluorinated silyl compounds.

2. The electrochemical capacitor according to claim 1, wherein: The additive includes hexamethyldisiloxane as the siloxane compound and fluorotrimethylsilane as the fluorinated silyl compound.

3. The electrochemical capacitor according to claim 1, wherein: A capacity ratio of the positive electrode to the negative electrode is 1.1 or more and 1.6 or less.

4. The electrochemical capacitor according to claim 1 or 3, wherein: The positive electrode and the negative electrode each have a polarizable electrode layer, The thickness of the polarizable electrode layer of the positive electrode is greater than the thickness of the polarizable electrode layer of the negative electrode.

5. The electrochemical capacitor according to claim 1 or 3, wherein: The electrolyte solution contains a chain ester compound.

6. The electrochemical capacitor according to claim 5, wherein: The chain ester compound includes at least one selected from the group consisting of propyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.

7. The electrochemical capacitor according to claim 1 or 3, wherein: The electrolyte contains quaternary alkylammonium ions.

8. The electrochemical capacitor according to claim 7, wherein: The quaternary alkylammonium ion includes a diethyldimethylammonium ion.

9. The electrochemical capacitor according to claim 1 or 3, wherein: The lactone compound includes γ-butyrolactone.

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