JP2014099443A - Electrolyte and electric double-layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte and an electric double-layer capacitor using the same capable of ensuring a high reliability by preventing changes in pH and/or creeping-up even when charging/discharging under severe conditions such as high temperature.SOLUTION: The electrolyte of the electric double-layer capacitor contains quaternary ammonium salt expressed by a general formula (1) below and carbonyl compound expressed by a general formula (2) below. (General formula 1)(General formula 2)

Description

  The present invention relates to an electrolytic solution used for various electronic devices and in-vehicle power storage devices, and an electric double layer capacitor using the electrolytic solution.

  FIG. 3 is a schematic cross-sectional view showing a current collector and a rubber seal used in a conventional electric double layer capacitor.

  Conventionally, an electric double layer capacitor has a positive electrode and a negative electrode in which an electrode layer containing activated carbon is formed on a metal foil, facing each other with a separator interposed therebetween, and the capacitor element is formed together with an electrolyte. It is accommodated in a metal case, and a rubber sealing body seals the opening of the metal case. And in order to pull out an electrode from a capacitor element, connecting members, such as a lead wire, are joined to each of a positive electrode and a negative electrode, and it is the structure pulled through the said rubber sealing body.

  A quaternary ammonium salt or a quaternary phosphonium salt is used as a solute in the electrolytic solution used for the electric double layer capacitor.

  However, these solutes have the property of being chemically active. Therefore, when electric double layer capacitors using these solutes are repeatedly charged and discharged under severe conditions such as high temperatures, the pH of the electrolyte in the vicinity of the negative electrode is biased to alkali, and the electrolyte is scuffing the surface of the negative electrode. There is a possibility that it will rise and leak outside from the rubber seal. Moreover, the lead wire which pulls out an electrode from a rubber sealing body or a negative electrode may be corroded by contacting with the electrolyte which goes up.

  In order to enhance the resistance to corrosion due to this leakage, in the electric double layer capacitor using lead wires as a method for drawing out the positive electrode and the negative electrode, the surfaces of the current collector 101 and the tab terminal 102 constituting the negative electrode have oxidation properties. A rubber sealing body 103 having a through hole 103a fitted into the tab terminal 102 and formed by vulcanization of butyl rubber with resin or peroxide is used to form a chemical film using a chemical agent. A configuration in which the hardness of the body 103 is in the range of 60 to 90 (according to a Wallace hardness meter) has been proposed.

  Thereby, even if a quaternary ammonium salt or a quaternary phosphonium salt is used as a solute of the electrolytic solution, the electrolytic solution can be prevented from leaking from the rubber sealing body 103 to the outside.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

JP-A-7-122467

  As described above, in order to use a quaternary ammonium salt or a quaternary phosphonium salt as a solute in the electrolytic solution of the electric double layer capacitor, it is necessary to take measures such as pH fluctuation or liquid leakage in the electrolytic solution. . However, as an electric double layer capacitor, in order to further overcome the above-described problems and improve reliability, an electrolytic solution in which fluctuations in pH and creeping up of the electrolytic solution are suppressed is required.

  Therefore, in the present invention, there is provided an electrolytic solution and an electric double layer capacitor using the same, in which the fluctuation of pH and the rising of the electrolytic solution are suppressed even when charging / discharging under severe conditions such as high temperature is performed. The purpose is to provide.

  In order to solve the above problems, an electrolytic solution of the present invention and an electric double layer capacitor using the same include a solute having a quaternary ammonium cation represented by the following (Chemical Formula 1), and the following (Chemical Formula 2): The carbonyl compound represented by these is included.

(R ^{1 to} R ⁴ are a substituent having 1 or 2 carbon atoms and 1 or 2 substituents having 1 carbon atom, and the carbon atom of the substituent having 1 carbon atom is at least one hydrogen atom. And N represents a nitrogen atom.)

(R ⁵ is a substituent composed of a main chain having 1 or more carbon atoms and a side chain consisting of any one of a hydrogen atom, a halogen atom, and a hydroxyl group, and R ⁶ is a hydrogen atom, an ester, or an organic functional group having 1 or more carbon atoms. Any one of the substituents or a cyclic structure formed by combining R ⁵ and R ⁵ )

  With this configuration, the electrolytic solution and the electric double layer capacitor of the present invention can suppress fluctuations in pH. This is because when the quaternary ammonium cation represented by the above (Chemical Formula 1) contained in the electrolytic solution reacts with the carbonyl group of the carbonyl compound represented by the above (Chemical Formula 2), the hydroxylation in the electrolytic solution is performed. This is because the product ions are consumed and reacted, so that hydroxide ions present in the electrolytic solution are reduced and alkalinization of the electrolytic solution is suppressed.

The partial notch perspective view showing the electric double layer capacitor in the example of the present invention Schematic diagram of H-type cell used for performance evaluation test in the present invention Schematic sectional view showing a negative electrode with a tab terminal and a rubber seal used in a conventional electric double layer capacitor

  Hereinafter, embodiments of the present invention and all claims will be described with reference to the drawings. However, the present invention is not limited to the following contents.

  FIG. 1 is a partially cutaway perspective view of a capacitor according to an embodiment of the present invention.

  In FIG. 1, a capacitor element 1 has a positive electrode 2 and a negative electrode 3 each having electrode layers 2b and 3b for absorbing and desorbing ions formed on the surfaces of current collectors 2a and 3a made of metal as a pair of electrodes. The separator 4 is wound or laminated with the separator 4 interposed between the anode 2 and the anode 3, and lead wires 5a and 5b are connected to the surfaces of the cathode 2 and the anode 3 as lead members, respectively. Thus, the capacitor element 1 and the electrolytic solution (not shown) are accommodated in a bottomed outer casing 6 that is an outer casing, and the lead wires 5a and 5b expose the opening end of the outer casing 6. It is sealed by the sealing member 7.

  For the positive electrode 2 and the negative electrode 3, for example, a high-purity aluminum foil having a thickness of about 15 μm (containing 99% or more Al) is used as the current collectors 2a and 3a, and this aluminum foil is subjected to electrolytic etching in a chlorine-based etching solution. To roughen the surface.

  Then, the electrode layers 2b and 3b are formed on the front and back surfaces of the roughened current collectors 2a and 3a, respectively. Examples of the material constituting the electrode layer 2b include activated carbon, a binder, and a conductive additive.

  The activated carbon is, for example, a phenol resin activated carbon having an average particle diameter of 5 μm, the binder is, for example, an aqueous solution of carboxymethyl cellulose (CMC), and the conductive assistant is, for example, acetylene black, mixed in a weight ratio of 10: 2: 1. Use things. This mixture is kneaded with a kneader to adjust to a predetermined viscosity.

  This paste is applied to the front and back surfaces of the current collectors 2a and 3a, and dried in an air atmosphere at 100 ° C. to form an electrode layer 2b having a thickness of 40 μm. Thereafter, the current collectors 2a and 3a provided with the electrode layers 2b and 3b are slit so as to have a predetermined width.

  Further, the electrode layers 2b and 3b formed on the front and back surfaces of the current collectors 2a and 3a are partially removed, and the lead wires 5a and 5b are connected to the unformed portions of the electrode layers 2b and 3b by a method such as needle caulking. To do.

The positive electrode 2 and the negative electrode 3 are made to face each other, and a separator 4 is interposed between the positive electrode 2 and the negative electrode 3 and wound to complete the capacitor element 1. For the separator 4, for example, cellulosic paper or PTFE having a thickness of about 35 μm and a density of 0.45 g / cm ³ is used.

For the electrolyte, for example, ethyltrimethylammonium tetrafluoroborate, which is a quaternary ammonium salt, is used as a solute. As the solute anion, those containing fluorine atoms are preferable because the withstand voltage characteristics are improved, and BF ₄ ⁻ or PF ₆ ⁻ is particularly preferable. As the solvent, for example, propylene carbonate, which is an organic solvent, is used and mixed so that the concentration of the solute is 0.5 to 2.0 mol / l.

  In this embodiment, benzophenone as an example of a carbonyl compound is contained in the electrolyte solution by not less than 0.1 wt% and not more than 5 wt% with respect to the weight of the electrolyte solution.

  For example, aluminum, copper, or nickel is used for the outer case 6 from the viewpoint of heat dissipation. However, the outer case 6 is not particularly limited as long as it is a material that is unlikely to react with the electrolytic solution, and the shape may be a prismatic case or a laminate type. .

  The sealing member 7 may be, for example, butyl rubber, but is not particularly limited as long as it is a rubber material having elasticity. In a state where the lead wires 5a and 5b protruding from the capacitor element 1 are passed through the through holes 7a provided in the sealing member 7, the sealing member 7 is disposed in the opening of the outer case 6 having a bottomed cylindrical shape, The sealing member 7 is crimped and gripped by drawing from the outer peripheral surface of the opening of the outer case 6 where the sealing member 7 is located toward the inside of the outer case 6 and by curling the opening end of the outer case 6. And fix. Thereby, sealing of the opening part of the exterior case 6 is completed.

  Thus, the electric double layer capacitor of the present invention is completed.

  The electrolytic solution and the electric double layer capacitor using the same according to the present invention include the quaternary ammonium salt represented by the above (Chemical Formula 1) and the carbonyl compound represented by the above (Chemical Formula 2) in the electrolytic solution. It is a configuration.

  With this configuration, the alkalinization of the electrolytic solution is suppressed, and the creeping of the electrolytic solution on the surface of the negative electrode 3 in the electric double layer capacitor can be suppressed, and the reliability of the electric double layer capacitor can be improved.

  This is because the carbonyl group provided in the carbonyl compound reacts with the cation used in the electrolytic solution of the present invention, and in this reaction, hydroxide ions are consumed, resulting in a decrease in hydroxide ions in the electrolytic solution. This is to weaken the alkalinity in the electrolytic solution.

  In order for the cation to react with the carbonyl compound, the cation must previously form a nitrogen ylide as shown in the following (Chemical Formula 3).

(C represents carbon, N represents nitrogen, and Ra to ^e represent organic or inorganic substituents.)
This nitrogen ylide is generated by a reaction between a cation and a hydroxide ion in the electrolytic solution. Further, this ylide reacts with the carbonyl group of the carbonyl compound contained in the electrolytic solution. That is, hydroxide ions in the electrolytic solution are consumed by this series of reactions.

In order to form the nitrogen ylide, the carbon atoms at least one of the substituents, attached directly to the nitrogen atom of the substituents R ^{1 to 4} existing around the nitrogen atoms constituting the cation, a hydrogen atom This hydrogen ion needs to react with hydroxide ions in the electrolyte. In order to facilitate the reaction with this hydroxide ion, the electrolyte solution of the present invention contains an ethyltrimethylammonium cation or a dimethyldiethylammonium cation, in which hydrogen ions are easily extracted from the carbon atom among the quaternary ammonium cations. It is preferable to use a salt containing.

  Examples of the carbonyl compound used in the present invention include aldehyde compounds, ketone compounds, carboxylic acid compounds, ester compounds, amide compounds, enone compounds, acid chlorides, and acid anhydrides.

  Among the carbonyl compounds used in the electrolytic solution of the present invention, aldehyde compounds include formaldehyde, acetaldehyde, propionaldehyde, vinyl aldehyde, benzaldehyde, cinnamaldehyde, berylaldehyde and the like, and ketone compounds include acetone, methyl ethyl ketone, and diethyl in particular. There are ketone, methyl isobutyl ketone, cyclohexanone, etc., and carboxylic acid compounds include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, Stearic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, lactic acid, malic acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicy Ester, oxalic acid, malic acid, citric acid, cinnamic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, pyruvic acid, aconitic acid, amino acid, nitrocarboxylic acid, ester compound Include methyl butyrate, methyl salicylate, ethyl formate, ethyl butyrate, ethyl caproate, isopentyl acetate, pentyl butyrate, octyl acetate, etc., and amide compounds include dimethylformamide, N-methylformamide, dimethylacetamide, N-ethylformamide , Diethylformamide, dimethylpropionamide, N-methylpyrrolidone, etc., enone compounds include nitroacetophenone, benzophenone, etc., and carboxylic acid chlorides include carboxyls of the compounds mentioned as examples of the carboxylic acid compounds. Group hydrogen And acid anhydrides include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, 3,34.4 ″ -benzophenonetetracarboxylic anhydride, maleic anhydride, methyltetrahydroanhydride Phthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic anhydride, succinic anhydride, alkenyl succinic anhydride, methylcyclohexene tetracarboxylic acid, polyadipic anhydride, polyazelinic anhydride And poly sebacic anhydride.

  Among these compounds, aldehyde compounds and ketone compounds are particularly preferable. This is because the solubility in an organic solvent is excellent.

  And it is preferable to provide an electron withdrawing group in the substitution which comprises the quaternary ammonium cation used for this invention in order to promote the production | generation of the said nitrogen ylide. By providing this electron withdrawing group, the electron density of the hydrogen atom involved in the formation of the nitrogen ylide is lowered to facilitate the extraction of the hydrogen atom.

The electron-withdrawing group, for example -F, -Cl, -Br, -OR, = O, -COR, -CO 2 R, -NO 2, -SO 2 R, -CN, -CR = CR 2 , —C≡R, —CH _x F _y , —CH _v F _w —CH _x F _y (where —, =, ≡ represents an atomic or molecular bonding state, and R represents an inorganic or organic substituent. , And others represent atoms based on the periodic table, and v and w are integers of 0 or more and 2 or less and satisfy v + w = 2, and x and y are integers of 0 or more and 3 or less and satisfy x + y = 3. .).

(Performance evaluation test)
The contents of the characteristic evaluation test for confirming the effect of the invention using the electrolytic solution and the electric double layer capacitor described in the above examples are shown below.

  The electrolyte solution 28 of sample 1 is the electrolyte solution of this example, and ethyltrimethylammonium tetrafluoroborate, which is a quaternary ammonium salt, is used as a solute, and propylene carbonate is used as a solvent, and the concentration is 0.1 mol / l. Using an electrolytic solution, benzophenone was used as an example of the carbonyl compound, and its content was 1.0 wt%.

  Sample 2 is an electrolytic solution having the same structure as Sample 1 except that the above compound is not added.

  Sample 3 is an electrolytic solution having the same structure as Sample 1 except that the above compound is not added to an electrolytic solution using tetraethylammonium tetrafluoroborate as a solute.

  These samples 1 to 3 were used for the test under the following conditions.

  FIG. 2 is a schematic diagram of an H-type cell used for measuring the pH variation of the electrolyte.

  The H-type cell used in this test is composed of an H-type glass case 26 including a pair of low and low-cylindrical cell portions 26a and a cylindrical relay portion 26b connecting the two cell portions 26a. And the positive electrode 22 and the negative electrode 23 made of Pt foil respectively accommodated in the cell part 26a, and the glass separator 24 arranged in the relay part 26b to isolate the positive electrode 22 and the negative electrode 23 from each other. Thus, the positive electrode 22 and the negative electrode 23 are electrically connected to the power source 29.

In this test, a current density of 1 mA / cm ² was continuously applied for 60 minutes to Samples 1 to 3 using this H-type cell in a dry room. Then, the pH of the negative electrode 23 in the electrolytic solution 28 was measured from the application start time to the 60 minute point, and the negative electrode pH at the stage where 20 minutes and 60 minutes had elapsed was compared in each sample.

  The results are shown as (Table 1) below.

  From Table 1, the change in pH of sample 1 to which the above compound was added was suppressed compared to samples 2 and 3 to which no compound was added.

  Next, a life test was conducted under the conditions of 60 ° C., 2.5 V, and 250 hours using the electric double layer capacitors using the electrolytes 1 to 3, and 250 hours later, each electric double layer capacitor Capacity retention was compared. The results are shown as (Table 2) below.

  From Table 2, it can be seen that the electric double layer capacitor of Sample 1 using the electrolytic solution of this example has suppressed capacitance deterioration compared to the electric double layer capacitors of Samples 2 and 3.

  As described above, it was confirmed that the effect of the present invention is particularly remarkable when a quaternary ammonium salt is used.

  The configuration of the present invention is not limited to the configuration of the above embodiment, and the quaternary ammonium salt is used as a cation contributing to charge / discharge of the electric double layer capacitor. However, the quaternary ammonium salt and the carbonium compound are used. Both may be configured to be added to the electrolyte as an additive. At that time, an onium salt, an imidazolium salt, or the like is preferable as a solute of the electrolytic solution, and the amount of the quaternary ammonium salt to be added is preferably added so that the molar ratio with the carbonyl compound is 1: 1. Conversely, in this embodiment, a carbonyl compound added to the electrolytic solution as an additive may be used as a solvent for the electrolytic solution.

  The organic solvent used in the electrolytic solution is not limited to the above-mentioned propylene carbonate, and may be γ-butyrolactone, γ-caprolactone, γ-valerolactone, etc. Other than lactones, carbonates such as propylene carbonate and ethylene carbonate In addition, similar effects can be obtained with sulfolanes. Similarly, the activated carbon used for the positive electrode and the negative electrode has also been described using a phenol resin-based activated carbon in this example, but is not limited thereto, and is not limited to this, coconut shell, wood powder, paper, petroleum coke, petroleum pitch, The material is not particularly limited as long as it is a porous material that adsorbs and desorbs ions on the surface thereof, such as a carbon material made from a raw material.

  As described above, the electrolytic solution of the present invention and the electric double layer capacitor using the same include a cation excellent in ylide formation such as ethyltrimethylammonium and dimethyldiethyl and a carbonyl compound excellent in electron withdrawing property in the electrolytic solution. Is included. Thereby, when the said compound acts on the water | moisture content in electrolyte solution, a hydrolysis can be suppressed and the fluctuation | variation of pH in electrolyte solution which may occur in repeating charging / discharging can be suppressed.

  In the electrolytic solution and the electric double layer capacitor in the present invention, fluctuations in pH are suppressed, and leakage of the electrolytic solution to the outside is suppressed. Therefore, reliability as a power storage device can be improved. As a result, it is expected to be used in in-vehicle or electronic devices where high reliability is required.

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Positive electrode 2a, 3a Current collector 2b, 3b Electrode layer 3 Negative electrode 4 Separator 5a, 5b Lead wire 6 Exterior case 7 Sealing member 7a Through-hole 22 Positive electrode 23 Negative electrode 24 Glass separator 26 Glass case 26a Cell part 26b Relay part 28 Electrolyte 29 Power supply

Claims (5)

An electrolytic solution containing a solute having a quaternary ammonium cation represented by the following (Chemical Formula 1) and a carbonyl compound represented by the following (Chemical Formula 2).

(R ^{1 to} R ⁴ are a substituent having 1 or 2 carbon atoms and 1 or 2 substituents having 1 carbon atom, and the carbon atom of the substituent having 1 carbon atom is at least one hydrogen atom. And N represents a nitrogen atom.)

(R ⁵ is a substituent composed of a main chain having 1 or more carbon atoms and a side chain consisting of any one of a hydrogen atom, a halogen atom, and a hydroxyl group, and R ⁶ is a hydrogen atom, an ester, or an organic functional group having 1 or more carbon atoms. Any one of the substituents or a cyclic structure consisting of R ⁵ and R ⁵ ) The electrolytic solution according to claim 1, wherein the carbonyl compound of the electrolytic solution is a ketone compound. The electrolytic solution according to claim 2, wherein the ketone compound of the electrolytic solution is benzophenone. At least one of the carbon atoms constituting the substituent of the quaternary ammonium cation has an electron withdrawing group, and this electron withdrawing group is represented by -F, -Cl, -Br, -OR, = O. _{, -COR, -CO 2 R, -NO} 2, -SO 2 R, -CN, -CR = CR 2, -C≡R, -CH x F y, -CH v F w -CH x F y ( provided that 2,-, =, ≡ represents an atomic or molecular bond state, R represents an inorganic or organic substituent, and the other represents an atom based on the periodic table. Electrolyte. Capacitor element in which a positive electrode capable of adsorbing / desorbing anions and a negative electrode capable of adsorbing / desorbing cations are opposed to each other with a separator interposed therebetween, an exterior body containing the capacitor element together with an electrolyte, and an opening of the exterior body is sealed A sealing member at least,
The electric double layer capacitor comprising the electrolytic solution according to claim 1.

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