JP2008252062A - Method of manufacturing electrode sheet for electric double-layer capacitor, and the electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor having superior long-term reliability and high energy density by improving the withstand voltage. <P>SOLUTION: An electrode for an electric double layer capacitor is exposed to a vapor of a volatile organosilicon compound, having a boiling point of 50 to 250°C and a flash point of 100 or lower °C, such as, hexamethyldisilazane. Alternatively, the electrode is immersed in a treatment agent containing the volatile organosilicon compound as a main ingredient material. This causes a surface functional group of carbon material to react with the organosilicon compound, to set off a chemical combination. In addition, applying a volatile organosilicon compound, having a boiling point of 50 to 250°C and a flash point of 100°C or lower as a treatment agent which enables surplus to be easily removed through a simplified drying process. As a result, gas generation caused by the surface functional group and reaction of the surface functional group to an electrolytic solution are inhibited, and the working voltage and the long-term reliability of the electric double-layer capacitor are improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode sheet and an electric double layer capacitor of an electric double layer capacitor having excellent long-term reliability, high withstand voltage and high energy density, and a method for manufacturing the same.

  An electric double layer capacitor is a capacitor that utilizes charges accumulated in an electric double layer formed at the interface between an electrolyte and a polarizable electrode. The electric double layer capacitor is used for supplying backup power for electronic devices, temporarily storing regenerative power generated during braking of an electric vehicle, and storing power in an electric power system by making use of its large capacitance.

  An electric double layer capacitor is composed of a pair of polarizable electrodes made of an electrode active material such as activated carbon, a conductive aid, a binder, a separator, an electrolyte, and the like. The electric double layer capacitor has excellent characteristics such as small performance deterioration due to charge / discharge cycles and high output density. However, since the energy density is lower than that of a lithium battery or the like, improvement thereof is desired.

  In an electric double layer capacitor, the energy stored in the capacitor is proportional to the square of the operating voltage, and thus it is effective to increase the withstand voltage of the capacitor. However, acceleration of deterioration due to an increase in the operating voltage is a problem. Non-Patent Document 1 describes that in a general electric double layer capacitor, the deterioration rate doubles every time the operating voltage increases by 0.1V.

JP 2001-44082 A “Electric Double Layer Capacitor and Power Storage System 2nd Edition” (Tatsuo Okamura, Nikkan Kogyo Shimbun, 2001) P.112

  In general, deterioration of an electric double layer capacitor is caused by electrolysis of water remaining on the electrode or decomposition of an electrolyte component by water, reaction between a surface functional group of a carbon material and an electrolyte during voltage application, and surface activity of activated carbon. Gas or sticky matter generated due to the elimination of the group accumulates in the pores of the carbon material, and the electrolyte solution in the pores decreases and the capacity decreases, or ion migration in the pores This is thought to be due to factors such as obstruction and increased internal resistance.

  In order to reduce moisture from the pores of the carbon material such as activated carbon, the activated carbon is heated at a high temperature in a vacuum or in an inert gas atmosphere. Heating is required, and the surface functional groups of the carbon material remain. In particular, it is difficult to perform the treatment after forming an electrode containing an organic binder. As for the decomposition of the electrolytic solution, a method of operating the potential window by selecting the electrolyte and the solvent of the electrolytic solution can be considered, but it is known that the degree of deterioration varies depending on the type of electrode, and sufficient countermeasures are taken. Not taken.

  In Patent Document 1, an attempt is made to reduce the influence of moisture and surface functional groups by treating the electrodes with a halogen-substituted compound to physically adsorb molecules of these compounds and making the electrodes hydrophobic. . However, in the technique of Patent Document 1, the surface functional groups are not removed, and the molecules are only physically adsorbed on the electrode surface, so that the molecules are detached when the electrode is dried or after the electrolyte is injected. There is a possibility, and conversely, in order to prevent detachment at the time of drying, the residual amount is increased, and a sufficient effect is not obtained in suppressing deterioration and other characteristics.

  The present invention has been made in view of such a technical situation, and an object of the present invention is to improve the withstand voltage by chemically modifying the surface functional group of the carbon material contained in the electrode. An object of the present invention is to provide an electric double layer capacitor having excellent long-term reliability and high energy density.

  The subject of the present invention is a method for producing an electrode sheet for an electric double layer capacitor comprising a polarizable electrode containing a carbon material and a binder as its constituent elements, wherein the carbon material of the polarizable electrode has a boiling point of 50 ° C. to 250 ° C. Surface treatment is performed with a volatile organosilicon compound having a point of 100 ° C. or lower.

  Hereinafter, various embodiments of the subject of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

  According to the subject of the present invention, after the electrode is fabricated, the surface of the carbon material is treated with a volatile organosilicon compound, whereby a part of the surface functional group of the carbon material is reacted with the organosilicon compound and capped by chemical bonding. Further, by using a volatile organosilicon compound, gas generation and secondary electrochemical reaction can be suppressed and reliability can be improved without leaving surplus.

  Moreover, by adding a metal oxide, particularly titanium oxide, to the electrode, gas generation and secondary electrochemical reaction can be suppressed. Furthermore, the metal oxide can be obtained by treating the electrode with an organosilane compound. By treating the surface including the surface, it is possible to prevent the decomposition product generated in the electrode to which the metal oxide has been added from accumulating in the pores of the activated carbon, thereby increasing the life of the electric double layer capacitor when using high voltage. Can be improved.

(Embodiment 1)
In the present embodiment, the polarizable electrode of the electric double layer capacitor electrode is exposed to a vapor of a volatile organosilicon compound such as hexamethyldisilazane, or the volatile organosilicon compound is used as a main material. The surface treatment is performed by a method of immersing in the treating agent. Here, the “treatment agent mainly composed of a volatile organosilicon compound” is a volatile solution containing 50% or more of a volatile organosilicon compound.

  In this way, by treating the surface of the sheet-like polarizable electrode with a volatile organosilicon compound, the surface functional group of the carbon material, which is the main component of the polarizable electrode, is reacted with the organosilicon compound to cause chemical bonding. By capping, gas generation due to surface functional groups and reaction with the electrolyte are suppressed. Moreover, since the organosilicon compound to be treated is volatile, the excess of the organosilicon compound can be volatilized and removed by simple drying. As a result, it is possible to obtain an electric double layer capacitor with improved reliability by suppressing gas generation and secondary electrochemical reaction.

  As another form, the same effect can be obtained by reacting the raw carbon material with a volatile organosilane compound in the stage before the preparation of the polarizable electrode and then producing the polarizable electrode. I can do it.

  Hereinafter, the configuration and manufacturing method of the electric double layer capacitor as described above will be sequentially described.

<Configuration of electric double layer capacitor>
FIG. 1 is a schematic diagram showing a schematic configuration of an electric double layer capacitor 1 according to the present embodiment. In particular, FIG. 1 is a longitudinal sectional view showing a sectional structure of the electric double layer capacitor 1. FIG. 2 is an exploded perspective view showing the electric double layer capacitor 1 into a container 12, an electrode 14, and a separator 16. In FIGS. 1 and 2, for convenience of illustration, the proportional relationship of dimensions is different from that of the actual electric double layer capacitor 1.

  As shown in FIGS. 1 and 2, the electric double layer capacitor 1 includes a container 12 that encloses an electrolyte solution 18, an electrode 14 that serves as a charge / discharge terminal, a separator 16 that prevents a short circuit of the electrode 14, and an electrode 14. And an electrolytic solution 18 that forms an interface between the two. In the electric double layer capacitor 1, when a voltage is applied to the extraction electrode 144 of the pair of electrodes 14, an electric double layer is formed between the polarizable electrode 146 of the electrode 14 and the electrolytic solution 18, and the electric double layer is formed in the electric double layer. Charge is accumulated.

{container}
As the container 12, a sealing container having durability against the electrolytic solution 18 is used.

{Electrode (electrode sheet for electric double layer capacitor)}
The electrode 14 includes an integrated electrode obtained by integrating a current collector 142 included in the container 12 and a take-out electrode 144 exposed to the outside of the container 12, and a polarizability formed on the current collector 142. A sheet-like structure including the electrode 146 is provided. In particular, the surface of the polarizable electrode 146 is treated with a volatile organosilicon compound, and as a result, the organosilicon compound is bonded to a part of the surface functional groups.

  The material of the current collector 142 may be a conductor having electrochemical and chemical corrosion resistance. For example, the material of the current collector 142 of the positive electrode is selected from metals such as stainless steel, aluminum, titanium, and tantalum. The material of the negative electrode current collector 142 can be selected from metals such as stainless steel, nickel, aluminum, and copper. If a high-purity metal is used as the material of the current collector 142, the electrical resistance of the current collector 142 can be reduced, which can contribute to lowering the resistance of the electric double layer capacitor 1. The current collector 142 is typically composed of a metal foil, and the surface on which the polarizable electrode 146 is formed is to prevent the current collector 142 and the electrode active material from peeling off. It is desirable to roughen the surface by etching.

  The extraction electrode 144 is typically made of a strip-shaped metal foil, and is attached to the end of the current collector 142 so as to protrude.

  A polarizable electrode 146 is formed on the surface of one current collector 142 facing the other current collector 142. However, the polarizable electrode 146 may be formed only on the surface of the current collector 142, or may be formed on both the front and back surfaces of the current collector 142.

  Furthermore, the polarizable electrode 146 may contain titanium oxide powder.

  The polarizable electrode 146 includes an electrode active material, a conductive additive, and a binder as main components, and is formed on the current collector 142 as an electrode film of a mixture thereof. Note that a conductive adhesive may be used for bonding between the current collector 142 and the polarizable electrode 146.

  Regarding the manufacturing method of the polarizable electrode 146 and the surface treatment thereof, first, the electrode active material, the conductive additive and the binder are mixed and kneaded and rolled into a sheet, or the electrode paste is used as a current collector foil. The polarizable electrode 146 is produced by a coating method in which an electrode is produced by applying and drying the electrode.

  Next, (1) The polarizable electrode 146 is exposed to the vapor of the volatile organosilicon compound by placing the polarizable electrode 146 in a sealed container in the atmosphere and simultaneously placing the volatile organosilicon compound in the container. (2) The pressure of the desiccator provided with the polarizable electrode 146 is lowered by a vacuum pump, and then the vapor of the volatile organosilicon compound is introduced into the desiccator to thereby make the polarizable electrode 146 a volatile organosilicon compound. (3) a method of directly immersing the polarizable electrode 146 in a liquid of a volatile organosilicon compound, and (4) bubbling the volatile organosilicon compound with nitrogen gas to form the polarizable electrode 146. By spraying, a carbon material (electrode active material) that is a main component of the polarizable electrode 146 is obtained by a method of exposing the polarizable electrode 146 to vapor of a volatile organosilicon compound. Process of bonding an organosilicon compound to the functional group of quality) surface (surface processing).

  Here, as an example of the organosilicon compound, a compound having a chemical formula as described in Chemical Formula 1 below can be used, and a compound that easily volatilizes in air at normal temperature and pressure is selected. In particular, those having a boiling point of 50 ° C. to 250 ° C. and a flash point of 100 ° C. or less are preferable. The boiling point is defined by the temperature at which a compound becomes a gas from a liquid, and the flash point is the lowest temperature at which an object placed in the atmosphere is ignited. Is defined as the lowest temperature sufficient to produce a vapor of the concentration of. Boiling point and flash point can each be taken as a measure of volatility. If the boiling point is lower than the above range, the organosilicon compound evaporates early during the treatment, which is inconvenient for homogeneous treatment, whereas if it is higher than the above range, the drying property of the organosilicon compound is lowered. If the flash point is above the above range, the volatility of the organosilicon compound is lowered, and surplus after the treatment is generated, which may reduce the performance. Therefore, it is preferable to use an organosilicon compound having a boiling point of 50 ° C. to 250 ° C. and a flash point of 100 ° C. or less.

  Specific examples include isopropenoxytrimethylsilane, acetoxytrimethylsilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxy. Silane compounds such as silane, methyltriisopropenoxysilane, acetoxytrimethylsilane, trimethylmethoxysilane, ethoxyethyldimethylsilane, trimethylbutylsilane, hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecamethylpentasiloxane, Siloxa such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane Compounds, silazane compounds such as hexamethyldisilazane. In particular, hexamethyldisilazane and isopropenoxytrimethylsilane (isopropenyloxytrimethylsilane) are particularly preferable from the viewpoint of ease of treatment and performance.

  As an example, when hexamethyldisilazane is used, it reacts with a hydroxyl group to generate ammonia and chemically bond as shown in FIG. When isopropenoxytrimethylsilane (isopropenyloxytrimethylsilane) is used, acetone is generated and chemically bonded. These by-products are released as gases.

  The electrode active material is typically a “carbon material” such as activated carbon, activated carbon fiber, non-porous activated charcoal, artificial graphite, etc., but is called a “nanocarbon material” such as fullerene, carbon nanotube or fullerene soot. A special carbon material can also be employed as the electrode active material. Here, activated carbon, activated carbon fiber, and non-porous activated charcoal are examples of so-called “activated charcoal”.

  Activating coals suitably used as electrode active materials because of their large specific surface area and potential specific surface area include palm pitch, petroleum coke, coal, phenol resin, furan resin, polyvinyl chloride resin, and polychlorinated chloride. Some are made from vinylidene resin, polyimide resin, polyamide resin, liquid crystal polymer, plastic waste or waste tire waste containing phenol resin, etc., but among these, they are made from petroleum coke or resin. It is particularly desirable to use one.

  The activated charcoal can be activated by well-known chemical activation or gas activation, but it is particularly desirable to perform the activation by alkali activation or steam activation.

  For example, when activating activated carbon by alkali activation, first, the raw material is heat-treated at 400 ° C. to 1000 ° C. in an inert gas atmosphere to carbonize the raw material, and then the alkali activation chemical is uniformly applied to the carbonized raw material. It is impregnated and heated in an inert gas atmosphere, and the carbonized raw material is activated by dehydration from the alkali activator and an oxidation reaction with the alkali activator. Examples of the alkali activating chemical include sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, and calcium carbonate. Among these, These may be used alone or in combination of two or more.

  Or when activating activated carbon by steam activation, first, the raw material is heat-treated at 400 ° C. to 1000 ° C. in an inert gas atmosphere to carbonize the raw material, and then carbonized at a temperature of 700 ° C. to 1000 ° C. The carbonized raw material is activated by blowing steam toward the raw material.

  The form of the electrode active material may be selected from forms having a large specific surface area such as crushed, granular, granular, fibrous, felted, woven, and sheet-like. That is, it is a powdered electrode active material. And when using a granular electrode active material, in order to improve the bulk density of the polarizable electrode 146 and reduce an electrical resistance, it is desirable to make the average particle diameter into 30 micrometers or less, and to make it into 20 micrometers or less. More desirable.

  As the conductive aid, one kind selected from carbon black (especially acetylene black and ketjen black), natural graphite, thermally expanded graphite, carbon fiber, nanocarbon material, ruthenium oxide and metal fiber such as aluminum and nickel. It is desirable to use the above conductive material, and it is more desirable to use acetylene black or ketjen black from the viewpoint that the conductivity can be effectively improved with a small amount.

  The blending amount of the conductive additive with respect to the electrode active material depends on the bulk density of the electrode active material, but is generally preferably 5 parts by weight or more with respect to 100 parts by weight of the electrode active material, and 8 parts by weight. More preferably, the above is used. However, if the blending amount of the conductive auxiliary agent is too large, the ratio of the electrode active material contained in the polarizable electrode 146 decreases and the capacitance of the electric double layer capacitor 1 decreases. The blending amount of the conductive assistant is desirably 50 parts by weight or less, and more desirably 30 parts by weight or less with respect to 100 parts by weight of the electrode active material.

  Binders include polytetrafluoroethylene, polyvinylidene fluoride, carboxymethylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, natural latex, styrene butadiene rubber (SBR) It is desirable to use one or more resins selected from latex, nitrile butadiene rubber (NBR) latex, other diene rubbers, butyl rubber (IIR) latex, acrylic rubber, and the like.

  The blending amount of the binder with respect to the electrode active material is preferably 0.5 parts by weight or more, and more preferably 1.0 part by weight or more with respect to 100 parts by weight of the electrode active material. This is because if the blending amount of the binder is below the lower limit, the binding property between the electrode active materials and the adhesion between the current collector 142 and the polarizable electrode 146 are lowered, and the electrode 14 may not be maintained. Further, the blending amount of the binder with respect to the electrode active material is desirably 30 parts by weight or less, and more desirably 20 parts by weight or less with respect to 100 parts by weight of the electrode active material. This is because if the binder content exceeds the upper limit, the electric resistance of the polarizable electrode 146 increases and the capacitance of the electric double layer capacitor 1 may decrease.

{Metal oxide}
Metal oxides added to the electrode include titanium oxide, lithium titanate, zinc oxide, magnesium oxide, hydroxytalcite, tungsten oxide, niobium oxide, tin oxide, vanadium oxide, indium oxide, tantalum oxide, zirconium oxide, and oxide. Mix one or more metal oxides such as molybdenum, manganese oxide, barium titanate, strontium titanate, calcium titanate, magnesium titanate, strontium niobate, cobalt oxide, nickel oxide, chromium oxide, silicon oxide, aluminum oxide. Can be used.

  Thus, when an electrode contains 1 or more types of said metal oxide, gas generation and a secondary electrochemical reaction can be suppressed and reliability can be improved. Furthermore, by treating the surface functional group derived from the metal oxide with an organosilicon compound, gas generation and secondary electrochemical reaction are suppressed, and accumulation of decomposition products in pores is suppressed, Reliability can be improved.

  Among these substances, it is particularly preferable to use titanium oxide as a metal oxide to be added to the electrode from the viewpoint of stability and safety. Thus, when an electrode contains a titanium oxide, gas generation and a secondary electrochemical reaction can be suppressed and reliability can be improved. Furthermore, by treating the surface functional group derived from the metal oxide with an organosilicon compound, gas generation and secondary electrochemical reaction are suppressed, and accumulation of decomposition products in pores is suppressed, Reliability can be improved.

{Separator}
The separator 16 provided in the gap between the pair of electrodes 14 is an insulating sheet that transmits ions contributing to electrical conduction and has electrochemical and chemical corrosion resistance. Examples of the separator 16 include cellulose-based separators made of natural pulp, natural cellulose, solvent-spun cellulose, or bacterial cellulose, non-woven separators made of glass fibers or non-fibrillated organic fibers, nylon 66, aromatic polyamide, Wholly aromatic polyamide, aromatic polyester, wholly aromatic polyester, wholly aromatic polyester amide, wholly aromatic polyether, wholly aromatic polyazo compound, polyphenylene sulfide (PPS), poly-p-phenylenebenzobisthiazole (PBZT), Poly-p-phenylenebenzobisoxazole (PBO), polybenzimidazole (PBI), polyetheretherketone (PEEK), polyamideimide (PAI), polyimide or polytetrafluoroethylene (PTFE) It can be suitably used a separator of fibrillated form or porous film and the material or the like.

  As the separator 16, a sheet having a thickness of approximately 20 μm to 50 μm, a porosity (porosity) of approximately 60% to 80%, and an average pore diameter of approximately several μm to several tens of μm can be used. Of course, two or more sheets may be used instead of one sheet alone. Various average porosity can be obtained, but even if the same material is used, the average porosity can be easily changed by changing the weight density.

{Electrolyte}
The electrolyte solution 18 that fills the gap between the pair of electrodes 14 is an electrolyte solution in which an electrolyte is dissolved in a solvent. As the electrolytic solution 18, both an aqueous electrolytic solution and a non-aqueous electrolytic solution can be adopted, but it is more preferable to employ a non-aqueous electrolytic solution that can improve the withstand voltage of the electric double layer capacitor 1.

The electrolyte is a salt containing a cation and an anion. For example, the cation is tetraethylammonium, triethylmethylammonium, spiro- (1,1 ′)-bipyrrolidinium, diethylmethyl-2-methoxyethylammonium (DEME), or the like. Quaternary ammonium or 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, 1-ethyl-3-methylimidazolium (EMI) or 1,2-dimethyl-3-propylimidazolium (DMPI) And the anion is BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ or CF ₃ SO ₃ ⁻ .

  Examples of the solvent for the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, N-methyloxazolidinone, and dimethyl. It is desirable to employ an organic solvent containing at least one selected from sulfoxide and trimethyl sulfoxide, and in order to improve electrochemical stability, chemical stability and conductivity, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl Employs an organic solvent containing one or more selected from carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane and γ-butyrolactone Rukoto is more desirable. However, high-melting solvents such as ethylene carbonate and sulfolane are preferably mixed with a low-melting solvent such as propylene carbonate because the electrolyte solution 18 becomes solid at low temperatures when used alone.

  The concentration of the electrolyte in the non-aqueous electrolytic solution is desirably 0.3 mol / L or more and 3.0 mol / L or less, and 0.7 mol / L or more and 2. in order to maintain good characteristics of the electric double layer capacitor 1. More desirably, it is 5 mol / L or less. This is because, within this range, the conductivity of the electrolyte solution 18 can be maintained well, and when this range is exceeded, the conductivity of the electrolyte solution 18 decreases at a low temperature of −20 ° C. or lower. This is because if it falls below this range, the conductivity of the electrolytic solution 18 is lowered at room temperature and low temperature.

  The concentration of water contained in the non-aqueous electrolyte is preferably 200 ppm or less, and more preferably 50 ppm or less, in order to improve the life and withstand voltage of the electric double layer capacitor 1.

In addition, it is also acceptable to use a liquid electrolyte or a gel electrolyte instead of an electrolyte solution in which an electrolyte is dissolved in a solvent. Examples of the liquid electrolyte include diethylmethyl-2-methoxyethylammonium (DEME) and N- (2-methoxyethyl) -N-methyl-N-pyrrolidinium BF ₄ ⁻ , PF ₆ ⁻ or (CF ₃ SO ₂ ). ₂ N ^- can be exemplified ionic liquid such as salt. Examples of gel electrolytes include boron tetrafluoride gel electrolytes, polymer solid electrolytes, electrolytes containing polyester compounds, and electrolytes of mixtures of ionic liquids such as imidazoliums and inorganic compounds. I can do it.

  Hereinafter, specific examples of the present embodiment will be described, but the present invention is not limited to the following examples.

Example 1
Steam activated charcoal (BET specific surface area 1300 m ² / g, average particle size 15 μm) as a carbon material, acetylene black as a conductive assistant, polytetrafluoroethylene as a binder are mixed in a ratio of 8: 1: 1, and ethanol is added dropwise. While kneading. Next, the kneaded product was roll-rolled and then dried at 200 ° C. for 30 minutes to remove ethanol, thereby obtaining a sheet-like molded product (polarizable electrode sheet) having a thickness of 100 μm. This was bonded to an aluminum foil with a conductive adhesive to obtain an electrode sheet. Two pieces of the prepared electrode sheet were cut into a 3 cm square with a 4 cm × 1 cm strip-shaped extraction electrode part, and the polarizable electrode on the extraction electrode part was removed. For 24 hours. Next, a desiccator equipped with a three-way tube with a switching cock was prepared, and one direction was connected to the desiccator by a tube, the other direction was connected to a vacuum pump, and the other direction was connected to a container containing hexamethyldisilazane. The cut electrode (electrode sheet) was placed in a desiccator, and the air in the desiccator was sucked with a vacuum pump. Subsequently, the cock was switched, the connection with the vacuum pump was cut off, and connected to a container containing hexamethyldisilazane (boiling point 126 ° C., flash point 12 ° C.), and hexamethyldisilazane vapor was introduced. After leaving still for about 10 minutes, the electrode was taken out, dried with a dryer at 80 ° C., and further vacuum dried at 200 ° C. for 24 hours to obtain an electrode for an electric double layer capacitor (electrode sheet).

  The activated carbon electrode sides of the two obtained electrodes were faced to each other with a cellulose-based separator in between and placed in an aluminum laminate pack. Next, a propylene carbonate solution (1 mol / L) of tetraethylammonium tetrafluoroborate (TEA-BF4) was injected as an electrolytic solution. The cell after injection was initialized with a voltage of 3.2 V by preliminary charging for 30 minutes and then packed with a vacuum laminate to obtain an electric double layer capacitor cell.

  In this embodiment, hexamethyldisilazane is more effective as a volatile organosilicon compound because it is rich in reactivity with functional groups and volatility.

(Example 2)
Isopropenoxytrimethylsilane (boiling point 94 ° C, flash point -1 ° C) is used as the volatile organosilicon compound, the electrode sheet is immersed in a solution of isopropenoxytrimethylsilane in a desiccator, and the activated carbon is activated with a vacuum pump. After sucking the air in the pores, the electrode sheet for the electric double layer capacitor and the electric double layer capacitor cell were produced in the same manner as in Example 1 except that the air pressure was returned to atmospheric pressure and dried with a dryer at 80 ° C. FIG. 4 shows a reaction diagram of isoppenoxytrimethylsilane and the surface functional group of the carbon material in this case.

  In this embodiment, isopropenoxytrimethylsilane is more effective as a volatile organosilicon compound because it is rich in reactivity with functional groups and volatility.

(Example 3)
Steam activated charcoal (BET specific surface area 1300 m ² / g, average particle size 15 μm) as a carbon material, acetylene black as a conductive assistant, polytetrafluoroethylene as a binder are mixed in a ratio of 8: 1: 1, and ethanol is added dropwise. While kneading. Next, the kneaded product was roll-rolled and then dried at 200 ° C. for 30 minutes to remove ethanol, thereby obtaining a sheet-like molded product (polarizable electrode sheet) having a thickness of 100 μm. This was bonded to an aluminum foil with a conductive adhesive to obtain an electrode sheet. Next, a desiccator equipped with a three-way tube with a switching cock was prepared, and one direction was connected to the desiccator by a tube, the other direction was connected to a vacuum pump, and the other direction was connected to a container containing hexamethyldisilazane. The cut electrode was placed in a desiccator, and the air in the desiccator was sucked with a vacuum pump. Subsequently, the cock was switched to disconnect the connection with the vacuum pump and connected to a container containing hexamethyldisilazane (boiling point 126 ° C., flash point 12 ° C.). After leaving still for about 10 minutes, the electrode was taken out and dried with a dryer at 80 ° C. to obtain an electrode sheet for an electric double layer capacitor.

  Two pieces of the prepared electrode sheet were cut into a 3 cm square with a 4 cm × 1 cm strip-shaped extraction electrode part, and the polarizable electrode on the extraction electrode part was removed. For 24 hours. Next, the activated carbon electrode sides of the two obtained electrodes were faced to each other with a cellulose separator interposed therebetween, and an electrode sheet or the like was placed in an aluminum laminate pack. Next, a propylene carbonate solution (1 mol / L) of tetraethylammonium tetrafluoroborate (TEA-BF4) was injected as an electrolytic solution. The cell after injection was initialized with a voltage of 3.2 V by preliminary charging for 30 minutes and then packed with a vacuum laminate to obtain an electric double layer capacitor cell.

  In this embodiment, hexamethyldisilazane is more effective as a volatile organosilicon compound because it is rich in reactivity with functional groups and volatility.

(Comparative Example 1)
As a comparative example, an electric double layer capacitor cell was produced in the same manner as in Example 1 except that the surface treatment with hexamethyldisilazane was not performed.

  After measuring the initial discharge capacity of each obtained electric double layer capacitor, as a performance reliability acceleration test, each capacitor was applied in a constant temperature bath at 70 ° C. while applying a voltage of 3.0 V for 500 hours. The durability test was carried out. From this result, the capacity retention ratio with respect to the initial capacity of the discharge capacity after the durability test was calculated. The results are shown in Table 1.

  From the results of Table 1, when used at a voltage (3.0 V) higher than the normal operating voltage (2.3-2.7 V), each Example 1-3 of the present invention compared to Comparative Example 1 , Capacity retention rate improved.

Example 4
Steam activated charcoal (BET specific surface area 1300 m ² / g, average particle size 15 μm), acetylene black as a conductive agent, titanium oxide (BET surface area 50 m ² / g, aggregated particle size 2 μm) as a conductive agent, polytetrafluoro as a binder Ethylene was mixed at a ratio of 8: 1: 1: 1 and kneaded while adding ethanol dropwise. Next, the kneaded product was roll-rolled and then dried at 200 ° C. for 30 minutes to remove ethanol, thereby obtaining a sheet-like molded product having a thickness of 100 μm. This was bonded to an aluminum foil with a conductive adhesive to obtain an electrode sheet. Two pieces of the prepared electrode sheet were cut into a 3 cm square with a 4 cm × 1 cm strip-shaped take-out electrode part, and after removing the polarizable electrode from the take-out electrode part, the temperature was changed to 200 ° C. Vacuum dried for 24 hours. Next, a desiccator equipped with a three-way tube with a switching cock was prepared, and one direction was connected to the desiccator by a tube, the other direction was connected to a vacuum pump, and the other direction was connected to a container containing hexamethyldisilazane. The cut electrode was placed in a desiccator, and the air in the desiccator was sucked with a vacuum pump. Subsequently, the cock was switched, the connection with the vacuum pump was cut off, and connected to a container containing hexamethyldisilazane (boiling point 126 ° C., flash point 12 ° C.), and hexamethyldisilazane vapor was introduced. After standing for about 10 minutes, the electrode was taken out, dried with a dryer at 80 ° C., and further vacuum dried at 200 ° C. for 24 hours to obtain an electrode for an electric double layer capacitor. Moreover, the electrode which does not contain titanium oxide was created without performing the treatment with hexamethyldisilazane in the same process until the hexamethyldisilazane treatment.

  The resulting hexamethyldisilazane-treated titanium oxide-containing electrode and non-titanium oxide-containing electrode are placed face-to-face across a cellulose separator, placed in an aluminum laminate pack, and tetraethylammonium tetrafluoroborate (TEA) as the electrolyte. -BF4) propylene carbonate solution (1 mol / L) was injected. The cell after pouring was initialized with a titanium oxide-added electrode as a negative electrode and precharged with a voltage of 3.2 V for 30 minutes, and then packed with a vacuum laminate to obtain an electric double layer capacitor cell.

(Comparative Example 2)
An electric double layer capacitor cell was produced in the same manner as in Example 4 except that the treatment with hexamethyldisilazane was not performed.

  After measuring the initial discharge capacity of each obtained electric double layer capacitor, as a performance reliability acceleration test, each capacitor was applied in a constant temperature bath at 70 ° C. while applying a voltage of 3.0 V for 500 hours. After being held, the capacitance was measured at 25 ° C. From this result, the capacity retention ratio with respect to the initial capacity of the discharge capacity after the durability test was calculated. The results are shown in Table 2.

  From the results shown in Table 2, the capacity retention rate is improved in Example 4 compared to Comparative Example 2 when used at a voltage (3.0V) higher than the normal operating voltage (2.3-2.7V). did.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  It is preferable to apply the electrode sheet for an electric double layer capacitor manufactured by the manufacturing method described in Embodiment 1 or the like to the electrode of the electric double layer capacitor.

  As a result, gas generation and secondary electrochemical reaction can be suppressed, and the reliability of the electric double layer capacitor can be improved.

It is a longitudinal cross-sectional view which shows the cross-section of the electric double layer capacitor which concerns on Embodiment 1 of this invention. It is a perspective view which decomposes | disassembles and shows an electric double layer capacitor in a container, an electrode, and a separator. It is a schematic diagram of reaction of the hexamethyldisilazane and the surface functional group of a carbon material. It is a schematic diagram of reaction of isoppenoxytrimethylsilane and the surface functional group of a carbon material.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Electric double layer capacitor, 12 container, 14 electrodes, 16 separator, 18 Electrolyte, 142 Current collector, 144 Extraction electrode, 146 minute polarity electrode

Claims (7)

In the method for producing an electrode sheet for an electric double layer capacitor having a polarizable electrode containing a carbon material and a binder as its constituent elements,
The carbon material of the polarizable electrode is surface-treated with a volatile organosilicon compound having a boiling point of 50 ° C. to 250 ° C. and a flash point of 100 ° C. or less,
Manufacturing method of electrode sheet for electric double layer capacitor. It is a manufacturing method of the electrode sheet for electric double layer capacitors according to claim 1,
The polarizable electrode is exposed to the vapor of the volatile organosilicon compound, or surface-treated by a method of immersing in a treating agent containing the volatile organosilicon compound as a main material,
Manufacturing method of electrode sheet for electric double layer capacitor. It is a manufacturing method of the electrode sheet for electric double layer capacitors according to claim 1 or 2,
The volatile organosilicon compound is hexamethyldisilazane,
Manufacturing method of electrode sheet for electric double layer capacitor. It is a manufacturing method of the electrode sheet for electric double layer capacitors according to claim 1 or 2,
The volatile organosilicon compound is isopropenoxytrimethylsilane,
Manufacturing method of electrode sheet for electric double layer capacitor. It has an electrode comprised from the electrode sheet for electric double layer capacitors manufactured by the manufacturing method of the electrode sheet for electric double layer capacitors according to any one of claims 1 to 4.
Electric double layer capacitor. The electric double layer capacitor according to claim 5,
Of the electrodes including a carbon material and a binder, at least one of the electrodes includes a metal oxide,
Electric double layer capacitor. The electric double layer capacitor according to claim 6,
The metal oxide is titanium oxide,
Electric double layer capacitor.

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