JP2007059544A - Wound type electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wound electric double layer capacitor relaxing and equalizing an expansion pressure on the inside and distorting no polarizable electrode, even when the electrode is expanded in the case of the application of a voltage. <P>SOLUTION: The wound electric double layer capacitor 10 has a wound body 18 with the wound polarizable electrodes 13 and 16 expanded in the applied direction of the voltage in the case of the application of the voltage through separators 11 composed of insulating sheets having a cushioning function, organic electrolytes brought into contact with the polarizable electrodes 13 and 16, and a cylindrical vessel 19 housing these wound body 18 and organic electrolytes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wound electric double layer capacitor, and more particularly to a wound electric double layer capacitor in which a polarizable electrode expands in a voltage application direction when a voltage is applied.

  Capacitors can be repeatedly charged and discharged with a large current and are promising for power storage with high charge / discharge frequency. Therefore, the capacitor is desired to improve energy density, rapid charge / discharge characteristics, durability, and the like.

It is known that an electric double layer capacitor can be obtained by immersing a carbonaceous electrode in an organic electrolyte. Non-Patent Document 1, pages 34 to 37, an electric double layer capacitor having a tank partitioned into two sections by a separator, an organic electrolyte filled in the tank, and two carbonaceous electrodes immersed in each section Is described. An organic electrolytic solution is a solution in which a solute is dissolved in an organic solvent. Tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) and the like are described as the solute, and propylene carbonate is described as the solvent. Activated carbon is used as the carbonaceous electrode. Activated carbon refers to amorphous carbon having a very large specific surface area because it has countless fine pores. In the present specification, amorphous carbon having a specific surface area of about 1000 m ² / g or more is referred to as activated carbon.

Patent Document 1 describes nonporous carbon as a carbonaceous electrode used in an electric double layer capacitor. This carbonaceous material has microcrystalline carbon similar to graphite, has a non-surface area of 300 m ² / g or less, and is smaller than activated carbon. A non-porous carbonaceous electrode generates a capacitance by a completely different mechanism from a carbonaceous electrode made of activated carbon. That is, it is considered that when a voltage is applied, an electric double layer is formed by intercalating electrolyte ions between layers of microcrystalline carbon similar to graphite with a solvent.

  Patent Document 2 describes that a carbonaceous electrode is produced using needle coke or infusibilized pitch as a raw material. Needle coke refers to calcined coke with well-developed acicular crystals and good graphitization. Needle coke has high electrical conductivity, a very low coefficient of thermal expansion, and high anisotropy based on the graphite crystal structure. Needle coke is generally produced by a delayed coking method using a specially treated coal tar pitch or petroleum heavy oil as a raw material.

  Patent Document 3 describes an electric double layer capacitor in which a non-porous carbonaceous electrode is immersed in an organic electrolyte. The organic electrolyte must exhibit ionic conductivity, and the solute is a salt in which a cation and an anion are combined. Examples of the cation include lower aliphatic quaternary ammoniums such as tetraethylammonium, tetrabutylammonium, and triethylmethylammonium, lower aliphatic quaternary phosphoniums such as tetraethylphosphonium, and imidazolinium derivatives. As anions, tetrafluoroboric acid and hexafluorophosphoric acid are described. The solvent of the organic electrolyte is a polar aprotic organic solvent. Specifically, ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane and the like are described.

  The non-porous carbonaceous electrode has a characteristic that it exhibits several times the capacitance as compared with a porous electrode made of activated carbon and expands in the direction of voltage application when an electric field is activated. When the carbonaceous electrode expands in this way, the volume of the capacitor itself also increases, so that the increase in capacitance per unit volume is diminished and the energy density of the capacitor cannot be sufficiently increased.

  The expansion of the capacitor itself can be reduced by mechanically pressing the carbonaceous electrode in advance. In this case, an expansion pressure is applied to the electrode, but it is necessary to make the expansion pressure uniform in order to prevent distortion and damage of the electrode. Therefore, it has been considered preferable for this type of electric double layer capacitor to have a structure in which a plurality of carbonaceous electrode sheets are stacked in a square shape via a separator and a dimension limiting mechanism is added.

  However, in order to laminate the carbonaceous electrode sheet into a square shape, processes such as sheet cutting and lamination, assembling a complex current collector, and the like are required and labor is required. In addition, the dimension limiting mechanism is generally bulky because it needs to maintain high strength. For this reason, the square electric double layer capacitor has a problem that its manufacturing efficiency is low and it is difficult to reduce the size and weight, and there is a problem that it is not suitable for applications requiring a large amount of small and light products such as a power source for an electric vehicle.

  On the other hand, since a cylindrical container can withstand a large pressure even if it is relatively thin compared to a rectangular container, it is easy to limit the internal pressure. And a dimension limiting mechanism is not necessary, or if so, it is not so bulky. Therefore, the cylindrical electric double layer capacitor is advantageous for reducing the size and weight.

  However, in order to use a cylindrical container, the carbonaceous electrode sheet must be wound and inserted. When the carbonaceous electrode expands while being wound in the cylindrical container, an expansion pressure is generated in the direction of the inner wall of the cylindrical container due to the expansion pressure, and an expansion pressure in the central direction is also generated in the central portion of the wound body. Arise. Therefore, the carbonaceous electrode is easily distorted. When the carbonaceous electrode is distorted, the expansion of carbon around the lead electrode portion becomes significant, the terminal is damaged, and in some cases, the electrode is broken apart into strips.

  In Patent Document 4, in a wound type electric double layer capacitor using a polarizable electrode that expands in the direction of voltage application when a voltage is applied, a mandrel is provided on the wound body of the polarizable electrode to eliminate the center space. Thus, it is described that the expansion pressure is kept uniform. However, it is difficult to appropriately control the degree and distribution of the expansion pressure only by the structure that externally regulates the deformation of the wound body.

  Patent Document 5 describes a separator that expands following the expansion even when the polarizable electrode expands when a voltage is applied, and a wound electric double layer capacitor having this separator. This separator is excellent in heat resistance, winding property, and elongation at break. However, the buffer function is insufficient, and it is difficult to equalize the expansion pressure accompanying the expansion of the electrode and to reduce the distortion of the electrode.

JP 11-317333 A JP 2002-25867 A JP 2000-77273 A JP 2000-68165 A JP 2004-207333 A Ikuo Okamura "Electric Double Layer Capacitor and Power Storage System" 2nd Edition, Nikkan Kogyo Shimbun, 2001 Satoshi Takeuchi, “Properties of Porous Materials and Their Applied Technologies”, Fuji Techno System Co., Ltd., 1999, pp. 56-61

  The present invention solves the above-mentioned conventional problems. The object of the present invention is to provide a winding in which, even if a polarizable electrode expands when a voltage is applied, the expansion pressure is relaxed and uniformed internally, and the electrode is not distorted. An electrical double layer capacitor is provided.

The present invention is a wound body in which a polarizable electrode that expands in the voltage application direction when a voltage is applied is wound through a separator made of an insulating sheet having a buffer function,
An organic electrolyte in contact with the polarizable electrode, and a cylindrical container for housing these,
A wound type electric double layer capacitor having the above is provided, whereby the above object is achieved.

  According to the present invention, by improving the manufacturability of a wound electric double layer capacitor having a polarizable electrode that expands when a voltage is applied, the manufacturing yield is significantly improved while maintaining a sufficient volume capacity density. .

  The electric double layer capacitor of the present invention is an electric double layer capacitor formed by immersing a polarizable electrode that expands in the direction of voltage application when a voltage is applied in an organic electrolyte. For example, a nonporous carbonaceous electrode containing nonporous carbon as an active ingredient exhibits a behavior that expands in the direction of voltage application when a voltage is applied, and corresponds to a polarizable electrode that expands in the direction of voltage application when a voltage is applied.

  A preferred non-porous carbon is a carbon powder obtained by firing a carbon raw material at 500 to 900 ° C. for 2 to 4 hours in an inert atmosphere and heat-treating in the presence of an alkali hydroxide powder and / or an alkali metal. As the carbon raw material, coke green powder, mesophase carbon, infusible vinyl chloride, or the like may be used.

  When a heavy petroleum oil obtained at the time of distillation of petroleum is subjected to high-temperature pyrolysis treatment, a carbonaceous solid having a needle-like structure is obtained. This solid immediately after production is called green needle coke. When used as a filler or the like, it is then calcined at a temperature of 1000 ° C. or higher, but the calcined one is called calcined needle coke and is distinguished from green needle coke. In this specification, powdery green needle coke is referred to as needle coke green powder.

  The non-porous carbonaceous electrode preferably uses needle coke green powder as a starting material. Needle coke green powder is easily crystallized even when fired at a relatively low temperature, and the ratio of the amorphous part to the crystalline part is easily controlled accordingly. An easily graphitizable organic substance has a structure when it is highly oriented by heat treatment, and is easily crystallized even when fired at a relatively low temperature, so that the ratio between the amorphous part and the crystalline part can be easily controlled.

  Normally, needle coke green powder is manufactured using petroleum pitch as a raw material. However, in this invention, you may use the coal-type needle coke green powder which removed the quinoline insoluble content from the soft pitch of coal, and was carbonized using the refined raw material. Coal-based needle coke generally has a high true specific gravity, a low coefficient of thermal expansion, a soft structure with a needle-like structure. In particular, compared with petroleum-based needle coke, it has the characteristics of a coarse particle size and a low thermal expansion coefficient. Moreover, elemental compositions are also different, and coal-based needle coke has a lower sulfur and nitrogen content than petroleum-based needle coke (Non-Patent Document 2).

  In producing the carbonaceous electrode used in the present invention, first, needle coke green powder is prepared. The center particle diameter of the raw material is 10 to 5000 μm, preferably 10 to 100 μm. In addition, the ash content in the carbonaceous electrode affects the generation of surface functional groups, and it is important to reduce it. Needle coke green powder used in the present invention has fixed carbon of 70 to 98% and ash content of 0.05 to 2%. Preferably, it has the characteristics that fixed carbon is 80 to 95% and ash content is 1% or less.

  The powder of needle coke green powder is baked at 500 to 900 ° C., preferably 600 to 800 ° C., more preferably 650 to 750 ° C. for 2 to 4 hours in an inert atmosphere, for example, an atmosphere of nitrogen or argon. It is considered that a crystal structure of a carbon structure is formed in this firing step.

  If the calcination temperature is less than 500 ° C, pores develop too much in the activation treatment, and if it exceeds 900 ° C, activation does not proceed. The firing time is essentially irrelevant to the reaction, but if it is generally less than 2 hours, heat is not transferred to the entire reaction system, and uniform nonporous carbon is not formed. It doesn't make sense to exceed 4 hours.

  The calcined carbon powder is mixed with an alkali hydroxide having a weight ratio of 1.8 to 2.2 times, preferably about 2 times. The powder mixture is calcined at 650 to 850 ° C., preferably 700 to 750 ° C. for 2 to 4 hours under an inert atmosphere. This process is called alkali activation, and it is considered that alkali metal atom vapor penetrates the carbon structure and has the effect of relaxing the crystal structure of carbon.

  If the amount of the alkali hydroxide is less than 1.0 times, the activation does not proceed sufficiently and the capacity is not developed at the first charge. If it exceeds 2.5 times, the activation proceeds too much and the surface area tends to increase, and the surface state is the same as that of normal activated carbon, so that it is difficult to withstand the withstand voltage. As the alkali hydroxide, KOH, CsOH, RbOH or the like may be used, but KOH is preferable because of its excellent activation effect and low cost.

  Further, if the firing temperature is lower than 650 ° C., KOH does not sufficiently penetrate into the carbon, and the effect of loosening the carbon layer is diminished. If the calcination temperature exceeds 850 ° C., in addition to the activation by KOH, the contradictory actions of crystallization of the equipment carbon are in parallel, making control difficult. If the material is sufficiently heated, the time is essentially unrelated, but if the firing time is less than 2 hours, the material does not have sufficient heat and a part that is not partially activated appears. There is no point in firing for more than 4 hours.

  The resulting powder mixture is then washed to remove the alkali hydroxide. In the washing, for example, particles are collected from the carbon after the alkali treatment, filled in a stainless steel column, 120 to 150 ° C., 10 to 100 kgf, preferably 10 to 50 kgf of pressurized water vapor is introduced into the column, This can be done by continuing to introduce pressurized steam until the pH is ˜7 (usually 6-10 hours). After completion of the alkali removal step, an inert gas such as argon or nitrogen is passed through the column and dried to obtain the target carbon powder.

The carbon powder obtained through the above steps has a specific surface area of 300 m ² / g or less, and has a small number of pores capable of incorporating various electrolyte ions, solvents, CO ₂ gas, etc., so-called “non-porous carbon” "are categorized. The specific surface area can be determined by the BET method using CO ₂ as an adsorbent.

  However, the carbon powder thus prepared using needle coke green powder as a raw material is not merely “non-porous carbon” but has some pores. That is, the carbon powder used in the present invention has a pore volume with a pore diameter of 0.8 nm or less of 0.01 to 0.1 ml / g, preferably 0.02 to 0.06 ml / g.

When the pore volume of the carbon powder having a pore diameter of 0.8 nm or less is less than 0.01 ml / g, the expansion rate at the time of charging the capacitor increases, and when it exceeds 0.1 ml / g, the withstand voltage characteristic is lowered. Note that the value of the pore volume referred to here is a value obtained from a high-resolution adsorption isotherm of carbon dioxide (273K, 10 ^{−7 to 1} Torr) on carbon of the electrode material by the DFT method (Density Functional Theory general density function analysis method) By analyzing the volume, a pore volume having a pore diameter of 0.8 nm or less can be obtained. The measuring device used was an adsorption device for micropore measurement, Autosorb-1-MP (with turbo molecular vacuum pump) manufactured by Quantachrome.

  The carbonaceous electrode can be produced by a method similar to the conventional method. For example, in order to produce a sheet-like electrode, the nonporous carbon obtained by the above method is pulverized to about 5 to 100 μm to adjust the particle size. Thereafter, for example, carbon black as a conductive auxiliary agent for imparting conductivity to the carbon powder and, for example, polytetrafluoroethylene (PTFE) as a binder are added and kneaded, and formed into a sheet by pressure drawing. Mold.

  In addition to carbon black, powdered graphite and the like can be used as the conductive auxiliary agent, and as the binder, PVDF, PE, PP and the like can be used in addition to PTFE. At this time, the blending ratio of non-porous carbon, conductive auxiliary agent (carbon black), and binder (PTFE) is generally about 10 to 1: 0.5 to 10: 0.5 to 0.25. It is.

  The produced carbonaceous electrode for an electric double layer capacitor is used for a wound electric double layer capacitor. FIG. 1 is a schematic diagram showing a general configuration of a wound electric double layer capacitor. The wound electric double layer capacitor 10 includes a negative electrode sheet 14 in which a negative electrode side polarizable electrode 13 is formed on a current collector 12 and a positive electrode sheet 17 in which a positive electrode side polarizable electrode 16 is formed on a current collector 15. Are wound in a cylindrical shape with the separator 11 interposed therebetween. The wound body may be provided with a metal or resin cylinder (not shown) as a mandrel.

  As the separator, an insulating sheet having a buffer function is used. The buffer function here is self-supporting with its original volume maintained under a weak pressure, but it absorbs at least part of the increased pressure by deforming so that the volume decreases as the pressure increases. The function to do. For example, a bulky nonwoven sheet or sponge sheet having a high porosity has a buffer function. Further, in a sheet having a large number of three-dimensional convex portions on a plane, when the convex portions do not deform so much under a weak pressure and have flexibility to be crushed accordingly when the pressure increases, the sheet is buffered. Has function.

  The separator may be any material that satisfies the criteria such as insulation, stability and retention with respect to the electrolyte, and heat resistance. The nonwoven fabric is preferably formed from, for example, polyolefin fibers or polyamide fibers. Specifically, polyethylene fiber and polypropylene fiber, 6 nylon fiber and nylon 6,6 fiber, polypropylene sheathed core-sheath type composite fiber coated with ethylene-vinyl alcohol copolymer and polypropylene fiber coated with polyethylene fiber The core-sheath type composite fiber etc. which were made can be mentioned.

  The paper material may be any material normally used as a separator for an electric double layer capacitor. Specific examples thereof include felt-like or mesh-like sheets mainly composed of cellulose fibers.

  If the cushioning function is insufficient with the flat sheet shape, for example, a structure such as three-dimensional unevenness and corrugation may be given to the entire sheet. The convex portion raised from the flat portion is flexible and can have a buffer function. A three-dimensional unevenness | corrugation and a waveform can be formed in the surface of a flat sheet | seat by embossing, for example. The shape, size, spacing, density, and the like of the unevenness and the corrugation may be appropriately determined according to the type of sheet to be selected, the application, the expandability of the electrode, and the like.

  In a preferred embodiment, a plurality of convex portions are formed on one surface of the sheet. The shape of the convex part is hemispherical, cylindrical, truncated cone, pyramid, truncated pyramid and the like. The height of the convex portion is one that has been embossed up to 1.1 to 1.3 times the thickness of the separator serving as the base material in total on both sides. If the total thickness including the height of the convex portion is less than 1.1 times in total on both sides, the expansion of the electrode cannot be sufficiently absorbed, and if the height of the convex portion exceeds 1.3 times, sufficient volume capacity is obtained. The density cannot be obtained. The diameter dimension of the bottom surface of the convex portion may be any as long as it occurs according to the height of the convex portion, and is, for example, 0.1 to 1.0 mm, preferably 0.1 to 0.3 mm.

The convex portions are preferably distributed almost regularly, and the density thereof is 10 to 100 pieces / cm ² , preferably 50 to 100 pieces / cm ² . If the density of the convex portions is less than 10 pieces / cm ² , it is inconvenient that sufficient stress cannot be generated unless the thickness of the substrate used is sufficiently increased. A plurality of similar convex portions may be formed on one side of the sheet, but both sides are preferred.

  When creating the wound body, the separator 11 is preferably wound so that the convex portions of the sheet are in contact with the current collectors 12 and 15. This is because if the convex portion is in contact with the carbonaceous electrode, it may be damaged during expansion.

  The wound body 18 is accommodated in, for example, a container 19 filled with an electrolytic solution (not shown) in advance, or is accommodated in the container 19 and then filled with the electrolytic solution. And it covers with the sealing board 21 to which the electrode terminal was attached, ensuring conduction | electrical_connection with the electrode sheets 14 and 17 and the electrode terminal 20. FIG. In this way, the wound electric double layer capacitor 10 is completed.

  As the electrolytic solution, a so-called organic electrolytic solution obtained by dissolving an electrolyte as an solute in an organic solvent can be used. Examples of the electrolyte include salts of lower aliphatic quaternary ammonium, lower aliphatic quaternary phosphonium or imidazolinium derivatives and tetrafluoroboric acid or hexafluorophosphoric acid as described in Patent Document 3, Those commonly used by those skilled in the art can be used.

  Among them, a preferable electrolyte is a pyrrolidinium compound salt. Preferred pyrrolidinium compound salts have the formula

[Wherein, each R is independently an alkyl group or an alkylene group linked together, and X ⁻ is a counter anion. ]
It has the structure shown by. The pyrrolidinium compound salt is known and may be synthesized by a method known to those skilled in the art.

  Preferred for the ammonium component of the pyrrolidinium compound salt is that in the above formula, each R is independently an alkyl group having 1 to 10 carbon atoms or an alkylene group having 3 to 8 carbon atoms linked together. More preferred are those wherein R is an alkylene group having 4 to 5 carbon atoms linked together. Further preferred are those in which R is a butylene group linked together. Such an ammonium component is called spirobipyrrolidinium (SBP).

  Pyrrolidinium compounds, especially spirobipyrrolidinium, have a seemingly complex molecular structure and appear to have a large ionic diameter. However, when this compound is used as the electrolyte ion of the organic electrolyte, the effect of suppressing the expansion of the non-porous carbonaceous electrode on the negative electrode side is particularly great, and the energy density of the electric double layer capacitor is greatly improved. Although not intended to be limited theoretically, it is thought that the effective ion diameter of pyrrolidinium compounds and spirobipyrrolidinium is small because the spread of the electron cloud is suppressed by the spiro ring structure.

The counter anion X ⁻ may be any one that has been conventionally used as an electrolyte ion of an organic electrolyte. For example, a tetrafluoroborate anion, a fluoroborate anion, a fluorophosphate anion, a hexafluorophosphate anion, a perchlorate anion, a borodisalicylate anion, and a borodisoxalate anion. Preferred counter anions are tetrafluoroborate anion and hexafluorophosphate anion. This is because they have a low molecular weight and a simple structure, and the expansion of the nonporous carbonaceous electrode on the positive electrode side is suppressed.

  An organic electrolyte for an electric double layer capacitor can be obtained by dissolving the pyrrolidinium compound salt as a solute in an organic solvent. The concentration of the pyrrolidinium compound salt in the organic electrolyte is adjusted to 0.8 to 3.5 mol%, preferably 1.0 to 2.5 mol%. When the concentration of the pyrrolidinium compound salt is less than 0.8 mol%, the number of ions contained is insufficient and sufficient capacity cannot be obtained. Moreover, even if it exceeds 2.5 mol%, it does not contribute to the capacity and is meaningless.

  A pyrrolidinium compound salt may be used independently and may mix multiple types. You may use together the electrolyte conventionally used for the organic electrolyte solution. However, the proportion of the pyrrolidinium compound salt in the solute is 50% by weight or more, preferably 75% by weight or more of the total solute weight. Preferred electrolytes for use in combination with the pyrrolidinium compound salt include triethylmethylammonium salt, tetraethylammonium salt and the like.

  As the organic solvent, those conventionally used for organic electric double layer capacitors may be used. For example, ethylene carbonate (EC), propylene carbonate (PC), γ-butyl lactone (GBL), sulfolane (SL) and the like are preferable because of their excellent solubility in pyrrolidinium compound salts and high safety. Also useful are those containing these as a main solvent and at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as a sub-solvent. This is because the low temperature characteristics of the electric double layer capacitor are improved. Further, when acetonitrile (AC) is used as the organic solvent, the conductivity of the electrolytic solution is increased, which is preferable in terms of characteristics. However, the use may be limited.

  When a non-porous carbonaceous electrode made of needle coke as a raw material and an electrolyte containing a pyrrolidinium compound salt are used in combination, the negative electrode expansion suppression effect is remarkably obtained, and the energy density of the electric double layer capacitor is greatly improved.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “part” or “%” is based on weight unless otherwise specified.

Example Potassium hydroxide pellets were previously pulverized by a mill to obtain powder. Coal needle coke green powder (NCGP) manufactured by Nippon Steel Co., Ltd. was calcined for 3 hours at a temperature shown in Table 1 while naturally circulating in an alumina crucible while circulating nitrogen in a muffle furnace. Next, the roughly fired product was mixed with 1.5 times the potassium hydroxide powder per weight ratio. Each was put in a nickel crucible and covered with a nickel lid to shut off the outside air. This was activated for 4 hours at 750 ° C. while circulating nitrogen in a muffle furnace. The fired product was taken out, washed lightly with pure water, and then washed by applying ultrasonic waves. The time is 1 minute. Next, water was separated using a Buchner funnel. The same washing operation was repeated until the pH of the washing water reached around 7. This was dried in a vacuum dryer at 200 ° C. for 10 hours.

The obtained carbon was pulverized for 1 hour with 10 mmφ alumina balls using a ball mill (AV-1 manufactured by Fujiwara Seisakusho). When the particle size was measured with a Coulter counter, all of them became powdery with a center particle diameter of about 10 microns. It was 80 m < ² > / g when the specific surface area of the obtained powdery carbon was measured by BET method. The pore volume with a pore diameter of 0.8 nm or less was 0.04 ml / g.

  Powdered carbon (CB) was mixed at a mixing ratio of 10: 1: 1 of acetylene black (AB) and polytetrafluoroethylene powder (PTFE), and kneaded in a mortar. In about 10 minutes, PTFE was stretched and formed into flakes. This was pressed with a press machine to obtain a carbon sheet. The thickness of the carbon sheet was adjusted as shown in Table 1 according to the example number.

  A plurality of carbonaceous electrodes having a width of 30 mm and a length of 250 mm are cut out from the carbon sheet, and then this electrode and a current collector made of an aluminum foil having a width of 33 mm, a length of 270 mm, and a thickness of 30 μm are paired with a pressure roller. A positive electrode sheet was prepared by pressure bonding at a line pressure of 6 t. A negative electrode sheet was produced in the same manner.

For the separator, embossed paper (specially processed paper of CTW type, total thickness 60 μm) manufactured by NKK (Nippon Advanced Paper) Co., Ltd. was prepared. On one side of this embossed paper, diamond-shaped convex portions having a height of 5 μm and a bottom surface diameter of mm are formed on both sides with a density of 70 mesh pieces / cm ² (the thickness of the base material is 50 microns and the embossed protrusions are Is 60 microns).

  A stack of embossed paper, negative electrode sheet, embossed paper, and positive electrode sheet is spirally wound so that one separator on the outer side of the negative electrode sheet is located on the innermost side, and the outer diameter is 13.5 mm. Thus, a wound element having a length of 33 mm was produced. The wound body element was placed in a bottomed cylindrical container having an inner diameter of 15.8 mm and a length of 45 mm to finish a lead linear capacitor shape.

An electrolyte solution is prepared by dissolving spirobipyrrolidinium tetrafluoroborate (SBPBF ₄ ) in propylene carbonate so as to be 2.0 mol%, and the aluminum case is injected and impregnated. The aluminum case was crimped and sealed with a rubber sealant interposed.

  A power system charge / discharge test device “CDT-RD20” is connected to the obtained wound type electric double layer capacitor, and constant current charging is performed at 5 mA for 7200 seconds, and after reaching a set voltage, at 5 mA A constant current discharge was performed. The set voltage was 4.0 V and 3.5 V, and was performed every three cycles.

  The behavior of the cells during charging / discharging was visually observed, and the capacitance of each cell was measured by a constant current method. The results are shown in Table 1.

Comparative Example A wound type electric double layer capacitor was prepared and tested in the same manner as in Example except that standard paper made by NKK (sheet shape without CTW embossing, thickness 50 μm) was used instead of embossed paper. did. The results are shown in Table 1.

※：電極厚さはアルミニウム３０μｍのエッチドアルミニウム箔の片面上に形成した厚さとする。 [Table 1]

*: The electrode thickness is the thickness formed on one side of 30 μm aluminum etched aluminum foil.

  In the comparative example not using embossed paper, an electrode having a thickness of 50 microns or more is structurally difficult, whereas in the example using embossed paper, an electrode having a thickness of 100 microns can be used. While maintaining the size, a capacitance of about 1.5 times could be achieved.

It is a schematic diagram which shows the general structure of a wound type electric double layer capacitor.

Explanation of symbols

10: Winding type electric double layer capacitor,
11 ... separator,
12, 15 ... current collector,
13, 16 ... polarizable electrodes,
14 ... negative electrode sheet,
17 ... positive electrode sheet,
18 ...
19 ... container,
20 ... Electrode terminal,
21 ... Sealing plate.

Claims (4)

A wound body in which a polarizable electrode that expands in the voltage application direction when a voltage is applied is wound through a separator made of an insulating sheet having a buffer function,
An organic electrolyte in contact with the polarizable electrode, and a cylindrical container for housing these,
A wound type electric double layer capacitor.   2. The electric double layer capacitor according to claim 1, wherein the separator is an insulating sheet having a three-dimensional convex portion, and the convex portion is deformed to exhibit a buffer function.   The electric double layer capacitor according to claim 1 or 2, wherein the separator is a paper material having a three-dimensional uneven portion almost regularly. The electric double layer capacitor according to any one of claims 1 to 3, wherein the polarizable electrode is a nonporous carbonaceous electrode having microcrystalline carbon similar to graphite.

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