JP2005294607A - Electric double-layer capacitor using activated carbon fiber and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor of high capacity that can suppress electrode expansion during usage and has decay resistance against repetitive charging and discharging and its manufacturing method. <P>SOLUTION: An electric double-layer capacitor using an activated carbon fiber as an electrode material employs an electrode material manufactured by forming fibers of mixture mainly composed of at least one kind of fiber formation high polymer for making an anti-graphitized carbon by heating the activated carbon fiber, and at least one kind of fiber formation high polymer for making a pro-graphitized carbon by heating same carbon fiber melted in the common solvent like water or organic solvent, extending and hardening the formed fibers and then carbon-activating the resulting composite fibers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric double layer capacitor having a high capacitance using a special activated carbon fiber, which has not been heretofore known, and a method for producing the same.

  In recent years, the use of electrical energy has been rapidly progressing for reasons such as responding to environmental loads and saving resources for global resources. For example, it is a well-known fact that hybrid vehicles and electric vehicles have been put to practical use in automobiles in addition to conventional internal combustion engines. Furthermore, it is clear that the next-generation automobile will have the function of generating electricity by itself using a fuel cell as well as using the stored electricity. The fact that photovoltaic power generation has come to be used in ordinary houses is a familiar example of the electrified society.

  By the way, a method for storing and taking out electric energy is important as the use of electricity becomes active. There are secondary batteries that repeatedly charge and discharge electricity for this purpose. However, since charge transfer due to chemical reaction is applied to charging and discharging, rapid charging and discharging cannot be performed, efficiency changes depending on environmental temperature, charging and discharging. The problem is that the capacity gradually decreases as the discharge is repeated. The above-mentioned electric vehicles and hybrid vehicles are equipped with a secondary battery for charging power and regenerative current, but this type of problem is due to the time required for charging, an increase in weight, and a short mileage. It is supposed to hinder the spread of the car itself.

  An electric double layer capacitor that has recently been attracting attention in place of the secondary battery is a power storage unit utilizing the phenomenon of the electric double layer, and is also called an electric double layer capacitor. The phenomenon of the electric double layer is a phenomenon in which when two different layers come into contact with each other, the interface is arranged at a distance with a positive charge and a negative charge. The electric double layer capacitor is a large-capacity capacitor that accumulates electric charge by applying voltage to the electric double layer generated at the interface between the solid electrode and the electrolyte. The electric double layer capacitor does not use a chemical reaction for charging / discharging like a conventional battery. Therefore, it is excellent in charge / discharge repeatability and rapid chargeability, and discharge of a large current is possible. Moreover, it is attracting attention because it is easy to maintain and does not adversely affect the environment.

  At present, this electric double layer capacitor is particularly expected to increase its capacity, and if this becomes possible, it is considered that the spread in various fields will proceed at a remarkable speed.

  Initially, activated carbon has been used as a solid electrode material used in the electric double layer capacitor. The activated carbon used for this purpose can be said to be a medium that provides a large surface area for the solvent and electrolyte ions to act electrochemically, so the specific surface area naturally depends on the pore diameter and the pore structure. Capacitor performance is greatly affected. In general, the capacity per unit weight of an electric double layer capacitor is proportional to the specific surface area of activated carbon. Therefore, many attempts have been made to use activated carbon with a high specific surface area in order to increase the capacity. Activated carbon is generally a carbon source derived from plants such as sawdust and coconut husk, or a synthetic high-molecular carbon source such as phenol resin, furfuryl alcohol resin, polyvinyl alcohol resin, vinyl chloride resin, or petroleum such as coke and pitch. It is manufactured by carbonizing and activating a carbon source derived from coal. As an activation method, gas activation in which heating is performed in an oxidizing gas such as water vapor or carbon dioxide is known. In this activation, pores are formed by a decarbonization reaction by a reaction between the oxidizing gas and carbon. Further, an alkali activation method is also used in which a carbon body is mixed with an alkali metal compound such as potassium hydroxide having the same mass to several times its mass and heated in an inert gas atmosphere to form pores.

From the examples so far, it is possible to produce activated carbon having a high specific surface area of 2500 m ² / g or more using the activation method as described above. When activated carbon having such a high specific surface area is used for an electric double layer capacitor, a high capacity can be expected, but it is known that in reality it is difficult to increase the capacity even if the specific surface area is excessively increased. .

  This indicates that although activated carbon has a high specific surface area, not all of it is used to form an electric double layer. In addition, excessive activation leads to a decrease in the density of the activated carbon, so although the electric double layer capacitor using activated carbon with a high specific surface area increases the capacity per unit weight, the capacity per unit volume is at a certain specific surface area. The result is that the value is the top and then decreases as the specific surface area increases. This is the reason why a high-capacity electric double layer capacitor cannot be formed only by using activated carbon having a high specific surface area.

  On the other hand, carbon materials with relatively high crystallinity, such as activated carbon activated with mesophase pitch alkali, that is, activated carbon made of so-called graphitizable carbon, shows a high capacity and a large volume even though it does not have a large specific surface area. It has been disclosed that an electric double layer capacitor having a high capacity per unit volume can be manufactured because of its high density (see, for example, Patent Document 1 and Patent Document 2).

  In activated carbon from graphitizable carbon, electrolyte ions are not adsorbed only within the pores, but are penetrated while adsorbing between the carbon layers and adsorbed between the layers. It is possible to increase the capacity that cannot be explained. As can be easily inferred from this, an electric double layer capacitor using activated carbon from graphitized carbon repeatedly expands and contracts the activated carbon electrode during charge and discharge, and the capacitor cell is gradually damaged. Not only is the durability inherent in the double layer capacitor impaired, but also the capacity per unit volume calculated by correcting the electrode volume during expansion is not so excellent. For this reason, there is a method in which the capacitor cell is put in a strong container to suppress expansion during charging, but it naturally increases the weight of the capacitor itself, which is a serious drawback.

  On the other hand, activated carbon from carbon material with low crystallinity such as phenol resin, so-called non-graphitized carbon, can be easily activated to have a high specific surface area by steam activation. Although the electric double layer capacitor made from activated carbon from such non-graphitizable carbon has a small capacity per unit volume, the electrode has a small expansion and contraction during charging and discharging, so it has high durability during long-term continuous use. This is advantageous.

  Therefore, it is considered that an electric double layer capacitor having a high capacity and high durability can be manufactured if an activated carbon having both advantages is obtained by combining the graphitizable carbon source and the non-graphitizable carbon source. Actually, in the method disclosed in Patent Document 3, carbonization is performed after mixing the graphitizable carbon source and the non-graphitizable carbon source, and activated carbon is obtained by a further activation method. According to the report, it is possible to manufacture an electric double layer capacitor that suppresses volume change during charge and discharge, has a high capacity per unit volume, and has excellent long-term reliability.

However, in this method, it is important to have a structure that encloses a non-graphitizable carbon source that suppresses expansion around a graphitizable carbon source that is highly expanded during charging. For this purpose, obtaining a uniform and fine mixing state of both components is an absolute condition, and the number of complicated and difficult mixing steps is increased. Furthermore, this method requires a step of grinding again after infusibilization. Of course, not only is it necessary to have production equipment dedicated to these processes, but it is also true that the equipment costs increase. In addition, the structure in which the non-graphitizable carbon source is wrapped around the easily graphitizable carbon source that has been constructed by grinding is broken. Furthermore, in such an electrode for an electric double layer capacitor using pulverized activated carbon, contact between the pulverized charcoal is not sufficiently made, and this leads to an increase in internal resistance, so it is necessary to add a little conductive auxiliary material. There is no inventive step in this regard compared to the prior art.
JP-A-2-185008 JP-A-10-121336 JP 2002-83748 A

  Electric double layer capacitors that have high capacity and can suppress the expansion of the electrode during use, and are excellent in durability against repeated charge and discharge, and are inexpensive, are expected to be industrially important and indispensable. However, on the other hand, in the conventional manufacturing method, it is difficult to achieve both high capacity and high performance and cost, and in view of the current situation where sufficient characteristics are not yet obtained, the present inventors have advanced intensive studies, A new manufacturing method was found and completed. That is, an object of the present invention is to provide an electric double layer capacitor having a high capacity and capable of suppressing expansion of an electrode during use, and thus excellent in durability against repeated charge and discharge, and a method for manufacturing the same. .

  As described above, carbon materials with low crystallinity such as phenol resin, so-called non-graphitized carbon activated carbon can be easily activated with water vapor and have a high specific surface area. Such activated carbon can be used as a polarizable electrode. Although the produced electric double layer capacitor has a small capacity per unit volume, it is advantageous in that it has high durability during long-term continuous use since the expansion and contraction of the electrode during charging and discharging is slight. On the other hand, for activated carbon that is a combination of an easily graphitizable carbon source and a non-graphitizable carbon source, which is advantageous for electrical performance, at present, a complicated and highly difficult mixing process to obtain a uniform and fine mixed state of both components In addition, there is a manufacturing problem that requires a manufacturing facility for re-grinding after infusibilization, and when using this activated carbon to produce an electric double layer capacitor, add a little conductive auxiliary material. In other words, there is no inventive step compared to the prior art in that it cannot take full advantage of its high performance.

  The present inventors thought that by using a composite activated carbon from an easily graphitizable carbon source and a non-graphitizable carbon source, a high-capacity and highly durable electric double layer capacitor could be manufactured. In the method, the process is complicated and expensive, and it is considered that the problem of not being able to take advantage of the performance of cornering when making the electrode material of the capacitor, easy to graphitize carbon source and non-graphitizable carbon source, We studied a simple and extremely homogeneous method of mixing and dispersing, and a method to maximize the performance of activated carbon.

  The method is as follows. First, regarding the shape of activated carbon, fiber-shaped activated carbon has a large contact area with the electrolyte compared to normal powder, granular, or spherical activated carbon, so that adsorption / desorption of electrolyte ions is fast, or contact between fibers. Judging from the fact that many points can be taken and low electrical resistance, or that it can be easily processed into paper, unemployed cloth, woven cloth, string, thread, etc., it is judged that activated carbon so-called activated carbon fiber having a fiber shape is good. did. As the activated carbon fiber, a phenol resin is selected as a main component because it is flexible and easy to process, and has a high yield after carbonization and activation. The phenol resin has low crystallinity and becomes a non-graphitizable carbon source upon firing. For this purpose, polyvinyl alcohol, cellulose diacetate, cellulose triacetate, and copolymers thereof, which are also non-graphitizable carbon sources, are used in combination in order to improve the spinnability during spinning and facilitate fiber production.

  Next, the following method is suitable for the method of mixing the graphitizable carbon source and the non-graphitizable carbon source simultaneously with the fiber formation. In other words, in order to blend a phenolic resin and other high molecular compounds, and further to make the mixed state uniform and fine, it is appropriate to make it a solution state dissolved in a common solvent. By spinning, it can be fiberized in a uniform mixed state. A wet spinning method, a dry wet spinning method or a dry spinning method is selected as a means for fiberizing from this solution state.

  For the above purpose, the present inventors have developed a novolak type phenol resin obtained by reacting phenols and aldehydes in the presence of an acidic catalyst as a non-graphitizable carbon source, or phenol in the presence of a basic catalyst. Resol type phenol resins obtained by reacting aldehydes with aldehydes or various modified phenol resins by known techniques such as boron modification, silicon modification, phosphorus modification, heavy metal modification, nitrogen modification, sulfur modification, oil modification, rosin modification, etc. In addition to these mixtures, or in addition to these phenolic resins, a mixture with at least one fiber-forming polymer compound that generates non-graphitizable carbon by heating, and as a graphitizable carbon source, graphitizable carbon is generated by heating. At least one type of fiber-forming polymer compound, and these are common water or organic solvents The mixture dissolved in the agent is used as a spinning stock solution, which is spun by wet or dry wet through pores in a bath having a solidifying ability for the fiber-forming polymer compound, or dry in air or an inert gas. After spinning, stretching, and further activating the composite fiber obtained by heat treatment or curing with aldehydes in the presence of a catalyst after carbonization, or making activated carbon fiber by continuously performing carbonization activation. I found it.

  Generally, a phenol resin fiber is produced by melt spinning a thermoplastic novolac resin, and then performing a three-dimensional crosslinking by reacting with an aldehyde under an acidic catalyst to make it heat infusible. However, applying this method and blending other high molecular compounds with the novolak resin used as a raw material for melt spinning, it is difficult to match two components having different spinnability well. In addition to its complex behavior compared to single components, it is difficult to control the yarn diameter stably and efficiently and with high accuracy, and in addition to other polymers added during plastic deformation during spinning. Since the compound itself is also stretched in the axial direction, it is difficult to obtain a desired uniform dispersion structure.

  In the present invention, the spinning method is limited to the wet spinning method, the dry wet spinning method, or the dry spinning method. The spinning method is uniform and fine in a solution state in which other fiber-forming polymer compounds such as phenol resin are dissolved in a common solvent. This is because they can be blended and further fiberized in a uniform mixed state by spinning directly from this solution state.

  In the present invention, the graphitizable carbon source and the non-graphitizable carbon source can be easily and easily mixed and dispersed very uniformly, and activated carbon fiber can be formed in that state. The activated carbon fiber of the present invention has a macroscopic large contact area with the electrolytic solution, so that the adsorption and desorption of electrolyte ions is fast, or the point of being able to have a low electrical resistance because many contact points between fibers can be taken, or paper, non-woven fabric, From the point that it can be easily changed to a shape such as a woven fabric, a string, and a thread, it was judged that activated carbon fiber having a fiber shape, so-called activated carbon fiber, is good. This activated carbon fiber is flexible and easy to process.

  The use of the activated carbon fiber of the present invention for an electric double layer capacitor makes it possible to suppress the expansion of the electrode at the time of use with a high capacitance, and therefore, an electric having excellent durability against repeated charge and discharge. A double layer capacitor can be obtained, and both high capacity, high performance and cost can be achieved.

  The present invention is described in detail below. The phenols used to obtain the phenol resin used in the present invention are limited to the phenols exemplified below as long as the phenols can be obtained by reacting aldehydes with an acidic or basic catalyst. For example, phenol, m-cresol, m-ethylphenol, m-propylphenol, m-butylphenol, p-butylphenol, o-butylphenol, resorcinol, hydroquinone, catechol, 3-methoxyphenol, 4-methoxyphenol 3-methylcatechol, 4-methylcatechol, methylhydroquinone, 2-methylresorcinol, 2,3-dimethylhydroquinone, 2,5-dimethylresorcinol, 2-ethoxyphenol, 4-ethoxyphenol, 4- Tilresorcinol, 3-ethoxy-4-methoxyphenol, 2-propenylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 3,4,5-trimethylphenol, 2-isopropoxyphenol, 4-pyro Poxyphenol, 2-allylphenol, 3,4,5-trimethoxyphenol, 4-isopropyl-3-methylphenol, pyrogallol, phloroglicinol, 1,2,4-benzenetriol, 5-isopropyl-3-methylphenol 4-butoxyphenol, 4-t-butylcatechol, t-butylhydroquinone, 4-t-pentylphenol, 2-t-butyl-5-methylphenol, 2-phenylphenol, 3-phenylphenol, 4-phenyl Enol, 3-phenoxyphenol, 4-phenoxyphenol, 4-hexyloxyphenol, 4-hexanoylresorcinol, 3,5-diisopropylcatechol, 4-hexylresorcinol, 4-heptyloxyphenol, 3,5-di-t -Butylphenol, 3,5-di-t-butylcatechol, 2,5-di-t-butylhydroquinone, di-sec-butylphenol, 4-cumylphenol, nonylphenol, 2-cyclopentylphenol, 4-cyclopentylphenol, bisphenol A, bisphenol F, etc. can be used, and the phenols may be used alone or in a mixture. Among these, phenol, o-cresol, m-cresol, p-cresol, bisphenol A, 2,3-xylenol, 3,5-xylenol, m-butylphenol, p-butylphenol, o-butylphenol, 4-phenylphenol, resorcinol More preferred is phenol.

  Next, the aldehydes used for obtaining the phenol resin used in the present invention are not limited to the aldehydes exemplified below. For example, formaldehyde, trioxane, furfural, paraformaldehyde, benzaldehyde, methyl hemiformal, Ethyl hemiformal, propyl hemiformal, butyl hemiformal, phenyl hemiformal, acetaldehyde, propylaldehyde, phenylacetaldehyde, α-phenylpropylaldehyde, β-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde , O-chlorobenzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde, p-nitrobenzaldehyde O-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, p-ethylbenzaldehyde, pn-butylbenzaldehyde, or a mixture thereof. Of these, formaldehyde, paraformaldehyde, furfural, benzaldehyde, and salicylaldehyde are preferable, and formaldehyde and paraformaldehyde are particularly preferable.

  Further, the acidic catalyst used for obtaining the phenol resin used in the present invention is not limited to the following examples, but examples include hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, butyric acid, lactic acid, and benzenesulfone. Examples thereof include salts with acids, p-toluenesulfonic acid, boric acid, metals such as zinc chloride and zinc acetate, and mixtures thereof.

  Further, the basic catalyst used for obtaining the phenol resin used in the present invention is not limited to the following examples. For example, sodium hydroxide, calcium hydroxide, barium hydroxide, lithium hydroxide, etc. And alkali metal or alkaline earth metal hydroxides, ammonium hydroxide, diethylamine, triethylamine, triethanolamine, ethylenediamine, hexamethylenetetramine, and mixtures thereof.

  Next, the fiber-type polymer compound and the solvent having the dissolving ability referred to in the present invention will be described. Examples of the fiber-shaped polymer compound used in the present invention include polyvinyl alcohol, cellulose diacetate, and cellulose triacetate as the non-graphitizable carbon source. On the other hand, examples of the graphitizable carbon source include polyacrylonitrile, polyvinyl butyral, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and copolymers thereof. As the solvent, for example, polyvinyl alcohol can be dissolved in water or a mixture of water and alcohol. When cellulose diacetate is used, acetone, methyl ethyl ketone, cyclohexanone, methyl formate, methyl acetate, ethyl acetate, tetrahydrofuran, dioxane and the like can be used. In the case of cellulose triacetate, it can be dissolved in methylene chloride, a mixed solution of methylene chloride and methanol, or the like. When polyacrylonitrile is used, it can be dissolved in dimethylformamide, dimethylacetamide, dioxane, dimethylsulfoxide, N-methylpyrrolidone and the like. When polyvinyl butyral is used, it can be dissolved in methanol, methanol and toluene, ethanol and toluene, or a solution obtained by mixing ethyl cellosolve or butyl cellosolve. When polyvinyl chloride is used, it can be dissolved in dimethyl sulfoxide, dimethylacetamide, dimethylformamide, or tetrahydrofuran.

  Furthermore, as a method of mixing and dispersing a polymer compound that is soluble in an organic solvent such as polyvinyl chloride or vinyl acetate and insoluble in water with a polymer compound that is soluble in water such as polyvinyl alcohol, It is preferable to use it as a water-based emulsion in which a polymer compound soluble in an organic solvent is previously dispersed in water.

  Next, a method for preparing a spinning dope from the phenol resin used in the present invention and other fiber-forming polymer compounds that become non-graphitizable or graphitizable carbon sources will be described. In this case, a mixture of a phenol resin and a fiber-forming polymer compound dissolved in a solvent capable of dissolving is used as a spinning dope.

  The solid content of the mixed solution used for spinning may be adjusted to 2 to 50% by weight, desirably 5 to 40% by weight, and most desirably 10 to 20% by weight. The temperature may be determined so as to have a viscosity of about 1 to 50 Pa · S, preferably about 5 to 10 Pa · S.

  The ratio of the non-graphitizable carbon source and the graphitizable carbon source in the composite fiber produced by spinning the mixed solution is determined according to the purpose of use, the specific surface area of the activated carbon fiber finally obtained, and the like. However, the weight ratio of the non-graphitizable carbon source to the graphitizable carbon source is suitably in the range of non-graphitizable carbon source: graphitizable carbon source = 95: 5 to 20:80.

  In the present invention, as the non-graphitizable carbon source, in addition to the phenol resin alone, a fiber-forming polymer compound that is a non-graphitizable carbon source can be used in combination. The weight ratio of the resin to the other non-graphitizable carbon source needs to be in the range of phenol resin: other non-graphitizable carbon source = 100: 0 to 20:80. In terms of ease of spinning, increasing the fiber-forming polymer compound that is a non-graphitizable carbon source increases the spinnability and is good, but if it exceeds 50 parts by weight, liquid carbonization tends to occur during carbonization. It becomes difficult to maintain the fiber shape. In the present invention, the phenol resin is used as the non-graphitizable carbon source in the present invention. The phenol resin can be easily heat infusible by heat treatment or reaction with an aldehyde in the presence of a catalyst, and the fiber shape maintaining property during the carbonization process is particularly excellent. This is because.

  The fiber-forming polymer compound used as a non-graphitizable or graphitizable carbon source used in the present invention can be used alone or in combination of two or more. The same applies to the phenol resin.

  There is no particular limitation on the method of mixing the mixed solution used for spinning. It is desirable to put a predetermined amount of the fiber-forming polymer compound and the phenol resin solution in a mixing container and continue stirring for 30 minutes or more with a stirring blade. If the viscosity is high and difficult to stir at this time, the temperature can be raised to about 40 to 60 ° C, but if stirring is continued for 30 minutes or more at a temperature exceeding 80 ° C, there is a problem that the phenol resin begins to harden. In addition, it is necessary to be careful because the organic solvent is concentrated as it is volatilized in an open state.

  The mixed solution that has been uniformly stirred is used as the spinning solution. From the viewpoint of preventing yarn breakage during spinning, an operation of degassing fine bubbles in the mixed solution is desirable. Further, in order to maintain a uniform mixed state in the stock solution storage tank of the spinning device, 5-20R. P. It is desirable to keep stirring gently at M.

  The spinning device used in the present invention is not particularly limited as long as it is a general wet spinning device, and can be used. In addition, depending on the spinning device, there is a dry-wet method in which a spinning solution is once discharged from a spinning nozzle into air or an inert gas. This can also be used, but dry spinning is also possible. In this case, the gas used for drying is generally air heated to the boiling point of the solvent or more, but especially when the flash point or ignition point is low or the temperature is high due to desolvation, oxidation is a problem. It is necessary to use an inert gas such as nitrogen or argon.

  Which method should be used for spinning may be selected according to the type, concentration, and characteristics of the fiber-forming polymer compound to be used, but a wet spinning device is desirable from the viewpoint of preventing fiber sticking immediately after nozzle discharge. . In the case of wet spinning, a solidification bath having a solidification ability for the fiber-forming polymer compound in the spinning dope is used.

  The composition of the solvent and the solidification bath differs depending on the type of the fiber-forming polymer compound. For example, when polyacrylonitrile is used, it is dissolved in dimethylformamide, dimethylacetamide, dioxane, or a mixture of water and alcohol, and this is used. As a solidifying bath, water, a water / alcohol mixed solution is effective. In the case of using polyvinyl butyral, water, water and an alcohol mixed solution are effective as a bath for dissolving in methanol and solidifying the polyvinyl butyral. When water or a mixture of water and alcohol is used in the coagulation bath, an operation such as addition of inorganic salts such as ammonium sulfate or sodium sulfate is also effective in order to increase the coagulation rate due to the salting out / dehydration effect. Conversely, when spinning is difficult, such as when the coagulation rate is too fast, or when spinning is difficult, the solvent used for dissolving the spinning stock solution is mixed with the coagulation bath, etc. This is also effective in the present invention.

  What is necessary is just to select the temperature which becomes the solidification ability desired in the range of -5 degreeC to 60 degreeC as the temperature of a solidification bath. In general, the higher the temperature of the solidification bath, the higher the solidification ability, but if it is too high, the viscosity of the phenol resin in the spinning stock solution may decrease too much and elute in the solidification solution, and stretching in the bath will be difficult. Therefore, it is desirable to set the temperature within the range of 5 ° C to 40 ° C.

  At this time, in order to make the fiber diameter uniform, it is desirable to discharge the spinning solution from the spinning nozzle to the solidification bath through a device such as a gear pump that controls the discharge amount to be constant. The speed at which the yarn generated in the solidification bath is drawn out is 1.1 times to less than 500 times, preferably 4 times to 100 times, more preferably 5 times to 10 times the discharge linear velocity of the spinning nozzle. Is most preferred. Depending on the mixing ratio of the fiber-forming polymer compound used, if it is stretched too much, it becomes difficult to maintain the fiber form during solidification. If it is less than 1.1 times, the fibers tend to stick together.

  The yarn obtained by the above operation is stretched with dry heat or wet heat so as to have a predetermined thickness. In the case of stretching by wet heat, for example, the film is stretched from 2.0 times to 4.0 times in a temperature range of 10 ° C. to 80 ° C., preferably in a temperature range of 30 ° C. to 50 ° C. while immersed in a liquid having the same composition as the solidification bath. It is desirable.

  In the case of dry-heat stretching, a method of stretching from 2.0 times to 4.0 times in an atmosphere of 60 ° C. to 120 ° C., preferably 80 ° C. to 100 ° C. can be mentioned.

  After the stretching is completed by dry heat or wet heat, the phenol resin is then cured. In the case where the used resin is cured by heating, for example, like a resol type phenolic resin, the resin can be cured by performing heat treatment by wet heat or dry heat method subsequent to stretching. The heat treatment conditions are 100 to 220 ° C., preferably 120 to 180 ° C. for 5 to 120 minutes, preferably 20 to 60 minutes. Further, as a method of increasing the curing rate, there is a method of adding an additive that becomes acidic during heat treatment. For this purpose, a typical inorganic acid or organic acid can be used as the acid. Alternatively, an acid salt such as sodium sulfate may be used. On the other hand, a compound that imparts acidity upon heating may be used. In other words, there are esters and salts that liberate a substance that exhibits acidity when the basic part is thermally decomposed when heated, while the basicity and acidity are close to neutrality at room temperature. For example, carboxylic acid esters such as dimethyl oxalate, acid anhydrides such as maleic anhydride and phthalic anhydride, organic halides such as monochloroacetic acid sodium salt, ethylamine hydrochloride and triethanolamine hydrochloride And amines such as

  Ammonium salts such as ammonium chloride and ammonium sulfate that are neutral or weakly alkaline at room temperature, release acidic substances by reaction with formaldehyde generated by heating or methylol groups in phenolic resins, and promote curing. And urea derivatives.

  Furthermore, a urea adduct is one in which an acid is entrapped in a very stable crystal structure at room temperature and acts as an acid for the first time at a melting point close to the heat treatment temperature. Examples include urea salicylate adduct, urea stearate adduct or urea heptanoate adduct.

  These acids or acidic substances, or compounds that liberate acid at high temperatures, for example, are added in advance to a stringing bath or by a method such as spraying an aqueous solution before heat treatment, etc. Is used.

  Furthermore, when the phenol resin used is a novolak type phenol resin, it is necessary to perform a curing treatment with an aldehyde in the presence of a catalyst. For this purpose, for example, it is common to cure by heating in a liquid phase in the presence of an acidic catalyst such as hydrochloric acid and formaldehyde, but it may be performed by heating in a gas phase. Furthermore, after treatment with an aldehyde in the presence of an acidic catalyst, a method of subsequently curing with an aldehyde in the presence of a basic catalyst such as ammonia, and further after the above normal curing reaction, after washing and drying, A known curing treatment such as curing by heating at a temperature of 100 ° C. to 300 ° C. in an inert gas such as nitrogen, helium, or carbon dioxide can be performed.

  As the phenolic resin, either a novolak type or a resol type can be used. However, as described above, the novolak type requires a time-consuming curing process compared to the resol type, and further, during this curing reaction, an acid or There are limitations such as selection of a fiber-forming polymer compound that is not easily altered by the base and that can supply the reaction solution to the internal phenol resin. It is desirable to use a resol type in consideration of the ease of the process for industrial production and versatility.

  In drying, it is effective to attach a mineral oil or a hydrophobic oil such as silicon or fluorine before drying so that the yarns do not stick together.

  By the above operation, a composite fiber composed of a graphitizable carbon source and a non-graphitizable carbon source that is a precursor of the activated carbon fiber targeted by the present invention can be obtained. The composite fiber obtained by the present invention is characterized in that each component is mixed in a uniform and fine state by a common solvent. The form of the composite fiber can be freely selected according to the purpose of use. For example, there is no problem in selecting a form such as staple or tow that is convenient for processing on fabric, knitted fabric, felt, paper, etc., or performing a crimping process so that processing is easy. .

  Subsequently, in order to use the obtained composite fiber as activated carbon fiber, it is necessary to perform carbonization. In the present invention, it is important to maintain the fiber shape. For this purpose, a so-called solid phase carbonization reaction is required, and for this purpose, infusibilization is performed prior to carbonization. Of each component, the phenol resin component has already been heat infusible as described above. In the infusibilization step of the fiber-forming polymer compound that is a non-graphitizable or easily graphitizable carbon source other than the phenol resin, it is treated in an oxidizing atmosphere, usually in air at 150 to 400 ° C., preferably 250 to 350 ° C. It is done by doing. By this reaction, a cross-linking reaction by oxygen proceeds between the molecules of the fiber-forming polymer compound in the composite fiber. At this time, if the infusibilization temperature is less than 200 ° C., it is not suitable because the crosslinking reaction due to oxidation hardly proceeds. On the other hand, if the temperature exceeds 400 ° C., the carbonization yield is drastically reduced by the carbonization combustion reaction, which is not suitable. Since the heating temperature required for infusibilization and the treatment time differ depending on the composition of each resin in the composite fiber, they may be determined by preliminary experiments.

  Next, carbonization is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere at this time is preferably an atmosphere of an inert gas such as nitrogen, argon, helium, xenon, or neon, or a mixed gas thereof. The carbonization temperature is 300 ° C to 2000 ° C, preferably 500 ° C to 1000 ° C. The treatment time is generally 10 minutes to 30 hours.

  Next, activated carbon fibers can be obtained by activating the carbon fibers. This activation step can be performed by either gas activation or chemical activation. In the case of the gas activation method, activated carbon fibers can be obtained by introducing water vapor, air, or an oxidizing gas in which these are mixed. Apart from this, the presence of alkali metal compounds such as sodium hydroxide and potassium hydroxide, alkaline earth metal compounds such as calcium hydroxide, inorganic salts such as boric acid, phosphoric acid, sulfuric acid and hydrochloric acid, and inorganic salts such as zinc chloride Although a chemical activation method that activates below is also possible, as a means for more effectively exhibiting the characteristics of the activated carbon fiber of the present invention, in particular, alkali activation by mixing and firing an alkali metal compound and carbon fiber The method is preferred. The alkali metal compound may be a carbonate such as potassium carbonate or sodium carbonate, but one of alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, cesium hydroxide, lithium hydroxide or a mixture thereof is used. In general, potassium hydroxide is most preferred. In the alkali activation method, the alkali metal compound is mixed at a weight ratio of 1 to 4 times, preferably 1.2 to 2.5 times, more preferably 1.5 to 2.3 times with respect to the carbon fiber. Is held in a non-oxidizing atmosphere at a temperature of 600 ° C. to 1000 ° C., preferably 700 to 950 ° C. for 1 to 20 hours, preferably 2 to 7 hours. Under the above-mentioned conditions, the alkali metal compound erodes the carbon fiber violently and forms activated carbon fiber having a porous structure while releasing carbon monoxide and carbon dioxide.

  When alkali activation is performed, it is desirable that the generated activated carbon fiber is washed with water to remove the remaining alkali component, and further neutralized with a dilute acid, and then sufficiently washed with water again.

  In the present invention, it is possible to use either a chemical activation method represented by a gas activation method or an alkali activation method, but a method of processing these in combination is also possible.

  The above-described method is an example in which the composite fiber is once converted to carbon fiber and then activated carbon fiber again. However, there is no problem even if carbonization and activation are continuously performed.

Through the above activation process, the activated carbon fiber has a specific surface area of 300 to 3000 m ² / g.

  In the present invention, it is easy to process into various forms by taking advantage of the fiber form, and it can be made into woven fabric, knitted fabric, felt, paper, and the like. In this case, activated carbon fiber cloth, knit, paper, etc. can be easily obtained by making various forms using the composite fiber before carbonization and then carbonizing or further activating it.

  In the present invention, this activated carbon fiber is used as an electrode material to form an electric double layer capacitor. The method for producing the electrode is not particularly limited, and a known conventional method can be used. For example, a method of mixing an activated carbon fiber with a binder such as polyethylene, polytetrafluoroethylene, or polyvinylidene fluoride and making a raw material for forming an electrode is applicable. Although it is the shape of the activated carbon fiber to be used, it can be used in a shape such as milled or pulverized from one having a fiber shape in an activated state. Adding a conductive auxiliary material such as flaky graphite or carbon black to the electrode molding raw material is also an effective means for improving the conductivity.

  Next, this electrode forming raw material is formed according to the purpose. Conventionally used methods such as a press method and a roll rolling method can be used to form a plate, but in practice, the electrode material is most preferably a paper having a low internal resistance. The thickness is usually 0.1 to 5 mm, most preferably 0.3 to 3 mm. The electrode forming raw material thus formed can be pressure-bonded onto a metal foil, which is a current collector, via a conductive binder or the like, whereby a current collector-integrated electrode can be produced.

  Furthermore, as described above, activated carbon fiber cloth, knit, paper, and the like can be easily produced, and therefore, a technique that can greatly shorten the process, such as directly bonding them to a current collector, can be employed.

  When using the activated carbon fiber in the present invention, compared to the method using activated carbon such as normal granular, powdered or spherical, the amount of contact between the fibers is high, the conductivity is high, and the amount of conductive auxiliary material used can be reduced. it can. When powdered or granular or spherical activated carbon is used, it is customary to use about 10 to 20% by weight of conductive auxiliary material in all components, but in the present invention, about 1 to 5% of conductive auxiliary material is sufficient. In some cases, for example, when an activated carbon fiber cloth is used, no conductive auxiliary material is used. Reducing the amount of conductive auxiliary material that does not contribute to the electrostatic capacity makes it possible to increase the density of the electrodes, and the effect is extremely great.

  The current collector of the electrode must be electrochemically resistant to the electrolytic solution, but is not particularly limited, and general aluminum foil, stainless steel foil, copper foil, titanium foil Tantalum foil, nickel foil, etc. can be used.

  The electrode material obtained in this way is cut into a predetermined size and shape according to the application, and inserted into an outer container with a separator in between. As the separator, for example, a microporous polypropylene, a polyethylene film, or polypropylene, a polyethylene nonwoven fabric, or the like can be used. An electric double layer capacitor unit cell can be made through a process of injecting and sealing the electrolyte into this. The electrolytic solution that can be used in the present invention may be an aqueous electrolytic solution or an organic electrolytic solution. As an aqueous electrolyte, dilute sulfuric acid is generally used because of its availability and capacity when used as a capacitor, but other inorganic salts such as tetrafluoroboric acid, nitric acid, sodium hydroxide, potassium hydroxide, water Ammonium oxide can also be used. As an organic electrolyte, propylene carbonate is used as a solvent, and tetraethylammonium tetrafluoroborate, tetraethylphosphonium tetrafluoroborate, methyltriethylammonium tetrafluoroborate, lithium perchlorate, etc. are suitable as an electrolyte. Used. In addition, γ-butyrolactone, dimethyl sulfoxide, dimethylformamide, dimethoxyethane, ethylene carbonate, acetonitrile, tetrahydrofuran, etc. can be used alone or as a mixture of two or more as the solvent, and as the electrolyte, various metals other than those exemplified above can be used. Salts formed by cations such as ions, quaternary ammonium cations and quaternary phosphonium cations and various anions can be used. Regardless of the aqueous electrolyte system or the organic electrolyte system, the concentration of each electrolyte can be appropriately selected within a range of 5 to 95%.

  The activated carbon fiber used in the electric double layer capacitor of the present invention is not simply a mixture of activated carbon composed of graphitizable carbon and activated carbon composed of non-graphitizable carbon. It is characterized by the fact that it is uniformly mixed at an extremely fine level to form an activated carbon fiber. Therefore, when used as an electrode material for electric double layer capacitors, it is difficult to graphitize when it expands and contracts during charging and discharging. The activated carbon made of carbon surrounds the periphery of the activated carbon made of graphitizable carbon, thereby suppressing the expansion of the activated carbon made of graphitizable carbon and reliably suppressing the breakage.

  For this reason, the activated carbon fiber of the present invention is an activated carbon fiber having both advantages of an easily graphitizable carbon source and a non-graphitizable carbon source, and suppresses expansion of the electrode during use by using this as an electrode material. It is possible to manufacture a high-capacity electric double layer capacitor excellent in durability against repeated charging and discharging if possible.

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to only these examples.
[Measurement and sample preparation]
In this example, the specific surface area of the activated carbon is measured by B.sub.2 adsorption by nitrogen adsorption under liquid nitrogen temperature conditions. E. According to the T method.
In addition, the capacitance was obtained by cutting the electrode sheets obtained in Examples and Comparative Examples into 10 mm × 10 mm, and facing the two sheets through an insulating porous separator, and impregnating the electrolyte. Then, both outer sides were sandwiched with platinum as a current collector to produce an electric double layer capacitor, which was used as a sample for measuring capacitance. The sample was dimensioned before starting the measurement.

[Example 1]
Charge 400 g of phenol and 440 g of 50% formalin into a reaction vessel, add 74 g of 25% aqueous ammonia and react at 60 ° C. for 3 hours, then dehydrate until the internal temperature of the reaction mixture rises to 80 ° C. under reduced pressure of 80 mmHg. Concentration reaction was performed, and the resol-type phenol resin (solid content 55%) which was liquid at normal temperature was kept as it was at 80 ° C. and 80 mmHg.
Next, polyacrylonitrile having a molecular weight of 200,000 was placed in dimethylformamide so that the solid content ratio would be polyacrylonitrile resin: resole type phenol resin = 40: 60, and stirred at room temperature for 1 hour, and then stirred at 80 ° C. for 1 hour in a nitrogen stream. It cooled after confirming that it melt | dissolved completely. This was extruded as a spinning stock solution into a dimethylformamide aqueous solution having a dimethylformamide concentration of 10 wt% and 25 ° C. while maintaining a constant discharge rate from a spinneret having a hole diameter of 0.1 mm and a hole number of 80. The number of rotations of the winding roller was adjusted so that the draw ratio was 2 to 3 in the coagulation bath. The immersion time in the coagulation bath was about 60 seconds. The wound spool is further stretched twice in a 5 wt% dimethylformamide aqueous solution at 50 ° C, then air-dried for 5 minutes at room temperature while maintaining the tension state, and further subjected to a dry heat treatment at 130 ° C for 30 minutes. Went.
The obtained composite fiber was treated in air at 350 ° C. for 10 minutes to make it infusible. Next, this was put into a carbonization furnace, heated from a normal temperature to 700 ° C. at a rate of 5 ° C./min in a nitrogen stream, further maintained at 700 ° C. for 30 minutes, and then cooled to 100 ° C. in a nitrogen stream and taken out. .
The taken-out carbon fiber was put into a high-purity alumina crucible, mixed with 200 parts by weight of potassium hydroxide with respect to 100 parts by weight of carbon fiber, heated to 750 ° C. at a rate of temperature increase of 4 ° C./min under a nitrogen stream, Furthermore, the activation was completed by holding at 750 ° C. for 2 hours. The obtained activated carbon fibers were sufficiently washed with pure water, neutralized by immersion in 0.3% hydrochloric acid at room temperature for 5 minutes, and then further thoroughly washed with pure water. After washing, the activated carbon fiber was vacuum dried at 200 ° C. for 2 hours. The fine phenol resin fibers thus obtained were pulverized with a test cutter mill so that the fiber length was about 1 mm, and 2% by weight of acetylene black was added as a conductive aid, and 7% of polytetrafluoroethylene was added as a binder. After weight percent was added and kneaded in a mortar, it was rolled to a thickness of 1 mm, and a capacitance measurement sample was prepared as described above [Measurement and Sample Preparation].
This electrode was completely immersed in a propylene carbonate solution of tetraethylammonium tetrafluoroborate having a concentration of 1 mol / L to prepare a test cell.
A charge voltage of 2.3 V was applied to the test cell, and charging and discharging were repeated 20 times at a current density of 40 mA / g. The capacitance was determined from the average value of the discharge energy from the 10th time to the 20th time. The measurement results are shown in Table 1.

[Example 2]
Charge 400 g of phenol and 440 g of 50% formalin into a reaction vessel, add 74 g of 25% aqueous ammonia and react at 60 ° C. for 3 hours, then dehydrate and concentrate under reduced pressure of 80 mmHg until the internal temperature of the reaction mixture rises to 80 ° C. The reaction was further performed, and the mixture was kept as it was at 80 ° C. and 80 mmHg to obtain a transparent liquid resol type phenol resin (solid content: 80%) at room temperature. Next, 100 g of cellulose diacetate having an acetylation degree of 55% and a polymerization degree of 120 is placed in 900 g of acetone and stirred at room temperature for about 1 hour, followed by stirring and mixing for 30 minutes while maintaining at 60 ° C. in a flask equipped with a reflux condenser. It was confirmed that it was dissolved, and cooled to obtain a cellulose diacetate solution (solid content 10%). Furthermore, a vinyl chloride-vinyl acetate copolymer (Solvine C5 manufactured by Nissin Chemical Industry, vinyl chloride: vinyl acetate = 75 wt%: 25 wt%, polymerization degree 400) was prepared.
The above-mentioned resol-type phenolic resin and vinyl chloride-vinyl acetate copolymer are mixed in an acetone solution of a cellulose diacetate solution (solid content: 10%). The weight ratio of the solid content is cellulose diacetate: phenol resin: vinyl chloride-vinyl acetate. It added so that it might become a polymer = 40: 40: 20, and it stirred with the small homogenizer, and obtained the uniform slightly yellow emulsion mixed liquid.
Next, this was extruded into an acetone aqueous solution having an acetone concentration of 5 wt% and 10 ° C. while maintaining a constant discharge amount from a spinneret having a hole diameter of 0.07 mm and a hole number of 50. The number of rotations of the winding roller was adjusted so that the draw ratio was 2 to 3 in the coagulation bath. The immersion time in the coagulation bath was about 60 seconds.
The wound spool is further stretched 3 times in an aqueous solution of 5 wt% acetone at 50 ° C, then air-dried for 15 minutes at room temperature while maintaining the tension state, and further subjected to a dry heat treatment at 120 ° C for 60 minutes. went.
The obtained conjugate fiber was treated in air at 250 ° C. for 20 minutes to make it infusible. Next, this was put into a carbonization furnace, heated at a rate of 5 ° C./min from normal temperature to 700 ° C. in a nitrogen stream, further held at 700 ° C. for 30 minutes, and then cooled to 100 ° C. in a nitrogen stream and taken out. .
The taken-out carbon fiber was put into a high-purity alumina crucible, mixed with 150 parts by weight of potassium hydroxide with respect to 100 parts by weight of carbon fiber, and heated to 700 ° C. at a rate of 5 ° C./min under a nitrogen stream. Furthermore, the activation was completed by maintaining at 700 ° C. for 2 hours. The obtained activated carbon fibers were sufficiently washed with pure water, neutralized by immersion in 0.3% hydrochloric acid at room temperature for 5 minutes, and then further thoroughly washed with pure water. After washing, the activated carbon fiber was vacuum dried at 200 ° C. for 2 hours. The fine phenol resin fiber thus obtained was pulverized with a test cutter mill so that the fiber length was about 1 mm, and 2% by weight of acetylene black was added as a conductive aid, and 7% of polytetrafluoroethylene was added as a binder. After weight percent was added and kneaded in a mortar, it was rolled to a thickness of 1 mm, and a sample for measuring capacitance was prepared as described above [Measurement and Sample Preparation].
This electrode was completely immersed in a propylene carbonate solution of tetraethylammonium tetrafluoroborate having a concentration of 1 mol / L to prepare a test cell. A charge voltage of 2.3 V was applied to the test cell, and charging and discharging were repeated 20 times at a current density of 40 mA / g. The capacity was determined from the average value of the discharge energy at the 10th to 20th times. The measurement results are shown in Table 1.

Example 3
The same resol type phenolic resin as in Example 2 and polyacrylonitrile having a molecular weight of 200,000 were placed in dimethylformamide so that the solid content ratio was polyacrylonitrile resin: resol type phenolic resin = 40: 60, and stirred at room temperature for 1 hour, and then a nitrogen stream The mixture was stirred for 1 hour at 80 ° C. and cooled to confirm that it was completely dissolved.
This solution was spun in an inert atmosphere at a temperature of 180 ° C. using a spinneret having a hole diameter of 1.2 mm and 18 holes. The spinning speed was 200 meters / minute. Subsequently, heat treatment was carried out at 190 ° C. for 20 minutes while maintaining the tension state to obtain a composite fiber.
The obtained conjugate fiber was treated in air at 250 ° C. for 20 minutes to make it infusible. Then, it put into the carbonization furnace, heated up at a speed | rate of 5 degree-C / min from normal temperature to 800 degreeC in nitrogen stream, and also hold | maintained at 800 degreeC for 30 minutes. Next, activation was performed for 180 minutes with water vapor using nitrogen as a carrier, and then the mixture was cooled to 100 ° C. in an air stream and taken out.
Next, 2% by weight of acetylene black, which is a conductive aid, is added to the activated carbon fiber, 5% by weight of polytetrafluoroethylene as a binder, kneaded by a ball mill, and then rolled to a thickness of 1 mm. Measurement and Sample Preparation] A capacitance measurement sample was prepared as described above.
This electrode was completely immersed in a propylene carbonate solution of tetraethylammonium tetrafluoroborate having a concentration of 1 mol / L to prepare a test cell. A charge voltage of 2.3 V was applied to the test cell, and charging and discharging were repeated 20 times at a current density of 40 mA / g. The capacity was determined from the average value of the discharge energy at the 10th to 20th times. The measurement results are shown in Table 1.

Example 4
The same resol type phenolic resin as in Example 2, a 7.5 wt% aqueous solution (0.4 wt% boric acid) of a fully saponified polyvinyl alcohol (polymerization degree 1700), an aqueous vinyl chloride-vinyl acetate copolymer emulsion (Nissin) Vine Blanc 601 manufactured by Kagaku Kogyo Co., Ltd., with a solid content of 43%), added so that the weight ratio of the solid content is phenol resin: polyvinyl alcohol: vinyl chloride-vinyl acetate = 40: 20: 40, and stirred uniformly with a small homogenizer A slightly yellow emulsified mixture was obtained.
Next, this was extruded as a spinning stock solution into a coagulation bath at 40 ° C. composed of 1 wt% sodium hydroxide and 30 wt% sodium sulfate while maintaining a constant discharge rate from a spinneret having a hole diameter of 0.07 mm and 50 holes. The number of rotations of the take-up roller was adjusted so that the draw ratio was 2 to 5 in the coagulation bath. After passing through the coagulation bath, the fiber was washed with water to remove sodium hydroxide adhering to the fiber. Thereafter, air-drying was performed for 15 minutes at room temperature while maintaining a tension state, and further, a heat treatment for 60 minutes was performed at 120 ° C.
The obtained composite fiber was treated in air at 250 ° C. for 20 minutes to be infusibilized, then placed in a carbonization furnace, heated in a nitrogen stream from room temperature to 600 ° C. at a rate of 5 ° C./min, After maintaining at 600 ° C. for 30 minutes, activation was performed with water vapor using nitrogen as a carrier for 20 minutes, and the mixture was cooled to 100 ° C. in a nitrogen stream and taken out.
Next, 2% by weight of acetylene black, which is a conductive aid, is added to the activated carbon fiber, 5% by weight of polytetrafluoroethylene as a binder, kneaded by a ball mill, and then rolled to a thickness of 1 mm. Measurement and Sample Preparation] A capacitance measurement sample was prepared as described above.
This electrode was completely immersed in a propylene carbonate solution of tetraethylammonium tetrafluoroborate having a concentration of 1 mol / L to prepare a test cell. A charge voltage of 2.3 V was applied to the test cell, and charging and discharging were repeated 20 times at a current density of 40 mA / g. The capacity was determined from the average value of the discharge energy at the 10th to 20th times. The measurement results are shown in Table 1.

[Comparative Example 1]
Under the same conditions as in Example 1 except that a commercial phenol resin fiber (trade name, Kynol KF0270M fiber diameter 14μ) was carbonized and activated under the same conditions as in Example 1 instead of the composite fiber in this test. Table 1 shows the results of creating and measuring a sample for measuring capacitance.

[Comparative Example 2]
Table 1 shows the results of measurement using a commercially available coconut shell activated carbon prepared under the same conditions as in Example 1 and measuring the volume.

[Comparative Example 2]
A petroleum pitch having a softening point of 300 ° C., which is an easily graphitized carbon source, is pulverized to an average particle size of 250 μm using a ball mill, and heated to 350 ° C. at a heating rate of 1 ° C./min in a rotary kiln in an air atmosphere. Hold for a minute to make it infusible. The infusible pitch powder was heated to 900 ° C. at a rate of temperature increase of 5 ° C./min under a nitrogen stream and held for 2 hours to obtain carbide. This carbide was put into a high-purity alumina crucible and subjected to activation, washing, neutralization and washing under the same conditions as in Example 2. Further, as in Experiment 2, 2% by weight of acetylene black was added as a conductive additive, 7% by weight of polytetrafluoroethylene was added as a binder, kneaded in a mortar, and then rolled to a thickness of 1 mm. Samples for capacitance measurement were prepared as described in [Sample preparation].
This electrode was completely immersed in a propylene carbonate solution of tetraethylammonium tetrafluoroborate having a concentration of 1 mol / L to prepare a test cell. A charge voltage of 2.3 V was applied to the test cell, and charging and discharging were repeated 20 times at a current density of 40 mA / g. The capacity was determined from the average value of the discharge energy at the 10th to 20th times. The measurement results are shown in Table 1.

Claims (6)

  A composite fiber comprising a fiber-forming polymer compound that is a graphitizable carbon source and a fiber-forming polymer compound that is a non-graphitizable carbon source is an activated carbon fiber, and this is used as an electrode material. Multilayer capacitor.   The fiber-forming polymer compound that is a graphitizable carbon source is at least one selected from polyacrylonitrile, polyvinyl butyral, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and copolymers thereof. The electric double layer capacitor according to claim 1.   The fiber-forming polymer compound that is a non-graphitizable carbon source is at least one selected from a phenol resin, polyvinyl alcohol, cellulose diacetate, cellulose triacetate, and copolymers thereof. 2. The electric double layer capacitor according to 1.   At least one fiber-forming polymer compound that generates non-graphitizable carbon when heated by a non-graphitizable carbon source, at least one fiber-forming polymer that generates graphitizable carbon when heated by a graphitizable carbon source A compound obtained by dissolving a compound in a common solvent is used as a spinning stock solution, and after spinning, the composite fiber obtained by curing is carbonized and activated, and activated carbon fiber is used as an electrode material. A method for producing an electric double layer capacitor, characterized by being used as:   5. The weight ratio of the non-graphitizable carbon source to the graphitizable carbon source in the composite fiber is in the range of non-graphitizable carbon source: graphitizable carbon source = 95: 5 to 20:80. The manufacturing method of the electrical double layer capacitor as described in 2 ..   Among the non-graphitizable carbon sources in the composite fiber, the weight ratio of the phenol resin and the other non-graphitizable carbon source is in the range of phenol resin: other non-graphitizable carbon source = 100: 0-20: 80. The method for producing an electric double layer capacitor according to claim 4.