JP2008053541A - Electrode active material for electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode active material for an electric double-layer capacitor in which irreversible capacitance or internal resistance of the electrical double-layer capacitor is not increased even when electrolytic activation is performed. <P>SOLUTION: An electrode active material for an electric double-layer capacitor is composed of a plurality of non-porous carbon particles each including crystallite carbon similar to graphite, wherein the non-porous carbon grain has a grain size of ≥3 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode active material for an electric double layer capacitor in which a non-porous carbonaceous electrode is immersed in an organic electrolyte.

  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 non-porous carbon has a microcrystalline carbon similar to graphite, has a specific 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 ammonium such as tetraethylammonium, tetrabutylammonium, and triethylmethylammonium, lower aliphatic quaternary phosphonium 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.

  An electric double layer capacitor formed by immersing a non-porous carbonaceous electrode in an organic electrolyte exhibits charge / discharge characteristics different from those using activated carbon as the carbonaceous electrode. The charge / discharge characteristics are described in Non-Patent Document 1, pages 77 to 81, for example. FIG. 1 is a graph showing an example of a behavior in which the voltage changes with time when constant current charging and discharging are repeated for this type of electric double layer capacitor (Non-Patent Document 1, page 80, FIG. 3- (Quoted from 15).

  In the charge / discharge curve of FIG. 1, the voltage rises in a short time during the first constant current charge, and the voltage rise suddenly slows from 2.2V. In the constant current charging curve, since the capacitance is represented by the slope, the above curve shows that the capacitance is small at the initial stage of charging, and the capacitance appears substantially from 2.2V.

  On the other hand, in the second and subsequent charging, the voltage increases monotonously, and a certain capacitance is obtained from the beginning of charging as in the case of the conventional activated carbon electrode. In other words, once this type of electric double layer capacitor experiences a voltage, the capacitance increases and a large capacitance can be obtained.

  Patent Documents 4 and 5 describe an electrolytic activation method for an electric double layer capacitor. “Electrolytic activation” refers to an initial charging process of this type of electric double layer capacitor, that is, a process in which a non-porous carbonaceous electrode first experiences a voltage. It is expressed in this way on the assumption that the first charging process plays the role of activating the electrostatic capacity. This document describes that the electrolytic activation conditions are optimized to increase the capacitance of the electric double layer capacitor.

  However, it is desired to further improve the characteristics of the electric double layer capacitor in order to be used practically as an auxiliary power source for an electric vehicle, a battery, a power generation device and the like.

  The present inventors have found a new problem peculiar to this type of electric double layer capacitor. That is, when the particle diameter of the non-porous carbon particles is reduced, the negative electrode side is deeply charged during the electroactivation, resulting in an increase in irreversible capacity and an increase in internal resistance.

JP 11-317333 A JP2002-25867 JP 2000-77273 A JP 2000-277397 A JP 2001-223143 A Ikuo Okamura "Electric Double Layer Capacitor and Power Storage System" 3rd Edition, Nikkan Kogyo Shimbun, 2005 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 an electrode active material for an electric double layer capacitor that does not increase the irreversible capacity and internal resistance of the electric double layer capacitor even when electrolytic activation is performed. Is to provide.

The present invention relates to an electrode active material for an electric double layer capacitor comprising a plurality of non-porous carbon particles having microcrystalline carbon similar to graphite.
An object of the present invention is to provide an electrode active material for an electric double layer capacitor in which the non-porous carbon particles have a particle diameter of 3 μm or more, whereby the above object is achieved.

  When the electrode active material for an electric double layer capacitor of the present invention is used, an electric double layer capacitor in which irreversible capacity and internal resistance do not increase even when electrolytic activation is performed can be obtained.

  The electric double layer capacitor that is the subject of the present invention is an electric double layer capacitor that exhibits a behavior in which the capacitance increases when voltage is experienced. Generally, the electric double layer is formed by immersing a non-porous carbonaceous electrode in an organic electrolyte. It is a capacitor.

  A non-porous carbonaceous electrode is a carbonaceous electrode formed using non-porous carbon as an electrode active material. 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 heavy petroleum oil obtained at the time of petroleum distillation is subjected to high-temperature pyrolysis, a carbonaceous electrode 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 the alkali metal vapor penetrates the carbon structure and has the effect of loosening 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 ° C. 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 the 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 adjust the particle size. The obtained carbon powder is composed of a plurality of non-porous carbon particles having microcrystalline carbon similar to graphite. The carbon powder in this state has a particle size distribution and includes non-porous carbon particles having a relatively small particle size.

  Therefore, if the carbon powder in this state is used as it is as an electrode active material, the irreversible capacity of the electric double layer capacitor may increase or the internal resistance may increase when electrolytic activation is performed. In order to avoid this, the particle size of the non-porous carbon particles contained in the carbon powder needs to be adjusted to a predetermined value or more. Specifically, the particle diameter of the non-porous carbon particles is adjusted to 3 μm or more, preferably 4 μm or more, more preferably 5 μm or more.

  The particle diameter of the nonporous carbon particles is generally adjusted to 100 μm or less, preferably 80 μm or less, more preferably 50 μm or less. If the particle size of the non-porous carbon particles exceeds 100 μm, the thickness of the carbonaceous electrode becomes non-uniform and the capacity of the electric double layer capacitor is reduced. Further, the surface roughness is deteriorated and the self-discharge is increased.

  Adjustment of the particle diameter of the non-porous carbon particles may be performed by classifying the carbon powder. Although the classification method is not particularly limited, a screening test method (JIS Z 8815), an airflow classification method, or the like is used. In order to remove fine particles having a particle diameter of less than 3 μm from the carbon powder, for example, an airflow classifier may be used. Further, in order to remove coarse particles having a particle diameter exceeding 60 μm from the carbon powder, for example, an ultrasonic vibration sieve or a pulverizing classifier may be used.

  For example, carbon black as a conductive auxiliary agent for imparting conductivity to the carbon powder (ie, electrode active material) having a particle diameter adjusted as described above, and polytetrafluoroethylene (PTFE) as a binder, for example. Are kneaded and formed into a sheet by pressure drawing.

  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 can be used for an electric double layer capacitor having a conventionally known structure. The structure of the electric double layer capacitor is shown, for example, in FIGS. 5 and 6 of Patent Document 1, FIG. 6 of Patent Document 2, FIGS. 1 to 4 of Patent Document 3, and the like. In general, such an electric double layer capacitor can be assembled by impregnating an electrolytic solution after forming a positive electrode and a negative electrode by superposing sheet-like carbon electrodes via a separator.

  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 preferably, 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 1
The potassium hydroxide pellets were pulverized in advance with a mill to obtain powder. Nippon Steel-made coal-based needle coke green powder (NCGP) was calcined at about 800 ° C. for 3 hours while being naturally cooled 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.

This carbon was pulverized with 10 mmφ alumina balls for 1 hour using a ball mill (AV-1 manufactured by Fujiwara Seisakusho). Then, pulverization and classification were performed using a jet mill (model STJ-200) manufactured by Seishin Corporation. The degree of pulverization was controlled by adjusting the air volume (m ³ / min) and pressure (MPa), and the pulverized powder was recovered with a cyclone (model JCY-20). Moreover, the fine powder part less than 5 micrometers was collect | recovered with the filter cloth. When the particle size distribution was measured with a particle system distribution measuring apparatus (model LA-950) manufactured by HORIBA, it was 3.8 μm to 19.7 μm. The fine particles removed were about 0.4% by weight of the total. 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 between 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 by a press machine to obtain a carbonaceous sheet having a thickness of 200 microns.

This carbonaceous sheet was punched into a 20 mmφ disk and assembled into a three-electrode cell as shown in FIG. The reference electrode used was a sheet of # 1711 activated carbon formed by the same method as above. These cells were dried in a vacuum at 220 ° C. for 24 hours and cooled. An electrolyte solution was prepared by dissolving spirobipyrrolidinium tetrafluoroborate (SBPBF ₄ ) in propylene carbonate so as to be 2.0 mol%. And the obtained electrolyte solution was inject | poured into the cell, and the electrical double layer capacitor was produced.

Measurement of charge / discharge efficiency during electric field activation The electric double layer capacitor cell obtained was subjected to constant current and constant voltage charging under the conditions of rated current (1 mA / cm ² ) and rated voltage (3.7 V). The current capacity spent at that time is Eid. Next, the battery was discharged to 0 V at the rated current. Let Eic be the current capacity at that time. The charge / discharge efficiency was calculated by the following formula. The results are shown in Table 1.
Charging / discharging efficiency (%) = Eic / Eid × 100

Measurement of Capacitance and Internal Resistance Next, three cycles of charge / discharge were performed under the conditions of a rated current (1 mA / cm ² ) and a rated voltage (3.5 V).
The capacitance at the third cycle was determined by a method of obtaining from the integrated discharge power called the energy conversion method, and the value divided by the sum of the volumes of the polarizable electrodes of both electrodes was adopted as the volume density (F / cc). As the initial internal resistance, a value obtained by dividing the voltage drop in the state in which the current immediately after the start of discharge was divided by the discharge current at that time was adopted. The charging conditions and the measurement results are shown in Table 1.

Example 2
An electric double layer capacitor was prepared and tested in the same manner as in Example 1 except that the particle size of the carbon powder was adjusted to 4.2 to 32.8 μm. The results are shown in Table 1.

Example 3
An electric double layer capacitor was prepared and tested in the same manner as in Example 1 except that the particle diameter of the carbon powder was adjusted to 5.3 to 46.8 μm. The results are shown in Table 1.

Comparative Example An electric double layer capacitor was prepared and tested in the same manner as in Example 1 except that fine particles having a particle diameter of less than 3 μm were not removed. The results are shown in Table 1.

[ Table 1]

It is an assembly drawing which shows the structure of the electric double layer capacitor of an Example.

Explanation of symbols

1, 11 ... Insulating washer,
2 ... Top cover,
3 ... Spring,
4, 8 ... collector electrode,
5, 7 ... carbonaceous electrode,
6 ... separator,
9 ... Guide,
10, 13 ... O-ring,
12 ... the body,
14 ... Presser plate,
15 ... Reference electrode,
16 ... Bottom cover.

Claims (5)

In an electrode active material for an electric double layer capacitor comprising a plurality of non-porous carbon particles having microcrystalline carbon similar to graphite,
An electrode active material for an electric double layer capacitor, wherein the non-porous carbon particles have a particle diameter of 3 μm or more.   The electrode active material for electric double layer capacitors according to claim 1, wherein the non-porous carbon particles have a particle diameter of 3 to 60 μm. In an electric double layer capacitor in which a carbonaceous electrode containing an electrode active material is immersed in an organic electrolyte,
An electric double layer capacitor, wherein the electrode active material is the electrode active material according to claim 1. Preparing a plurality of non-porous carbon particles having graphite-like microcrystalline carbon; and adjusting the particle size of the non-porous carbon particles to 3 μm or more;
A method for producing an electrode active material for an electric double layer capacitor. The method according to claim 4, wherein a particle diameter of the non-porous carbon particles is adjusted to 3 to 60 μm.

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