JP2008166544A - Non-porous carbon having adjusted ignition loss and electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of improving characteristics such as capacitance of an electric double-layer capacitor. <P>SOLUTION: The non-porous carbon having fine crystals similar to graphite having ignition loss of 5-18% is manufactured by a method including: a pre-baking step of baking an easily graphitized carbon at 800-1,000°C for 2-8 hours under an inert atmosphere: an alkali activation step of mixing the baked powder with alkali hydride powder of a quantity of 1-5 times by weight ratio, and baking the powder mixture at 600-900°C for 2-8 hours under an inert atmosphere; a step of cleaning the activated powder mixture to remove the alkali hydride; and a post-baking step of baking the obtained carbon powder at 200-800°C for 2-8 hours under an inert atmosphere. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor in which a polarizable electrode is immersed in non-porous carbon having a crystallite-like microcrystal and 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.

Patent Document 1 describes nonporous carbon as a polarizable electrode used in an electric double layer capacitor. This carbon material has graphite-like microcrystals and a specific surface area of 300 m ² / g or less, which is relatively small. It is considered that an electrode containing non-porous carbon forms an electric double layer by inserting an electrolyte ion between fine graphite-like microcrystal layers with a solvent when a voltage is applied.

  Patent Document 2 describes that a polarizable 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 an electrode containing nonporous carbon 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 imidazolium 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 obtained by immersing an electrode containing non-porous carbon in an organic electrolyte exhibits different charge / discharge characteristics as compared with an electric double layer capacitor using activated carbon as an electrode active material. 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 within a short time during the first constant current charge starting from 0 V, and the voltage rise suddenly slows from about 2.2 V. In other words, the slope (dV / dt) is substantially constant before about 2.2V, decreases sharply at about 2.2V, and becomes substantially constant again after about 2.2V. It has become.

  In the constant current charging curve, the capacitance corresponds to the slope of the curve. A high slope value means a low capacitance, and a low slope value means a high capacitance. Then, the first constant current charging curve in FIG. 1 shows that the electrostatic capacity is small at the initial stage of charging, and the electrostatic capacity is substantially developed from about 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.

  However, in order to put it into practical use as an auxiliary power source for electric vehicles, batteries, power generators, etc., it is desired that electric double layer capacitors further improve characteristics such as capacitance.

JP 2005-286178 A JP2002-25867 JP 2000-77273 A Ikuo Okamura "Electric Double Layer Capacitor and Power Storage System" 3rd Edition, Nikkan Kogyo Shimbun, 2005

  The present invention solves the above-mentioned conventional problems, and its object is to provide characteristics such as capacitance of an electric double layer capacitor in which a polarizable electrode containing non-porous carbon is immersed in an organic electrolyte. Is to improve.

The present invention is a pre-firing step of calcining graphitizable carbon at 800 to 1000 ° C. for 2 to 8 hours in an inert atmosphere;
An alkali activation step in which the calcined powder is mixed with 1 to 5 times the weight of the alkali hydroxide powder and the powder mixture is calcined at 600 to 900 ° C. for 2 to 8 hours in an inert atmosphere;
A step of washing the activated powder mixture to remove alkali hydroxide; and a post-baking step of baking the obtained carbon powder at 200 to 800 ° C. for 2 to 8 hours in an inert atmosphere;
And non-porous carbon having graphite-like microcrystals with a loss on ignition of 5 to 18%.

  The present invention provides a polarizable electrode comprising non-porous carbon having graphite-like microcrystals obtained by this method.

  Furthermore, the present invention provides an electric double layer capacitor in which this polarizable electrode is immersed in an organic electrolyte.

  The non-porous carbon of the present invention has a low electrostatic capacity expression voltage. Therefore, even when an electrolyte having a relatively large ion size is used, the capacity can be expressed by electrolytic activation as in the case of using an electrolyte having a relatively small ion size. In addition, the electric double layer capacitor using non-porous carbon has an increased capacitance, and has improved durability and voltage resistance.

  In the present specification, the “capacitance expression voltage” refers to a voltage at which an electrostatic capacity develops during the first constant current charge, and is represented by the symbol “Ve”. Ve is an important characteristic value related to the capacity development of non-porous carbon.

  The expression of the electrostatic capacity is shown as the point at which the charging curve starts to depart from the imaginary line that overlaps the initial voltage rising from 0 V in the initial constant current charging curve. However, depending on the shape of the constant current charging curve, it may be difficult to clearly read that point.

In such a case, the voltage change is recorded over time while charging the constant current constant voltage (CCCV) of the electric double layer capacitor under a predetermined charging condition, and the curvature is increased in the process of increasing the voltage of the obtained charging curve. It is good also as that the electrostatic capacitance was expressed when became maximum. That is, at the initial stage of charging when the CCCV charging curve is rising, the voltage at the point where the curvature is maximum may be regarded as the electrostatic capacity expression voltage (Ve). The predetermined charging condition is a charging current of 1 mA / cm ² as in the embodiment. The initial charging period is, for example, up to 10,000 seconds after starting charging, preferably up to 5000 seconds, more preferably up to 3000 seconds, and further preferably up to 2000 seconds. Ve may be determined by performing preliminary measurement in advance.

  In the present invention, the term “electrode including nonporous carbon” means a polarizable electrode formed using nonporous carbon as an electrode active material (active ingredient). Preferred non-porous carbon is carbon powder obtained by heat-treating a carbon raw material in an inert atmosphere and further heat-treating in the presence of an alkali hydroxide powder and / or an alkali metal. As the carbon raw material, graphitizable carbon generally called soft carbon can be used. The graphitizable carbon may be carbon that is graphitized by heating. For example, coke green powder, mesophase carbon, infusible vinyl chloride and the like correspond to graphitizable carbon.

  For example, a graphite precursor obtained by removing quinoline insolubles from a soft pitch of coal and carbonizing using a refined raw material may be used as the carbon raw material. Although the reason is not clear, such a graphite precursor contains trace elements such as nitrogen and sulfur, and is considered to have an appropriate elemental composition.

  In producing the non-porous carbon of the present invention, for example, the graphitizable carbon is first prepared. The center particle diameter of graphitizable carbon is 10 to 5000 μm, preferably 10 to 100 μm. Further, the ash content in the polarizable electrode affects the generation of surface functional groups, and it is important to reduce it. The graphitizable carbon used in the present invention is 70 to 98% fixed carbon and 0.05 to 2% ash. Preferably, it has the characteristics that fixed carbon is 80 to 95% and ash content is 1% or less.

  The powdery graphitizable carbon is first fired in an inert atmosphere, for example, in an atmosphere of nitrogen or argon for 2 to 8 hours. This firing process is called a pre-baking process. The pre-baking temperature is adjusted so that the furnace temperature is 800 to 1000 ° C. At this time, it is considered that the crystal structure of the carbon structure peculiar to the present invention is formed by the temperature and heat applied to the graphitizable carbon. When the pre-baking temperature is less than 800 ° C., the alkali activation proceeds excessively, and when it exceeds 1000 ° C., the alkali activation proceeds insufficiently. A preferable pre-baking temperature is 840 ° C to 960 ° C, more preferably 900 to 950 ° C.

  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 8 hours.

  The pre-fired carbon powder is mixed with an alkali hydroxide having a weight ratio of 1 to 5 times, preferably 1.8 to 2.2 times, more preferably about 1.5 to 2.0 times. The powder mixture is then fired at 600 to 900 ° C. for 2 to 8 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. A preferable alkali activation temperature is 700 to 800 ° C, more preferably 720 to 780 ° C.

  When the amount of the alkali hydroxide is less than 1 time or the firing temperature is less than 600 ° C., the activation does not proceed sufficiently, and the capacity does not appear at the first charge. If the amount of the alkali hydroxide exceeds 5 times or the firing temperature exceeds 900 ° C., the activation proceeds too much and the surface area tends to increase. The specific gravity decreases and the energy density decreases. 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.

  If the material is sufficiently warmed, the firing 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 8 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 about 7 (usually 6 to 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 carbon powder.

  The obtained carbon powder is fired for 2 to 8 hours under an inert atmosphere. This firing process is called a post-baking process. The post-baking temperature is adjusted so that the furnace temperature is 200 to 800 ° C. When post-baking is performed, the functional group on the carbon surface is removed, and the withstand voltage of the electric double layer capacitor is improved. A preferable post-baking temperature is 250 to 600 ° C, more preferably 300 to 500 ° C.

  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 8 hours.

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 that can take in various electrolyte ions, solvents, CO ₂ gas, etc., so-called “non-porous carbon” "are categorized. The specific surface area can be determined by a BET method using CO ₂ as an adsorbent.

  Moreover, this non-porous carbon powder has a low ignition loss. The loss on ignition refers to the mass reduced when the non-porous carbon powder is ignited under predetermined conditions as compared to before ignition. The loss on ignition indicates the amount of volatile components remaining in the non-porous carbon powder. As such a volatile component, an alkali metal atom that has penetrated into the carbon structure during alkali activation can be considered.

  For example, it is appropriate to heat the sample from 300 ° C. to 800 ° C. while raising the temperature at a rate of 5 ° C./min in an atmosphere in which high-purity nitrogen gas is passed. In this case, the loss on ignition of the carbon powder is 20% or less, preferably 3 to 19%, more preferably 5 to 18%. If the ignition loss is outside these ranges, the durability and voltage resistance of the electric double layer capacitor will not be improved.

  The ignition loss of non-porous carbon can be adjusted by appropriately adjusting either the pre-calcining temperature or the post-calcining temperature, preferably the pre-calcining temperature, or both the pre-calcining temperature and the post-calcining temperature. The reason is not clear, but if the pre-baking temperature is low, the crystal structure of the carbon structure becomes coarse, and if it is high, the crystal structure becomes dense, so that the amount of volatile components that penetrate into the carbon structure and are subsequently removed is increased or decreased. It is thought that it is.

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

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

  The produced polarizable 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 FIG. 1 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.

  A preferred 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.

  What is preferable about the cation of a pyrrolidinium compound salt is a thing whose R is each independently a C1-C10 alkyl group or a C3-C8 alkylene group connected together in the said formula. More preferred are those wherein R is an alkylene group having 4 to 5 carbon atoms linked together. Further preferred are those in which R is a butylene group linked together. Such a cation 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 electrode containing nonporous carbon 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 these have a low molecular weight and a simple structure, and the expansion of the electrode containing nonporous carbon on the positive electrode side is suppressed.

  By dissolving the electrolyte in the organic solvent using the electrolyte as a solute, an organic electrolytic solution for an electric double layer capacitor can be obtained. The concentration of the electrolyte 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 electrolyte 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.

  The electrolyte may be used alone or a plurality of types may be mixed. You may use together the electrolyte conventionally used for the organic electrolyte solution. However, the ratio of the electrolyte in the solute is 50% by weight or more, preferably 75% by weight or more of the total solute weight. Among electrolytes, for example, preferable electrolytes for use in combination with pyrrolidinium compound salts include triethylmethylammonium salts and tetraethylammonium salts.

  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-butyrolactone (GBL), sulfolane (SL), and the like are preferable because of their excellent electrolyte solubility 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.

  The electric double layer capacitor of the present invention has a voltage change curve different from the conventional one in the constant current charging process of electric field activation. “Electric field activation” refers to an initial charging process of an electric double layer capacitor formed by immersing an electrode containing non-porous carbon in an organic electrolyte, that is, a process in which a voltage is first experienced by a polarizable electrode. . It is expressed in this way on the assumption that the first charging process plays the role of activating the electrostatic capacity.

FIG. 2 is a graph showing a behavior in which the voltage changes with time when an electric double layer capacitor formed by immersing an electrode containing nonporous carbon in an organic electrolyte is subjected to constant current charging for the first time. It is. At this time, the charging current is 1 mA / cm ² and the end point of the voltage is a voltage (3.7 V) equal to or higher than the rated voltage (3.5 V in this case). Curve b shows the voltage change of the electric double layer capacitor of the present invention, and curves a and c show the voltage change of the conventional electric double layer capacitor.

  In the curve b, the electrostatic capacity expression voltage at which the voltage increase starts to become slow is lower than that in the curve c. Moreover, in the curve b, the bending which shows the expression of an electrostatic capacitance is sharper than the curve a. As shown by the curve b, when the electrostatic capacity expression voltage is relatively low and the bending indicating the expression of the electrostatic capacity is sharp, uniform pores that contribute to the capacity are formed, mainly in the depth direction. Sufficient electric field activation proceeds, and the capacitance of the electric double layer capacitor increases. Further, the durability of the electric double layer capacitor is also improved.

Specifically, when constant current charging at 1 mA / cm ² is performed up to 3.7 V for the first time, the electrostatic capacity expression voltage is 3.3 V or less, 3.2 V or less, less than 3.2 V, preferably 1 0.5 to less than 3.2 V, 1.5 to 3.1 V, 2.0 to 3.0 V, 2.4 to 3.0 V, 2.2 to 2.9 V, and 2.4 to 2.9 V. When the electrostatic capacity expression voltage exceeds 3.3 V, the electrolytic solution is deteriorated, and the electrostatic capacity and durability of the electric double layer capacitor are not sufficiently improved.

  The initial capacitance that develops within the time until the voltage between the electrodes reaches Ve is 12 F / cc or less, 10 F / cc or less, 9 F / cc or less, preferably 8.5 F / cc or less, more preferably 8 F / cc. cc or less. Preferably, the initial capacitance is 1 to 10 F / cc, 3 to 9 F / cc, preferably 4.5 to 9 F / cc, more preferably 5 to 9 F / cc, and 6 to 9 F / cc. When the initial capacitance exceeds 12 F / cc, the bending that indicates the development of the capacitance becomes dull, and the capacitance and durability of the electric double layer capacitor are insufficiently improved.

  In order to clearly express Ve of the electric double layer capacitor and adjust it to a low level of, for example, 1.5 to 3.2 V, preferably 2.0 to 3.0 V, more preferably 2.2 to 2.9 V Is preferably set to a relatively high temperature in the furnace in the pre-baking step. For example, the furnace temperature at the time of pre-baking is suitably set within a range of preferably 840 to 960 ° C, more preferably 900 to 950 ° C.

  The non-porous carbon prepared by the method of the present invention has a low Ve and can be electrolytically activated at a low voltage. This indicates that the pore diameter of the portion where the cation is adsorbed is large in the non-porous carbon. For this reason, the electric double layer capacitor of the present invention can be put to practical use even if a cation having a relatively large ion diameter is used as an electrolyte component, with a small increase in rated voltage (that is, actual use voltage).

  That is, in the electric double layer capacitor of the present invention, even when a cation having a relatively large ionic diameter is used, the capacity is expressed by electrolytic activation as in the case of using an electrolyte having a relatively small ionic diameter such as SBP. Can be made. Further, even when a cation having a relatively large ion diameter is used, the performance such as the capacity of the electric double layer capacitor is equivalent to that when a cation having a relatively small ion diameter is used.

Examples of the cation having a relatively large ion diameter include tetraethylammonium (TEA ⁺ ), tetrabutylammonium (TBA ⁺ ), triethylmethylammonium (TEMA ⁺ ), tetraethylphosphonium (TEP ⁺ ), and 1-ethyl-3-methyl. Examples include imidazolium (EMI ⁺ ). As the anion which is a counter anion of the cation, the same anion as described for SBP can be used.

  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
Production of non-porous carbon Remove quinoline insolubles from the soft pitch of coal, and put graphite precursor powder (made by Nippon Steel Co., Ltd.) carbonized using the refined raw material into an alumina crucible, which is muffled While circulating nitrogen in a furnace, the temperature was raised to 840 to 950 ° C. over 3 hours, followed by firing and natural cooling. Next, the fired product was mixed with 1.5 times the potassium hydroxide powder per weight ratio. Each was put in an alumina crucible and covered with an alumina lid to shut off the outside air.

  While this mixture was circulated with nitrogen in a muffle furnace, the temperature in the furnace was adjusted to 750 ° C., and the mixture was activated for 4 hours. The fired product was taken out, washed lightly with pure water, and then washed by applying ultrasonic waves. The time is 1 minute. The water was then separated using a Buchner funnel. The same washing operation was repeated until the pH of the washing water reached around 7. Then, the washed product was dried with a vacuum dryer.

  The dried carbon powder was put in a crucible, post-fired at 300 ° C. for 10 hours, then taken out and allowed to cool to room temperature.

Production of Capacitor Cell The obtained carbon was pulverized with 10 mmφ alumina balls for 1 hour using a ball mill (AV-1 manufactured by Fujiwara Seisakusho). When the particle size was measured with a Coulter counter, all of them became powdery with a center particle diameter of about 10 microns.

  Powdered carbon (CB) was mixed at a mixing ratio of 10: 1: 1 of acetylene black (AB) and polytetrafluoroethylene powder (PTFE), and kneaded in a mortar. In about 10 minutes, PTFE was stretched and formed into flakes. This was pressed with a press machine to obtain a carbon sheet having a thickness of 300 microns.

The carbo sheet was punched into a 20 mmφ disk and assembled into a three-electrode cell as shown in FIG. This disk contains 83.3% non-porous carbon. 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%. Then, the obtained electrolytic solution was injected into the cell to produce an electric double layer capacitor cell.

Measurement of loss on ignition About 7 mg of non-porous carbon powder prepared as described above before being formed into a polarizable electrode was weighed. This powder was set in a differential thermothermal gravimetric simultaneous measurement apparatus (TG-DTA) manufactured by SII Nanotechnology. As a measurement atmosphere, high purity nitrogen gas was flowed at a flow rate of 200 mL / min. The internal temperature of the differential thermogravimetric simultaneous measurement apparatus was set to 300 ° C. and kept isothermal. Thereafter, constant temperature increase was started at a rate of 5 ° C./min, and the temperature was increased to 1000 ° C. while recording the mass. The weight loss at 800 degrees was adopted as the value of ignition loss. The result was 18.2%.

Measurement of Capacitance Expression Voltage (Ve) The triode cell was charged at a constant current of 1 mA / cm ² up to the rated voltage (3.7 V). A curve b in FIG. 4 shows a voltage change with time in the charging process. When Ve was determined from this curve, it was 2.5V.

Capacitance measurement Among the created capacitor cells, a power system charge / discharge test device “CDT-RD20” is connected to a capacitor cell different from that used for Ve measurement, and constant current charging at 1 mA / cm ² is performed. It went to 3.7V. The initial capacitance developed within the time until the voltage between the electrodes reached the capacitance development voltage was 8.0 F / cc.

Constant current constant voltage charge was performed for 25200 seconds, and constant current discharge was performed at 1 mA / cm ² . Curves b in FIGS. 5 and 6 are graphs showing a behavior in which the voltage changes over time when the obtained electric double layer capacitor is charged and discharged for the first time. Then, 3 cycles of charging / discharging were implemented with the rated voltage of 3.5V.

  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). The results are shown in Table 2.

Measurement of Durability As described in Japan Electronic Machinery Industry Standard EIAJ RC-2377, 3.13, 4.23 (durability) a) (DC test) of JIS C 5101-1 was performed under the following conditions.

[Table 1]

  Thereafter, the volume density of the capacitor cell was obtained again, and the rate of change was adopted as durability. The results are shown in Table 2.

Example 2
Create capacitor cells except be used in an amount of triethyl methyl ammonium tetrafluoroborate (TEMABF ₄₎ a 1.4 mole% instead of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄₎ in the same manner as in Example 1 And tested for properties and performance. The results are shown in Table 2. A curve g in FIG. 6 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Example 3
A capacitor cell was prepared in the same manner as in Example 1 except that the temperature in the furnace in the pre-baking step was adjusted to 850 to 960 ° C. over 3 hours, and the characteristics and performance were tested. The results are shown in Table 2.

  A curve d in FIG. 4 shows a voltage change with time in the charging process. A curve d in FIG. 5 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Example 4
Create capacitor cells except be used in an amount of triethyl methyl ammonium tetrafluoroborate (TEMABF ₄₎ a 1.8 mole% instead of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄₎ in the same manner as in Example 1 And tested for properties and performance. The results are shown in Table 2. A curve h in FIG. 6 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Comparative Example 1
A capacitor cell was prepared in the same manner as in Example 1 except that the furnace temperature in the pre-baking step was adjusted to 650 ° C., and the characteristics and performance were tested. The results are shown in Table 2.

  A curve a in FIG. 4 shows a change in voltage over time during the charging process. A curve a in FIG. 5 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Comparative Example 2
Create capacitor cells except be used in an amount of triethyl methyl ammonium tetrafluoroborate (TEMABF ₄₎ a 1.4 mole% instead in the same manner as in Comparative Example 1 of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄₎ And tested for properties and performance. The results are shown in Table 2.

Comparative Example 3
A capacitor cell was prepared in the same manner as in Example 1 except that the furnace temperature in the pre-baking process was adjusted to 970 ° C. and the furnace temperature in the alkali activation process was adjusted to 770 ° C., and the characteristics and performance were tested. did. The results are shown in Table 2.

  A curve e in FIG. 4 shows a voltage change with time in the charging process. A curve e in FIG. 5 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Comparative Example 4
Create capacitor cells except be used in an amount of triethyl methyl ammonium tetrafluoroborate (TEMABF ₄₎ a 1.8 mole% instead of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄₎ in the same manner as in Comparative Example 3 And tested for properties and performance. The results are shown in Table 2.

Comparative Example 5
A capacitor cell was prepared in the same manner as in Example 1 except that the furnace temperature in the pre-baking step was adjusted to 980 ° C., and the characteristics and performance were tested. The results are shown in Table 2.

  A curve f in FIG. 4 shows a voltage change with time in the charging process. A curve f in FIG. 5 is a graph showing a behavior in which the voltage changes with time when the obtained electric double layer capacitor is charged and discharged for the first time.

Comparative Example 6
Create capacitor cells except be used in an amount of triethyl methyl ammonium tetrafluoroborate (TEMABF ₄₎ a 1.8 mole% instead of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄₎ in the same manner as in Comparative Example 5 And tested for properties and performance. The results are shown in Table 2.

It is the graph which showed the example of the behavior which a voltage changes with time when constant current charge and discharge are repeated to an electric double layer capacitor formed by immersing an electrode containing nonporous carbon in an organic electrolyte. It is the graph which showed the behavior which a voltage changed with time when constant current charge was performed for the first time with respect to the electric double layer capacitor formed by immersing the electrode containing non-porous carbon in organic electrolyte. It is an assembly drawing which shows the structure of the electric double layer capacitor of an Example. It is the graph which showed the behavior in which a voltage changes with time, when charging the capacitor cell of an example for the first time. It is the graph which showed the behavior in which a voltage changes with time when charging / discharging was performed for the capacitor cell of an example for the first time. It is the graph which showed the behavior in which a voltage changes with time when charging / discharging was performed for the capacitor cell of an example for the first time.

Explanation of symbols

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

Claims (5)

A pre-calcination step of calcining graphitizable carbon at 800-1000 ° C. for 2-8 hours under an inert atmosphere;
An alkali activation step in which the calcined powder is mixed with 1 to 5 times the weight of the alkali hydroxide powder and the powder mixture is calcined at 600 to 900 ° C. for 2 to 8 hours in an inert atmosphere;
A step of washing the activated powder mixture to remove alkali hydroxide; and a post-baking step of baking the obtained carbon powder at 200 to 800 ° C. for 2 to 8 hours in an inert atmosphere;
And non-porous carbon having graphite-like microcrystals with a loss on ignition of 5 to 18%.   The non-porous carbon according to claim 1, wherein the graphitizable carbon is a graphite precursor obtained by removing quinoline insolubles from a soft pitch of coal and carbonizing using a refined raw material.   A polarizable electrode comprising non-porous carbon having graphite-like microcrystals whose capacitance development voltage is adjusted by the method according to claim 1.   An electric double layer capacitor comprising the polarizable electrode according to claim 3 immersed in an organic electrolyte.   The organic electrolyte is a compound selected from the group consisting of spirobipyrrolidinium, tetraethylammonium, tetrabutylammonium, triethylmethylammonium, tetraethylphosphonium and 1-ethyl-3-methylimidazolium as the cation component of the electrolyte The electric double layer capacitor according to claim 4, comprising:

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