JP4066506B2 - A method for producing a carbonaceous material. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carbonaceous substance stable in air and exhibiting a low natural electric potential in an electrolyte solution, and to obtain an electric double layer capacitor using the carbonaceous substance as the electrode material of the capacitor and having improved electric voltage resistance, cycle durability, durability on the application of electric voltages, and energy density. SOLUTION: This carbonaceous substance contains elements comprising alkali metals, alkaline earth metals and rare earth metals in a total amount of 100-2,000 ppm, and has a natural electric potential of 1.50-2.85 V, when Li/Li<+> is used as a counter electrode in a nonaqueous electrolyte solution. The electric double layer capacitor using the nonaqueous electrolyte solution uses the carbonaceous substance as the main material of the electrodes.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is related to method for manufacturing a carbonaceous material quality. The carbonaceous material produced by the present invention has a natural potential in a non-aqueous electrolyte lower than that of normal carbon. It is suitable for technical fields such as multilayer capacitors, lithium ion secondary batteries, air batteries, and gas sensors.
[0002]
[Prior art]
Carbonaceous materials such as activated carbon, coke, graphite, and carbon fiber are heavy metals that have high electrical conductivity, high corrosion resistance, are electrochemically stable, and can reversibly occlude and release ionic species such as lithium ions. They are widely used as electrode materials for electric double layer capacitors, negative electrodes for lithium ion secondary batteries, dry battery electrodes, steelmaking electrodes, sensor electrodes and the like because they are not included or are inexpensive. However, since the natural potentials in these carbonaceous electrolytes are all 3.0 V (vs. Li / Li ⁺ ), the usable potential range is limited.
[0003]
On the other hand, electric double layer capacitors that can be charged and discharged with a large current are promising for applications such as electric vehicles and auxiliary power supplies. Therefore, it is desired to realize an electric double layer capacitor having a high energy density, capable of rapid charge / discharge, and excellent durability during high voltage application and charge / discharge cycle durability.
The energy stored in the capacitor cell is calculated by 1/2 · C · V ² , where C is the capacitance per cell (F), and V is the voltage (V) that can be applied to the cell. Since the square of the value of the applicable voltage V is reflected in the energy, it is effective to increase the voltage (withstand voltage) applied to the capacitor in order to improve the energy density. As a result, there was a problem that the internal resistance increased and the capacitance decreased in a short time. Therefore, the withstand voltage per unit cell is about 2.4V in the case of a non-aqueous electrolyte electric double layer capacitor, although it depends on the type of solvent and solute of the electrolyte used in the conventional electric double layer capacitor ( (Japanese Unexamined Patent Publication No. 7-50001), when used at a high voltage of 2.5 V or more, an increase in internal series resistance or a decrease in capacitance occurs in a short time. Therefore, it is attempted to apply a voltage of 2.5V to 2.8V by examining in detail the positive and negative electrodes, separator, electrolyte, container, and the like. For example, as a result of selecting a method for improving durability by heat-treating an electrode using activated carbon obtained by KOH activation of phenol resin, petroleum coke, etc. in an inert atmosphere, and selecting raw materials, phenol resin, furan resin, In the case of acrylonitrile resin, the durability was slightly improved (Japanese Patent Laid-Open No. 8-16375), and a method for improving the durability by using porous aluminum for the current collector of the capacitor (Japanese Patent Laid-Open No. 8-339941) Etc. are known.
[0004]
In order to increase the energy density, the applied voltage is set to 3 V or more as disclosed in Japanese Patent Application Laid-Open No. Hei 8-07048, in which a lithium electrode is contacted and a graphite electrode occluded lithium is used as a negative electrode, activated carbon is used as a positive electrode, lithium ion Capacitors using electrolytes containing solutes in the solute, and Japanese Patent Application Laid-Open No. 9-232190, a positive electrode is a combination of a polarizable electrode material containing activated carbon powder and a collector of stainless steel fibers in a mixed state Capacitors have been proposed. In Japanese Patent Laid-Open No. 9-205041, the withstand voltage is improved by using an electrolytic solution mainly composed of 2-methylsulfolane as the electrolytic solution.
[0005]
[Problems to be Solved by the Invention]
However, these examples were not satisfactory to any extent. For example, the above-described method of heat-treating an electrode using activated carbon obtained by KOH activation of phenol resin, petroleum coke or the like in an inert atmosphere has a problem that the initial capacitance is simultaneously reduced. Further, it can be said that the durability cannot be fundamentally improved by the methods disclosed in JP-A-8-16375 and JP-A-8-339941. As a measure for improving the energy density by increasing the applied voltage to 3 V or higher, Japanese Patent Laid-Open No. 9-232190 and Japanese Patent Laid-Open No. 9-205041 disclose that the maximum applied voltage is 3.3 V and a voltage higher than that is applied. I can't. In addition, the method disclosed in Japanese Patent Application Laid-Open No. 8-1007048 has a problem of durability because it involves an oxidation-reduction reaction between the electrode and the electrolytic solution. In addition, since the negative electrode (nonpolarizable electrode) contains lithium, the positive electrode (polarizable electrode) is already about 3 V in an uncharged state, and when a voltage of up to 4.3 V is applied as in the example described The potential change due to charging is about 1.3V. Therefore, the energy density when used as a capacitor is smaller than that of a normal capacitor.
In a conventional activated carbon electrode of an electric double layer capacitor, gas is generated or a reaction product is deposited on a polarizable electrode by continuous application of a high voltage exceeding 2.5 V. This has the disadvantage of causing a significant increase in internal resistance or a decrease in capacitance.
[0006]
In view of this, the present inventors have disclosed in Japanese Patent Application No. 9-183670 that the natural potential of the carbonaceous electrode is arbitrarily adjusted so that the potential during charging is substantially equal to the high potential side (oxidation side) of the electrolyte. It has been proposed that the decomposition of the electrolytic solution can be suppressed and the voltage that can be applied and the durability of the electric double layer capacitor can be improved by making the decomposition start voltage or less.
This will be briefly described. When a propylene carbonate solution of a quaternary alkyl ammonium salt, which is a typical non-aqueous electrolyte, is used as the electrolyte, and an electrode substantially made of a carbonaceous material is used as the electrode, the decomposition start voltage on the oxidation side of the electrolyte Is said to be around 4.4 V (vs. Li / Li ⁺ ). On the other hand, the natural potential of a normal carbonaceous electrode is around 3 V (vs. Li / Li ⁺ ). When the applied voltage of the capacitor is 2.8 V, the polarization on the positive electrode side after charging is about 1.4 V, and the potential on the oxidation side Is 4.4 V (vs. Li / Li ⁺ ) or more, and it is considered that the electrolytic decomposition of the electrolyte occurs. As a result, when the conventional carbonaceous electrode is used, the capacity is reduced due to gas generated by the decomposition of the electrolytic solution, so that durability is a problem when used for a long time. Therefore, in the invention of Japanese Patent Application No. Hei 9-183670, by reducing the natural potential of the carbonaceous electrode so that the potential on the positive electrode side after charging is equal to or lower than the oxidative decomposition starting voltage of the electrolyte, It has been proposed that the energy density can be improved significantly.
[0007]
However, the natural potential of conventional carbonaceous materials is around 3 V (vs. Li / Li ⁺ ), and in order to lower the natural potential of carbonaceous electrodes, carbonaceous materials with a base metal such as metallic lithium as a counter electrode in a non-aqueous electrolyte are used. An operation such as electrochemical doping of lithium ions into the electrode is required. A carbonaceous material that is stable in the air and exhibits a low natural potential in the electrolytic solution has not been obtained so far without performing these potential control operations.
[0008]
[Means for Solving the Problems ]
Therefore, as a result of intensive studies to examine the above-mentioned problems, the present inventors mixed a carbonaceous raw material having developed crystallinity with a base metal or a compound containing a base metal, and after heat treatment, It has been found that a carbonaceous material exhibiting a low natural potential can be obtained by drying, and the present invention has been achieved. That is, an object of the present invention is to provide an electric double layer capacitor having improved characteristics such as withstand voltage, cycle durability, durability during voltage application, and energy density when used as an electrode material of an electric double layer capacitor. is to provide a method for manufacturing a carbonaceous substance showing a low self-potential in a stable and electrolyte in the air which can provide, this object is plane spacing d ₀₀₂ as measured by X-ray diffraction is more than 0.344nm A carbonaceous raw material of 0.365 nm or less is mixed with a metal selected from the group of metal elements consisting of alkali metals, alkaline earth metals, and rare earth metals, or a compound containing these metals, and the mixture is heat-treated and then washed with water. · dried, an alkali metal, the total content of metal elements selected from the metallic element group consisting of alkaline earth metals and rare earth metals 100ppm or 2000p achieved by pm hereinafter, self-potential in the case of a counter electrode of Li in propylene carbonate solution containing on whether One LiBF ₄ 1.0 mol / L is to 2.85V less carbonaceous material above 1.50V Is done.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. According to the method of the present invention, one or more substances selected from alkali metals such as metal potassium and potassium hydroxide, alkaline earth metals and rare earth metals and compounds containing these metals, and a carbonaceous raw material having developed crystallinity. After heat-treating the mixture, and washing and drying, the carbonaceous material contains one or more elements selected from alkali metals, alkaline earth metals and rare earth metals in a weight ratio of 100 ppm or more and 2000 ppm or less in total, A carbonaceous material that is stable in air and has a natural potential of 1.50 V or more and 2.85 V or less (vs. Li / Li ⁺ ) when Li / Li ⁺ is used as a counter electrode in a non-aqueous electrolyte solution is produced. be able to.
[0010]
The coal quality raw material, wood of the plant, sawdust, coconut shells, pulp waste, coal fossil fuel-based, petroleum heavy oil, or tar and pitch thereof pyrolyzed coal and petroleum, petroleum coke, Carbon fiber, carbon fiber, carbon black, carbon aerogel, activated carbon, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, liquid crystal high molecule, plastic wastes, it is preferable one or more substances which also chosen pressurized et al was heat-treated material to carbonization, such as waste tires.
[0011]
A heat-treated product of graphitizable carbon or graphitizable organic compound that is easy to graphitize is particularly preferable because the base metal is occluded in a stable state in the carbon. Examples of graphitizable organic compounds and carbon include tar, pitch, mesophase, and polyimide resins that are polycyclic aromatic ring compounds such as coal and petroleum, and polyvinyl chloride resins and polyvinylidene chloride resins that are aliphatic compounds. It is done. Carbonaceous materials made from petroleum and coal such as petroleum coke, coal coke, and fluid coke, which are graphitizable carbon, are particularly preferred because they are inexpensive and have basically developed crystallinity. These carbonaceous materials can be used as the carbonaceous raw material used in the production method of the present invention as they are or by further developing crystallinity by carbonization treatment.
[0012]
Carbonaceous materials that have been heat-treated at a high temperature of 900 ° C. or higher with graphitizable carbon such as petroleum coke and coal coke do not need to be further carbonized. Other organic substances or carbonaceous materials need to be carbonized at a temperature of 900 ° C. or higher under an inert atmosphere. In order to sufficiently develop crystallinity, carbonization may be performed at a high temperature of 1300 ° C. or higher. Further, even if a non-graphitizable organic compound such as a phenol resin or a furan resin is used, the present invention can be achieved by optimizing the curing conditions and carbonizing at 1400 ° C. or higher to sufficiently develop crystallinity. It can be used as a carbonaceous raw material used in the production method . The interplanar spacing d ₀₀₂ measured by X-ray diffraction of the carbonaceous material having developed crystallinity is 0.365 nm or less, and the size Lc in the c-axis direction of the crystal particles is 2.5 nm or more. preferable. The carbonaceous shape includes various shapes such as crushing, granulation, granule, fiber, felt, woven fabric, and sheet shape, any of which can be used in the present invention.
[0013]
The substance mixed with the carbonaceous raw material is preferably one or more substances selected from alkali metals, alkaline earth metals and rare earth metals, and compounds containing these metals. Specifically, potassium, sodium, lithium And base metals such as rubidium, magnesium, barium, yttrium, or compounds such as potassium hydroxide, sodium hydroxide, rubidium hydroxide, potassium carbonate, sodium carbonate, lithium-aluminum alloy, lithium-aluminum alloy, etc. . Of these, metal potassium, potassium hydroxide, potassium carbonate, and rubidium hydroxide are particularly preferable because potassium and rubidium are easily occluded in the form of positive ions or atoms in the carbon crystal by heat treatment with carbon. It is considered that a negative charge is stored in the carbon phase by the charge transfer interaction with ions or atoms occluded in these carbons, and as a result, the natural potential of the carbonaceous material is lowered.
[0014]
Heat treatment of a mixture of a carbonaceous raw material and a metal or a compound containing a metal is usually performed by oxidizing oxygen, carbon dioxide, hydrogen, carbon monoxide, or the like in an inert gas such as nitrogen, argon, xenon, or the like. For 10 minutes or more at a temperature of 500 ° C. to 1300 ° C. in an atmosphere containing a reductive or reducing gas. For example, in the case of a mixture of potassium metal and a carbonaceous raw material, it is preferable to perform heat treatment at 600 ° C. or higher in an inert atmosphere in order to increase the diffusion rate of metal potassium into carbon. Further, in the case of potassium hydroxide, it is preferable to heat-treat at 650 ° C. or higher because metal potassium, potassium oxide, potassium carbonate and the like are generated and easily introduced into the carbonaceous raw material.
[0015]
Impurities are sufficiently removed from the product after the heat treatment by repeatedly washing with water or boiling water and neutralizing with an acid such as hydrochloric acid. Here, it is preferable that the acid is added excessively and the water washing is repeated until the filtrate of the subsequent washing has a pH of 6 or more. Then, the target carbonaceous substance is obtained by drying at 100 degreeC or more. The content of alkaline earth metal, alkali metal, and rare earth metal elements quantified by a spectroscopic analyzer such as atomic absorption method in the carbonaceous material is the carbonaceous raw material species, heat treatment temperature, carbonaceous raw material. Since it differs depending on the type of substance to be mixed and the amount added, etc., it cannot be generally stated, but it is usually 100 ppm or more and 2000 ppm or less, preferably 500 ppm or more and 1000 ppm or less. It is desirable to remove as much as possible extra elements such as alkali metals, alkaline earth metals and rare earth metals that do not contribute to lowering the natural potential of the carbonaceous material by repeating the above washing and hydrochloric acid neutralization operations. .
[0016]
Conventionally, it is known that a carbon material in which lithium is occluded is used as an electrode for a secondary battery or the like. In this case, lithium in the carbon material can be reversibly occluded and desorbed. Yes. On the other hand, in the production method of the present invention , since washing and hydrochloric acid neutralization operations are repeated, elements such as lithium existing in such a state in the carbonaceous material obtained by the heat treatment are finally It is thought that it was removed from the carbonaceous material obtained .
[0017]
Measurement of the natural potential of the carbonaceous material obtained by the production method of the present invention is performed using a normal electrochemical technique. The potential measurement in the non-aqueous electrolyte is not strictly defined as a potential reference such as a standard hydrogen electrode in an aqueous solution, but in reality, electrodes such as silver-silver chloride electrodes, platinum electrodes, lithium electrodes, etc. In general, it is widely used. In the present invention, it can be measured by the same method. As a simple measuring method, there is a method of measuring a potential difference between metallic lithium and an electrode body mainly composed of the carbonaceous substance in a nonaqueous electrolytic solution. The natural potential of the carbonaceous material in the non-aqueous electrolyte by such a measuring method is 1.50 V or more and 2.85 V or less (vs. Li / Li ⁺ ).
[0018]
The carbonaceous material obtained by the production method of the present invention can be used as a main material of an electrode for an electric double layer capacitor using a nonaqueous electrolytic solution. An electrode mainly composed of a carbonaceous material (carbonaceous electrode) is composed of a carbonaceous material and a binder. Further, a conductive substance may be further added to impart conductivity to the electrode. The polarizable electrode can be formed by a conventionally known method. For example, it can be obtained by adding and mixing polytetrafluoroethylene to a mixture of a carbonaceous material and acetylene black and then press molding. Also, a molded product can be obtained by adding and mixing a coal pitch with a relatively high softening point to a carbonaceous material as a binder and then firing the molded product in an inert atmosphere to a temperature higher than the thermal decomposition temperature of the binder. . Furthermore, it is possible to sinter only a carbonaceous material without using a conductive agent and a binder to form a polarizable electrode. The electrode may be a thin coating film, a sheet-shaped or plate-shaped molded body, or a plate-shaped molded body made of a composite.
[0019]
As a conductive agent used for carbonaceous electrodes, carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, titanium oxide, aluminum, nickel, stainless steel, etc. At least one conductive agent selected is preferred. Acetylene black and ketjen black are particularly preferable in that the conductivity is effectively improved with a small amount, and the blending amount of the conductive agent is preferably about 10 to 30% of the weight.
As the binder, at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxymethylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, and phenol resin is used. preferable.
[0020]
The current collector of the electric double layer capacitor may be electrochemically and chemically resistant as long as it is not particularly limited. For example, the positive electrode includes stainless steel, aluminum, titanium, and tantalum, and the negative electrode includes stainless steel and nickel. Copper or the like is preferably used.
The electrolyte is preferably a non-aqueous electrolyte. The solute of the non-aqueous electrolyte is R ₄ N ⁺ , R ₄ P ⁺ (where R is an alkyl group represented by C _n H _{2n + 1} ), quaternary onium cation such as triethylmethylammonium ion, and BF A salt in combination with an anion of ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ or CF ₃ SO ₃ ^— or a lithium salt whose cation is a lithium ion is used. Lithium _{salt, LiBF 4, LiClO 4, LiPF} 6, LiSbF 6, LiAsF 6, LiCF 3 SO 3, LiC (CF 3 SO 2) 3, LiB (C 6 H 5) 4, LiC 4 F 9 SO 3, LiC One or more substances selected from ₈ F ₁₇ SO ₃ , LiB (C ₆ H ₅ ) ₄ and LiN (CF ₃ SO ₂ ) ₂ are preferred. In particular, from the viewpoint of electrical conductivity, stability, and low cost, the cation is R ₄ N ⁺ (where R is an alkyl group represented by C _n H _{2n + 1} ), triethylmethylammonium ion, and anion, A salt in which BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , and SbF ₆ ⁻ are combined is preferable.
[0021]
The solute concentration in these non-aqueous electrolytes is preferably 0.5 to 2.0 mol / liter so that the characteristics of the electric double layer capacitor can be sufficiently extracted, and particularly at a concentration of 0.7 mol / liter to 1.9 mol / liter, high electrical conductivity It is preferable because of the property. The solvent of the non-aqueous electrolyte is not particularly limited, but propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, N- An organic solvent composed of one or more selected from methyl oxazolidinone, dimethyl sulfoxide, and trimethyl sulfoxide is preferable. One or more kinds selected from propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, and γ-butyrolactone from the viewpoint of excellent electrochemical and chemical stability and electrical conductivity The organic solvent is particularly preferred. However, a high-melting-point solvent such as ethylene carbonate cannot be used alone because it becomes a solid at a low temperature, and must be a mixed solvent with a low-melting-point solvent such as propylene carbonate.
The water content in the non-aqueous electrolyte solution is preferably 200 ppm or less, more preferably 50 ppm or less so that a high withstand voltage can be obtained.
[0022]
A polarizable electrode made mainly of a carbonaceous material obtained by the production method of the present invention may be used for both electrodes of an electric double layer capacitor or only for one electrode. For example, a polarizable electrode mainly composed of carbon such as activated carbon as the positive electrode, and a negative electrode composed mainly of lithium metal, lithium alloy, or a carbon material that can reversibly absorb and desorb lithium ions in advance. In an electric double layer capacitor composed of a non-polarizable electrode as a material and a non-aqueous electrolyte containing a lithium salt, it was obtained by the production method of the present invention instead of a polarizable electrode mainly composed of activated carbon or the like . A carbonaceous material can be used as the positive electrode material. By using the carbonaceous material obtained by the production method of the present invention, it is possible to increase the voltage that can be applied compared to the case where conventional activated carbon is used as the positive electrode material, so that the energy density of the electric double layer capacitor is greatly increased. Can be increased.
[0023]
Further, those obtained by further regulating the natural potential of the electrochemically lithium ions carbonaceous electrode of the by a technique such as to lightly doped, with a non-aqueous electrolyte solution in electrodes, is used as an electric double layer capacitor electrode You can also. In addition , activated carbon powder having a specific surface area of 300 m ² / g or more, such as a KOH-activated product using phenol resin pyrolyzate or petroleum coke as a raw material, which exhibits high capacity at room temperature, was obtained by the production method of the present invention . What added and shape | molded about 10 to 70 weight% to the carbonaceous substance can also be used as an electrode for electric double layer capacitors .
[0024]
As described above, since the carbonaceous material obtained by the production method of the present invention and the molded body thereof have a lower natural potential in the non-aqueous electrolyte than ordinary carbon, the withstand voltage, charge / discharge capacity, etc. constitute the electrode. Can be used in technical fields such as electric double layer capacitors, lithium ion secondary batteries, air batteries, gas sensors, etc., which are greatly affected by the potential of the material, especially high withstand voltage, high energy density, charge / discharge cycle durability, voltage application It can be suitably used for electric double layer capacitors that are strongly required to be durable.
[0025]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated with a specific Example, this invention is not limited by a following example.
[0026]
Example 1
The coal pitch was heat treated at 1500 ° C. for 4 hours and then pulverized with a ball mill to obtain a carbonaceous raw material having an average particle size of about 20 μm. An X-ray diffraction pattern of the carbonaceous raw material is shown in FIG. Plane spacing d ₀₀₂ as measured by X-ray diffraction pattern was 0.344 nm. The carbonaceous raw material was mixed with granular potassium hydroxide having a weight ratio of 2 times, mixed, then placed in a nickel crucible and heat-treated at 800 ° C. for 2 hours in a nitrogen stream. The cooled product was washed once with water, boiled in a 10% aqueous hydrochloric acid solution for 1 hour, and then repeatedly washed with water until the pH of the filtrate after washing was 6 or more. Then, to obtain a coal quality material was dried at 115 ° C.. When the content of potassium in the carbonaceous material was quantified with an emission spectroscopic analyzer, it was 660 ppm.
[0027]
(Reference Example 1)
A mixture of 80% by weight of carbonaceous material, 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene was kneaded, and then using a tablet press made by JASCO, the diameter was 10.5 mm and the thickness was 0.5 mm. Thus, a disk-shaped molded body was produced by pressure molding at a pressure of 50 kgf / cm ² . The molded body was dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr or less, and then transferred to a glove box under an argon atmosphere. This molded body was used as a positive electrode body, and this was bonded to the center of the inner bottom of a stainless steel 316L coin cell. Next, a metal lithium sheet having a thickness of 0.5 mm was punched into a circle having a diameter of 13 mm, and this was used as a negative electrode. A polyethylene separator was sandwiched between the produced positive electrode and negative electrode, and both electrodes were made to face each other. Then, a propylene carbonate solution containing LiBF ₄ having a concentration of 1.0 mol / liter was impregnated into both electrodes. Thereafter, the coin cell was caulked and sealed using an insulating gasket made of polypropylene and an upper cover of a coin cell made of stainless steel 304. The natural potential of the carbonaceous material electrode measured by connecting a voltmeter between the positive electrode (carbonaceous material electrode) and the negative electrode (metallic lithium) of the obtained coin cell was 2.79 V (vs. Li / Li ⁺ ). . In FIG. 2, 1 is a case of a stainless steel container, 2 is a positive electrode, 3 is a gasket, 4 is a separator, 5 is a negative electrode, and 6 is an upper lid of the stainless steel container.
[0028]
(Reference Example 2 )
The two carbonaceous material molded bodies prepared in Reference Example 1 were dried in a vacuum of 0.1 torr or less at 300 ° C. for 3 hours, and then the molded bodies were used as positive and negative electrode bodies. Assembly was performed in a glove box under a nitrogen atmosphere. The obtained two molded bodies were used as positive and negative electrodes, and a coin cell similar to that of Reference Example 1 was assembled by impregnating both electrodes with a propylene carbonate solution of triethylmethylammonium tetrafluoroborate having a concentration of 1.3 mol / liter. An electric double layer capacitor was obtained. The initial capacitance obtained by applying a voltage of 2.8 V or 3.8 V to the obtained electric double layer capacitor at room temperature for 1 hour and then discharging to 1.0 V at a constant current of 1.16 mA is as follows: In the case of 2.8V application, it was 1.03F, and in the case of 3.8V application, it was 1.33F. Moreover, the change rate of the electrostatic capacitance after applying a voltage of 3.8 V at room temperature for 800 hours was −15%.
[0029]
(Example 2)
Except for using a carbonaceous raw material having an interplanar spacing d ₀₀₂ of 0.349 nm after heat treatment of a coal tar pitch from which quinoline-insoluble components have been removed at 900 ° C. for 3 hours in a rotary kiln, to obtain a carbonaceous material quality in the same manner as in example 1. Potassium content of the carbonaceous substance was Tsu 780ppm der. Further, the except for the use of carbonaceous materials to produce a coin cell in the same manner as in Reference Example 1, was 2.80V was measured natural potential of the carbonaceous material electrodes (Li / Li ^+).
[0030]
(Reference Example 3 )
An electric double layer capacitor similar to Reference Example 2 was constructed except that the two carbonaceous material molded bodies obtained in Example 2 were used as electrode bodies for the electric double layer capacitor. The initial capacitance of the obtained electric double layer capacitor was 1.11F when 2.8V was applied and 1.38F when 3.8V was applied. Moreover, the change rate of the electrostatic capacitance after applying a voltage of 3.8 V at room temperature for 800 hours was −12%.
[0031]
(Reference Example 4 )
Activated carbon powder (potassium content: 25 ppm, average particle size: about 20 μm, specific surface area: 1680 m ² / specifically obtained by repeating water washing and acid neutralization of the carbonaceous material of Reference Example 1 after steam activation. A coin cell similar to that in Reference Example 1 was constructed except that g,) was used. The natural potential of the carbonaceous material electrode as the positive electrode was 3.01 V (vs. Li / Li ⁺ ).
[0032]
(Reference Example 5 )
An electric double layer capacitor similar to that of Reference Example 2 was constructed except that the two activated carbon molded bodies obtained in Reference Example 4 were used as electrode bodies for the electric double layer capacitor. The initial capacitance of the obtained electric double layer capacitor was 1.19F when 2.8V was applied and 1.36F when 3.8V was applied. Moreover, the change rate of the electrostatic capacitance after applying a voltage of 3.8 V for 800 hours at room temperature was -39%.
[0033]
(Comparative Example 1 )
A coal tar pitch was obtained by heat treatment at 500 ° C. for 2 hours and then pulverization. After adding and mixing 2.3 times the weight ratio of granular potassium hydroxide to coal pitch powder with an interplanar spacing d ₀₀₂ of 0.372 nm, it is placed in a nickel crucible and placed in a nitrogen stream at 650 ° C. for 1 hour. Heat treated. After cooling, washing and drying were carried out in the same manner as in Example 1, followed by heat treatment at 1000 ° C. for 1 hour in a nitrogen stream to obtain activated carbon powder. The potassium content in the activated carbon powder was 30 ppm. Next, a coin cell similar to that of Reference Example 1 was obtained using this activated carbon powder. The natural potential of the carbonaceous material electrode was 3.08 V (vs. Li / Li ⁺ ).
[0034]
(Reference Example 6 )
An electric double layer capacitor similar to Reference Example 2 was constructed except that the two activated carbon molded bodies obtained in Comparative Example 1 were used as electrode bodies of an electric double layer capacitor. The initial capacitance of the obtained electric double layer capacitor was 1.19F when 2.8V was applied and 1.35F when 3.8V was applied. Moreover, the change rate of the electrostatic capacitance after applying a voltage of 3.8 V at room temperature for 800 hours was −65%.
[Brief description of the drawings]
1 is a diagram showing an X-ray pattern of a carbonaceous raw material of Example 1. FIG.
FIG. 2 is an explanatory diagram of coin-type cells used in reference examples and comparative examples of the present invention.
[Explanation of symbols]
1: Stainless steel container case 2: Positive electrode 3: Gasket 4: Separator 5: Negative electrode 6: Upper cover of stainless steel container

Claims (7)

Metal selected from a carbonaceous raw material having an interplanar spacing d ₀₀₂ of 0.344 nm or more and 0.365 nm or less measured by X-ray diffraction, and a metal element group consisting of alkali metal, alkaline earth metal and rare earth metal, or these metals The total content of metal elements selected from the group of metal elements consisting of alkali metals, alkaline earth metals and rare earth metals , characterized in that the mixture is mixed with a compound containing, and the mixture is heat-treated and then washed and dried. In a propylene carbonate solution containing 100 ppm to 2000 ppm and containing LiBF ₄ at 1.0 mol / L
A method for producing a carbonaceous material having a natural potential of 1.50 V or more and 2.85 V or less when Li is used as a counter electrode . Method for producing a carbonaceous material of claim 1, wherein the spacings carbonaceous feedstock is measured by X-ray diffraction are: 0.349nm than 0.344 nm. Metal elements selected from the group of metal elements consisting of alkali metals, alkaline earth metals and rare earth metals mixed with carbonaceous raw materials or compounds containing these metal elements are metal potassium, potassium hydroxide, potassium carbonate and hydroxide 3. The method for producing a carbonaceous material according to claim 1, wherein the carbonaceous material is selected from the group consisting of rubidium. The method for producing a carbonaceous material according to any one of claims 1 to 3 , wherein the heat treatment is performed by holding the mixture at 500 to 1300 ° C for 10 minutes or more. 5. The production of a carbonaceous material according to any one of claims 1 to 4 , wherein the water washing includes a step of bringing the heat-treated mixture into contact with an acid aqueous solution and then washing with water until the washing solution has a pH of 6 or more. Method. The method for producing a carbonaceous material according to any one of claims 1 to 5, wherein the size Lc in the C-axis direction of the crystallite of the carbonaceous raw material is 2.5 nm or more. Mixing, heat treatment, washing with water and drying so as to produce a carbonaceous material having a total content of metal elements selected from the group of metal atoms consisting of alkali metals, alkaline earth metals and rare earth metals of 500 ppm or more and 1000 ppm or less A method for producing a carbonaceous material according to any one of claims 1 to 6.

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