JP2006282444A - Method for manufacturing spherical alga-like carbon having large specific surface area and electric double layer capacitor using the same - Google Patents

Method for manufacturing spherical alga-like carbon having large specific surface area and electric double layer capacitor using the same Download PDF

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JP2006282444A
JP2006282444A JP2005104242A JP2005104242A JP2006282444A JP 2006282444 A JP2006282444 A JP 2006282444A JP 2005104242 A JP2005104242 A JP 2005104242A JP 2005104242 A JP2005104242 A JP 2005104242A JP 2006282444 A JP2006282444 A JP 2006282444A
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carbon
surface area
specific surface
marimocarbon
electric double
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Hisahiro Ando
寿浩 安藤
Kiyoharu Nakagawa
清晴 中川
Hirokazu Oda
廣和 小田
Yoichi Sato
洋一 佐藤
Tetsuya Ishii
徹哉 石井
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National Institute for Materials Science
Sekisui Chemical Co Ltd
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National Institute for Materials Science
Sekisui Chemical Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/34—Carbon-based characterised by carbonisation or activation of carbon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for increasing the specific surface area of spherical alga-like carbon, that is, a method for manufacturing spherical alga-like carbon having a large specific surface area, and an electric double layer capacitor using the spherical moss-based carbon. <P>SOLUTION: Potassium hydroxide is mixed into spherical alga-like carbon and this mixture is heat-treated in inert gas to obtain the objective spherical alga-like carbon having the large specific surface area. The discharge capacity of the electric double layer capacitor using the spherical alga-like carbon activated at 700°C is about 3 times as large as that of an electric double layer capacitor using untreated spherical moss-based carbon, and the discharge capacity of the electric double layer capacitor using the untreated spherical alga-like carbon is about 1.4 times as large as that of an electric double layer capacitor using conventional activated carbon, accordingly the discharge capacity of the electric double layer capacitor using the spherical alga-like carbon having the large specific surface area as a polarizable electrode is about 4.2 times as large as that of the electric double layer capacitor using the conventional activated carbon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は高比表面積マリモカーボンの製造方法及びこれを用いた電気二重層キャパシタに関する。   The present invention relates to a method for producing high specific surface area marimocarbon and an electric double layer capacitor using the same.

電気自動車、燃料電池自動車、或いはハイブリッド自動車のバッテリー電源のバックアップ用電源、また、パーソナルコンピューターのメモリーバックアップ用電源などへの電気二重層キャパシタの利用が盛んに検討されている。電気二重層キャパシタは、正負両電極の間に電圧が印加されると、分極性電極の表面に電解液中のイオンが吸着されて分極性電極の電荷と電解液中のイオンとで電気二重層を形成し、これによって電気エネルギーを蓄積する。電気二重層キャパシタの蓄電容量は使用される電極材料の比表面積に比例し、比表面積が大きいほどイオンが多く吸着され蓄電容量が増加する。電気二重層キャパシタは、電気二重層を利用して蓄電するため、化学反応を利用して蓄電する２次電池に較べて急速な充放電に耐えることができ、特に、自動車の減速時に散逸させる運動エネルギーを回収する回生エネルギー蓄電システムに必要不可欠となっている。   The use of an electric double layer capacitor for a backup power source of a battery power source of an electric vehicle, a fuel cell vehicle, or a hybrid vehicle and a memory backup power source of a personal computer has been actively studied. When a voltage is applied between the positive and negative electrodes, an electric double layer capacitor adsorbs ions in the electrolyte on the surface of the polarizable electrode, and the electric double layer is formed by the charge of the polarizable electrode and the ions in the electrolyte. Thereby storing electrical energy. The storage capacity of the electric double layer capacitor is proportional to the specific surface area of the electrode material used, and the larger the specific surface area, the more ions are adsorbed and the storage capacity increases. The electric double layer capacitor uses the electric double layer to store electricity, so it can withstand rapid charge / discharge compared to a secondary battery that stores electricity using a chemical reaction. It is indispensable for a regenerative energy storage system that recovers energy.

しかしながら、電気二重層キャパシタの蓄電容量は電極面積によって制限されるため、化学反応を利用する２次電池に較べて蓄電容量密度が小さいことが難点であり、電気二重層キャパシタの蓄電容量密度をさらに向上することが求められている。   However, since the storage capacity of the electric double layer capacitor is limited by the electrode area, it is difficult for the storage capacity density to be smaller than that of a secondary battery using a chemical reaction. There is a need to improve.

従来の電気二重層キャパシタの分極性電極には無定型炭素である活性炭がもっぱら用いられている。活性炭は、炭素を成分とする原料を炭化して整粒し、さらに賦活して製造される。活性炭は極めて多くの細孔を有するために比表面積が極めて大きく、これらの細孔の表面が電気二重層を形成するために蓄電容量が大きい。   Activated carbon, which is amorphous carbon, is exclusively used for the polarizable electrodes of conventional electric double layer capacitors. Activated carbon is produced by carbonizing a raw material containing carbon as a component, sizing and further activating. Activated carbon has a very large specific surface area because it has an extremely large number of pores, and the surface of these pores forms an electric double layer, so that the storage capacity is large.

従来は、電気二重層キャパシタの蓄電容量を増やすために、活性炭や椰子殻炭等の無定型炭素を水蒸気或いは水酸化カリウムを用いて賦活することにより微細孔を増やし、比表面積を増加することで行ってきている。しかしながら、比表面積、すなわち単位質量あたりの表面積を増やすことによって蓄電容量は増大するが、それと共に活性炭は急激に密度が低くなり、このため活性炭の単位質量あたりに必要な分極性電極の表面積が急激に増大し電気二重層キャパシタが大型化してしまうという課題がある（非特許文献１参照）。   Conventionally, in order to increase the storage capacity of the electric double layer capacitor, the amorphous carbon such as activated carbon and coconut shell charcoal is activated by using steam or potassium hydroxide to increase the fine pores and increase the specific surface area. Have gone. However, increasing the specific surface area, i.e., the surface area per unit mass, increases the storage capacity, but at the same time, the activated carbon rapidly decreases in density, and therefore the surface area of the polarizable electrode required per unit mass of activated carbon rapidly increases. There is a problem that the electric double layer capacitor increases in size (see Non-Patent Document 1).

本発明者らは既に、従来の活性炭に代えて、マリモカーボン（特許文献１参照）、カーボンナノフィラメント（特許文献２参照）、或いは、カーボンナノチューブといった炭素原子から成るナノ（ｎｍ）オーダーの特異な構造を有するカーボン繊維を分極性電極の材料とすることにより、活性炭を分極性電極に用いた従来の電気二重層キャパシタよりも蓄電容量を大きくできることを見いだした（特許文献３，４参照）。
これらのカーボン繊維の構造は様々であるが、いずれも単層グラファイト層で構成されており、グラファイト層のグラファイト・エッジは、電気二重層が形成される位置として作用する（特許文献３参照）。すなわち、カーボン繊維は、活性炭に比し、比表面積は小さいが、グラファイト・エッジ密度がより大きいために、カーボン繊維を分極性電極とした電気二重層キャパシタの蓄電容量が、活性炭を分極性電極に用いた電気二重層キャパシタの蓄電容量よりも大きくなると考えられる。
中でも、マリモカーボンは、粒径が５００ｎｍ以下の酸化ダイヤモンドを核として、カーボンナノチューブ等のカーボン繊維が放射状に成長した、径がμｍオーダーの球状の微粒子、すなわちマリモ状のカーボン繊維であるが、カーボン繊維にグラファイト・エッジが存在し、これらのカーボン繊維が核の回りに極めて高密度に成長しているため、マリモカーボンを分極性電極として用いた電気二重層キャパシタは、数あるカーボン繊維の内でも優れて蓄電容量が大きいことが見いだされている（特許文献４参照）。
特願２００４−１５３１２９号 特開２００４−２７７２４１号公報 特願２００３−３６８３５６号 特願２００５−００７６８２号 田村英雄監修、“電子とイオンの機能化学シリーズ Ｖｏｌ．２ 大容量電気二重層キャパシタの最前線”ｐ４０、株式会社エヌ・ティー・エス ２００２年１月 初版第一刷 菊池英一，瀬川幸一，多田旭男，射水雄三，服部 英 共著“新しい触媒化学”第二版 ｐ１８６〜ｐ１９０ 三共出版 The present inventors have already replaced the conventional activated carbon with a peculiarity of nano (nm) order composed of carbon atoms such as marimocarbon (see Patent Document 1), carbon nanofilament (see Patent Document 2), or carbon nanotube. It has been found that by using a carbon fiber having a structure as a material for a polarizable electrode, the storage capacity can be made larger than that of a conventional electric double layer capacitor using activated carbon as a polarizable electrode (see Patent Documents 3 and 4).
Although the structures of these carbon fibers are various, all are composed of a single-layer graphite layer, and the graphite edge of the graphite layer acts as a position where an electric double layer is formed (see Patent Document 3). In other words, carbon fiber has a smaller specific surface area than activated carbon, but the graphite edge density is larger, so the storage capacity of an electric double layer capacitor using carbon fiber as a polarizable electrode is higher than activated carbon as a polarizable electrode. This is considered to be larger than the storage capacity of the electric double layer capacitor used.
Among them, marimocarbon is a spherical fine particle with a diameter of μm, that is, carbon fiber such as carbon nanotubes, with carbon oxide such as carbon nanotubes growing radially with diamond oxide having a particle size of 500 nm or less as a core. Since the graphite edges are present in the fibers and these carbon fibers grow very densely around the core, the electric double layer capacitor using marimocarbon as a polarizable electrode is one of many carbon fibers. It has been found that the power storage capacity is excellent (see Patent Document 4).
Japanese Patent Application No. 2004-153129 JP 2004-277241 A Japanese Patent Application No. 2003-368356 Japanese Patent Application No. 2005-007682 Supervised by Hideo Tamura, “Functional Chemistry Series of Electrons and Ions Vol.2 The Forefront of High-Capacity Double-Layer Capacitors” p40, NTS Corporation January 2002 First Edition First Print Eiichi Kikuchi, Koichi Segawa, Asao Tada, Yuzo Imizu, Ei Hattori "New Catalytic Chemistry" 2nd edition p186-p190 Sankyo Publishing

ところで、特許文献４の図４に示されているように、マリモカーボンを分極性電極とした電気二重層キャパシタの放電容量（蓄電容量）は活性炭を分極性電極とした電気二重層キャパシタに比べて、約１．４倍大きいが、マリモカーボンの比表面積は活性炭の比表面積の約１／１４である。
本発明者らは、マリモカーボンの比表面積を増大することができれば、マリモカーボンを分極性電極とした電気二重層キャパシタの蓄電容量をさらに増大できることに想到し本発明に至った。 As shown in FIG. 4 of Patent Document 4, the discharge capacity (storage capacity) of an electric double layer capacitor using marimocarbon as a polarizable electrode is larger than that of an electric double layer capacitor using activated carbon as a polarizable electrode. Although the specific surface area of marimocarbon is about 1.4 times larger, it is about 1/14 of the specific surface area of activated carbon.
The present inventors have conceived that if the specific surface area of marimocarbon can be increased, the storage capacity of an electric double layer capacitor using marimocarbon as a polarizable electrode can be further increased, and the present invention has been achieved.

本発明は、マリモカーボンの比表面積を増大する方法、すなわち、高比表面積マリモカーボンの製造方法を提供し、さらには、高比表面積マリモカーボンを用いた電気二重層キャパシタを提供することを目的とする。   The present invention provides a method for increasing the specific surface area of marimocarbon, that is, a method for producing marimocarbon with a high specific surface area, and further provides an electric double layer capacitor using the high specific surface area marimocarbon. To do.

上記目的を達成するため、本発明の高比表面積マリモカーボンの製造方法は、マリモカーボンに水酸化カリウム（ＫＯＨ）を混合し、この混合物を不活性ガス中で熱処理することを特徴とする。マリモカーボンと水酸化カリウムとの混合比は、質量比で１〜４が好ましい。熱処理温度は６００〜８００℃が好ましく、熱処理時間は１〜３時間が好ましい。また、マリモカーボンのカーボン繊維は、カーボンナノチューブ、カップ積層型カーボンナノフィラメント、又はコイン積層型カーボンナノフィラメントであれば好ましい。   In order to achieve the above object, the method for producing marimocarbon of high specific surface area according to the present invention is characterized by mixing marimocarbon with potassium hydroxide (KOH) and heat-treating the mixture in an inert gas. The mixing ratio of marimocarbon and potassium hydroxide is preferably 1 to 4 in terms of mass ratio. The heat treatment temperature is preferably 600 to 800 ° C., and the heat treatment time is preferably 1 to 3 hours. The carbon fiber of marimocarbon is preferably a carbon nanotube, a cup laminated carbon nanofilament, or a coin laminated carbon nanofilament.

この方法によれば、マリモカーボンのカーボン繊維に、２ｎｍ以下の径のミクロ孔、及び２〜５０ｎｍ径のメソ孔が複数形成され、これらの孔の表面積がマリモカーボンの表面積を増大させるので高比表面積のマリモカーボンが製造できる。また、孔の表面にはグラファイト・エッジが露出するので、グラファイト・エッジの密度が増大し電気二重層キャパシタの分極性電極として用いた場合に、蓄電容量が増大する。   According to this method, a plurality of micropores having a diameter of 2 nm or less and mesopores having a diameter of 2 to 50 nm are formed in the carbon fiber of marimocarbon, and the surface area of these pores increases the surface area of marimocarbon. A marimocarbon with a surface area can be produced. In addition, since the graphite edge is exposed on the surface of the hole, the density of the graphite edge increases, and the storage capacity increases when used as a polarizable electrode of an electric double layer capacitor.

本発明の高比表面積マリモカーボンを用いた電気二重層キャパシタは、分極性電極と電解液を用いる電気二重層キャパシタにおいて、分極性電極が、高比表面積マリモカーボンから成ることを特徴とする。
高比表面積マリモカーボンのカーボン繊維は、カーボンナノチューブであれば好ましく、また、カーボンナノチューブは多層カーボンナノチューブであれば好ましい。
高比表面積マリモカーボンのカーボン繊維は、カップ積層型カーボンナノフィラメント又はコイン積層型カーボンナノフィラメントであれば好ましい。 The electric double layer capacitor using the high specific surface area marimocarbon of the present invention is characterized in that in the electric double layer capacitor using a polarizable electrode and an electrolyte, the polarizable electrode is made of high specific surface area marimocarbon.
The carbon fiber of the high specific surface area marimocarbon is preferably a carbon nanotube, and the carbon nanotube is preferably a multi-walled carbon nanotube.
The carbon fiber of the high specific surface area marimocarbon is preferably a cup laminated carbon nanofilament or a coin laminated carbon nanofilament.

電気二重層キャパシタは、電気二重層が形成できる電極、すなわち分極性電極と、電解液と、電解液のイオンのみを通過させるセパレータと、分極性電極に電荷を供給する又は分極性電極の電荷を集電して取り出す集電極を有しており、背面に集電極を有する一対の分極性電極をセパレータを挟んで対向させた構造体に電解液を封入したセルから成る。
本発明の高比表面積マリモカーボンを用いた電気二重層キャパシタは、分極性電極が、高比表面積マリモカーボンから成るので、従来のマリモカーボンを用いた電気二重層キャパシタに比べて比表面積が大きいので、グラファイト・エッジの密度が大きく、従って、蓄電容量が大きい。
高比表面積マリモカーボンのカーボン繊維は、カーボンナノチューブであれば好ましく、またカーボンナノチューブは多層カーボンナノチューブであれば好ましい。
高比表面積マリモカーボンのカーボン繊維は、カップ積層型カーボンナノフィラメント又はコイン積層型カーボンナノフィラメントであれば好ましい。 An electric double layer capacitor is an electrode capable of forming an electric double layer, that is, a polarizable electrode, an electrolytic solution, a separator that allows only ions of the electrolytic solution to pass through, a charge to the polarizable electrode, or a charge of the polarizable electrode. It has a collector electrode that collects and collects electricity, and is composed of a cell in which an electrolyte solution is sealed in a structure in which a pair of polarizable electrodes having a collector electrode on the back face is opposed to each other with a separator interposed therebetween.
In the electric double layer capacitor using the high specific surface area marimocarbon of the present invention, since the polarizable electrode is made of high specific surface area marimocarbon, the specific surface area is larger than that of the conventional electric double layer capacitor using marimocarbon. The density of the graphite edge is large, and therefore the storage capacity is large.
The carbon fiber of the high specific surface area marimocarbon is preferably a carbon nanotube, and the carbon nanotube is preferably a multi-walled carbon nanotube.
The carbon fiber of the high specific surface area marimocarbon is preferably a cup laminated carbon nanofilament or a coin laminated carbon nanofilament.

本発明の高比表面積マリモカーボンの製造方法によれば、高比表面積マリモカーボンを製造することができる。また、本発明の高比表面積マリモカーボンを用いた電気二重層キャパシタは従来のマリモカーボンを用いた電気二重層キャパシタに比べて蓄電容量が大きい。   According to the method for producing high specific surface area marimocarbon of the present invention, high specific surface area marimocarbon can be produced. In addition, the electric double layer capacitor using the high specific surface area marimocarbon of the present invention has a larger storage capacity than the conventional electric double layer capacitor using marimocarbon.

以下、本発明の高比表面積マリモカーボンの製造方法、及び、高比表面積マリモカーボンを用いた電気二重層キャパシタを実施例に基づき詳細に説明する。
初めにマリモカーボンの製造方法を説明する。
マリモカーボンは、粒径が数〜５００ｎｍの酸化ダイヤモンドを触媒担体とし、ニッケル（Ｎｉ）、コバルト（Ｃｏ）、パラジウム（Ｐｄ）等の遷移金属を触媒とした触媒を炭化水素の流気中で浮遊、撹拌すると共に、加熱して炭化水素を熱分解することによって製造できる。酸化ダイヤモンドは市販の人工ダイヤモンドで良く、また、触媒金属を担持する前にダイヤモンド表面を酸化処理することが望ましい。炭化水素は、炭素数が１から３０の炭化水素であれば良く、メタン、エタン、プロパンなどの飽和炭化水素の他に、エチレン、アセチレン、プロピレンなどの不飽和炭化水素を用いても良い。
マリモカーボンは、酸化ダイヤモンドと、酸化ダイヤモンドの表面に成長した複数のカーボン繊維とからなる、径がμｍオーダーの球状の微粒子、すなわちマリモ状のカーボン繊維である。カーボン繊維は、触媒金属がＮｉ又はＣｏである場合にはカーボンナノチューブになり、Ｐｄである場合にはコイン積層型カーボンナノグラファイト又はカップ積層型カーボンナノフィラメントになる。
これらのカーボン繊維は互いに形状が異なるが、いずれも、単層グラファイト層から形成されており、これらのグラファイト層のグラファイト・エッジが電気二重の形成に寄与する。 EXAMPLES Hereinafter, the manufacturing method of the high specific surface area marimo carbon of this invention and the electric double layer capacitor using the high specific surface area marimo carbon are demonstrated in detail based on an Example.
First, a method for producing marimocarbon will be described.
Marimocarbon floats a catalyst using transition metal such as nickel (Ni), cobalt (Co), palladium (Pd), etc. in a hydrocarbon stream, using diamond oxide with a particle size of several to 500 nm as a catalyst carrier. It can be produced by stirring and heating to thermally decompose hydrocarbons. The diamond oxide may be a commercially available artificial diamond, and it is desirable to oxidize the diamond surface before supporting the catalytic metal. The hydrocarbon may be a hydrocarbon having 1 to 30 carbon atoms, and may be an unsaturated hydrocarbon such as ethylene, acetylene or propylene in addition to a saturated hydrocarbon such as methane, ethane or propane.
Marimocarbon is a spherical fine particle having a diameter on the order of μm, that is, a marimo-like carbon fiber, composed of oxidized diamond and a plurality of carbon fibers grown on the surface of the oxidized diamond. The carbon fiber becomes a carbon nanotube when the catalytic metal is Ni or Co, and becomes a coin laminated carbon nanographite or a cup laminated carbon nanofilament when it is Pd.
Although these carbon fibers are different in shape from each other, they are all formed from a single-layer graphite layer, and the graphite edges of these graphite layers contribute to the formation of an electric double.

実施例では、触媒金属にＮｉ、炭化水素にエタンを用い、反応温度５００℃、反応時間５時間でマリモカーボンを作製した。
図１は、本実施例で作製したマリモカーボンの走査電子顕微鏡（ＳＥＭ）像を示す図である。図１から、マリモカーボンはほぼ球形であることがわかり、表面が毳立っていることがわかる。毳立っているものがカーボン繊維である。
図２はマリモカーボンの構造を示す模式図である。
図２に示すように、本実施例のマリモカーボンは、酸化ダイヤモンド１を核として、カーボンナノチューブ２が放射状に高密度に成長した、径がμｍオーダーの球状の微粒子、すなわち、マリモ状のカーボン繊維である。 In the examples, marimocarbon was produced using Ni as the catalyst metal and ethane as the hydrocarbon, with a reaction temperature of 500 ° C. and a reaction time of 5 hours.
FIG. 1 is a diagram showing a scanning electron microscope (SEM) image of marimocarbon produced in this example. From FIG. 1, it can be seen that the marimocarbon is almost spherical and the surface is standing upright. What stands out is carbon fiber.
FIG. 2 is a schematic diagram showing the structure of marimocarbon.
As shown in FIG. 2, the marimocarbon of the present example is a spherical fine particle having a diameter of the order of μm in which carbon nanotubes 2 are grown radially and densely with oxide diamond 1 as a nucleus, that is, marimo-like carbon fiber. It is.

次に、マリモカーボンを賦活した、すなわち、マリモカーボンの比表面積の増大を行った。賦活方法は、得られた粉末状のマリモカーボンと粉末状のＫＯＨとを混合し、不活性ガス中で熱処理することで行った。
粉末状のマリモカーボンと粉末状のＫＯＨとを質量比で１対４の割合で混合した。ＫＯＨの比が１未満では賦活できず、４より大きくても、４と比べて賦活の程度に大きな差はなかった。この混合物を６００〜８００℃の温度で１〜３時間、窒素中で熱処理した。賦活の熱処理条件は、下記に説明するように、７００℃、２時間が最適であった。 Next, marimocarbon was activated, that is, the specific surface area of marimocarbon was increased. The activation method was performed by mixing the obtained powdery marimocarbon and powdery KOH and heat-treating them in an inert gas.
Powdered marimocarbon and powdered KOH were mixed at a mass ratio of 1: 4. Activation was not possible when the KOH ratio was less than 1, and even if it was greater than 4, there was no significant difference in the degree of activation compared to 4. The mixture was heat treated in nitrogen at a temperature of 600-800 ° C. for 1-3 hours. The heat treatment conditions for activation were optimum at 700 ° C. for 2 hours as described below.

図３は賦活後のマリモカーボンのＳＥＭ像を示す図である。図からわかるように、マリモカーボンのカーボンナノチューブの表面には、複数の白い微細な点が存在する。この白い点は、下記に説明するように、カーボンナノチューブに形成されたミクロ孔及びメソ孔である。
ＫＯＨは活性炭の賦活にも使用されており、Ｋ（カリウム）が炭素の層をこじ開けて比表面積を増大させると言われている。マリモカーボンをＫＯＨで賦活するとマリモカーボンのカーボンナノチューブの表面にミクロ孔及びメソ孔が形成されることがわかる。 FIG. 3 is a view showing an SEM image of marimocarbon after activation. As can be seen from the figure, there are a plurality of fine white dots on the surface of the marimocarbon carbon nanotube. The white dots are micropores and mesopores formed in the carbon nanotubes as described below.
KOH is also used for activation of activated carbon, and K (potassium) is said to open the carbon layer and increase the specific surface area. It can be seen that when the marimocarbon is activated with KOH, micropores and mesopores are formed on the surface of the marimocarbon carbon nanotubes.

図４は温度７００℃での賦活前後のマリモカーボンのＸ線回折像を示す図である。（ａ）は賦活前、（ｂ）は賦活後のＸ線回折像である。図のピークはグラファイト結晶の回折ピークである。図から、賦活前後でＸ線回折像に変化が見られないことがわかる。すなわち、上記の賦活条件ではマリモカーボンを構成するグラファイト構造に変化が生じないことがわかる。   FIG. 4 is a diagram showing X-ray diffraction images of marimocarbon before and after activation at a temperature of 700.degree. (A) is an X-ray diffraction image before activation, and (b) is an X-ray diffraction image after activation. The peak in the figure is the diffraction peak of the graphite crystal. From the figure, it can be seen that there is no change in the X-ray diffraction image before and after activation. That is, it turns out that a change does not arise in the graphite structure which comprises marimo carbon on said activation conditions.

次に、マリモカーボンの比表面積（ｍ2 ／ｇ）、及びミクロ孔、メソ孔の細孔容積（ｍリットル／ｇ）を測定した。測定は、冷却した試料にＮ2 ガスを流してＮ2 を吸着させ、等温吸着平衡圧曲線から求めるＢＥＴ法（非特許文献２参照）を用いた。
図５は賦活したマリモカーボンの比表面積、及びミクロ孔、メソ孔の細孔容積を示す図である。比較試料は、未処理試料すなわち賦活しないマリモカーボン、温度７００℃で２時間賦活したマリモカーボン、及び、温度８００℃で２時間賦活したマリモカーボンである。
図から、比表面積の増大は賦活温度７００℃で最大になり、未処理試料に比べて約２．７倍に増加することがわかる。また、賦活温度８００℃では、賦活温度７００℃に比べて比表面積が減少し、ミクロ孔の細孔容積が減少すると共にミクロ孔より大きな孔であるメソ孔の細孔容積が増大していることがわかる。 Next, the specific surface area (m 2 / g) of marimocarbon and the pore volume (ml / g) of micropores and mesopores were measured. The measurement was performed using a BET method (see Non-Patent Document 2) obtained from an isothermal adsorption equilibrium pressure curve by flowing N 2 gas through a cooled sample to adsorb N 2 .
FIG. 5 is a diagram showing the specific surface area of activated marimocarbon and the pore volume of micropores and mesopores. The comparative samples are untreated samples, ie, non-activated marimocarbon, marimocarbon activated for 2 hours at 700 ° C., and marimocarbon activated for 2 hours at 800 ° C.
From the figure, it can be seen that the increase in the specific surface area becomes maximum at an activation temperature of 700 ° C. and increases about 2.7 times that of the untreated sample. In addition, at an activation temperature of 800 ° C., the specific surface area is reduced compared to the activation temperature of 700 ° C., the pore volume of the micropores is decreased, and the pore volume of the mesopores that are larger than the micropores is increased. I understand.

図６はマリモカーボンの比表面積、及びミクロ孔、メソ孔の細孔容積が賦活によって増大する様子を示す模式図である。（ａ）は未処理試料のマリモカーボンのカーボンナノチューブの断面を示し、（ｂ）は温度７００℃で賦活したマリモカーボンのカーボンナノチューブの断面を、（ｃ）は温度８００℃で賦活したマリモカーボンのカーボンナノチューブの断面を示す。
図６（ａ）に示したシームレスに先端が閉じられた多層カーボンナノチューブ３は、温度７００℃の賦活によって図６（ｂ）に示すように、カーボンナノチューブの表面に孔４が複数形成される。この賦活温度では、孔４の大きさは比較的小さく、ミクロ孔とメソ孔がそれぞれ存在する。温度８００℃の賦活では、図６（ｃ）に示すように、孔４の数の増大よりも、孔４の容積の増大が優先的に進むものと考えられ、メソ孔が増えて全細孔容積が増大するが、同時にミクロ孔の合体等も生ずるようになり比表面積は減少する、と考えられる。 FIG. 6 is a schematic view showing a state in which the specific surface area of marimocarbon and the pore volume of micropores and mesopores are increased by activation. (A) shows the cross section of the untreated sample of marimocarbon carbon nanotubes, (b) shows the cross section of the marimocarbon carbon nanotubes activated at a temperature of 700 ° C., and (c) shows the marimocarbon carbon nanotubes activated at a temperature of 800 ° C. The cross section of a carbon nanotube is shown.
As shown in FIG. 6B, the multi-walled carbon nanotube 3 with the seamlessly closed tip shown in FIG. 6A has a plurality of holes 4 formed on the surface of the carbon nanotube as shown in FIG. At this activation temperature, the size of the holes 4 is relatively small, and there are micropores and mesopores, respectively. In the activation at a temperature of 800 ° C., as shown in FIG. 6 (c), it is considered that the increase in the volume of the holes 4 preferentially proceeds rather than the increase in the number of the holes 4, and the number of mesopores increases and all the pores increase. Although the volume increases, at the same time, coalescence of micropores occurs and the specific surface area is considered to decrease.

次に、賦活したマリモカーボン、すなわち、高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタを作製し、放電容量（蓄電容量）を測定した。
次に電気二重層キャパシタの作製方法を説明する。
バインダーとしてテフロン（登録商標）樹脂を用いた。テフロン（登録商標）樹脂とマリモカーボンとエタノールとを所定の比率で混合し、乳鉢で良く混練してスラリーを作製し、このスラリーを鋳型に入れて１１０℃、２時間の真空乾燥によって板状に成型した。この板から１ｃｍ×１ｃｍの大きさで切り出したものを分極性電極とした。
ポリプロピレン不織布をセパレータとして、上記２枚の分極性電極を対向させ、電解液として１モル％濃度のＨ2 ＳＯ4 水溶液を用い、真空中で１時間放置して、分極性電極に電解液を含浸させた。なお、集電極と分極性電極は接着剤を用いずに、圧着によって接触させた。
試料として、未処理のマリモカーボン、温度７００℃で賦活したマリモカーボン、及び温度８００℃で賦活したマリモカーボンをそれぞれ用いて、上記の方法で電気二重層キャパシタを作製した。 Next, an electric double layer capacitor using a activated marimocarbon, that is, a high specific surface area marimocarbon, as a polarizable electrode was prepared, and the discharge capacity (storage capacity) was measured.
Next, a method for manufacturing the electric double layer capacitor will be described.
Teflon (registered trademark) resin was used as a binder. Teflon (registered trademark) resin, marimocarbon, and ethanol are mixed at a predetermined ratio and kneaded well in a mortar to prepare a slurry. The slurry is placed in a mold and dried into a plate by vacuum drying at 110 ° C. for 2 hours. Molded. What was cut out from this plate with a size of 1 cm × 1 cm was used as a polarizable electrode.
Using a polypropylene nonwoven fabric as a separator, the above two polarizable electrodes face each other, and a 1 mol% concentration H 2 SO 4 aqueous solution is used as an electrolytic solution, which is left in a vacuum for 1 hour to impregnate the polarizable electrode with the electrolytic solution. I let you. The collector electrode and the polarizable electrode were brought into contact with each other without using an adhesive.
As samples, untreated marimocarbon, marimocarbon activated at a temperature of 700 ° C., and marimocarbon activated at a temperature of 800 ° C. were used to produce an electric double layer capacitor by the above method.

図７は、本発明の高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタの構成を示す模式図である。本発明の電気二重層キャパシタ５は、電気二重層が形成できる電極、すなわち分極性電極６と、電解液７と、電解液７のイオンのみを通過させるセパレータ８と、分極性電極６に電荷を供給する又は分極性電極６の電荷を集電して取り出す集電極９と、集電極９に接続した端子１０を有しており、端子１０を介して充放電する。分極性電極６は複数の高比表面積マリモカーボン１１から成り、複数の高比表面積マリモカーボン１１は高密度に、且つ電解液７が十分染み込む隙間を有して充填されている。   FIG. 7 is a schematic view showing a configuration of an electric double layer capacitor using the high specific surface area marimocarbon of the present invention as a polarizable electrode. The electric double layer capacitor 5 of the present invention has an electrode capable of forming an electric double layer, that is, a polarizable electrode 6, an electrolytic solution 7, a separator 8 that allows only ions of the electrolytic solution 7 to pass through, and a charge to the polarizable electrode 6. It has a collector electrode 9 that collects and takes out the charge of the polarizable electrode 6 that is supplied or is charged, and a terminal 10 connected to the collector electrode 9, and is charged and discharged via the terminal 10. The polarizable electrode 6 is composed of a plurality of high specific surface area marimocarbons 11, and the plurality of high specific surface area marimocarbons 11 are filled with a high density and a gap into which the electrolyte solution 7 is sufficiently soaked.

放電容量の測定は、充電電流密度１．０ｍＡ／ｃｍ2 で１ｖｏｌｔまで充電し、その後、放電電流密度０．１〜１．０ｍＡ／ｃｍ2 の範囲の種々の一定電流密度で放電させ、放電電流を放電時間で積分して全放電電荷量を求め、全放電電荷量と充電電圧とから放電容量を求めた。
図８は本発明の高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタの特性を示す図である。図から、温度７００℃で賦活したマリモカーボンを用いた電気二重層キャパシタの放電容量は、未処理のマリモカーボンを用いた電気二重層キャパシタの放電容量に比べて約３倍大きいことがわかる。この結果は、マリモカーボンのカーボン繊維に、２ｎｍ以下の径のミクロ孔、及び２〜５０ｎｍ径のメソ孔が複数形成され、これらの孔の表面積がマリモカーボンの表面積を増大させ、孔の表面にはグラファイト・エッジが露出するので、グラファイト・エッジの密度が増大し、電気二重層キャパシタの蓄電容量が増大したものと考えられる。
また、特許文献１の図４に示されているように、未処理のマリモカーボンを用いた電気二重層キャパシタの放電容量は、従来の活性炭を用いた電気二重層キャパシタの放電容量に比べて約１．４倍大きいので、本発明の高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタの放電容量は、従来の活性炭を用いた電気二重層キャパシタの放電容量に比べて、約４．２倍大きいことがわかる。 Measurements of the discharge capacity at a charging current density of 1.0 mA / cm 2 was charged to 1 Volt, then discharged at various constant current density in the range of discharge current density 0.1~1.0mA / cm 2, discharge current Was integrated by the discharge time to determine the total discharge charge amount, and the discharge capacity was determined from the total discharge charge amount and the charge voltage.
FIG. 8 is a diagram showing the characteristics of an electric double layer capacitor using the high specific surface area marimocarbon of the present invention as a polarizable electrode. From the figure, it can be seen that the discharge capacity of the electric double layer capacitor using marimocarbon activated at a temperature of 700 ° C. is about three times larger than the discharge capacity of the electric double layer capacitor using untreated marimocarbon. This result shows that a plurality of micropores with a diameter of 2 nm or less and mesopores with a diameter of 2 to 50 nm are formed in the carbon fiber of marimocarbon, and the surface area of these pores increases the surface area of marimocarbon, and on the surface of the pores. Since the graphite edge is exposed, it is considered that the density of the graphite edge is increased and the storage capacity of the electric double layer capacitor is increased.
Further, as shown in FIG. 4 of Patent Document 1, the discharge capacity of the electric double layer capacitor using untreated marimocarbon is approximately the discharge capacity of the electric double layer capacitor using conventional activated carbon. Since it is 1.4 times larger, the discharge capacity of the electric double layer capacitor using the high specific surface area marimocarbon of the present invention as a polarizable electrode is about 4 times that of a conventional electric double layer capacitor using activated carbon. It can be seen that it is twice as large.

本発明の方法によれば、高比表面積のマリモカーボンを製造することができる。
また、本発明の高比表面積のマリモカーボンを電気二重層キャパシタの分極性電極とした電気二重層キャパシタは、従来の活性炭を分極性電極とした電気二重層キャパシタに比べて約４倍の蓄電容量が得られ、従って、電気自動車、燃料電池自動車、或いはハイブリッド自動車のバッテリー電源のバックアップ用電源、或いは、パーソナルコンピューターのメモリーバックアップ用電源等に用いれば極めて有用である。 According to the method of the present invention, marimocarbon having a high specific surface area can be produced.
In addition, the electric double layer capacitor using the marimocarbon having a high specific surface area of the present invention as the polarizable electrode of the electric double layer capacitor has a storage capacity approximately four times that of the conventional electric double layer capacitor using activated carbon as the polarizable electrode. Therefore, it is extremely useful when used as a backup power source for a battery power source of an electric vehicle, a fuel cell vehicle, or a hybrid vehicle or a memory backup power source for a personal computer.

実施例で作製したマリモカーボンの走査電子顕微鏡像を示す図である。It is a figure which shows the scanning electron microscope image of the marimo carbon produced in the Example. マリモカーボンの構造を示す模式図である。It is a schematic diagram which shows the structure of a marimo carbon. 賦活後のマリモカーボンの走査電子顕微鏡像を示す図である。It is a figure which shows the scanning electron microscope image of the marimo carbon after activation. 賦活前後のマリモカーボンのＸ線回折像を示す図である。It is a figure which shows the X-ray-diffraction image of the marimo carbon before and behind activation. 賦活したマリモカーボンの比表面積、及びミクロ孔、メソ孔の細孔容積を示す図である。It is a figure which shows the specific surface area of the activated marimo carbon, and the pore volume of a micropore and a mesopore. マリモカーボンの比表面積、及びミクロ孔、メソ孔の細孔容積が賦活によって増大する様子を示す模式図である。It is a schematic diagram which shows a mode that the specific surface area of a marimo carbon and the pore volume of a micropore and a mesopore increase by activation. 本発明の高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタの構成を示す図である。It is a figure which shows the structure of the electric double layer capacitor which used the high specific surface area marimo carbon of this invention as a polarizable electrode. 本発明の高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタの特性を示す図である。It is a figure which shows the characteristic of the electric double layer capacitor which used the high specific surface area marimo carbon of this invention as a polarizable electrode.

符号の説明Explanation of symbols

１ 酸化ダイヤモンド
２ カーボンナノチューブ
３ 多層カーボンナノチューブ
４ 孔
５ 高比表面積マリモカーボンを分極性電極とした電気二重層キャパシタ
６ 分極性電極
７ 電解液
８ セパレータ
９ 集電極
１０ 端子 DESCRIPTION OF SYMBOLS 1 Oxidized diamond 2 Carbon nanotube 3 Multi-walled carbon nanotube 4 Hole 5 Electric double layer capacitor 6 having high specific surface area marimo carbon as polarizable electrode 6 Polarized electrode 7 Electrolytic solution 8 Separator 9 Collector electrode 10 Terminal

Claims (9)

マリモカーボンに水酸化カリウムを混合し、この混合物を不活性ガス中で熱処理することを特徴とする、高比表面積マリモカーボンの製造方法。   A method for producing high specific surface area marimocarbon, comprising mixing marimocarbon with potassium hydroxide and heat-treating the mixture in an inert gas. 前記マリモカーボンと水酸化カリウムとの混合比は、質量比で１〜４であることを特徴とする、請求項１に記載の高比表面積マリモカーボンの製造方法。   The method for producing high specific surface area marimocarbon according to claim 1, wherein a mixing ratio of the marimocarbon and potassium hydroxide is 1 to 4 in terms of mass ratio. 前記熱処理の温度は６００〜８００℃、熱処理時間は１〜３時間であることを特徴とする、請求項１に記載の高比表面積マリモカーボンの製造方法。   The method for producing high specific surface area marimocarbon according to claim 1, wherein the heat treatment temperature is 600 to 800 ° C. and the heat treatment time is 1 to 3 hours. 前記マリモカーボンのカーボン繊維は、カーボンナノチューブ、カップ積層型カーボンナノフィラメント又はコイン積層型カーボンナノフィラメントであることを特徴とする、請求項１に記載の高比表面積マリモカーボンの製造方法。   The method for producing high specific surface area marimocarbon according to claim 1, wherein the carbon fiber of the marimocarbon is a carbon nanotube, a cup laminated carbon nanofilament, or a coin laminated carbon nanofilament. 分極性電極と電解液を用いる電気二重層キャパシタにおいて、分極性電極が高比表面積マリモカーボンから成ることを特徴とする、高比表面積マリモカーボンを用いた電気二重層キャパシタ。   An electric double layer capacitor using a high specific surface area marimocarbon, wherein the polarizable electrode is made of a high specific surface area marimocarbon in an electric double layer capacitor using a polarizable electrode and an electrolyte. 前記高比表面積マリモカーボンのカーボン繊維はカーボンナノチューブであることを特徴とする、請求項５に記載の高比表面積マリモカーボンを用いた電気二重層キャパシタ。   The electric double layer capacitor using the high specific surface area marimocarbon according to claim 5, wherein the carbon fiber of the high specific surface area marimocarbon is a carbon nanotube. 前記カーボンナノチューブは多層カーボンナノチューブであることを特徴とする、請求項６に記載の高比表面積マリモカーボンを用いた電気二重層キャパシタ。   The electric double layer capacitor using a high specific surface area marimocarbon according to claim 6, wherein the carbon nanotube is a multi-walled carbon nanotube. 前記高比表面積マリモカーボンのカーボン繊維は、カップ積層型カーボンナノフィラメントであることを特徴とする、請求項５に記載の高比表面積マリモカーボンを用いた電気二重層キャパシタ。   The electric double layer capacitor using the high specific surface area marimo carbon according to claim 5, wherein the carbon fiber of the high specific surface area marimo carbon is a cup laminated carbon nanofilament. 前記高比表面積マリモカーボンのカーボン繊維は、コイン積層型カーボンナノフィラメントであることを特徴とする、請求項５に記載の高比表面積マリモカーボンを用いた電気二重層キャパシタ。   6. The electric double layer capacitor using a high specific surface area marimo carbon according to claim 5, wherein the carbon fiber of the high specific surface area marimo carbon is a coin laminated carbon nanofilament.
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