JP2004014762A

JP2004014762A - Carbon material for electric double layered capacitor and its manufacturing method

Info

Publication number: JP2004014762A
Application number: JP2002165465A
Authority: JP
Inventors: Toshiharu Nonaka; 野中　俊晴; Toshio Saotome; 五月女　敏男; Kazuyuki Murakami; 村上　一幸; Hidetoshi Morotomi; 諸富　秀俊
Original assignee: JFE Chemical Corp
Current assignee: JFE Chemical Corp
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2004-01-15
Anticipated expiration: 2022-06-06
Also published as: JP4313547B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide active carbon for the electrode of an electric double layered capacitor, which is high in volume capacitance and capable of restraining the electrode from increasing in volume when it is used as active carbon for the electrode of an electric double layered capacitor by controlling the crystal structure of carbide material and activating it under an optimal condition. <P>SOLUTION: The active carbon has a pore volume of 0.9 to 1.5 cc/g obtained through a nitrogen adsorption isotherm in electrode at a temperature of 77 K, and the volume ratio of pores 15 Å or below in size to all the pores is set at 30 to 50:100 in the active carbon. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、電気二重層コンデンサーの電極用炭素材料およびその製造方法に関する。
【０００２】
【従来の技術】
従来、易黒鉛化性炭素材料からなる炭化物（以下「原料炭化物」という）を、アルカリ賦活した炭素材料（以下「活性炭」という）を電極材料として用いた電気二重層コンデンサーは、体積当たりの静電容量が高く、その実用化の目処が付き始めている。
【０００３】
【発明が解決しようとする課題】
しかしながら、従来の原料炭化物をアルカリ賦活して得られる活性炭は、電気二重層コンデンサーの電極として用いた場合、充放電時に電極の体積が２〜３倍に膨張することがあるため、積層型や巻回型の電気二重層コンデンサーにおいては、ケース内に前記体積膨張量に見合う空間を設けるか、ケース強度を強めるかの対策が必要となり、その結果、コンデンサーが大きくなり、コストアップに繋がるという問題がある。
【０００４】
本発明は、原料炭化物の結晶構造を制御し、それを最適な条件で賦活することにより、体積容量が高く、電気二重層コンデンサーの電極用活性炭として使用した場合、該電極の体積膨張を抑えることができる電気二重層コンデンサーの電極用活性炭を提供することを目的とする。
【０００５】
【課題を解決するための手段】
上記目的は以下の本発明によって達成される。すなわち、本発明は、７７Ｋでの窒素吸着等温線から求められる全細孔容積が０．９〜１．５ｃｃ／ｇであり、１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０〜５０％であることを特徴とする電気二重層コンデンサー用活性炭を提供する。該活性炭は、Ｘ線回折測定から求められるｄ_００２が、０．３８０〜０．４１５ｎｍであることが好ましい。
【０００６】
また、本発明は、Ｘ線回折測定から求められるｄ_００２の、活性炭と原料炭化物との比（活性炭ｄ_００２／原料炭化物ｄ_００２）（以下「Ｒ」という）が１．０４〜１．２０であり、かつ７７Ｋでの窒素吸着等温線から求められる全細孔容積が０．９〜１．５ｃｃ／ｇであり、１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０〜５０％であることを特徴とする電気二重層コンデンサー用活性炭を提供する。
【０００７】
また、本発明は、１次ＱＩの含有量が０．１〜１０質量％である軟化点５０〜１２０℃のコールタールピッチを、窒素ブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４７〜０．３６０ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活することを特徴とする前記何れかの活性炭の製造方法を提供する。
【０００８】
また、本発明は、１次ＱＩの含有量が０〜６質量％である軟化点５０〜１２０℃のコールタールピッチを、エアーブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４９〜０．３６３ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活することを特徴とする前記何れかの活性炭の製造方法を提供する。
【０００９】
【発明の実施の形態】
次に好ましい実施の形態を挙げて本発明をさらに詳しく説明する。
本発明の請求項１の活性炭は、下記のａ及びｂの構成を有することを特徴とする。
ａ．７７Ｋでの窒素吸着等温線から求められる全細孔容積が０．９〜１．５ｃｃ／ｇであること。
ｂ．１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０〜５０％であること。
本発明の請求項３の活性炭は、前記のａおよびｂの構成に加えて下記構成ｃを有することを特徴とする。
ｃ．Ｘ線回折測定から求められるｄ_００２の、活性炭と原料炭化物との比（活性炭ｄ_００２／原料炭化物ｄ_００２）が１．０４〜１．２０であること。
【００１０】
前記構成ａについては、全細孔容積が０．９ｃｃ／ｇ未満であると、該活性炭を電気二重層コンデンサーの電極として用いた場合、充放電時に電極の体積が１５０％以上に膨張する。一方、全細孔容積が１．５ｃｃ／ｇを越えると、電極に用いた場合、電極の嵩密度が上がらず、電極の体積容量が小さくなり、何れにしても本発明の目的が達成されない。
【００１１】
前記構成ｂについては、１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０％未満であると、該活性炭を電気二重層コンデンサーの電極として用いた場合、体積容量が上がらず、一方、５０％を越えると、充放電時に電極の体積が１５０％以上に膨張し、何れにしても本発明の目的が達成されない。
【００１２】
前記構成ｃについては、Ｒが１．０４より小さい値である活性炭を電気二重層コンデンサーの電極として用いた場合、充放電時に電極の体積が１５０％以上に膨張する場合がある。一方、Ｒが１．２０よりも大きな値であると、電極の導電性が悪くなり、電極の内部抵抗が高くなる場合があるので、何れにしても本発明において好ましくはない。
【００１３】
一般に原料炭化物のアルカリ賦活による活性炭の細孔形成は、炭素のガス化反応によるメソポアの生成と、積層した芳香族平面の面間に賦活剤であるアルカリ金属が侵入することでミクロ細孔が発達すると言われている。アルカリ金属の侵入によるミクロ細孔の発達により、積層した芳香族平面が乱れ、前記Ｒの値が変化する。すなわち、Ｒの値が小さすぎると、前記の通り充放電時に電極の体積膨張が大きく、一方、Ｒの値が大きすぎると電極として不適当になる。すなわち、本発明で使用する原料炭化物は、その結晶構造が適度に乱れていた方が、賦活して得られる活性炭からなる電極の体積膨張を緩和するために好ましいものと推測される。
【００１４】
上記本発明の活性炭を製造する好ましい第１の製造方法は、１次ＱＩ（キノリン不溶分）の含有量が０．１〜１０質量％でありかつ軟化点５０〜１２０℃のコールタールピッチを、窒素ブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４７〜０．３６０ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活する方法である。この方法により、前記ａ〜ｃの構成を有する本発明の活性炭が得られる。
【００１５】
一般にコールタールピッチの１次ＱＩの含有量を制御することで、原料炭化物の結晶構造を制御することが可能である。ここで、１次ＱＩとは、ピッチ中に微量に含まれるカーボンブラック状の微小球状物質が集合したものである。元来、コールタールピッチにはコークス乾留過程で生成した炭素含有率の高い成分から構成される１次ＱＩが存在する。その含有率はコークス炉の乾留条件や使用する石炭によって異なるが、一般に数質量％から十数質量％含有するとされている。
【００１６】
本発明の上記第１の方法では、この１次ＱＩの含有量を０．１〜１０質量％に制御する必要がある。１次ＱＩの含有量が０．１質量％未満では、原料となる炭化物の結晶構造が高度に発達し、賦活処理において原料炭化物の賦活が困難になり、そのため、賦活剤としてのアルカリ金属水酸化物が多量に必要となり、得られる活性炭のコストアップの要因となる。また、少量のアルカリ金属水酸化物を用いると、得られる活性炭の細孔があまり発達せず、この活性炭は静電容量は高いが、該活性炭からなる電気二重層コンデンサーの電極の充放電時における体積膨張が大きくなる。
【００１７】
本発明で用いるピッチの１次ＱＩの含有量が１０質量％を超える場合には、沈降分離、遠心分離あるいは濾過などの公知の分離技術で、１次ＱＩの含有量を前記の範囲とすればよい。一方、１次ＱＩの含有量が０または痕跡程度である場合には、カーボンブラックなどの１次ＱＩをピッチに添加して前記の範囲とすることができる。
【００１８】
また、上記本発明方法では、上記１次ＱＩを含有するピッチの軟化点は、５０〜１２０℃であり、好ましくは７０〜１００℃である。軟化点が５０℃未満では、後の熱処理において揮発する成分が多くあるため、１次ＱＩの含有率が上昇してしまい、本発明の効果が得られない。一方、軟化点が１２０℃を超えるとピッチの熱重合による２次ＱＩが発生するため、１次ＱＩの定量が困難になる。
【００１９】
上記本発明の方法においては、上記の１次ＱＩの含有量および軟化点を有するピッチを、窒素ブロー下で熱処理し、該熱処理物を不融化および炭化処理して原料炭化物を得る。上記熱処理は３５０〜４５０℃の温度、好ましくは３８０℃〜４５０℃の温度で１〜１３時間行ない、ピッチの軟化点を２００〜３７５℃、好ましくは２５０〜３７５℃とする。熱処理温度が３５０℃よりも低いとピッチの軟化点が上昇するのに時間がかかり、コスト的に好ましくない。一方、熱処理温度が４５０℃よりも高いと、熱処理中においてコーキングが起こり、熱処理物の反応器からの抜き出しがスムースに行われないので好ましくない。
【００２０】
上記不融化処理は、前記熱処理した軟化点２５０〜３７５℃のピッチを微細に粉砕した後、その粉砕形状を保つために行なう。この不融化処理は２００〜３５０℃、好ましくは２５０〜３００℃で０．５〜１０時間程度酸化ガスフロー下で行う。さらに炭化処理は、５００〜１，０００℃、好ましくは６００〜８００℃の温度で１〜１０時間不活性ガス雰囲気下で行い、原料炭化物の結晶性の制御を行う。上記温度が５００℃よりも低いと、炭化に長時間を要しコスト的に不利であり、一方、上記処理温度が１，０００℃を超える温度であると、後のアルカリ賦活が殆ど進行しないので好ましくない。このようにして得られる原料炭化物のＸ線回折測定から求められるｄ_００２は０．３４７〜０．３６０ｎｍである。
【００２１】
上記で得られた原料炭化物を賦活処理することにより、本発明の活性炭が得られる。賦活処理自体は従来公知の方法でよく、例えば、賦活剤としては水酸化ナトリウムや水酸化カリウムなどアルカリ金属の水酸化物が用いられるが、得られる活性炭にミクロ細孔からメソ細孔にシャープな細孔径分布を与える水酸化カリウムが好ましい。賦活剤の使用量は原料炭化物の質量の２〜４倍であり、賦活温度は５００〜１，０００℃、好ましくは５００〜８００℃であり、賦活時間は３０分〜１０時間、好ましくは３０分〜４時間である。この賦活処理は不活性ガス雰囲気下に行う。
【００２２】
上記賦活処理は、結晶性が比較的高い原料炭化物を用いた場合には、上記範囲内において比較的高温および長時間行い、結晶性が比較的低い原料炭化物を用いた場合には、上記範囲内において比較的低温および短時間行うことが好ましい。所定の温度および時間で賦活処理した後、約１００℃で水蒸気を吹き込み、アルカリ金属を失活させてアルカリ金属水酸化物に戻し、得られた活性炭を濾過し、エタノール／水混合溶媒中で−０．１ＭＰａまで真空脱気を行い、ガスが出なくなったことを確認後、酸洗い、超音波洗浄を繰り返す。水洗後、濾液が中性であることを確認し、熱風乾燥および真空乾燥を行い、本発明の活性炭が得られる。このようにして得られる本発明の活性炭のＸ線回折測定から求められるｄ_００２は０．３８０〜０．４１５ｎｍである。
【００２３】
本発明の好ましい第２の製造方法は、１次ＱＩの含有量が０〜６質量％である軟化点５０〜１２０℃のコールタールピッチを、エアーブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４９〜０．３６３ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活する方法である。この方法により、前記ａ〜ｃの構成を有する本発明の活性炭が得られる。なお、この方法では、エアの吹き込みにより、炭化物結晶構造内にエーテル結合が形成され、原料炭化物の結晶の発達が制御されるものと思われる。
【００２４】
上記方法におけるピッチの１次ＱＩの含有量の調整は、前記第１の方法と同様に行うことができ、ピッチの軟化点は前記第１の方法と同様である。熱処理は２５０〜３５０℃の温度で１〜１２時間行ない、ピッチの軟化点を前記の第１の方法と同様の軟化点とする。熱処理温度が２５０℃よりも低いと、ピッチの軟化点が上昇するのに時間がかかり、コスト的に好ましくない。一方、熱処理温度が３５０℃よりも高いと、熱処理中においてピッチとエアとの反応でピッチが発火する危険性があり好ましくない。なお、上記第２の方法における不融化、炭化、賦活などの条件およびそれらの数値の意義は前記第１の方法の場合と同様である。
【００２５】
以上の如き本発明の方法によって得られる本発明の活性炭は、電気二重層コンデンサーの電極材料として使用した場合、体積容量が高く、充放電時において電極の膨張が充分に抑えられている。従って本発明の活性炭は、電気二重層コンデンサーの電極用活性炭として有用である。
【００２６】
なお、電気二重層コンデンサーの充放電時における電極の膨張の原理は完全には明らかにされていないが、原料炭化物を温和な条件でアルカリ賦活した、比表面積の比較的小さい活性炭で顕著に起る現象である。この現象は電界賦活と呼ばれているが、電解液中のイオンが上記活性炭の細孔をこじ開けるようにして静電容量を発現するため、電極が膨張することは不可避である。
【００２７】
本発明は、上記の如き課題を、前記説明の通り、原料炭化物の結晶構造をピッチ中のＱＩの含有量により調整するとともに、該炭化物の賦活条件の組み合わせを最適化することで解決したものである。
【００２８】
【実施例】
次に実施例および比較例を挙げて本発明をさらに具体的に説明する。なお、本発明は下記の実施例によって何ら制限されるものではない。
＜実施例１＞
タールピッチ（軟化点：５２℃、１次ＱＩ：０．１質量％）を窒素ガス吹込み下、４５０℃で１３時間加熱を行い、軟化点３７５℃の１次ＱＩ低濃度の高軟化点ピッチを得た。このピッチを平均粒径３０μｍに粉砕し、空気気流下２８０℃で３０分間不融化処理を行い、次いで７００℃で２時間窒素気流下で炭化処理した。この原料炭化物に重量比で３倍のＫＯＨを混練後、８００℃で１時間窒素ガスフロー下で賦活を行った後、常法に従いＫＯＨを除去して本発明の活性炭を得た。
【００２９】
＜実施例２＞
タールピッチ（軟化点：１１０℃、１次ＱＩ：６質量％）に４質量％のカーボンブラックを１５０℃で加熱攪拌し均一に分散させる。得られた１次ＱＩ添加ピッチの軟化点は１１９℃、１次ＱＩの含有量は１０質量％であった。熱処理、不融化、炭化までを実施例１と同様の操作で行い、ＫＯＨ比２倍、７００℃で１時間窒素フロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３０】
＜実施例３＞
タールピッチ（軟化点：１１９℃、１次ＱＩ：６質量％）を熱処理、不融化、炭化までを実施例１と同様の操作で行い、ＫＯＨ比３倍、８００℃で１時間窒素フロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３１】
＜実施例４＞
タールピッチ（軟化点：１１０℃、１次ＱＩ：６質量％）に３倍量のキノリンを加え、１５０℃で加熱攪拌してピッチを溶解させる。ピッチ溶液を濾過し、濾液を減圧下（５０ｍｍＨｇ約６．５Ｋｐａ）、１５０〜２００℃に加熱してキノリンを除去する。得られた１次ＱＩ除去ピッチの軟化点は１１３℃、１次ＱＩの含有量は２質量％であった。熱処理、不融化、炭化までは実施例１と同様の操作で行い、ＫＯＨ比２．５倍、８００℃で１時間、窒素ガスフロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３２】
＜実施例５＞
タールピッチ（軟化点：８０℃、１次ＱＩ：０質量％）を空気バブリング下、２５０℃で１０時間熱処理を行った。不融化は２５０℃で４時間、炭化は７００℃で１時間行い、ＫＯＨ比３倍、７５０℃で１時間窒素フロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３３】
＜実施例６＞
タールピッチ（軟化点：４５℃、１次ＱＩ：０．１質量％）に等量のキノリンを加え、１５０℃で加熱攪拌しピッチを溶解させる。ピッチ溶液を濾過し、濾液を減圧下（５０ｍｍＨｇ約６．５Ｋｐａ）、１５０〜２００℃に加熱してキノリンを除去する。得られた１次ＱＩ除去ピッチの軟化点は５１℃、１次ＱＩの含有量は痕跡程度であった。このピッチをエアーブロー下で３５０℃で４時間熱処理を行った。このピッチを２５０℃で２時間不融化、７００℃で２時間炭化を行った。ＫＯＨ比３倍、８００℃で１時間窒素フロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３４】
＜実施例７＞
タールピッチ（軟化点：１１９℃、１次ＱＩ：６質量％）をエアーブロー下３２０℃で３時間熱処理を行った。このピッチを２８０℃で０．５時間不融化、７００℃で２時間炭化を行った。ＫＯＨ比３倍、８００℃で１時間窒素フロー下で賦活を行なった以外は実施例１と同様にして本発明の活性炭を得た。
【００３５】
＜比較例１＞
タールピッチ（軟化点：８０℃、１次ＱＩ：０質量％）を窒素ブロー下、４５０℃で１３時間熱処理を行い、軟化点３７５℃の熱処理ピッチを得た。２８０℃で０．５時間不融化、７００℃で２時間炭化後、ＫＯＨ比３倍、８００℃で１時間、窒素フロー下で賦活を行って比較例の活性炭を得た。
【００３６】
＜比較例２＞
タールピッチ（軟化点：１１０℃、１次ＱＩ：６質量％）に２質量％のカーボンブラックを１５０℃で溶融混合した。得られたピッチは軟化点１２１℃、１次ＱＩ８質量％であった。２５０℃で１２時間エアーブロー下で熱処理を行い、軟化点２５０℃のピッチを得た。このピッチを平均粒径３０μｍに粉砕後、２５０℃で４時間不融化、７００℃で２時間炭化を行った。ＫＯＨ比３倍、８００℃で１時間、窒素フロー下で賦活を行って比較例の活性炭を得た。
【００３７】
＜比較例３＞
タールピッチ（軟化点：５０℃、１次ＱＩ：０．１質量％）に等量のキノリンを加え、１５０℃で加熱攪拌しピッチを溶解させる。ピッチ溶液を濾過し、濾液を減圧下（５０ｍｍＨｇ約６．５Ｋｐａ）、１５０〜２００℃に加熱してキノリンを除去する。得られた１次ＱＩ除去ピッチの軟化点は５２℃、１次ＱＩの含有量は０．０５質量％であった。エアーブロー下での熱処理を３６０℃で３時間で行い、平均粒径３０μｍに粉砕後、２８０℃で０．５時間不融化、７００℃で２時間炭化後、ＫＯＨ比３倍、８００℃で１時間賦活を行って比較例の活性炭を得た。
【００３８】
上記実施例および比較例において用いたピッチの１次ＱＩの含有量、軟化点（℃）、熱処理、不融化、炭化および賦活条件などを下記表１に示した。

【００３９】
前記実施例および比較例で得られた活性炭の物性およびキャパシタ特性を下記表２に示した。上記物性およびキャパシタ特性は下記の方法で測定した。
・細孔容積の測定
装置はマイクロメリティックス（株）社製のＴｒｉｓｔａｒ　３０００を使用し、７７Ｋでの窒素吸着等温線よりＢＪＨ法で求めた。
・静電容量などの測定
活性炭：バインダー：導電材＝９５：３：２の質量割合で混練後、圧延して電極シートを作成した。２枚の電極シートを図１に示すビーカーセル中の０．８Ｍのテトラエチルアンモニウムテトラフルオロボレート［（Ｃ_２Ｈ_５）_４ＮＢＦ_４］中に含浸した。このセルを変位測定装置に固定した。変位測定装置はフレーム固定台、シャフト固定台およびセル固定台からなり、変位センサー取付アームに変位センサーが取り付けてある。電極はサンプル押えブロックで押さえられ、充放電時に正負両極合計の膨張が観測される。膨張率は初期の電極厚み（電極２枚分）を１００％として示し、膨張が安定する２０サイクル後の値を示した。静電容量は３サイクル目の放電曲線から計算した。内部抵抗はＩＲドロップから算出した。
【００４０】
・Ｒ値の測定（ｄ_００２の解析）
理学電機製のＲＵ−３００を用いて広角法（線源ＣｕＫｒ線、管電圧４０ＫＶ、管電流３００ｍＡ）による測定を行い計算した。活性炭と原料炭化物のｄ_００２の測定をそれぞれ行い、その比（Ｒ＝活性炭のｄ_００２／原料炭化物のｄ_００２）を求めた。
以上の結果を下記表２に示す。
【００４１】

【００４２】
【発明の効果】
以上説明したように、本発明によれば、原料炭化物の結晶構造を、ピッチ中の一次ＱＩの含有量で制御し、それを最適な条件で賦活することにより、体積容量が高く、膨張を抑えた電気二重層コンデンサーの電極用活性炭を提供することができる。
【図面の簡単な説明】
【図１】実施例で使用した変位測定装置を説明する図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carbon material for an electrode of an electric double layer capacitor and a method for producing the same.
[0002]
[Prior art]
Conventionally, an electric double layer capacitor using a carbon material (hereinafter, referred to as “raw carbon”) made of easily graphitizable carbon material as an electrode material and an alkali-activated carbon material (hereinafter, referred to as “activated carbon”) as an electrode material has an electrostatic capacitance per volume. The capacity is high and the prospect of its practical use is beginning to appear.
[0003]
[Problems to be solved by the invention]
However, when activated carbon obtained by conventional alkali activation of a raw material carbide is used as an electrode of an electric double layer capacitor, the volume of the electrode may expand two to three times during charging and discharging. In a round-type electric double layer capacitor, it is necessary to provide a space in the case corresponding to the volume expansion amount or to increase the strength of the case, and as a result, the capacitor becomes large, leading to an increase in cost. is there.
[0004]
The present invention controls the crystal structure of a raw material carbide and activates it under optimal conditions, so that the volume capacity is high, and when used as activated carbon for an electrode of an electric double layer capacitor, the volume expansion of the electrode is suppressed. It is an object of the present invention to provide an activated carbon for an electrode of an electric double layer capacitor that can be used.
[0005]
[Means for Solving the Problems]
The above object is achieved by the present invention described below. That is, in the present invention, the total pore volume determined from the nitrogen adsorption isotherm at 77K is 0.9 to 1.5 cc / g, and the ratio of the pore volume of 15 ° or less to the total pore volume (15 ° or less) (Pore volume / Total pore volume × 100) is 30 to 50%. The activated carbon preferably has a d ₀₀₂ obtained from X-ray diffraction measurement of 0.380 to 0.415 nm.
[0006]
Further, the present invention relates to the use of _{d 002} obtained by X-ray diffraction measurement, the ratio of the activated carbon and the raw material carbides (activated carbon _{d 002} / feedstock carbide _{d 002)} (hereinafter referred to as "R") is at 1.04 to 1.20 And the total pore volume determined from the nitrogen adsorption isotherm at 77 K is 0.9 to 1.5 cc / g, and the ratio of the pore volume of 15 ° or less to the total pore volume (pores of 15 ° or less) Volume / total pore volume × 100) of 30 to 50%.
[0007]
Further, the present invention provides a heat treatment of a coal tar pitch having a softening point of 50 to 120 ° C. having a primary QI content of 0.1 to 10% by mass under nitrogen blow to infusibilize and carbonize the heat treated product. Te, the _{d 002} obtained by X-ray diffraction measurement of the carbide in the range of 0.347～0.360Nm, production of the any of the activated carbon then the carbide characterized by activation with an alkali metal hydroxide Provide a method.
[0008]
The present invention also provides a coal tar pitch having a primary QI content of 0 to 6% by mass and a softening point of 50 to 120 ° C., which is heat-treated under air blowing to infusibilize and carbonize the heat-treated product. the d ₀₀₂ obtained by X-ray diffraction measurement of the carbide in the range of 0.349～0.363Nm, a manufacturing method of the any of the activated carbon then the carbide characterized by activation with an alkali metal hydroxide provide.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described in more detail with reference to preferred embodiments.
The activated carbon of claim 1 of the present invention is characterized by having the following configurations a and b.
a. The total pore volume determined from the nitrogen adsorption isotherm at 77K is 0.9 to 1.5 cc / g.
b. The ratio of the pore volume of 15 ° or less to the total pore volume (pore volume of 15 ° or less / total pore volume × 100) is 30 to 50%.
The activated carbon according to claim 3 of the present invention is characterized in that it has the following configuration c in addition to the above configurations a and b.
c. Things _{d 002} obtained by X-ray diffraction measurement, the ratio of the activated carbon and the raw material carbides (activated carbon _{d 002} / feedstock carbide _{d 002)} is 1.04 to 1.20.
[0010]
Regarding the configuration a, when the total pore volume is less than 0.9 cc / g, when the activated carbon is used as an electrode of an electric double layer capacitor, the volume of the electrode expands to 150% or more during charging and discharging. On the other hand, when the total pore volume exceeds 1.5 cc / g, when used for an electrode, the bulk density of the electrode does not increase and the volume capacity of the electrode decreases, and in any case, the object of the present invention is not achieved.
[0011]
Regarding the configuration b, when the ratio of the pore volume of 15 ° or less to the total pore volume (pore volume of 15 ° or less / total pore volume × 100) is less than 30%, the activated carbon is transferred to the electric double layer capacitor. When used as an electrode, the volume capacity does not increase. On the other hand, when it exceeds 50%, the volume of the electrode expands to 150% or more during charge and discharge, and the object of the present invention is not achieved in any case.
[0012]
Regarding the configuration c, when activated carbon having a value of R smaller than 1.04 is used as an electrode of an electric double layer capacitor, the volume of the electrode may expand to 150% or more during charging and discharging. On the other hand, if R is a value larger than 1.20, the conductivity of the electrode is deteriorated, and the internal resistance of the electrode may be increased.
[0013]
In general, the formation of pores in activated carbon by alkali activation of raw material carbides is caused by the formation of mesopores by the gasification reaction of carbon and the development of micropores by the penetration of alkali metal, an activator, between the planes of the stacked aromatic planes. It is said that. The development of micropores due to the intrusion of the alkali metal disturbs the stacked aromatic planes and changes the value of R. That is, if the value of R is too small, the volume expansion of the electrode during charge / discharge is large as described above, while if the value of R is too large, it becomes unsuitable as an electrode. That is, it is presumed that the raw material carbide used in the present invention preferably has an appropriately disordered crystal structure in order to reduce the volume expansion of the electrode made of activated carbon obtained by activation.
[0014]
A preferred first production method for producing the activated carbon of the present invention is a method for producing coal tar pitch having a primary QI (quinoline insoluble matter) content of 0.1 to 10% by mass and a softening point of 50 to 120 ° C, A heat treatment is performed under a nitrogen blow to infusibilize and carbonize the heat-treated material so that d ₀₀₂ obtained from X-ray diffraction measurement of the carbide is in a range of 0.347 to 0.360 nm. It is a method of activating with a substance. According to this method, the activated carbon of the present invention having the above-described structures a to c is obtained.
[0015]
Generally, by controlling the primary QI content of the coal tar pitch, it is possible to control the crystal structure of the raw material carbide. Here, the primary QI is an aggregate of carbon black-like microspheres contained in a minute amount in the pitch. Originally, the coal tar pitch has a primary QI composed of a component having a high carbon content generated in the coke carbonization process. Although its content varies depending on the conditions of carbonization of the coke oven and the coal used, it is generally said that the content is from several mass% to more than ten mass%.
[0016]
In the first method of the present invention, it is necessary to control the content of the primary QI to 0.1 to 10% by mass. When the content of the primary QI is less than 0.1% by mass, the crystal structure of the carbide as the raw material is highly developed, and it becomes difficult to activate the raw material carbide in the activation treatment. A large amount of the material is required, which increases the cost of the obtained activated carbon. In addition, when a small amount of an alkali metal hydroxide is used, the pores of the obtained activated carbon do not develop much, and this activated carbon has a high capacitance, but during charging and discharging of the electrodes of an electric double layer capacitor made of the activated carbon. The volume expansion increases.
[0017]
When the content of the primary QI of the pitch used in the present invention exceeds 10% by mass, the content of the primary QI should be within the above range by a known separation technique such as sedimentation, centrifugation or filtration. Good. On the other hand, when the content of the primary QI is 0 or a trace, a primary QI such as carbon black can be added to the pitch to make the pitch fall within the above range.
[0018]
In the method of the present invention, the softening point of the pitch containing the primary QI is 50 to 120 ° C, preferably 70 to 100 ° C. When the softening point is lower than 50 ° C., many components are volatilized in the subsequent heat treatment, so that the content of the primary QI increases, and the effect of the present invention cannot be obtained. On the other hand, if the softening point exceeds 120 ° C., secondary QI occurs due to thermal polymerization of the pitch, and it becomes difficult to determine the primary QI.
[0019]
In the method of the present invention, the pitch having the above-mentioned primary QI content and softening point is heat-treated under nitrogen blow, and the heat-treated product is infusibilized and carbonized to obtain a raw material carbide. The heat treatment is performed at a temperature of 350 to 450 ° C, preferably 380 to 450 ° C for 1 to 13 hours, and the softening point of the pitch is set to 200 to 375 ° C, preferably 250 to 375 ° C. If the heat treatment temperature is lower than 350 ° C., it takes time to increase the softening point of the pitch, which is not preferable in terms of cost. On the other hand, if the heat treatment temperature is higher than 450 ° C., coking occurs during the heat treatment, and the heat-treated product is not smoothly extracted from the reactor, which is not preferable.
[0020]
The infusibilization treatment is performed to finely pulverize the heat-treated softening point having a softening point of 250 to 375 ° C. and then maintain the pulverized shape. This infusibilization treatment is performed at 200 to 350 ° C., preferably 250 to 300 ° C., for about 0.5 to 10 hours under an oxidizing gas flow. Further, the carbonization treatment is performed at a temperature of 500 to 1,000 ° C., preferably 600 to 800 ° C. for 1 to 10 hours under an inert gas atmosphere to control the crystallinity of the raw material carbide. If the above temperature is lower than 500 ° C., carbonization takes a long time, which is disadvantageous in cost. On the other hand, if the above treatment temperature is higher than 1,000 ° C., the subsequent alkali activation hardly proceeds. Not preferred. The d ₀₀₂ obtained from the X-ray diffraction measurement of the raw material carbide thus obtained is 0.347 to 0.360 nm.
[0021]
The activated carbon of the present invention can be obtained by activating the raw material carbide obtained above. The activation treatment itself may be a conventionally known method, for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is used as the activator, but the obtained activated carbon has a sharp from micropores to mesopores. Potassium hydroxide which gives a pore size distribution is preferred. The amount of the activator used is 2 to 4 times the mass of the raw material carbide, the activation temperature is 500 to 1,000 ° C, preferably 500 to 800 ° C, and the activation time is 30 minutes to 10 hours, preferably 30 minutes. ~ 4 hours. This activation treatment is performed in an inert gas atmosphere.
[0022]
The activation treatment is performed at a relatively high temperature and for a long time within the above range when using a raw material carbide having relatively high crystallinity, and within the above range when using a raw material carbide having relatively low crystallinity. At a relatively low temperature for a short time. After activation treatment at a predetermined temperature and time, steam is blown at about 100 ° C. to deactivate the alkali metal and return it to an alkali metal hydroxide, and the obtained activated carbon is filtered and mixed in an ethanol / water mixed solvent. Vacuum degassing is performed to 0.1 MPa, and after confirming that no gas is generated, pickling and ultrasonic cleaning are repeated. After washing with water, it is confirmed that the filtrate is neutral, and hot air drying and vacuum drying are performed to obtain the activated carbon of the present invention. _{D 002} obtained by X-ray diffraction measurement of the activated carbon of the present invention thus obtained is 0.380～0.415Nm.
[0023]
In a preferred second production method of the present invention, a coal tar pitch having a primary QI content of 0 to 6% by mass and a softening point of 50 to 120 ° C. is heat-treated under air blowing to make the heat-treated product infusible. And carbonizing to set d ₀₀₂ obtained by X-ray diffraction measurement of the carbide to a range of 0.349 to 0.363 nm, and thereafter activating the carbide with an alkali metal hydroxide. According to this method, the activated carbon of the present invention having the above-described structures a to c is obtained. In this method, it is considered that the blowing of air forms an ether bond in the carbide crystal structure, thereby controlling the development of the crystal of the raw material carbide.
[0024]
The adjustment of the primary QI content of the pitch in the above method can be performed in the same manner as in the first method, and the softening point of the pitch is the same as in the first method. The heat treatment is performed at a temperature of 250 to 350 ° C. for 1 to 12 hours, and the softening point of the pitch is set to the same softening point as in the first method. If the heat treatment temperature is lower than 250 ° C., it takes time to increase the softening point of the pitch, which is not preferable in terms of cost. On the other hand, if the heat treatment temperature is higher than 350 ° C., the pitch may be ignited by the reaction between the pitch and the air during the heat treatment, which is not preferable. The conditions of infusibilization, carbonization, activation and the like in the second method and the significance of the numerical values are the same as in the case of the first method.
[0025]
When the activated carbon of the present invention obtained by the method of the present invention as described above is used as an electrode material of an electric double layer capacitor, the activated carbon has a high volume capacity, and the expansion of the electrode during charge and discharge is sufficiently suppressed. Therefore, the activated carbon of the present invention is useful as an activated carbon for an electrode of an electric double layer capacitor.
[0026]
Although the principle of electrode expansion during charge and discharge of an electric double layer capacitor is not completely clarified, it occurs remarkably in activated carbon with a relatively small specific surface area, where the raw material carbide has been alkali-activated under mild conditions. It is a phenomenon. Although this phenomenon is called electric field activation, since the ions in the electrolytic solution pry open the pores of the activated carbon to develop a capacitance, it is inevitable that the electrodes expand.
[0027]
The present invention solves the above-mentioned problems by adjusting the crystal structure of the raw material carbide by the content of QI in the pitch and optimizing the combination of the activation conditions of the carbide, as described above. is there.
[0028]
【Example】
Next, the present invention will be described more specifically with reference to examples and comparative examples. The present invention is not limited by the following examples.
<Example 1>
Tar pitch (softening point: 52 ° C., primary QI: 0.1 mass%) is heated at 450 ° C. for 13 hours under nitrogen gas blowing, and the primary QI low concentration high softening point pitch having a softening point of 375 ° C. Got. This pitch was pulverized to an average particle size of 30 μm, subjected to an infusibilization treatment at 280 ° C. for 30 minutes in an air stream, and then carbonized at 700 ° C. for 2 hours in a nitrogen stream. After kneading three times the weight ratio of KOH to this raw material carbide, activation was performed at 800 ° C. for 1 hour under a nitrogen gas flow, and then KOH was removed according to a conventional method to obtain an activated carbon of the present invention.
[0029]
<Example 2>
4% by mass of carbon black is heated and stirred at 150 ° C. in a tar pitch (softening point: 110 ° C., primary QI: 6% by mass) to be uniformly dispersed. The softening point of the obtained primary QI-added pitch was 119 ° C., and the content of the primary QI was 10% by mass. Activated carbon of the present invention was treated in the same manner as in Example 1 except that heat treatment, infusibilization, and carbonization were performed in the same manner as in Example 1, and activation was performed at 700 ° C. for 1 hour under a nitrogen flow at twice the KOH ratio. Obtained.
[0030]
<Example 3>
A tar pitch (softening point: 119 ° C., primary QI: 6% by mass) is subjected to heat treatment, infusibilization, and carbonization in the same manner as in Example 1, and the KOH ratio is 3 times, at 800 ° C. for 1 hour under a nitrogen flow. An activated carbon of the present invention was obtained in the same manner as in Example 1 except that activation was performed.
[0031]
<Example 4>
Three times the amount of quinoline is added to the tar pitch (softening point: 110 ° C., primary QI: 6% by mass), and the pitch is dissolved by heating and stirring at 150 ° C. The pitch solution is filtered, and the filtrate is heated to 150-200 ° C. under reduced pressure (50 mmHg about 6.5 Kpa) to remove quinoline. The softening point of the obtained primary QI removal pitch was 113 ° C., and the content of the primary QI was 2% by mass. Heat treatment, infusibilization, and carbonization were performed in the same manner as in Example 1. The procedure was the same as in Example 1 except that activation was performed under a nitrogen gas flow at a KOH ratio of 2.5 times at 800 ° C. for 1 hour. The activated carbon of the invention was obtained.
[0032]
<Example 5>
The tar pitch (softening point: 80 ° C, primary QI: 0% by mass) was heat-treated at 250 ° C for 10 hours under air bubbling. Activated carbon of the present invention was prepared in the same manner as in Example 1 except that infusibilization was performed at 250 ° C. for 4 hours, carbonization was performed at 700 ° C. for 1 hour, and KOH ratio was tripled and activation was performed at 750 ° C. for 1 hour under nitrogen flow. Obtained.
[0033]
<Example 6>
An equivalent amount of quinoline is added to tar pitch (softening point: 45 ° C, primary QI: 0.1% by mass), and the mixture is heated and stirred at 150 ° C to dissolve the pitch. The pitch solution is filtered, and the filtrate is heated to 150-200 ° C. under reduced pressure (50 mmHg about 6.5 Kpa) to remove quinoline. The softening point of the obtained primary QI removal pitch was 51 ° C., and the content of the primary QI was about a trace. This pitch was heat-treated at 350 ° C. for 4 hours under air blow. The pitch was made infusible at 250 ° C. for 2 hours and carbonized at 700 ° C. for 2 hours. Activated carbon of the present invention was obtained in the same manner as in Example 1 except that activation was performed at 800 ° C. for 1 hour under a nitrogen flow at a KOH ratio of 3 times.
[0034]
<Example 7>
The tar pitch (softening point: 119 ° C, primary QI: 6% by mass) was heat-treated at 320 ° C for 3 hours under air blowing. The pitch was infusibilized at 280 ° C. for 0.5 hour and carbonized at 700 ° C. for 2 hours. Activated carbon of the present invention was obtained in the same manner as in Example 1 except that activation was performed at 800 ° C. for 1 hour under a nitrogen flow at a KOH ratio of 3 times.
[0035]
<Comparative Example 1>
The tar pitch (softening point: 80 ° C., primary QI: 0 mass%) was heat-treated at 450 ° C. for 13 hours under nitrogen blow to obtain a heat-treated pitch having a softening point of 375 ° C. After infusibilizing at 280 ° C. for 0.5 hour and carbonizing at 700 ° C. for 2 hours, activation was performed at a KOH ratio of 3 and at 800 ° C. for 1 hour under a nitrogen flow to obtain activated carbon of a comparative example.
[0036]
<Comparative Example 2>
2% by mass of carbon black was melt-mixed at 150 ° C. with tar pitch (softening point: 110 ° C., primary QI: 6% by mass). The obtained pitch had a softening point of 121 ° C. and a primary QI of 8% by mass. Heat treatment was performed at 250 ° C. for 12 hours under air blowing to obtain a pitch having a softening point of 250 ° C. This pitch was pulverized to an average particle size of 30 μm, infusibilized at 250 ° C. for 4 hours, and carbonized at 700 ° C. for 2 hours. Activation was performed at 800 ° C. for 1 hour under a nitrogen flow at a KOH ratio three times to obtain activated carbon of a comparative example.
[0037]
<Comparative Example 3>
An equal amount of quinoline is added to tar pitch (softening point: 50 ° C, primary QI: 0.1% by mass), and the mixture is heated and stirred at 150 ° C to dissolve the pitch. The pitch solution is filtered, and the filtrate is heated to 150-200 ° C. under reduced pressure (50 mmHg about 6.5 Kpa) to remove quinoline. The softening point of the obtained primary QI removal pitch was 52 ° C., and the content of the primary QI was 0.05% by mass. Heat treatment under air blow was performed at 360 ° C for 3 hours, pulverized to an average particle size of 30 µm, infusibilized at 280 ° C for 0.5 hour, carbonized at 700 ° C for 2 hours, KOH ratio 3 times, and 800 ° C for 1 hour. Activation was performed for a time to obtain activated carbon of Comparative Example.
[0038]
Table 1 below shows the primary QI content, softening point (° C.), heat treatment, infusibility, carbonization and activation conditions of the pitch used in the above Examples and Comparative Examples.

[0039]
Table 2 below shows the physical properties and capacitor characteristics of the activated carbons obtained in the above Examples and Comparative Examples. The above physical properties and capacitor characteristics were measured by the following methods.
The pore volume was measured by a BJH method using a nitrogen adsorption isotherm at 77 K using a Tristar 3000 manufactured by Micromeritics Co., Ltd.
Measurement of capacitance and the like Activated carbon: binder: conductive material = kneaded at a mass ratio of 95: 3: 2, and then rolled to prepare an electrode sheet. Two electrode sheets were impregnated in 0.8 M tetraethylammonium tetrafluoroborate [(C ₂ H ₅ ) ₄ NBF ₄ ] in the beaker cell shown in FIG. This cell was fixed to a displacement measuring device. The displacement measuring device comprises a frame fixing stand, a shaft fixing stand and a cell fixing stand, and a displacement sensor is attached to a displacement sensor attaching arm. The electrodes are held down by the sample holding block, and the expansion of the positive and negative electrodes is observed during charge and discharge. The expansion rate is shown as a value after 20 cycles when the initial electrode thickness (for two electrodes) is 100% and the expansion is stabilized. The capacitance was calculated from the discharge curve at the third cycle. The internal resistance was calculated from the IR drop.
[0040]
Measurement of R value (d ₀₀₂ analysis)
Using RU-300 manufactured by Rigaku Denki, measurement was performed by a wide-angle method (CuKr line source, tube voltage 40 KV, tube current 300 mA) and calculation was performed. Performs each measured _{d 002} of activated carbon and the raw material carbides was determined _{(d 002} of _{d 002} / feedstock carbide R = activated carbon) the ratio.
The above results are shown in Table 2 below.
[0041]

[0042]
【The invention's effect】
As described above, according to the present invention, the crystal structure of the raw material carbide is controlled by the content of the primary QI in the pitch, and activated under optimal conditions, thereby increasing the volume capacity and suppressing the expansion. Activated carbon for an electrode of an electric double layer capacitor.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a displacement measuring device used in an embodiment.

Claims

７７Ｋでの窒素吸着等温線から求められる全細孔容積が０．９〜１．５ｃｃ／ｇであり、１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０〜５０％であることを特徴とする電気二重層コンデンサー用炭素材料。The total pore volume determined from the nitrogen adsorption isotherm at 77 K is 0.9 to 1.5 cc / g, and the ratio of the pore volume of 15 ° or less to the total pore volume (pore volume of 15 ° or less / total (Pore volume x 100) of 30 to 50%.

Ｘ線回折測定から求められるｄ_００２が、０．３８０〜０．４１５ｎｍである請求項１に記載の炭素材料。Carbon material according to claim 1 _{d 002} obtained by X-ray diffraction measurement, it is 0.380～0.415Nm.

Ｘ線回折測定から求められるｄ_００２の、賦活後炭素材料と賦活前炭素材料との比（賦活後炭素材料ｄ_００２／賦活前炭素材料ｄ_００２）が１．０４〜１．２０であり、かつ７７Ｋでの窒素吸着等温線から求められる全細孔容積が０．９〜１．５ｃｃ／ｇであり、１５Å以下の細孔容積の全細孔容積に占める割合（１５Å以下の細孔容積／全細孔容積×１００）が３０〜５０％であることを特徴とする電気二重層コンデンサー用炭素材料。Of _{d 002} obtained by X-ray diffraction measurement, the ratio of the activated after the carbon material and activated before the carbon material (activated after the carbon material _{d 002} / activated before carbon material _{d 002)} is 1.04 to 1.20, and The total pore volume determined from the nitrogen adsorption isotherm at 77 K is 0.9 to 1.5 cc / g, and the ratio of the pore volume of 15 ° or less to the total pore volume (pore volume of 15 ° or less / total (Pore volume x 100) of 30 to 50%.

１次ＱＩの含有量が０．１〜１０質量％である軟化点５０〜１２０℃のコールタールピッチを、窒素ブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４７〜０．３６０ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活することを特徴とする請求項１〜３の何れか１項に記載の炭素材料の製造方法。A coal tar pitch having a softening point of 50 to 120 ° C. having a primary QI content of 0.1 to 10% by mass is heat-treated under nitrogen blow, and the heat-treated product is rendered infusible and carbonized to form X of the carbide. the _{d 002} determined from ray diffraction measurement in a range of 0.347～0.360Nm, then the carbon product according to any one of claims 1 to 3, characterized in that activated with an alkali metal hydroxide Manufacturing method of carbon material.

１次ＱＩの含有量が０〜６質量％である軟化点５０〜１２０℃のコールタールピッチを、エアーブロー下で熱処理し、該熱処理物を不融化および炭化して、該炭化物のＸ線回折測定から求められるｄ_００２を０．３４９〜０．３６３ｎｍの範囲とし、その後該炭化物をアルカリ金属水酸化物で賦活することを特徴とする請求項１〜３の何れか１項に記載の炭素材料の製造方法。A coal tar pitch having a softening point of 50 to 120 ° C. having a primary QI content of 0 to 6% by mass is heat-treated under air blowing, the heat-treated material is rendered infusible and carbonized, and X-ray diffraction of the carbide is performed. the _{d 002} obtained from the measurement in the range of 0.349～0.363Nm, carbon material according to any one of claims 1 to 3, then the carbide characterized by activation with an alkali metal hydroxide Manufacturing method.

請求項１〜３の何れか１項に記載の炭素材料からなる電極を有することを特徴とする電気二重層コンデンサー。An electric double layer capacitor comprising an electrode made of the carbon material according to claim 1.