JP2004107814A - Method for producing activated carbon fiber and electric double layer capacitor using the same - Google Patents
Method for producing activated carbon fiber and electric double layer capacitor using the same Download PDFInfo
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical class C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 64
- 239000003990 capacitor Substances 0.000 title claims abstract description 47
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 40
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 73
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- 238000000034 method Methods 0.000 claims abstract description 17
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- 238000003763 carbonization Methods 0.000 claims description 20
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- 238000004438 BET method Methods 0.000 description 3
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- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 3
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- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
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- 239000006230 acetylene black Substances 0.000 description 1
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- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
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- 238000000227 grinding Methods 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
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- 238000002347 injection Methods 0.000 description 1
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- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000002074 melt spinning Methods 0.000 description 1
- 230000006984 memory degeneration Effects 0.000 description 1
- 208000023060 memory loss Diseases 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000005011 phenolic resin Substances 0.000 description 1
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- 239000002798 polar solvent Substances 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 0.000 description 1
- 235000011181 potassium carbonates Nutrition 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- 235000011118 potassium hydroxide Nutrition 0.000 description 1
- 239000004304 potassium nitrite Substances 0.000 description 1
- 235000010289 potassium nitrite Nutrition 0.000 description 1
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical compound [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 description 1
- 229910052939 potassium sulfate Inorganic materials 0.000 description 1
- 235000011151 potassium sulphates Nutrition 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 150000003242 quaternary ammonium salts Chemical class 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
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- 150000003839 salts Chemical class 0.000 description 1
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- 239000011257 shell material Substances 0.000 description 1
- 235000011121 sodium hydroxide Nutrition 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- CBXCPBUEXACCNR-UHFFFAOYSA-N tetraethylammonium Chemical compound CC[N+](CC)(CC)CC CBXCPBUEXACCNR-UHFFFAOYSA-N 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- QEMXHQIAXOOASZ-UHFFFAOYSA-N tetramethylammonium Chemical compound C[N+](C)(C)C QEMXHQIAXOOASZ-UHFFFAOYSA-N 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-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
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Carbon And Carbon Compounds (AREA)
- Inorganic Fibers (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、活性炭素繊維の製造方法に関し、さらに詳しくは、メソフェーズピッチ系炭素繊維をアルカリ金属化合物で処理する活性炭素繊維の製造方法に関する。本発明の製造方法にて得られる活性炭素繊維は、高性能電気二重層キャパシタの電極材として用いるのに好適である他、吸着や浄水などの活性炭としての利用分野においても好適に使用することができる。
【０００２】
【従来の技術】
近年、携帯電話やノート型パソコンなどの新しい電子機器が次々に出現し、これら商品の小型軽量化、携帯化などの開発競争から、それに内蔵されるＩＣメモリやマイコンなども小型高性能化が進んでいる。ところが、このようなＩＣメモリなどの素子やマイコンは、電力瞬断時に電子機器のメモリ消却や機能停止などの誤作動を起こす恐れがある。実際、コンピューター機器は、適切な対策を講じなければ１０〜２０％のわずかな電圧低下であっても、電圧低下が０．００３〜０．０２秒間続くだけで、機能停止やメモリ喪失などが起こり、電子機器の機能が麻痺してしまう。
【０００３】
この対策として、Ｎｉ−Ｃｄ電池やアルミ電解コンデンサがバックアップ電源として用いられてきた。しかし、これらの電源は使用温度範囲、充放電のサイクル回数、容量、急速充放電性およびコストなどの点で充分なものではなかった。この市場ニーズに応え開発されたものが電気二重層キャパシタである。当初、電気二重層キャパシタには活性炭が電極材として用いられてきたが、最近、より高比表面積を有する活性炭素繊維を用いた電気二重層キャパシタが注目されるようになってきている。
【０００４】
さらに従来の小電力分野から電気自動車用バッテリーの補助電源などの大容量分野への応用が考えられ、一部、減速時の回生運動エネルギーをキャパシタに充電し、加速時に逆に放電してエンジンの出力の補助をさせるという目的でキャパシタを搭載した乗用車が参考出品の段階に来ている。
電気二重層の研究の歴史は古く１８７９年のＨｅｌｍｈｏｌｔｚに遡ることができる。一般に、異なる二層が接触すると、界面に正、負の電荷が短距離を隔てて配列する。この界面にできた電荷分布を電気二重層と呼ぶ。
【０００５】
電気二重層キャパシタは、この電気二重層に電圧を加えて電荷を蓄積するものである。しかし、実用化には長時間を要し、ようやく１９８０年代の初めになって、この原理を用いたファラッド単位の大容量コンデンサの出現をみた。
電気二重層キャパシタは、電極表面と電解液との界面に形成される電気二重層を利用した大容量のコンデンサであり、充放電に通常の二次電池のような化学反応を伴わない。このために、二次電池と比較して内部抵抗が格段に低く大電流放電が可能である。さらに、充放電回数の制限が無いという特徴も有している。
【０００６】
しかし、電気二重層キャパシタの最大の問題点は、二次電池に比べてエネルギー密度が低いという点であって、この点を改良すべく現在各種の検討がなされている。
電気二重層キャパシタには、プロピレンカーボネートなどの有機系極性溶媒に過塩素酸リチウムあるいは４級アンモニウム塩などの電解質を溶解させた有機溶媒系電解液を使用するものと、硫酸水溶液あるいは水酸化カリウム水溶液のような水溶液系電解液を使用するものとの、大きく分けて２種類が存在する。
【０００７】
水溶液系電解液を使用した場合には、キャパシタの容量を、有機溶媒系電解液を使用した場合の約１．３倍から２倍に上げることができ、さらに内部抵抗を１／５から１／１０に下げることができる。
水溶液系電解液を使用した場合に内部抵抗を下げることができる理由は、水溶液系電解液の電気抵抗が低いことに起因しているが、水溶液系電解液を使用する場合には、電圧を１Ｖ余りまでにしか上げることができないため体積当たりの蓄電エネルギー量は少ないという短所も併せ持っている。
【０００８】
一方、有機溶媒系電解液を使用した場合には、電気二重層キャパシタの電圧を最高３Ｖ以上まで上げることができることから、キャパシタの体積当たりの蓄電エネルギー量（蓄電エネルギー量＝１／２ＣＶ２で与えられる。Ｃ：キャパシタ容量、Ｖ：電圧）を上げることが可能であるため、容積当たりのエネルギーの高密度化という観点からは、有機溶媒系電解液の方が有利である。
【０００９】
これらの電気二重層キャパシタの電極材料としては、比表面積の大きな活性炭や活性炭素繊維が最適と考えられ、各方面で炭素材料の最適化の研究が盛んである。
電気二重層キャパシタの電極材は、通常、ヤシ殻、石炭やフェノール樹脂などの難黒鉛系炭素材（いわゆる、ハードカーボン）を原料とし、水蒸気や二酸化炭素などによるガス賦活により得られる高比表面積の活性炭を用いて製造されている。このような活性炭を電極材として用いた電気二重層キャパシタでは、炭素材と水蒸気や二酸化炭素などとの反応による脱炭素現象によって得られた細孔により、電気二重層が形成される界面を増加させて、単位重量当たりの充放電容量を向上させることができる。
【００１０】
しかし、一般的に、単位重量当たりの放電容量が大きな電気二重層キャパシタ用電極を得るためには、ＢＥＴ法で２０００ｍ２／ｇ以上の比表面積を有する活性炭が必要とされ、この場合、賦活収率が２０重量％以下まで低下するような賦活処理が必要となり、得られる活性炭の製造コストを上昇させるだけでなく、活性炭そのものの嵩密度が低く、電極材としての嵩密度を高くできないなどの問題点を有している。
【００１１】
また、本発明者らの測定によると、これら難黒鉛系炭素材を原料とし、かつＢＥＴ比表面積が２０００ｍ２／ｇの活性炭を用いた電極材の有機溶媒系での放電容量は、３０Ｆ／ｇ程度であり、この値は、上記比表面積から期待される値には達していない。これは、ＢＥＴ法で示される比表面積がすべて電気二重層の形成に利用されているわけではないことを示しているものと考えられる。
【００１２】
ところで、活性炭の製造において、比表面積を大きくするために炭素繊維をアルカリ金属化合物の共存下にて賦活する方法（以下、アルカリ賦活という）が提案されている（特開平１−１３９８６５号公報参照）。
また、この技術をピッチなどの易黒鉛系炭素材、特に、メソフェーズピッチを炭化して得た炭素材に使用する試みがなされている。例えば、特開平５−２４７７３１号公報では、メソフェーズを５０％以上含むピッチ（以下、メソフェーズピッチという）を紡糸して得たピッチ繊維を不融化・炭化し、得られた炭素繊維（以下、メソフェーズピッチ系炭素繊維ということがある）をアルカリ賦活する、高比表面積（特に、２０００ｍ２／ｇ以上）の活性炭素繊維の製造法が開示されている。
【００１３】
さらに、近年では、易黒鉛系炭素材をアルカリ賦活して得た活性炭素繊維を、電気二重層キャパシタ用の電極材として用いることが試みられている。例えば、特開平５−２５８９９６号公報には、メソフェーズピッチ系炭素繊維をアルカリ賦活して得た、比表面積３０００ｍ２／ｇ以上の活性炭素繊維を、水または酸類で脱灰した後、繊維の形状が残らない程度に粉砕、成形してなる電気二重層コンデンサー用電極、メソフェーズピッチ系炭素繊維をアルカリ賦活して得られる比表面積５００〜２０００ｍ２／ｇの活性炭素繊維を電極材として用いた電気二重層キャパシタ（特開平１０−１２１３３６号公報参照）、および特定の方法で得られたメソフェーズピッチ系炭素繊維を粉砕した後に、アルカリ賦活して得られ、かつ特定の細孔分布を有する活性炭素繊維を電極材として用いた電気二重層キャパシタ（特開平１１−２２２７３２号参照）が提案されている。
【００１４】
このような活性炭素繊維は、電極材として用いた場合に、従来の活性炭素繊維と比較して、比表面積が小さくても高い充放電特性が得られるため、単位体積当たりの充放電容量を向上させ得るという利点がある。したがって、電気二重層キャパシタの電極材として用いた場合に、活物質単位重量当たりの静電容量および単位体積当たりの静電容量の高い活性炭素繊維の出現が切望されているとともに、そのような活性炭素繊維を製造し得る方法も切望されているのが現状である。
【００１５】
【発明が解決しようとする課題】
本発明は、上記の従来技術の欠点を解消し、特に電気二重層キャパシタの電極材として用いた場合、活物質単位重量当たりの静電容量および単位体積当たりの静電容量の高い電極材となり得る活性炭素繊維の製造方法を提供することを課題とする。
【００１６】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために、種々の研究を重ねた結果、メソフェーズピッチを原料として用いて、紡糸工程、不融化工程、炭化工程、粉砕工程、アルカリ賦活工程、洗浄工程および乾燥工程の各工程を、その順序にて行って活性炭素繊維を製造することにより、特に電気二重層キャパシタの電極材として用いた場合に、単位体積当たりの静電容量の高い電極材となり得る活性炭素繊維が得られることを見出し、本発明を完成するに至ったものである。
【００１７】
すなわち、本発明の第１の発明によれば、メソフェーズピッチを原料として用いて、紡糸工程、不融化工程、炭化工程、粉砕工程、アルカリ賦活工程、洗浄工程および乾燥工程の各工程を、その順序にて行う活性炭素繊維の製造方法が提供される。
また、本発明の第２の発明によれば、第１の発明において、メソフェーズピッチの温度３００〜３８０℃における粘度が５０〜５０，０００ｃｐであり、軟化点が２５０〜３２０℃であり、メソフェーズ含有率が７０％以上であり、金属不純物含有量が１，０００重量ｐｐｍ以下である活性炭素繊維の製造方法が提供される。
【００１８】
また、本発明の第３の発明によれば、第１または第２の発明において、紡糸工程における紡糸温度が３００〜３８０℃であり、かつ得られたピッチ繊維の直径が５〜２０μｍである活性炭素繊維の製造方法が提供される。
また、本発明の第４の発明によれば、第１ないし第３のいずれかの発明において、不融化工程を酸素含有ガス雰囲気中において、不融化温度２５０〜３５０℃にて行い、かつ得られた不融化繊維の不融化度が２０重量％以下である活性炭素繊維の製造方法が提供される。
【００１９】
また、本発明の第５の発明によれば、第１ないし第４のいずれかの発明において、炭化工程を不活性ガス雰囲気中において、炭化温度５００〜９００℃にて行い、かつ得られた炭素繊維の真密度が１．３０〜１．８０ｇ／ｃｍ３であり、Ｘ線回折により測定された面間隔が０．３４５〜０．３６５ｎｍであり、Ｃ／Ｈ原子比が２〜８である活性炭素繊維の製造方法が提供される。
【００２０】
また、本発明の第６の発明によれば、第１ないし第５のいずれかの発明において、粉砕工程において得られた炭素繊維粉砕物のレーザー回折法により測定された平均粒径が１〜１００μｍであり、金属不純物含有量が１，０００重量ｐｐｍ以下である活性炭素繊維の製造方法が提供される。
また、本発明の第７の発明によれば、第１ないし第６のいずれかの発明において、粉砕工程において得られた炭素繊維粉砕物に、該炭素繊維粉砕物に対する重量比にて１．５〜２．５倍のアルカリ金属化合物を混合し、不活性ガス雰囲気中、３５０〜５００℃で２〜４時間保持した後、昇温速度３００℃以上で７００〜８００℃まで昇温し、その温度で２〜４時間保持する活性炭素繊維の製造方法が提供される。
【００２１】
さらに、本発明の第８の発明によれば、第１ないし第７のいずれかの発明における活性炭素繊維の製造方法で得られた活性炭素繊維を電極として用いる電気二重層キャパシタが提供される。
【００２２】
【発明の実施の形態】
以下、本発明について詳細に説明する。
（Ｉ）活性炭素繊維の製造方法
本発明に係るメソフェーズ系活性炭素繊維の製造方法では、（１）メソフェーズピッチを原料として用い（Ａ）紡糸工程、（Ｂ）不融化工程、（Ｃ）炭化工程、（Ｄ）粉砕工程、（Ｅ）アルカリ賦活工程（Ｆ）洗浄工程および（Ｊ）乾燥工程の各工程を含み、各工程をその順序にて行う。
【００２３】
以下、本発明の活性炭素繊維の製造方法を詳細に説明する。
（１）メソフェーズピッチ
本発明の活性炭素繊維の製造方法において、原料として用いられるメソフェーズピッチは石油、石炭など、さまざまな原料から製造される。本発明においては、導電性が高い光学的異方性相（メソフェーズ）を含有するメソフェーズピッチを活性炭素繊維の原料として用いる。さらに、本発明者らが、ピッチ性状とキャパシタ容量との関係を鋭意検討した結果、偏光顕微鏡観察により測定される光学的等方性成分を全く含まない光学的異方性相（メソフェーズ）が１００％であるメソフェーズピッチを使用することが、特に好ましいことが分かった。すなわち、光学的等方性成分が混在したメソフェーズピッチを使用した場合、ピッチ構造が不均一となり、アルカリ賦活反応が不均一化することにより細孔構造の制御が難しくなり、また、紡糸性・不融化性も悪化する傾向が見られる。
【００２４】
本発明で用いられるメソフェーズピッチは、温度３００〜３８０℃における粘度が５０〜５０，０００ｃｐであり、軟化点が２５０〜３２０℃であり、メソフェーズ含有率が７０％以上、好ましくは９０％以上、より好ましくは１００％であり、金属不純物含有量が１，０００重量ｐｐｍ以下である。
メソフェーズピッチの温度３００〜３８０℃における粘度が５０ｃｐ未満であると粘度が低く曳糸性が失われるため繊維形状が得られなくなり、一方、５０，０００ｃｐを超えると粘度が高すぎて紡糸ノズルから射出できない状態となるため、いずれも好ましくない。
【００２５】
また、その軟化点が２５０℃未満であると不融化が困難となり、一方、３２０℃を超えると紡糸温度が高くなるため紡糸中に炭化反応が進行し紡糸が困難となるため、いずれも好ましくない。
さらに、メソフェーズ含有率が７０％未満であると、ピッチ構造が不均一となり紡糸性および不融化性が悪化するとともに、アルカリ賦活反応においても不均一化が起こり細孔構造の制御が困難となるため好ましくない。
【００２６】
さらに、その金属不純物含有量が１，０００重量ｐｐｍを超えると、賦活後の活性炭素繊維中に残留する金属分が多くなり、キャパシタ電極性能が低下するため好ましくない。
（Ａ）紡糸工程
紡糸方法は、従来の溶融紡糸、遠心紡糸、渦流紡糸などに限定されるものではないが、メルトブロー紡糸法を用いることが好ましい。メソフェーズピッチ系炭素繊維においては、繊維内部における黒鉛層面の配向が重要であり、この配向の程度は、紡糸工程時のピッチ粘度、紡糸速度、冷却速度、ノズル構造などによってほぼ制御される。
【００２７】
また、後工程であるアルカリ賦活工程においては、アルカリ金属化合物が黒鉛層間を押し広げて進入することが重要な要因と考えられ、よりスムーズにアルカリ賦活を促進するためには、アルカリ金属化合物が進入し易い黒鉛層端面が繊維表面に存在する構造が好適である。さらに、黒鉛層面の配向構造は、アルカリ賦活収率にも影響を与えると推測される。これらに加え、紡糸装置の建設費や運転費などの製造コスト面および糸径の制御などの品質面も勘案し、総合的にメルトブロー紡糸法が好ましい。さらに、このメルトブロー紡糸法は、特にマット、フェルト状の炭素繊維集合体を製造するのに適している。
【００２８】
本発明の紡糸工程においては、温度３００〜３８０℃にて紡糸が行われ、該工程で得られるピッチ繊維の直径は、５〜２０μｍである。
上記紡糸温度が３００℃未満であると紡糸温度が低すぎてピッチの曳糸性が失われるため繊維形状が得られなくなり、一方、３８０℃を超えると紡糸中にピッチの炭化が進行し紡糸が困難となるため、いずれも好ましくない。
【００２９】
また、紡糸工程で得られるピッチ繊維の直径が５μｍ未満であると繊維径の制御が難しく繊維径が不均一となり、一方、２０μｍを超えると繊維内部までの賦活が起こりにくくなり活性炭素繊維の物性が不均一となるため、いずれも好ましくない。
（Ｂ）不融化工程
メソフェーズピッチは熱可塑性有機化合物であり、繊維形態を保持したまま熱処理（炭化処理）するためには、紡糸工程の後、不融化処理が必要である。この不融化工程は、常法により液相または気相で連続的に不融化処理することが可能であるが、空気、酸素、二酸化窒素 などの酸素含有ガス雰囲気中で行う。たとえば、空気中での不融化処理においては、平均昇温速度１〜１５℃／分、好ましくは３〜１２℃／分で、処理温度範囲２５０〜３５０℃、より好ましくは２８０〜３３０℃で行われる。該不融化処理時間は、１５分〜５時間程度でよい。上記不融化工程は本発明において必須の工程であり、不融化工程を経ない、すなわち紡糸したままのピッチ繊維を用いて、アルカリ金属化合物と均一混合して熱処理するアルカリ賦活処理を行うと、ピッチ繊維が再溶融するため紡糸工程において形成された黒鉛層面の配向を乱すばかりでなく、極端な場合は繊維形状を無くしてしまうことがある。
【００３０】
上記不融化温度が２５０℃未満であると不融化の反応速度が遅いため不融化工程に長時間を要し、不融化が十分に達成されない可能性があり、一方、３５０℃を超えると燃焼反応が起こり炭素繊維が燃える可能性があるため、いずれも好ましくない。
また、不融化工程で得られる不融化繊維の不融化度が２０重量％を超えると酸素が過度に付加しているため、その後の炭化工程での収率が著しく低下するので好ましくない。なお、不融化度とは、以下の数式によって算出された値である。
【００３１】
不融化度（％）＝（不融化後の繊維重量−不融化前の繊維重量）／（不融化前の繊維重量）×１００
（Ｃ）炭化工程
上記のようにして得られた不融化繊維は、そのままでもアルカリ賦活工程に供することもできるが、本発明の製造方法においてはアルカリ賦活処理前に炭化処理を行う。すなわち、上記で得られた不融化繊維は低揮発分を多く含むため、アルカリ賦活工程での賦活収率が低くなるだけでなく、アルカリ賦活反応において揮発するタール状物が反応系内を汚染することがあるため、これらの低揮発分を炭化により予め除去する必要がある。炭化工程は窒素などの不活性ガス雰囲気中で行われるが、処理温度範囲は５００〜９００℃、より好ましくは６００〜９００℃である。この炭化処理温度が５００℃未満であると低揮発分の除去が不十分であり、一方、９００℃を超えると、炭素繊維の黒鉛構造が発達しすぎ、後工程でのアルカリ賦活速度が極端に遅くなり反応に長時間を要するばかりか、炭化コストが増加する観点よりも好ましくない。このため、高い導電性が必要な特殊な用途以外においては、１０００℃以下、より好ましくは９００℃以下の軽度な炭化が好ましい。該炭化処理時間は、１〜４時間程度でよい。
【００３２】
また、炭化工程で得られる炭素繊維の真密度は１．３０〜１．８０ｇ／ｃｍ３であり、Ｘ線回折により測定される面間隔は０．３４５〜０．３６５ｎｍであり、Ｃ／Ｈ原子比は２〜８である。
上記炭素繊維の真密度が１．３０ｇ／ｃｍ３未満であると賦活反応速度が非常に高く、反応を制御することが困難となり、一方、１．８０ｇ／ｃｍ３を超えると炭化が過度に進行して炭素の反応性が低下し賦活反応が困難となるため、いずれも好ましくない。
【００３３】
また、Ｘ線回折により測定される面間隔が０．３４５ｎｍ未満であるとアルカリ金属が面間を通って内部へ浸透し難くなるため賦活が均一に進行しなくなり、一方、０．３６５ｎｍを超えると反応速度が高くなり過ぎて賦活反応の制御が困難となるため、いずれも好ましくない。
さらに、Ｃ／Ｈ原子比が２未満であると炭素構造が未発達であり賦活が過度に進行し、一方、８を超えると炭素骨格構造が過度に発達し賦活反応が進行し難くなるため、いずれも好ましくない。
【００３４】
（Ｄ）粉砕工程
上記のようにして得られた炭化繊維は、マット、フェルト状のままにて賦活して電極材とすることもできるが、本発明の製造方法においては、賦活助材であるアルカリ金属化合物との均一混合、賦活反応による比表面の均一性および電極材の嵩密度を向上させるためにアルカリ賦活工程前に粉砕処理（ミルド化）を行う。この場合、レーザー回折方式による平均粒径で表示すれば、１〜１００μｍに粉砕し、より好ましくは１０〜３０μｍに粉砕する。平均粒径が１μｍ未満であると、均一なアルカリ賦活が困難となり、一方、１００μｍを超えると電極材の嵩密度が大きくならないので、いずれも好ましくない。
【００３５】
炭素繊維粉砕物の金属不純物含有量は１，０００重量ｐｐｍ以下であり、該金属不純物含有量が１，０００重量ｐｐｍを超えるとキャパシタ電極性能が低下するので、好ましくない。
ミルド化の方法としては、ビクトリーミル、ジェットミル、高速回転ミルなどを用いることが有効である。また、ミルド化には、ヘンシェルミキサーやボールミル、擂潰機などを用いる方法もあるが、これらの方法によると繊維の直径方向への加圧力が働き、繊維軸方向への縦割れの発生が多くなりアルカリ賦活の効率および均一性を低下させるので好ましくない。また、ミルド化に長時間を要し適切なミルド化方法とは言い難い。ミルド化を効率よく行うためには、たとえばブレードを取付けたローターを高速で回転することにより、繊維を寸断する方法が適切である。繊維長は、ローターの回転数、ブレードの角度などを調整することによりコントロールすることが可能である。
【００３６】
（Ｅ）アルカリ賦活工程
本発明におけるアルカリ賦活工程で用いられるアルカリ金属化合物としては、水酸化カリウム、水酸化ナトリウム、炭酸カリウム、亜硝酸カリウム、硫酸カリウムおよび塩化カリウムなどを例示でき、中でも水酸化カリウムが特に好ましい。
【００３７】
このようなアルカリ金属化合物は、炭化繊維粉砕物に対する重量比にて１．５〜２．５（倍）、好ましくは１．８〜２．２（倍）の量で用いる。
アルカリ金属化合物の重量比が１．５（倍）未満では得られる活性炭素繊維の細孔形成の効率が低下する傾向があり、一方、重量比が２．５（倍）を超えて添加してもその効果が得られず、中和などの後処理工程のコスト増となり、また装置の保守性および安全性の面からも好ましくない。
【００３８】
アルカリ賦活処理は、具体的に、このような重量比の炭化繊維粉砕物とアルカリ金属化合物とを均一に混合した後、窒素などの不活性ガス中、３５０〜５００℃、好ましくは３８０〜４５０℃にて、好ましくは２〜４時間、さらに好ましくは２〜３時間保持した後、昇温速度３００℃／時間以上、好ましくは４００℃／時間以上、さらに好ましくは５００℃／時間以上にて７００〜８００℃、好ましくは７３０〜７７０℃まで昇温して、その温度にて好ましくは２〜４時間、さらに好ましくは２〜３時間保持することにより行う。
【００３９】
炭化繊維粉砕物とアルカリ金属化合物とを均一に混合後、不活性ガス中における保持温度が３５０℃未満であるとアルカリ金属化合物中の水分の除去が不十分となり、その後の昇温で著しく発泡する。一方、５００℃を超えると脱水と賦活反応が同時に進行し、性能が低下する。また、その時の保持時間が２時間未満であると脱水が不十分であり、一方、４時間を超えても、その効果は変わらないため、いずれも好ましくない。さらに、昇温後の保持温度が７００℃未満であると賦活反応が十分に進行せず、容量が発現しない。一方、８００℃を超えると炭化が進行し、賦活により形成された細孔が収縮して容量が低下する。また、その時の保持時間が２時間未満であると賦活反応が不十分であり、一方、４時間を超えても賦活が終了しておりその効果が見られないので、いずれも好ましくない。
【００４０】
上記アルカリ賦活処理には、トレーなどの賦活反応容器を使用する。賦活反応容器は、加熱・昇温を行う反応炉に投入し、上記の温度条件下にて賦活処理を行うが、該反応炉はバッチ式、連続式の制限はない。たとえば、ボックス炉、ベルト炉、トレープレッシャー炉などを使用することが可能である。
すなわち、アルカリ賦活処理は、通常、ニッケル製のアルカリ賦活反応容器に反応体である炭化繊維粉砕物とアルカリ金属化合物との混合物を導入し、該反応容器全体を窒素ガスなどの不活性ガス雰囲気の反応炉内にて、加熱・昇温することにより行う。
【００４１】
（Ｆ）洗浄工程
上記のようにして得られた活性炭素繊維は、常温に冷却した後、たとえば温水および温塩酸水などによる洗浄にて未反応のアルカリ金属化合物を除去するとともに、含有する遷移金属および／または遷移金属化合物を低減させる。なお、遷移金属および／または遷移金属化合物含有量は、活性炭素繊維を７００℃の空気中で灰化した後、灰分を酸で溶解してＩＣＰ発光分光法を用いて測定する。
【００４２】
上記アルカリ賦活工程にて使用した未反応のアルカリ金属化合物の除去は、たとえば５０〜９０℃の温水を、活性炭素繊維１００重量部に対して１００〜１５００重量部用いて１〜３回、バッチ式にて洗浄することにより行う。
また、上記洗浄後のアルカリ金属化合物の中和は、たとえば０．１〜６規定、４０〜６０℃の塩酸水などを、活性炭素繊維１００重量部に対して１００〜１５００重量部用いて１〜３回、バッチ式にて洗浄することにより行う。
【００４３】
さらに、最終の脱塩酸洗浄として、たとえば５０〜９０℃の温水を、活性炭素繊維１００重量部に対して１００〜１５００重量部用いて１〜５回、バッチ式にて洗浄することが望ましい。
（Ｊ）乾燥工程
上記の洗浄工程後、活性炭素繊維を乾燥処理する。乾燥は、常圧あるいは減圧下で１１０〜１５０℃にて１〜２４時間の条件で行えばよい。
【００４４】
このようにして得られた活性炭素繊維は、ＢＥＴ比表面積で３００ｍ２ ／ｇ以上、好ましくは５００〜２８００ｍ２ ／ｇ、より好ましくは６００〜２５００ｍ２ ／ｇの比表面積を有するメソフェーズピッチ系活性炭素繊維であり電気二重層キャパシタ用の電極材として優れた特性を示す。該ＢＥＴ比表面積が３００ｍ２ ／ｇ未満では充分な放電容量が得られず、またその上限は特に制限されないが、いたずらに比表面積を大きくしてもキャパシタ容量はそれに比例して大きくならず賦活に時間がかかるばかりでなく、賦活収率が低下するため好ましくなく、通常２８００ｍ２ ／ｇ以下である。比表面積は、窒素吸着によるＢＥＴ法により測定し、測定精度を考慮して一の位を四捨五入して十の桁から表示した値である。
【００４５】
（ＩＩ）電気二重層キャパシタ
本発明に係る電気二重層キャパシタは、以上説明した活性炭素繊維を含む電極を備えている。
本発明において、電極を作製する方法は特に限定されず、従来知られている電極の製造法を使用することができる。
【００４６】
たとえば、本発明の電極は、上記の活性炭素繊維に、ポリエチレンやポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などのバインダーを添加して混合し、得られた混合物を加圧ロール成形にてシート状あるいは板状に成形して製造することが可能である。
このような電極を製造する際に、導電材料としての黒鉛粉やアセチレンブラックなどのカーボンブラックなどを添加することもできる。
【００４７】
このようにして作成された電極は所望の大きさ、形状に切断し、セパレータを両極の間に介在させ、容器に挿入後、電解液を注入し、封口板、ガスケットを用いて封口をかしめて単極セルとすることができる。
このような電気二重層キャパシタの電解液としては、高電圧を適用できる有機溶媒系電解液が好ましい。
【００４８】
有機溶媒としては、たとえば、プロピレンカーボネート、γ−ブチロラクトン、ジメチルスルフォキシド、ジメチルフォルムアミド、アセトニトリル、エチレンカーボネート、テトラヒドロフラン、ジメトキシエタンなどを挙げることができる。これらの有機溶媒は、１種または２種以上の混合溶媒として用いることもできる。
【００４９】
また、このような有機溶媒に溶解される電解質としては、金属の陽イオン；アンモニウムイオン、テトラメチルアンモニウムイオンおよびテトラエチルアンモニウムイオンなどの４級アンモニウムカチオン；およびカルボニウムカチオンなどの陽イオンと適当な陰イオンとの塩を挙げることができる。
このような陰イオンとしては、ＣｌＯ４ −、ＢＦ４ −、ＰＦ４ −、ＰＦ６ −、ＡｓＦ６ −などが挙げられる。
【００５０】
具体的な電解質としては、例えば、ＬｉＣｌＯ４、ＮａＢＦ４、Ｅｔ４Ｎ・ＢＦ４（式中Ｅｔはエチル基である）などが挙げられる。
また、本発明に係る活性炭素繊維は、電気二重層を形成した場合の単位重量当たりの放電容量が、２０〜４５Ｆ／ｇ、特に３０〜４５Ｆ／ｇであることが望ましい。
【００５１】
【実施例】
以下本発明を実施例によりさらに具体的に説明するが、本発明はそれに限定されるものではない。
【００５２】
【実施例１】
（１）活性炭素繊維の製造
軟化点が２８５℃であるメソフェーズピッチを原料として用い、紡糸温度３５０℃にて平均繊維直径１２μｍの不織布状ピッチ繊維を得た。当該ピッチ繊維を空気中、３２０℃にて０．５時間不融化処理した。得られた繊維の不融化度は、６重量％であった。さらに、得られた不融化繊維を窒素ガス雰囲気中、８００℃にて１時間炭化処理することにより、真密度が１．５５ｇ／ｃｍ３であり、面間隔が０．３５５ｎｍであり、Ｃ／Ｈ原子比が４である炭化繊維を得た。さらに、当該炭化繊維を高速回転ミルにて粉砕することにより、レーザー回折法による平均粒径２５μｍ、累積粒度分布から求めた平均粒径３０μｍの炭素繊維ミルドを得た。
【００５３】
上記で得られた炭素繊維ミルドと水酸化カリウムとを、１：２の重量比で混合し、窒素ガス雰囲気中、４００℃にて３時間、さらに８００℃にて２時間アルカル賦活処理を行った。その後、さらに９０℃の温水、１５重量倍での脱アルカリ洗浄を３回、１規定で６０℃、１５重量倍での塩酸洗浄を３回および９０℃の温水、１５重量倍での脱塩酸洗浄を３回行った後、空気中、１１０℃にて２４時間、乾燥を行った。
【００５４】
得られた活性炭素繊維のＢＥＴ比表面積は８００ｍ２／ｇであり、細孔径は０．８０ｎｍであり、細孔容積は０．３５ｍｌ／ｇであった。
（２）電気二重層キャパシタの製造
上記の活性炭素繊維に導電フィラーとしての黒鉛粉末および結着剤としてのＰＴＦＥを重量比にて８１：９：１０となるように混練後、該混練物を圧延することにより、厚さ１５０μｍ、電極密度０．８５ｇ／ｃｃの電極シートを作成した。該電極シートから直径１８ｍｍの２枚の分極性電極３，４を切り出し、これら２枚の分極性電極と、直径２０ｍｍ、厚さ７５μｍのＰＴＦＥ製セパレータ５、電解液などを用いて図１のボタン型電気二重層キャパシタを製造した。電解液としては、１．８Ｍ（ｍｏｌ／ｌｉｔｅｒ）のトリエチルメチルアンモニウム・テトラフルオロボレート［（Ｃ２Ｈ５）３ＣＨ３ＮＢＦ４］のプロピレンカーボネート溶液を用いた。
【００５５】
得られた電気二重層キャパシタを用いて充放電試験を行った結果、活物質単位重量当たりの静電容量は、４０Ｆ／ｇであり、単位体積当たりの静電容量は、３４Ｆ／ｃｃであった。
【００５６】
【比較例１】
（１）活性炭の製造
回転か焼装置に２０メッシュの篩を通した石油精製コークス１００重量部と、含水率１５重量％の粒状水酸化カリウム２００重量部とを仕込み、窒素ガス雰囲気下にて７００℃まで昇温して、攪拌下にて約２時間活性化（アルカリ賦活）のための加熱処理を行った。その後、生成物を冷却して、水で十分に洗浄してから真空炉内にて、１１０℃で２４時間加熱して乾燥を行った。
【００５７】
得られた活性炭のＢＥＴ比表面積は９００ｍ２／ｇであり、細孔径は０．７８ｎｍであり、細孔容積は０．３８ｍｌ／ｇであった。
（２）電気二重層キャパシタの製造
実施例１と同様の方法にて電極シートを作成し、厚さ１５０μｍ、電極密度０．８３ｇ／ｃｃの電極シートを得た。該電極シートを用いて実施例１と同様にして電気二重層キャパシタを製造した。
【００５８】
得られた電気二重層キャパシタを用いて充放電試験を行った結果、活物質単位重量当たりの静電容量は、２５．５Ｆ／ｇであり、単位体積当たりの静電容量は、２１．１Ｆ／ｃｃであった。
【００５９】
【発明の効果】
本発明の活性炭素繊維の製造方法によれば、繊維径が一定である炭素繊維粉砕物をアルカリ賦活処理しているので、繊維内部まで均一に賦活反応が進行し、粒子間のバラツキが小さい。その結果、該活性炭素繊維を電気二重層キャパシタの電極材として用いた場合、単位重量当たりの静電容量が向上する。
【００６０】
また、本発明の活性炭素繊維の製造方法によれば、メソフェーズピッチを原料として用いているので、分極性電極としての導電性が高く、かつ等方性材料と比べて高い電極密度が得られる。その結果、該活性炭素繊維を電気二重層キャパシタの電極材として用いた場合、単位体積当たりの静電容量が向上する。
【図面の簡単な説明】
【図１】断面図
【符号の説明】
１，２． 集電極
３，４． 分極性電極
５． セパレータ
６． ガスケット
７． ケース[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing activated carbon fibers, and more particularly, to a method for producing activated carbon fibers by treating mesophase pitch-based carbon fibers with an alkali metal compound. The activated carbon fiber obtained by the production method of the present invention is suitable not only for use as an electrode material of a high-performance electric double layer capacitor, but also for use in activated carbon such as adsorption and water purification. it can.
[0002]
[Prior art]
In recent years, new electronic devices such as mobile phones and notebook computers have appeared one after another, and due to the development competition for miniaturization, lightness, and portability of these products, IC memories and microcomputers incorporated therein have been downsized and have high performance. In. However, such an element such as an IC memory or a microcomputer may cause malfunction such as erasing the memory or stopping the function of the electronic device at the moment of a power interruption. In fact, computer equipment, even with a small voltage drop of 10% to 20% without proper measures, may cause a malfunction or memory loss if the voltage drop lasts only for 0.003 to 0.02 seconds. In addition, the function of the electronic device is paralyzed.
[0003]
As a countermeasure, Ni-Cd batteries and aluminum electrolytic capacitors have been used as backup power supplies. However, these power supplies have not been sufficient in terms of the operating temperature range, the number of charge / discharge cycles, the capacity, rapid charge / discharge performance, cost, and the like. An electric double layer capacitor has been developed in response to this market need. At first, activated carbon was used as an electrode material in electric double layer capacitors, but recently, electric double layer capacitors using activated carbon fibers having a higher specific surface area have attracted attention.
[0004]
Furthermore, applications from the conventional low-power field to high-capacity fields such as auxiliary power sources for electric vehicle batteries are considered. Passenger cars equipped with capacitors for the purpose of assisting output have come to the stage of reference exhibition.
The history of research on electric double layers can be traced back to 1879, Helmholtz. In general, when two different layers come into contact, positive and negative charges are arranged at a short distance at the interface. The charge distribution formed at this interface is called an electric double layer.
[0005]
The electric double layer capacitor accumulates electric charge by applying a voltage to the electric double layer. However, it took a long time to put it to practical use, and finally, in the early 1980's, the appearance of large-capacity capacitors in Farad units using this principle was seen.
An electric double layer capacitor is a large-capacity capacitor using an electric double layer formed at an interface between an electrode surface and an electrolytic solution, and does not involve a chemical reaction in charging and discharging as in a normal secondary battery. For this reason, the internal resistance is much lower than that of the secondary battery, and a large current discharge is possible. Further, it has a feature that there is no limitation on the number of times of charging and discharging.
[0006]
However, the biggest problem with the electric double layer capacitor is that the energy density is lower than that of the secondary battery, and various studies have been made to improve this point.
An electric double layer capacitor uses an organic solvent-based electrolytic solution in which an electrolyte such as lithium perchlorate or a quaternary ammonium salt is dissolved in an organic polar solvent such as propylene carbonate, and a sulfuric acid aqueous solution or a potassium hydroxide aqueous solution. There are roughly two types, one using an aqueous electrolyte solution as described above.
[0007]
When an aqueous electrolyte is used, the capacity of the capacitor can be increased to about 1.3 to 2 times that when an organic solvent is used, and the internal resistance can be reduced from 1/5 to 1 /. Can be reduced to 10.
The reason why the internal resistance can be reduced when the aqueous electrolyte is used is that the electric resistance of the aqueous electrolyte is low. However, when the aqueous electrolyte is used, the voltage is 1 V. It also has the disadvantage that the amount of stored energy per volume is small because it can be raised only too much.
[0008]
On the other hand, when an organic solvent-based electrolytic solution is used, the voltage of the electric double layer capacitor can be increased up to 3 V or more, so the amount of stored energy per capacitor volume (the amount of stored energy = 1/2 CV 2 is given. (C: capacitor capacity, V: voltage), the organic solvent-based electrolyte is more advantageous from the viewpoint of increasing the density of energy per volume.
[0009]
Activated carbon or activated carbon fiber having a large specific surface area is considered to be optimal as an electrode material for these electric double layer capacitors, and research on optimization of carbon materials is being actively conducted in various fields.
The electrode material of an electric double layer capacitor is usually made of a non-graphitic carbon material (so-called hard carbon) such as coconut shell, coal or phenol resin, and has a high specific surface area obtained by gas activation with steam or carbon dioxide. Manufactured using activated carbon. In an electric double layer capacitor using such activated carbon as an electrode material, the pores obtained by the decarbonization phenomenon caused by the reaction between the carbon material and water vapor or carbon dioxide increase the interface at which the electric double layer is formed. Thus, the charge / discharge capacity per unit weight can be improved.
[0010]
However, in general, in order to obtain an electrode for an electric double layer capacitor having a large discharge capacity per unit weight, activated carbon having a specific surface area of 2000 m 2 / g or more is required by the BET method. An activation treatment is required to reduce the ratio to 20% by weight or less, which not only raises the production cost of the obtained activated carbon, but also lowers the bulk density of the activated carbon itself and makes it impossible to increase the bulk density as an electrode material. Have a point.
[0011]
According to the measurement by the present inventors, the discharge capacity in an organic solvent system of an electrode material using these non-graphite-based carbon materials as raw materials and activated carbon having a BET specific surface area of 2000 m 2 / g is 30 F / g. This value does not reach the value expected from the above specific surface area. This is considered to indicate that not all of the specific surface area indicated by the BET method is used for forming the electric double layer.
[0012]
Meanwhile, in the production of activated carbon, a method of activating carbon fibers in the presence of an alkali metal compound to increase the specific surface area (hereinafter, referred to as alkali activation) has been proposed (see JP-A-1-139865). .
Attempts have also been made to use this technology for easily graphitic carbon materials such as pitch, particularly carbon materials obtained by carbonizing mesophase pitch. For example, in Japanese Patent Application Laid-Open No. Hei 5-247773, pitch fibers obtained by spinning a pitch containing 50% or more of mesophase (hereinafter, referred to as mesophase pitch) are made infusible and carbonized, and the obtained carbon fibers (hereinafter, mesophase pitch) are produced. A method for producing an activated carbon fiber having a high specific surface area (particularly, 2000 m 2 / g or more) for activating alkali carbon fibers (which may be referred to as a system carbon fiber) is disclosed.
[0013]
Further, in recent years, an attempt has been made to use an activated carbon fiber obtained by alkali-activating a graphite-based carbon material as an electrode material for an electric double layer capacitor. For example, JP-A-5-258996 describes that activated carbon fibers having a specific surface area of 3000 m 2 / g or more obtained by alkali-activating mesophase pitch-based carbon fibers are demineralized with water or acids, and then the shape of the fibers is adjusted. For an electric double layer capacitor obtained by pulverizing and molding to the extent that no residual carbon remains, and an electrode using an activated carbon fiber having a specific surface area of 500 to 2000 m 2 / g obtained by alkali-activating mesophase pitch-based carbon fiber as an electrode material. A multilayer capacitor (see JP-A-10-121336) and a mesophase pitch-based carbon fiber obtained by a specific method are pulverized and then activated with alkali to obtain an activated carbon fiber having a specific pore distribution. An electric double layer capacitor used as an electrode material (see Japanese Patent Application Laid-Open No. H11-222732) has been proposed.
[0014]
When such an activated carbon fiber is used as an electrode material, compared to conventional activated carbon fibers, high charge / discharge characteristics can be obtained even when the specific surface area is small, so that the charge / discharge capacity per unit volume is improved. There is an advantage that it can be done. Therefore, when used as an electrode material of an electric double layer capacitor, the appearance of an activated carbon fiber having a high capacitance per unit weight of the active material and a high capacitance per unit volume has been eagerly desired, and such an active carbon fiber has been desired. At present, there is a long-felt need for a method capable of producing carbon fibers.
[0015]
[Problems to be solved by the invention]
The present invention solves the above-mentioned disadvantages of the prior art, and particularly when used as an electrode material of an electric double layer capacitor, can be an electrode material having a high capacitance per unit weight of the active material and a high capacitance per unit volume. It is an object to provide a method for producing activated carbon fiber.
[0016]
[Means for Solving the Problems]
The present inventors, in order to solve the above problems, as a result of repeated research, using mesophase pitch as a raw material, spinning step, infusibilization step, carbonization step, grinding step, alkali activation step, washing step and By performing each step of the drying step in the order described above to produce activated carbon fibers, particularly when used as an electrode material of an electric double layer capacitor, an activity that can be an electrode material having a high capacitance per unit volume. They have found that carbon fibers can be obtained, and have completed the present invention.
[0017]
That is, according to the first aspect of the present invention, each step of the spinning step, the infusibilizing step, the carbonizing step, the pulverizing step, the alkali activating step, the washing step, and the drying step is performed using mesophase pitch as a raw material. And a method for producing an activated carbon fiber.
Further, according to the second invention of the present invention, in the first invention, the viscosity of the mesophase pitch at a temperature of 300 to 380 ° C is 50 to 50,000 cp, the softening point is 250 to 320 ° C, and the mesophase contains A method for producing an activated carbon fiber having a ratio of 70% or more and a metal impurity content of 1,000 ppm by weight or less is provided.
[0018]
According to a third aspect of the present invention, in the first or second aspect, the activity is such that the spinning temperature in the spinning step is 300 to 380 ° C and the diameter of the obtained pitch fiber is 5 to 20 µm. A method for producing a carbon fiber is provided.
Further, according to the fourth invention of the present invention, in any one of the first to third inventions, the infusibilizing step is performed at an infusibilizing temperature of 250 to 350 ° C. in an oxygen-containing gas atmosphere. A method for producing activated carbon fibers, wherein the degree of infusibilization of the infusibilized fibers is 20% by weight or less.
[0019]
According to the fifth invention of the present invention, in any one of the first to fourth inventions, the carbonization step is performed at a carbonization temperature of 500 to 900 ° C. in an inert gas atmosphere, and the obtained carbon is obtained. An activity in which the true density of the fiber is 1.30 to 1.80 g / cm 3 , the plane spacing measured by X-ray diffraction is 0.345 to 0.365 nm, and the C / H atomic ratio is 2 to 8. A method for producing a carbon fiber is provided.
[0020]
Further, according to the sixth invention of the present invention, in any one of the first to fifth inventions, the carbon fiber pulverized product obtained in the pulverization step has an average particle diameter measured by a laser diffraction method of 1 to 100 μm. And a method for producing activated carbon fibers having a metal impurity content of 1,000 ppm by weight or less.
According to the seventh aspect of the present invention, in any one of the first to sixth aspects, the carbon fiber pulverized product obtained in the pulverizing step is added to the carbon fiber pulverized substance in a weight ratio of 1.5 to 1.5. After mixing the alkali metal compound up to 2.5 times and keeping it at 350 to 500 ° C. for 2 to 4 hours in an inert gas atmosphere, the temperature was raised to 700 to 800 ° C. at a rate of 300 ° C. or higher, and the temperature was raised. For 2 to 4 hours.
[0021]
Further, according to an eighth aspect of the present invention, there is provided an electric double layer capacitor using an activated carbon fiber obtained by the method for producing an activated carbon fiber according to any one of the first to seventh aspects as an electrode.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
(I) Method for Producing Activated Carbon Fiber In the method for producing mesophase-based activated carbon fiber according to the present invention, (1) a mesophase pitch is used as a raw material, (A) a spinning step, (B) an infusibilizing step, and (C) a carbonizing step. , (D) a pulverizing step, (E) an alkali activating step, (F) a washing step, and (J) a drying step, and each step is performed in that order.
[0023]
Hereinafter, the method for producing the activated carbon fiber of the present invention will be described in detail.
(1) Mesophase pitch In the method for producing activated carbon fibers of the present invention, mesophase pitch used as a raw material is produced from various raw materials such as petroleum and coal. In the present invention, a mesophase pitch containing an optically anisotropic phase (mesophase) having high conductivity is used as a raw material for activated carbon fibers. Furthermore, as a result of the present inventors diligently examining the relationship between the pitch property and the capacitance of the capacitor, it was found that an optically anisotropic phase (mesophase) containing no optically isotropic component measured by a polarizing microscope was 100%. It has been found to be particularly preferred to use a mesophase pitch that is%. That is, when a mesophase pitch in which optically isotropic components are mixed is used, the pitch structure becomes non-uniform, and the alkali activation reaction becomes non-uniform, which makes it difficult to control the pore structure. There is a tendency that the meltability also deteriorates.
[0024]
The mesophase pitch used in the present invention has a viscosity at a temperature of 300 to 380 ° C of 50 to 50,000 cp, a softening point of 250 to 320 ° C, and a mesophase content of 70% or more, preferably 90% or more. Preferably, it is 100%, and the metal impurity content is 1,000 ppm by weight or less.
If the viscosity at a temperature of 300 to 380 ° C. of the mesophase pitch is less than 50 cp, the viscosity is low and the spinnability is lost, so that the fiber shape cannot be obtained. On the other hand, if the viscosity exceeds 50,000 cp, the viscosity is too high and injection from the spinning nozzle is performed. Both are not preferable because they cannot be performed.
[0025]
When the softening point is less than 250 ° C., infusibilization becomes difficult. On the other hand, when the softening point exceeds 320 ° C., the spinning temperature becomes high, so that the carbonization reaction proceeds during spinning and spinning becomes difficult. .
Further, when the content of the mesophase is less than 70%, the pitch structure becomes non-uniform, the spinnability and the infusibility deteriorate, and the alkali activation reaction also causes non-uniformity, making it difficult to control the pore structure. Not preferred.
[0026]
Further, if the content of the metal impurities exceeds 1,000 ppm by weight, the amount of metal remaining in the activated carbon fiber after activation increases, which is not preferable because the performance of the capacitor electrode deteriorates.
(A) Spinning Step The spinning method is not limited to conventional melt spinning, centrifugal spinning, vortex spinning, and the like, but it is preferable to use a melt blow spinning method. In the mesophase pitch-based carbon fiber, the orientation of the graphite layer surface inside the fiber is important, and the degree of this orientation is substantially controlled by pitch viscosity, spinning speed, cooling speed, nozzle structure, and the like during the spinning process.
[0027]
Also, in the alkali activation step, which is a subsequent step, it is considered that an important factor is that the alkali metal compound spreads between the graphite layers and enters, and in order to promote the alkali activation more smoothly, the alkali metal compound enters. A structure in which a graphite layer end face which is easy to be present is present on the fiber surface is preferable. Further, it is presumed that the orientation structure of the graphite layer surface also affects the alkali activation yield. In addition to these, the melt blow spinning method is preferable in consideration of the production cost such as the construction cost and operation cost of the spinning device and the quality such as control of the yarn diameter. Furthermore, the melt blow spinning method is particularly suitable for producing a mat or felt-like carbon fiber aggregate.
[0028]
In the spinning step of the present invention, spinning is performed at a temperature of 300 to 380 ° C, and the pitch fibers obtained in this step have a diameter of 5 to 20 µm.
If the spinning temperature is lower than 300 ° C., the spinning temperature is too low and the spinnability of the pitch is lost, so that the fiber shape cannot be obtained. On the other hand, if the spinning temperature is higher than 380 ° C., carbonization of the pitch proceeds during spinning and spinning is stopped. Both are not preferred because they make it difficult.
[0029]
When the diameter of the pitch fiber obtained in the spinning step is less than 5 μm, it is difficult to control the fiber diameter, and the fiber diameter becomes non-uniform. On the other hand, when the pitch fiber exceeds 20 μm, activation to the inside of the fiber becomes difficult to occur, and the physical properties of the activated carbon fiber Are non-uniform, so neither is preferred.
(B) Infusibilization Step Mesophase pitch is a thermoplastic organic compound, and in order to perform heat treatment (carbonization treatment) while maintaining the fiber form, infusibility treatment is required after the spinning step. In this infusibilization step, it is possible to continuously carry out infusibilization treatment in a liquid phase or gaseous phase by an ordinary method. This is performed in an oxygen-containing gas atmosphere. For example, in the infusibilizing treatment in air, the heating is performed at an average heating rate of 1 to 15 ° C./min, preferably 3 to 12 ° C./min, and in a treatment temperature range of 250 to 350 ° C., more preferably 280 to 330 ° C. Is The infusibilization time may be about 15 minutes to 5 hours. The infusibilizing step is an essential step in the present invention, and does not go through the infusibilizing step, that is, using the pitch fiber as spun, and performing an alkali activation treatment of uniformly mixing and heat-treating with an alkali metal compound. Since the fibers are re-melted, not only the orientation of the graphite layer surface formed in the spinning process is disturbed, but in extreme cases, the fiber shape may be lost.
[0030]
If the infusibilization temperature is lower than 250 ° C, the infusibilization reaction rate is slow, so that the infusibilization step requires a long time and the infusibilization may not be sufficiently achieved. All of them are not preferable because carbon fibers may be burned.
On the other hand, if the degree of infusibilization of the infusibilized fiber obtained in the infusibilization step exceeds 20% by weight, oxygen is excessively added, and the yield in the subsequent carbonization step is unpreferably reduced. The degree of infusibilization is a value calculated by the following equation.
[0031]
Degree of infusibilization (%) = (fiber weight after infusibilization−weight of fiber before infusibilization) / (weight of fiber before infusibilization) × 100
(C) Carbonization Step The infusibilized fiber obtained as described above can be subjected to the alkali activation step as it is, but in the production method of the present invention, the carbonization treatment is performed before the alkali activation treatment. That is, since the infusibilized fiber obtained above contains a large amount of low volatile components, not only the activation yield in the alkali activation step is reduced, but also tar-like substances volatilized in the alkali activation reaction contaminate the reaction system. Therefore, it is necessary to remove these low volatile components by carbonization in advance. The carbonization step is performed in an atmosphere of an inert gas such as nitrogen, and the treatment temperature range is 500 to 900C, more preferably 600 to 900C. If the carbonization temperature is lower than 500 ° C., the removal of low volatile components is insufficient. On the other hand, if the temperature exceeds 900 ° C., the graphite structure of the carbon fiber develops too much, and the alkali activation rate in the subsequent step becomes extremely high. It is not preferable from the viewpoint that the reaction becomes slow and not only takes a long time for the reaction but also increases the carbonization cost. Therefore, except for special applications requiring high conductivity, mild carbonization of 1000 ° C. or lower, more preferably 900 ° C. or lower is preferable. The carbonization time may be about 1 to 4 hours.
[0032]
The true density of the carbon fiber obtained in the carbonization step is 1.30 to 1.80 g / cm 3 , the plane spacing measured by X-ray diffraction is 0.345 to 0.365 nm, and the C / H atom The ratio is between 2 and 8.
When the true density of the carbon fiber is less than 1.30 g / cm 3 , the activation reaction rate becomes extremely high, and it becomes difficult to control the reaction. On the other hand, when the true density exceeds 1.80 g / cm 3 , carbonization proceeds excessively. Thus, the reactivity of carbon is reduced and the activation reaction becomes difficult, and neither is preferred.
[0033]
Further, when the plane spacing measured by X-ray diffraction is less than 0.345 nm, the alkali metal hardly penetrates into the interior through the planes, so that the activation does not progress uniformly. On the other hand, when the plane spacing exceeds 0.365 nm. Since the reaction rate becomes too high and it is difficult to control the activation reaction, none of them is preferable.
Further, if the C / H atomic ratio is less than 2, the carbon structure is undeveloped and the activation proceeds excessively. On the other hand, if it exceeds 8, the carbon skeleton structure develops excessively and the activation reaction becomes difficult to proceed. Neither is preferred.
[0034]
(D) Pulverizing Step The carbonized fiber obtained as described above can be activated as a mat or felt to form an electrode material, but in the production method of the present invention, it is an activation aid. A pulverizing treatment (milling) is performed before the alkali activation step in order to improve the uniformity of the specific surface by the uniform mixing with the alkali metal compound and the activation reaction and the bulk density of the electrode material. In this case, when expressed as an average particle size by a laser diffraction method, the powder is pulverized to 1 to 100 μm, and more preferably to 10 to 30 μm. When the average particle size is less than 1 μm, it is difficult to uniformly activate the alkali, while when the average particle size is more than 100 μm, the bulk density of the electrode material does not increase.
[0035]
The content of metal impurities in the pulverized carbon fiber is 1,000 ppm by weight or less, and if the content of metal impurities exceeds 1,000 ppm by weight, the performance of the capacitor electrode deteriorates, which is not preferable.
As a milling method, it is effective to use a victory mill, a jet mill, a high-speed rotation mill, or the like. Milling can also be performed using a Henschel mixer, a ball mill, a crusher, or the like.However, according to these methods, pressure is applied in the diameter direction of the fiber, and longitudinal cracks are often generated in the fiber axis direction. It is not preferable because it lowers the efficiency and uniformity of alkali activation. In addition, milling takes a long time, and is not an appropriate milling method. For efficient milling, it is appropriate to, for example, rotate the rotor with the blade attached thereto at high speed to cut the fibers. The fiber length can be controlled by adjusting the number of rotations of the rotor, the angle of the blade, and the like.
[0036]
(E) Alkali Activation Step Examples of the alkali metal compound used in the alkali activation step in the present invention include potassium hydroxide, sodium hydroxide, potassium carbonate, potassium nitrite, potassium sulfate and potassium chloride. Particularly preferred.
[0037]
Such an alkali metal compound is used in a weight ratio of 1.5 to 2.5 (fold), preferably 1.8 to 2.2 (fold), based on the weight ratio of the ground carbonized fiber.
If the weight ratio of the alkali metal compound is less than 1.5 (fold), the efficiency of pore formation of the obtained activated carbon fiber tends to decrease, while if the weight ratio exceeds 2.5 (fold), However, such an effect cannot be obtained, which increases the cost of a post-treatment step such as neutralization, and is not preferable in terms of maintainability and safety of the apparatus.
[0038]
The alkali activation treatment is, specifically, after uniformly mixing the pulverized carbonized fiber and the alkali metal compound in such a weight ratio, in an inert gas such as nitrogen at 350 to 500 ° C, preferably 380 to 450 ° C. , Preferably for 2 to 4 hours, more preferably for 2 to 3 hours, and then at a heating rate of 300 ° C / hour or more, preferably 400 ° C / hour or more, more preferably 500 ° C / hour or more. The temperature is raised to 800 ° C., preferably 730 to 770 ° C., and the temperature is maintained for preferably 2 to 4 hours, more preferably 2 to 3 hours.
[0039]
After uniformly mixing the ground carbonized fiber and the alkali metal compound, if the holding temperature in the inert gas is less than 350 ° C., the removal of moisture in the alkali metal compound becomes insufficient, and the foaming is remarkably caused by the subsequent temperature rise. . On the other hand, when the temperature exceeds 500 ° C., the dehydration and the activation reaction proceed simultaneously, and the performance deteriorates. Further, if the holding time at that time is less than 2 hours, the dehydration is insufficient, and if the holding time is more than 4 hours, the effect is not changed. Further, when the holding temperature after the temperature rise is lower than 700 ° C., the activation reaction does not sufficiently proceed, and the capacity does not appear. On the other hand, when the temperature exceeds 800 ° C., carbonization proceeds, the pores formed by the activation shrink, and the capacity decreases. If the holding time at that time is less than 2 hours, the activation reaction is insufficient. On the other hand, if the holding time is more than 4 hours, the activation is completed and the effect is not seen.
[0040]
An activation reaction vessel such as a tray is used for the alkali activation treatment. The activation reaction vessel is charged into a reactor for heating and raising the temperature, and the activation treatment is performed under the above temperature conditions, but the reaction furnace is not limited to a batch type or a continuous type. For example, a box furnace, a belt furnace, a tray pressure furnace, or the like can be used.
That is, in the alkali activation treatment, usually, a mixture of a crushed carbonized fiber and an alkali metal compound as a reactant is introduced into an alkali activation reaction container made of nickel, and the entire reaction container is placed in an inert gas atmosphere such as nitrogen gas. This is performed by heating and raising the temperature in the reactor.
[0041]
(F) Washing step After the activated carbon fiber obtained as described above is cooled to room temperature, the unreacted alkali metal compound is removed by washing with, for example, hot water or hot hydrochloric acid, and the transition metal contained therein is removed. And / or reduce transition metal compounds. The content of the transition metal and / or the transition metal compound is measured by ashing the activated carbon fiber in air at 700 ° C., dissolving the ash with an acid, and using ICP emission spectroscopy.
[0042]
The removal of the unreacted alkali metal compound used in the alkali activation step is performed, for example, by using hot water at 50 to 90 ° C. for 100 to 1500 parts by weight with respect to 100 parts by weight of the activated carbon fiber, 1 to 3 times in a batch method. This is performed by washing with.
Further, the neutralization of the alkali metal compound after the above-mentioned washing is carried out, for example, by using 0.1 to 6N, hydrochloric acid aqueous solution at 40 to 60 ° C. or the like using 100 to 1500 parts by weight with respect to 100 parts by weight of the activated carbon fiber. This is performed by washing three times in a batch system.
[0043]
Further, as the final dehydrochlorination washing, it is desirable to wash in a batch manner 1 to 5 times, for example, using 100 to 1500 parts by weight of warm water at 50 to 90 ° C. per 100 parts by weight of activated carbon fibers.
(J) Drying Step After the above-mentioned washing step, the activated carbon fiber is dried. Drying may be performed at 110 to 150 ° C. under normal pressure or reduced pressure for 1 to 24 hours.
[0044]
Activated carbon fibers obtained in this manner, 300 meters 2 / g or more in BET specific surface area, preferably 500~2800m 2 / g, more preferably mesophase pitch based active carbon having a specific surface area of 600~2500m 2 / g It is a fiber and exhibits excellent properties as an electrode material for electric double layer capacitors. If the BET specific surface area is less than 300 m 2 / g, a sufficient discharge capacity cannot be obtained, and the upper limit thereof is not particularly limited. Not only is it time-consuming, but also the activation yield decreases, which is not preferred, and is usually 2800 m 2 / g or less. The specific surface area is a value measured by a BET method using nitrogen adsorption, rounded to one decimal place in consideration of measurement accuracy, and displayed from the tens digit.
[0045]
(II) Electric Double Layer Capacitor The electric double layer capacitor according to the present invention includes the electrode containing the activated carbon fiber described above.
In the present invention, a method for producing an electrode is not particularly limited, and a conventionally known method for producing an electrode can be used.
[0046]
For example, in the electrode of the present invention, a binder such as polyethylene, polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF) is added to the activated carbon fiber and mixed, and the resulting mixture is subjected to pressure roll forming. It can be manufactured by molding into a sheet or plate.
When such an electrode is manufactured, graphite powder or carbon black such as acetylene black can be added as a conductive material.
[0047]
The electrode prepared in this manner is cut into a desired size and shape, a separator is interposed between the two electrodes, and after insertion into a container, an electrolytic solution is injected, and a sealing plate is caulked using a gasket. It can be a monopolar cell.
As the electrolyte for such an electric double layer capacitor, an organic solvent-based electrolyte to which a high voltage can be applied is preferable.
[0048]
Examples of the organic solvent include propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, dimethylformamide, acetonitrile, ethylene carbonate, tetrahydrofuran, dimethoxyethane, and the like. These organic solvents can be used as one kind or a mixture of two or more kinds.
[0049]
Examples of the electrolyte dissolved in such an organic solvent include cations of metals; quaternary ammonium cations such as ammonium ion, tetramethylammonium ion and tetraethylammonium ion; and cations such as carbonium cation and an appropriate anion. Salts with ions can be mentioned.
Examples of such anions include ClO 4 − , BF 4 − , PF 4 − , PF 6 − , AsF 6 − and the like.
[0050]
Specific examples of the electrolyte include LiClO 4 , NaBF 4 , and Et 4 N · BF 4 (where Et is an ethyl group).
In the activated carbon fiber according to the present invention, the discharge capacity per unit weight when the electric double layer is formed is preferably 20 to 45 F / g, particularly preferably 30 to 45 F / g.
[0051]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.
[0052]
Embodiment 1
(1) Production of Activated Carbon Fiber A nonwoven fabric pitch fiber having an average fiber diameter of 12 μm was obtained at a spinning temperature of 350 ° C. using a mesophase pitch having a softening point of 285 ° C. as a raw material. The pitch fibers were infusibilized in air at 320 ° C. for 0.5 hour. The degree of infusibilization of the obtained fiber was 6% by weight. Further, the obtained infusibilized fiber was carbonized at 800 ° C. for 1 hour in a nitrogen gas atmosphere, so that the true density was 1.55 g / cm 3 , the spacing between faces was 0.355 nm, and C / H A carbonized fiber having an atomic ratio of 4 was obtained. Further, the carbonized fiber was pulverized with a high-speed rotating mill to obtain a carbon fiber mill having an average particle size of 25 μm by a laser diffraction method and an average particle size of 30 μm obtained from a cumulative particle size distribution.
[0053]
The obtained carbon fiber mill and potassium hydroxide were mixed at a weight ratio of 1: 2, and an alkali activation treatment was performed at 400 ° C. for 3 hours and further at 800 ° C. for 2 hours in a nitrogen gas atmosphere. . Thereafter, three further alkaline washings with hot water at 90 ° C. and 15 times by weight are performed three times, and a washing with hydrochloric acid at 60 ° C. and 15 times by weight is performed three times at 1N, and dehydrochlorination washing with hot water at 90 ° C. and 15 times by weight. , And dried in air at 110 ° C. for 24 hours.
[0054]
The BET specific surface area of the obtained activated carbon fiber was 800 m 2 / g, the pore diameter was 0.80 nm, and the pore volume was 0.35 ml / g.
(2) Production of Electric Double Layer Capacitor After the above-mentioned activated carbon fiber was kneaded with graphite powder as a conductive filler and PTFE as a binder in a weight ratio of 81: 9: 10, the kneaded product was rolled. As a result, an electrode sheet having a thickness of 150 μm and an electrode density of 0.85 g / cc was prepared. The two polarizable electrodes 3 and 4 having a diameter of 18 mm are cut out from the electrode sheet, and the two polarizable electrodes, a PTFE separator 5 having a diameter of 20 mm and a thickness of 75 μm, an electrolytic solution, and the like are used to form the button shown in FIG. Type electric double layer capacitor was manufactured. As an electrolytic solution, a propylene carbonate solution of 1.8 M (mol / liter) triethylmethylammonium tetrafluoroborate [(C 2 H 5 ) 3 CH 3 NBF 4 ] was used.
[0055]
A charge / discharge test was performed using the obtained electric double layer capacitor. As a result, the capacitance per unit weight of the active material was 40 F / g, and the capacitance per unit volume was 34 F / cc. .
[0056]
[Comparative Example 1]
(1) Production of activated carbon 100 parts by weight of petroleum refined coke passed through a 20-mesh sieve through a rotary calciner and 200 parts by weight of granular potassium hydroxide having a water content of 15% by weight were charged in a nitrogen gas atmosphere at 700 parts by weight. The temperature was raised to ° C., and a heat treatment for activation (alkali activation) was performed under stirring for about 2 hours. Thereafter, the product was cooled, sufficiently washed with water, and dried by heating at 110 ° C. for 24 hours in a vacuum furnace.
[0057]
The BET specific surface area of the obtained activated carbon was 900 m 2 / g, the pore diameter was 0.78 nm, and the pore volume was 0.38 ml / g.
(2) Production of Electric Double Layer Capacitor An electrode sheet was prepared in the same manner as in Example 1 to obtain an electrode sheet having a thickness of 150 μm and an electrode density of 0.83 g / cc. An electric double layer capacitor was manufactured in the same manner as in Example 1 using the electrode sheet.
[0058]
A charge / discharge test was performed using the obtained electric double layer capacitor. As a result, the capacitance per unit weight of the active material was 25.5 F / g, and the capacitance per unit volume was 21.1 F / g. cc.
[0059]
【The invention's effect】
According to the method for producing activated carbon fibers of the present invention, since the ground carbon fiber having a constant fiber diameter is subjected to the alkali activation treatment, the activation reaction proceeds uniformly to the inside of the fibers, and the dispersion between particles is small. As a result, when the activated carbon fiber is used as an electrode material of an electric double layer capacitor, the capacitance per unit weight is improved.
[0060]
Further, according to the method for producing activated carbon fiber of the present invention, since mesophase pitch is used as a raw material, the conductivity as a polarizable electrode is high, and a higher electrode density can be obtained as compared with an isotropic material. As a result, when the activated carbon fiber is used as an electrode material of an electric double layer capacitor, the capacitance per unit volume is improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view.
1,2. Collector electrodes 3,4. Polarizing electrode5. Separator 6.
Claims (8)
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| WO2012087497A1 (en) * | 2010-11-30 | 2012-06-28 | Corning Incorporated | Porous carbon for electrochemical double layer capacitors |
| JP2020531405A (en) * | 2017-08-14 | 2020-11-05 | トカイ カーボン コリア カンパニー，リミティド | Manufacturing method of activated carbon for electrode material |
| JP2021507537A (en) * | 2017-12-19 | 2021-02-22 | トカイ カーボン コリア カンパニー，リミティド | Manufacturing method of activated carbon for electrode material |
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| JP2009502475A (en) * | 2005-07-27 | 2009-01-29 | シェブロン フィリップス ケミカル カンパニー エルピー | Selective hydrogenation catalyst and production and use thereof |
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| US9550173B2 (en) | 2005-07-27 | 2017-01-24 | Chevron Philips Chemical Company Lp | Selective hydrogenation catalyst and methods of making and using same |
| WO2012087497A1 (en) * | 2010-11-30 | 2012-06-28 | Corning Incorporated | Porous carbon for electrochemical double layer capacitors |
| US8482900B2 (en) | 2010-11-30 | 2013-07-09 | Corning Incorporated | Porous carbon for electrochemical double layer capacitors |
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| JP2013544446A (en) * | 2010-11-30 | 2013-12-12 | コーニング インコーポレイテッド | Porous carbon in electrochemical double layer capacitors |
| JP2020531405A (en) * | 2017-08-14 | 2020-11-05 | トカイ カーボン コリア カンパニー，リミティド | Manufacturing method of activated carbon for electrode material |
| JP2021507537A (en) * | 2017-12-19 | 2021-02-22 | トカイ カーボン コリア カンパニー，リミティド | Manufacturing method of activated carbon for electrode material |
| US11072532B2 (en) | 2017-12-19 | 2021-07-27 | Tokai Carbon Korea Co., Ltd | Method for manufacturing activated carbon for electrode material |
| JP7130750B2 (en) | 2017-12-19 | 2022-09-05 | トカイ カーボン コリア カンパニー，リミティド | Manufacturing method of activated carbon for electrode material |
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