JP3866785B2 - Activated carbon for electrodes of electric double layer capacitors - Google Patents
Activated carbon for electrodes of electric double layer capacitors Download PDFInfo
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- JP3866785B2 JP3866785B2 JP24058095A JP24058095A JP3866785B2 JP 3866785 B2 JP3866785 B2 JP 3866785B2 JP 24058095 A JP24058095 A JP 24058095A JP 24058095 A JP24058095 A JP 24058095A JP 3866785 B2 JP3866785 B2 JP 3866785B2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 101
- 239000003990 capacitor Substances 0.000 title claims description 28
- 239000008151 electrolyte solution Substances 0.000 claims description 12
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 10
- 239000007864 aqueous solution Substances 0.000 claims description 10
- 235000013162 Cocos nucifera Nutrition 0.000 claims description 7
- 244000060011 Cocos nucifera Species 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 6
- 239000003792 electrolyte Substances 0.000 description 12
- 230000004913 activation Effects 0.000 description 9
- 239000003960 organic solvent Substances 0.000 description 8
- 239000002245 particle Substances 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 6
- 230000000704 physical effect Effects 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 239000011230 binding agent Substances 0.000 description 2
- 239000007772 electrode material Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000015654 memory Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000005011 phenolic resin Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- -1 activated carbon (activated carbon 15 Chemical class 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 239000000908 ammonium hydroxide Substances 0.000 description 1
- 150000001721 carbon Chemical group 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000003610 charcoal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910017053 inorganic salt Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 125000004430 oxygen atom Chemical group O* 0.000 description 1
- 239000002006 petroleum coke Substances 0.000 description 1
- 150000004714 phosphonium salts Chemical group 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 150000003242 quaternary ammonium salts Chemical group 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000011592 zinc chloride Substances 0.000 description 1
- 235000005074 zinc chloride Nutrition 0.000 description 1
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
- H01G11/44—Raw materials therefor, e.g. resins or coal
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/318—Preparation characterised by the starting materials
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/336—Preparation characterised by gaseous activating agents
-
- 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
- H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/11—Powder tap density
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- 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
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Power Engineering (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Inorganic Chemistry (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
- Carbon And Carbon Compounds (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、電解液を使用する電気二重層コンデンサの電極として好適な活性炭に関するものである。
【０００２】
【従来の技術】
電気二重層コンデンサは、固体と液体の界面に生じる電気二重層を利用したコンデンサであり、静電容量が電池と比べ非常に大きく、且つ充放電サイクル特性や急速充電にも優れ、またメンテナンスフリーで、環境汚染を招く恐れがないため、マイコンやＩＣメモリの小型バックアップ電源として最近特に注目されている。
電気二重層コンデンサにおける上記固体は分極性電極であり、通常粉末活性炭が使用される。
電気二重層コンデンサに用いられる電解液は、有機溶媒系と水溶液系に大別される。
有機溶媒系は耐電圧が高いため小型化に有利であり、また外装に金属を用いることもできる。水溶液系では電解液の導電率が高いために低等価直列抵抗（ＥＳＲ）化に向いており、湿度に影響されず環境特性に優れるという特徴を有している。
このような有利な特性を有する電気二重層コンデンサにおいて、もし電極の単位容積当たりの静電容量をさらに高めることができれば、その用途は単にマイコンやＩＣメモリのバックアップ電源にとどまらず、たとえば、各種モータの初期駆動、電気自動車、排気ガス浄化触媒のプレヒータ等の電源としても有望である。そこで、電極の単位容積当たり一層高容量の電気二重層コンデンサを得るためこれまでも様々な改良が試みられてきた。その一つに電極となる活性炭の改良がある。
【０００３】
コンデンサ素子の容量は、用いる活性炭電極の表面積と電解液中の電気二重層容量によって決定されるのであるから、容量密度の向上を図るには理論上比表面積の大きな活性炭を用いるのが有利である。そこでたとえば、特開昭６３−７８５１４に示されているように石油コークスを原料とし、比表面積が２０００〜３５００ｍ2／ｇで、かさ密度が０．２〜１．０ｇ／ｍｌ、全細孔容積０．５〜３．０ｍｌ／ｇといった比較的高比表面積活性炭の電極への利用が提案されている。また特開平７−１３５１２７には、高容量電気二重層コンデンサの電極として活性炭の酸素原子／炭素原子比が０．１以上という特性を有する活性炭、特にフェノール樹脂系活性炭と結合剤としてフェノール樹脂を用いた活性炭でその特性を有するものも提案されている。さらに、特再平０３−８１２２０３には、活性炭原料をアルカリ金属の水酸化物浴中７００℃未満で熱処理して得られる高静電容量の炭素質素材も提案されている。
【０００４】
【発明が解決しようとする課題】
しかし、これまでに提案されている電気二重層コンデンサ電極用活性炭のうち、たとえばアルカリや塩化亜鉛などの薬品で賦活されたいわゆる薬品賦活炭は、製造直後は２５０ファラッド（Ｆ）／ｍｌ以上という極めて高い静電容量を示すものもあるが、その静電容量は短時間内に著しい経時低下を起こし、６カ月以上経過するとその静電容量は製造当初の１０分の１以下に低下してしまい、実用には供し難い。これに対して、水蒸気賦活などの薬品によらない賦活法で製造された活性炭は静電容量の経時低下は殆どないものの、これまで実用化されて来たもののうち、有機溶媒系電解質を用いるものでは高々２０Ｆ／ｇ、８Ｆ／ｍｌ程度、水溶液系電解質を用いるものでも高々４０Ｆ／ｇ、１６Ｆ／ｍｌ程度であり、前述した新たな用途開発のためには、さらにその電極体積当りの静電容量を一段と高める必要がある。
【０００５】
【課題を解決するための手段】
本発明者らは、単位容積当り静電容量がより大なる電気二重層コンデンサ電極を得るために、使用する粉末活性炭の原料の種類、賦活法、活性炭の比表面積、粒子径などの相互の関係について鋭意研究を重ねた結果、水蒸気賦活された活性炭であって、これまで高い静電容量を得るのに好適と思われていた2000〜3500m2/gのＢＥＴ比表面積のものよりやや低めの1000〜1500m2/gのＢＥＴ比表面積で、且つ中位径が6〜10μmとこれまでこの分野で用いられてきた活性炭の粒径よりやや大なる粒径を有する活性炭が思いがけなくも電極の単位容積当り極めて高い静電容量の電気二重層コンデンサを与え、しかもその高静電容量が６カ月以上の長期に亙って殆ど低下しないということを知見し、本発明を完成した。
すなわち、本発明は、
（１）
水蒸気賦活されたヤシ殻活性炭であって、中位径が6〜10μm、タップ法による見掛け密度が0.500〜0.650g/ml、且つ、電解液が有機溶媒系のものである場合ＢＥＴ比表面積が 1200 〜 1500m 2 /g であり、電解液が水溶液系のものである場合、ＢＥＴ比表面積が 1000 〜 1300m 2 /gである電解液を使用する電気二重層コンデンサの電極用活性炭、
（２）
中位径が7〜9μmである請求項１記載の活性炭、
（３）
電解液が水溶液系のものである場合、その電解液が硫酸である（１）記載の活性炭、
（４）
（１）記載の活性炭からなる電気二重層コンデンサ電極、
である。
【０００６】
【発明の実施の形態】
本発明に用いられる活性炭の原料には、イオウなどの不純物の含量が少ないヤシ殻が用いられる。このヤシ殻は、通常の炭化条件、たとえば400〜800℃で30分〜3時間程度熱処理をして炭化し、得られたヤシ殻炭を10〜100メッシュに破砕して、500〜1000℃、通常は約850℃前後の温度で、10分〜10時間、好ましくは30分〜5時間かけて、水蒸気賦活する。この水蒸気賦活においては、賦活温度が低く、賦活時間が短ければ、得られる活性炭の比表面積は小となり、賦活温度が高く賦活時間が長くなる従って、比表面積は大となる。得られた賦活炭は水洗、乾燥し、目的とする粒度に粉砕し、必要により分級により粒度を調整する。本発明の目的に適う活性炭の粒度はコールターカウンタで測定した中位径が6〜10μm、好ましくは7〜9μm、さらに好ましくは7.5〜8.5μmである。またその活性炭のＢＥＴ比表面積は、電気二重層コンデンサに用いる溶媒が、たとえば、プロピレンカーボネイトのような有機溶媒系の場合、通常 1200 〜 1500m 2 /g 、好ましくは 1250 〜 1450m 2 /g 、さらに好ましくは、 1300 〜 1400m 2 /g であり、溶媒がたとえば硫酸のような水溶液系である場合は、通常 1000 〜 1300m 2 /g 、好ましくは 1050 〜 1250m 2 /g 、さらに好ましくは 1100 〜 1200m 2 /g である。また活性炭のタップ法による見掛け密度は、通常0.500〜0.650g/mlであり、特に電解液が有機溶媒系の場合は、0.530〜0.600g/mlが好ましく、水溶液系の場合は0.570〜0.640g/mlが好ましい。本発明の活性炭を用いて電気二重層コンデンサの電極を製造するには、自体公知の方法を採用することができる。たとえば、活性炭、バインダおよび水の混合物を混合機でよく混練する。得られたペースト状混合物をロールを用いて圧延し、200〜300℃程度の加熱下延伸処理をして、適当な厚み、たとえば0.6mm程度のシート状電極材料とする。このシート状電極材料を円板状に打ち抜いて分極性電極とする。
【０００７】
このようにして得られた円板状物を２〜数枚セパレータを介して重ね、外装容器に収納して、その中に電解液を注入することにより電気二重層コンデンサユニットセルを作ることができる。
電解液としては有機溶媒系のものと水溶液系のものがある。有機溶媒系電解液の溶媒としてはプロピレンカーボネートが一般的であり、電解質としてはこれまで知られている種々の第４級ホスホニウム塩、第４級アンモニウム塩のいずれもが使用できる。水溶液系電解液としては、希硫酸が一般的であるが、他の無機塩、たとえば４フッ化ホウ酸、硝酸なども使用できる。さらに水酸化カリ、水酸化ナトリウム、水酸化アンモニウムなどの無機塩を溶質とする水溶液も便宜に使用できる。それぞれの電解質の濃度は１０〜９０重量％の範囲で適宜選択することができる。
【０００８】
実施例１
ヤシ殻を４００〜８００℃で１時間炭化し、ロータリーキルンで８５０℃の加熱下それぞれ６０分、９０分、１２０分、１８０分間水蒸気賦活したものを洗浄、乾燥して粉砕し、コールターカウンタの測定による中位径７，５μｍの粉末活性炭（活性炭１〜４）を得た。それぞれの活性炭から直径１５ｍｍ、厚さ０．６ｍｍの円板状電極を作り、それを２枚重ね合わせてコンデンサユニットセルの電極を作った。
得られたそれぞれの粉末活性炭の物性、それから作られた上記電極と（Ｃ２Ｈ５）４ＰＢＦ ４ ０．５モル／プロピレンカーボネート電解液を用いて作ったコンデンサユニットセルの製造直後の静電容量および製造６カ月後のユニットセルの静電容量を測定し、その結果を〔表１〕に示す。
【表１】
実施例２
ヤシ殻を４００〜８００℃で１時間炭化し、流動炉で９００℃の加熱下、それぞれ６０分、９０分、１２０分、１８０分間水蒸気賦活し、洗浄、乾燥粉砕して中位径７，５μｍの粉末活性炭（活性炭５〜８）を得た。それぞれの活性炭から実施例１と同様にしてコンデンサユニットセルの電極を作った。
得られたそれぞれの粉末活性炭の物性、それから作られた上記電極と４０％硫酸電解液を用いて作ったコンデンサユニットセルの製造直後および製造６カ月後のコンデンサユニットセルの静電容量を測定し、その結果を〔表２〕に示す。
【表２】
実施例３
実施例１と同様にして作ったＢＥＴ比表面積１３５０ｍ2／ｇの活性炭を得、これを粉砕して、それぞれ粒径の異なる６種類の粉末活性炭（活性炭９〜１４）を得た。
実施例１と同様の方法で活性炭の物性、コンデンサユニットセルの静電容量を測定し、その結果を〔表３〕に示す。
【表３】
実施例４
実施例２と同様にして作ったＢＥＴ比表面積１１４０ｍ2／ｇの活性炭を得、これを粉砕して、それぞれ粒径の異なる６種類の粉末活性炭（活性炭１５〜２０）を得た。
実施例２と同様の方法で活性炭の物性、コンデンサユニットセルの静電容量を測定し、その結果を〔表４〕に示す。
【表４】
【発明の効果】
本発明の電気二重層コンデンサの電極用活性炭は、電極の単位容積当たり高い静電容量の電極を与え、しかも充放電の繰り返しや経時による劣化が低く長期に亙り安定した高静電容量の確保が可能である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to activated carbon suitable as an electrode of an electric double layer capacitor using an electrolytic solution.
[0002]
[Prior art]
An electric double layer capacitor is a capacitor that uses an electric double layer generated at the interface between a solid and a liquid. Its capacitance is much larger than that of a battery, and it has excellent charge / discharge cycle characteristics and quick charge, and is maintenance-free. Since there is no risk of environmental pollution, it has recently attracted particular attention as a compact backup power source for microcomputers and IC memories.
The solid in the electric double layer capacitor is a polarizable electrode, and usually powdered activated carbon is used.
Electrolytic solutions used for electric double layer capacitors are roughly classified into organic solvent systems and aqueous solution systems.
The organic solvent system has a high withstand voltage and is advantageous for downsizing, and a metal can be used for the exterior. The aqueous solution system is suitable for low equivalent series resistance (ESR) due to the high conductivity of the electrolytic solution, and is characterized by excellent environmental characteristics without being affected by humidity.
In the electric double layer capacitor having such advantageous characteristics, if the electrostatic capacity per unit volume of the electrode can be further increased, its use is not limited to a backup power source of a microcomputer or an IC memory. It is also promising as a power source for initial driving, electric vehicles, preheaters for exhaust gas purification catalysts, and the like. Therefore, various improvements have been attempted so far in order to obtain an electric double layer capacitor having a higher capacity per unit volume of the electrode. One of them is the improvement of activated carbon that serves as an electrode.
[0003]
Since the capacity of the capacitor element is determined by the surface area of the activated carbon electrode to be used and the electric double layer capacity in the electrolyte, it is theoretically advantageous to use activated carbon having a large specific surface area in order to improve the capacity density. . Therefore, for example, as disclosed in JP-A-63-78514, petroleum coke is used as a raw material, the specific surface area is 2000 to 3500 m 2 / g, the bulk density is 0.2 to 1.0 g / ml, and the total pore volume. Use of activated carbon having a relatively high specific surface area of 0.5 to 3.0 ml / g for an electrode has been proposed. Japanese Patent Laid-Open No. 7-135127 uses activated carbon having an oxygen atom / carbon atom ratio of 0.1 or more as an electrode of a high-capacity electric double layer capacitor, particularly a phenol resin activated carbon and a phenol resin as a binder. An activated carbon having the characteristics has been proposed. Further, Japanese Patent Publication No. 03-812203 proposes a high-capacity carbonaceous material obtained by heat-treating an activated carbon material in an alkali metal hydroxide bath at less than 700 ° C.
[0004]
[Problems to be solved by the invention]
However, among the activated carbons for electric double layer capacitor electrodes that have been proposed so far, for example, so-called chemical activated charcoal activated by chemicals such as alkali and zinc chloride is extremely high at 250 Farad (F) / ml or more immediately after production. Some of them exhibit high capacitance, but the capacitance significantly decreases over time within a short time, and after 6 months or more, the capacitance decreases to 1/10 or less of the original production, It is difficult to put to practical use. In contrast, activated carbon produced by an activation method that does not rely on chemicals such as steam activation has almost no decrease in capacitance over time, but among those that have been put to practical use so far, those using organic solvent electrolytes Is about 20F / g and 8F / ml at most, and even about 40F / g and 16F / ml even when using an aqueous electrolyte, in order to develop the above-mentioned new applications, the capacitance per electrode volume is further increased. Need to be further increased.
[0005]
[Means for Solving the Problems]
In order to obtain an electric double layer capacitor electrode having a larger capacitance per unit volume, the present inventors have interrelationships such as the type of powdered activated carbon material used, the activation method, the specific surface area of activated carbon, and the particle size. As a result of extensive research on the activated carbon, the activated carbon activated with water vapor, which is considered to be suitable for obtaining a high capacitance so far, has a BET specific surface area of 2000-3500 m 2 / g, which is slightly lower than 1000 Activated carbon with a BET specific surface area of ~ 1500m 2 / g and a median diameter of 6 ~ 10μm, which is a little larger than the particle diameter of activated carbon used in this field, is unexpectedly per unit volume of the electrode. The present inventors completed the present invention by finding that an electric double layer capacitor having an extremely high capacitance was provided, and that the high capacitance hardly decreased over a long period of 6 months or more.
That is, the present invention
(1)
Steam activated activated coconut shell activated carbon having a median diameter of 6 to 10 μm, an apparent density by tap method of 0.500 to 0.650 g / ml, and a BET specific surface area of 1200 when the electrolyte is an organic solvent type Activated carbon for an electrode of an electric double layer capacitor using an electrolytic solution having a BET specific surface area of 1000 to 1300 m 2 / g when the electrolytic solution is of an aqueous solution type, up to 1500 m 2 / g ,
(2)
The activated carbon according to claim 1, having a median diameter of 7 to 9 µm.
( 3 )
When the electrolyte is an aqueous solution , the activated carbon according to (1) , wherein the electrolyte is sulfuric acid,
( 4 )
(1) An electric double layer capacitor electrode comprising the activated carbon as described above,
It is.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
As the raw material of the activated carbon used in the present invention, coconut shells having a low content of impurities such as sulfur are used. This coconut shell is carbonized by heat treatment for about 30 minutes to 3 hours at normal carbonization conditions, for example, 400 to 800 ° C., and the resulting coconut shell charcoal is crushed into 10 to 100 mesh, 500 to 1000 ° C., Usually, steam activation is performed at a temperature of about 850 ° C. for 10 minutes to 10 hours, preferably 30 minutes to 5 hours. In this steam activation, if the activation temperature is low and the activation time is short, the specific surface area of the activated carbon obtained is small, the activation temperature is high and the activation time is long, and therefore the specific surface area is large. The obtained activated charcoal is washed with water, dried, pulverized to the desired particle size, and if necessary, the particle size is adjusted by classification. The particle size of the activated carbon suitable for the purpose of the present invention is such that the median diameter measured with a Coulter counter is 6 to 10 μm, preferably 7 to 9 μm, more preferably 7.5 to 8.5 μm. The BET specific surface area of the activated carbon, solvent used in the electric double layer capacitor, for example, if the organic solvent such as propylene carbonate, usually 1200 ~ 1500m 2 / g, preferably 1250 ~ 1450m 2 / g, more preferably is 1300 ~ 1400m 2 / g, when the solvent for example an aqueous solution system, such as sulfuric acid is generally 1000 ~ 1300m 2 / g, preferably 1050 ~ 1250m 2 / g, more preferably 1100 ~ 1200 m 2 / g . The apparent density of the activated carbon by the tap method is usually 0.500 to 0.650 g / ml, particularly 0.530 to 0.600 g / ml when the electrolytic solution is an organic solvent system, and 0.570 to 0.640 g / ml when the aqueous solution system is used. ml is preferred. In order to produce an electrode of an electric double layer capacitor using the activated carbon of the present invention, a method known per se can be employed. For example, a mixture of activated carbon, binder and water is kneaded well with a mixer. The obtained paste-like mixture is rolled using a roll and stretched under heating at about 200 to 300 ° C. to obtain a sheet-like electrode material having an appropriate thickness, for example, about 0.6 mm. This sheet-like electrode material is punched into a disc shape to obtain a polarizable electrode.
[0007]
An electric double layer capacitor unit cell can be made by stacking two or more disk-like materials obtained in this way through separators, storing them in an outer container, and injecting an electrolyte into them. .
Electrolytic solutions include organic solvent-based and aqueous solutions. Propylene carbonate is generally used as the solvent for the organic solvent-based electrolytic solution, and any of various known quaternary phosphonium salts and quaternary ammonium salts can be used as the electrolyte. As the aqueous electrolyte, dilute sulfuric acid is generally used, but other inorganic salts such as tetrafluoroboric acid and nitric acid can also be used. Furthermore, an aqueous solution having an inorganic salt such as potassium hydroxide, sodium hydroxide or ammonium hydroxide as a solute can also be used conveniently. The concentration of each electrolyte can be appropriately selected within a range of 10 to 90% by weight.
[0008]
Example 1
Coconut shells are carbonized at 400-800 ° C for 1 hour, heated in a rotary kiln at 850 ° C for 60 minutes, 90 minutes, 120 minutes, 180 minutes respectively, washed, dried and ground, and measured by Coulter counter Powdered activated carbon (activated carbon 1 to 4) having a median diameter of 7.5 μm was obtained. A disk-shaped electrode having a diameter of 15 mm and a thickness of 0.6 mm was made from each activated carbon, and two electrodes were stacked to form a capacitor unit cell electrode.
Physical properties of each of the obtained powdered activated carbons, capacitance immediately after the production of the capacitor unit cell made by using the above-mentioned electrode made therefrom and (C 2 H 5 ) 4 PBF 4 0.5 mol / propylene carbonate electrolyte And the electrostatic capacitance of the unit cell 6 months after manufacture was measured, and the result is shown in [Table 1].
[Table 1]
Example 2
Coconut shell is carbonized at 400-800 ° C for 1 hour, heated at 900 ° C in a fluidized furnace, steam activated for 60 minutes, 90 minutes, 120 minutes, 180 minutes, respectively, washed, dried and pulverized, with a median diameter of 7.5 µm Powdered activated carbon (activated carbon 5-8) was obtained. Capacitor unit cell electrodes were prepared from each activated carbon in the same manner as in Example 1.
The physical properties of each of the obtained powdered activated carbon, the capacitance of the capacitor unit cell immediately after the manufacture of the capacitor unit cell made using the above-mentioned electrode made from it and a 40% sulfuric acid electrolyte, and 6 months after the manufacture, The results are shown in [Table 2].
[Table 2]
Example 3
Activated carbon having a BET specific surface area of 1350 m 2 / g prepared in the same manner as in Example 1 was obtained and pulverized to obtain 6 types of powdered activated carbon (activated carbon 9 to 14) having different particle sizes.
The physical properties of the activated carbon and the capacitance of the capacitor unit cell were measured in the same manner as in Example 1, and the results are shown in [Table 3].
[Table 3]
Example 4
Activated carbon having a BET specific surface area of 1140 m 2 / g produced in the same manner as in Example 2 was obtained and pulverized to obtain 6 types of powdered activated carbon (activated carbon 15 to 20) having different particle sizes.
The physical properties of the activated carbon and the capacitance of the capacitor unit cell were measured in the same manner as in Example 2, and the results are shown in [Table 4].
[Table 4]
【The invention's effect】
The activated carbon for an electrode of the electric double layer capacitor of the present invention gives an electrode with a high capacitance per unit volume of the electrode, and also ensures a stable high capacitance over a long period of time with low repeated charge / discharge and deterioration over time. Is possible.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24058095A JP3866785B2 (en) | 1995-08-24 | 1995-08-24 | Activated carbon for electrodes of electric double layer capacitors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24058095A JP3866785B2 (en) | 1995-08-24 | 1995-08-24 | Activated carbon for electrodes of electric double layer capacitors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0963907A JPH0963907A (en) | 1997-03-07 |
| JP3866785B2 true JP3866785B2 (en) | 2007-01-10 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP24058095A Expired - Fee Related JP3866785B2 (en) | 1995-08-24 | 1995-08-24 | Activated carbon for electrodes of electric double layer capacitors |
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| Country | Link |
|---|---|
| JP (1) | JP3866785B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9799459B2 (en) | 2014-08-08 | 2017-10-24 | Corning Incorporated | High pore volume utilization carbon and electric double layer capacitor |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5969936A (en) * | 1997-03-24 | 1999-10-19 | Asahi Glass Company Ltd. | Electric double layer capacitor and electrolyte therefor |
| WO2004110928A1 (en) * | 2003-06-13 | 2004-12-23 | Kuraray Chemical Co., Ltd | Activated carbon product in sheet form and element of device for preventing transpiration of fuel vapor |
-
1995
- 1995-08-24 JP JP24058095A patent/JP3866785B2/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9799459B2 (en) | 2014-08-08 | 2017-10-24 | Corning Incorporated | High pore volume utilization carbon and electric double layer capacitor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0963907A (en) | 1997-03-07 |
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