JP2004006803A - Electric double layer capacitor - Google Patents
Electric double layer capacitor Download PDFInfo
- Publication number
- JP2004006803A JP2004006803A JP2003107847A JP2003107847A JP2004006803A JP 2004006803 A JP2004006803 A JP 2004006803A JP 2003107847 A JP2003107847 A JP 2003107847A JP 2003107847 A JP2003107847 A JP 2003107847A JP 2004006803 A JP2004006803 A JP 2004006803A
- Authority
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- Prior art keywords
- formula
- electric double
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- double layer
- electrolyte
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- 239000003990 capacitor Substances 0.000 title claims abstract description 56
- 239000003792 electrolyte Substances 0.000 claims abstract description 31
- PYLWMHQQBFSUBP-UHFFFAOYSA-N monofluorobenzene Chemical compound FC1=CC=CC=C1 PYLWMHQQBFSUBP-UHFFFAOYSA-N 0.000 claims abstract description 30
- 239000005486 organic electrolyte Substances 0.000 claims abstract description 16
- 150000001768 cations Chemical class 0.000 claims abstract description 7
- 239000008151 electrolyte solution Substances 0.000 claims description 55
- 239000000243 solution Substances 0.000 claims description 20
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims description 16
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 12
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- 239000002904 solvent Substances 0.000 claims description 11
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 10
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 claims description 8
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 claims description 8
- 125000000383 tetramethylene group Chemical group [H]C([H])([*:1])C([H])([H])C([H])([H])C([H])([H])[*:2] 0.000 claims description 8
- 125000000217 alkyl group Chemical group 0.000 claims description 5
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 62
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
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- 239000003513 alkali Substances 0.000 description 4
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- 239000004743 Polypropylene Substances 0.000 description 3
- 239000000853 adhesive Substances 0.000 description 3
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- 239000012298 atmosphere Substances 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
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- 238000004804 winding Methods 0.000 description 3
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 2
- 241000196324 Embryophyta Species 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
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- UEMGWPRHOOEKTA-UHFFFAOYSA-N 1,3-difluorobenzene Chemical compound FC1=CC=CC(F)=C1 UEMGWPRHOOEKTA-UHFFFAOYSA-N 0.000 description 1
- CMJLMPKFQPJDKP-UHFFFAOYSA-N 3-methylthiolane 1,1-dioxide Chemical compound CC1CCS(=O)(=O)C1 CMJLMPKFQPJDKP-UHFFFAOYSA-N 0.000 description 1
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- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- RAXXELZNTBOGNW-UHFFFAOYSA-O Imidazolium Chemical compound C1=C[NH+]=CN1 RAXXELZNTBOGNW-UHFFFAOYSA-O 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N Phenol Chemical compound OC1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
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- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 1
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- 230000015556 catabolic process Effects 0.000 description 1
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- 229920002678 cellulose Polymers 0.000 description 1
- 150000005678 chain carbonates Chemical class 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- MVPPADPHJFYWMZ-UHFFFAOYSA-N chlorobenzene Chemical compound ClC1=CC=CC=C1 MVPPADPHJFYWMZ-UHFFFAOYSA-N 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 239000000306 component Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 150000005676 cyclic carbonates Chemical class 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
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- 230000006866 deterioration Effects 0.000 description 1
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- 239000000835 fiber Substances 0.000 description 1
- 125000001153 fluoro group Chemical group F* 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- ZTOMUSMDRMJOTH-UHFFFAOYSA-N glutaronitrile Chemical compound N#CCCCC#N ZTOMUSMDRMJOTH-UHFFFAOYSA-N 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
- 239000003273 ketjen black Substances 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
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- 150000002739 metals Chemical class 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
- 150000002825 nitriles Chemical class 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- LYGJENNIWJXYER-UHFFFAOYSA-N nitromethane Chemical compound C[N+]([O-])=O LYGJENNIWJXYER-UHFFFAOYSA-N 0.000 description 1
- 229920000620 organic polymer Polymers 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
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- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 description 1
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- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- WVLBCYQITXONBZ-UHFFFAOYSA-N trimethyl phosphate Chemical compound COP(=O)(OC)OC WVLBCYQITXONBZ-UHFFFAOYSA-N 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 238000003466 welding Methods 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
- H01G11/54—Electrolytes
- H01G11/58—Liquid electrolytes
-
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は電気二重層キャパシタ、特に自己放電特性及び信頼性に優れる電気二重層キャパシタに関する。
【０００２】
【従来の技術】
従来の電気二重層キャパシタの形状としては、集電体上に形成した活性炭を主体とする一対の分極性電極の間にセパレータを挟んだ素子を、電解液とともに金属ケース中に収納し、ガスケットを介して金属蓋によって密封したコイン型、又は一対のシート状分極性電極の間にセパレータを介して巻回してなる素子を電解液と共に円筒型の金属ケース中に収容し、ケースの開口部から電解液が蒸発しないように封口した円筒型のものがある。
【０００３】
また、大電流大容量向けとして、多数のシート状分極性電極を、間にセパレータを介して積層してなる素子が組み込まれた積層型の電気二重層キャパシタも提案されている（特許文献１〜３参照）。すなわち、矩形に成形されたシート状分極性電極を正極及び負極とし、間にセパレータを介して交互に積層して素子とし、正極及び負極それぞれの端部に正極リード部材及び負極リード部材をかしめにより接続した状態でケース中に収容し、素子に電解液を含浸して蓋で密閉している。
【０００４】
従来の電気二重層キャパシタの電解液には、硫酸などの鉱酸、アルカリ金属塩又はアルカリを含む水系電解液の他、各種有機電解液が用いられている。有機電解液の溶媒としては、プロピレンカーボネート、γ−ブチロラクトン、アセトニトリル、ジメチルホルムアミド（特許文献４参照）や、スルホラン誘導体等（特許文献５参照）が知られている。耐電圧を比較すると、水系電解液は０．８Ｖに対し、有機電解液は２．５〜３．３Ｖであり、キャパシタの静電エネルギーは耐電圧の２乗に比例するので、静電エネルギーの点では有機電解液の方が有利である。
【０００５】
電気二重層キャパシタの耐電圧は、基本的には電解液の電気化学的な分解電圧によって制限される。電解液として水系電解液に比べ耐電圧の高い有機電解液を使用する場合、水の理論分解電圧（１．２３Ｖ）より高い２Ｖ以上の電圧を印加して使用するため、電解液中に含まれる不純物、特に水分によって電気分解が起こる。そのため、有機電解液は、溶媒、電解質ともに高度に精製されかつ脱水されて使用される。
【０００６】
一方、電気二重層キャパシタの電極には高比表面積の電極材料が使用されるが、上記有機電解液と組み合わせる場合、一般には活性炭が電極材料として使用される。活性炭は数ｎｍ程度の微細孔を有する多孔質材料であるが、高い吸着能を有するため環境中の水分を吸着しやすい。したがって、活性炭は電気二重層キャパシタの製造工程において高度に脱水されている必要がある。通常、活性炭の細孔中から水分を完全に除去するためには、真空中又は不活性ガス雰囲気中において３００℃以上の高温での脱水処理が必要とされる。しかし、通常活性炭粒子は有機ポリマー等のバインダを用いて集電体上に形成されて電極を構成しており、３００℃以上の高温処理ではバインダが熱分解するため、通常２００℃以下の熱処理しかできない。このため、活性炭電極中の水分を完全に除去するのは困難である。
【０００７】
また、活性炭表面と電解液とが接していない部分、すなわち電解液の含浸が不充分で電解液によって濡れていない活性炭表面や、残存水分の電気分解によって発生したガスが活性炭細孔内にとどまっている部分の存在により、電荷を蓄積する面積が小さくなり、容量発現率が低下し、抵抗が上昇するという問題があった。さらに、発生したガスは活性炭細孔内に徐々に蓄積され、セパレータを介して対向する相対する電極に電解液を含浸させてなる素子体の外部には排出されず、素子体内部に留まることが判明した。このような状況下において長期間電気二重層キャパシタを使用すると、発生したガスによって活性炭の細孔内部に存在する電解液が追い出され、本来得られるはずの容量が得られなくなり、また細孔内のイオンの移動による電気導通経路が遮断される。そのため、電気二重層キャパシタの静電容量の減少や内部抵抗の上昇等の性能低下が起こる。さらに、細孔中の残存水分を完全に除去できないため、吸着した電荷による電気分解が継続的に起こる。このため、電圧を印加して回路を開いた後の電圧保持性が悪いという問題があった。
【０００８】
一方、特許文献６においては、電解液中にベンゼン又はその誘導体を含有させると、活性炭の細孔内壁に存在する擬黒鉛表面と親和性が高いため、細孔内の残存水分と置換吸着されやすく、電圧印加によりこれらの水分が電気分解されて発生したガスは、微細孔内ではなく微細孔外、すなわち活性炭粒子内のマイクロポア又は粒子間隙に存在するか、さらには泡として素子体の外部へ排出されると推定されているが、最近では、より自己放電特性及び信頼性に優れる電気二重層キャパシタ及びそのための電解液を提供することが求められている。
【０００９】
【特許文献１】
特開平０４−１５４１０６号公報（特許請求の範囲、第１図）
【特許文献２】
特開平０３−２０３３１１号公報（特許請求の範囲、第３図）
【特許文献３】
特開平０４−２８６１０８号公報（請求項１）
【特許文献４】
特開昭４９−０６８２５４号公報（特許請求の範囲）
【特許文献５】
特開昭６２−２３７７１５号公報（特許請求の範囲）
【特許文献６】
特開２０００−２５２１７１号公報（段落番号００１４、００１５）
【００１０】
【発明が解決しようとする課題】
本発明は、自己放電特性及び信頼性に優れる電気二重層キャパシタ及びそのための有機電解液を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明は、一対の分極性電極と該分極性電極との界面に電気二重層を形成する電解液とを有する電気二重層キャパシタにおいて、前記電解液が式１で表されるフルオロベンゼン（式１中、ｎは１〜６の整数である。）を含有する有機電解液からなることを特徴とする電気二重層キャパシタを提供する。
【００１２】
【化６】
また、本発明は、式１で表されるフルオロベンゼン（式１中、ｎは１〜６の整数である。）と、式２（ただし、式２中、Ｒ１はｎ−プロピル基であり、Ｒ２、Ｒ３、Ｒ４はそれぞれ独立にメチル基又はエチル基である。ここで、Ｒ１〜Ｒ４から選ばれる２つが共同でテトラメチレン基を形成していてもよい。）、式３（ただし、式３中、Ｒ５、Ｒ６はそれぞれ独立に炭素数１〜３のアルキル基である。）及び式４（ただし、式４中、Ｒ７は−（ＣＨ２）ｎＯＣＨ３で表されるメトキシアルキル基であり、ｎは１〜３の整数であり、Ｒ８、Ｒ９、Ｒ１０はそれぞれ独立にメチル基又はエチル基である。ここで、Ｒ８〜Ｒ１０から選ばれる２つが共同でテトラメチレン基を形成していてもよい。）からなる群から選ばれる１種以上のカチオンを有する電解質と、を含有する有機電解液を提供する。
【００１４】
【化７】
【発明の実施の形態】
本発明において、フルオロベンゼンとしては、誘電率の大きいものが好ましく、モノフルオロベンゼン、ジフルオロベンゼン、トリフルオロベンゼンからなる群から選ばれる１種以上が好ましい。ジフルオロベンゼンの構造としては、ｏ−ジフルオロベンゼン又はｍ−ジフルオロベンゼンが好ましい。同様にトリフルオロベンゼンの構造としては１，２，３−トリフルオロベンゼン、１，２，４−トリフルオロベンゼンが好ましい。
【００１６】
本発明においてフルオロベンゼンが電解液中に含まれる量は、電極に含まれる炭素質材料の細孔特性や残存水分量により適宜調整される。しかし、フルオロベンゼンは、有機電解液中に完全に溶解している状態に保たれることが好ましい。また、フルオロベンゼンが加わると有機電解液の誘電率は低下するので、フルオロベンゼンの量は、有機電解液の誘電率の低下に伴うイオン伝導性の低下が少ない範囲に抑えることが好ましい。したがって、フルオロベンゼンは、電解液全質量中に０．１〜３０％、特に１〜２０％含まれることが好ましい。
【００１７】
本発明における作用原理は必ずしも明確ではないが、電解液中に含まれるフルオロベンゼンは、炭素質材料の細孔内壁に存在する擬黒鉛表面と親和性が高く、加熱処理によっては除去できずに微細孔内に残存する水分と置換吸着されやすいと思われる。これらの水分は、電解液を含浸させた素子体に電圧が印加されると、容易に電気分解されガス化される。
【００１８】
電気二重層形成による電荷蓄積は、大部分は細孔内部で起こるので、電解液中にフルオロベンゼンを含まない従来の電気二重層キャパシタでは、電解液を含浸させた素子体に電圧印加すると微細孔内に残存する水分の電気分解により発生するガスが微細孔内に留まり性能が劣化していた。ところが本発明では、上述したように電圧印加により残存水分が電気分解して発生するガスは微細孔内ではなく微細孔外、すなわち活性炭粒子内のマイクロポア又は粒子間隙に存在するか、さらには泡として素子体の外部へ排出されると思われる。したがって電気二重層キャパシタの性能劣化は軽微に抑制できると推定される。
【００１９】
この効果は、ベンゼン又はその塩素誘導体を電解液に加えた場合でもみられるもので、特許文献６に開示されている。しかし、作動原理は明確ではないが、ベンゼン環を有する化合物が存在すると電解液の活性炭表面との親和性が向上することに加え、さらにフルオロ基は強電子吸引性を有するため、フルオロベンゼンを含む溶媒自体が高い誘電率を示すことになる。そのため、ベンゼンやその塩素誘導体よりもフルオロベンゼンは有機電解液の有機溶媒に対する相溶性が高く、より高い効果を示すと考えられる。
【００２０】
上述のとおり、上記素子体に電圧を印加すると分解ガスが発生するが、このガスは電気二重層キャパシタセルの内圧を上昇させる。したがって、製造工程における電圧印加は、乾燥雰囲気中で開放状態にて行い、発生したガスをキャパシタセル外へ排出させることが好ましい。ここで開放状態とは、素子体をセル内に収容していない状態、又はセル内に収容していてもセルが密閉されていない状態を示す。このときの乾燥雰囲気としては露点−２０℃以下であることが好ましく、特に−３０℃以下、さらには−４０℃以下であることが好ましい。
【００２１】
また、素子体に印加する電圧は、水の分解電圧より高い２Ｖ以上が好ましく、２．５Ｖ以上がさらに好ましい。素子体に電圧を印加する温度は１５〜８５℃、特に２０〜７０℃が好ましい。加温しつつ電圧を印加すると電気二重層キャパシタの耐久性を高める効果が大きく、電圧印加時間を短縮できる。しかし、その温度が高すぎると初期容量が低下し内部抵抗が上昇しやすい。
【００２２】
本発明の電気二重層キャパシタの電解液に使用する電解質は、電気伝導性、溶解度、電気化学的安定性の点で、式２で表される第四級オニウムカチオン（ただし、式２中、Ｒ１、Ｒ２、Ｒ３、Ｒ４はそれぞれ独立にメチル基、エチル基又はｎ−プロピル基である。ここで、Ｒ１〜Ｒ４から選ばれる２つが共同でテトラメチレン基を形成していてもよい。）、式３で表されるイミダゾリウムカチオン（ただし、式１中、Ｒ５、Ｒ６はそれぞれ独立に炭素数１〜３のアルキル基である。）及び式４で表される第四級オニウムカチオン（ただし、式４中、Ｒ７は−（ＣＨ２）ｎＯＣＨ３で表されるメトキシアルキル基であり、ｎは１〜３の整数であり、Ｒ８、Ｒ９、Ｒ１０はそれぞれ独立にメチル基又はエチル基である。ここで、Ｒ８〜Ｒ１０から選ばれる２つが共同でテトラメチレン基を形成していてもよい。）からなる群から選ばれる１種以上のカチオンを有するものが特に好ましい。
【００２３】
【化８】
さらにアニオンは、ＢＦ４ −、ＰＦ６ −、ＣＦ３ＳＯ３ −、及び（ＣＦ３ＳＯ２）２Ｎ−からなる群から選ばれるアニオンが好ましい。特に電気伝導性、電気化学的安定性の点でＢＦ４ −がより好ましい。
【００２５】
電解液中の上記電解質の濃度は、電気二重層形成に必要なイオン量を確保し、充分な電気伝導性を得る目的から０．５ｍｏｌ／ｋｇ以上であることが好ましく、特に１．０ｍｏｌ／ｋｇ以上であることが好ましい。
【００２６】
本発明で使用する有機溶媒としては、公知のものが使用できる。例えば、プロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート等の環状カーボネート、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート等の鎖状カーボネート、γ−ブチロラクトン、γ−バレロラクトン等の環状ラクトン、アセトニトリル、グルタロニトリル等のニトリル、スルホラン、３−メチルスルホラン等のスルホラン誘導体、ジメチルホルムアミド、１，２−ジメトキシエタン、ニトロメタン、トリメチルホスフェート等の１種又は２種以上の有機溶媒を溶媒とする溶液が好ましい。特に、プロピレンカーボネート、ブチレンカーボネート、スルホラン、ジメチルカーボネート及びエチルメチルカーボネートからなる群から選ばれる１種以上であると好ましい。
上記の電解質、溶媒及びフルオロベンゼンからなる有機電解液は、金属不純物及び水分が少ないほど好ましく、通常、水分は１０ｐｐｍ以下のものが好適に使用される。
【００２７】
本発明においては、電解液全質量中、式５又は式６で表される電解質が３０〜６０％、モノフルオロベンゼンが０．１〜３０％、ジメチルカーボネートが２０〜６９％の割合で含まれる有機電解液とすると、式５の電解質で１３〜１８ｍＳ／ｃｍ、式６の電解質で１５〜２０ｍＳ／ｃｍの高い電気伝導度が得られ、３．０Ｖ程度の高電圧を印加しても信頼性に優れ、抵抗上昇を抑えられるため好ましい。また、このとき、電解質全質量中、エチルメチルカーボネートが０．１〜３０％の割合で含まれる有機電解液とすると、低温特性を向上できるためより好ましい。
【００２８】
【化９】
さらに、電解液全質量中、式７で表される電解質が１５〜６０％、モノフルオロベンゼンが０．１〜３０％、プロピレンカーボネートが１０〜８５％の割合で含まれる有機電解液とすると１５〜２３ｍＳ／ｃｍの高い電気伝導度が得られ、高出力放電できるため好ましい。
【００３０】
【化１０】
本発明の電気二重層キャパシタに使用される分極性電極は、電気化学的に不活性な高比表面積の材料を主体とするものであればよく、主として活性炭、カーボンブラック、金属微粒子、導電性酸化物微粒子からなるものが好ましい。なかでも、金属集電体の表面に活性炭等の高比表面積の炭素材料粉末からなる電極層が形成されたものを使用することが好ましい。
【００３２】
具体的には、電極層は比表面積の大きい活性炭、ポリアセンなどの炭素材料粉末（比表面積２００〜３０００ｍ２／ｇ程度）を主成分とし、これに導電性物質としてカーボンブラック、アセチレンブラック、ケッチェンブラック又はカーボンウィスカーを、及び結合剤として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）、カルボキシメチルセルロース等を加え、アルコール等の液体潤滑剤の存在下で混練し、ロール圧延等によりシート状に成形し、乾燥したシート状成型物を金属集電体の両面に熱圧着するか導電性接着剤等を介して接合することにより形成することが好ましい。
【００３３】
なお、混練するかわりに上記結合剤を溶解できる溶媒又は該溶媒を含む混合溶媒（水、Ｎ−メチルピロリドン等）を活性炭と導電剤と結合剤とに混合してスラリーとし、これを金属集電体の両表面に塗布、乾燥して電極層を成形してもよい。なお、電極層の厚さは特に制限されないが、通常１０μｍ〜０．５ｍｍ程度である。
【００３４】
活性炭材料としては、やしがら等の天然植物組織、フェノール等の合成樹脂、石炭、コークス、ピッチ等の化石燃料由来のものが使用できる。活性炭の賦活方法としては、用いる原料によって異なるが、通常水蒸気賦活法、アルカリ賦活法（特にＫＯＨ賦活法）が適用される。天然植物組織や、化石燃料由来の活性炭では、金属不純物量が比較的多く含まれることから、一般には酸洗浄等による精製が必要である。同様に、アルカリ賦活法によって賦活された活性炭では、賦活に用いたアルカリ金属や、賦活装置からアルカリとの反応によって持ち込まれた金属不純物量が多いため、洗浄操作が必須となる。この中では、合成樹脂を原料とする水蒸気賦活炭が金属不純物の点では最も好適である。
【００３５】
本発明の電気二重層キャパシタの素子構成としては、特に限定されず、コイン型構造、円筒型構造、角型構造のいずれにおいても好適に適用できる。例えば、コイン型構造は、集電体上に活性炭を主成分とする電極層を設けた一対の電極間にセパレータを配置して素子を形成し、該素子を電解液とともにコイン型の金属ケース内に金属封口蓋体及び両者を絶縁するガスケットにより密封して形成することができる。
【００３６】
また、円筒型構造は一対の帯状の電極体、具体的には金属集電体の両面に活性炭等を主成分とする電極層を形成した帯状の正極電極体と、金属集電体の両面に同じ構成の電極層を形成した帯状の負極電極体とを、帯状のセパレータを間に介すようにして交互に積層し、巻回してなる巻回素子体を円筒型の金属ケースに収容し、電解液を含浸させた後、正極電極体及び負極電極体よりそれぞれ引き出された集電リードを、例えば電気絶縁性の封口蓋体に設けられた電極端子にそれぞれ接続するとともに、該封口蓋体を金属ケースに嵌合するものである。
【００３７】
角型構造は矩形の金属集電体の両側に電極層が形成され、かつ集電リードを備えている複数の正極電極体及び複数の負極電極体を、セパレータを介して交互に積層して集電リードが引き出されている積層素子体を形成し、角型の金属ケースに収容し、電解液を含浸させ、該封口蓋体を角型ケースに嵌合するものである。
【００３８】
集電体は電気化学的、化学的に耐蝕性のある金属であればよく、コイン型構造の場合は金属封口蓋体や金属ケースなどのハウジング部材が集電体を兼ねることが多いが、円筒型構造や角型構造の場合の集電体としてはアルミニウム、ステンレス鋼、ニッケル、タンタルなどの金属の粗面化箔、網等を用い、特にステンレス鋼、アルミニウム、それらの合金の箔や網等が好ましく用いられる。さらに好ましいのは、９９．９％、より好ましくは９９．９９％純度のアルミニウム箔である。本発明においてはこのような金属箔からなる金属集電体で、厚さが１０μｍ〜０．５ｍｍ程度のものを用いることが好ましい。
【００３９】
円筒型構造や角型構造の場合、金属集電体には集電リードを形成する。集電体上に電極層の形成されていないテープ状又はリボン状の部分を設け、そこに導電性のタブ端子、線、テープ、リボン等を溶接等により接合してこれを集電リードとするのが好ましい。また、集電体の一部に電極層を形成していない部分を設け、この部分を集電リードとして用いてもよい。例えば円筒型構造の場合具体的には、帯状の集電体の長さ方向の一方の端に沿って電極層が形成されていない帯状部を設け、対極を帯状部が逆向きになるように配置してセパレータを介して重ね、巻回して得られた素子の両端面（上記帯状部）を集電リードとすることができる。
【００４０】
本発明におけるセパレータは特に限定されず、イオンを通過する多孔質セパレータであればよく、微孔性ポリエチレンフィルム、微孔性ポリプロピレンフィルム、ポリエチレン不織布、ポリプロピレン不織布、ガラス繊維混抄不織布、ガラスマットフィルタ、セルロース紙、サイザル麻やマニラ麻等が好適に使用できる。セパレータの厚さは２０〜２００μｍ、特に３０〜１００μｍとするのが好ましい。電解液に対する吸液性、保液性、内部抵抗の点では、セパレータの空隙率が高いほど好ましいが、空隙率が高いほどピンホール等の欠陥が増大し、自己放電不良に繋がるので、通常５０〜９０％の範囲が好ましく、さらに好ましくは６０〜８５％である。
【００４１】
【実施例】
以下、本発明を実施例及び比較例によって詳しく説明するが、本発明はこれらの実施例によって限定されない。
【００４２】
［例１（実施例）］
水蒸気賦活された比表面積２０００ｍ２／ｇのフェノール樹脂系活性炭とＰＴＦＥとカーボンブラックとの質量比で８：１：１の混合物にエタノールを加えて混練した。これをシート状に成形後、厚さ０．６ｍｍにロール圧延し、得られた電極のシートを直径１２ｍｍの円盤に打ち抜いた。
【００４３】
この円盤状の電極を、コイン型セルの集電体兼ハウジング部材とするステンレス製ケースの正極側及び負極側の内側に、それぞれ黒鉛系導電性接着剤を用いて接着した。次にこのステンレス製ケースごと減圧下で加熱処理して水分等を除き、プロピレンカーボネートとモノフルオロベンゼンとの質量比で９５：５の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を電解液として電極中に含浸させ、両電極の間にポリプロピレン繊維不織布製のセパレータ（厚さ１６０μｍ、空隙率７０％）を挟み、ステンレスケースを絶縁体であるガスケットを介してかしめ封口し、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００４４】
［例２（実施例）］
電解液として、プロピレンカーボネートと１，２−ジフルオロベンゼンとの質量比で９６：４の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にしてコイン型電気二重層キャパシタを得た。
【００４５】
［例３（実施例）］
溶融ＫＯＨ賦活された比表面積２０００ｍ２／ｇのフェノール樹脂系活性炭とＰＴＦＥとカーボンブラックとの質量比で８：１：１の混合物にエタノールを加えて混練し、シート状に成形後厚さ０．１ｍｍにロール圧延して帯状のシートを得た。得られたシートを電極シートとして導電性接着剤を用いて、表面をエッチングしたアルミニウム箔に張り付けた。次に減圧下で加熱処理して水分等を除き、ガラス繊維セパレータ（厚さ１００μｍ、空隙率８０％）を正負極の電極間に挟み、直径２ｍｍの巻芯で巻き取り、直径７ｍｍ、高さ２０ｍｍの巻回型の素子とした。これに電解液としてアセトニトリルと１，２，３−トリフルオロベンゼンとの質量比で９７：３の混合溶媒に１．２ｍｏｌ／ｋｇの（Ｃ２Ｈ５）４Ｎ＋ＢＦ４ −を溶解した溶液を含浸させて、ブチルゴムを挿入しかしめ機にて封口し円筒型の電気二重層キャパシタを得た。
【００４６】
［例４（実施例）］
レゾール樹脂を窒素雰囲気中６５０℃で焼成し溶融ＫＯＨ賦活された比表面積２０００ｍ２／ｇの活性炭とＰＴＦＥとカーボンブラックとの質量比で８：１：１の混合物にエタノールを加えて混練し、シート状に成形後、厚さ０．６ｍｍにロール圧延し、得られた電極シートを直径１２ｍｍの円盤状に打ち抜いた。
この円盤状の電極を正極及び負極として用い、電解液として、スルホランとエチルメチルカーボネートとモノフルオロベンゼンとの質量比で８５：１５：５の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００４７】
［例５（実施例）］
電解液として、ジメチルカーボネートとモノフルオロベンゼンとの質量比で６０：４０の混合溶媒に２．２ｍｏｌ／ｋｇの上記式５で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００４８】
［例６（実施例）］
電解液として、ジメチルカーボネート、エチルメチルカーボネート及びモノフルオロベンゼンの質量比で６０：１０：３０の混合溶媒に２．２ｍｏｌ／ｋｇの上記式５で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００４９】
［例７（実施例）］
電解液として、ジメチルカーボネートとモノフルオロベンゼンとの質量比で６０：４０の混合溶媒に２．４ｍｏｌ／ｋｇの上記式６で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００５０】
［例８（実施例）］
電解液として、ジメチルカーボネート、エチルメチルカーボネート及びモノフルオロベンゼンの質量比で６０：１０：３０の混合溶媒に２．４ｍｏｌ／ｋｇの上記式６で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００５１】
［例９（実施例）］
電解液として、プロピレンカーボネートとモノフルオロベンゼンとの質量比で８０：２０の混合溶媒に２．５ｍｏｌ／ｋｇの上記式７で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００５２】
［例１０（比較例）］
電解液として、プロピレンカーボネート溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にしてコイン型の電気二重層キャパシタを得た。
【００５３】
［例１１（比較例）］
電解液として、プロピレンカーボネート溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にしてコイン型の電気二重層キャパシタを得た。
【００５４】
［例１２（比較例）］
電解液として、アセトニトリル溶媒に１．２ｍｏｌ／ｋｇの（Ｃ２Ｈ５）４Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例３と同様にして円筒型の電気二重層キャパシタを得た。
【００５５】
［例１３（比較例）］
電解液として、スルホランとエチルメチルカーボネートとの質量比で８：２の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例４と同様にしてコイン型の電気二重層キャパシタを得た。
【００５６】
［例１４（比較例）］
電解液として、プロピレンカーボネートとベンゼンとの質量比で９５：５の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にしてコイン型の電気二重層キャパシタを得た。
【００５７】
［例１５（比較例）］
電解液として、プロピレンカーボネートとモノクロロベンゼンとの質量比で９５：５の混合溶媒に１．５ｍｏｌ／ｋｇの（Ｃ２Ｈ５）３（ＣＨ３）Ｎ＋ＢＦ４ −を溶解した溶液を用いた以外は例１と同様にしてコイン型の電気二重層キャパシタを得た。
【００５８】
［例１６（比較例）］
電解液として、ジメチルカーボネート溶媒に２．２ｍｏｌ／ｋｇの上記式５で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００５９】
［例１７（比較例）］
電解液として、ジメチルカーボネート溶媒に２．４ｍｏｌ／ｋｇの上記式６で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００６０】
［例１８（比較例）］
電解液として、プロピレンカーボネート溶媒に２．５ｍｏｌ／ｋｇの上記式７で表される塩を溶解した溶液を用いた以外は例１と同様にして、直径１８．４ｍｍ、厚さ２．０ｍｍのコイン型電気二重層キャパシタを得た。
【００６１】
［評価］
例１〜８及び例９〜１８のそれぞれの電解液組成と、電気二重層キャパシタを表１及び表２に示す電圧で開回路にて７２時間保持した後の電圧保持率を、それぞれ表１及び表２に示す。印加する電圧は、性能の比較が明確になるように、例１と例１０と例１４と例１５、例２と例１１、例３と例１２、例４と例１３、例５と例６と例１６、例７と例８と例１７、例９と例１８をそれぞれ同じ電圧とした。また、例１〜１８の電気二重層キャパシタに電圧保持率の評価時と同じ電圧を印加し、初期の静電容量と内部抵抗を測定し、さらに、７０℃の恒温恒湿槽中に１０００時間保持した後の容量変化率を測定した。その結果を表３に示す。
【００６２】
【表１】
【表２】
【表３】
表１及び表２からわかるように、本発明の電気二重層キャパシタは、フルオロベンゼンを含まない電解液を用いた比較例よりも電圧保持性、自己放電特性に優れる。また、表３からわかるように、本発明の電気二重層キャパシタは７０℃で電圧印加するときの容量低下が少なく、信頼性に優れている。
【００６６】
【発明の効果】
本発明の構成によれば、自己放電特性及び信頼性に優れた特性を有する電気二重層キャパシタを提供できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor excellent in self-discharge characteristics and reliability.
[0002]
[Prior art]
A conventional electric double layer capacitor has a shape in which an element having a separator sandwiched between a pair of polarizable electrodes mainly composed of activated carbon formed on a current collector is housed in a metal case together with an electrolyte, and a gasket is provided. A coin-type sealed with a metal lid or an element formed by winding a separator between a pair of sheet-like polarizable electrodes through a separator is housed in a cylindrical metal case together with an electrolytic solution, and electrolysis is performed from the opening of the case. Some cylinders are sealed so that the liquid does not evaporate.
[0003]
In addition, a multilayer electric double layer capacitor in which an element formed by laminating a large number of sheet-like polarizable electrodes with a separator interposed therebetween is also proposed for large current and large capacity (Patent Documents 1 to 3). 3). That is, a sheet-shaped polarizable electrode formed into a rectangular shape is used as a positive electrode and a negative electrode, and alternately stacked with separators between them to form an element. It is housed in a case in a connected state, and the element is impregnated with an electrolytic solution and sealed with a lid.
[0004]
As an electrolytic solution of a conventional electric double layer capacitor, various organic electrolytic solutions are used in addition to an aqueous electrolytic solution containing a mineral acid such as sulfuric acid, an alkali metal salt or an alkali. As solvents for organic electrolytes, propylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide (see Patent Document 4), sulfolane derivatives and the like (see Patent Document 5) are known. Comparing the withstand voltage, the aqueous electrolyte is 0.8V, the organic electrolyte is 2.5 to 3.3V, and the electrostatic energy of the capacitor is proportional to the square of the withstand voltage. In this respect, the organic electrolyte is more advantageous.
[0005]
The withstand voltage of the electric double layer capacitor is basically limited by the electrochemical decomposition voltage of the electrolyte. When an organic electrolytic solution having a higher withstand voltage than an aqueous electrolytic solution is used as an electrolytic solution, a voltage of 2 V or higher, which is higher than the theoretical decomposition voltage of water (1.23 V), is applied and used. Electrolysis occurs due to impurities, especially moisture. Therefore, the organic electrolytic solution is used after being highly purified and dehydrated together with both the solvent and the electrolyte.
[0006]
On the other hand, an electrode material having a high specific surface area is used for the electrode of the electric double layer capacitor, but when combined with the organic electrolyte, activated carbon is generally used as the electrode material. Activated carbon is a porous material having micropores on the order of several nanometers. Therefore, the activated carbon needs to be highly dehydrated in the manufacturing process of the electric double layer capacitor. Usually, in order to completely remove moisture from the pores of the activated carbon, dehydration treatment at a high temperature of 300 ° C. or higher is required in a vacuum or in an inert gas atmosphere. However, normally activated carbon particles are formed on a current collector using a binder such as an organic polymer to constitute an electrode, and the binder is thermally decomposed at a high temperature treatment of 300 ° C. or higher. Can not. For this reason, it is difficult to completely remove moisture in the activated carbon electrode.
[0007]
Also, the portion where the activated carbon surface is not in contact with the electrolyte solution, that is, the activated carbon surface that is not sufficiently impregnated with the electrolyte solution and is not wetted by the electrolyte solution, or the gas generated by electrolysis of residual moisture remains in the activated carbon pores. Due to the presence of the portion, there is a problem that the area for accumulating charges is reduced, the capacity development rate is lowered, and the resistance is increased. Further, the generated gas is gradually accumulated in the activated carbon pores, and is not discharged to the outside of the element body formed by impregnating the opposing electrode through the separator with the electrolytic solution, but may remain inside the element body. found. If an electric double layer capacitor is used for a long time under such conditions, the generated gas expels the electrolyte present in the pores of the activated carbon, and the capacity that should be originally obtained cannot be obtained. The electric conduction path by the movement of ions is interrupted. For this reason, performance degradation such as a decrease in capacitance of the electric double layer capacitor and an increase in internal resistance occurs. Furthermore, since the residual moisture in the pores cannot be completely removed, electrolysis due to the adsorbed charges continuously occurs. For this reason, there was a problem that the voltage holding property after applying a voltage to open the circuit was poor.
[0008]
On the other hand, in Patent Document 6, when benzene or a derivative thereof is contained in the electrolytic solution, it has a high affinity with the pseudographite surface existing on the pore inner wall of the activated carbon, so that the residual moisture in the pore is easily substituted and adsorbed. The gas generated by the electrolysis of water due to voltage application is not inside the micropores but outside the micropores, that is, in the micropores or particle gaps inside the activated carbon particles, or even as bubbles to the outside of the element body. Although it is estimated that it will be discharged | emitted, recently, it is calculated | required to provide the electric double layer capacitor which is more excellent in a self-discharge characteristic and reliability, and the electrolyte solution therefor.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 04-154106 (Claims, Fig. 1)
[Patent Document 2]
Japanese Patent Laid-Open No. 03-203111 (Claims, FIG. 3)
[Patent Document 3]
Japanese Patent Laid-Open No. 04-286108 (Claim 1)
[Patent Document 4]
JP 49-068254 A (Claims)
[Patent Document 5]
JP-A-62-237715 (Claims)
[Patent Document 6]
JP 2000-252171 A (paragraph numbers 0014 and 0015)
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide an electric double layer capacitor excellent in self-discharge characteristics and reliability and an organic electrolyte therefor.
[0011]
[Means for Solving the Problems]
The present invention provides an electric double layer capacitor having a pair of polarizable electrodes and an electrolytic solution for forming an electric double layer at the interface between the polarizable electrodes, wherein the electrolytic solution is fluorobenzene represented by formula 1 (formula 1 And n is an integer of 1 to 6.) An electric double layer capacitor is provided.
[0012]
[Chemical 6]
Further, the present invention relates to fluorobenzene represented by formula 1 (in formula 1, n is an integer of 1 to 6) and formula 2 (provided that in formula 2, R1Is an n-propyl group and R2, R3, R4Each independently represents a methyl group or an ethyl group. Where R1~ R4Two selected from may form a tetramethylene group jointly. ), Formula 3 (however, in Formula 3, R5, R6Are each independently an alkyl group having 1 to 3 carbon atoms. ) And formula 4 (wherein R in formula 4)7Is-(CH2)nOCH3And n is an integer of 1 to 3,8, R9, R10Each independently represents a methyl group or an ethyl group. Where R8~ R10Two selected from may form a tetramethylene group jointly. And an electrolyte having one or more cations selected from the group consisting of:
[0014]
[Chemical 7]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the fluorobenzene preferably has a large dielectric constant, and is preferably at least one selected from the group consisting of monofluorobenzene, difluorobenzene, and trifluorobenzene. As the structure of difluorobenzene, o-difluorobenzene or m-difluorobenzene is preferable. Similarly, the structure of trifluorobenzene is preferably 1,2,3-trifluorobenzene or 1,2,4-trifluorobenzene.
[0016]
In the present invention, the amount of fluorobenzene contained in the electrolyte is appropriately adjusted depending on the pore characteristics of the carbonaceous material contained in the electrode and the residual moisture content. However, the fluorobenzene is preferably kept in a state of being completely dissolved in the organic electrolyte. In addition, when fluorobenzene is added, the dielectric constant of the organic electrolytic solution is lowered. Therefore, the amount of fluorobenzene is preferably suppressed within a range in which the decrease in ionic conductivity accompanying the decrease in the dielectric constant of the organic electrolytic solution is small. Therefore, it is preferable that fluorobenzene is contained in an amount of 0.1 to 30%, particularly 1 to 20% in the total mass of the electrolytic solution.
[0017]
The principle of action in the present invention is not necessarily clear, but fluorobenzene contained in the electrolyte has a high affinity with the pseudographite surface present on the inner wall of the pores of the carbonaceous material, and it cannot be removed by heat treatment and is fine. It seems to be easily substituted and adsorbed by moisture remaining in the pores. These moisture are easily electrolyzed and gasified when a voltage is applied to the element body impregnated with the electrolytic solution.
[0018]
Charge accumulation due to the formation of the electric double layer mostly occurs inside the pores. Therefore, in a conventional electric double layer capacitor that does not contain fluorobenzene in the electrolytic solution, when a voltage is applied to the element body impregnated with the electrolytic solution, fine pores are formed. Gas generated by electrolysis of water remaining in the inside stayed in the micropores, and the performance deteriorated. However, in the present invention, as described above, the gas generated by the electrolysis of residual moisture by voltage application is not in the micropores but outside the micropores, that is, in the micropores or particle gaps in the activated carbon particles, or even in the bubbles. It seems that it is discharged to the outside of the element body. Therefore, it is estimated that the performance deterioration of the electric double layer capacitor can be suppressed slightly.
[0019]
This effect can be seen even when benzene or its chlorine derivative is added to the electrolyte, and is disclosed in Patent Document 6. However, although the principle of operation is not clear, the presence of a compound having a benzene ring improves the affinity of the electrolytic solution with the activated carbon surface, and further, since the fluoro group has strong electron withdrawing properties, it contains fluorobenzene. The solvent itself will exhibit a high dielectric constant. Therefore, it is considered that fluorobenzene has higher compatibility with an organic solvent of an organic electrolyte than benzene and its chlorine derivative, and exhibits a higher effect.
[0020]
As described above, when a voltage is applied to the element body, a decomposition gas is generated. This gas increases the internal pressure of the electric double layer capacitor cell. Therefore, it is preferable that the voltage application in the manufacturing process is performed in an open state in a dry atmosphere and the generated gas is discharged out of the capacitor cell. Here, the open state indicates a state where the element body is not accommodated in the cell, or a state where the cell is not sealed even if it is accommodated in the cell. The dry atmosphere at this time is preferably a dew point of −20 ° C. or lower, particularly preferably −30 ° C. or lower, and further preferably −40 ° C. or lower.
[0021]
The voltage applied to the element body is preferably 2 V or higher, more preferably 2.5 V or higher, which is higher than the water decomposition voltage. The temperature at which the voltage is applied to the element body is preferably 15 to 85 ° C, particularly preferably 20 to 70 ° C. When a voltage is applied while heating, the effect of increasing the durability of the electric double layer capacitor is great, and the voltage application time can be shortened. However, if the temperature is too high, the initial capacity is lowered and the internal resistance is likely to increase.
[0022]
The electrolyte used for the electrolytic solution of the electric double layer capacitor of the present invention is a quaternary onium cation represented by the formula 2 (wherein R in the formula 2 is R in terms of electrical conductivity, solubility, and electrochemical stability).1, R2, R3, R4Each independently represents a methyl group, an ethyl group or an n-propyl group. Where R1~ R4Two selected from may form a tetramethylene group jointly. ), An imidazolium cation represented by formula 3 (wherein R in formula 1)5, R6Are each independently an alkyl group having 1 to 3 carbon atoms. ) And the quaternary onium cation represented by formula 4 (wherein R in formula 47Is-(CH2)nOCH3And n is an integer of 1 to 3,8, R9, R10Each independently represents a methyl group or an ethyl group. Where R8~ R10Two selected from may form a tetramethylene group jointly. Particularly preferred are those having one or more cations selected from the group consisting of:
[0023]
[Chemical 8]
Furthermore, the anion is BF4 −, PF6 −, CF3SO3 −, And (CF3SO2)2N−An anion selected from the group consisting of BF particularly in terms of electrical conductivity and electrochemical stability4 −Is more preferable.
[0025]
The concentration of the electrolyte in the electrolytic solution is preferably 0.5 mol / kg or more for the purpose of ensuring the amount of ions necessary for forming the electric double layer and obtaining sufficient electric conductivity, and in particular, 1.0 mol / kg. The above is preferable.
[0026]
Known organic solvents can be used as the organic solvent used in the present invention. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, cyclic lactones such as γ-butyrolactone, γ-valerolactone, acetonitrile, glutaronitrile, etc. A solution containing one or two or more organic solvents such as nitrile, sulfolane, sulfolane derivatives such as 3-methylsulfolane, dimethylformamide, 1,2-dimethoxyethane, nitromethane, trimethyl phosphate, etc. is preferable. In particular, at least one selected from the group consisting of propylene carbonate, butylene carbonate, sulfolane, dimethyl carbonate, and ethyl methyl carbonate is preferable.
The organic electrolyte solution composed of the above electrolyte, solvent and fluorobenzene is preferably as less as possible with metal impurities and moisture, and usually the moisture is preferably 10 ppm or less.
[0027]
In the present invention, the electrolyte represented by the formula 5 or 6 is contained in a proportion of 30 to 60%, monofluorobenzene is 0.1 to 30%, and dimethyl carbonate is 20 to 69% in the total mass of the electrolytic solution. When an organic electrolyte is used, high electrical conductivity of 13 to 18 mS / cm is obtained with the electrolyte of Formula 5 and 15 to 20 mS / cm with the electrolyte of Formula 6, and reliability is ensured even when a high voltage of about 3.0 V is applied. It is preferable because it is excellent in resistance and resistance rise can be suppressed. In this case, it is more preferable to use an organic electrolyte containing 0.1 to 30% of ethyl methyl carbonate in the total mass of the electrolyte because the low temperature characteristics can be improved.
[0028]
[Chemical 9]
Further, when the total amount of the electrolyte is 15 to 60% of the electrolyte represented by Formula 7, 0.1 to 30% of monofluorobenzene, and 10 to 85% of propylene carbonate, the organic electrolyte contains 15%. A high electric conductivity of ˜23 mS / cm is obtained, which is preferable because high power discharge can be performed.
[0030]
Embedded image
The polarizable electrode used in the electric double layer capacitor of the present invention may be mainly composed of an electrochemically inactive high specific surface area material, mainly activated carbon, carbon black, metal fine particles, conductive oxidation. Those composed of fine particles are preferable. Especially, it is preferable to use what formed the electrode layer which consists of carbon material powder of high specific surface areas, such as activated carbon, on the surface of a metal electrical power collector.
[0032]
Specifically, the electrode layer is a carbon material powder such as activated carbon or polyacene having a large specific surface area (specific surface area of 200 to 3000 m).2/ G) as a main component, and carbon black, acetylene black, ketjen black or carbon whisker as a conductive substance, and polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), carboxymethyl cellulose as a binder Etc., knead in the presence of a liquid lubricant such as alcohol, molded into a sheet by roll rolling, etc., and hot-pressed the dried sheet-shaped product on both sides of the metal current collector or conductive adhesive, etc. It is preferable to form it by joining via.
[0033]
Instead of kneading, a solvent capable of dissolving the binder or a mixed solvent containing the solvent (water, N-methylpyrrolidone, etc.) is mixed with activated carbon, a conductive agent and a binder to form a slurry, which is used as a metal current collector. The electrode layer may be formed by applying to both surfaces of the body and drying. The thickness of the electrode layer is not particularly limited, but is usually about 10 μm to 0.5 mm.
[0034]
As the activated carbon material, natural plant tissues such as palm, synthetic resins such as phenol, and those derived from fossil fuels such as coal, coke, and pitch can be used. The activated carbon activation method varies depending on the raw material used, but usually a steam activation method or an alkali activation method (particularly a KOH activation method) is applied. Since natural plant tissues and activated carbon derived from fossil fuels contain a relatively large amount of metal impurities, purification by acid washing or the like is generally required. Similarly, in the activated carbon activated by the alkali activation method, since the amount of the alkali metal used for activation and the amount of metal impurities brought in by reaction with the alkali from the activation device is large, a cleaning operation is essential. Of these, steam activated charcoal using synthetic resin as the raw material is most suitable in terms of metal impurities.
[0035]
The element configuration of the electric double layer capacitor of the present invention is not particularly limited, and can be suitably applied to any of a coin-type structure, a cylindrical structure, and a square structure. For example, in a coin-type structure, an element is formed by arranging a separator between a pair of electrodes provided with an electrode layer mainly composed of activated carbon on a current collector, and the element is placed in a coin-type metal case together with an electrolyte. It can be formed by sealing with a metal sealing lid and a gasket that insulates both.
[0036]
In addition, the cylindrical structure has a pair of strip electrode bodies, specifically, a strip-shaped positive electrode body in which an electrode layer mainly composed of activated carbon or the like is formed on both surfaces of the metal current collector, and both surfaces of the metal current collector. A strip-shaped negative electrode body in which electrode layers having the same configuration are formed and alternately stacked with a strip-shaped separator interposed therebetween, and a wound element body is housed in a cylindrical metal case, After impregnating the electrolytic solution, the current collector leads respectively drawn out from the positive electrode body and the negative electrode body are connected to, for example, electrode terminals provided on the electrically insulating sealing lid body, and the sealing lid body is It fits into a metal case.
[0037]
In the rectangular structure, electrode layers are formed on both sides of a rectangular metal current collector, and a plurality of positive electrode bodies and a plurality of negative electrode bodies each having a current collector lead are alternately stacked via a separator. A laminated element body from which electric leads are drawn out is formed, accommodated in a rectangular metal case, impregnated with an electrolytic solution, and the sealing lid is fitted into the rectangular case.
[0038]
The current collector may be an electrochemically and chemically corrosion-resistant metal. In the case of a coin-type structure, a housing member such as a metal sealing lid or a metal case often serves as the current collector. As the current collector in the case of a mold structure or a square structure, roughened foils or nets of metals such as aluminum, stainless steel, nickel, and tantalum are used, and in particular, stainless steel, aluminum, foils and nets of their alloys, etc. Is preferably used. Further preferred is an aluminum foil having a purity of 99.9%, more preferably 99.99%. In the present invention, it is preferable to use a metal current collector made of such a metal foil and having a thickness of about 10 μm to 0.5 mm.
[0039]
In the case of a cylindrical structure or a square structure, a current collector lead is formed on the metal current collector. A tape-like or ribbon-like part without an electrode layer is provided on the current collector, and conductive tab terminals, wires, tapes, ribbons, etc. are joined thereto by welding or the like, and this is used as a current collecting lead. Is preferred. Further, a part where the electrode layer is not formed may be provided in a part of the current collector, and this part may be used as a current collecting lead. For example, in the case of a cylindrical structure, specifically, a band-shaped part where an electrode layer is not formed is provided along one end in the length direction of the band-shaped current collector, and the counter electrode is arranged in the opposite direction. Both end faces (the band-like portions) of the element obtained by arranging, stacking and winding via a separator can be used as current collecting leads.
[0040]
The separator in the present invention is not particularly limited as long as it is a porous separator that allows ions to pass through. Microporous polyethylene film, microporous polypropylene film, polyethylene nonwoven fabric, polypropylene nonwoven fabric, glass fiber mixed nonwoven fabric, glass mat filter, cellulose Paper, sisal, Manila, etc. can be used suitably. The thickness of the separator is preferably 20 to 200 μm, more preferably 30 to 100 μm. The higher the porosity of the separator, the better in terms of liquid absorbency, liquid retention, and internal resistance with respect to the electrolytic solution. However, the higher the porosity, the more defects such as pinholes increase, leading to poor self-discharge. The range of -90% is preferable, More preferably, it is 60-85%.
[0041]
【Example】
Hereinafter, although an example and a comparative example explain the present invention in detail, the present invention is not limited by these examples.
[0042]
[Example 1 (Example)]
Steam-activated specific surface area 2000m2/ G of phenol resin-based activated carbon, PTFE and carbon black in a mass ratio of 8: 1: 1 was added with ethanol and kneaded. After forming this into a sheet shape, it was roll-rolled to a thickness of 0.6 mm, and the obtained electrode sheet was punched into a disk having a diameter of 12 mm.
[0043]
This disk-shaped electrode was bonded to the inside of the positive electrode side and the negative electrode side of a stainless steel case serving as a current collector / housing member of a coin-type cell using a graphite-based conductive adhesive. Next, this stainless steel case is heat-treated under reduced pressure to remove moisture and the like, and 1.5 mol / kg (C2H5)3(CH3) N+BF4 −The electrode is impregnated into the electrode as an electrolyte, a polypropylene fiber nonwoven fabric separator (thickness 160 μm, porosity 70%) is sandwiched between the two electrodes, and the stainless steel case is caulked through an insulating gasket. Sealing was performed to obtain a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm.
[0044]
[Example 2 (Example)]
As an electrolytic solution, 1.5 mol / kg of (C) in a 96: 4 mixed solvent in a mass ratio of propylene carbonate and 1,2-difluorobenzene.2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0045]
[Example 3 (Example)]
Specific surface area of 2000m with molten KOH activation2/ G of phenol resin activated carbon, PTFE and carbon black in a mass ratio of 8: 1: 1, ethanol is added and kneaded, formed into a sheet and then roll-rolled to a thickness of 0.1 mm to form a belt-like sheet Got. The obtained sheet was attached to an aluminum foil whose surface was etched using a conductive adhesive as an electrode sheet. Next, heat treatment is performed under reduced pressure to remove moisture, etc., and a glass fiber separator (thickness 100 μm, porosity 80%) is sandwiched between positive and negative electrodes, wound with a core having a diameter of 2 mm, diameter 7 mm, height A 20 mm winding type element was obtained. As an electrolyte, 1.2 mol / kg of (C) in a mixed solvent of 97: 3 by mass ratio of acetonitrile and 1,2,3-trifluorobenzene was used.2H5)4N+BF4 −A solution in which the solution was dissolved was impregnated, and a butyl rubber was inserted and sealed with an inserter to obtain a cylindrical electric double layer capacitor.
[0046]
[Example 4 (Example)]
Resol resin was fired at 650 ° C. in a nitrogen atmosphere and activated with molten KOH, specific surface area 2000 m2/ G of activated carbon, PTFE, and carbon black at a mass ratio of 8: 1: 1, ethanol was added and kneaded, formed into a sheet, then rolled into a thickness of 0.6 mm, and the resulting electrode sheet Was punched into a disk shape having a diameter of 12 mm.
This disc-shaped electrode was used as a positive electrode and a negative electrode, and as an electrolyte, 1.5 mol / kg of (C) in a mixed solvent of 85: 15: 5 by mass ratio of sulfolane, ethyl methyl carbonate, and monofluorobenzene.2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0047]
[Example 5 (Example)]
The same procedure as in Example 1 was used except that a solution obtained by dissolving 2.2 mol / kg of the salt represented by the above formula 5 in a mixed solvent of 60:40 by mass ratio of dimethyl carbonate and monofluorobenzene was used as the electrolytic solution. Thus, a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained.
[0048]
[Example 6 (Example)]
As an electrolytic solution, a solution obtained by dissolving 2.2 mol / kg of the salt represented by the above formula 5 in a mixed solvent of dimethyl carbonate, ethyl methyl carbonate and monofluorobenzene in a mass ratio of 60:10:30 was used. In the same manner as in Example 1, a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained.
[0049]
[Example 7 (Example)]
The same procedure as in Example 1 was used except that a solution obtained by dissolving 2.4 mol / kg of the salt represented by the above formula 6 in a 60:40 mixed solvent in a mass ratio of dimethyl carbonate and monofluorobenzene was used as the electrolytic solution. Thus, a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained.
[0050]
[Example 8 (Example)]
As an electrolytic solution, a solution obtained by dissolving 2.4 mol / kg of the salt represented by the above formula 6 in a mixed solvent of dimethyl carbonate, ethyl methyl carbonate, and monofluorobenzene in a mass ratio of 60:10:30 was used. In the same manner as in Example 1, a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained.
[0051]
[Example 9 (Example)]
The same procedure as in Example 1 was used, except that a solution obtained by dissolving 2.5 mol / kg of the salt represented by the above formula 7 in a mixed solvent of 80:20 by mass ratio of propylene carbonate and monofluorobenzene was used as the electrolytic solution. Thus, a coin-type electric double layer capacitor having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained.
[0052]
[Example 10 (comparative example)]
As an electrolytic solution, 1.5 mol / kg (C2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0053]
[Example 11 (comparative example)]
As an electrolyte, 1.5 mol / kg (C2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0054]
[Example 12 (comparative example)]
As an electrolytic solution, 1.2 mol / kg (C2H5)4N+BF4 −A cylindrical electric double layer capacitor was obtained in the same manner as in Example 3 except that a solution in which was dissolved was used.
[0055]
[Example 13 (comparative example)]
As an electrolytic solution, 1.5 mol / kg of (C) in a mixed solvent of 8: 2 by mass ratio of sulfolane and ethyl methyl carbonate.2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 4 except that a solution in which was dissolved was used.
[0056]
[Example 14 (comparative example)]
As an electrolytic solution, 1.5 mol / kg of (C) in a 95: 5 mixed solvent in a mass ratio of propylene carbonate and benzene.2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0057]
[Example 15 (comparative example)]
As an electrolytic solution, 1.5 mol / kg of (C) in a mixed solvent of 95: 5 by mass ratio of propylene carbonate and monochlorobenzene.2H5)3(CH3) N+BF4 −A coin-type electric double layer capacitor was obtained in the same manner as in Example 1 except that a solution in which was dissolved was used.
[0058]
[Example 16 (comparative example)]
A coin having a diameter of 18.4 mm and a thickness of 2.0 mm was used in the same manner as in Example 1 except that a solution obtained by dissolving 2.2 mol / kg of the salt represented by the above formula 5 in a dimethyl carbonate solvent was used as the electrolytic solution. Type electric double layer capacitor was obtained.
[0059]
[Example 17 (comparative example)]
A coin having a diameter of 18.4 mm and a thickness of 2.0 mm was obtained in the same manner as in Example 1 except that a solution obtained by dissolving 2.4 mol / kg of the salt represented by the above formula 6 in a dimethyl carbonate solvent was used as the electrolytic solution. Type electric double layer capacitor was obtained.
[0060]
[Example 18 (comparative example)]
A coin having a diameter of 18.4 mm and a thickness of 2.0 mm was used in the same manner as in Example 1 except that a solution obtained by dissolving 2.5 mol / kg of the salt represented by Formula 7 in a propylene carbonate solvent was used as the electrolytic solution. Type electric double layer capacitor was obtained.
[0061]
[Evaluation]
The electrolytic solution compositions of Examples 1 to 8 and Examples 9 to 18 and the voltage holding ratios after holding the electric double layer capacitors in the open circuit at the voltages shown in Tables 1 and 2 for 72 hours are shown in Table 1 and It shows in Table 2. The applied voltages are shown in Example 1, Example 10, Example 14, Example 15, Example 2, Example 11, Example 3, Example 12, Example 4, Example 13, Example 5 and Example 6 so that the performance comparison becomes clear. Example 16, Example 7, Example 8, Example 17, Example 9 and Example 18 were set to the same voltage. In addition, the same voltage as in the evaluation of the voltage holding ratio was applied to the electric double layer capacitors of Examples 1 to 18, the initial capacitance and internal resistance were measured, and further, 1000 hours in a constant temperature and humidity chamber at 70 ° C. The capacity change rate after holding was measured. The results are shown in Table 3.
[0062]
[Table 1]
[Table 2]
[Table 3]
As can be seen from Tables 1 and 2, the electric double layer capacitor of the present invention is superior in voltage holding property and self-discharge characteristics as compared with a comparative example using an electrolytic solution not containing fluorobenzene. Further, as can be seen from Table 3, the electric double layer capacitor of the present invention is excellent in reliability because of little decrease in capacity when voltage is applied at 70 ° C.
[0066]
【The invention's effect】
According to the configuration of the present invention, an electric double layer capacitor having excellent self-discharge characteristics and excellent reliability can be provided.
Claims (10)
を含有する有機電解液。
An organic electrolyte containing
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