JP4618929B2 - Activated carbon for electric double layer capacitors - Google Patents
Activated carbon for electric double layer capacitors Download PDFInfo
- Publication number
- JP4618929B2 JP4618929B2 JP2001121932A JP2001121932A JP4618929B2 JP 4618929 B2 JP4618929 B2 JP 4618929B2 JP 2001121932 A JP2001121932 A JP 2001121932A JP 2001121932 A JP2001121932 A JP 2001121932A JP 4618929 B2 JP4618929 B2 JP 4618929B2
- Authority
- JP
- Japan
- Prior art keywords
- activated carbon
- double layer
- electric double
- electrode
- less
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 244
- 239000003990 capacitor Substances 0.000 title claims description 56
- 239000011148 porous material Substances 0.000 claims description 38
- 239000001301 oxygen Substances 0.000 claims description 24
- 229910052760 oxygen Inorganic materials 0.000 claims description 24
- 230000004913 activation Effects 0.000 claims description 23
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 23
- 238000000034 method Methods 0.000 claims description 20
- 235000013162 Cocos nucifera Nutrition 0.000 claims description 12
- 239000011255 nonaqueous electrolyte Substances 0.000 claims description 11
- 241000737241 Cocos Species 0.000 claims description 8
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- 229910052744 lithium Inorganic materials 0.000 claims description 8
- 238000010000 carbonizing Methods 0.000 claims description 7
- 239000003610 charcoal Substances 0.000 claims description 3
- 239000004927 clay Substances 0.000 claims 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 15
- -1 nickel metal hydride Chemical class 0.000 description 15
- 239000007772 electrode material Substances 0.000 description 12
- 239000000126 substance Substances 0.000 description 12
- 239000007789 gas Substances 0.000 description 11
- 238000004519 manufacturing process Methods 0.000 description 11
- 239000002994 raw material Substances 0.000 description 11
- 238000012360 testing method Methods 0.000 description 11
- 239000005011 phenolic resin Substances 0.000 description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 239000012298 atmosphere Substances 0.000 description 8
- 239000011230 binding agent Substances 0.000 description 8
- 230000007423 decrease Effects 0.000 description 8
- 239000003792 electrolyte Substances 0.000 description 8
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 8
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 7
- 229910001873 dinitrogen Inorganic materials 0.000 description 7
- 239000008151 electrolyte solution Substances 0.000 description 7
- 238000000465 moulding Methods 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 239000006230 acetylene black Substances 0.000 description 6
- 238000007599 discharging Methods 0.000 description 6
- 229920000049 Carbon (fiber) Polymers 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 125000000524 functional group Chemical group 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 5
- 230000000704 physical effect Effects 0.000 description 5
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 5
- 239000004810 polytetrafluoroethylene Substances 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 229910001220 stainless steel Inorganic materials 0.000 description 5
- 239000010935 stainless steel Substances 0.000 description 5
- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 4
- 244000060011 Cocos nucifera Species 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 239000001569 carbon dioxide Substances 0.000 description 4
- 239000004917 carbon fiber Substances 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 230000018109 developmental process Effects 0.000 description 4
- 239000011888 foil Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 3
- 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
- 230000003213 activating effect Effects 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 150000001768 cations Chemical class 0.000 description 3
- 239000006258 conductive agent Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000000835 fiber Substances 0.000 description 3
- 239000011261 inert gas Substances 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- ZZXUZKXVROWEIF-UHFFFAOYSA-N 1,2-butylene carbonate Chemical compound CCC1COC(=O)O1 ZZXUZKXVROWEIF-UHFFFAOYSA-N 0.000 description 2
- PPDFQRAASCRJAH-UHFFFAOYSA-N 2-methylthiolane 1,1-dioxide Chemical compound CC1CCCS1(=O)=O PPDFQRAASCRJAH-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 125000000217 alkyl group Chemical group 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000001913 cellulose Substances 0.000 description 2
- 229920002678 cellulose Polymers 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000011300 coal pitch Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- GAEKPEKOJKCEMS-UHFFFAOYSA-N gamma-valerolactone Chemical compound CC1CCC(=O)O1 GAEKPEKOJKCEMS-UHFFFAOYSA-N 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000003273 ketjen black Substances 0.000 description 2
- MJIHNNLFOKEZEW-UHFFFAOYSA-N lansoprazole Chemical compound CC1=C(OCC(F)(F)F)C=CN=C1CS(=O)C1=NC2=CC=CC=C2N1 MJIHNNLFOKEZEW-UHFFFAOYSA-N 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 239000003960 organic solvent Substances 0.000 description 2
- 239000011301 petroleum pitch Substances 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 229920001721 polyimide Polymers 0.000 description 2
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 2
- 238000005979 thermal decomposition reaction Methods 0.000 description 2
- 239000002759 woven fabric Substances 0.000 description 2
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 description 2
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 description 1
- VWIIJDNADIEEDB-UHFFFAOYSA-N 3-methyl-1,3-oxazolidin-2-one Chemical compound CN1CCOC1=O VWIIJDNADIEEDB-UHFFFAOYSA-N 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- 229920000106 Liquid crystal polymer Polymers 0.000 description 1
- 239000004977 Liquid-crystal polymers (LCPs) Substances 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 229920006282 Phenolic fiber Polymers 0.000 description 1
- 239000004642 Polyimide Substances 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 229920001328 Polyvinylidene chloride Polymers 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 1
- 229920002125 Sokalan® Polymers 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- IUHFWCGCSVTMPG-UHFFFAOYSA-N [C].[C] Chemical class [C].[C] IUHFWCGCSVTMPG-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000001110 calcium chloride Substances 0.000 description 1
- 229910001628 calcium chloride Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000005539 carbonized material Substances 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- GTKRFUAGOKINCA-UHFFFAOYSA-M chlorosilver;silver Chemical compound [Ag].[Ag]Cl GTKRFUAGOKINCA-UHFFFAOYSA-M 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 229920006037 cross link polymer Polymers 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000011883 electrode binding agent Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000007849 furan resin Substances 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 150000002576 ketones Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910001547 lithium hexafluoroantimonate(V) Inorganic materials 0.000 description 1
- 229910001540 lithium hexafluoroarsenate(V) Inorganic materials 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052987 metal hydride Inorganic materials 0.000 description 1
- 229920000609 methyl cellulose Polymers 0.000 description 1
- 239000001923 methylcellulose Substances 0.000 description 1
- 239000011268 mixed slurry Substances 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 229920003986 novolac Polymers 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000006864 oxidative decomposition reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 150000002926 oxygen Chemical class 0.000 description 1
- 239000002006 petroleum coke Substances 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 229920001568 phenolic resin Polymers 0.000 description 1
- 239000013502 plastic waste Substances 0.000 description 1
- 239000004584 polyacrylic acid Substances 0.000 description 1
- 229920006122 polyamide resin Polymers 0.000 description 1
- 239000009719 polyimide resin Substances 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 239000005033 polyvinylidene chloride Substances 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 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
- DPLVEEXVKBWGHE-UHFFFAOYSA-N potassium sulfide Chemical compound [S-2].[K+].[K+] DPLVEEXVKBWGHE-UHFFFAOYSA-N 0.000 description 1
- 235000011151 potassium sulphates Nutrition 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 229910001925 ruthenium oxide Inorganic materials 0.000 description 1
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 229910000162 sodium phosphate Inorganic materials 0.000 description 1
- 229910052938 sodium sulfate Inorganic materials 0.000 description 1
- 235000011152 sodium sulphate Nutrition 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 150000003462 sulfoxides Chemical class 0.000 description 1
- 229920001059 synthetic polymer Polymers 0.000 description 1
- 229920003002 synthetic resin Polymers 0.000 description 1
- 239000000057 synthetic resin Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 239000011271 tar pitch Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000010920 waste tyre Substances 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 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
- H01G11/04—Hybrid capacitors
- H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
-
- 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
-
- 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
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Carbon And Carbon Compounds (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
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用活性炭に関する。詳しくは、やしがらを原料とする、高い出力密度を有し、耐久性にも優れた特性の電気二重層キャパシタ用活性炭に関する。
【0002】
【従来の技術】
近年、地球環境対策の点から、自動車分野でも燃費のさらなる向上、排気ガスを更に浄化するための開発が行われている。この開発の取り組みの一環として、ハイブリッド自動車、電気自動車の技術開発が進められている。これらの技術開発に関連して駆動系パワーアシストあるいはエネルギー回生の用途に電気二重層キャパシタの実用化が注目されている。電気二重層キャパシタは、分極性電極と電解液の界面に形成される電気二重層に電荷を蓄積することを原理としており、鉛蓄電池、ニッケル水素二次電池等の二次電池と比べて大電流による急速充放電ができることが長所である。分極性電極の材料としては、界面が大きく、かつ導電性に優れる点から、通常、活性炭が用いられる。ハイブリッド自動車、電気自動車用途で求められる電気二重層キャパシタは、静電容量(F)のみならず、100アンペアオーダーの大電流で繰り返し充電・放電が可能な高い出力(W)密度が求められており、多くの技術的課題を残している。そこで、出力密度を上げるために、活性炭を主体とする多孔性電極、集電体、セパレータの厚さを適正化したり(特開平11-317332号公報)、アルミニウムを含浸した活性炭の複合電極を分極性電極とする(特表平10-509560号公報)等の電極作製技術が提案されている。
【0003】
一方、電気二重層キャパシタの電極材料に、活性炭に代表される炭素質物質を使用することが、特公昭60−15138号公報、特開昭63−187614号公報、特開平1−321620号公報、特開平3−180013号公報、特公平6−56827号公報、特公平4−44407号公報、特公平4−70770号公報等に提示されている。
特開平1−321620号公報には、粉末活性炭を1000℃で熱処理したものをキャパシタ用電極材として用いることが示され、又、特開平3−180013号公報では、活性炭の含有酸素量を、25〜35重量%とすることにより電気二重層キャパシタの静電容量を向上させることが可能であるとしているが、いずれの公報においても用いる活性炭の種類や物性については記載されていない。
【0004】
特公平4−70770号公報では、平均細孔径が1.5nm(15Å)以上の活性炭をキャパシタ用電極材として用いたものが温度特性に優れるとされており、また特開昭63−187614号公報では、高い静電容量を示す粉末活性炭は、比表面積1800〜3500m2/g、平均細孔径0.5〜1.5nm(5〜15Å)であり、かつ全細孔容積に占める直径2.0nm(20Å)以上の細孔容積が全細孔容積の20〜40%であるとされているが、これらの公報には本願発明におけるように、平均細孔径1.95nm(19.5Å)以上、2.20nm(22.0Å)以下の特定の範囲を選択し、かつ細孔直径5.0nm(50Å)〜30.0nm(300Å)間の細孔容積を0.05cm3/g以上0.15cm3/g以下とすることについて記載されていない。
【0005】
繊維状炭素については、特公昭60−15138号公報にフェノール系繊維を炭化したのち賦活処理して得た繊維状炭素がキャパシタ用電極材として適していることが示され、特公平6−56827号公報には、表面の酸性官能基の濃度が1.0ミリ当量/g以下の炭素繊維又は炭素粉末をキャパシタ用電極材として用いられ、500m2/g以上の比表面積のものが好ましいこと、具体的にはフェノール樹脂系活性炭繊維を用いることが記載されている。又、特公平4−44407号公報では、特定のフェノール樹脂発泡体を炭化賦活したものをキャパシタ用電極材として用いることが記載されている。
しかして、特公昭60−15138号公報、特公平6−56827号公報及び特公平4−44407号公報などに記載されたフェノール樹脂系材料を炭化した後、賦活処理して得られる活性炭は、比表面積に関しては本発明におけるものとほぼ同等ではあるが、一般に賦活原料となるフェノール樹脂系炭素化物が、均一な非晶質炭素であるため、これを賦活して得られる活性炭に形成される細孔の大部分は細孔直径が15Å以下となる。そのため、後述する比較例4に示されるように、平均細孔径は、通常18Å以下程度と、本発明における平均細孔径よりも小さく、5.0から30.0nmの比較的大きい細孔領域には実質的な細孔分布を有さないものである。
【0006】
しかも、これらの公報に記載された電気二重層キャパシタ用電極材は、いずれも体積当たりあるいは重量当たりの静電容量(F/g、F/cm3)を大きくすることをめざしたものであるため、その具体的実施例での充放電試験においては、電極単位面積当たりの放電電流密度は0.1〜2mA/cm2程度とかなり小さいものであり、高電流密度、例えば10mA/cm2以上の大きな電流密度における電極材料としての効果は全く確認されておらず、これらは上述の高出力用途に適した活性炭に関しては何等開示するものではない。また、特公昭60−15138号公報に記載されたフェノール樹脂を原料とした活性炭炭素繊維織布は、粉末活性炭を成型または塗布して得られる電極と比較し、電気抵抗が小さいというのが特長であり、その意味では高出力が期待できて好ましい。しかしながら、その電極の嵩密度が小さく、重量当たりの出力は大きいが体積当たりの容量が小さいという欠点があった。
【0007】
したがって、これらの公報に記載された活性炭を電極材に用いた電気二重層キャパシタは、静電容量が比較的大きいためエネルギー密度は増加するものの、単位体積あたりの出力密度はかならずしも大きいとは言えない。
さらに、電気二重層キャパシタに求められる特長は、従来の二次電池と比べて、使用可能な充電放電サイクル回数が大きく、連続電圧印加試験時の容量低下が小さい等の耐久性が高いことである。前述の特開平3−180013号公報に記載された、多量の酸素を含有する活性炭を電極材に使用した電気二重層キャパシタでは、充放電時に抵抗増加等による大幅な容量低下が起こるため、耐久性に大きな課題がある。
上記の如き公知の活性炭を用いる電極材においても、その電極作製法を改善することにより電極の内部抵抗を低減し、出力密度をある程度増加させることは可能であるが、高い出力密度を有し、かつ耐久性に優れた電気二重層キャパシタ用活性炭は依然として見い出されていないと言える。
【0008】
【発明が解決しようとする課題】
本発明は、体積当たりの出力密度が大きく、かつ、大電流下での充放電サイクルを繰り返したり、或いは一定電圧を長時間連続して印加した場合でも、出力密度の低下が少ない電気二重層キャパシタに適した活性炭を提供することを目的とする。
【0009】
【課題を解決するための手段】
本発明者らは、上記の課題を解決すべく鋭意検討した結果、特定の原料を適切な条件下で賦活処理することにより得られた活性炭が、適切な細孔分布、比表面積、表面状態、及び電気化学特性を有し、それによって体積当たりの出力密度が大きく、かつ耐久性に優れることを見出し、本発明に到達した。即ち、本発明の要旨は、やしがらを炭化してなる活性炭であって、BET比表面積が2000m2/g以上2500m2/g以下であり、平均細孔径が1.95nm(19.5Å)以上2.20nm(22.0Å)以下であり、クランストンインクレー法で算出した細孔直径5.0nm(50Å)から30.0nm(300Å)間の細孔容積が0.05cm3/g以上0.15cm3/g以下であり、かつ活性炭1g当たりの酸素含有量が1mg以上20mg以下であることを特徴とする電気二重層キャパシタ用活性炭に存する。
【0010】
本発明の好ましい態様として、上記の電気二重層キャパシタ用活性炭において、活性炭1g当たりの酸素含有量が2mg以上10mg以下であり、かつ非水系電解液中における対極リチウムでの自然電位が2.85V以上3.03V以下であること、及び該活性炭がやしがら炭化物を水蒸気賦活して取得されることを挙げることができる。
【0011】
【発明の実施の形態】
以下、本発明を詳細に説明する。本発明の電気二重層キャパシタ用活性炭は、やしがらを炭化してなる活性炭であって、BET比表面積が2000m2/g以上2500m2/g以下であること、平均細孔径が1.95nm(19.5Å)以上2.20nm(22.0Å)以下であること、クランストンインクレー法で算出した細孔直径5.0nm(50Å)〜30.0nm(300Å)の細孔容積が0.05cm3/g以上0.15cm3/g以下であること、及び活性炭1g当たりの酸素含有量が1mg以上20mg以下であることの各物性を充たすことが必須であって、好ましくは、活性炭1g当たりの酸素含有量が2mg以上10mg以下であり、かつ非水系電解液中における対極リチウムでの自然電位が2.85V以上3.03V以下である物性を更に充たすことである。
【0012】
これらの物性を充たす本発明の活性炭を分極性電極材料とする電気二重層キャパシタにおいては、活性炭の嵩密度が高く、かつ活性炭の細孔中に存在する電解液の電解質イオン、溶媒分子のイオン導電性が大きくなり、大電流での充放電であっても、十分に高い出力を発現することが可能である。また、活性炭に存在する含酸素量を適切な量に調節し、かつ、非水系電解液中における活性炭電極の自然電位を適切な範囲に調節することにより、電気二重層キャパシタの耐久性をより向上させることが可能である。
さらに、本発明は、やしがらを原料とした活性炭からこのような優れた特性を発現させることが出来るので、フェノール樹脂等の高価な合成樹脂を原料としたものと比べて生産性、コスト性に優れる特長を有するのである。
【0013】
本発明の電気二重層キャパシタ用活性炭は、活性炭の比表面積は大きすぎると嵩密度が低下して、単位体積あたりの出力が低下するので、窒素吸着法によるBET法により求めたBET比表面積は、2000m2/g以上2500m2/g以下であることを必須とし、好ましくは2000m2/g以上2400m2/g以下であり、より好ましくは2050m2/g以上2250m2/g以下である。比表面積がこの範囲を超えて小さすぎると単位重量あたりの出力が低下し好ましくない。
また本発明の電気二重層キャパシタ用活性炭は、平均細孔径が1.95nm(19.5Å)以上2.20nm(22.0Å)以下であることを必須とする。平均細孔径が小さすぎると、大電流下における充放電時に細孔内での電解イオンの拡散抵抗によると思われる電気抵抗が増加するため高出力用途には適さず、他方、大きすぎると、活性炭の嵩密度が低下し、単位体積当たりの出力が低下するため好ましくない。好ましくは2.00nm(20.0Å)以上2.15nm(21.5Å)以下であり、より好ましくは2.02nm(20.2Å)以上2.15nm(21.5Å)以下である。
【0014】
更に、本発明の電気二重層キャパシタ用活性炭は、クランストンインクレー法で算出した細孔直径5.0nm(50Å)〜30.0nm(300Å)間の細孔容積は、0.05cm3/g〜0.15cm3/gであることを必須とする。細孔容積が大きすぎると電極の嵩密度が低下し、体積当たりの出力が小さくなるため好ましくない。また小さすぎると電極の内部抵抗が増加し、結果として出力密度が小さくなる。好ましくは0.07〜0.13cm3/gであり、より好ましくは0.08〜0.12cm3/gである。
【0015】
本発明の電磁二重層キャパシタ用活性炭は、原料がやしがらであることを必須とする。通常、やしがら以外の活性炭の原料としては、石油系ピッチ、石油コークス、タールピッチを紡糸した繊維、合成高分子、フェノール樹脂、フラン樹脂、ポリ塩化ビニル樹脂、ポリ塩化ビニリデン樹脂、ポリイミド樹脂、ポリアミド樹脂、液晶高分子、プラスチック廃棄物、廃タイヤ等多種多用のものが挙げられるが、例えばフェノール樹脂を活性炭の原料とした場合、2000m2/g以上の比表面積を有するものを得ることは可能であるが、平均細孔径、及び5.0nm(50Å)〜30.0nm(300Å)間の細孔容積を本発明における特定範囲に調節することは困難である。
【0016】
本発明の活性炭は、やしがらを炭化後、賦活することにより得られるが、賦活法は、ガス賦活法と薬品賦活法に大別される。ガス賦活法は、薬品賦活が化学的な活性化であるのに対して、物理的な活性化ともいわれ、炭化された原料を高温で水蒸気、炭酸ガス、酸素、その他の酸化ガスなどと接触反応させることにより活性炭を生成する。薬品賦活法は、原料に賦活薬品を均等に含浸させて、不活性ガス雰囲気中で加熱し、薬品の脱水および酸化反応により活性炭を得る方法である。使用される薬品としては、塩化亜鉛、りん酸、りん酸ナトリウム、塩化カルシウム、硫化カリウム、水酸化カリウム、水酸化ナトリウム、炭酸カリウム、炭酸ナトリウム、硫酸ナトリウム、硫酸カリウム、炭酸カルシウム等がある。
活性炭の製法に関しては特に制限されず、生成した活性炭が前記特性を満足する限り、上記方法に限られないが、これらの賦活法のうち、水蒸気賦活法で得られる活性炭が電気二重層キャパシタの耐久性に優れ、かつ製造コストも安い特長を有するので水蒸気賦活法が有利である。
また、活性炭の形状は、破砕状、粒状、顆粒、繊維、フェルト、織物、シート状等各種の形状があるが、いずれも本発明に使用することができる。
【0017】
本発明における水蒸気賦活法で得られる活性炭は、やしがらを粉砕・調粒したものを、不活性雰囲気中で炭化処理(乾留)して得られたやしがらチャーを、800℃以上1300℃以下、好ましくは850℃以上1200℃以下、より好ましくは900℃以上1100℃以下で、30体積%以上100体積%以下の水蒸気ガス雰囲気を含む窒素、アルゴン、燃焼排ガス等の不活性ガス中で熱処理することにより得られる。
賦活前のやしがら、あるいはやしがらチャー、及び賦活処理して得られた活性炭を、塩酸、硝酸、硫酸等の酸水溶液中で洗浄して、炭素中に含まれる金属不純物、灰分等を除去したものも本発明に含まれる。
賦活処理後の活性炭を、窒素、アルゴン、ヘリウム、キセノン等の不活性雰囲気下で、500〜2500℃、好ましくは700〜1500℃で熱処理し、不要な表面官能基を除去したり、炭素の結晶性を発達させて電子伝導性を増加させても良い。
粒状の活性炭の場合、電極の嵩密度の向上、内部抵抗の低減という点で、平均粒子径は30μm以下が好ましく、より好ましくは7〜20μmである。
【0018】
本発明の電気二重層キャパシタ用活性炭は、非水系電解液を用いた電気二重層キャパシタにおいて、該電解液中での自然電位が、Li/Li+を対極とした場合、2.85V以上3.03V以下であることが好ましく、より好ましくは、2.90〜3.00Vである。自然電位が大きすぎると、例えば、活性炭を正極として組み立てた電気二重層キャパシタに2.5V以上を印加した場合、正極の充電後の電位が約4.3V(対Li/Li+)となり、電解液の酸化分解電位(4.3V以上)に達するので、その結果、電解液の分解反応が生じ、電気二重層キャパシタの耐久性は低下する。なお、自然電位が2.85Vより小さいものは、上記の製法においては、通常得られない。
本発明における正極の炭素質電極の自然電位測定は、通常の電気化学的手法を用いて行われる。非水系電解液での電位測定は、水溶液での標準水素電極のような電位基準は厳密には定義されていないが、実際には、銀−塩化銀電極、白金電極、リチウム電極等の電極を用いて一般に広く行われており、本発明においても同様な方法で測定可能である。
【0019】
活性炭中に含まれる酸素量は電気二重層キャパシタの耐久性に影響を及ぼすので、その含酸素量を適切な量に調節することが好ましい。本発明では、活性炭1gあたりの含酸素量は1mg以上20mg以下が好ましく、より好ましくは2mg以上10mg以下である。本発明の含酸素量とは、真空中またはアルゴンガス、窒素ガス等の不活性ガス雰囲気中で、活性炭を1000℃付近で熱処理し、その際に発生した分解ガス中に含まれる一酸化炭素(CO)、二酸化炭素(CO2)を定量し、これらの分子に含まれる酸素量を総和で示す値である。ここで、熱分解温度が1000℃付近であることから、この酸素量は、活性炭中の含酸素官能基、すなわち、カルボキシル基、フェノール基、ケトン類等に相当しており、言い換えれば、本発明中の含酸素量とは、活性炭中に含まれる含酸素官能基の総量を示す指標であると言える。
活性炭1g中の含酸素量が上記範囲を超えて多すぎると、電気二重層キャパシタの充放電時にセル内に含酸素官能基の分解または電解液との反応によると推定されるガス発生による電気抵抗の増加が生じ、キャパシタの耐久特性は低下するために好ましくない。また上記範囲より少なすぎると、電極作製時に電極用結着剤との親和性が低下し、結果として電極の嵩密度が低下するため、単位体積あたりの出力が低下するので好ましくない。
【0020】
本発明の活性炭を用いて電気二重層キャパシタを構成する場合について、以下に述べる。
活性炭を主体とする分極性電極は、常法により形成され、主に活性炭とバインダーから構成されるが、電極に導電性を付与するために、さらに導電性物質を添加しても良い。活性炭は、従来より知られている方法により成形することが可能である。例えば、活性炭とアセチレンブラックの混合物に、ポリテトラフルオロエチレンを添加・混合した後、プレス成形することにより成形体として得ることが出来る。また、活性炭に比較的軟化点の高い石炭ピッチをバインダーとして添加・混合後、成型したものを、不活性雰囲気中でバインダーの熱分解温度以上まで焼成して成型体を得ることもできる。さらに、導電剤、バインダーを用いず、活性炭のみを焼結して分極性電極とすることも可能である。電極は、薄い塗布膜、シート状または板状の成形体、さらには複合物からなる板状成形体のいずれであっても良い。
なお、バインダーとの混合に先立ち、活性炭を所望の粒状に粉砕することもできるが、活性炭を比較的大粒径のままバインダーと混合して一緒に粉砕し、混合スラリー又はドライな粉砕物として得ることもできる。
【0021】
活性炭電極に用いられる導電剤としては、アセチレンブラック、ケッチェンブラック等のカーボンブラック、天然黒鉛、熱膨張黒鉛、炭素繊維、酸化ルテニウム、酸化チタン、アルミニウム、ニッケル等の金属ファイバーからなる群より選ばれる少なくとも一種の導電剤が好ましい。少量で効果的に導電性が向上する点で、アセチレンブラック及びケッチェンブラックが特に好ましく、活性炭との配合量は、活性炭の嵩密度により異なるが多すぎると活性炭の割合が減り容量が減少するため、活性炭の重量の5〜50%、特に10〜30%程度が好ましい。
【0022】
バインダーとしては、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、カルボキシセルロース、メチルセルロース、フルオロオレフィン共重合体架橋ポリマー、ポリビニルアルコール、ポリアクリル酸、ポリイミド、石油ピッチ、石炭ピッチ、フェノール樹脂のうち少なくとも1種類以上用いるのが好ましい。
集電体は電気化学的及び化学的に耐食性があればよく、特に限定するものではないが、例えば、正極としてはステンレス、アルミニウム、チタン、タンタル等が挙げられ、負極では、ステンレス、ニッケル、アルミニウム、銅等が好適に使用される。
【0023】
電解液は非水系電解液が好ましい。非水系電解液の溶質としては、R4N+、R4P+(ただし、RはCnH2n+1で示されるアルキル基:n=1〜4)、トリエチルメチルアンモニウムイオン等で示される第4級オニウムカチオンと、BF4 -、PF6 -、ClO4 -、SbF6 -またはCF3SO3 -なるアニオンとを組み合わせた塩、または、カチオンがリチウムイオンであるリチウム塩を用いる。リチウム塩としては、LiBF4,LiClO4,LiPF6,LiSbF6,LiAsF6,LiCF3SO3,LiC(CF3SO2)3,LiB(C6H5)4,LiC4F9SO3,LiC8F17SO3,LiN(CF3SO2)2から選ばれる1つ以上の物質が好ましい。特に、電気導電性、安定性、及び低コスト性という点から、カチオンとしてR4N+(ただし、RはCnH2n+1で示されるアルキル基:n=1〜4)及びトリエチルメチルアンモニウムイオン、アニオンとして、BF4 -、PF6 -、ClO4 -、及びSbF6 -を組み合わせた塩が好ましい。
【0024】
これらの非水系電解液中の溶質濃度は電気二重層キャパシターの特性が十分引き出せるように、0.3〜2.0モル/リットルが好ましく、特に、0.7モル/リットル以上1.9モル/リットル以下の濃度では、高い電気導電性が得られて好ましい。特に、−20℃以下の低温で充放電するとき、2.0モル/リットル以上の濃度では、電解液の電気導電性が低下し好ましくない。0.3モル/リットル以下では室温下、低温下とも電気電導度が小さく好ましくない。
電解液としてはテトラエチルアンモニウムテトラフルオロボレート(Et4NB4)のプロピレンカーボネート溶液が好ましく、Et4NB4の濃度としては0.5〜1.0モル/リットルが好ましい。
【0025】
非水系電解液の溶媒は特に限定するものではないが、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、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、スルホラン、メチルスルホラン、γ−ブチロラクトン、γ−バレロラクトン、N−メチルオキサゾリジノン、ジメチルスルホキシド、及びトリメチルスルホキシドから選ばれる1種類以上からなる有機溶媒が好ましい。電気化学的及び化学的安定性、電気伝導性に優れる点から、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、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、スルホラン、メチルスルホラン、γ−ブチロラクトンから選ばれる1種類以上の有機溶媒が特に好ましい。ただし、エチレンカーボネート等の高融点溶媒は、単独では低温下では固体となるため使用できず、プロピレンカーボネート等との低融点溶媒との混合溶媒とする必要がある。
非水系電解液中の水分は、高い耐電圧が得られるように200ppm以下、さらには50ppm以下が好ましい。
【0026】
【実施例】
以下、本発明を具体的な実施例により更に説明するが、本発明はその要旨を超えない限り以下の実施例により限定されるものではない。
【0027】
実施例1〜6,比較例1〜5
活性炭の製造例
やしがらチャー(50g)を、水蒸気を含む窒素ガスを流通させたロータリーキルンに入れ、水蒸気賦活を行った。賦活温度、賦活時間、及び窒素ガス中の水蒸気濃度は下記表−1に示す通りである。得られた賦活物を、塩酸中で洗浄後、脱塩水で繰り返し洗浄した。洗浄後、賦活物を乾燥し、乾燥後、これらの賦活物を粉砕して平均粒径が10〜20μmの活性炭粉末を得た(実施例1〜6、比較例1、3)。比較例2では、やしがらチャーのかわりに、瀝青炭の粉砕物を、また、比較例4,5では、フェノール樹脂(ノボラック)硬化物を夫々窒素雰囲気中700℃で炭化して得られた炭化物を用いたこと以外は、実施例1と同様な条件で活性炭粉末を製造した。
【0028】
【表1】
【0029】
活性炭の物性測定
得られた活性炭粉末のBET比表面積、細孔直径5.0nm(50Å)〜30.0nm(300Å)間の細孔容積、及び全細孔容積は、ソープトマチック1800型(ファイソン社製)を用い、該活性炭粉末の液体窒素温度における各相対圧力下での窒素ガスの各平衡吸着量を測定して得られる活性炭の吸着等温線より算出した。
活性炭粉末の平均細孔直径は、活性炭の細孔形状を円柱状に仮定し、上記の窒素ガスの吸着等温線から求めた全細孔容積とBET比表面積から算出した。
活性炭中の含有酸素量は、以下のようにして求めた。
約1gの活性炭粉末を入れた石英硝子製反応管を約1000℃に加熱し、その際に発生したガスをガスクロマトグラフ分析装置に注入し、発生ガス中のCO及びCO2成分を定量した。定量したCO及びCO2中の各々の酸素量の和を求め、活性炭1g当たりの含有酸素量を算出した。
以上のようにして算出した活性炭の物性値を表−2に示す。
【0030】
【表2】
【0031】
試験例1
(活性炭のキャパシタ特性評価−1:初期性能)
上記活性炭の製造例で得られた各活性炭について、活性炭粉末80重量%、アセチレンブラック10重量%、ポリテトラフルオロエチレン10重量%からなる混合物を混練した後、錠剤成型器(日本分光社製)を用い、油圧プレスで直径10mm、厚さ0.5mmとなるように50kgf/cm2の圧力で加圧成形して円盤状の成型体を得、これを正極成型体とした。同様にして成型体をさらに1枚作製し、これを負極成型体とした。得られた2枚の成型体を0.1torr以下の真空中、300℃で3時間乾燥した。乾燥した2枚の成型体を窒素ガス雰囲気中のドライボックス中に移した後、正・負極の成型体を電解液である(C2H5)4NBF4のプロピレンカーボネート溶液に真空含浸した。次に、ポリエチレン製セパレータを介して、電解液を含浸させた正極成型体及び負極成型体を対向させた後、これらをステンレス製コインセル中にかしめ封じて、コインセル型電気二重層キャパシタを得た。
【0032】
得られたコインセル型電気二重層キャパシタを25℃の恒温漕中で、HJ−201型充放電試験装置(北斗電工社製)にて2.5Vの電圧を印加後、電流密度20mA/cm2の定電流で放電した。得られた放電曲線の2.5Vから1.0Vの間の勾配から初期の静電容量(F)を求めた。また、放電直後の電圧降下(IR降下:IR−drop)を放電曲線から読みとった。IR−dropが大きいと、結果として取り出せるエネルギー密度が小さくなり好ましくない。結果を表−3に示す。
【0033】
【表3】
【0034】
試験例2
(活性炭のキャパシタ特性評価−2:初期性能)
活性炭の製造例で得られた各活性炭8重量部、導電性カーボンブラック3重量部、セルロース系バインダー3重量部の混合物に蒸留水を添加した後、これらを混練して電極塗布用ペーストを得た。得られたペーストをエッチングしたアルミ箔に塗布・乾燥することにより活性炭ペーストの膜厚が40μmの電極体を得た。上記の電極体から有効電極面積7.07cm×7.07cm(50cm2)の2枚の電極体を得て、各々を正極、負極とした。この正極と負極とを活性炭電極膜を内側にして、セルロース系セパレータを介して対向させて電気化学素子を得た。この素子を硝子板で挟み込み、さらに硝子板の外側をステンレス製板で挟み込んだ後、該素子をボルトナットで固定し、電気二重層キャパシタ素子とした。得られたキャパシタ素子を真空中で加熱乾燥して不純物を取り除いた。次に、(C2H5)4NBF4のプロピレンカーボネート溶液を電解液として素子に含浸させて、これを電気二重層キャパシタとした。
【0035】
得られた電気二重層キャパシタを25℃の恒温槽中で、市販の充放電試験装置により2.5V印加した後、放電した。放電曲線から、静電容量(F/cm3)、内部抵抗(Ω)、及び2.5Vから1.5V間を2秒間で放電した場合の出力密度(W/cm3)を算出した。ただし、単位体積当たりのキャパシタ特性(F/cm3、W/cm3)は、得られた放電曲線から求めた静電容量(F)及び出力(W)を活性炭電極膜の体積当たりに換算することにより算出した。算出したキャパシタ特性を表−4に示す。
【0036】
【表4】
【0037】
試験例3
(活性炭のキャパシタ特性評価−3:耐久性)
電気二重層キャパシタの耐久性能試験は以下のようにして実施した。
上記活性炭の製造例で得られた各活性炭について、活性炭粉末80重量%、アセチレンブラック10重量%、ポリテトラフルオロエチレン10重量%からなる混合物を混練した後、錠剤成型器(日本分光社製)を用い、油圧プレスで直径10mm、厚さ0.5mmとなるように50kgf/cm2の圧力で加圧成形して円盤状の成型体を得、これを正極成型体とした。同様にして成型体をさらに1枚作製し、これを負極成型体とした。得られた2枚の成型体を0.1torr以下の真空中、300℃で3時間乾燥した。乾燥した2枚の成型体を窒素ガス雰囲気中のドライボックス中に移した後、正・負極の成型体を電解液である(C2H5)4NBF4のプロピレンカーボネート溶液に真空含浸した。次に、ポリエチレン製セパレータを介して、電解液を含浸させた正極成型体及び負極成型体を対向させた後、これらをステンレス製コインセル中にかしめ封じて、コインセル型電気二重層キャパシタを得た。
【0038】
得られたコインセル型電気二重層キャパシタを70℃の恒温漕中で、HJ−201型充放電試験装置(北斗電工社製)にて2.8Vの電圧を印加後、電流密度10mA/cm2の定電流で放電した。得られた放電曲線から初期の静電容量(F)を求めた。次に、2.8Vを500時間連続印加した後、放電して、耐久性試験後の静電容量(F)を求めた。初期に対する耐久性試験後の静電容量の変化率(%)を表−5に示した。
【0039】
【表5】
【0040】
試験例4
(活性炭の自然電位測定)
活性炭の製造例で得られた各活性炭について、活性炭粉末80重量%、アセチレンブラック10重量%、ポリテトラフルオロエチレン10重量%からなる混合物を混練した後、錠剤成型器(日本分光社製)を用い、油圧プレスで直径10mm,厚さ0.5mmとなるように50kgf/cm2の圧力で加圧成形して円盤状の成型体を得た。この成型体を0.1torr以下の真空中、300℃で3時間乾燥した。乾燥後の活性炭電極と直径10mmに打ち抜いた厚さ0.5mmの金属リチウム箔をポリエチレン製セパレータ(三菱化学社製)を介して対向させた後、活性炭電極と金属リチウム箔を外側から集電体である白金板で挟み込みこんだ。さらに集電体、活性炭電極、セパレータがよく接触するように一番外側から2枚の厚さ5mmで4個のボルト孔をもつテフロン板で挟み込んだのち、これを1モル/リットル濃度のLiBF4のプロピレンカーボネート溶液が入ったビーカーに浸漬した。次に、活性炭電極側と金属リチウム箔側の集電体の間に電位差計を介して結線して、活性炭電極の自然電位を測定した。各活性炭電極の対極をリチウムとした場合の自然電位(V vs Li/Li+)を表−2に示した。
【0041】
【発明の効果】
本発明のやしがらを原料とし、適切な細孔分布、、比表面積、表面状態、及び電気化学特性を有する活性炭を使用することにより、体積当たりの出力密度が大きく、かつ、大電流下での充放電サイクルの繰り返しや、一定電圧を長時間連続で印加した場合でも、出力密度の低下が少ない電気二重層キャパシタを提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to activated carbon for electric double layer capacitors. More specifically, the present invention relates to an activated carbon for electric double layer capacitors having a high output density and excellent durability using coconut palm as a raw material.
[0002]
[Prior art]
In recent years, from the viewpoint of global environmental measures, development for further improvement of fuel consumption and further purification of exhaust gas has been performed in the automobile field. As part of this development effort, technology development for hybrid and electric vehicles is underway. In connection with these technological developments, the practical use of electric double layer capacitors has attracted attention for applications such as drive system power assist or energy regeneration. The electric double layer capacitor is based on the principle that electric charge is stored in the electric double layer formed at the interface between the polarizable electrode and the electrolyte, and has a larger current than secondary batteries such as lead storage batteries and nickel metal hydride secondary batteries. It is an advantage that can be charged and discharged quickly. As a material for the polarizable electrode, activated carbon is usually used because it has a large interface and excellent conductivity. Electric double layer capacitors required for hybrid and electric vehicle applications require not only capacitance (F) but also high output (W) density that can be repeatedly charged and discharged with a large current of 100 amp order. , Leaving many technical challenges. Therefore, in order to increase the output density, the thickness of the porous electrode mainly composed of activated carbon, the current collector, and the separator is optimized (Japanese Patent Laid-Open No. 11-317332), or the activated carbon composite electrode impregnated with aluminum is separated. An electrode manufacturing technique such as a polar electrode (Japanese Patent Publication No. 10-509560) has been proposed.
[0003]
On the other hand, the use of a carbonaceous material typified by activated carbon as the electrode material of the electric double layer capacitor is disclosed in JP-B-60-15138, JP-A-63-187614, JP-A-1-321620, JP-A-3-180013, JP-B-6-56827, JP-B-4-44407, JP-B-4-70770 and the like.
JP-A-1-321620 discloses that powdered activated carbon heat-treated at 1000 ° C. is used as a capacitor electrode material. In JP-A-3-180013, the oxygen content of the activated carbon is 25 Although it is said that the capacitance of the electric double layer capacitor can be improved by setting it to 35% by weight, the type and physical properties of the activated carbon used in any publication are not described.
[0004]
Japanese Patent Publication No. 4-70770 discloses that an activated carbon having an average pore diameter of 1.5 nm (15 mm) or more as an electrode material for capacitors is excellent in temperature characteristics, and Japanese Patent Laid-Open No. 63-187614 discloses. , Powdered activated carbon showing high capacitance has a specific surface area of 1800-3500m2/ G, average pore diameter of 0.5 to 1.5 nm (5 to 15 mm), and the pore volume of 2.0 nm (20 mm) or more of the total pore volume is 20 to 40% of the total pore volume. However, in these publications, as in the present invention, a specific range having an average pore diameter of 1.95 nm (19.5 mm) or more and 2.20 nm (22.0 mm) or less is selected, and the pore diameter is 5.0 nm. The pore volume between (50mm) and 30.0nm (300mm) is 0.05cm.Three/ G or more 0.15cmThree/ G or less is not described.
[0005]
Regarding fibrous carbon, Japanese Patent Publication No. 60-15138 discloses that fibrous carbon obtained by carbonizing phenolic fiber and then activation treatment is suitable as an electrode material for capacitors, and Japanese Patent Publication No. 6-56827. In the publication, carbon fiber or carbon powder having a surface acidic functional group concentration of 1.0 milliequivalent / g or less is used as an electrode material for capacitors.2It is described that those having a specific surface area of not less than / g are preferable, specifically, the use of phenol resin-based activated carbon fibers. Japanese Examined Patent Publication No. 4-44407 discloses that a specific phenol resin foam is carbonized and activated as a capacitor electrode material.
Thus, activated carbon obtained by carbonizing a phenol resin material described in JP-B-60-15138, JP-B-6-56827, JP-B-4-44407, etc. Although the surface area is almost the same as that in the present invention, since the phenol resin-based carbonized material that is generally an activation raw material is uniform amorphous carbon, pores formed in activated carbon obtained by activating this In most cases, the pore diameter is 15 mm or less. Therefore, as shown in Comparative Example 4 to be described later, the average pore diameter is usually about 18 mm or less, which is smaller than the average pore diameter in the present invention, in a relatively large pore region of 5.0 to 30.0 nm. It does not have a substantial pore distribution.
[0006]
Moreover, the electrode materials for electric double layer capacitors described in these publications all have capacitances per volume or weight (F / g, F / cm).ThreeIn the charge / discharge test in the specific example, the discharge current density per unit area of the electrode is 0.1 to 2 mA / cm.2Is fairly small and has a high current density, eg 10 mA / cm2The effect as an electrode material in the above large current density is not confirmed at all, and these do not disclose anything about the above-mentioned activated carbon suitable for high-power applications. In addition, the activated carbon carbon fiber woven fabric using a phenol resin as a raw material described in Japanese Patent Publication No. 60-15138 is characterized in that it has a lower electrical resistance than an electrode obtained by molding or applying powdered activated carbon. In that sense, high output can be expected, which is preferable. However, there is a drawback that the bulk density of the electrode is small and the output per weight is large but the capacity per volume is small.
[0007]
Therefore, although the electric double layer capacitor using activated carbon described in these publications as an electrode material has a relatively large capacitance, the energy density increases, but the output density per unit volume is not necessarily high. .
Furthermore, the characteristics required for the electric double layer capacitor are that it has high durability, such as a large number of usable charge / discharge cycles and a small capacity drop during a continuous voltage application test, as compared with a conventional secondary battery. . In an electric double layer capacitor using activated carbon containing a large amount of oxygen as an electrode material described in the above-mentioned JP-A-3-180013, a large capacity drop occurs due to an increase in resistance at the time of charge and discharge. There is a big problem.
Even in the electrode material using the known activated carbon as described above, it is possible to reduce the internal resistance of the electrode by improving the electrode manufacturing method and increase the output density to some extent, but it has a high output density, Moreover, it can be said that the activated carbon for electric double layer capacitors excellent in durability has not yet been found.
[0008]
[Problems to be solved by the invention]
The present invention provides an electric double layer capacitor having a large output density per volume and a small decrease in output density even when a charge / discharge cycle under a large current is repeated or a constant voltage is continuously applied for a long time. It aims at providing the activated carbon suitable for.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained an activated carbon obtained by activating a specific raw material under appropriate conditions, suitable pore distribution, specific surface area, surface state, In addition, the present inventors have found that it has an electrochemical characteristic, and thereby has a high power density per volume and excellent durability, and has reached the present invention. That is, the gist of the present invention is activated carbon obtained by carbonizing coconut palm having a BET specific surface area of 2000 m.2/ G or more 2500m2/ G or less and the average pore diameter is 1.95 nm (19.5 mm) or more and 2.20 nm (22.0 mm) or less., KuThe pore volume between 5.0 nm (50 mm) and 30.0 nm (300 mm) calculated by the Lanston inclay method is 0.05 cm.Three/ G or more 0.15 cmThree/ G or less,And the oxygen content per 1 g of activated carbon is 1 mg or more and 20 mg or less.It exists in the activated carbon for electric double layer capacitors characterized by this.
[0010]
As a preferred embodiment of the present invention, in the above activated carbon for electric double layer capacitor, the oxygen content per gram of activated carbon is2mg or more10The natural potential at the counter lithium in the non-aqueous electrolyte solution is 2.85 V or more and 3.03 V or less, and that the activated carbon is obtained by steam activation of carbide from the palm. be able to.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. The activated carbon for an electric double layer capacitor of the present invention is activated carbon obtained by carbonizing coconut palm, having a BET specific surface area of 2000 m2 / g or more and 2500 m2 / g or less, and an average pore diameter of 1.95 nm (19.5 mm). ) More than 2.20nm (22.0mm), KuThe pore volume of the pore diameter of 5.0 nm (50 mm) to 30.0 nm (300 mm) calculated by the Lanston inclay method is 0.05 cm3 / g or more and 0.15 cm3 / g or less,And the oxygen content per gram of activated carbon is 1 mg or more and 20 mg or lessIt is essential to satisfy each physical property, and preferably the oxygen content per gram of activated carbon is2mg or more1This is to further satisfy the physical properties of 0 mg or less and the natural potential of the counter electrode lithium in the non-aqueous electrolyte solution being 2.85 V or more and 3.03 V or less.
[0012]
In the electric double layer capacitor using the activated carbon of the present invention satisfying these physical properties as a polarizable electrode material, the bulk density of the activated carbon is high, and the electrolyte ions of the electrolyte existing in the pores of the activated carbon and the ionic conductivity of the solvent molecules Therefore, even when charging / discharging with a large current, a sufficiently high output can be expressed. In addition, by adjusting the oxygen content present in the activated carbon to an appropriate amount and adjusting the natural potential of the activated carbon electrode in the non-aqueous electrolyte to an appropriate range, the durability of the electric double layer capacitor is further improved. It is possible to make it.
Furthermore, since the present invention can express such excellent characteristics from activated carbon made from coconut palm as a raw material, productivity and cost performance compared to those made from expensive synthetic resin such as phenol resin are used. It has excellent characteristics.
[0013]
Since the activated carbon for electric double layer capacitors of the present invention has a large specific surface area of the activated carbon, the bulk density decreases and the output per unit volume decreases, so the BET specific surface area determined by the BET method by the nitrogen adsorption method is: 2000m2/ G or more 2500m2/ G or less, preferably 2000 m2/ G or more 2400m2/ G or less, more preferably 2050 m2/ G or more 2250m2/ G or less. If the specific surface area exceeds this range and is too small, the output per unit weight is unfavorable.
The activated carbon for electric double layer capacitors of the present invention must have an average pore diameter of 1.95 nm (19.5 mm) or more and 2.20 nm (22.0 mm) or less. If the average pore size is too small, the electrical resistance, which seems to be due to the diffusion resistance of electrolytic ions in the pores, increases during charging / discharging under a large current, so it is not suitable for high power applications. This is not preferable because the bulk density is reduced and the output per unit volume is reduced. It is preferably 2.00 nm (20.0 mm) or more and 2.15 nm (21.5 mm) or less, more preferably 2.02 nm (20.2 mm) or more and 2.15 nm (21.5 mm) or less.
[0014]
Furthermore, the activated carbon for an electric double layer capacitor of the present invention has a pore volume between 0.05 nm (50 mm) and 30.0 nm (300 mm) calculated by the Cranston inclay method having a pore volume of 0.05 cm.Three/G-0.15cmThree/ G is essential. An excessively large pore volume is not preferable because the bulk density of the electrode is lowered and the output per volume is reduced. If it is too small, the internal resistance of the electrode increases, and as a result, the output density decreases. Preferably 0.07 to 0.13 cmThree/ G, more preferably 0.08 to 0.12 cm.Three/ G.
[0015]
The activated carbon for electromagnetic double layer capacitors of the present invention requires that the raw material is palm. Usually, as raw materials for activated carbon other than palm, petroleum pitch, petroleum coke, tar pitch spun fiber, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, Polyamide resin, liquid crystal polymer, plastic waste, waste tires, and many other things are listed. For example, when phenol resin is used as a raw material for activated carbon, 2000 m2It is possible to obtain one having a specific surface area of not less than / g, but the average pore diameter and the pore volume between 5.0 nm (50 Å) and 30.0 nm (300 調節) are adjusted to a specific range in the present invention. It is difficult.
[0016]
The activated carbon of the present invention can be obtained by carbonizing coconut palm and activating it, and activation methods are roughly classified into a gas activation method and a chemical activation method. The gas activation method is also called physical activation while chemical activation is chemical activation, and the carbonized raw material is contacted with water vapor, carbon dioxide, oxygen, other oxidizing gases, etc. at high temperatures. To produce activated carbon. The chemical activation method is a method in which an activated chemical is uniformly impregnated in a raw material, heated in an inert gas atmosphere, and activated carbon is obtained by dehydration and oxidation reaction of the chemical. Examples of chemicals used include zinc chloride, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, and calcium carbonate.
The production method of the activated carbon is not particularly limited, and is not limited to the above method as long as the produced activated carbon satisfies the above characteristics. Among these activation methods, activated carbon obtained by the steam activation method is the durability of the electric double layer capacitor. The water vapor activation method is advantageous because of its excellent properties and low production costs.
The activated carbon has various shapes such as crushed, granular, granule, fiber, felt, woven fabric and sheet, and any of them can be used in the present invention.
[0017]
The activated carbon obtained by the water vapor activation method in the present invention is obtained by subjecting a coconut char obtained by pulverizing and adjusting coconut palm to a carbonization treatment (dry distillation) in an inert atmosphere, from 800 ° C. to 1300 ° C. Hereinafter, heat treatment in an inert gas such as nitrogen, argon, combustion exhaust gas, etc., preferably containing 850 ° C. or more and 1200 ° C. or less, more preferably 900 ° C. or more and 1100 ° C. or less and a water vapor gas atmosphere of 30% by volume to 100% by volume. Can be obtained.
Before activation, coconut char or coconut char and activated carbon obtained by activation treatment are washed in an acid aqueous solution such as hydrochloric acid, nitric acid, sulfuric acid, etc. to remove metal impurities, ash, etc. contained in carbon. What was removed is also included in the present invention.
The activated carbon after the activation treatment is heat-treated at 500 to 2500 ° C., preferably 700 to 1500 ° C. in an inert atmosphere such as nitrogen, argon, helium, xenon, etc., to remove unnecessary surface functional groups or to obtain carbon crystals. The electronic conductivity may be increased by developing the sex.
In the case of granular activated carbon, the average particle diameter is preferably 30 μm or less, more preferably 7 to 20 μm, in terms of improving the bulk density of the electrode and reducing internal resistance.
[0018]
The activated carbon for an electric double layer capacitor of the present invention is an electric double layer capacitor using a non-aqueous electrolyte solution, and the natural potential in the electrolyte solution is Li / Li+When using as a counter electrode, it is preferably 2.85 V or more and 3.03 V or less, more preferably 2.90 to 3.00 V. If the natural potential is too large, for example, when 2.5 V or more is applied to an electric double layer capacitor assembled with activated carbon as the positive electrode, the potential after charging of the positive electrode is about 4.3 V (vs. Li / Li).+) And reaches the oxidative decomposition potential (4.3 V or higher) of the electrolytic solution. As a result, a decomposition reaction of the electrolytic solution occurs, and the durability of the electric double layer capacitor decreases. In addition, what a natural potential is smaller than 2.85V cannot usually be obtained in said manufacturing method.
The natural potential measurement of the carbonaceous electrode of the positive electrode in the present invention is performed using a normal electrochemical technique. In the potential measurement with a non-aqueous electrolyte, the potential reference such as a standard hydrogen electrode in an aqueous solution is not strictly defined, but in reality, an electrode such as a silver-silver chloride electrode, a platinum electrode, or a lithium electrode is used. In general, it can be measured by the same method in the present invention.
[0019]
Since the amount of oxygen contained in the activated carbon affects the durability of the electric double layer capacitor, it is preferable to adjust the oxygen content to an appropriate amount. In the present invention, the oxygen content per gram of activated carbon is preferably 1 mg to 20 mg, more preferably 2 mg to 10 mg. The oxygen content of the present invention refers to carbon monoxide (in a vacuum or an inert gas atmosphere such as argon gas, nitrogen gas, etc.) that is subjected to heat treatment of activated carbon at around 1000 ° C. CO), carbon dioxide (CO2) Is quantified, and the total amount of oxygen contained in these molecules. Here, since the thermal decomposition temperature is around 1000 ° C., this oxygen amount corresponds to an oxygen-containing functional group in activated carbon, that is, a carboxyl group, a phenol group, a ketone, etc. In other words, the present invention It can be said that the oxygen content in the medium is an index indicating the total amount of oxygen-containing functional groups contained in the activated carbon.
If the oxygen content in 1 g of activated carbon exceeds the above range and is too large, the electric resistance due to gas generation presumed to be due to decomposition of oxygen-containing functional groups in the cell or reaction with the electrolyte during charging / discharging of the electric double layer capacitor. Increase, and the durability characteristics of the capacitor deteriorate, which is not preferable. On the other hand, if it is less than the above range, the affinity with the electrode binder is reduced during electrode production, and as a result, the bulk density of the electrode is lowered.
[0020]
The case where an electric double layer capacitor is comprised using the activated carbon of this invention is described below.
A polarizable electrode mainly composed of activated carbon is formed by a conventional method and is mainly composed of activated carbon and a binder, but a conductive substance may be further added to impart conductivity to the electrode. Activated carbon can be formed by a conventionally known method. For example, after adding and mixing polytetrafluoroethylene to a mixture of activated carbon and acetylene black, a molded product can be obtained by press molding. Further, a molded product obtained by adding and mixing a coal pitch having a relatively high softening point to activated carbon as a binder and then molding it may be fired to a temperature equal to or higher than the thermal decomposition temperature of the binder in an inert atmosphere. Furthermore, it is possible to sinter only activated carbon without using a conductive agent and a binder to form a polarizable electrode. The electrode may be a thin coating film, a sheet-shaped or plate-shaped molded body, or a plate-shaped molded body made of a composite.
Prior to mixing with the binder, the activated carbon can be pulverized into a desired granular form, but the activated carbon is mixed with the binder with a relatively large particle size and pulverized together to obtain a mixed slurry or a dry pulverized product. You can also
[0021]
The conductive agent used for the activated carbon electrode is selected from the group consisting of carbon fibers such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, titanium oxide, aluminum, nickel, and other metal fibers. At least one conductive agent is preferred. Acetylene black and ketjen black are particularly preferable in that the conductivity is effectively improved in a small amount, and the blending amount with activated carbon varies depending on the bulk density of the activated carbon, but if the amount is too large, the proportion of activated carbon decreases and the capacity decreases. The weight of activated carbon is preferably 5 to 50%, particularly about 10 to 30%.
[0022]
As the binder, at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxycellulose, methylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, and phenol resin is used. Is preferred.
The current collector is not particularly limited as long as it has electrochemical and chemical corrosion resistance. Examples of the positive electrode include stainless steel, aluminum, titanium, tantalum, and the negative electrode includes stainless steel, nickel, and aluminum. Copper or the like is preferably used.
[0023]
The electrolyte is preferably a non-aqueous electrolyte. The solute of the non-aqueous electrolyte is RFourN+, RFourP+(However, R is CnH2n + 1An alkyl group represented by: n = 1 to 4), a quaternary onium cation represented by triethylmethylammonium ion or the like, and BFFour -, PF6 -, ClOFour -, SbF6 -Or CFThreeSOThree -Or a lithium salt in which the cation is a lithium ion. As the lithium salt, LiBFFour, LiClOFour, LiPF6, LiSbF6, LiAsF6, LiCFThreeSOThree, LiC (CFThreeSO2)Three, LiB (C6HFive)Four, LiCFourF9SOThree, LiC8F17SOThree, LiN (CFThreeSO2)2One or more substances selected from are preferred. In particular, R as a cation from the viewpoint of electrical conductivity, stability, and low cost.FourN+(However, R is CnH2n + 1As an alkyl group represented by: n = 1 to 4) and triethylmethylammonium ion, anion, BFFour -, PF6 -, ClOFour -, And SbF6 -The salt which combined these is preferable.
[0024]
The solute concentration in these non-aqueous electrolytes is preferably 0.3 to 2.0 mol / liter so that the characteristics of the electric double layer capacitor can be sufficiently extracted, and particularly at a concentration of 0.7 mol / liter to 1.9 mol / liter, Conductivity is obtained, which is preferable. In particular, when charging / discharging at a low temperature of −20 ° C. or less, a concentration of 2.0 mol / liter or more is not preferable because the electrical conductivity of the electrolytic solution is lowered. If it is 0.3 mol / liter or less, the electric conductivity is small and unfavorable at both room temperature and low temperature.
As the electrolyte, tetraethylammonium tetrafluoroborate (EtFourNBFour) Propylene carbonate solution is preferred, EtFourNBFourThe concentration of is preferably 0.5 to 1.0 mol / liter.
[0025]
The solvent of the non-aqueous electrolyte is not particularly limited, but propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, N- An organic solvent composed of one or more selected from methyl oxazolidinone, dimethyl sulfoxide, and trimethyl sulfoxide is preferable. One or more kinds selected from propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, and γ-butyrolactone from the viewpoint of excellent electrochemical and chemical stability and electrical conductivity The organic solvent is particularly preferred. However, a high-melting-point solvent such as ethylene carbonate cannot be used alone because it becomes a solid at a low temperature, and must be a mixed solvent with a low-melting-point solvent such as propylene carbonate.
The moisture in the non-aqueous electrolyte solution is preferably 200 ppm or less, more preferably 50 ppm or less so that a high withstand voltage can be obtained.
[0026]
【Example】
EXAMPLES Hereinafter, although this invention is further demonstrated by a specific Example, this invention is not limited by a following example, unless the summary is exceeded.
[0027]
Examples 1-6, Comparative Examples 1-5
Example of activated carbon production
Yashigara char (50 g) was placed in a rotary kiln in which nitrogen gas containing water vapor was circulated, and water vapor activation was performed. The activation temperature, activation time, and water vapor concentration in the nitrogen gas are as shown in Table 1 below. The obtained activation product was washed in hydrochloric acid and then repeatedly with demineralized water. After washing, the activated material was dried, and after drying, these activated materials were pulverized to obtain activated carbon powder having an average particle size of 10 to 20 μm (Examples 1 to 6, Comparative Examples 1 and 3). In Comparative Example 2, charcoal obtained by carbonizing bituminous charcoal in place of coconut char, and in Comparative Examples 4 and 5, carbonized phenolic resin (novolak) at 700 ° C. in a nitrogen atmosphere. An activated carbon powder was produced under the same conditions as in Example 1 except that was used.
[0028]
[Table 1]
[0029]
Measurement of activated carbon properties
The obtained activated carbon powder has a BET specific surface area, a pore volume between 5.0 nm (50 mm) and 30.0 nm (300 mm), and a total pore volume of Thorptomatic 1800 (manufactured by Phison). The activated carbon powder was calculated from the adsorption isotherm of activated carbon obtained by measuring each equilibrium adsorption amount of nitrogen gas under each relative pressure at the liquid nitrogen temperature of the activated carbon powder.
The average pore diameter of the activated carbon powder was calculated from the total pore volume and the BET specific surface area determined from the nitrogen gas adsorption isotherm assuming that the activated carbon pore shape was cylindrical.
The oxygen content in the activated carbon was determined as follows.
A quartz glass reaction tube containing about 1 g of activated carbon powder is heated to about 1000 ° C., and the gas generated at that time is injected into a gas chromatograph analyzer, and CO and CO in the generated gas are injected.2Ingredients were quantified. Quantified CO and CO2The sum of the amount of each oxygen was determined, and the amount of oxygen contained per gram of activated carbon was calculated.
The physical property values of activated carbon calculated as described above are shown in Table 2.
[0030]
[Table 2]
[0031]
Test example 1
(Capacitor characteristic evaluation of activated carbon-1: Initial performance)
For each activated carbon obtained in the above activated carbon production example, a mixture of 80% by weight of activated carbon powder, 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene was kneaded, and then a tablet molding machine (manufactured by JASCO Corporation) was used. Used, 50kgf / cm so that it is 10mm in diameter and 0.5mm in thickness with a hydraulic press2The disk was molded under pressure to obtain a disk-shaped molded body, which was used as a positive electrode molded body. Similarly, another molded body was produced, and this was used as a negative electrode molded body. The obtained two molded bodies were dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr or less. After the two dried molded bodies are transferred into a dry box in a nitrogen gas atmosphere, the positive and negative molded bodies are electrolytes (C2HFive)FourNBFFourThe propylene carbonate solution was vacuum impregnated. Next, the positive electrode molded body impregnated with the electrolytic solution and the negative electrode molded body were opposed to each other through a polyethylene separator, and then these were caulked and sealed in a stainless steel coin cell to obtain a coin cell type electric double layer capacitor.
[0032]
The obtained coin cell type electric double layer capacitor was applied at a current density of 20 mA / cm after applying a voltage of 2.5 V with a HJ-201 type charge / discharge tester (manufactured by Hokuto Denko) in a constant temperature bath at 25 ° C.2The battery was discharged at a constant current. The initial capacitance (F) was determined from the gradient between 2.5 V and 1.0 V of the obtained discharge curve. Further, the voltage drop immediately after the discharge (IR drop: IR-drop) was read from the discharge curve. When IR-drop is large, the energy density which can be taken out becomes small as a result, which is not preferable. The results are shown in Table-3.
[0033]
[Table 3]
[0034]
Test example 2
(Capacitor characteristic evaluation of activated carbon-2: Initial performance)
Distilled water was added to a mixture of 8 parts by weight of each activated carbon, 3 parts by weight of conductive carbon black, and 3 parts by weight of a cellulose binder obtained in the activated carbon production example, and these were kneaded to obtain an electrode coating paste. . The obtained paste was applied to an etched aluminum foil and dried to obtain an electrode body having an activated carbon paste thickness of 40 μm. Effective electrode area 7.07 cm × 7.07 cm (50 cm) from the above electrode body2) Were obtained, and each was used as a positive electrode and a negative electrode. The positive electrode and the negative electrode were opposed to each other through a cellulose-based separator with the activated carbon electrode film inside, to obtain an electrochemical element. This element was sandwiched between glass plates, and the outside of the glass plate was sandwiched between stainless steel plates. The element was then fixed with bolts and nuts to form an electric double layer capacitor element. The obtained capacitor element was heat-dried in vacuum to remove impurities. Next, (C2HFive)FourNBFFourThe propylene carbonate solution was impregnated as an electrolytic solution into the device to obtain an electric double layer capacitor.
[0035]
The obtained electric double layer capacitor was discharged in a constant temperature bath at 25 ° C. by applying 2.5 V with a commercially available charge / discharge test apparatus. From the discharge curve, capacitance (F / cmThree), Internal resistance (Ω), and power density (W / cm when discharging between 2.5V and 1.5V in 2 seconds)Three) Was calculated. However, capacitor characteristics per unit volume (F / cmThree, W / cmThree) Was calculated by converting the capacitance (F) and output (W) obtained from the obtained discharge curve per volume of the activated carbon electrode membrane. Table 4 shows the calculated capacitor characteristics.
[0036]
[Table 4]
[0037]
Test example 3
(Capacitor characteristic evaluation of activated carbon-3: durability)
The durability test of the electric double layer capacitor was conducted as follows.
For each activated carbon obtained in the above activated carbon production example, a mixture of 80% by weight of activated carbon powder, 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene was kneaded, and then a tablet molding machine (manufactured by JASCO Corporation) was used. Used, 50kgf / cm so that it is 10mm in diameter and 0.5mm in thickness with a hydraulic press2The disk was molded under pressure to obtain a disk-shaped molded body, which was used as a positive electrode molded body. Similarly, another molded body was produced, and this was used as a negative electrode molded body. The obtained two molded bodies were dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr or less. After the two dried molded bodies are transferred into a dry box in a nitrogen gas atmosphere, the positive and negative molded bodies are electrolytes (C2HFive)FourNBFFourThe propylene carbonate solution was vacuum impregnated. Next, the positive electrode molded body impregnated with the electrolytic solution and the negative electrode molded body were opposed to each other through a polyethylene separator, and then these were caulked and sealed in a stainless steel coin cell to obtain a coin cell type electric double layer capacitor.
[0038]
The obtained coin cell type electric double layer capacitor was applied at a current density of 10 mA / cm after applying a voltage of 2.8 V with a HJ-201 type charge / discharge test apparatus (manufactured by Hokuto Denko) in a constant temperature bath at 70 ° C.2The battery was discharged at a constant current. The initial capacitance (F) was determined from the obtained discharge curve. Next, after 2.8 V was continuously applied for 500 hours, the battery was discharged and the electrostatic capacity (F) after the durability test was obtained. Table 5 shows the change rate (%) of the capacitance after the durability test with respect to the initial stage.
[0039]
[Table 5]
[0040]
Test example 4
(Measurement of natural potential of activated carbon)
For each activated carbon obtained in the activated carbon production example, a mixture of 80% by weight of activated carbon powder, 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene was kneaded, and then a tablet molding machine (manufactured by JASCO Corporation) was used. , 50kgf / cm so that the diameter is 10mm and the thickness is 0.5mm with hydraulic press2A disk-shaped molded body was obtained by pressure molding under the pressure of The molded body was dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr or less. The dried activated carbon electrode and a 0.5 mm thick metal lithium foil punched out to a diameter of 10 mm are opposed to each other through a polyethylene separator (Mitsubishi Chemical Corporation), and then the activated carbon electrode and the metallic lithium foil are collected from the outside. It was sandwiched between platinum plates. Furthermore, the current collector, activated carbon electrode, and separator are sandwiched by two Teflon plates with a thickness of 4 mm and four bolt holes so that the collector, carbon dioxide electrode, and separator are in contact with each other.FourWas immersed in a beaker containing a propylene carbonate solution. Next, it connected with the potentiometer between the collectors of the activated carbon electrode side and the metal lithium foil side, and measured the natural potential of the activated carbon electrode. Natural potential (V vs Li / L) when the counter electrode of each activated carbon electrode is lithiumi +) Is shown in Table-2.
[0041]
【The invention's effect】
By using activated carbon having the appropriate pore distribution, specific surface area, surface state, and electrochemical properties, using the palm of the present invention as a raw material, the power density per volume is large, and under a large current. Even when the charging / discharging cycle is repeated or a constant voltage is continuously applied for a long time, an electric double layer capacitor with little decrease in output density can be provided.
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KR102572395B1 (en) * | 2017-05-10 | 2023-08-29 | 주식회사 쿠라레 | Modified activated carbon and its manufacturing method |
KR20210089643A (en) * | 2018-11-09 | 2021-07-16 | 주식회사 쿠라레 | Carbonaceous material, its manufacturing method, electrode active material for electrochemical device, electrode for electrochemical device, and electrochemical device |
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US10475595B2 (en) | 2016-05-20 | 2019-11-12 | Avx Corporation | Ultracapacitor for use at high temperatures |
US10658127B2 (en) | 2016-05-20 | 2020-05-19 | Avx Corporation | Nonaqueous electrolyte for an ultracapacitor |
US10679798B2 (en) | 2016-05-20 | 2020-06-09 | Avx Corporation | Ultracapacitor containing thin electrodes in a metal container |
US10840031B2 (en) | 2016-05-20 | 2020-11-17 | Avx Corporation | Ultracapacitor for use at high temperatures |
WO2018092721A1 (en) | 2016-11-15 | 2018-05-24 | 株式会社クラレ | Carbonaceous material for electric double layer capacitors and method for producing same |
KR20200083655A (en) | 2016-11-15 | 2020-07-08 | 주식회사 쿠라레 | Carbonaceous material for electric double layer capacitors and method for producing same |
US10879014B2 (en) | 2016-11-15 | 2020-12-29 | Kuraray Co., Ltd. | Carbonaceous material for electric double layer capacitors and method for producing same |
US11823837B2 (en) | 2016-11-15 | 2023-11-21 | Kuraray Co., Ltd. | Carbonaceous material for electric double layer capacitors and method for producing same |
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