An ether bridge between cations to extend the applicability of ionic liquids in electric double layer capacitorsElectronic supplementary information (ESI) available: 1H NMR and 13C NMR spectra of [C6O2(MIm)2]; chemical structure of [C8(MIm)2]-TFSI2; FTIR spectra of the ILs; Raman spectra of the ILs; AC impedance Nyquist plots of the ILs for conductivity measurements; linear scan voltammograms for determining the usable voltage ranges of the ILs; pore size distribution of the aMP carbon; cyclic v

• Main Authors: Huang, Hsin-Chieh, Yen, Yung-Che, Chang, Jui-Cheng, Su, Ching-Wen, Chang, Pei-Yi, Sun, I.-Wen, Hsieh, Chien-Te, Lee, Yuh-Lang, Teng, Hsisheng
• Format: Journal Article
• Language: English
• Published: 06.12.2016
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c6ta08203c

In this study, without the use of any organic solvents, the performance of an ionic liquid (IL) electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIm-TFSI), is improved by linking some of the EMIm + cations with an ether bridge (-O(CH 2 ) 2 O-) to form C 6 O 2 (MIm) 2 2+ dications in the IL. After replacing 5% of cations with dications, the resultant IL (EM-di5) exhibits a lowered freezing temperature and an amorphous ion arrangement. Spectroscopic analyses clarify that introducing dications reduces the interionic interaction in the IL. When carbon-based electric double-layer capacitors (EDLCs) are assembled using the ILs, the EM-di5 EDLC exhibits lower ion transport resistance and a wider operation temperature range (60 to −20 °C) than does the EMIm-TFSI EDLC (60 to 0 °C). The EM-di5 EDLC presents high electrode capacitances of 200 and 160 F g −1 over a 3.5 V window at 25 and −20 °C, respectively, because the presence of dications facilitates ion penetration into the micropores. The EM-di5 EDLC delivers a specific energy of 70 W h kg −1 at a specific power of 1.3 kW kg −1 (on total carbon mass) at −20 °C. This study presents a molecular-architecture strategy to extend the applicability of ILs in EDLCs to low-temperature environments with improved capacitance. Linking 5% cations with an ether bridge prevents EMIm-TFSI crystallization at low temperatures and promotes the performance of the resultant EDLC.