An ether bridge between cations to extend the applicability of ionic liquids in electric double layer capacitors

作者：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^*

来源：Journal of Materials Chemistry A, 2016, 4(48): 19160-19169.

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(CH2)(2)O-) to form C6O2(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 degrees C) than does the EMIm-TFSI EDLC (60 to 0 degrees 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 degrees 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 degrees C. This study presents a molecular-architecture strategy to extend the applicability of ILs in EDLCs to low-temperature environments with improved capacitance.

• 出版日期2016