Electrochemical characterisations and ageing of ionic liquid/γ-butyrolactone mixtures as electrolytes for supercapacitor applications over a wide temperature range

Electrochemical properties in mesoporous media of three different ionic liquids (1-propyl-1methylpyrrolidinium-bis(fluorosulfonyl) imide - Pyr(13)FSI, 1-butyl-1-methylpyrrolidinium-bis(trifluoromethanesulfonyl) imide - Pyr(14)TFSI and 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl) imide - EMITFSI) are investigated from -50 degrees C to 100 degrees C and compared with binary mixtures with gamma-butyrolactone (GBL). Buckypaper composed of Single-Wall Carbon Nanotubes (SWCNTs) are used to prepare and study coin-cell supercapacitors. Supercapacitor using Pyr(13)FSI/GBL present a rapid loss of capacitance after only a thousand cycles at 100 degrees C. On the contrary, EMITFSI/GBL and Pyr(14)TFSI/GBL prove to be very promising at high temperature (the capacitance loss after 10,000 cycles is 9% and 10%). More drastic ageing tests such as floating are also carried out for these two mixtures at 100 degrees C and -50 degrees C. 23% and 15% capacitance losses have been recorded after 500 h of floating at 100 degrees C for EMITFSI/GBL and Pyr(14)TFSI/GBL. The capacitance of supercapacitors based on Pyr(14)TFSI/GBL dropped by 20% after 200 h of floating at -50 degrees C rather than EMITFSI/GBL show a remarkable stability during floating at -50 degrees C, with 6.6% capacitance loss after 500 h (3 V at -50 degrees C). These results show that the mixture EMITFSI/GBL works properly all along the broad range of temperature [-50 degrees C to +100 degrees C] and thus proved that our approach is very promising for the development of high performances supercapacitors specifically adapted for extreme environment. (C) 2017 Elsevier B.V. All rights reserved.