Characteristics of non-aqueous quaternary solvent mixture and Na-salts based supercapacitor electrolytes in a wide temperature range

The electrochemical characteristics of 1 M NaPF6, NaClO4 and NaN(SO2F)(2) (i.e., NaFSl) solutions in a quaternary solvent mixture of ethylene carbonate, dimethyl carbonate, propylene carbonate and ethyl acetate, in a 1:1:1:0.5 ratio by volume, were studied for application as electrolytes of supercapacitors working in a wide temperature range (from -40 to 60 degrees C). Mainly microporous carbide derived carbon powder (synthesized from MO2C by chlorination at 800 degrees C) based electrodes exhibited nearly ideal capacitive behaviour at cell potentials up to 3.4V in the NaPF6 electrolyte, where also the limiting capacitance of 120 F g(-1) was practically retained down to -300 degrees C. The slower electrolyte ions diffusion processes at low temperature caused smaller capacitance and inferior power performance for the NaClO4 electrolyte based systems even at room-temperature. Cycle life measurements under floating potential conditions showed that the NaPF6 electrolyte has much better electrochemical stability at 3.0V floating compared to NaClO4. Electrochemical stability problems observed with the NaFSI electrolyte due to oxidation of aluminium current collectors were not overcome by the addition of small concentration of aluminium-stabilizing NaPF6 salt. (C) 2014 Elsevier Ltd. All rights reserved.