The decisive role of electrolyte concentration in the performance of aqueous chloride-based carbon/carbon supercapacitors with extended voltage window

Abstract

In the present study aqueous alkali metal chloride electrolytes are investigated as potential candidates for carbon/carbon supercapacitors. High-current capacitance retention is greatly enhanced by using the electrolyte concentrations at the maximum electrical conductivity, i.e. 6M LiCl, 5M NaCl and 2M KCl, in supercapacitor cells working at 1.6 V. The resistance of the symmetric cells is also significantly diminished by using the optimum electrolyte concentrations, with remarkable improvements not only in the equivalent series resistance, but also in the distributed resistance. Both high-rate capacitance and lower resistance are beneficial to increase the energy of supercapacitors working at high discharge rates. The small size of electrosorbed dehydrated chloride ions allows the use of less expensive carbons with narrower micropores instead of strongly activated carbons with larger micropores required for bulkier anions.