Electrochemical characterization of MnO2-based composite in the presence of salt-in-water and water-in-salt electrolytes as electrode for electrochemical capacitors

Abstract

Abstract The effect of the electrolyte on the electrochemical utilization of manganese dioxide as active material for electrochemical capacitor was studied by cyclic voltammetry and electrochemical impedance spectroscopy. MnO 2 -based composite electrodes were characterized in salt-in-water (0.65 M K 2 SO 4 , 5 M LiNO 3 , 0.5 M LiNO 3 and 0.5 M Ca(NO 3 ) 2 ) and water-in-salt (5 M LiTFSI (lithium bis-trifluoromethanesulfonimide)) electrolytes. Firstly, no effect of the cation valence on the specific capacitance was observed as similar values were measured in 0.5 M LiNO 3 and 0.5 M Ca(NO 3 ) 2 aqueous solutions at both low and high scan rate, when a MnO 2 -based composite electrode was cycled in the pseudocapacitive potential region. Secondly, it was found that in 5 M LiTFSI, a MnO 2 electrode is characterized by an extended potential stability window of about 1.4 V and exhibits a high specific capacitance of 239 F g −1 per active material mass at a scan rate of 2 mV s −1 . However due to the low ionic conductivity of this solution, the rate capability is limited at high scan rate.