Effect of Ion Species on the Electrochemical Characteristics of Liquid Electrolytes for High Performance EDLCs

Abstract

Electric double layer capacitors (EDLCs) have been considered one of the most promising electrochemical energy storage devices with high specific power and long cycle life. They are being used in power sources for hybrid electric vehicles and other energy storage systems. An electrolyte with high ionic conductivity and wide electrochemical window is one of the vital constituents of EDLCs and it plays an important role in EDLC performance. In particular, acetonitrile (ACN) has been widely used as an electrolyte solvent in EDLCs, because it can dissolve salts effectively and thus has high ionic conductivity.However, there are few reports on systematic studies of ion species in salt for EDLC. In this respect, we studied the correlation between ion species and electrochemical properties of ACN-based electrolytes. In this work, ammonium, pyrrolidinium and piperidinium-based salts were employed to achieve high ionic conductivity. Ionic conductivity of electrolyte consisting of smaller ions exhibited higher ionic conductivity. Among the various salts, 1-ethyl-2-methylpyrrolidinium tetrafluoroborate, N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide and 1,1-dimethyl piperidinium bis(fluorosulfonyl) imide exhibited high ionic conductivity and wide electrochemical stability window.