Shift to Post-Li-Ion Capacitors: Electrochemical Behavior of Activated Carbon Electrodes in Li-, Na- and K-Salt Containing Organic Electrolytes

Abstract

The interest in exploring intercalation ions-based energy storage systems, which can be alternatives to the well-established Li+ -based systems, is exponentially growing in the scientific community. This shift involves pure battery and hybrid battery-capacitor systems, which contains, at the same time, faradaic-type and double layer-type materials. In order to assess the feasibility of such hybrid system, the single materials have to be firstly analyzed independently. In this work, a commercial activated carbon is taken as an example of double layer-type material and is electrochemically investigated in several organic electrolytes with salts composed of various cations (Li+, Na+ and K+) and anions (PF6−, TFSI− and FSI−). The adsorption of these cations/anions on the activated carbon and their kinetic properties are studied by means of cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Finally, the effect of the different cations on ageing mechanism of symmetric capacitors is studied. The results reveal that the ageing mechanism induced by the Li-salts is different from those achieved with analogue salts containing Na and K cations.