Revisited insights into charge storage mechanisms in electrochemical capacitors with Li2SO4-based electrolyte

This paper provides a comprehensive overview of the recent state of the art in research on a neutral, water-based electrolyte, i.e., 1 mol⋅L⁻¹ Li₂SO₄ solution, for sustainable electrochemical capacitors. The fundamental physicochemical properties of aqueous electrolytic solutions (conductivity, viscosity, etc.) are discussed together with the electrochemical performance of carbon-based electrochemical capacitors. In addition to a critical review of the recent findings in the field, the paper discusses new data obtained with the operando approach; the discussion is supported by recent findings from the electrochemical quartz crystal microbalance, Raman spectroscopy and scanning electrochemical microscopy techniques. In this respect, interesting results concerning specific and selective ion adsorption have been obtained. In addition, a post-mortem analysis of carbon electrodes (N₂ adsorption) subjected to an ageing protocol is presented. Furthermore, the influence of an anti-ageing additive (tocopherol) on the electrode material and electrolyte has been investigated. Finally, the mechanisms governing capacitive- and redox-based interfacial interactions are proposed.