Redox-Additives in Aqueous, Non-Aqueous, and All-Solid-State Electrolytes for Carbon-Based Supercapacitor: A Mini-Review

Herein, we deliver a brief discussion on the classification, state-of-the-art progress, challenges, and perceptions of the redox-additive materials in the aqueous, nonaqueous, and solid-state electrolytes for high-performance supercapacitors. For the performance of electrochemical capacitors, electrolytes are found to be influential components, governing vital parameters including the voltage window, power, and energy density. To improve the electrolyte performance, the inclusion of redox additive species is counted as the best method where the redox reaction that occurs at the electrode–electrolyte interface mainly contributes to the overall enhancement of the device in terms of energy and power as well as stability. The method of preparation and utilization is quite simple, safe, and cost-effective in comparison with some active electrode materials. Hence, the chemistry behind redox additives seems to be of special interest, and the identification of novel redox additives is believed to be a hotspot in the area of supercapacitor electrode materials. In this, we focus on the interaction between carbon-based electrode materials in different redox-additive electrolytes and their challenges and propose different perspectives that concisely intend to enhance energy density without compromising other merits that are inherent.