Anion storage for hybrid supercapacitor

Hybrid supercapacitors (HSCs) have currently gained vital attention as promising energy storage devices owing to their higher energy density than conventional supercapacitors, not scarifying their power density, fast charging–discharging ability, and long cycle life. Herein, we report an inclusive review about the recent advances in the anion storage of aqueous and non-aqueous HSCs, where the energy density can be further improved by means of the enhanced capacitance and enlarged cell voltage. Furthermore, the anion storage mechanisms of HSCs, such as adsorption, intercalation, conversion, and alloying types are discussed, and the role of various anion carriers in various aqueous and non-aqueous electrolytes are also addressed. The anion-storing materials, electrolyte properties, and the corresponding electrochemical performances of the HSCs are collected in terms of the types of anion carriers and electrolyte solutions. Finally, we provide conclusive limitations and decisive future perspectives for the practical anion storing HSCs.