Comprehensive Insights into Potassium‐Ion Capacitors: Mechanisms, Materials, Devices and Future Perspectives

Abstract Alkali metal‐ion capacitors integrate two electrodes from both batteries and supercapacitors (SCs), combining the advantages of large capacity, high‐rate performance, and long cycle life. Potassium (K) has similar properties to sodium (Na) and lithium (Li), however, the abundance of K in the crust is the same with Na, and much higher than Li. Due to the fast kinetics and low self‐discharge of Potassium‐ion capacitors (PICs), PICs attract more interest from researchers in the field of electrochemical energy storage. The current dilemma is that the research on PICs is more inherited from sodium‐ion capacitors (SICs) and lithium‐ion capacitors (LICs). Despite advancements in electrode materials, there is still a lack of profound understanding of the intrinsic issues and key challenges of PICs. In order to provide a detailed and systematic analysis of the development of PICs, in this review, special attention is given on the following Accordingly, full eight key sections: i) development history, ii) defining equations, iii) energy storage mechanism, iv) device configuration, v) electrode materials, vi) electrolyte design, vii) key technologies, and viii) future perspectives. This review provides an intensive theoretical foundation for the development of PICs and is able to pave the path for the practical application of PICs.