Recent advances in aqueous and non-aqueous alkali metal hybrid ion capacitors

Alkali metal hybrid ion capacitors (AHICs) combine the advantages of batteries and supercapacitors and balance the disadvantages of both devices, which allows high energy and power densities and long cycling life to be maintained simultaneously. The paper first summarizes the working principles, classification, scientific issues, and performance evaluation methods of AHICs. Then, oriented towards performance and structural optimization, various battery-type and capacitor-type materials in aqueous and non-aqueous systems are discussed, focusing on their structure–property relationships, charge storage mechanisms, and electrochemical performance, respectively. Additionally, the common prelithiation/presodiation/prepotassiation methods used in AHICs are outlined. Finally, some challenges and future research directions in this field are presented.