Interlayer Engineering of KxMnO2 Enables Superior Alkali Metal Ion Storage for Advanced Hybrid Capacitors

Abstract The lack of ideal cathode materials is a great challenge in the development of hybrid capacitors based on various alkali metal ions. In this work, potassium‐ion pre‐intercalated K x MnO 2 nanowires with enlarged interplanar spacing and optimized ion diffusion channels are successfully obtained through a hydrothermal process, and exhibit superior electrochemical property in lithium‐, sodium‐, and potassium‐ion‐based hybrid supercapacitors (HSCs). The potassium‐ion hybrid supercapacitor (KIC) assembled with a K x MnO 2 cathode and activated carbon anode delivers a high energy density of 49.2 Wh kg −1 , a high power density of 4.7 kW kg −1 , and outstanding cycling performance up to 7000 cycles with almost no capacitance decay, which outperforms most of the KICs reported previously. This ion intercalation engineering provides a strategy to design high‐performance cathodes for hybrid capacitors and other battery systems.