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

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 KxMnO2 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 KxMnO2 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. Give a little KIC: Potassium‐ion pre‐intercalated KxMnO2 nanowires with enlarged interplanar spacing and optimized ion diffusion channels are successfully obtained through a hydrothermal process, and exhibit superior electrochemical properties in lithium‐, sodium‐, and potassium‐ion‐based hybrid supercapacitors (HSCs). A potassium‐ion hybrid supercapacitor (KIC) assembled with a KxMnO2 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 previously reported KICs.