Interlayer Engineering of K_xMnO₂ 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 K_xMnO₂ 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_xMnO₂ 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.