Dual-Carbon Electrode-Based High-Energy-Density Potassium-Ion Hybrid Capacitor

Potassium-ion hybrid capacitors (KIHCs) have attracted growing attention due to the natural abundance and low cost of potassium. However, KIHCs are still limited by sluggish redox reaction kinetics in electrodes during the accommodation of large-sized K⁺. Herein, a starch-derived hierarchically porous nitrogen-doped carbon (SHPNC) anode and active carbon cathode were rationally designed for dual-carbon electrode-based KIHCs with high energy density. The hierarchical structure and rich doped nitrogen in the SHPNC anode result in a distensible interlayer space to buffer volume expansion during K⁺ insertion/extraction, offers more electrochemical active sites to achieve high specific capacity, and has highly efficient channels for fast ion/electron transports. The in situ Raman and ex situ TEM demonstrated a reversible electrochemical behavior of the SHPNC anode. Thus, the SHPNC anode delivers superior cycling stability and a high reversible capacity (310 mA h g^-1 at 50 mA g^-1). In particular, the KIHCs assembled by the SHPNC anode and commercial active carbon cathode can deliver a high energy density of 165 W h kg^-1 at a current density of 50 mA g^-1 and an ultra-long cycle life of 10,000 cycles at 1 A g^-1 (calculated based on the total mass of the anode and cathode).