High‐Performance Hybrid Supercapacitor Enabled by a High‐Rate Si‐based Anode

A hybrid supercapacitor constructed of a Si‐based anode and a porous carbon cathode is demonstrated with both high power and energy densities. Boron‐doping is employed to improve the rate capability of the Si‐based anode (B‐Si/SiO 2 /C). At a high current density of 6.4 A/g, B‐Si/SiO 2 /C delivers a capacity of 685 mAh/g, 2.4 times that of the undoped Si/SiO 2 /C. Benefiting from the high rate performance along with low working voltage, high capacity, and good cycling stability of B‐Si/SiO 2 /C, the hybrid supercapacitor exhibits a high energy density of 128 Wh/kg at 1229 W/kg. Even when power density increases to the level of a conventional supercapacitor (9704 W/kg), 89 Wh/kg can be obtained, the highest values of any hybrid supercapacitor to date. Long cycling life (capacity retention of 70% after 6000 cycles) and low self‐discharge rate (voltage retention of 82% after 50 hours) are also achieved. This work opens an avenue for development of high‐performance hybrid supercapacitors using high‐performance Si‐based anodes.