A Nonpresodiate Sodium‐Ion Capacitor with High Performance

Sodium‐ion capacitors (SICs) have received intensive attention due to their high energy density, high power density, long cycle life, and low cost of sodium. However, the lack of high‐performance anode materials and the tedious presodiation process hinders the practical applications of SICs. A simple and effective strategy is reported to fabricate a high‐performance SIC using Fe 1− x S as the anode material and an ether‐based electrolyte. The Fe 1− x S electrode is found to undergo a reversible intercalation reaction after the first cycle, resulting in fast kinetics and excellent reversibility. The Fe 1− x S electrode delivers a high capacity of 340 mAh g −1 at 0.05 A g −1 , 179 mAh g −1 at high current of 5 A g −1 and an ultralong cycling performance with 95% capacity retention after 7000 cycles. Coupled with a carbon‐based cathode, a high‐performance SIC without the presodiation process is successfully fabricated. The hybrid device demonstrates an excellent energy density of 88 Wh kg −1 and superior power density of 11 500 W kg −1 , as well as an ultralong lifetime of 9000 cycles with over 93% capacity retention. An innovative and efficient way to fabricate SICs with both high energy and power density utilizing ether‐based electrolytes can be realized to eliminate the presodiation process.