Tailored Plum Pudding‐Like Co₂P/Sn Encapsulated with Carbon Nanobox Shell as Superior Anode Materials for High‐Performance Sodium‐Ion Capacitors

Abstract Sodium‐ion capacitors (SICs) are emerging energy storage devices with high energy, high power, and durable life. Sn is a promising anode material for lithium storage, but the poor conductivity of the a‐NaSn phase upon sodaition hinders its implementation in SICs. Herein, a superior Sn‐based anode material consisting of plum pudding‐like Co 2 P/Sn yolk encapsulated with nitrogen‐doped carbon nanobox (Co 2 P/Sn@NC) for high‐performance SICs is reported. The 8–10 nm metallic nanoparticles produced in situ are uniformly dispersed in the amorphous Sn matrix serving as conductive fillers to facilitate electron transfer in spite of the formation of electrically resistive a‐NaSn phase during cycling. Meanwhile, the carbon shell buffers the large expansion of active Sn and provides a stable electrode–electrolyte interface. Owing to these merits, the yolk–shell Co 2 P/Sn@NC demonstrates a large capacity of 394 mA h g −1 at 100 mA g −1 , high rate capability of 168 mA h g −1 at 5000 mA g −1 , and excellent cyclability with 87% capacity retention after 10 000 cycles. By integrating the Co 2 P/Sn@NC anode with a peanut shell‐derived carbon cathode in the SIC, high energy densities of 112.3 and 43.7 Wh kg −1 at power densities of 100 and 10 000 W kg −1 are achieved.