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

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 Co2P/Sn yolk encapsulated with nitrogen-doped carbon nanobox (Co2P/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 Co2P/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 Co2P/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.