Rational phosphating layer design in biomass-derived hard carbons toward fast charging capability of sodium ion battery anodes

Continuous side reactions between a biomass-derived hard carbon (HC) surface and the electrolyte affect its cycling stability and fast-charging performance. Therefore, constructing a stable solid electrolyte interface (SEI) while facilitating easier desolvation of sodium ions in the electrolyte is key to achieving stable fast charging. Theoretical calculations confirmed that Na₃P can induce the formation of a Na⁺ solvation structure with low solvent coordination, thus achieving a lower desolvation energy barrier and faster Na⁺ diffusion capability through the SEI. We used bamboo powder, partially de-lignified, as a precursor for hard carbon. After sublimating red phosphorus in a sealed tube with deposition upon cooling, a phosphide layer was constructed on the hard carbon surface. During charge-discharge cycling, an SEI enriched with Na₃P components was formed on the surface. The final full cell assembled with HC-3 wt% P matched with the cathode exhibited excellent rate performance, with a reversible discharge capacity of 78 mAh g^-1 at 10 C, significantly exceeding the performance of recently reported bamboo powder-based hard carbon. The assembled pouch cell maintained stable cycling for 1000 cycles at 0.5 C. This work provides guidance from the perspective of SEI regulation and design for enhancing the fast-charging performance of biomass-derived hard carbon anodes in sodium-ion batteries.