P-doped hard carbon microspheres for sodium-ion battery anodes with superior rate and cyclic performance

As the first potential anode material used in sodium ion batteries (SIBs), hard carbon has received extensive attention owing to its available resources, inexpensiveness, and high electrochemical properties. The unsatisfactory sodium storage capacity and rate properties constrain its use in real-life applications. Herein, phosphorus (P)-doped hard carbon microspheres (PHCS) with a unique interconnected structure, expanded layer spacing (0.411 nm), and enlarged specific surface area (287.82 m² g⁻¹) are prepared using a facile pyrolysis strategy. They easily achieve a superior sodium storage capacity (293.5 mA h g⁻¹ at 0.1 A g⁻¹), remarkable rate performance (162.5 mA h g⁻¹ at 5 A g⁻¹), and exceptional cyclic stability (more than 2000 cycles at 5 A g⁻¹) when applied as anode materials. In addition, density functional theory (DFT) calculations reveal that P-doping facilitates the adsorption of Na⁺ on the material and lowers its structural resistance, which greatly improves the capacity for sodium storage. This study develops a promising design strategy to prepare P-doped hard carbon for SIB performance-enhanced anodes.