Electronic/Ionic Co-Modulation by N/P Co-Doping toward High-Rate Sodium Storage in Coal-Derived Hard Carbon

Hard carbon is one of the most promising anode materials for sodium-ion batteries, but its rate performance remains limited by sluggish sodium-storage kinetics. In this work, an electronic/ionic comodulation strategy was developed through N/P codoping to regulate coal-derived hard carbon. Specifically, N doping improves the electronic conductivity of the carbon framework and enhances Na⁺ adsorption, while P doping enlarges the interlayer spacing and promotes Na⁺ diffusion. As a result, the codoped hard carbon develops a hierarchical structure with expanded interlayer spacing, abundant defects, and coexisting open and closed pores. Kinetic analyses together with theoretical calculations indicate that N/P codoping modulates the local electronic environment and improves Na⁺ transport behavior, thereby enhancing the overall sodium-storage kinetics of hard carbon. The optimized anode delivers a reversible capacity of ∼240 mAh g^-1 at 30 mA g^-1 and retains 126 mAh g^-1 over 250 cycles even at 1500 mA g^-1. A full cell paired with a NaFe₁/₃Ni₁/₃Mn₁/₃O₂ cathode also delivers a stable capacity of ∼65 mAh g^-1 at 360 mA g^-1. These results indicate that N/P codoping is an effective approach for improving the high-rate sodium-storage performance of coal-derived hard carbon.