Experimental design and theoretical evaluation of nitrogen and phosphorus dual-doped hierarchical porous carbon for high-performance sodium-ion storage

Starch has a wide range of sources and can be used as a high-quality precursor for sodium-ion battery anode materials. However, the carbonization yield and specific capacity of carbon materials obtained by directly pyrolyzing starch are low. Herein, starch is used as the carbon source, and ammonium polyphosphate (APP) is used as the cross-linking agent and dopant to prepare a nitrogen and phosphorus co-doped porous carbon (NPPC). As the anode for sodium-ion batteries, NPPC-2 exhibits a high reversible capacity of 385.8 mA h g−1 at 50 mA g−1. Even after 1000 cycles at a large current density of 5 A g−1, the reversible capacity can still be maintained at 126.9 mA h g−1. Based on detailed data and first-principles calculations, the excellent performance of NPPC is due to the effective doping of nitrogen and phosphorus elements, which distorts the graphite sheet, introduces defects, and increases the graphite layer spacing, thereby enhancing the adsorption capacity of the carbon material for sodium ions, reducing the diffusion barrier of sodium ions. This work provides a new idea for heteroatom doping and carbon material modification.