Tuning morphology, defects and functional group types in hard carbon via phosphorus doped for rapid sodium storage

The introduction of heteroatom is a practical tactic that can enhance the ability of carbon materials to store Na⁺. In this article, N, O, P co-doped hierarchical porous carbon (NOPC) is produced via co-carbonization with phytic acid and soybean protein as precursors. Phytic acid, as a multifunctional additive, macroscopically promotes the formation of a hierarchical pore structure in which micropores and mesopores coexist. It is necessary for the transmission of Na⁺ and penetration of electrolytes. It microscopically regulates different types of surface functional groups, induces defects to enhance the spacing between graphite layers, and enhances the adsorption and intercalation capacity of Na⁺. The macroscopic and microscopic co-working changes the NOPC to have a reversible capacity of 359.5 mA h g⁻¹ at 0.05 A g⁻¹. Using density functional theory, it is confirmed that the co-doping of N/O/P can increase the capture capacity of Na⁺ and reduce the diffusion barrier of carbon materials. Ex-situ XRD, ex-situ Raman and ex-situ TEM were used to verify the structural stability and cycle stability of the NOPC. This study is based on experimental design and theoretical calculations used to prove that synthesis strategy is an effective method for preparing heteroatom-doped carbon with excellent capacity to store sodium.