Exploring the effect of phosphorus doping on the utility of g-C3N4 as an electrode material in Na-ion batteries using DFT method.

The suitability of P-doped g-C3N4 for sodium storage was assessed using density functional theory. The electronic structure of P-doped g-C3N4 was calculated and the results indicate that the presence of the P atom causes the band gap of g-C3N4 to narrow. Na adsorption on a P-g-C3N4 sheet was investigated. Projected density of states (PDOS) analysis revealed that pyridinic nitrogen atoms in g-C3N4 play the main role in Na adsorption. High binding energies were calculated for Na storage on g-C3N4, leading to a high voltage range (1-3 V) and a high Na diffusion barrier (2.3 eV). Doping the substrate with more P atoms resulted in lower voltages (below 2.2 V), easier Na diffusion (with a barrier of 1.2 eV), and therefore a material that was better suited than g-C3N4 for use in anodes.