Sodium Storage Mechanism and Electrochemical Properties of Various P‐Doped Graphenes for Anode Materials in Sodium‐Ion Batteries

ABSTRACT

Heteroatom doping is an effective approach to enhance sodium storage capacities of carbon materials. In this study, we synthesized P‐doped porous carbon (C–P) materials with defects derived from lignite humic residues. The effects of introduced P, O, vacancy defects and combinations of these defects on Na storage capacities have been investigated using a combination method of density functional theory (DFT) calculations and experiments. Binding energies, geometrical and electronic structures of Na on graphene surfaces with various defects are calculated. The results indicate that the introduction of defects, particularly P‐dopings, enhances the interaction between graphene and Na, improving the sodium storage capacity of the graphene. This is attributed to increased density of states of the modified graphenes at the Fermi level and strong covalent interaction between Na and P. These results are supported by experimental data, highlighting the role of the P‐doping in improving sodium storage. Experimental studies demonstrate that P‐doped porous carbon (C–P) with possible common defects such as O‐adsorbed, P‐doped, vacancy defects and combinations of these defects exhibits a reversible specific capacity of 179.5 mAh g ⁻¹ with over 90% capacity retention after 150 cycles at a current density of 0.1 A g ⁻¹ , and maintain a reversible specific capacity of 147.4 mAh g ⁻¹ after 1500 cycles at 1.0 A g ⁻¹ , superior to other analogous materials.