N-substituted defective graphene sheets: promising electrode materials for Na-ion batteries

Using density functional theory calculations, we have investigated the adsorption of Na on pristine and N-substituted defective graphene sheets (graphitic, pyridinic, and pyrrolic structures) and explored their application in Na-ion batteries. The adsorption energy and the charge transfer of Na on the various types of sheet were calculated. The effects of N-substitution were also studied by electronic structure analysis, including the total electronic density of states, partial electron density of states, and charge density differences. The results show that electron-rich structures have a negative influence on Na binding, while electron-deficient structures are beneficial. The Na storage capacities of different sheets were evaluated by optimizing multiple Na atom adsorbed structures. We found that more Na atoms can be stored on electron-deficient sheets, making them promising for practical application as electrode materials in Na-ion batteries.