Impact of doping on sodium self-diffusion in Na2Ti3O7

There is intensive research by the community to improve materials for energy storage applications beyond lithium-ion batteries. The use of sodium as the charge carrier has benefits and can revolutionize the field. The wide use of sodium-ion batteries is partially hindered by the slow diffusion of sodium ions in the anode. Here, we use density functional calculations to investigate the diffusion properties of sodium ions in Na2Ti3O7. We introduce trivalent [aluminum (Al), gallium, and scandium] and tetravalent (silicon, germanium, and tin) substitutional dopants to calculate their impact on the Na self-diffusion process. Considering a potential migration pathway, sodium atoms migrate via the vacancy mechanism with an energy barrier of 0.69 eV in undoped Na2Ti3O7. This is substantially reduced by 0.3 eV when an Al atom substitutes for a titanium atom in the pathway of migration.