Theoretical study of charge and discharge process and NMR in Na ion battery anode material Sn

Sn can be used as an anode material for secondary battery Na ion batteries because it can work with Na with a composition ratio of up to Na₁₅Sn₄ by alloying with Na. For practical application, it was reported from both experiments and calculations that there were multiple plateaus in the charging curve of Na-Sn system based on the structural change in the sodiation/desodiation process of Na-Sn system. In this study, we investigated the detailed mechanism of charge and discharge processes in Sn anodes by theoretically clarifying the structural changes, charge and discharge curves, and ²³Na NMR chemical shift properties of the anode material Sn in Na ion batteries.
We used VASP-5.3.2 to optimize the structure of Na-Sn systems with different composition ratios during the charge/discharge process, and calculated their formation energy. The boundary composition ratio was clarified from the charging curve obtained by estimating the change in potential with respect to the Na/Sn composition ratio.
We calculated chemical shift tensors for Na-Sn system, Na and NaCl by GIPAW method. As a result of theoretical calculation of the 23Na chemical shift, it was possible to obtain a number of shielding effect values corresponding to the number of independent Na sites in each Na-Sn composition.