Intrinsic defects, diffusion and dopants in AVSi₂O₆ (A= Li and Na) electrode materials

The alkali metal pyroxenes of the AVSi ₂O ₆ (A = Li and Na) family have attracted considerable interest as cathode materials for the application in Li and Na batteries. Computer modelling was carried out to determine the dominant intrinsic defects, Li and Na ion diffusion pathways and promising dopants for experimental verification. The results show that the lowest energy intrinsic defect is the V–Si anti-site in both LiVSi ₂O ₆ and NaVSi ₂O ₆. Li or Na ion migration is slow, with activation energies of 3.31 eV and 3.95 eV, respectively, indicating the necessity of tailoring these materials before application. Here, we suggest that Al on the Si site can increase the amount of Li and Na in LiVSi ₂O ₆ and NaVSi ₂O ₆, respectively. This strategy can also be applied to create oxygen vacancies in both materials. The most favourable isovalent dopants on the V and Si sites are Ga and Ge, respectively.