Structural stability and ion transport mechanism of divalent cation doped anti-perovskites: Insights from molecular dynamics investigation

Molecular dynamics simulations of divalent cation doped anti-perovskites, Li 3-2x M x OCl, with x =0.1 and for M= Mg, Ca, Sr and Ba, are carried out at 450 K to investigate the microscopic structural and dynamical properties. It is predicted that for larger dopants, Ca, Sr and Ba, these materials are thermodynamically unstable at 450 K, limiting their utility as solid electrolytes for battery applications. On the other hand, the Mg-doped anti-perovskites Li 2.8 Mg 0.1 OCl are quite stable in their cubic phase and produces high ionic conductivity of about 1 mS/cm at 450 K. These simulations are supplemented with nudged elastic band calculations on Li 2.8 Mg 0.1 OCl. The study unravels microscopic insights on the nature of the vacancy-driven Li + transport in the system, and the cooperativity of the anionic sub-lattice in promoting the ionic conductivity of the system.