Theoretical design of Na-rich anti-perovskite as solid electrolyte: The effect of cluster anion in stability and ionic conductivity

Abstract

The next-generation solid-state batteries need safe and efficient solid-state electrolytes. However, the conventional solid-state electrolytes materials often suffer from low ionic conductivity. The emerging anti-perovskites are potential solid electrolytes materials for their rich cations and tunable crystal structure. Here, the first-principles density functional theory (DFT) calculations are employed to investigate the stability, electronic properties, elastic constants and the ions migration of sodium-rich anti-perovskite Na3SA (A ​= ​AlF4¯, ClO4¯, ICl4¯, IO4¯). Calculations show that the clusters substitution at anion position A of Na3SA displays larger band gap and faster Na ion transport than that of halogen anions (e.g., Cl, Br, I). Among them, the band gaps of Na3SAlF4 and Na3SClO4 exceed 3.5 ​eV, which indicates their excellent electrochemical stability. The AlF4¯ cluster exhibits high sodium ion conductivity (6.55 ​× ​10-2 ​S ​cm-1), low activation energy (0.19 ​eV) and small migration barrier (0.46 ​eV) according to the ab initio molecular dynamics (AIMD) simulations and transition states study. Molecular dynamics simulations suggest that the enhanced ionic conductivity is due to the rotation of cluster ions which promotes the migration of sodium ions; moreover, the large volume created by anion clusters leads to larger lattices which is also benefit for fast ion transport. Therefore, this work designs Na-rich anti-perovskite with high ionic conductivity by substitution of anion clusters and also provides the Na ion transport mechanism for reference in solid-state electrolytes.