Effects of fluorination on crystal structure and electrochemical performance of antiperovskite solid electrolytes

The development of all-solid-state lithium batteries (ASSLBs) depends on exploiting solid-state electrolytes (SSEs) with high ionic conductivity and electrochemical stability. Fluorination is generally considered to be an effective strategy to improve the ionic conductivity and electrochemical stability of inorganic SSEs. Here, we report the partial fluorination of the chlorine sites in an antiperovskite, by which the orthorhombic Li2OHCl was transformed into cubic Li2OHCl0.9F0.1, resulting in a fourfold increase in ionic conductivity at 30 °C. The ab initio molecular dynamics simulations suggest that both the crystal symmetry and the anions electronegativity influence the diffusion of Li+ in the antiperovskite structure. Besides, from the perspective of experiments and calculations, it is confirmed that fluorination is a feasible method to improve the electrochemical stability of antiperovskite SSEs. The LiFePO4 | Li cell based on Li2OHCl0.9F0.1 is also assembled and exhibits stable cycle performance, which indicates that fluorination of antiperovskite SSEs is an effective way to produce high-performance SSEs for practical application of ASSLBs.