Strain engineering of antiperovskite materials for solid-state Li batteries: a computation-guided substitution approach

Abstract

Li₂OHCl is a promising solid-state electrolyte (SSE) for all-solid-state Li-ion batteries thanks to its simple synthesis and low precursor costs. However, its low ionic conductivity is a challenge for its use in devices. This study employs density functional theory (DFT) calculations to investigate the effect of strain on Li⁺ transport, showing that the migration energy barrier decreases if tensile strain is applied. In practice, such strain can be obtained by isovalent doping, i.e., by substituting Cl with larger I and Br atoms. Further DFT calculations and experiments show that tensile strain not only enhances conductivity but also stabilizes the highly conductive cubic phase at room temperature. An optimized composition (i.e., Li₂OHCl_0.921I_0.079) reaches an ionic conductivity of 0.50 mS cm⁻¹ at 373 K, which is five times larger than that of Li₂OHCl at the same temperature. Furthermore, a Li/Li₂OHCl_0.921I_0.079/Li symmetric cell can cycle for more than 800 h, and a Li/Li₂OHCl_0.921I_0.079/LiFePO₄ battery achieves 50% capacity retention after 274 cycles with significantly enhanced performance compared to Li₂OHCl. These findings highlight the potential of strain engineering to enhance the conductivity of SSEs and motivate further research on designing fast ion conductors.