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

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., Li2OHCl0.921I0.079) 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/Li2OHCl0.921I0.079/Li symmetric cell can cycle for more than 800 h, and a Li/Li2OHCl0.921I0.079/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. Introducing the tensile strain can improve the Li+ conductivity and simultaneously stabilize the cubic phase at low temperatures.

Automated summary

This study investigates the effect of strain on Li+ transport and finds that tensile strain can decrease the migration energy barrier. Tensile strain not only enhances conductivity but also stabilizes the highly conductive cubic phase at room temperature. An optimized composition (Li2OHCl0.921I0.079) achieves an ionic conductivity of 0.50 mS cm-1 at 373 K, five times larger than that of Li2OHCl. Furthermore, introducing tensile strain improves the Li+ conductivity and simultaneously stabilizes the cubic phase at low temperatures, resulting in significantly enhanced battery performance.