Effect of the mechanical strength on the ion transport in a transition metal lithium halide electrolyte: first-principle calculations

The transition metal lithium halides (such as Li3InCl6, Li3ScCl6 and Li3ErBr6) have high ionic conductivity and good stability with air that can be used as solid electrolyte. However, the effect of mechanical strength on ion transport cannot be ignored in transition metal lithium halides. The relationship between the ion transport and mechanical strength of the transition metal lithium halide solid electrolyte were investigated by the first -principle based density functional theory. The bulk structure was optimized, the mechanical properties and ion transport of the solid electrolyte were analyzed, and the mechanical constants and ideal strength were calculated. The elastic energy band (NEB) method was used to simulate the diffusion of lithium ions in the bulk phase. The results show that Li3InCl6, Li3ScCl6 and Li3ErBr6 have better ductility, as their bulk shear modulus ratios are all greater than 1.75. The Li3ScCl6 inorganic solid electrolyte with higher shear modulus (7.568 GPa) and tensile stress (3.0885 GPa) is more favorable for inhibiting the growth of lithium dendrites. The Li3ScCl6 has a lower migration energy barrier along the O-T-O channel than that of Li3ScCl6 and Li3ErBr6 in the bulk structure. The energy barrier for lithium ion migration has changed in the channel of the solid electrolyte due to the effect of mechanical strength. The lattice distortion will affect the transport of lithium ions. These results provide comprehensive insights into the practical application of these halides as solid electrolytes.