Local structural changes and inductive effects on ion conduction in antiperovskite solid electrolytes

Solid-state electrolytes (SSEs) with high ionic conductivities are the key components in solid-state batteries, and the ionic conductivities of SSEs are strongly related to their underlying crystal structures. However, the current structural descriptions mainly focus on static average structure, with certain limitations due to an incomplete understanding of the ionic conduction mechanism in solid electrolytes. Herein, a relationship between ionic transport and local lattice dynamics at an atomic scale is presented. The local structural changes by altering the fractional occupancy of the halide anions in antiperovskite Li2OHX (Cl, Br) are investigated using atomic pair distribution function (PDF), and the corresponding Li+ transport behaviors are obtained by electrochemical impedance spectroscopy (EIS). The increased lattice polarization and distortion are observed to decrease both activation barriers and Arrhenius prefactor upon changing the Br contents. It indicates that the synergistic effects of local structural changes on the activation barrier and Arrhenius prefactor both should be considered for promoting ionic transport. The investigation shows an in-depth understanding of ion conduction in solid electrolytes and delivers a new insight for developing new ionic conductors.