Role of Cation Size on Order-Disorder Phase Transition and Cation Hopping Mechanism based on LiCB11H12

Abstract

Complex hydrides are of great interest for being potential candidates for the solid electrolyte of all-solid-state batteries owing to their exceptionally high ionic conductivity at a high-temperature phase. Hereafter, we study a model system (LiCB11H12) using molecular dynamics (MD) simulations based on a reported force field to investigate the role of cation size in the order-disorder phase-transition temperature (Ttran) and cationic diffusion. The MD results indicate that the lowering of Ttran is due to the high cell volume (by introducing a large-size cation) that eases the anionic rotation. The results are further confirmed by performing a few additional MD simulations by keeping fixed cation size while varying cell volumes. In addition, we obtain comparative insights into cationic density distribution, the bottlenecks of the cationic path, and its hopping mechanism when increasing cationic sizes. These findings are of fundamental importance for guiding a lower transition temperature and higher cationic diffusion for practical applications.