Comparative Study of Tavorite and Trip lite LiFeSO4F as Cathode Materials for Lithium Ion Batteries: Structure, Defect Chemistry, and Lithium Conduction Properties from Atomistic Simulation

Abstract

To explore the possibility of LiFeSO4F with two polyrnorphs (tavorite and triplite) as the cathode material for lithium ion batteries, structure, defect chemistry, and Li+ ion conduction properties are studied by atomistic simulation with empirical potential parameters. We investigate the correct structure of tavorite LiFeSO4F, which was newly determined. The concentration of intrinsic defects in the tavorite form is very low in comparison with the triplite form. Configurations of FeO4F2 octahedra in the triplite form are in favor of corner-sharing connections over edge-sharing ones. Even though calculated migration energies prove that both isomorphs are Li+ ion conductors, the Li+ ions in the triplite LiFeSO4F move in the restricted migration paths (one- or two-dimensional), whereas the tavorite isomorph has a continuous three-dimensional Li+ ion conducting network.