Anti-perovskite cathodes for lithium batteries

Abstract

It was recently discovered that Li₂FeChO (Ch = S, Se, Te) anti-perovskites exhibit an outstanding rate capability and a good discharge capacity as Li-ion battery cathodes. In this work, we use density functional theory calculations to study the origin of the electrochemical characteristics of anti-perovskite cathodes using Li₂FeSO as a model material. We evaluate the phase stability, ion-transport, and structural stability of this material and, interestingly, found that Li₂FeSO is meta-stable at 0 K. The experimentally observed anti-perovskite phase likely originates from either entropy stabilization or sluggish decomposition kinetics. When delithiated, the stability of the material worsens. Additionally, over-delithiation may lead to irreversible structural change. The good rate capability of Li₂FeSO is attributed to the high Li conductivity, where the low Li ion diffusion barrier (∼0.32 eV) rivals those of state-of-art superionic Li conductors. In the search for materials with a voltage higher than that of Li₂FeSO, we screen Co, Cr, Cu, Mn, Mo, Ni, and V substitutions into the Fe site of Li₂FeSO. While Cu and Ni substitutions may offer higher average voltages, the corresponding materials are less stable than Li₂FeSO.