Polymorphs of LiFeSO4F as cathode materials for lithium ion batteries – a first principle computational study

Abstract

We have investigated polymorphs of LiFeSO₄F, tavorite and triplite, which have been reported as cathode materials for lithium ion batteries. The predicted voltages are 3.64 and 3.90 V for tavorite and triplite, respectively, which agreed excellently with experimental data. It is found that the lithiated states (LiFeSO₄F) of the polymorphs are almost degenerate in energy. The difference in voltage is mainly due to the difference in the stabilities of the delithiated states (FeSO₄F). This is rationalized by the Fe³⁺–Fe³⁺ repulsion in the edge sharing geometry of the triplite structure.