Effect of vanadium substitution in LixFeF3 by first-principles calculations

We calculate the stable atomic and electronic states of vanadium-substituted trirutile-type LixFeF3 (LixFe1−yVyF3) and discuss the effect of V substitution in LixFe1−yVyF3 based on the relative energy, Bader charge, and density of states. We find that the x = 0.50 configurations are the most stable for all y values studied here. In the cases where Fe and V coexist, we found that the compositions where Li insertions (x) were the same as the Fe substitutions (1 − y) were energetically stable. Our results suggest that Fe (or V) in LixFe1−yVyF3 preferentially decreases (or increases) its formal valence state with Li insertion (or extraction). This result will lead to the elucidation of the mechanism for the smooth transition from Li insertion to conversion reaction to solve the critical problem of FeF3 positive electrode material.