Improved structure stability and performance of a LiFeSO4F cathode material for lithium-ion batteries by magnesium substitution

Abstract

Tavorite LiFeSO₄F with high Li-ion conductivity has been considered a promising alternative to LiFePO₄. However, its poor cycle stability and low electronic conductivity limit the practical application of Tavorite LiFeSO₄F. In the present study, we employ a solvothermal method to produce magnesium-substitution LiMg_xFe_1−xSO₄F (x = 0, 0.02, 0.04) cathode materials in which the Mg substitutes the Fe(2) sites. The first-principles calculations demonstrate that Mg-substitution could reduce the bandgap of LiFeSO₄F and increase its electronic conductivity to 2.5 × 10⁻¹¹ S cm⁻¹. Meanwhile, CI-NEB and BV calculations reveal that the diffusion energy barrier of lithium along the (100) direction after Mg substitution is lower than the pristine sample, and the electrochemical inactive Mg²⁺ could improve the structure stability. The results show that the Mg-substituted LiFeSO₄F exhibits enhanced cycle stability and rate performance compared with the pristine LiFeSO₄F, suggesting that the use of electrochemically inactive ion substitution may be critical for the development of high-performance LiFeSO₄F cathode materials for lithium-ion batteries.