Improved structure stability and performance of a LiFeSO 4 F cathode material for lithium-ion batteries by magnesium substitution.

Tavorite LiFeSO 4 F with high Li-ion conductivity has been considered a promising alternative to LiFePO 4 . However, its poor cycle stability and low electronic conductivity limit the practical application of Tavorite LiFeSO 4 F. In the present study, we employ a solvothermal method to produce magnesium-substitution LiMg x Fe 1- x SO 4 F ( 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 LiFeSO 4 F 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 Mg 2+ could improve the structure stability. The results show that the Mg-substituted LiFeSO 4 F exhibits enhanced cycle stability and rate performance compared with the pristine LiFeSO 4 F, suggesting that the use of electrochemically inactive ion substitution may be critical for the development of high-performance LiFeSO 4 F cathode materials for lithium-ion batteries.