Titanium-Substituted Tavorite LiFeSO4 F as Cathode Material for Lithium Ion Batteries: First-Principles Calculations and Experimental Study

Titanium-substituted LiTi_x Fe_1-2x SO₄ F (x=0, 0.01, 0.02, 0.03) cathode materials were synthesized by a solvothermal method. X-ray diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were used to investigate the effects of Ti substitution on the structure of LiFeSO₄ F, and it was shown that Ti substitutes the Fe(2) site. First-principles calculations and UV-visible spectroscopy demonstrate that Ti substitution reduces the bandgap of LiFeSO₄ F which improves the electronic conductivity from 8.3×10^-12  S cm^-1 to 3.9×10^-11  S cm^-1 . CI-NEB and BV calculations show that the Li diffusion energy barriers along the (100), (010) and (101) directions are decreased after Ti substitution, and the Li diffusion coefficient is increased from 4.99×10^-11  cm²  S^-1 to 1.59×10^-10  cm²  S^-1 . The improved electronic conductivity and ionic diffusivity mean that the Ti-substituted material shows improved electrochemical properties compared to the pristine LiFeSO₄ F.