Theoretical evaluation of properties and behaviors of LiFeSO4F as a Li-ion battery cathode material: a DFT study

Cathode is the most important part of Li-ion batteries and it determines performance and behavior of these energy storage devices. LiFeSO4F as a cathode material with Tavvorite structure and C2/c space group is investigated by density functional theory (DFT) using Wine2k program package. Calculation were performed by different methods GGA, GGA+U and PBE-Fock-α (a Hybrid Functionals method, HF). Structural calculations were demonstrated structural stability after Lithium ion extraction. Theoretical voltage was evaluated, using total energy of the considered structures. The most agreeable calculated voltage in comparison with the experimental value (3.9 V) belongs to HF method. According to obtained Density of States (DOS) diagrams, lithiated structure is n-type semiconductor and delithiated structure is p-type semiconductor. This material had been suggested as a potentially high rate capable cathode due to its unclose structure and high diffusion coefficient of Li-ions in the structure; however, inversely-biased-diode phenomenon turns it as low rate capable in comparison with oxide cathode materials. For the first time, internist-like and extrinsic-like band gap were calculated and reported for the cathode material.