Cation mixing (Li_0.5Fe_0.5)₂SO₄F cathode material for lithium-ion batteries

We study the crystal structure of a triplite-structured (Li_0.5Fe_0.5)SO₄F with full Li⁺/Fe2⁺ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li⁺/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li⁺ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO₄ with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.