Cation mixing (Li0.5Fe0.5)2SO4F cathode material for lithium-ion batteries

We study the crystal structure of a triplite-structured (Li0.5Fe0.5)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.