Synthesis and electrochemical properties of pure LiFeSO4F in the triplite structure

Recently in the Li-ion battery community there has been an intense amount of attention focusing on developing positive electrodes which operate on the Fe2+/Fe3+ redox potential given that the environmental and economic advantages of Fe-based compounds compared to other transition metals are tremendous. Here we report that we have succeeded in preparing for the first time LiFeSO4F in the triplite structure which shows an open circuit voltage of 3.9 V versus Li with a reversible capacity of approximately 85 mA h g− 1, still well below the theoretical value of 148 mA h g− 1 due to poor electrode kinetics. Nevertheless, we additionally found that the volume change on removal of Li is 0.6%. Once optimized, this triplite phase of LiFeSO4F could stand as a promising contender to LiFePO4.

► We prepared a monoclinic version of the earlier reported tavorite LiFeSO4F.
► This triplite phase is related to tavorite and shows a redox activity at 3.90 V.
► Gives incentive to try to transform other compounds into triplite.