A 3.9 V polyanion-type cathode material for Li-ion batteries

Monoclinic phase LiFeSO₄F was synthesized by a simple fast solid state reaction from the mixture of FeSO₄·7H₂O and LiF pulverized by high energy ball milling. m-LiFeSO₄F was confirmed by GITT measurement to be a 3.9 V polyanion-type cathode materials for Li-ion batteries. Its electrochemical activity can be enhanced by addition of carbon. A discharge capacity of 105 mA·h/g (70% of theoretical value) was achieved for a m-LiFeSO₄F/CNT composite. Phase separation behavior during lithium extraction and insertion was observed by ex-situ XRD test.