High-Performance LiF@C-Coated FeF₃·0.33H₂O Lithium-Ion Batteries with an Ionic Liquid Electrolyte

A new lithium-ion battery cathode material of LiF@C-coated FeF₃·0.33H₂O of 20 nm primary particles and 200-500 nm secondary particles is synthesized. The redox reaction mechanisms of the new cathode material and the influence of different electrolytes on the electrochemical performance of LiF@C-coated FeF₃·0.33H₂O are investigated. We show that LiF@C-coated FeF₃·0.33H₂O using a LiFSI/Pyr_1,3 FSI ionic liquid electrolyte exhibits high reversible capacities of 330.2 and 147.6 mAh g^-1 at 200 and 3600 mA g^-1, respectively, as well as maintains high capacity over cycling. Electrochemical characterization shows that the high performance is attributed to higher electronic conductivity of the coating, continuous compensation of the loss of LiF product through the coating, higher ionic conductivity of both the coating and the electrolyte, and higher stability of the electrolyte.