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A new lithium-ion battery cathode material of LiF@C-coated FeF 3 ·0.33H 2 O 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 FeF 3 ·0.33H 2 O are investigated. We show that LiF@C-coated FeF 3 ·0.33H 2 O 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.

To prepare a hierarchical micro-nano structure FeF3·0.33H2O simply and economically, a one-pot method with dual surfactants was used. Scanning electron microscopy and a Fourier transformation infrared spectrometer revealed that polyvinyl pyrrolidone (PVP) regulates the morphology of the material, while cetyltrimethylammonium bromide (CTAB) can reshape FF@PVP, it can not only remove PVP at room temperature, but also obtain a hierarchical micro-nano structure. The electrochemical results show that the hierarchical micro-nano structure FF(1.5CTAB 0.5PVP) has the best electrochemical performance. It maintained a high specific capacity of 109.4 mAh g−1 after 100 cycles at 1 C. In particular, under the ultra-high rate discharge of 20 C, the ultra-high specific discharge capacity of 66.4 mAh g−1 was reached. The FF(1.5CTAB 0.5PVP)’s excellent electrochemical performance is mainly due to a large contact area between the electrolyte and active materials.

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