Iron fluoride with excellent cycle performance synthesized by solvothermal method as cathodes for lithium ion batteries

Hollow prismatic/cylindric iron fluoride with a wall thickness of 0.1-0.5 μm and a length of 1-3 μm has been synthesized by a simple and mild solvothermal method. This compound with a mixed crystal structure of FeF3·3H2O and FeF3·0.33H2O, has an initial discharge capacities of 106.7 mAh g−1 and a capacity retention of 60% after 100 cycles at the rate of 0.5C (1 C is 237 mA g−1) in the voltage of 2.0-4.5 V. To overcome the poor electronic conductivity of fluorides, the as-prepared iron fluoride has been ball-milled with 15 wt.% acetylene black (AB) and heat-treated to obtain FeF3·0.33H2O/C nanocomposites. The nanocomposites deliver discharge capacity of 160.2 mAh g−1 at the rate of 0.5C. Even at the high rate of 5 C, the initial discharge capacity is still as high as 137.5 mAh g−1. The capacity retentions reach up to 85.0% and 75.7% after 100 cycles at 0.5 C and 5 C, respectively.