Iron trifluoride synthesized via evaporation method and its application to rechargeable lithium batteries

Abstract

Facile synthesis of rhombohedral type FeF3 introduced via two consecutive steps is introduced: i) acidic treatment of Fe2O3 followed by thermal evaporation at 80 degrees C resulting in hydrated beta-FeF3 center dot 3H(2)O and ii) a simple thermal decomposition of the as-received beta-FeF3 center dot 3H(2)O at 400 degrees C under an Ar atmosphere. A Rietveld refinement of x-ray diffraction data for the as-synthesized FeF3 indicates the formation of a highly crystalline FeF3 structure with a R (3) over barc space group. To overcome the high ionicity and improve the diffusivity, FeF3 is ball-milled with the aid of carbon (acetylene black). The electrochemical performance of nanosized FeF3 is not favored in voltage range of 1.5-4.5 V because the repetitive intercalation-conversion reaction accelerates the structural disruption within a few cycles, although a high capacity (518 mAh (g-fluoride)(-1) at 20 mA g(-1)) is observed, assisted by the three-electron redox of Fe3+/0. Raising the lower cut-off voltage to 2 V. which allows only intercalation reaction, the FeF3 delivers a high capacity of 224 mAh g(-1) with significantly improved capacity retention (71% at 100th cycle).