Pulsed laser deposited iron fluoride thin films for lithium-ion batteries

Iron fluoride thin films were successfully grown by Pulsed Laser Deposition (PLD), and their physico-chemical properties and electrochemical behaviours were examined by adjusting the deposition conditions, such as the target nature (FeF2 or FeF3), the substrate temperature (Ts ≤ 600 °C), the gas pressure (under vacuum or in oxygen atmosphere) and the repetition rates (2 and 10 Hz). Irrespective of the FeF2 or FeF3 target nature, iron fluoride thin films, deposited at 600 °C under vacuum, showed X-ray diffraction (XRD) patterns corresponding to the FeF2 phase. On the other hand, iron fluoride thin films deposited at room temperature (RT) from FeF2 target were amorphous, whereas the thin films deposited from FeF3 target consisted of a two-phase mixture of FeF3 and FeF2 showing sharp and broad diffraction peaks by XRD, respectively. Their electrochemical behaviour in rechargeable lithium cells was investigated in the 0.05-3.60 V voltage window. Despite a large irreversible capacity on the first discharge, good cycling life was observed up to 30 cycles. Finally, their electrochemical properties were compared to the ones of iron oxide thin films.