Electrochemical Behavior of Iron(III) Fluoride Trihydrate as a Cathode in Lithium‐Ion Batteries

Abstract

Abstract The tetragonal compound FeF 3 (H 2 O) 3 is synthesized through a facile liquid‐phase method. FeF 3 (H 2 O) 3 /C is prepared by mechanical milling with carbon black and investigated for its application as a cathode material. This material exhibits two types of thermodynamic lithiation scheme, at 3.0 and 1.5 V, which correspond to a Li + ‐intercalation process (1 Li + ) and a conversion reaction (>1 Li + ), respectively. A reversible capacity of about 300 mAh g −1 can be achieved at a current density of 10 mAg −1 . In particular, the intercalation/deintercalation process above 2.0 V exhibits good cycling performance and rate properties. The relatively high diffusion coefficients ( D cv =7.27×10 −13 –1.07×10 −12 m 2 s −1 ) of Li + through the FeF 3 (H 2 O) 3 lattice are calculated by using the Randles–Sevcik equation, which reveal fast Li + ‐ion migration in this process. In contrast, the conversion reaction is strongly dependent on the current density. Electrochemical impedance spectroscopy indicates that the FeF 3 (H 2 O) 3 /C cathode forms a relatively stable solid electrolyte interphase film, with a low Schottky contact resistance in comparison with that of the FeF 3 /C cathode, which makes it a potential candidate for cathode applications.