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

Abstract

AbstractThe tetragonal compound FeF3(H2O)3 is synthesized through a facile liquid‐phase method. FeF3(H2O)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 (Dcv=7.27×10−13–1.07×10−12 m2 s−1) of Li+ through the FeF3(H2O)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 FeF3(H2O)3/C cathode forms a relatively stable solid electrolyte interphase film, with a low Schottky contact resistance in comparison with that of the FeF3/C cathode, which makes it a potential candidate for cathode applications.