The facile in situ preparation and characterization of C/FeOF/FeF 3 nanocomposites as LIB cathode materials

Abstract

C/FeOF/FeF₃ nanocomposite was synthesized by a facile in situ partial oxidation method. High-resolution transmission electron microscopy (HR-TEM) showed a special texture comprised of interpenetrating nanodomains of FeOF and FeF₃. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that the introduction of nanodomain FeOF enhanced both the electronic and ionic conductivity of the composite material. Therefore, the improvement of electron and lithium-ion dynamics resulted in the significant enhancement of the electrochemical performances of the material at ambient temperature. At a current density of 20 mA g⁻¹ within potential range 1.5–4.5 V, the specific capacities of the first ten circles were maintained at about 400 mAh g⁻¹ _. This material also exhibited excellent cycling capacity retention capability especially for high C rates. When the current density further increased to 100 and 200 mA g⁻¹, a steady capacity of 80 and 60 mAh g⁻¹ was observed, respectively. Furthermore, nearly no capacity loss was observed for the followed cycles. The discharge platforms based on intercalation and conversion reaction were also heightened by about 0.4 V, which increased the contribution of high voltage capacities. Compared to C/FeF₃, C/FeOF/FeF₃ is showing more of capacitive behavior, which also contributes to the high specific capacity delivered and is believed to be closely related to the enlarged nanodomain interfaces between two electrochemical active materials. An expansion-cracking-oxidation mechanism was proposed to explain the formation of this interpenetrating nanodomains of FeOF and FeF₃.