Excellent cycle performance of Co-doped FeF3/C nanocomposite cathode material for lithium-ion batteries

Fe1-xCoxF3 (x = 0, 0.03, 0.05, 0.07) compounds are synthesized via a liquid- phase method. To further improve their electrochemical properties, a ball milling process with acetylene black (AB) has been used to form Fe1-xCoxF3/C (x = 0, 0.03, 0.05, 0.07) nanocomposites. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), charge-discharge tests, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and the galvanostatic intermittent titration technique (GITT). It is found that Co-doping significantly improves the electrochemical performance. Fe0.95Co0.05F3/C exhibits excellent electrochemical performance with discharge capacities of 151.7, 136.4 and 127.6 m Lambda h g(-1) at rates of 1C, 2C and 5C in the voltage range of 2.0-4.5 V vs. Li+/Li, and its capacity retentions remain as high as 92.0%, 92.2% and 91.7%, respectively, after 100 cycles. Co-doping could decrease the charge transfer resistance, increase the lithium diffusion coefficient during the lithiation process and improve the electrochemical reversibility. The preparation of Co-doped FeF3/C offers a new method to improve the performance of FeF3: cationic doping, which is a significant step forward for developing high-power lithium batteries.