Jinli Tan

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 mA 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.

Sandwich-like cobalt sulfide–graphene composite – an anode material with excellent electrochemical performance for sodium ion batteries

Recently, sodium-ion batteries have been considered alternatives to lithium-ion batteries. However, the poor cycling performance and unsatisfactory rate capability of existing anodes hinder the development of sodium-ion batteries. Here we fabricate a sandwich-like cobalt sulfide–reduced graphene oxide (CoS/rGO) composite using a hydrothermal method as the anode material for sodium ion batteries. According to the SEM analysis, CoS nanoparticles anchor on both sides of the reduced graphene oxide nanosheets in such a way that the nanoporous structure with a large amount of void spaces can be prepared. And the cycling performance of the sandwich-like CoS/rGO composite is drastically enhanced compared with that of the bare CoS nanoparticles. After 100 cycles, the discharge capacity of CoS/rGO still remains at 230 mA h g−1, while the specific capacity of the bare CoS nanoparticles at the first cycle is 601 mA h g−1, dropping rapidly to 68 mA h g−1 after only 40 cycles. Furthermore, CoS/rGO gives an excellent rate capability even up to a large current of 2 A g−1. It is noted that the synergistic effect between CoS and graphene can contribute to the improved electrochemical performance.