Synthesis And Electrochemical Properties Of One-dimensional Core-shell Structure LiFePO₄/C Composite

The key of energy conversion and storage are the advance and development of new materials, and both of them are vital in order to meet the challenges of global warming and the finite nature of fossil fuels. One of the great challenges in the 21 st century is unquestionable energy conversion and storage. Lithium-ion batteries are used as an effective tool for energy conversion, because of their high energy density and high electromotive force, and got widespread attention.In this paper, Fe C2O4·4H2O, H3PO4, Li Ac·2H2O and biological carbon fibers were acted as raw materials. Li Fe PO4/C composites with one-dimensional core-shell structure were successfully synthesized via evaporated self-assembly assisted by biological carbon fibers at room-temperature. The structure, morphology and composition of the as-prepared products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and thermogravimetric analysis(TG). In the experiment, the optimum conditions for lithium iron phosphate calcination were at 700°C in 15 hours.This paper explored the positive roles of cotton, catkins and PVA content for the synthesis of one-dimensional core-shell structure of Li Fe PO4/C composite. Through adjusting the content of the carbon, we synthesized Li Fe PO4/C composite with one-dimensional core-shell structure. When cotton was aced as the carbon source, the electrochemical properties of the material increased with the increase of cotton content. The battery had better electrochemical performance when the content of cotton was 5%, meanwhile the initial discharge capacity reached 159 m Ah·g-1 and the cycling performance was significantly higher than the other conditions. According to the images of SEM, a smaller and more uniform liner structure was got in catkins experiments. Meanwhile, when the catkins content is 5%, the electrochemical performance is better than other conditions, which the initial discharge capacity is 162 m Ah·g-1. When PVA acts as carbon source, by adjusting the control content of PVA, Li Fe PO4/C nanowires was successfully synthesized. Analyzed by SEM, it is obvious that uniform nanowires and better electrochemical performance can be got when the content of PVA was 6 wt%. In the cycle performance curve, it still shows excellent electrochemical performance even at as high as 20 C rate. The addition of PVA also has an important influence on the electrochemical capability based on the CV and EIS.