Synthesis And Modification Research Of Li₂FeSiO₄ Cathode Materials

Polyanion cathode material, Li2 Fe Si O4 has several advantages such as high theoretical capacity, high security, abundant raw materials, environmental friendliness, thus it has been widely studied in the past decade. However, Li2 Fe Si O4 is a poor conductor of electrons and has slow lithium ion diffusion, impacting its practical application. In the paper, Li2 Fe Si O4 was selected as the research object. X-ray diffraction(XRD) was used to confirm the crystal structure. The microstructure of the materials was characterized by Scanning Electron Microscopy(SEM). Raman spectroscopy(Raman) was used to test the structure of the coated carbon. Galvanostatic charge-discharge was carried out to test the electrochemical properties Electrochemical impedance spectra(EIS) were measured.First, lithium ion battery cathode materials Li2 Fe Si O4 was prepared by ordinary drying and vacuum freeze-drying assisted sol-gel, studying the effects of two drying methods on the physical characteristics and electrochemical performance of the material. It was found that the freeze-dried materials had a better electrochemical prformance, because the freeze-dried material obtained had better dispersion, smaller particles, larger surface area and smaller resistance value compared to the material obtained by ordinary drying,.Li2Fe Si O4 was synthesized by microwave-assisted method. The morphology was controlled by adjusting the ratio of raw material and microwave temperature. It was found that the proportion of raw materials and the microwave temperature have little effect on the morphology, being spherical. Therefore, only the material obtained by microwaving for 1 h at 180 ° C at 1: 6 of the Fe / Li were modified by carbon-coated to improve the electrochemical properties. At the low rate, 0.2 and 0.5 C, the more the carbon content, the better the electrochemical performance. However, at the high rate,2, 5 and 10 C, the sample of 10.21% carbon content had the most discharge capacity, being 42.12, 91.37 and 73.37 m Ah g-1, respectively.