Study On The Synthesis And Electrochemical Performance Of Polyanionic-based LiFePO₄ /C And Li₂ FeSiO₄ /C Cathode Materials

Polyanionic-based LiFePO₄ is considered as the promising candidate for the next-generation cathode materials of Li-ion batteries because low raw material cost, environmental friendliness, high theoretical specific capacity, good cycle performance and excellent safety. Recently, polyanionic Li₂FeSiO₄ is developed as a new class of safe cathode materials for lithium ion batteries, which has similar crystalline structure, chemical and thermal stability with LiFePO₄. Furthermore, with more abundant resources, lower raw materials cost, and being more environmentally friendly than LiFePO₄, the Li₂FeSiO₄ holds great attraction as potentially cheap cathode material.In this paper, LiFePO₄/C and Li₂FeSiO₄/C cathode materials were prepared by sol-gel method and solid state reaction method, the effects of calcination temperature, calcination time, cabron source, carbon amount on morphology and electrochemical properties of LiFePO₄/C and Li₂FeSiO₄/C cathodes were investigated by scanning electron microscope (SEM), X ray diffraction (XRD), galvanostatic charge-discharge cycling, elecrochemical impedance spectra (EIS) and cyclic voltammogram (CV), respectively.LiFePO₄/C cathode materials were prepared by sol-gel method in which the glycine was first used as chelating agent, and the effect of calcination temperature, calcination time, cabron source, carbon amount on morphology and electrochemical properties of LiFePO₄/C were investigated. The results showed that the particle size of LiFePO₄/C increases with the increasing calcination temperature and the time of heat-treatment, but it reduces with the increase of carbon amount. The material prepred at 700oC for 12 h and used sucrose as cabron source has the best electrochemical properties with a specific capacity of 162 mAh g^-1 at 0.1 C, and 158 mAh g^-1 has been maintained after 20 cycles.LiFePO₄/C cathodes were also prepared by improved solid state reaction, and the effect of calcination temperature, calcination time, cabron source, carbon amount on morphology and electrochemical properties of LiFePO₄/C were investigated. The results showed that the particle size increases with increasing the temperature and time of heat-treatment, but it reduces with the increase of carbon amount. The material prepred at 750oC for 14 h and used sucrose as cabron source has the best electrochemical properties, which presents 155,145,139,132,120,85 mAh g^-1 at 0.1,0.2,0.5,1,2,5 C.Li₂FeSiO₄/C cathode materials were prepared by sol-gel method, the effects of calcination temperature, calcination time, carbon amount on morphology and electrochemical properties of Li₂FeSiO₄/C cathodes were investigated. The results showed that the material prepred at 650oC for 12 h has the best electrochemical properties, which presents 150 mAh g^-1 at 1/16 C, and a specific capacity of 97% has been maintained after 20 cycles.