Synthesis and characterization of nano-sized LiFePO4cathode materials prepared by a citric acid-based sol–gel route

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Abstract
LiFePO4/carbon composite cathode materials were synthesized by a sol–gel process. The citric acid in the developed sol–gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of LiFePO4 particles. Nano-sized LiFePO4 particles without the impurity phase were successfully synthesized. The grain size of LiFePO4 particles in the range of 20–30 nm is obtained at calcined temperatures from 450 to 850 °C. Increasing the calcination temperature leads to a decrease in the carbon content but an increase in the conductivity of the composites in the range of 400–850 °C. However, the conductivity slightly decreases if the calcination temperature further increases to 950 °C. The LiFePO4/carbon composite synthesized at 850 °C shows the highest conductivity (10−3 S cm−1), the highest specific capacity, and the best rate capability among the synthesized materials. It is worthy to note that the cell performance of the LiFePO4 depends on the electrochemical cycling procedure employed.