The cycling performance of LiFePO 4/C cathode materials

Abstract

Olivine LiFePO 4/C cathode materials were synthesized by carbothermal reduction method at different temperatures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), particle size analysis and charge–discharge test. The results showed that both the crystallization degree and particle size increased remarkably with the synthesis temperature increasing. The LiFePO 4/C synthesized at 750 °C showed a highest initial discharge specific capacity of 145 mA hg −1 at 1C rate, which decreased to 60 mA hg −1 after 500 cycles. However, the sample prepared at 850 °C exhibited a lower initial discharge capacity of 135 mA hg −1 at 1C rate, whose capacity could also reach 105 mA hg −1 after 500 cycles. The material synthesized at lower sintering temperature had lower crystallization degree and plenty of nano-sized microstructure, leading to its higher electrochemical activity and initial discharge capacity. But at the same time, the lower sintering temperature also leads to the instability of the crystal structure and the solution of active materials, which results in the degradation of discharge capacity on long-time cycling. In short, synthesizing the material with perfect crystallization degree and moderate particle size is an effective way to improve the cycling performance of LiFePO 4/C cathode materials.