Double role of silicon in improving the rate performance of LiFePO 4 cathode materials

LiFeP 1- x Si x O 4 /(C + y Li 2 SiO 3 ), (0 ≤ x ≤ 0.04, 0 ≤ y ≤ 2%) composites with a particle size of about 200 nm were synthesized via a simple solid state route. In this work, silicon plays double roles-silicon doping in lattice to enhance the electronic conductance of LiFePO 4 , meanwhile Li 2 SiO 3 with high Li-ion conductivity and carbon hybrid coating can decrease the interface resistance between LiFePO 4 grain and electrolyte. In this work, starch and TEOS were used as carbon source and the silicon source respectively. XRD, SEM, TEM, EIS and galvanostatic charge-discharge test are used to characterize these samples. The effects of the modification on the microstructure and electrochemical performances of LiFePO 4 cathodes at 25 °C are systematically investigated. The results show the sample with x = 0.03 and y = 1.0 wt % exhibits excellent rate capacity and cycle performance among the investigated materials. Based on half-cell testing, the best sample achieves a high special discharge capacity of 119 mAh g −1 at 5C rate and a capacity of 94 mAh g −1 at the 10C rate with an excellent cycle life in the usual cycling voltage range 2.5–4.2 V. EIS result demonstrates that the R ct of the samples decrease greatly due to the modification of LiFePO 4 via doping and coating.