Synthesis And Modification Of La_0.7Sr_0.3MnO₃ Coated LiFePO₄/C Cathode Materials

LiFePO₄/C composite materials were synthesized in a reducing atmosphere with the precursor prepared by sol-gel method. Metal oxide La_0.7Sr_0.3MnO₃ was selected as the co-coating material for LiFePO₄/C particals to improve the electrochemical properties. The microstructure and morphologies of these composites were investigated by XRD and TEM. The electrochemical performances were evaluated by galvanostatic charge-discharge, impedance spectroscopy and cyclic voltammogram after the materials were assembled into button cells.In order to study the influences of LSM coating, the composite materials with different amounts of LSM and carbon were synthesized. The amounts of LSM additive were between 3 wt% and 9 wt%. The results indicated that the co-coating of carbon and LSM could greatly enhance the electrochemical performances of LiFePO₄, especially when the content of LSM was 6 wt%. The material with 6 wt% LSM showed the highest discharge capacity of 141.5 mAh·g^-1, 120.1 mAh·g^-1, 99.9 mAh·g^-1 and 80.7 mAh·g^-1 at 0.1C, 0.2C, 0.5C and 1C, respectively, while the material without LSM merely showed 119.0 mAh·g^-1, 47.1 mAh·g^-1, 26.6 mAh·g^-1 and 20.6 mAh·g^-1.The advantage of LSM coated material was remarkable at high charge/discharge rates. The material with 7 wt% LSM delivered excellent cycle performance at 0.1C. After 10 cycles the capacity remained to be 126.1 mAh·g^-1, with the capacity loss ratio being 2.8%. At 1C rate, the cycle performance of the material with 6 wt% LSM was outstanding. The capacity loss was only 4.6% after 10 cycles. The three cyclic voltammogram curves of material with 3% LSM were almost overlapping, demonstrating that the continuous integrated LSM conductive layer between LiFePO₄ particles resulted in negligible polarization during cycling.