Synthesis And Study Of Sr_0.85 Ce_0.15 CoO_3-δ And Carbon Co-coated LiFePO 4 Cathode Materials

Metal oxide Sr_0.85Ce_0.15CoO_3-δ(SCC) was synthesized by a gel combustion method. SCC and carbon co-coating LiFePO₄ was prepared by liquid phase method and solid state method. The microstructure and morphologies of these composites were investigated by XRD, TEM and SEM. The TEM and SEM showed that the SCC uniformly distributed on the surface of LiFePO₄ particles and filled the gaps of the carbon coating layer. The electrochemical performances were evaluated by galvanostatic charge-discharge, impedance spectroscopy and potential step chronoamperometry after the materials were assembled into button cells.In order to study the influences of SCC coating, the composite materials with different amounts of SCC were synthesized. The amounts of SCC additive were between 1wt% and 6wt%. The results of galvanostatic charge-discharge indicated that the co-coating of SCC and carbon could improve the discharge capacity of LiFePO₄, especially at the high rates. The sample coated with 3wt% SCC showed the highest discharge capacity of 157mAh/g, 149mAh/g, 142mAh/g, 137mAh/g, 120 mAh/g and 94 mAh/g at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, respectively, while the material without SCC merely showed 153mAh/g, 144mAh/g, 136mAh/g, 120mAh/g, 102mAh/g and 65mAh/g. The SCC and carbon co-coating could improve the rate performance of LiFePO₄. The sample with 3wt% SCC showed the best cycle performance. The capacity loss ratio was 41.9% after 55 cycles, while the capacity loss ratio of uncoated sample was 58.6%.The results of impedance spectroscopy indicated that coated with SCC could decrease the Rct of LiFePO₄. The Rct of sample coated with 3wt% SCC was 49?. The lithium ion diffusion coefficient was calculated though potential step chronoamperometry measurement. The results revealed that the 3wt% SCC coating sample had the highest lithium ion diffusion coefficient of 2.26×10-9cm2·s-1.