Synthesis And Modification Of La_0.6 Sr_0.4 CoO_3-δ Coated LiFePO ₄ /C Composite Cathodes

In order to improve the electrochemical properties of LiFePO₄/C, the surfaces of LiFePO₄/C particles were coated with highly conductive metal oxide La0.6Sr0.4CoO3- (LSC). The effects of LSC coating were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy, potential step chronoamperometry and cyclic voltammetry. The results of HRTEM and XRD showed that the incomplete carbon network could be repaired by nanometer-sized LSC while the co-coated composite retained the structure of LiFePO₄.LiFePO₄/C/LSC composite materials with different amounts of LSC were made via a suspension mixing method. The amounts of additive LSC were between 1wt.% and 6wt.%. The LSC coating could greatly enhance the electrochemical performances of LiFePO₄/C, especially when the content of LSC was 4wt.%. The 4wt.% LSC-coated LiFePO₄/C sample exhibited the best electrochemical performance with discharge capacities of 156.5mAh·g^-1, 151.6mAh·g^-1, 144.5mAh·g^-1, 136.6mAh·g^-1, 125.4mAh·g^-1 and 95.9mAh·g^-1 at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, respectively. The material without LSC merely showed 153.3mAh·g^-1, 144.1mAh·g^-1, 136.0mAh·g^-1, 120.2mAh·g^-1, 102.1mAh·g^-1 and 65.0mAh·g^-1. Via suspension mixing method, appropriate amount of LSC coating could improve the electrochemical performances, especially at high rate.LiFePO₄/C/LSC composite materials with different amounts of LSC were made via a ball mill mixing method. The amounts of additive LSC were 2wt.%, 3wt.% and 4wt.% when ZrO2 grinding balls were adopted. The amounts of additive LSC were 4wt.% when conductive metal grinding balls were adopted. Among all the samples made by ball mill mixing method, the 4wt.% LSC-coated LiFePO₄/C sample which was made using ZrO2 grinding balls exhibited the best electrochemical performance with discharge capacities of 152.3mAh·g^-1, 145.6mAh·g^-1, 137.2mAh·g^-1, 129.5mAh·g^-1, 117.3mAh·g^-1 and 84.9mAh·g^-1 at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, respectively. Via ball mill mixing method, appropriate amount of LSC coating could improve the electrochemical performances at high rates.