Effects of Fe2P and Li3PO4 additives on the cycling performance of LiFePO4/C composite cathode materials

In this study, a solution method was employed to synthesize LiFePO4-based powders with Li3PO4 and Fe2P additives. The composition, crystalline structure, and morphology of the synthesized powders were investigated by using ICP-OES, XRD, TEM, and SEM, respectively. The electrochemical properties of the powders were investigated with cyclic voltammetric and capacity retention studies. The capacity retention studies were carried out with LiFePO4/Li cells and LiFePO4/MCMB cells comprised LiFePO4-based materials prepared at various temperatures from a stoichiometric precursor. Among all of the synthesized powders, the samples synthesized at 750 and 775 °C demonstrate the most promising cycling performance with C/10, C/5, C/2, and 1C rates. The sample synthesized at 775 °C shows initial discharge capacity of 155 mAh g−1 at 30 °C with C/10 rate. From the results of the cycling performance of LiFePO4/MCMB cells, it is found that 800 °C sample exhibited higher polarization growth rate than 700 °C sample, though it shows lower capacity fading rate than 700 °C sample. For Fe2P containing samples, the diffusion coefficient of Li+ ion increases with increasing amount of Fe2P, however, the sample synthesized at 900 °C shows much lower Li+ ion diffusion coefficient due to the hindrance of Fe2P layer on the surface of LiFePO4 particles.