Effects of particle size and carbon coating on electrochemical properties of LiFePO₄/C prepared by hydrothermal method

In this study, well-crystallized phase pure LiFePO₄/C (LFP/C) powders were synthesized using the hydrothermal reaction method. To improve the electronic conductivity of the LFP/C powder after ball-milling, the LFP/C powders were double-coated with carbon. Scanning electron microscopy and transmission electron microscopy were employed to observe the micromorphology of the samples and the carbon coating, which was analyzed using Raman spectroscopy. Furthermore, the electrochemical properties were evaluated using cyclic voltammetry, electrochemical impedance spectra, and the charge–discharge cycling test. The ball-mill and the process for double-coating carbon decrease the particle size and increase the conductivity of the LFP/C, thereby reducing the Li-ion diffusion length and improving the reversibility of the Li-ion intercalation/de-intercalation in the LFP/C crystallites. The capacity of the small-particle LFP/C with the double-layer carbon coating was 133 mAh/g at 0.1 °C, and remained at 83 mAh/g as the charge–discharge rate increased to 10 °C. In addition, good cycle stability was observed, with a retention rate of 98 % after 50 cycles at 1 °C.