Effect of First-Stage Temperature on the Hydrothermal Synthesis of Flower-Like Lithium Iron Phosphate

A controllable synthesis of flower-like lithium iron phosphate LiFePO4 (LFP) was obtained via a two-stage heating during hydrothermal process. In the first stage, the temperature was held at 105 °C (LFP1), 120 °C (LFP2), 150 °C (LFP3) and 190 °C (LFP4) for 5 h. In the final stage, the temperature was held constant at 400 °C under H2/N2 atmosphere for 4 h. To increase the electrochemical reversibility and electronic conductivity, LFP is treated with polyethylene glycol (PEG) as the templating agent and carbon sources for the as-prepared materials. This is to obtain a modified LFP cathode with optimum electrical contact between the electroactive materials and the carbon-filled electrode matrix which is found to be effective in terms of raising the electrochemical performance of the Li-ion batteries. Results show that as the first-stage temperature increased, the corresponding electrochemical performance of the resulting sample has been increased up to a temperature of 150 °C. Galvanostatic charge-discharge test indicates that flower-like LiFePO4/C composite, LFP3, exhibits initial discharge capacity of 118 mAh g-1 at 0.1C rates. The performance improvement was attributed to a reduction of the thickness and particle size of the flower-like LiFePO4 particles. Results of X-ray diffraction (XRD) revealed that the structure of the latter represents phase of the ordered olivine structure without any impurities. Cyclic voltammetry indicates that the improvement in redox cycling could be attributed to an increase of the electrochemical active surface area (ECSA) and the related increase in microporosity as evidenced by SEM analysis.