Synthesis of Iron Phosphate Via Coprecipitation Method for LiFePO₄ Cathode

In this study, ferric phosphate precursors were prepared by controlling precipitation time, and the resulting LiFe PO₄ active materials were thoroughly investigated. Microscale LiFePO₄ cathode materials, designed for high energy density at the cell level, were successfully synthesized through a 10 h co-precipitation. As the reaction time increased, smaller primary particles were aggregated more tightly, and the secondary particles exhibited a more spherical shape. Meanwhile, ammonia did not work effectively as a complexing agent. The carbon coated LiFePO₄ (LiFePO₄/C) synthesized from the 10 h ferric phosphate precursor exhibited larger primary and secondary particle sizes, a lower specific surface area, and higher crystallinity due to the sintering of the primary particles. Enhanced battery performance was achieved with the LiFePO₄/C that was synthesized from the precursor with the smaller size, which exhibited the discharge capacity of 132.25 mAh·g^-1 at 0.1 C, 70 % capacity retention at 5 C compared with 0.1 C, and 99.9 % capacity retention after the 50th cycle. The better battery performance is attributed to the lower charge transfer resistance and higher ionic conductivity, resulting from smaller primary particle sizes and a shorter Li⁺ diffusion path.