Effect of Particle Size of FePO4•2H2O on the Physical and Electrochemical Properties of LiFePO4/C Cathode for LIBs

Particle size is a very important factor for the electrochemical performance of materials. However, the effect of the particle size of FePO4·2H2O on the properties of LiFePO4 remains unclear during carbon thermal reduction using FePO4·2H2O as a raw material. Here, LiFePO4/C composites are synthesized by an aqueous rheological phase-assisted carbon thermal reduction method using FePO4·2H2O with different particle sizes as raw materials. The particle size of LiFePO4 is positively correlated with the particle size of FePO4·2H2O. The LiFePO4 materials prepared using small-sized FePO4·2H2O show high purity and small particle size, thus exhibiting an improved rate capacity of 160 mA h g–1 at 0.1 C and 135 mA h g–1 at 5 C and cycling stability with a capacity retention of 98.9% after 100 cycles at 2 C. Intriguingly, the LiFePO4 materials prepared using large-sized FePO4 show a longer slope voltage at the end of the discharge curve, which could be accounted for by an Fe3+ phase on the surface of the large-sized LiFePO4. Our studies provide a new understanding of the effect of the particle size of FePO4·2H2O on the properties of LiFePO4 materials during carbon thermal reduction.