Impact of Synthesis Conditions and Carbon Source on the Voltage Polarization Growth of Lithium Manganese Iron Phosphate

A high-performance LiMn0.8Fe0.2PO4 (LMFP82)-positive electrode material is prepared using a simple surfactant-assisted synthesis method. Polyvinylpyrrolidone (PVP) is used as a surfactant and carbon source that leads to a thin and uniform carbon coating on the surface of nanosized LMPF82 primary particles. The synthesis parameters were varied systematically to clarify the effects of carbon content and calcination temperature on the electrochemical performance of these LMFP82 materials. The best performing LMFP82 sample, made with 20 wt % initial PVP content and calcined at 700 °C, showed a high initial discharge capacity of 155 mAh g–1 at 0.05C to 4.2 V, impressive rate performance with 142 mAh g–1 at 5C and 30 °C, high cycling stability with no capacity fade after 100 cycles at 0.2C, and low voltage polarization that remains stable over cycling. This study shows that the amount of carbon precursor impacts the specific capacity but not the voltage polarization growth, when within reasonable bounds (10–30 wt %). The calcination temperature on the other hand affects both specific capacity and voltage polarization growth and needed to be carefully optimized to 700 °C for optimal performance.