Synthesis of high rate performance LiFe1−xMnxPO4/C composites for lithium-ion batteries

A series of LiFe1−xMnxPO4/C composites (x=0, 0.1, 0.3, 0.5, 1) are synthesized via an ion exchange method, utilizing LiOH·H2O, FeSO4·7H2O, MnSO4·H2O, Na3PO4·12H2O, and H3PO4 as the raw materials, citric acid as the carbon source, and reductant, and H2O as the solvent. The composites containing Mn have larger lattice parameters compared to pure LiFeMnPO4/C, due to the larger ionic size of Mn2+ compared to Fe2+. The composites also consist of spherical nanoparticles with a thicker carbon coating. LiFe0.9Mn0.1PO4/C exhibited the best electrochemical properties as the cathode in lithium-ion batteries, with a discharge capacity close to the theoretical value of LiFePO4, better capacity retention rate (98.5% vs. 94.5%) and excellent cycle stability. The improvements were attributed to the Mn-complex. Electrochemical impedance spectra demonstrate that the Mn-composites can improve electronic and ionic conductivity, indicating that introduction of Mn is a viable way to improve the conductivity in olivine-like LiFePO4 cathode materials, and enhance the battery performance.