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

Abstract A series of LiFe 1−x Mn x PO 4 /C composites (x=0, 0.1, 0.3, 0.5, 1) are synthesized via an ion exchange method, utilizing LiOH·H 2 O, FeSO 4 ·7H 2 O, MnSO 4 ·H 2 O, Na 3 PO 4 ·12H 2 O, and H 3 PO 4 as the raw materials, citric acid as the carbon source, and reductant, and H 2 O as the solvent. The composites containing Mn have larger lattice parameters compared to pure LiFeMnPO 4 /C, due to the larger ionic size of Mn 2+ compared to Fe 2+ . The composites also consist of spherical nanoparticles with a thicker carbon coating. LiFe 0.9 Mn 0.1 PO 4 /C exhibited the best electrochemical properties as the cathode in lithium-ion batteries, with a discharge capacity close to the theoretical value of LiFePO 4 , 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 LiFePO 4 cathode materials, and enhance the battery performance.