Synthesis of LiMn_(0.7)Fe_(0.3)PO_4/C Composite Cathode Materials for Lithium-ion Batteries

摘要

LiMn_(0.7)Fe_(0.3)PO_4/C composite cathode material was prepared by using a solid state reaction method. The effects of annealing temperatures on the structural and electrochemical performance of LiMn_(0.7)Fe_(0.3)PO_4/C were investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), charge-discharge tests and electrochemical impedance spectra (EIS). The results showed that all of samples have pure ordered olivine phase with orthorhombic Pnma structure. The electrochemical performance of LiMn_(0.7)Fe_(0.3)PO_4/C can be improved remarkably with increasing temperature from 550°C to 650°C due to increased crystallization, cation-order and decreased charge transfer resistance. However, increase temperature to 700°C leads to bigger crystal particle size and decreased cation-order, thus higher resistance and deteriorated electrochemical properties. The sample prepared at optimized temperature of 650°C presents a remarkable improved electrochemical performance. It delivers an initial capacity of 125.1 mAh·g~(-1) at 0.2C, 95 mAh·g~(-1) at 5C, and a capacity retention of 98.0% after 30 cycles.