The Controllable Synthesis And The Electrochemical Performance Of The LiFePO₄with Different Morphologies

In recent years, olivine LiFePO4has been considered as one of the most potential cathode materials for lithium ion batteries due to its several advantages such as low-cost, non-toxicity, excellent thermal stability and good cycle performance.This paper reviewed the research progress of olivine LiFePO4, then the LiFePO4of different morphologies were synthesized controllably, and their crystal structure, morphology and electrochemical performance were characterized.First, The LiFePO4nanorods were synthesized by a two-step method (hydrothermal in combined with solid-state reaction). The crystal structure、morphology and the electrochemical performance were characterized by X-ray diffraction SEM、TEM and electrochemical performance test. Results showed that the Fe3(PO4)2.H2O nanorods were synthesized as precursors by a facile hydrothermal method. Then olivine phase pure LiFePO4nanorods were synthesized based on the Fe3(PO4)2.H2O nanorods precursors by a solid-state method. The LiFePO4nanorods exhibited excellent high-rate performance, achieving a discharge capacity of125and104mAh/g at1C and5C, respectively.Secondly, A series of hollow LiFel-xMnxPO4compounds (with x=0,0.25,0.5,0.75,1) were synthesized by a facile hydrothermal reaction. The electrodes were characterized using X-ray diffraction to examine their crystal structure. Scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM) were employed to characterize the morphology of these materials. We demonstrated that the electrochemical performance of these compounds has been enhanced due to the single-crystalline hollow structure, and the energy density of these electrodes is increased with high Mn content. Further, the LiFe0.25Mn0.75PO4has a promising capacity of153mAh/g at C/10.Finally, the NH4FePO4·H2Oprecursors were synthesized by hydrothermal method, effects of the different reaction condition on the precursors crystal structure and morphology were investigated, the results show that the optimum condition of the precursor is synthesized at180℃ for1h by hydrothermal method. Then, the LiFePO4microplates was synthesized by hydrothermal method after the lithium acetate was added into the precursor reactor. Effect of the Li content on the product structure, morphology and electrochemical performance were investigated, the result shows that when the mol ratio of Li and Fe is5, the LiFePO4displays better structure、morphology and electrochemical performance.