Study On Liquid-phase Synthesis And Electrochemical Performance Of LiFePO₄ As Cathode Material

Olivine-structured Li FePO4 is considered as one of promising cathode materials for lithium-ion batteries due to its advantages such as abundant raw materials, high capacity,good cycle performance, preferable safety and environmentally friendliness. LiFePO4 as the research target, this paper adopted liquid phase synthesis and studied the affecting factors and the material modification.To the production of Li FePO4, the reaction liquid circulation and post-treatment explored.The cathode material Li FePO4 was synthesized by liquid phase synthesis, using FeSO4·7H2O,NH4H2PO4,H2O2, CH3 COOLi and glucose as raw materials. The precursor FePO4 is prepared by FeSO4 and NH4H2PO4 which is 0.05mol/L,0.1 mol/L,1mol/L,1.2mol/L,respectively. The structure, morphology and electrochemical performance of the material were analyzed by XRD,SEM,EDS and galvanostatic charge/discharge tests. The result suggests that LiFePO4 which was prepared by the precursor FePO4·xH2O at 1 mol/L, exhibited the best initial discharge capacity of 157.2 mAh·g-1 at 0.1C.LiFePO4 on the surface modification is coated by kinds of carbon conductive agents. The results showed that with polyethylene glycol 400 as carbon source, the carbonized material particle size decreases and the initial discharge capacity is 159.9 mAh·g-1at 0.1C. With glucose as carbon source, LiFePO4/C is 146.9 mAh·g-1 for the initial discharge capacity at 0.1C.LiFePO4 is modified by the ion doping. With MgO, V2O5 as the raw materials, LiFe1-x MxPO4 is synthesized. According to the structure ? the electrochemical performance and the spectroscope, the result showed that the ion doping is successful. The initial discharge capacity is137.9 mAh·g-1,139.0 mAh·g-1 for Mg2+, V5+.In addition, we study the reaction liquid circulation in liquid phase synthesis. The reaction liquid can be directly used in the synthesis of FePO4·xH2O without any treatment and the ethanol should be distilled before the synthesis of LiFePO4. The results showed that the high purity of FePO4·xH2O can be achieved even prepared with the aqueous which was used for five times. LiFePO4 cathode material prepared with the distilled ethanol exhibited the best initial discharge capacity of 156.3 mAh·g-1 and the capacity retention ratio 99.49% after 30 cycles at 0.1 C rate.