Preparation And Modification Of LiFePO₄as Cathode Materials For Lithium-ion Batteries

Lithium iron phosphate (LiFePO4), as a cathode material for lithium ion batteries, with olivine structure have many advantages, such as high capacity, a perfectly flat voltage, thermal stability and good cyclic stability, low cost and environmentally. The development of communication equipment and electric vehicle make new requirement on lithium ion batteries for cycling stability and high power capacity. Nonetheless, LiFePO4still have three inherently weakness, which are low electronic conductivity, low tap density and low lithium ion diffusivity. So as to overcome the defects, the first way is to optimized methods to prepare small size particles of LiFePO4, the second methode is to coat electronical conductive materials (metal powder and carbon), the third method is that doping metal ions into Li or Fe site which can enhance the intrinsic electronic conductivity. Using solid state reaction to synthetize LiFePO4and modified the samples by metal ion doping and carbon coating. The samples were characterized by XRD, SEM, TEM, EIS CV methodes.1、LiFePO4/C cathode materials was synthesized for lithium rechargeable batteries by two step ball-milling and high tempetature solid state reaction, using FeC2O4·H2O, LiH2PO4as raw materisls and anthracene as carbon source. The LiFePO4/C composite with3.86%carbon content exhibited the best electrochemical performance.2、Series of Li(1-x)NaxFePO4/C (x=0.01,0.03,0.05) and LiFe(1-y)VyPO4/C (y=0.01,0.03,0.05) samples were synthesized by solid state reaction., The charge and discharge tests show that Li0.97Na0.03FePO4/C and LiFe0.97V0.03PO4/C displayed perfect electrochemical performance and stabilities. After discharge100cycles at5C, about100.68%and101.88%of the capacity is maintained.3、Series of Li(1-x)NaxFe(1-y)VyPO4/C (x=0.01y=0.01, x=0.03y=0.01, x=0.01y=0.03, x=0.03y=0.03) samples were synthesized by solid state reaction. Compared with Li0.97Na0.03FePO4/C and LiFe0.97V0.03PO4/C, Li0.99Na0.01Fe0.97V0.03PO4/C showed the best electorchemical properties. The capacity of Li0.99Na0.01Fe0.97V0.03PO4/C was152.5mAh/g at0.5C, After charge and discharge100cycles at10C, about98.8%of the capacity is maintained.