The Preparation And Performance Study Of LiFePO₄/C As Cathode Materials In Lithium Ion Batteries

LiFePO4/C was synthesized with LiH2PO4,Fe2O3,C6H12O6·H2O and C3H8O3 by the method of high temperature mechanical chemistry.In order to improve the electrochemical performance of LiFePO/C,LiFePO/C(8 wt%)was modified by anion F-and cation Mg2+,Al3+,Ti4+,V5+when optimum amount of carbon coated was determined.Physical properties and electrochemical performances of products were characterized by X-ray diffraction(XRD),Transmission electron microscopy(TEM),scanning electron microscopy(SEM),laser particle size(PSD),charge-discharge test(CD),cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)etc.1.Experimental results show that LiFePO4/C(8 wt%)can achieve a initial discharge capacity of 144.23 mAhg-1,120.13 mAhg-1,97.02 mAhg-1 when discharge rates were set as 0.1C,0.5C and 1C.Moreover,after recycling 50 times,LiFePO4/C(8 wt%)still has a capacity retention ratio of 99.56%2.The proper doping amount of F-,Mg2+,Al3+ will improve the discharge capacity of products at high rate.The initial discharge capacities of LiFePO3.98F0.02/C,LiFe0.98Mg0.02PO4/C and LiFe0.99Al0.01PO4/C are 127 mAhg-1,129.406 mAhg-1 and 131.33 mAhg-1 at 0.5C,and the results of 1C are 118 mAhg-1,115.71 mAhg-1,117.06 mAhg-1.3.The proper doping amount of Ti4+,V5+can improve the discharge capacity of products both at high rate and low rate.The initial discharge capacities of LiFe0.98Ti0.02PO4/C and LiFe0.985V0.015PO4/C are 150.82 mAhg-1,159.275 mAhg-1 at 0.1C,and the results of 0.5C are 140 mAhg-1,137.21 Ahg-1,and the results of 1C are 125 mAhg-1,12.34 mAhg-1.