Preparetion And Modification Of LifePO₄/C Cathode Material For Li-ion Batteries

LiFePO₄is becoming the most promising positive material of lithium battery due toits high theoretical capacity, safety, environmental friendship, rich resource. But itsweakness, low electronic conductivity and Li-ionic diffusion, restricts its property.LiFePO₄/C is synthesized by the carbothermal reduction method combining withstar-balling technique and modification, doping and coating, is applied to overcome itsdisadvantage, as well as improve the electrochemical performance of LiFePO₄. Thestructure, pattern and component of modified LiFePO₄/C are studied by X-ray diffraction（XRD）, field-emission scanning electron microscopy （FE-SEM）, transmission electronmicroscopy （TEM）, energy dispersive spectrometer （EDS）, micro-roman spectroscopy andX-ray photoelectron spectroscopy （XPS）. The electrochemical performance of the materialelectrode is analyzed by galvanostatioc charge/discharge, cycle voltammetry （CV） andelectrochemical impedance spectra （EIS）Electrode materials are modified by vanadium and magnesium through doping andcoating, and effects of additive content on LiFePO₄/C are systematically analyzed.Comparing two kinds of vanadium modification, coating is more effective than doping onimproving the electrochemical property of LiFePO₄material. The electrochemicalperformance of LiFePO₄is obviously improved by coating with small amount of V₂O₃.LiFePO₄/C-V₂O₃（1.0mol%） shows the most excellent performance, whose first dischargecapacity is160.1mAh/g at1C rate. Only a little of vanadium steps into LiFePO₄lattice inV-doped samples, and a few kinds of vanadium compositions are prepared when thevanadium content is over1.0mol%. The improvement of electrochemical performanceresults from the presence of impurity phases, which is similar to vanadium coating. MgOcoating is superior in terms of improving cyclic performance of LiFePO₄electrode, whileMg-doping is more prominent on prompting the capacity and rate capability of LiFePO₄material. The specific capacity and rate capability are efficaciously enhanced by a smallamount of Mg doping and the discharge capacity of Li_0.985Mg_0.015PO₄/C is increased to161.9mAh/g. It indicates that different influence may produce by different modified way for the same substance.