Synthesis And Modification Of Nano LiFePO₄as Cathode Materials

The olivine-structured orthophosphate LiFePO₄has been regarded as the mostpromising and popular in cathode material next generation for lithium-ion batteriesbecause of its high operating voltage, good circulation, low prince, environmental friendlyand safety. However, pure LiFePO₄shows poor reversible capacity performance andcharging/discharging performance at big rate. In recent years, Researchers are trying tocontrol material particle size, carbon coated, add conductive polymer, doping metal cationand halogen ion, and other ways to improve the performance of LiFePO₄, and haveachieved good results.In this paper, LiFePO₄/C cathode materials prepared by solid-phase sintering,researched process route of the synthesis, and based on this studied the low and highvalence metal cation doping. The thermal stability of LiFePO₄was analyzed by TG-DTA;The structure and morphology of the materials were characterized by XRD, Raman, SEM.The Electrochemical performance of the materials was tested by Constant currentcharge/discharge cycling test, CV and EIS.Experimental results show that the preparation material showed good structure，nonoise peaks with the1.02%Li content。With the increased amount of lithium began toproduce a little noise peaks. The discharge capacity is139.2mAh/g at0.2C.Na-doping basis, found that two step process relative step process, and has bettercrystalline and smaller particle size. Doping Na-3%crystallinity samples most neat, in0.2C reached127.7mAh/g at the initial discharge capacity. Relative to no-doping samples.Na with promote particle size, structure tends to reduce material neat effect.V-doping LiFePO₄samples can also improve the electrochemical properties. Doping7%V samples have the highest charge/discharge specific capacity and the bestperformance of the circulation rate, and for the first time discharge specific capacity for139.4mAh/g. V-sample charge/discharge platform of doping is bad, not enough flatstability. Compared with Na/V mix, were mixed in two ways. Mix-doping samples Na/V（1:4）showed the highest charge/discharge specific capacity of135.2mAh/g. However, Itshowed the worst cycle stability after50times cycle, only86.5%of the specific capacityfor the first time. With3%of co-doping samples performance is excellent, the initialdischarge specific capacity is146.0mAh/g,5C big electricity flowing down to95.3mAh/g. Two ways has certain influence each other.For Process improvement by carbon-encapsulated found that in common with largesample influence other doping are have very good rate of performance.