Study On Preparation And Electrochemical Properties Of Lithium Ion Battery Electrode Materials Of Graphene And Lithium Iron Phosphate

Lithium ion batteries because of its fast charge/discharge process, nomemory, and high capacity have become the chief direction of the development ofnew energy. Lithium iron phosphate as the cathode material of lithium ion batteryhas wide raw material sources, friendly to the environment and safe, which hasgradually become the main material for power lithium ion battery. As the lithiumiron phosphate has a low electronic conductivity and energy density that limit itactual application in lithium ion battery. So the mainly purpose of our paper is toenhance the rate performance and cycle performance of lithium iron phosphate.The main contents of the article include the preparation of graphene nanosheets(GS) and lithium iron phosphate, and the carbon and graphene were used tomodify the electrode based on lithium iron phosphate, in order to optimize thepreparation of the cathode materials for lithium ion batteries with highelectrochemical performance.In the process of synthesis of graphene，an easy novel approach which offersa fast pathway of macroscopic quantity preparation of graphene nanosheets atroom temperature has been firstly proposed via Lithium aluminium tetrahydride(LiAlH4) and Phosphorus tribromide (PBr3) as the deoxidizer based on graphiteoxide (GO). The results show that the as prepared graphene has a few layers,about~3layers. It is found that the GS as anode material used for lithium ionbattery has high initial coulombic efficiency (83.1%). The first discharge/chargecapacity of the prepared GS was1029.4and855.1mAh/g at a current density of100mA/g, respectively. After21cycles, the reversible capacity still kept at760.7mAh/g, indicating the stability cyclic performance.In the process of synthesis of LiFePO4precursor, sol-gel and hydrothermalmethods were used in the preparation. The results exhibit that the LiFePO4/Csample was prepared by hydrothermal method has better micro morphology andelectrochemical performance, and the reaction time, temperature and carboncontent were also investigated in detail in the process of synthesis. The resultsshowed that the sample was prepared at130℃for5h and the glucose is15%asthat of LiFePO4/C has the best crystallinity and particle dispersion than others. Ata rate of0.2,0.5,1,3C, the discharge capacity is159.4,155.6,151.9and141.9mAh/g, respectively, which exhibits an excellent rate performance. At a rate of5,10,20,30C, the capacity retention is97%,99.6%,97.1%,95.6%,respectively, shows a stability cyclic performance.In the process of preparation of LiFePO4/GS composite materials, the effectof the amount of graphene on morphology and electrochemical properties ofLiFePO4/GS was studied in deatil. The study found that few amount of graphenewill cause the large particle size; large amount of graphene can lead to thewrapped graphene layer on the surface of LiFePO4particles become thicker anddecline its electrochemical performance in the preparation process of LiFePO4/GScomposites. The results show that when the amount of graphene is5%, theLiFePO4/GS sample has the best properties, the particle size is about100nm andthere are about4~5graphene layers wrapped on the surface of LiFePO4particles.At a rate of0.2,0.5,1,5C, the specific capacity is154.4,150.5,145.9,124.3mAh/g, and the capacity retention is99.1%after cycle200times at the rateof5C, which show an excellent rate performance and cycle life.