Hydrothermal Synthesis Of LiFePO₄/C Comosite Materal For Lithium-Ion Batteries

LiFePO₄/C composite material is an ideal anode material for lithium ionbatteries which has fine properties of high safety, green initiative, high circlelife, and abundant raw materials. The hydrothermal method allows rawmaterials mixed and reacted at the molecular level at a relative low reactiontemperature as compared to the solid phase method which reacts in atemperature higher than600℃, hence reducing energy comsumption greatly.In this work, pure LiFePO₄was synthesized by the hydrothermalhomogeneous precipitation method, and a controllable compound material ofLiFePO₄/C with uniform carbon coating layer was prepared by using thehydrothermal method. A new preparation technology for FePO₄wasdeveloped as well. The main achievements are as follows:1. Hydrothermal homogeneous precipitation method was adopted firstlyto prepare pure LiFePO₄with urea as the precipitation agent to control the pHof the solution, LiAc as the lithium source, FeSO₄as the iron source, andNH4H2PO₄as the phosphorus source. The systematic study on the effects ofthe hydrothermal temperature, urea consumption, phosphorus source dosageon LiFePO₄preparation has been conducted. 2. One step hydrothermal carbon coating method was proposed to preparecomposite material of LiFePO₄/C. The form of the carbon prepared by thismethod is not a carbon layer on the particle’s surface, but forming a grainmixed with LiFePO₄. The influences of the usage of glucose and urea, and thereaction temperature on the preparation of the LiFePO₄/C were studied.3. Two steps hydrothermal carbon coating method was adopted as well toprepare composite material of LiFePO₄/C. The thickness of coated carbonlayer on the particle surface of LiFePO₄could be effectively controlled by theamount of glucose, ammonia water dosage and reaction temperature. Theamount of glucose and reaction temperature had positive relation with thethickness of coated carbon layer, while the amount of mmonia water wasinversely related with he thickness of coated carbon layer.4. A new cheapper technology for the preparation of FePO₄wasdeveloped. FeSO₄, a cheap chemical by-product, was working as the ironsourceto prepare the pure FePO₄. Systematic experiments on the effects of theproportion between the iron and phosphate, the reaction temperature, thereaction pH value on the preparation process were conducted.