The Modification Of Lithium Iron Phosphate Cathode Materials For Li-ion Batteries

Because of its high theoretical capacity（170mAh/g）， stable and moderate voltageplatform，environmental protection, high security, LiFePO₄is one of the preferredmaterial of positive electrode materials for the future lithium-ion batteries material.However, its low ion diffusion rate and electronic conductivity cause the poor electricalproperties. These drawbacks limit its large-scale application of power battery.Based on the various improved thoughts, this experiment seek for the high capacity ofLiFePO₄by adding silane coupling agent KH550and fast ionic conductor Li₈Al_0.4Si_1.2P_0.4O₈.Study the influence on the surface morphology and capacity by technical conditions（adding mode, sintering temperature, adding content） of adding silane coupling agent,fast ion conductor during the preparation. The microstructure and morphology of samplewere analyzed by XRD diffraction and SEM electronic scanning, the electrical propertieswere test by the constant current charge and discharge test.The sample adding silane coupling agent was synthesized by carbothermal reductionmethod. The result shows that adding silane coupling agent has not change it’solivine-type. Adding2.5%KH550befor carbonization of glucose, the grains of thesample are wee, clear and show olivine-type obviously; at the same time thephenomenon of reunion become weaken and the carbonization of glucose has the bestdispersity.Adding silane coupling agent can raise the electric propertie of lithium ironphosphate. Adding2.5%KH550before carbonization of glucose, the sample has thebest first discharge capacity, which achieved to139mAh/g.The sample adding fast ion conductort was synthesized by carbothermal reductionmethod. The result shows that adding fast ion conductort has not change its olivine-type;and improved the particle morphology, electric capacity obviously. The grains of thesample （synthesizing by embedding mode,650℃sintering temperature,3%addingcontent） are wee, clear and show olivine-type obviously; has the best first dischargecapacity, which achieved to144mAh/g.