Liquid Phase Synthesis And Properties Of Lithium Iron Phosphate

Compared with the expensive and toxic LiCoO2 lithium ion battery cathode material,Olivine-type lithium iron phosphate is a new generation of potential lithium-ion battery cathode material.Due to its low cost,non-toxic and safe.But LiFePO4 exist some disadvantages such as low electrical conductivity,the electronically conductive and lithium ion transport rate is slow,which restricts the high-rate charge-discharge performance;low bulk density,resulting in low volumetric capacity.These two drawbacks hinder the practical application of the material.So it is important to improve the conductivity and volume of olivine structure LiFePO4.In this paper,in order to improve the electrochemical properties of lithium iron phosphate material,the LiFePO4/C composites synthesized by sol-gel method.XRD,SEM,infrared spectroscopy,particle size analysis techniques were used to analyze the micro structure and surface morphology of LiFePO4/C powder,and constant current charge and discharge,cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)Technical were used to test its electrochemical properties.The pre-sintering process and carbon source introduced methods were studied;the influence of different lithium source and different carbon sources,lithium content,carbon content to the organizational structure and electrochemical properties of LiFePO4/C composite was analyzed and compared.The results show that:the optimal process of synthesizing LiFePO4/C composite materials using the sol-gel method is:LiOH as a lithium source,the lithium content of the Li/Fe = 1.05,the lithium iron phosphate precursor was synthesized.Precursor was calcined at 400 ℃ for 10h,and then the carbon source glucose was introduced by the liquid mechanical activation method.And when the carbon content of 4%(converted to the weight of C),the lithium iron phosphate was carbon-coated.LiFePO4/C composite material was prepared after the second sintering.The first discharge capacity of the material is 144.9mAh/g at 0.2C magnification.Efficiency reached 90%for the first time,the capacity is higher than pure lithium iron phosphate.The discharge capacity do not decay after 30 charge-discharge cycles,it shows good electrochemical performance.