Synthesis And Characterization Of Lithium Iron Phosphate As A Cathode For Lithium Ion Batteries

With the development of the society and energy problem prominent increasingly,people pay more and more attention to improve the utilization rate of resources. Lithiumion batteries were widely paid close attention due to its high working voltage, long cyclelife, big energy density and the advantages of environmentally friendly. So, vigorouslydevelop rechargeable lithium ion battery with low cost and high energy density was animportant scientific significance. And it was also considered have a potential commercialvalue. The iron series of positive electrode materials for its low cost, abundant raw andgreen environmental protection advantages, especially the lithium iron phosphate cathodematerial, received extensive attention by battery industry.Lithium iron phosphate cathode material with its high discharge specific capacity,cycle performance, good thermal stability and many other advantages has been studied bydomestic and foreign scientists. As an important raw material, the iron phosphate also hasbeen paid more and more attention.Iron phosphate was prepared by wet-process phosphoric acid as phosphorus source and ferrous sulfate as iron source, through the synthesis and precipitation process,The influe-n ce of different molar weight ratio, reaction pH, ammonia drops of acceleration, thedosage of surfactant PEG (10000) and the calcination temperature about the synthesis ofiron phosphate was studied, and the prepared iron phosphate used as phosphorus and ironsources in the sol-gel method of lithium iron phosphate material. The structure andmicrostructure of the lithium iron phosphate and phosphoric acid iron materials werecharacterized by the particle size distribution, tap density, BET specific surface area,infrared spectrum (IR), X-ray diffraction (XRD) and scanning electron microscope (SEM),at the same time the electrochemical performance of lithium iron phosphate material testedby electrochemical workstation and battery testing system.The results showed that the optimum conditions of preparing iron phosphate as: themolar weight ratio of phosphorus and iron is1.0:1, the dosage of PEG was3.0%of thequality of ferrous sulfate, the rate of ammonia drops was35.62ml/h, the reaction of pH control in2.5.The phosphoric acid iron prepared under this conditions was an amorphousiron phosphate powder with dehydrate, and after450℃calcination the rthophosphoricacid iron powder have a structure of nanosheet.The thickness of iron phosphate particlewas about70-100nm and1000nm average particle size with good dispersion and uniformparticle size distribution. This technology has cheap raw material, simple operation, shortsynthetic time and the advantages of small energy consumption, and its’ a kind of newmethod for energy saving.Using the iron phosphate which prepared under the optimizing conditions as the rawmaterials to product lithium iron phosphate/carbon composite material by sol-gelmethod.Through the characterization, the lithium iron phosphate cathode material have agood crystallinity and crystal shape is complete as a peridot crystal, uniform particle sizedistribution, less reunion phenomenon. This lithium iron phosphate’s surface is porous, andits specific surface area can reach up to13.61m2/g, D50=3.6μm, narrow particle sizedistribution, the tap density was1.24g/cm3.The lithium iron phosphate/carbon compositedby electrochemical detection has a better performance at the first cycle of dischargespecific capacity and stable performance. Discharge specific capacity for the first time in0.1C ratio can reach145.5mAh/g, and after40times charge and discharge cycle, its alsostady at143.1mAh/g, the attenuation rate was just1.61%. The same amples in0.2C,0.5C and1.0C,the first discharge specific capacity were138.7mAh/g,129.1mAh/g and119.2mAh/g, respectively, after40cycles dropped to128.9mAh/g,128.9mAh/g and101.5mAh/g, the attenuation rate was7.1%,10.3%and17.5%respectively. The chargetransfer impedance is small，the material of the production process good reversibility, lesspolarization, electrochemical performance was stable.