Preparation And Electrochemical Performance Of Lithium Iron Phosphate And Lithium Manganese Iron Phosphate

Lithium iron phosphate(LiFePO4)possesses advantages including low cost,eco-friendliness,good electrochemical and thermal stability,suitable voltage(3.4 V vs.Li/Li+),long cycle life(>2000 cycles),and high theoretical capacity(170 mAh g-1),making it a vital cathode material in lithium-ion batteries and various energy storage devices.However,low electronic conductivity and lithium-ion diffusion coefficient are inherent defects,limiting its large-scale high-rate performance.Carbon coating modification improves the electrochemical performance of LiFePO4,but the influence mechanism of carbonization process,carbon sources,structures,and morphology on LiFePO4/C still require further investigation.The high-temperature solid-phase method is a widely used preparation technique due to its simplicity,low cost,and high yield,although LiFePO4 obtained through this method typically exhibits uneven particle size distribution and easy particle agglomeration.In order to solve these problems,the current research direction is on the structure of carbonization products of various carbon sources and the mechanism of their influence on the electrochemical performance of LiFePO4/C morphology.In order to better integrate with social production,mass production of low-cost and high-capacity lithium ion cathode materials,this experiment used gelatin as a carbon source to prepare nitrogen-doped carbon LiFePO4 through a simple high-temperature solid-phase method.The cathode materials were characterized by XRD,TG,Raman,SEM,XPS,and TEM,and the primary research work is outlined below:1.Lithium carbonate,ammonium dihydrogen phosphate and ferrous oxalate are used as raw materials.A significant advantage of additive gelatin is that it contains more than 82%protein and is milled in proportion as a source of carbon and nitrogen.When carbon is coated,the effects of different amounts of gelatin on the electrical conductivity and particle aggregation degree of lithium iron phosphate,and then the effects on the charge-discharge specific capacity of the material are studied.The experimental results show that for the lithium iron phosphate material,by changing the amount of gelatin,it is determined that when the mass of gelatin is 15%of the theoretical product lithium iron phosphate,the synthesized material not only has a significantly improved electrochemical performance,but also has a discharge specific capacity of 164.7 mAh g-1 at 0.3 C rate.The lithium ion diffusion coefficient of the material has also been improved(1.43×10-11 cm2 s-1).2.This study explores the effect of partial replacement of Fe ions with Mn ions on the electrochemical performance of LiMn0.6Fe0.4PO4/NC materials.Through X-ray diffraction(XRD)technique,it was found that the XRD peaks of all samples were shifted relative to the standard pattern of LiFePO4 and the standard pattern of LiMnPO4,indicating that it was a solid solution between the two.In the electrochemical performance test,the samples where Mn replaced Fe showed better electrochemical performance,indicating that the replacement could enhance the electrochemical performance of the material.In addition,the redox pair also became two pairs,about 3.5V and 4.1V,corresponding to the redox reaction between Fe2+and Fe3+and Mn2+and Mn3+,respectively.With the replacement of Fe by part of Mn,the appropriate amount of Mn increases,and the energy density is expected to increase.