Preparation And Electrochemical Performance Of Lithium Iron Phosphate Batteries With Binary Carbon Sources

In recent years,with the development of industry,these problems including energy depletion and environmental pollution are becoming more and more serious.For human health and sustainable development of society,human beings urgently need to search for new-style green renewable energy.Lithium-ion batteries conform to the trend of the times and gradually go into our attention.Because of high energy density,low cost,long service life,good cycle stability,non-toxic harmless and many other advantages,LiFePO₄ of olivine-type structure becomes one of the most development and application prospects in the cathode materials for lithium-ion batteries nowadays.It is more complex for traditional synthesis process of LiFePO₄ and not suitable for large-scale industrial production.In addition,the specific structure of the material leads to its low conductivity and lithium ion mobility.These are obstacles to hinder the development and application of LiFePO₄.In order to solve the above problems,this paper analyzed and studied the LiFePO₄ from the two aspects of grinding process and carbon source composition.The paper chose FeSO₄·7H₂O and NH₄H₂PO₄ as raw material to synthesize FePO₄ firstly.Glucose and sucrose were employed as carbon sources.LiFePO₄/C composites were prepared via the route of FePO₄ intermediate.By changing the composition of the reagent dispersant,the paper compared the properties of LiFePO₄/C materials prepared by two different grinding processes,which was I-type dispersant absolute ethyl alcohol and II-type dispersant absolute ethyl alcohol/ deionized water,so as to optimize the synthesis process.Based on the optimized grinding process,the paper chose five different ratios of glucose-based residue carbon and sucrose-based residue carbon to prepare LiFePO₄/C materials.By comparing their performance,the paper investigated the effects of carbon source components on LiFePO₄/C.The structure and morphology of the LiFePO₄/C composites were investigated by XRD,FESEM and HRTEM.The electrochemical performance of batteries was tested via constant current charge and discharge method.The results showed that the introduction of a small amount of deionized water in the absolute ethyl alcohol dispersant could promote the dispersion of sugar molecules in the process of synthesis of lithium iron phosphate,which made the integrated performance of the prepared battery better.By comparing the properties of materials prepared with different ratios of residue carbon in binary carbon sources,the paper found that the discharge capacity of LiFePO₄/C batteries exhibited a “volcano”-type relationship vs.mass percentage of sucrose-based residue carbon in whole residue carbon.Integrating the experimental results from the two aspects of grinding process and carbon source composition,the paper confirmed an optimized synthesis route.Glucose and sucrose was used as carbon source and the mass ratio of both residue carbons was 1:1.The mass fraction of residue carbon was 3.8%.The dispersant was absolute ethyl alcohol with deionized water and its volume ratio was 17:3.This route is highly possible to achieve industrial production because of its rich source of raw materials,cheap carbon source,simple synthesis process,short preparation cycle and so on.