Synthesis And Electrochemical Characterization Of Lifepo₄Electrode Material By Coated With Surfactant

With the energy crisis and environmental pollution intensifies, human care for the development and use of clean energy, however, as a kind of efficient and clean new energy storage device, the use of lithium-ion batteries has received much attention. The olivine structure LiFePO4(LFP) as a cathode material for lithium-ion batteries, with low price, non-polluting, high theoretical capacity, good cycling stability and other advantages, more and more popular by human. However, the low electronic conductivity and lithium ion diffusion rate is a serious impact of the large commercial applications scale. In this paper, the surfactant-coated LiFePO4were used to improve the problems. Surfactant has the effects of control the particlesize and morphology, dispersed particles. Using XRD, SEM and TEM methods to characterize the structure and morphology, and the constant current charging and discharging system were used to study the electrochemical properties of LiFePO4/C materials. The main contents are as follows:First, using carbon thermal reduction method, and the low cost FeCl3·6H2O as raw materials, study the mass of the ionic surfactant cetyl trimethyl ammonium bromide (CTAB) and non-ionic surfactant poly vinylpyrrolidone (PVP), reaction time and calcination temperature how to impact on the structure and morphology of LiFePO4and electrochemical properties. The results show that:PVP as carbon source, the prepared LiFePO4/C particles dispersed more evenly, no significant agglomeration, the outside of LiFePO4particles coated with a layer thickness of the carbon about2nm. Finally, the charge-discharge tests show that the electrode material with PVP has the best electrochemical performance under the best condition, at0.2C rate, the discharge capacity can reached162.8mAh/g; but CTAB as carbon source, the prepared LiFePO4/C materials under the best conditions, the discharge specific capacity can reach158mAh/g, under the same rate; without surfactant the specific capacity of LiFePO4particles is only104.7mAh/g.Second, a simple solvothermal process has been synthesized to self-assembled LiFePO4/C microspheres with the presence of poly vinylpyrrolidone (PVP), mixture of ethylene glycol and water as solven, and study the reaction temperature and reaction time effect on the electrochemical performance of LiFePO4/C. Research shows that: when the reaction temperature is200℃and reaction time is24h, ethylene ratio of1:2with water, the morphology and the electrochemical performance of the sample are the best. Self-assembled LiFePO4/C microspheres with a size of about2.5um, and consists of spherical particles with the size of about110nm, dispersed well, no agglomeration, and the outer of the sample coated with a layer of2nm thickness carbon. The electrochemical properties of the material at different discharge rate showed that, the sample has a good rate performance, at0.2C,5C,10C,20C rates, the discharge capacity is167.6mAh/g、137.9mAh/g、114.3mAh/g、109.1mAh/g、93.5mAh/g, it also have excellent cycle performance.