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Hybrid Coating And In-situ Carbon Coating Modification Of LiMnPO4 Synthesized By Hydrothermal Process

Posted on:2017-11-21Degree:MasterType:Thesis
Country:ChinaCandidate:W L ZhangFull Text:PDF
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Lithium manganese phosphate?LiMnPO4?,with relatively low cost,environmental friendliness and high safety,can deliver a high theoretical energy density?697 Wh kg-1?on the stable electrochemical window of present electrolyte systems.Unfortunately,LiMnPO4 suffers from intrinsic low electronic conductivity,limited lithium ion diffusion kinetic and large volumetric change in charge/discharge process,which deteriorates its high rate and cycling performance.All these demerits hinder the practical application of LiMnPO4.In this paper,the influences of modified precursor lithium phosphate?Li3PO4?on the electrochemical performance of LiMnPO4 are studied.Furthermore,various hybrid coating layer,being composed of carbon and metallic oxide,is coated on the surface of LiMnPO4 to improve its electrochemical performance.LiMnPO4 particles were prepared by a hydrothermal process with Li3PO4 as a precursor.Li3PO4 was modified by calcination and carbon coating layer in advance.The results illustrate that the crystallinity of Li3PO4 can be improved by calcination.LiMnPO4/C with small particles size and slight aggregation was prepared using 5 wt% carbon coated Li3PO4 precursor.The initial discharge capacity of LiMnPO4/C above is 131.5 mAh?g-1 at 0.1 C.LiMnPO4 particles are separately modified by hybrid coating layers of Co3O4/C and Fe2O3/C using wet ball-milling technique.XRD result reveals that the hybrid coating layer has no influence on the crystal structure of LiMnPO4.This incomplete carbon network on the surface of LiMnPO4 can be patched by filling moderate nanosized oxide at interrupt points of carbon layer.The integrated hybrid coating layer can effectively protect LiMnPO4 particles from electrolyte erosion,resulting in improved structural stability.In comparison with LiMnPO4/C,Co3O4-LiMnPO4/C samples exhibit improved cycle performance,the capacity retention of which is above 95% after 50 cycles at 0.1 C.Similarly,2 wt% Fe2O3-LiMnPO4/C sample can exhibit improved cycle performance not only at the above test conditions under which shows a higher capacity retention of 96.5%,but also at high temperature of 55 C.The improved cycling performance implies that the integrated Fe2O3/C hybrid coating layer can effectively reduce Mn dissolution into the electrolyte and keep the structural stability of LiMnPO4.An in-situ carbon coating is also used to improve the nonuniform and incomplete carbon coating layer on the surface of LiMnPO4 which is prepared by wet-milling method.It is found that the concentration of carbon source?glucose?in hydrothermal process can influence the particle size distribution,morphology and electrochemical performance of the final LiMnPO4/C product.
Keywords/Search Tags:Lithium manganese phosphate, Li3PO4 modification, Hybrid coating, In-situ carbon coating
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