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

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.