One-Pot Microwave-Hydrothermal Synthesis and Characterization of Carbon-Coated LiMPO4 (M=Mn, Fe, and Co) Cathodes

Olivine LiMPO4 (M=Mn, Fe, and Co) cathodes with a thin layer of carbon coating have been prepared by a rapid, one-pot, microwave-assisted hydrothermal process within a short reaction time (15 min) at temperatures as low as 230 degrees C. The carbon coating is achieved by an in situ hydrothermal carbonization of glucose during the synthesis process. The resulting LiMPO4/C nanocomposites are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM) before and after heating at 700 degrees C for 1 h in a flowing argon atmosphere. Although both LiMnPO4 and LiFePO4 prepared under acidic conditions exhibit nanosize rods, LiCoPO4 prepared under basic conditions display micron-size cubes. The uniform nanocarbon coating achieved as indicated by the TEM data enhances the electronic conductivity and leads to excellent electrochemical performance for LiFePO4/C in lithium cells. In contrast, both LiMnPO4/C and LiCoPO4/C exhibit inferior electrochemical performances even after carbon coating due to, respectively, the significantly low electronic conductivity and the lack of compatible electrolyte.