One-Pot Microwave-Hydrothermal Synthesis and Characterization of Carbon-Coated LiMPO[sub 4] (M=Mn, Fe, and Co) Cathodes

Abstract

Olivine LiMPO4LiMPO4 ( M=MnM=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 (15min)(15min) at temperatures as low as 230°C230°C . The carbon coating is achieved by an in situ hydrothermal carbonization of glucose during the synthesis process. The resulting LiMPO4∕CLiMPO4∕C nanocomposites are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy (TEM) before and after heating at 700°C700°C for 1h1h in a flowing argon atmosphere. Although both LiMnPO4LiMnPO4 and LiFePO4LiFePO4 prepared under acidic conditions exhibit nanosize rods, LiCoPO4LiCoPO4 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∕CLiFePO4∕C in lithium cells. In contrast, both LiMnPO4∕CLiMnPO4∕C and LiCoPO4∕CLiCoPO4∕C exhibit inferior electrochemical performances even after carbon coating due to, respectively, the significantly low electronic conductivity and the lack of compatible electrolyte.