Microwave Assisted Polyol Method Synthesis Of LiMnPO₄/C As Cathode Materials For Lithium-Ion Batteries

Because of its high energy density, long cycle life, safety and good benefits, LiMnPO4 is considered to be an ideal cathode material for the next generation of lithium-ion batteries. Nevertheless, the intrinsic low electric conductivity and ionic conductivity limit its practical application.In this paper, a microwave-assisted polyol method was used to the preparation of LiMnPO₄/C with MnSO4·H2O、H3PO4（85%） and LiOH·H2O as reactants and the mixture of DEG&H2O as solvent. The materials were characterized by X-ray analysis, scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, charge and discharge, cyclic voltammetry and electrochemical impedance spectra.The results show that the type and amount of surfactant has a great influence on the particle size and morphology of the prepared LiMnPO4. LiMnPO4 prepared without surfactant exhibits a spindle-like shape with a length of-200 nm, a width of-50 nm, and the samples prepared with CTAB or PVPk90 are the aggregates of rod and shuttle. However, LiMnPO4 synthesized with PVPk30 is flate with the thickness of about 100-150nm. As the concentration of PVPk30 increased to 0.2M, the thickness of LiMnPO4 reduced to about 70nm.Precursor of LiMnPO4 can be synthesized by microwave assisted polyol processes in 15:2 （v/v） DEG-water mixed solvent at 700rpm/min and 120℃ for 30min. The flaky LiMnPO4/C with a diameter of 50-80nm and the thickness of-10nm can be obtained by the heat treatment of precursor mixed with 35wt% sucrose at 300℃ for 1h and then calcination at 600℃ for 5h. The prepared flaky LiMnPO4/C coated with about 5nm carbon layer has an olivine type structure with Pmnb space group.And this sample delivers an initial discharge capacity of 1 with a capacity retention ratio of 95.3% after 50 cycles at 1C.