Study On Wet-Milling Processes For Synthesis Of Porous LiMn_0.85Fe_0.15PO₄/C Hollow Sphere

Phospho-olivines LiMPO4 (M=Fe, Mn) have been intensively researched as cathode materials for rechargeable lithium ion batteries owing to their high cycling stability, low cost, good safety characteristics and abundant raw materials. LiFePO4 has been used as the cathode material for HEVs as their drive force". Compared with LiFePO4, the theoretical energy density of LiMnPO4 is 20% larger than that of LiFePO4. Because of the redox potential of the Mn3+/Mn2+couple is higher than that of the Fe3+/Fe2+couple (4.1V vs.3.4V, respectively).However, the pure LiMnPO4 crystal displays a quite poor electronic and lithium-ionic conductivity, which lead to its poor electrochemical performance and limit its large-scale application in hybrid electric vehicles.To improve the electrochemical performance of LiMnPO4, we developed a wet milling-spray drying-solid state reaction process (WSS) to prepare porous LiMn0.85Fe0.15PO4/C hollow sphere nanocomposites. In this work, the effects of wet milling processes on the morphology and the electrochemical performance of LiMn0.85Fe0.15PO4/C were investigated by size distribution, X-ray diffraction, FE-SEM, TEM, BET analysis, CV, EIS, Raman spectrum analysis and so on. The results indicate that the particle size of the slurry first decrease and then increase with the increase of stirrer speed, circulation speed and solid concentration, while that first decrease and then constant with the increase of sucrose content and milling time. When the slurry is milled with sucrose 19%, stirrer speed 2800r·min-1, milling time 6h, circulation speed 1.5L·min-1and solid concentration 100g·L-1, porous LiMn0.85Fe0.1sPO4/C hollow spheres can be fabricated by WSS. The prepared hollow spheres are fell in 2～15 μm and composed of primary particle (40-100nm) coated with a carbon layer and abundant mesoporous with an average pore diameter of 21.42 nm.The carbon content of LiMn0.85Fe0.15PO4/C is 6.4% and its specific surface area (BET) is 49.56 m2·g-1.The porous LiMn0.85Fe0.15PO4/C hollow spheres deliver a discharge capacity 135mAh·g-1 with no capacity loss after 50 cycles at 1C, exhibiting good electrochemical performance due to a high electronic conductivity and quick Li+ permeation in the unique geometrical structures of porous LiMn1_xFexPO4/C hollow sphere electrodes...