Synthesis Of LiMnPO₄/C Lithium-Ion Battery Cathode Materials By A Wet Milling-Assisted Solid-State Method

LiMnPO4 is recognized to be one of the promising cathode materials for lithium-ion batteries. However, LiMnPO4 is suffered from extremely poor electronic conductivity and sluggish lithium ion conductivity. These shortages limit its practical application. The following three measures are popularly adopted to improve its electrochemical performance:(1) surface coating, (2) reducing particle size, and (3) ions doping.In this theme, wet milling assisted solid state reaction method was used to prepare LiMnPO4/C. The effects of process parameters of wet milling on the structure and performance of prepared LiMnPO4/C were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopic (TEM), specific surface area and pore analyzer, constant current charge/discharge test, electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) techniques.LiMnPO4/C can be prepared by milling a slurry with 2 g·L-1 PVP at a ball-to-powder ration of 45:1 and a ball milling speed of 1250 r·min-1 for 3.5 h. The prepared LiMnPO4/C is olivine structure and pseudo-spherical secondary particles with a carbon content of 12.6%. This sample delivers an initial discharge capacity of 104 mA·h·g-1 with a retention rate of 94% after 50 cycles at 0.5 C and a discharge capacity of 96 mA·h·g-1 at 2 C.Fe-doping can improve the discharge capacity and rate performance of LiMnPO4/C. Among the Fe-doping materials, LiMn0.85Fe0.15PO4/C delivers an initial discharge capacity of 116 mA·h·g-1 without attenuation after 50 cycles at 0.5 C. It delivers a discharge capacity of 118 mA·h·g-1 even at 2 C. The improved cycling stability and rate performance can be attributed to the solid solution formed in the LiMnPO4 lattices with Fe doping, which could improve the electron and lithium ion conductivity.