Preparation and Electrochemical Properties of LiMn_(0.8)Fe_(0.2)PO_4/C Nanocomposite

Olivine-structured LiMn0.8Fe0.2PO4/C solid solution was successfully prepared by a Sol-Gel approach combined with a high-temperature solid-state reaction, and characterized by X-ray diffraction(XRD), scanning electron microscope(SEM) and transmission electron microscope(TEM). The results revealed that LiMn0.8Fe0.2PO4nanoparticles were evenly dispersed in the in-situ formed carbon conductive network. When the nanocomposite served as a cathode material for lithium-ion batteries(LIBs), except a short plateau(~3.5 V vs Li+/Li) ascribed to Fe3+/Fe2+couples in the charging/discharging profile, the long plateau at higher voltage(~4.1 V vs Li+/Li) is corresponding to the redox reaction of Mn during the Li+extraction/insertion in the LiMn0.8Fe0.2PO4lattice, and this high voltage plateau can significantly enhance the energy density of relevant LIBs. In addition, the chemical diffusion behavior of lithium in the LiMn0.8Fe0.2PO4/C electrode was investigated in detail using galvanostatic intermittent titration technique(GITT)and electrochemical impedance spectroscope(EIS), and the chemical diffusion coefficients of lithium, DLi, obtained by GITT and EIS were 5×10-15 1×10-14cm2/s and 1.27×10-13 2.11×10-13cm2/s, respectively. The results indicate that the value of DLi increases with elevated test temperature, and it can be inferred that the electrochemical properties of such materials can be improved by raising the working temperature.