Enhanced conductivity and electrical relaxation studies of carbon-coated LiMnPO4 nanorods

Lithium manganese phosphate (LiMnPO4) nanorods were synthesized using the modified polyol method. Polyvinylpyrrolidone was used as a stabilizer to control the shape and size of LiMnPO4 nanorods. Resin coating process was used to coat the carbon over the LiMnPO4 nanorods. X-ray diffraction and Fourier transform infrared spectroscopy results showed the formation of LiMnPO4 crystalline phase. The TEM image shows a uniform coating of the nano size (2.3 nm) carbon over the surface of LiMnPO4 nanorods and the EDS spectrum of the carbon-coated LiMnPO4 nanorods confirming the presence of carbon element along with the other Mn, P, and O elements. Impedance measurements were made on pure and carbon-coated LiMnPO4 nanorods, and their conductivities were evaluated by analyzing the measured impedance data using the WinFIT software. More than two orders of magnitude of conductivity enhancement was observed in the carbon-coated LiMnPO4 nanorods compared to pure ones, and the conductivity enhancement may be attributed to the presence of carbon over LiMnPO4 nanorods. Temperature dependence of conductivity and ac conductivity were calculated using impedance data of pure and carbon-coated LiMnPO4 nanorods. CR2032 type lithium ion coin cells were fabricated using pure and carbon-coated LiMnPO4 nanorods and characterized by measuring charge–discharge cycles between 2.9 and 4.5 V at room temperature. More than 25 % of improved capacity was achieved in the carbon-coated LiMnPO4 nanorods when compared to pure ones synthesized using modified polyol and resin coating processes.