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.