Synthesis and Electrochemical Characteristics of an Orthorhombic LiMnO2 Cathode Material Modified With Poly(Vinyl-Pyrrolidone) for Lithium Ion Batteries

The orthorhombic LiMnO2 (o-LiMnO2) cathode materials modified with poly(vinyl-pyrrolidone) (PVP) for lithium ion batteries are synthesized by using a solid-state reaction and subsequently the hydrothermal method. The modified materials are characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscope (SEM), and electrochemical techniques. It is shown that the bare o-LiMnO2 sample with high purity is synthesized at 750 °C under nitrogen atmosphere using Mn2O3 and LiOH·H2O as precursors, and it has a higher discharge capacity than other samples containing impurity phases. The poly(vinylpyrrolidone) (PVP) is modified into the bare o-LiMnO2 particles by the hydrothermal method at 140 °C for 4 days. The C=O and C–N bonds in PVP bond with the Mn atoms in the o-LiMnO2; a partially modified PVP successfully intercalates into the lattice of o-LiMnO2 and opens its interlayers. The highest specific capacity and most improved cycling property are obtained for PVP-o-LiMnO2 with about 3.7 wt.% PVP. The enhancement of the cycling property of PVP-o-LiMnO2 can be attributed to the protection of the spinel-like structure formed upon cycling by PVP.