Facile one pot synthesis and Li-cycling properties of MnO2
Abstract
For the first time, a molten salt method was attempted to prepare MnO2 with three different precursors of Mn(CH3COO)2, Mn(NO3)2 and MnSO4·H2O by using 0.375 M LiNO3, 0.18 M NaNO3 : 0.445 M KNO3 as a molten salt heated at 380 °C for the application of lithium batteries. The prepared compounds were characterized by various techniques such as, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), a surface area analyzer and scanning electron microscopy (SEM), respectively. XRD results revealed the cubic phase of λ-MnO2 and tetragonal phase of α-MnO2 and the morphology of the compounds shows spherical particles as well as rod shaped nano-sized particles. The electrochemical performance of the compounds has been evaluated by, galvanostatic cycling (GC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Li-cycling results indicated that the performance of nano-rod shaped α-MnO2 prepared by MnSO4·H2O exhibits a stable and high reversible capacity of 845 mA h g−1 (87.5% capacity retention) at the end of the 50th cycle, cycled at a constant current density of 60 mA g−1, in the potential range of 0.005–3.0 V vs. Li. The MnO2 compound prepared by using three different precursors shows a stable coulombic efficiency of 99% after a few cycles.