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 50^th 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.