λ-MnO2 nanoparticles and β-MnO2 nanorods were successfully prepared from spent LiMn2O4 cathode materials by controlling appropriate leaching conditions in this study. Their electrochemical properties were investigated as electrode materials for primary cells and supercapacitors. The composition

morphology and electrochemical properties of the obtained samples were characterized by X-ray powder diffraction (XRD)

scanning electron microscopy (SEM)

transmission electron microscopy (TEM)

constant current charge-discharge and cyclic voltammetry measurements. The results indicated that λ-MnO2 nanoparticles could be prepared at ambient temperature and pressure

with 0.5 mol·L-1 H2SO4 leaching the spent LiMn2O4 for 3 h

and β-MnO2 nanorods could be synthesized under hydrothermal conditions of 140℃

with 2 mol·L-1 H2SO4 leaching the spent LiMn2O4 for 24 h. The λ-MnO2 and β-MnO2 samples delivered discharge capacities of 142 mA·h·g-1