A simple acid leaching technique is demonstrated to produce lambda-MnO2 by treating LiMn2O4 with H2SO4. lambda-MnO2 shows high intercalation capacities as the positive electrode material for rechargeable aqueous batteries. The structure and morphology of the nano-particles are characterized by X-ray power diffraction, inductively coupled plasma, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy. The electrochemical performance of lambda-MnO2 is investigated by cyclic voltammetry, constant current charge-discharge tests and electrochemical impedance spectroscopy. lambda-MnO2 has ideal battery behaviors for polyvalent cations (Mg2+, Zn2+) to intercalate/deintercalate in the aqueous electrolyte. The lambda-MnO2 electrode shows a high initial discharge capacity of 545.6 mAh g(-1) at 13.6 mA g(-1) in 0.5 mol dm(-3) MgCl2 with a columbic efficiency of nearly 100%. In addition, it shows good cycling stability and maintains a capacity of 155.6 mAh g(-1) after 300 cycles in 1 mol dm(-3) MgCl2 electrolyte. (C) 2013 Elsevier Ltd. All rights reserved.