Highly crystalline macroporous β-MnO2: Hydrothermal synthesis and application in lithium battery

A highly crystalline macroporous beta-MnO2 was hydrothermally synthesized using stoichiometric reaction between KMnO4 and MnCl2. The as-prepared material has a pore size of ca. 400 nm and a shell thickness of 300-500 nm. The formation of the macroporous morphology is related to self-assembling from nanowires of alpha-MnO2, and could be obtained at high reactant concentrations (e.g., 0.8 M KMno(4)) but not at low ones (e.g., below 0.04M KMnO4). Compared to conventional bulk beta-MnO2 processing very low capacity, our macroporous material exhibits good electrochemical activity, e.g., obtaining an initial discharge capacity of 251 mAh g(-1) and sustaining as ca. 165 mAh g(-1) at 10 mA g(-1). The electrochemical activity of the as-prepared beta-MnO2 is related to its macroporous morphology and small shell thickness: the former leads to that electrolyte can flood pore of the material and its inner surface is available for lithium ion diffusion, while the latter helps to release the stress from phase transformation during the initial discharging. The X-ray diffraction characterizations of the macroporous beta-MnO2 electrodes suggest that, upon initial discharging, such a beta-MnO2 will be irreversibly transformed to an orthorhombic LixMnO2 and then cycled within the new developed phase in the subsequent lithium insertion/extraction processes. (C) 2010 Elsevier Ltd. All rights reserved.