Lithium intercalation in amorphous manganese dioxide, synthesized by a room temperature aqueous oxidation route, is analyzed. As reported before, the material yields a very high intercalation capacity and also shows promising rate capability as cathodes for rechargeable lithium batteries. The present study investigates the structure of the material using x-ray powder diffraction conducted on composite cathode pellets at various stages of discharge and after discharge/charge cycling. Contrary to the behavior of a number of crystalline manganese oxides that exhibit a tendency to undergo a transformation to a spinel-like phase, the amorphous manganese dioxide does not show such a tendency and remains X-ray amorphous upon lithium intercalation and cycling. In fact, the material appears to become even more disordered upon repeated cycling. The results indicate the kinetic stability of the amorphous structure in allowing high-capacity, single-phase and reversible lithium intercalation and suggest the potential of far-from-equilibrium structures as superior intercalation hosts.
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