A New MnOx Cathode Material for Rechargeable Lithium Batteries

Abstract

Different manganese oxide phases have been synthesized. Rietveld analysis of XRD profiles and galvanostatic cycling in 2025 coin cells were performed for structural and electrochemical characterization. A new two-phase product, containing α-MnO2 and β-MnO2 components, was found to deliver better electrochemical results than single phase α-MnO2, β-MnO2 or α/ramsdellite-MnO2. It is shown that the β-MnO2 phase is responsible for the high discharge capacities and that the α-MnO2 is responsible for a stable structure during lithium intercalation and extraction, as the hollandite structure shows a small unit-cell volume change. This new cathode material is therefore a β-MnO2 phase stabilized with α-MnO2. Furthermore, the reaction of the new α/β-MnO2 with LiOH was examined. Some lithium atoms of LiOH are intercalated within the channels as Li2O in order to stabilize the structure, so that no capacity loss after the first cycle appears, whilst others form a Li2O·MnO2 phase that delivers an additional structure stabilization and therefore a better cycling performance. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)