In situ x-ray absorption fine structure studies of a manganese dioxide electrode in a rechargeable MnO₂/Zn alkaline battery environment

Electronic and structural aspects of a MnO₂ electrode in a rechargeable MnO₂/Zn battery environment have been investigated by in situ Mn K-edge x-ray absorption fine structure (XAFS). The relative amplitudes of the three major Fourier transform shells of the extended XAFS function of the rechargeable MnO₂ electrode in the undischarged state were similar to those found for ramsdellite, a MnO₂ polymorph with substantial corner-sharing linkages among the basic MnO₆ octahedral units. The analyses of the background-subtracted pre-edge peaks and absorption edge regions for the nominally 1-e^- discharged electrode were consistent with Mn³⁺ as being the predominant constituent species, rather than a mixture of Mn⁴⁺ and Mn²⁺ sites. Furthermore, careful inspection of both the x-ray absorption near edge structure and EXAFS indicated that the full recharge of MnO₂, which had been previously discharged either by one or two equivalent electrons, generates a material with decreased corner-sharing linkages compared to the original undischarged MnO₂.