(693h) Combined Experimental and Theoretical Study of Oxygen Mobility in Hydrated Alpha-MnO2

Alpha-MnO₂ is of interest as a cathode material for conventional lithium cells and as an electrode/electrocatalyst for hybrid Li-ion/Li-O₂ cells. It has a framework structure with large 2x2 tunnels that can contain water; the H₂O component can be ion-exchanged with lithium to create a Li₂O-stablized electrode. When used in Li-O₂ cells, it is possible that the electrocatalytic process is associated with the removal from and reintroduction of lithium and oxygen into the host structure during charge and discharge, respectively. In this contribution, we present a study of the oxygen mobility via water intercalation in alpha-MnO₂. We present evidence of the dehydration of alpha-MnO₂ from temperature-resolved in-situ synchrotron powder x-ray diffraction, thermogravimetric analysis, and in-situ UV-resonance Raman spectroscopy; and structural, thermodynamic, and kinetic information from density functional theory calculations. We also present our analysis of the charge state of the hydration species from density functional theory, redox titration, and x-ray absorption near-edge spectroscopy. Finally, we discuss implications for improved sustainability in the practical usage of alpha-MnO₂ for reversible Li or Li-O₂ storage.