In situ high-energy synchrotron X-ray diffraction studies and first principles modeling of α-MnO2 electrodes in Li-O2 and Li-ion coin cellsThe submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract no. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide lice

Despite their technological challenges, non-aqueous rechargeable lithium-oxygen cells offer extremely high theoretical energy densities and are therefore attracting much attention in a rapidly emerging area of electrochemical research. Early results have suggested that, among the transition metal oxides, alpha manganese dioxide (α-MnO 2 ) appears to offer electrocatalytic properties that can enhance the electrochemical properties of Li-O 2 cells, particularly during the early cycles. In this study, we have investigated the hybrid Li-ion/Li-O 2 character of α-MnO 2 electrodes in Li-O 2 coin cells by in situ high-energy synchrotron X-ray diffraction, and compared the results with conventional Li/α-MnO 2 coin cells assembled under argon. Complementary first principles density functional theory calculations have been used to shed light on competing lithium insertion and lithium and oxygen insertion reactions within the α-MnO 2 tunnel structure during discharge, relative to lithium peroxide or lithium oxide formation. In situ synchrotron diffraction and first principles modeling shows structural changes in α-MnO 2 during cycling in Li-O 2 battery cells, as lithium and oxygen are incorporated into and removed from tunnels in the structure.