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.
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.