title: Revealing the reaction mechanisms of Li-O2batteries using environmental transmission electron microscopy.
abstract: The performances of a Li-O2battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, Li2O2,forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O2batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O2nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO2, which subsequently disproportionates into Li2O2and O2. The release of O2creates a hollow nanostructure with Li2O outer-shell and Li2O2inner-shell surfaces. Our findings show that, in general, the way the released O2is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O2cells.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
authors.forename: Langli
authors.initials: L
authors.lastname: Luo
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
authors.forename: Bin
authors.identifier: 0000-0001-8797-3275
authors.initials: B
authors.lastname: Liu
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.|School of Environmental and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300387, China.
authors.forename: Shidong
authors.initials: S
authors.lastname: Song
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
authors.forename: Wu
authors.initials: W
authors.lastname: Xu
authors.affiliation: Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
authors.forename: Ji-Guang
authors.identifier: 0000-0001-7343-4609
authors.initials: JG
authors.lastname: Zhang
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang