--- res: bibo_abstract: - Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li–O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li–O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li–O2 reaction mechanism ought to be reconsidered.@eng bibo_authorlist: - foaf_Person: foaf_givenName: Christian foaf_name: Prehal, Christian foaf_surname: Prehal - foaf_Person: foaf_givenName: Aleksej foaf_name: Samojlov, Aleksej foaf_surname: Samojlov - foaf_Person: foaf_givenName: Manfred foaf_name: Nachtnebel, Manfred foaf_surname: Nachtnebel - foaf_Person: foaf_givenName: Ludek foaf_name: Lovicar, Ludek foaf_surname: Lovicar foaf_workInfoHomepage: http://www.librecat.org/personId=36DB3A20-F248-11E8-B48F-1D18A9856A87 orcid: 0000-0001-6206-4200 - foaf_Person: foaf_givenName: Manfred foaf_name: Kriechbaum, Manfred foaf_surname: Kriechbaum - foaf_Person: foaf_givenName: Heinz foaf_name: Amenitsch, Heinz foaf_surname: Amenitsch - foaf_Person: foaf_givenName: Stefan Alexander foaf_name: Freunberger, Stefan Alexander foaf_surname: Freunberger foaf_workInfoHomepage: http://www.librecat.org/personId=A8CA28E6-CE23-11E9-AD2D-EC27E6697425 orcid: 0000-0003-2902-5319 bibo_doi: 10.1073/pnas.2021893118 bibo_issue: '14' bibo_volume: 118 dct_date: 2021^xs_gYear dct_identifier: - UT:000637398300050 dct_isPartOf: - http://id.crossref.org/issn/0027-8424 - http://id.crossref.org/issn/1091-6490 dct_language: eng dct_publisher: National Academy of Sciences@ dct_subject: - small-angle X-ray scattering - oxygen reduction - disproportionation - Li-air battery dct_title: In situ small-angle X-ray scattering reveals solution phase discharge of Li–O2 batteries with weakly solvating electrolytes@ ...