Anomalous Enhancement of Li-O2 Battery Performance with Li2O2 Films Assisted by NiFeOx Nanofiber Catalysts: Insights into Morphology Control

It is generally understood that particle-shaped Li2O2 is preferred in Li-O-2 batteries (LOBs) because the dominance of Li2O2 films may lead to poor electrochemical performance. The influence of Li2O2 morphology and its nucleation mechanism are probed by experiments along with the first-principle calculations. It is revealed that the LOBs with Li2O2 films deliver unexpectedly improved capacities, longer cycles, and significantly reduced overpotentials assisted by NiFeOx nanofiber catalysts. The energetically favored Li 2a vacancies under LiO2-rich conditions, small crystallites, and large contact areas with the electrode/electrolyte explain the anomalous performance enhancement. Li2O2 films are formed by a heterogeneous nucleation mechanism and the voltage applied, electrolyte, electrode surface, and use of catalysts are identified as the parameters controlling the mechanisms. The mapped correlations among these parameters shed light on the control of Li2O2 morphology for developing high-performance LOBs.