Revealing the Local Cathodic Interfacial Chemism Inconsistency in a Practical Large-Sized Li-O2 Model Battery with High Energy Density to Underpin Its Key Cyclic Constraints.

Due to the theoretical ultrahigh energy density of the Li-O2 battery chemistry, it has been hailed as the ultimate battery technology. Yet, practical Li-O2 batteries usually need to be designed in a large-sized pattern to actualize a high specific energy density, and such batteries often cannot be cycled effectively. To understand the inherent reasons, we specially prepared large-sized (13 cm × 13 cm) Li-O2 model batteries with practical energy output (6.9 Ah and 667.4 Wh/kgcell) for investigations. By subregional and postmortem analysis, the cathode interface was found to have severe local inhomogeneity after discharge, which was highly associated with the electrolyte and O2 maldistribution. The quantitative results by X-ray photoelectron spectroscopy (XPS) evidenced that this local inhomogeneity can exacerbate the generation of lithium acetate during charge, where the locally higher ratio of unutilized carbon surface and less Li2O2 after discharge would result in increased lithium acetate formation for a subsequent local overcharge. Moreover, verification experiments proved that the byproduct lithium acetate, which had been of less concern, was recalcitrant and triggered much larger polarization compared with the commonly reported byproduct Li2CO3 during battery operations, further revealing the key limiting factors leading to the poor rechargeability of batteries by its accumulation at a pouch-type cell level.