Electrolyte Effects on the Deposition Location of Discharge Products beyond Conductive Substrates in Lithium−Oxygen Batteries

Abstract In lithium−oxygen batteries (Li−O2 batteries, LOBs), the solution pathway involving the disproportionation of solvated lithium superoxide (LiO2s) is recognized as a major discharge reaction route. In this pathway, the deposition of lithium peroxide (Li2O2), the main discharge product, also occurs beyond the conductive substrate. The accumulation of such deposits, which lack electronic contact with the electrode, can mitigate pore clogging of the positive electrode and enable higher discharge capacities, while it deteriorates charge−discharge reversibility. Therefore, establishing guidelines for controlling the spatial distribution of Li2O2 deposition according to the desired battery characteristics, such as high capacity or reversibility, is of critical importance. In this study, we investigated the effects of solvent and lithium salt selection on the fraction of Li2O2 deposited outside the conductive substrate and elucidated the governing factors. A newly designed hybrid nonwoven positive electrode with spatially adjacent conductive and non-conductive regions was employed, and quantitative colorimetric measurements were combined with finite element method simulations. The results revealed that both the LiO2s diffusivity and the disproportionation rate govern the deposition location, along with the solvent donor number. Specifically, solvents with relatively low disproportionation rate constants and high donor numbers, such as N,N-dimethylacetamide, promote long-range LiO2s migration, resulting in enhanced Li2O2 deposition outside the conductive substrate. In contrast, the solubility of dissolved oxygen and its diffusivity have only a limited influence on the fraction of Li2O2 deposited outside the conductive substrate. These findings provide a rational design framework for controlling the deposition location of discharge products through electrolyte design in LOBs.