Revisiting Solvent-Dependent Roles of the Electrolyte Counteranion in Li-O2 Batteries upon CO2 Incorporation

Abstract

Lithium-oxygen batteries are promising next-generation high-energy storage candidates. Replacing pure O2 with air and uncovering moisture and CO2-contamination effects on the O2 electrochemistry, however, represent necessary steps toward commercialization. Representatively, a CO2-induced shift toward Li2CO3 formation has been systematically disclosed in a number of electrolyte solvents. Here, we show that in tetraglyme only Li2CO3 is formed without Li2O2. Using explicit theoretical calculations, we reveal that discharge is governed by the strong chelation effect induced by oxygen lone electron pairs of the glyme, which emphasizes the importance of assessing direct interatomic interactions between Li+ and solvent molecules when determining preferred reaction pathways in these O2/CO2 systems. The choice of the electrolyte counteranion investigated here for the first time, however, has no apparent effect on the O2/CO2 electrochemistry, leading to Li2CO3. Galvanostatic results and product analysisnonetheless reveal that highly dissociated Li+ counteranions in tetraglyme favorably stabilize soluble peroxocarbonate reaction intermediates during discharge, whereas highly associated salts accelerate Li2CO3 precipitation, dramatically narrowing the cell capacity. Importantly, these observations are also distinct from prior conclusions from rationally designed electrolytes under pure O2 conditions and emphasize the need to revisit established correlations between uncovered counteranion···Li+···solvent interaction degrees and the balance between mechanistic pathways in practical Li-air devices. © 2022 American Chemical Society