When lithium-oxygen batteries discharge, O 2 is reduced at the cathode to form solid Li 2 O 2. Understanding the fundamental mechanism of O 2 reduction in aprotic solvents is therefore essential to realizing their technological potential. Two different models have been proposed for Li 2 O 2 formation, involving either solution or electrode surface routes. Here, we describe a single unified mechanism, which, unlike previous models, can explain O 2 reduction across the whole range of solvents and for which the two previous models are limiting cases. We observe that the solvent influences O 2 reduction through its effect on the solubility of LiO 2, or, more precisely, the free energy of the reaction LiO 2 ∗ â €...â ‡Œâ €...Li (sol) + â €‰+â €‰O 2 â (sol) â €‰+â €‰ion pairsâ €‰+â €‰higher aggregates (clusters). The unified mechanism shows that low-donor-number solvents are likely to lead to premature cell death, and that the future direction of research for lithium-oxygen batteries should focus on the search for new, stable, high-donor-number electrolytes, because they can support higher capacities and can better sustain discharge.
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All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)