Solvent Degradation in Nonaqueous Li‑O₂ Batteries: Oxidative Stability versus H‑Abstraction

Developing rechargeable Li-O₂ batteries hinges on identifying stable solvents resistant to decomposition. Here, we focus on solvent stability against adsorption-induced H-abstraction during discharge. Using a detailed thermodynamic analysis, we show that a solvent’s propensity to resist H-abstraction is determined by its acid dissociation constant, pK_a, in its own environment. Upon surveying hundreds of solvents for their pK_a values in different media, we find linear correlations between the pK_a values across various classes of solvents in any two given media. Utilizing these correlations, we choose DMSO as the common standard to compare the relative stability trends. We construct a stability plot based on the solvent’s HOMO level and its pK_a in DMSO, which reveals that most solvents obey a correlation where solvents with lower HOMO levels tend to have lower pK_a values in DMSO. However, this is at odds with the stability requirement that demands deep HOMO levels and high pK_a values. Thus, stable solvents need to be outliers to this observed correlation.