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

Developing rechargeable Li-O-2 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.