Charge Transport in Alkali-Metal Superoxides: A Systematic First-Principles Study

Charge-transport mechanisms within the discharge products of alkali-metal/O2 batteries can strongly influence the performance of these systems. To date, discharge products comprising alkali peroxides (Li2O2 and Na2O2) and superoxides (LiO2, NaO2, and KO2) have been observed. In general, cells that discharge to a superoxide exhibit lower overpotentials than those that form the corresponding peroxide. These lower overpotentials have been hypothesized to originate from more efficient charge transport within the superoxides. While the transport mechanisms in the peroxides have been well studied, consensus regarding the intrinsic conductivity across the alkali-metal superoxides is lacking. Here, we present a systematic first-principles study of charge-transport mechanisms across the alkali-metal (Li, Na, K) superoxides. Our study draws on our prior investigations of the alkali peroxides and of sodium superoxide, while adding new analyses for lithium and potassium superoxides (LiO2 and KO2). In the case of KO2,...