Simultaneous Stabilization of Potassium Metal and Superoxide in K-O2 Batteries on the Basis of Electrolyte Reactivity.

In superoxide batteries based on O2 /O2- redox chemistry, identifying an electrolyte to stabilize both the alkali metal and its superoxide remains challenging owing to their reactivity towards the electrolyte components. Bis(fluorosulfonyl)imide (FSI- ) has been recognized as a "magic anion" for passivating alkali metals. The KFSI-dimethoxyethane electrolyte passivates the potassium metal anode by cleavage of S-F bonds and the formation of a KF-rich solid-electrolyte interphase (SEI). However, the KFSI salt is chemically unstable owing to nucleophilic attack by superoxide and/or hydroxide species. On the other hand, potassium bis(trifluorosulfonyl)imide (KTFSI) is stable to KO2 , but results in mossy potassium deposits and irreversible plating and stripping. To circumvent this dilemma, we developed an artificial SEI for the metal anode and thus long-cycle-life K-O2 batteries. This study will guide the development of stable electrolytes and artificial SEIs for metal-O2 batteries.