Tailoring electrolyte activity for a highly stable LiOH redox process in lithium–oxygen batteries

Abstract

Lithium–oxygen (Li–O₂) batteries offer ultrahigh theoretical energy density, but suffer from limited cycle life and high overpotentials, particularly in LiOH-based systems. While LiOH chemistry provides superior environmental tolerance compared to Li₂O₂ systems, the inherent four-electron redox process creates substantial charging overpotentials that compromise performance. Here, we tailor electrolyte activity to enable an efficient LiOH redox process by integrating 1-phenylpyrrolidine (PPD) as a redox mediator within an ionic liquid electrolyte. PPD possesses an optimal oxidation potential and stable p–π conjugation, enabling homogeneous chemical decomposition of LiOH and overcoming electrode–electrolyte contact limitations. The ionic liquid 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C₃C₁im TFSI) is engineered to regulate water reactivity and maintain hydrogen-bond networks, thereby promoting selective LiOH formation over Li₂O₂ during discharge, while providing high oxidative stability to suppress mediator degradation—an issue prevalent in ether-based electrolytes. This electrolyte–mediator synergy shifts the charging mechanism from sluggish interfacial charge transfer to a fast, solution-mediated chemical route, delivering 180 stable cycles with markedly reduced overpotentials and ∼10× longer cycle life. This work offers molecular-level design principles for tailoring electrolyte activity to achieve high-efficiency and durable Li–O₂ batteries based on LiOH chemistry.