Tailoring electrolyte activity for 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 1phenylpyrrolidine (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.