Understanding LiOH Chemistry in a Ruthenium‐Catalyzed Li–O 2 Battery

Abstract

Non‐aqueous Li–O 2 batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li 2 O 2 , have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru‐catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e − oxygen reduction reaction, the H in LiOH coming solely from added H 2 O and the O from both O 2 and H 2 O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li 2 O 2 , LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long‐lived battery. An optimized metal‐catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals.