Understanding LiOH Chemistry in a Ruthenium‐Catalyzed Li–O2 Battery

Tao Liu,Clare P. Grey,James T. Frith,Gunwoo Kim,Nuria Garcia‐Araez,Zigeng Liu

doi:10.1002/ange.201709886

Tao Liu, Clare P. Grey + Show 4 more

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https://doi.org/10.1002/ange.201709886

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Abstract

AbstractNon‐aqueous Li–O2 batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li2O2, 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 H2O and the O from both O2 and H2O. 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 Li2O2, 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.

Highlights

Non-aqueous Li-O2 batteries are promising for generation energy storage
In the dimethyl sulfoxide (DMSO) case, it was suggested that at low water contents (~150 ppm), a mixture of Li2O2 and LiOH was formed on discharge, and that on charging, Li2O2 is first converted to LiOH, the latter getting decomposed by Ru catalysts at voltages of as low as ~3.2 V
Using quantitative nuclear magnetic resonance and operando electrochemical pressure and mass spectrometry measurements, we show that on discharging, a total of 4 electrons per O2 is involved in LiOH formation, this process incurring fewer side reactions compared to Li2O2

Summary

Introduction

Non-aqueous Li-O2 batteries are promising for generation energy storage. New battery chemistries based on LiOH, rather than Li2O2, have recently been reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. [7] The other case employs a Ru-based solid catalyst in a water-added dimethyl sulfoxide (DMSO) or tetraglyme electrolyte.[8] Ru was proposed to catalyze LiOH formation and decomposition in a tetraglyme electrolyte with 4600 ppm water.

Results

Conclusion