Influence of Binders and Solvents on Stability of Ru/RuO x Nanoparticles on ITO Nanocrystals as Li-O 2 Battery Cathodes.

Fundamental research on Li-O ₂ batteries remains critical, and the nature of the reactions and stability are paramount for realising the promise of the Li-O ₂ system. We report that indium tin oxide (ITO) nanocrystals with supported 1-2 nm oxygen evolution reaction (OER) catalyst Ru/RuO _x nanoparticles (NPs) demonstrate efficient OER processes, reduce the recharge overpotential of the cell significantly and maintain catalytic activity to promote a consistent cycling discharge potential in Li-O ₂ cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuO _x nanoparticles lower the charge overpotential compared with those for ITO and carbon-only cathodes and have the greatest effect in DMSO electrolytes with a solution-processable F-free carboxymethyl cellulose (CMC) binder (<3.5 V) instead of polyvinylidene fluoride (PVDF). The Ru/RuO _x /ITO nanocrystalline materials in DMSO provide efficient Li ₂ O ₂ decomposition from within the cathode during cycling. We demonstrate that the ITO is actually unstable from the first cycle and is modified by chemical etching, but the Ru/RuO _x NPs remain effective OER catalysts for Li ₂ O ₂ during cycling. The CMC binders avoid PVDF-based side-reactions and improve the cyclability. The deterioration of the ITO nanocrystals is mitigated significantly in cathodes with a CMC binder, and the cells show good cycle life. In mixed DMSO-EMITFSI [EMITFSI=1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide] ionic liquid electrolytes, the Ru/RuO _x /ITO materials in Li-O ₂ cells cycle very well and maintain a consistently very low charge overpotential of 0.5-0.8 V.
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