Influence of binders and solvents on stability of Ru/RuOx nanoparticles on ITO nanocrystals as Li–O2 battery cathodes

Li-O2 battery research at a fundamental level remains critical, and nature of reactions and stability are paramount for realising the promise of the Li-O2 system. We report that ITO nanocrystals with supported 1-2 nm OER catalyst Ru/RuOx nanoparticles demonstrate efficient OER processes, significantly reducing the cell's recharge overpotential, and maintain catalytic activity to promote a consistent cycling discharge potential in Li-O2 cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuOx nanoparticles lower the charge overpotential compared to ITO and carbon-only cathodes and have the greatest effect in DMSO electrolytes with a solution-processable F-free CMC binder (< 3.5 V) vs PVDF. Ru/RuOx/ITO nanocrystalline materials in DMSO provide efficient Li2O2 decomposition from within the cathode during cycling. We demonstrate that the ITO is actually unstable from the first cycle and completely dissolves by chemical etching, but Ru/RuOx NPs remain effective OER catalysts for Li2O2 during cycling. CMC binders avoid PVDF-based side reactions in either electrolyte, improving efficient cyclability. ITO nanocrystal deterioration is significantly mitigated in cathodes using a CMC binder, and cells show good cycle life. In mixed DMSO-EMITFSI ionic-liquid electrolytes, Ru/RuOx/ITO materials in Li-O2 cells cycle very well and maintain a consistently very low charge overpotential of 0.5 - 0.8 V.