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

Fundamental research on Li–O₂batteries remains critical, and the nature of the reactions and stability are paramount for realising the promise of the Li–O₂system. We report that indium tin oxide (ITO) nanocrystals with supported 1–2 nm oxygen evolution reaction (OER) catalyst Ru/RuO_xnanoparticles (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–O₂cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuO_xnanoparticles 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 Li₂O₂decomposition 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_xNPs remain effective OER catalysts for Li₂O₂during 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–O₂cells cycle very well and maintain a consistently very low charge overpotential of 0.5–0.8 V.