A PtRu catalyzed rechargeable oxygen electrode for Li–O2 batteries: performance improvement through Li2O2 morphology control

Abstract

Albeit ultrahigh in energy density, the Li–O₂ battery technology still suffers from the high overpotential of Li₂O₂ oxidation upon charging and the low cyclability. In the present work, we use Pt₂Ru/C as the oxygen-electrode catalyst and study how it improves the cell performance and changes the reaction mechanism, as compared with a carbon electrode. Multiple methods, including X-ray diffraction, transmission/scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry, have been employed for material characterization and reaction monitoring. The Li–O₂ cell with a Pt₂Ru/C catalyst shows lower charge voltage, higher specific capacity, and enhanced cyclability than does a carbon catalyst. The key for this improvement is ascribed to the morphology change of Li₂O₂. Whereas the Li₂O₂ formed in the carbon electrode is rod-shaped, the Li₂O₂ in the Pt₂Ru/C electrode is mud shaped and closely attached to the electrode substrate, thus benefiting the subsequent Li₂O₂ oxidation. This study indicates that the charging performance of the Li–O₂ battery can be improved not only by using proper catalysts, but also by controlling the Li₂O₂ morphology during discharge.