Oxygen-Buffering Oxides Stabilize Li ₂ RuO ₃ by Suppressing Redox-Driven Nanoparticle Migration

Oxygen-redox-induced structural degradation and nanoscale fragmentation remain major barriers to fully exploiting the high capacity of Li 2 RuO 3 (LRO) and related anionic-redox cathodes. Here we show that incorporating oxygen-buffering oxides, CeO 2 and Pr 6 O 11, effectively suppresses electrochemically driven nanoparticle migration and markedly enhances the cycling stability and rate capability of LRO. CeO 2 forms homogeneous, well-contacted composites with LRO while remaining chemically inert up to 800 °C, whereas Pr 6 O 11 reacts with LRO at 600 °C to form a new perovskite-related phase, LiPr 2 RuO 6 . In both systems, the LRO phase remains free of Ce and Pr ions and is solely responsible for Li-intercalation via Ru- and O-redox processes. Deep delithiation induces a P 2 1 / m → P 3 1 m transformation accompanied by lattice-oxygen redox, which promotes electrolyte decomposition and nanoscale pulverization. The modifiers mitigate these effects by buffering oxygen-redox activity. This reduces particle-level stress, suppresses fragmentation, and confines nanoscale fragments, which retards long-range nanoparticle migration. Pr 2 LiRuO 6 provides the strongest oxygen-buffering effect, yielding the greatest enhancement in electrochemical performance. These findings highlight oxygen-buffering composite design as a powerful strategy for stabilizing oxygen-redox cathodes.