Coupling of Oxygen Dimer and Trapped O2 with Strong Magnetic Frustration in Layered Li-rich Cathodes

Anion redox in layered Li-rich cathodes provides a high capacity but triggers a series of cascading issues. Current research predominantly focuses on how oxygen species participate in redox and how transition metals move, often ignoring the influence of magnetic frustration. This work systematically investigates the potential link between the evolution of magnetic frustration, structural evolution and oxygen redox in honeycomb Li2RuO3. Our findings indicate that the phase transition from C2/c to R3 exacerbates the magnetic frustration during Ru oxidation. Subsequently, during oxygen oxidation, the strong magnetic frustration drives the generation of (O2)n− and trapped O2, which serves to relieve and eventually eliminate the magnetic frustration. This (O2)n−/O2 formation mechanism, termed "magnetic-frustration-driven mechanism", provides a plausible explanation for the formation of trapped O2 in the systems with strong covalent TM–O bonds. Accordingly, we emphasize that improvement strategies should not only enhance the covalent TM–O bonds but also relieve strong magnetic frustration.