Reactive oxygen species in layered oxide cathodes: origins, interfacial cascade degradation, and stabilization strategies

Layered transition-metal oxides are key cathodes for high-energy lithium-ion and sodium-ion batteries, yet high-voltage operation often destabilizes lattice oxygen. Deep alkali-metal extraction reconstructs the transition-metal–oxygen (TM–O) electronic structure and increases O 2p participation in charge compensation, promoting oxygen-hole localization, O O coupling, and oxygen-vacancy formation. These processes can lead to the generation and release of reactive oxygen species (ROS). Together, lattice oxygen instability and ROS evolution couple bulk structural degradation with interfacial reactions, accelerating phase transitions, near-surface reconstruction, particle cracking, electrolyte decomposition, gas evolution, transition-metal dissolution, and cathode/electrolyte interphase degradation. This review summarizes the thermodynamic basis, generation pathways, and bulk-to-interface evolution of ROS in layered oxide cathodes, together with key methods for probing lattice oxygen-ROS evolution. Three representative drivers of oxygen instability are emphasized: high-valence TM–O electronic-structure reconstruction in Ni-rich layered oxides, local Li O Li configurations in Li-rich layered oxides, and desodiation-induced stacking strain in layered sodium oxides. Stabilization strategies based on bulk compositional regulation, ordered-structure design, surface coating, and electrolyte engineering are then discussed. Finally, challenges in identifying oxygen-related species and coordinating bulk, surface, and interfacial stabilization are outlined, providing guidance for designing high-energy layered cathodes with improved durability and safety.