In Situ Phosphoester Polymer Layer Locking Oxygen Migration in Ni‐Rich Cathodes Under Ultra‐High Voltage

. Physically, the crosslinked polymer network regulates oxygen transport and captures evolved oxygen species, thereby mitigating parasitic reactions. This dual-function interlayer suppresses gas evolution, reduces strain accumulation, and stabilizes bulk structural integrity under ultra-high-voltage operation. Consequently, the modified cathode delivers 81.5% capacity retention after 100 cycles at 1 C under 4.6 V, which is an improvement of 25.3% over the pristine counterpart, and enables stable cycling of a 3.2 Ah pouch full cell. This scalable in situ interfacial strategy provides an effective pathway to suppress oxygen-related degradation in Ni-rich cathodes, advancing safer and higher-energy lithium batteries.