A Self‐Assembled Single‐Ion Membrane via In Situ Neutralization Enables Triple Stability in Ultrahigh‐Nickel Cathodes

Ultrahigh‐nickel layered oxides (Ni ≥ 90%) offer exceptional specific capacity but suffer from severe air sensitivity, poor thermal stability, and rapid capacity decay. To date, it is still a significant challenge to address all three bottlenecks simultaneously with a single and integrated strategy, which have severely hindered the large‐scale commercial deployment of ultrahigh‐nickel layered oxide cathodes. Herein, a novel self‐assembling single‐ion conductor membrane, featuring exceptional hydrophobicity, outstanding thermal stability (>445°C), and strong Donnan exclusion against PF 6 − anions, is rationally engineered to holistically enhance the air stability, heat resistance, and electrochemical performance of ultrahigh‐nickel layered oxide cathodes. The N‐cyano‐sulfonamide group on membrane undergoes an in‐situ neutralization reaction with residual LiOH/Li 2 CO 3 on the LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM9055), which drives it migration toward the cathode surface and form a self‐assembled protective coating with pronounced hydrophobicity and strong Donnan exclusion. As a result, 3.5 Ah NCM9055/Gr pouch battery demonstrates a commendable capacity retention of 94.97% after 500 cycles. meanwhile the onset temperature of thermal runaway was significantly elevated from 124.2°C to 158.2°C. This work establishes a unified interfacial engineering paradigm that simultaneously addresses the long‐standing triad of bottlenecks plaguing ultrahigh‐nickel layered oxide cathodes, offering a scalable and industrially viable pathway toward safe, long‐life, high‐energy‐density lithium‐ion batteries (LIBs).