A Tough, Adhesive, and Protective Binder Shield for Stabilizing High‐Nickel Cathodes in Lithium‐Ion Batteries

High‐nickel layered oxide cathodes, LiNi x Co y Mn z O 2 (NCM), offer high theoretical capacities and energy densities but suffer from structural degradation and interfacial instability, limiting their practical application in lithium‐ion batteries. To address these challenges, a tough, adhesive, and protective binder is developed based on polyacrylic acid (PAA)‐grafted polyvinylidene fluoride (PVDF) cross‐linked with branched polyethyleneimine (PEI) (PVDFA‐N). Systematic tuning of the binder composition enables precise control over mechanical properties and the establishment of structure‐property‐performance relationships. The optimized PVDFA‐N binder exhibits high toughness and strong adhesion, delivering excellent electrochemical performance even under high mass loading and lean binder conditions. Post‐mortem analyses and density functional theory (DFT) calculations reveal that strong interfacial adhesion and the presence of chelating functional groups allow the binder to act as a protective shield, effectively suppressing structural degradation, transition metal ion dissolution, and inhomogeneous cathode‐electrolyte interphase (CEI) formation. Moving beyond the conventional role of mechanical adhesion, this study establishes a new paradigm for binder design by highlighting the active role of the binder in surface protection, offering a promising pathway toward durable, high‐energy lithium‐ion batteries.