Ionic Liquid Regulated Wetting and Chemo-Mechanical Stabilization of NCM811 Cathodes

Traditional poly(vinylidene difluoride) (PVDF) binders fail to protect LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) cathodes due to non-selective interfacial adhesion, causing severe structural pulverization, interfacial debonding, and unstable cathode electrolyte interfacial (CEI) growth during cycling.  Herein, we reveal the cation-dependent interfacial affinity of ionic liquids. An imidazolium-based ionic liquid (EMIM[TFSI]) preferentially wets and encapsulates NCM811 particles, forming a robust interfacial layer with superior elastic modulus (3.4 GPa vs. PVDF 0.49 GPa) and lower dissipation (0.15 vs. PVDF 0.27 keV), whereas pyrrolidinium- and piperidinium-based ILs predominantly plasticized the PVDF-rich phase. The conformal EMIM[TFSI] wetting buffers lattice strain efficiently, suppresses transition-metal dissolution, and induces the formation of thin, uniform, and robust CEI. Benefiting from the integrated chemo-mechanical stabilization, the EMIM[TFSI] modified NCM811 cathode delivers 83% capacity retention after 200 cycles at 1 C, and 0.1 Ah pouch cells achieve 84% retention at 0.5 C. This study establishes that ionic liquid binders offer a rational chemo-mechanical engineering strategy for high-performance NCM811 cathodes.