Sulfur-Fluoride Exchange-Driven Covalent Grafting Tunes the Electric Double Layer for Stabilizing LiNi 0.9 Co 0.05 Mn 0.05 O ₂ Cathode

The aggressive pursuit of energy-dense lithium-ion batteries has identified nickel-rich cathodes (e.g., LiNi 0.9 Co 0.05 Mn 0.05 O 2, NCM90) as indispensable candidates. However, their practical deployment is hindered by severe interfacial degradation driven by Ni 4+ and oxygen evolution. While bulk electrolyte engineering is well-explored, deterministic control over the interfacial microenvironment, specifically the electric double layer (EDL), remains a pressing challenge. Herein, we introduce a transformative strategy to reconfigure the EDL via sulfur-fluorine exchange (SuFEx)-driven covalent grafting of 4-nitrobenzenesulfonyl fluoride (NBSF) onto the NCM90 surface. The resulting interfacial dipole field repels detrimental carbonate solvents while inducing anion enrichment at the inner Helmholtz plane. This tailored EDL reshapes interfacial reaction pathways, suppressing solvent dehydrogenation and parasitic oxidation to yield a protective cathode–electrolyte interphase (CEI). Consequently, Ah-level graphite||NCM90 pouch cells achieve 91.5% capacity retention over 300 cycles, outperforming the unmodified system (76.5%). By correlating surface dipole modification, EDL reorganization, and interfacial reactivity, this work provides a mechanistic framework for interface engineering in advanced energy storage systems.