Steric and Electronic Synergy of CEI Modifier Regulates Bulk and Interphase for 4.5 V Li||NCM811 Batteries

The unstable cathode-electrolyte interphase (CEI) and sluggish Li+ transport kinetics severely limit the practical capacity and cycle life of NCM811 batteries. Herein, we introduce additive 4-fluorobenzenesulfonamide (FBSA) to modulate the solvation environment and CEI composition. Through the electron-withdrawing effect of the sulfonyl group and the steric hindrance of the fluorophenyl group, FBSA achieves a balanced coordination configuration while compressing the Li+ solvation sheath. This sustains favorable bulk ion transport and reduces the interfacial desolvation barrier. Moreover, FBSA shows preferential oxidation capability, inducing a robust CEI enriched with LiF and Li2SOx (x = 3, 4) that markedly alleviates the structural degradation of NCM811. As expected, the Li||NCM811 battery demonstrates excellent cycling stability at 4.5 V (74.85% after 100 cycles at 3 C). This work highlights FBSA's potential to break the inherent limitations of carbonate electrolytes in bulk ion transport and interfacial stability, providing a promising strategy for high-voltage NCM811 batteries.