Ultra‐Stable High‐Voltage Cycling of Li‐Ion Batteries via Interphase Engineering with 3,5‐Bis(trifluoromethyl)phenyl Isocyanate

ABSTRACT This paper introduces a novel electrolyte additive, 3,5‐bis(trifluoromethyl)phenyl isocyanate (3,5‐Bis(CF 3 )PhNCO), designed to mitigate interfacial instability and structural degradation of single‐crystal LiNi 0.92 Co 0.06 Mn 0.02 O 2 cathodes under 4.6 V high‐voltage cycling. Distinct from conventional monofunctional additives, 3,5‐Bis(CF 3 )PhNCO integrates strongly reactive ‐NCO groups and electronegative ‐CF 3 groups, enabling a unique synergistic working mechanism. The ‐NCO moiety scavenges moisture and neutralizes acidic species (e.g., HF) to suppress electrolyte hydrolysis, while the ‐CF 3 groups enhance hydrophobicity and induce preferential oxidative decomposition for the formation of a robust cathode‐electrolyte interphase (CEI). Driven by this synergistic effect, the additive constructs a ∼20 nm nitrogen‐rich CEI layer, which effectively alleviates uneven Li + deposition, stabilizes the valence states of transition metals, and inhibits microcracking of the NCM92 cathode‐effects validated by focused ion beam (FIB) 3D reconstruction, X‐ray absorption fine structure spectroscopy (XAFS), and COMSOL Multiphysics simulations. Electrochemically, with 2 wt.% additive incorporation, the cells achieved an excellent capacity retention of 87.08% after 150 cycles at a 0.5 C rate, while full cells maintained 86.67% of their capacity after 1400 cycles at 1 C. This work establishes theoretical and experimental frameworks for multifunctional additive design, offering critical guidance for developing high‐energy‐density, long‐life lithium‐ion battery cathodes.