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

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.