Residual‐Lithium‐to‐LiF Conversion Enables a LiF–Fluorinated Carbon Interphase for Reconstruction‐Resistant Ni‐Rich Cathodes

ABSTRACT High nickel layered oxide cathodes offer high energy density but suffer from rapid degradation caused by residual lithium and surface reconstruction into electrochemically inactive NiO rock‐salt phases. Here, we introduce a monomer‐derived fluorine surface engineering route for Li[Ni 0.90 Co 0.05 Mn 0.05 ]O 2 (NCM90): thermal decomposition of a small amount of 2‐perfluorohexyl ethyl acrylate converts residual surface lithium to LiF while forming an island‐like fluorinated amorphous carbon matrix, yielding a LiF/a‐C: F composite coating (LiF/FC). The coating suppresses rock‐salt formation by mitigating Ni 4+ lattice oxygen interactions during delithiation and acts as a passivating, stress‐buffering interphase that limits electrolyte contact and preserves structural integrity. As a result, LiF/FC‐coated NCM90 delivers improved initial coulombic efficiency (94.61%–94.94%) and 88.54% capacity retention (178 mAh g −1 ) after 200 cycles at 0.5 C (2.7–4.3 V), ∼1.6‐fold higher than pristine NCM90. Post‐mortem analyses confirm reduced microcracking and transition metal dissolution, consistent with suppressed surface reconstruction. This solvent‐free thermal strategy provides a simple pathway to stabilize high Ni cathodes for durable lithium‐ion batteries.