Unlocking Electrochemical-Driven Surface Oxygen Vacancies-Regulated Cathode–Electrolyte Interphase for Stabilizing Li-Ion Cells

A stable cathode–electrolyte interphase (CEI) significantly enhances the durability of lithium-ion batteries; however, the intricate chemistry underlying its formation makes predesign exceedingly challenging. This work demonstrates that surface oxygen vacancy (OV) concentration dually regulates CEI thickness and composition. We develop an in situ strategy where Li 2 C 4 O 4 incorporation into LiCoO 2 (LCO) spontaneously decomposes during cycling, generating surface OVs. Combined experimental and theoretical calculations reveal these OVs enhance interfacial electron/Li⁺ migration rates while stabilizing the CEI. Notably, through 18 O isotope labeling with time-of-flight secondary ion mass spectrometry, we innovatively provide direct experimental evidence that surface lattice oxygen serves as the predominant oxygen source for CEI oxygen-containing decomposition products, establishing the mechanism for OV-mediated CEI modulation. Based on this theory, the linear correlation and causal relationship among Li 2 C 2 O 4 content, surface OV concentration, and LiF/Li x PO y F z ratio in CEI are revealed. This strategy endows the OV-rich LCO cathode with 71.1% capacity retention after 600 cycles at 1 C within 3–4.4 V (23.9% for bare LCO) and achieves universal validation at 4.5 V and in LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). This study elucidates the critical function of surface OVs in prolonging cycle life and establishes a new design principle for tailored cathode interfaces and CEI chemistry.