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

In situ electrochemically induced surface oxygen vacancies (OVs) by Li 2 C 4 O 4 decomposition enable dual regulation of cathode electrolyte interphase (CEI) thickness and composition, a novel strategy for tailored CEI engineering in Li ion batteries. For the first time, 18 O isotope labeling combined with TOF SIMS directly verifies that lattice oxygen of LiCoO 2 (LCO) serves as the predominant oxygen source for Li x PO y F z in CEI, clarifying the long debated LiPF 6 decomposition mechanism at the cathode inte rface. The OV mediated strategy endows LCO with 71.1% capacity retention after 600 cycles at 1 C (3–4.4 V) (vs. 23.9% for bare LCO) and achieves universal applicability in 4.5 V high voltage systems and NCM811 cathodes, establishing a new design principle for stable high performance cathodes.