Achieving Highly Reversible O1 Phase Transition in LiCoO ₂ Cathodes at 4.65 V Through YF ₃ ‐Induced Trifunctional Synergistic Effect

ABSTRACT The practical application of LiCoO 2 (LCO) cathodes operated above 4.55 V (vs. Li + /Li) is fundamentally limited by severe structural degradation caused by irreversible H1‐3/O1 phase transitions and exacerbated interfacial parasitic reactions, which collectively lead to rapid capacity fading. Herein, a YF 3 ‐assisted modification strategy is proposed to construct a trifunctional synergistic effect that simultaneously enhances bulk structural robustness and interfacial stability. First, fluorine anion substitution strengthens Co─O bond covalency and suppresses oxygen release during deep delithiation. Second, in situ generated Y 2 O 3 nanoparticles establish a stable heterojunction with LCO grains, which not only mitigates interfacial side reactions but also serves as a mechanical buffer to alleviate anisotropic lattice stress. Third, a controlled amount of Li/Co anti‐site defects is introduced by YF 3 ‐induced slight lithium deficiency during synthesis, in which Co ions occupying Li sites act as structural pillars to stabilize CoO 2 slabs. Benefiting from this trifunctional synergistic effect, the modified LCO exhibits a highly reversible O1 phase transition and superior cycling stability at 4.65 V, delivering 226.3 mAh g −1 at 0.2 C and retaining 175.2 mAh g −1 after 400 cycles at 2 C. This work provides an effective and generalizable approach for designing durable high‐voltage cathode materials for advanced lithium‐ion batteries.