Differential Surface Dynamics of LiCoO ₂ Through Solid Electrolyte Interface and Artificial Layer Under Varied Potential Conditions

ABSTRACT In rechargeable batteries, the integrity of the active material surface plays an important role in facilitating ion and electron transfer during electrochemical reactions. This study investigates two critical surface failure modes: electrolyte side reactions and irreversible phase transition, particularly evident at high potentials of LiCoO ₂ (LCO). By employing an artificial coating and solid electrolyte interface (SEI), represented by Al ₂ O ₃ and lithium bis(oxalate)borate (LiBOB) electrolyte additive, respectively, this work elucidates the underlying mechanism of LCO degradation across various potential regimes. The findings reveal that LCO degradation at lower voltage (4.2–4.6 V vs. Li/Li ⁺ ) is dominantly attributed to electrolyte side reactions, whereas LCO degradation at higher voltage (≥ 4.7 V vs. Li/Li ⁺ ) accelerates failure due to irreversible structural evolution. An Al ₂ O ₃ coating, featuring an Al‐doped surface, effectively mitigates surface‐propagated high‐voltage cathode failure by introducing a robust surface matrix. Moreover, artificial coating with a doping layer can suppress phase transitions and boost high‐voltage battery performance. Despite the electrolyte additive LiBOB's inability to prevent the high‐voltage phase transition in LCO, this study demonstrates that LiBOB‐SEI mitigates side reactions at lower voltage but lacks effectiveness against phase transition. image