Densification of Cathode/Electrolyte Interphase to Enhance Reversibility of LiCoO₂ at 4.65 V

Abstract For LiCoO₂ (LCO) operated beyond 4.55 V (vs Li/Li⁺), it usually suffers from severe surface degradation. Constructing a robust cathode/electrolyte interphase (CEI) is effective to alleviate the above issues, however, the correlated mechanisms still remain vague. Herein, a progressively reinforced CEI is realized via constructing Zr─O deposits (ZrO₂ and Li₂ZrO₃) on LCO surface (i.e., Z‐LCO). Upon cycle, these Zr─O deposits can promote the decomposition of LiPF₆, and progressively convert to the highly dispersed Zr─O─F species. In particular, the chemical reaction between LiF and Zr─O─F species further leads to the densification of CEI, which greatly reinforces its toughness and conductivity. Combining the robust CEI and thin surface rock‐salt layer of Z‐LCO, several benefits are achieved, including stabilizing the surface lattice oxygen, facilitating the interface Li⁺ transport kinetics, and enhancing the reversibility of O3/H1‐3 phase transition, etc. As a result, the Z‐LCO||Li cells exhibit a high capacity retention of 84.2% after 1000 cycles in 3–4.65 V, 80.9% after 1500 cycles in 3–4.6 V, and a high rate capacity of 160 mAh g⁻¹ at 16 C (1 C = 200 mA g⁻¹). This work provides a new insight for developing advanced LCO cathodes.