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.