Selective Facet Growth and Surface Reconstruction Achieving Structure-Robust High-Voltage LiCoO₂.

Abstract

Propagation of the surface defects degrades the bulk structure and destroys the Li⁺ diffusion channels in the layered oxide cathode materials, deteriorating the performance of the secondary batteries. We herein propose an effective strategy to form intrinsically stable surface structures and achieve the excellent cyclability of high-voltage LiCoO₂ (HV-LCO) by regulating its crystal facets and reconstructing its surface in a LiCl molten salt. Incorporation of the selectively grown inactive (003) facet and the rock salt-passivated (010) facet successfully suppresses the oxygen loss and structural degradation on the surface and stabilizes the Li⁺ diffusion channels up to 4.6 V (vs. Li⁺/Li). The suppressed CoO₆ slab gliding and H3/H1-3/O1 phase transition ensure structural stability at deep delithiation states. Based on the first-principles calculations and the structural and electrochemical characterizations, a correlation was clarified between the specifically exposed surface facets and the suppressed structural degradation. These findings underline the importance of the surface facets and will inspire ideas to improve the performance of high-voltage cathode materials by synergistically modifying their surface structure and crystal morphology.