Unveiling Long-Term Storage Failure Mechanisms of Single-Crystal High-Nickel Cathodes During Air Exposure

Single-crystal high-nickel cathode (SC-HN) materials are promising candidates for advanced lithium-ion batteries due to their exceptional volumetric and gravimetric energy densities. However, SC-HN materials face air instability, causing distinct storage failure mechanisms compared to polycrystalline high-nickel cathode (PC-HN) materials. The characteristics of SC-HN, such as their lower specific surface area and reduced grain boundaries, make their failure mechanisms distinct and not directly applicable to PC-HN materials. To address these unique degradation pathways, this study systematically investigated the storage failure mechanisms of SC-HN material under ambient air exposure. Using advanced characterization techniques including soft X-ray absorption spectra (sXAS), wide-angle X-ray scattering (WAXS), aberration-corrected scanning transmission electron microscopy (STEM), and etching-based X-ray photoelectron spectroscopy (XPS), we conducted comprehensive multi-dimensional analyses over 6 months to track the evolution of chemical and structural changes. The results reveal that SC-HN materials experience a nonlinear progression of structural and surface composition degradation, and surface structural transformations are found to be the main cause of performance decline. The findings deepen understanding of SC-HN air instability and provide a basis for targeted strategies to enhance storage stability.