Abstract
Ni-rich layered oxide cathodes (e.g., LiNi₀.₈Mn₀.₁Co₀.₁O₂) are promising for high-energy-density lithium-ion batteries but suffer from severe capacity fading due to complex degradation mechanisms. This study employs advanced characterization techniques, including synchrotron-based X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM), to elucidate structural, chemical, and morphological degradation pathways. Commercial LiNi₀.₈₃Co₀.₁₁Mn₀.₀₆O₂ cathodes were cycled at 4.3 V vs. Li/Li⁺ for up to 500 cycles. Results reveal that capacity loss correlates with irreversible phase transitions from layered to rock-salt structure at the surface, exacerbated by microcrack formation and electrolyte decomposition. Quantitative analysis shows a 40% reduction in Ni oxidation state from Ni³⁺ to Ni²⁺ after 500 cycles, along with a 15% increase in cation mixing. Surface coating with Al₂O₃ mitigates degradation, retaining 85% capacity versus 65% for uncoated samples. These findings provide critical insights for designing durable Ni-rich cathodes.
Keywords
Ni-rich layered oxide, cathode degradation, lithium-ion batteries, X-ray characterization, phase transition, cation mixing, surface coating, capacity fading