4.8 Article

Anionic redox induced anomalous structural transition in Ni-rich cathodes

期刊

ENERGY & ENVIRONMENTAL SCIENCE
卷 14, 期 12, 页码 6441-6454

出版社

ROYAL SOC CHEMISTRY
DOI: 10.1039/d1ee02987h

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资金

  1. Scientific User Facilities Division, Office of Basic Sciences, U.S. Department of Energy
  2. U.S. Department of Energy (DOE) - Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) [DE-AC05-00OR22725]
  3. Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the US Department of Energy (DOE) through the Advanced Battery Materials Research (BMR) Program
  4. Battery500 Consortium [DE-SC0012704]
  5. DOE Office of Science [DE-SC0012704]
  6. Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory [DE-SC0012704]
  7. Scientific Data and Computing Center, a component of the Computational Science Initiative [DE-SC0012704]
  8. U.S. Department of Energy [DE-AC05-00OR22725]

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Ni-rich cathodes undergo a four-stage structural evolution during the initial cycle, with a universal structural transition occurring at around 75% delithiation. This transition, marked by an anomalous increase in average TM-O bond lengths, is induced by the direct oxidation of lattice oxygen ions. The onset of this transition correlates well with the release of oxygen gas and decline in capacity retention, highlighting its crucial role in the degradation process.
Ni-rich cathodes have emerged as one of the most promising candidates for power next generation electric vehicles. However, they often suffer from poor capacity retention when charged to high voltages and the origin of this degradation remains elusive. Here, by using high throughput operando neutron diffraction, a universal four-stage structural evolution of Ni-rich cathodes is revealed during the initial cycle for the first time. Particularly, we discovered a universal structural transition in Ni-rich cathodes at similar to 75% delithiation irrespective of Ni or substituent contents. This transition is hallmarked by the anomalous increase of average TM-O bond lengths, contradicting the conventional wisdom that TM-O bond lengths decrease during charge (oxidation). This anomaly is induced by the direct oxidation of lattice oxygen ions, which is rooted in the drastic decrease of oxygen-to-TM charge transfer gap at high degrees of delithiation. The onset of this anomalous transition matches very well with the onset of oxygen gas release and severe decline of capacity retention in Ni-rich cathodes, suggesting that this bulk structural transition plays an indispensable role in the degradation process. These findings shed light on the elusive degradation mechanism of Ni-rich cathodes, providing valuable clues to stabilize oxidized oxygen ions for stable cycling of layered oxide cathodes at high voltages.

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