Abstract
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 ∼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.
| Original language | English |
|---|---|
| Pages (from-to) | 6441-6454 |
| Number of pages | 14 |
| Journal | Energy and Environmental Science |
| Volume | 14 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 2021 |
Funding
Research conducted at the NOMAD beamlines at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Sciences, U.S. Department of Energy. J. L. would like to thank Dr Joerg Neuefeind and Dr. Matthew Tucker for fruitful discussions and support for the operando battery experiments at NOMAD. The authors would also like to thank Harley Skorpenske for assisting set up of the electrochemical measurements at NOMAD. Z. D. and L. G. would like to acknowledge support from the U.S. Department of Energy (DOE) under Contract No. DE-AC05-00OR22725, which was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO). S. T. and E. H. are supported by the 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, including Battery500 Consortium under contract no. DE-SC0012704. This research used beamline 7-BM of the National Synchrotron Light Source II, a US DOE Office of Science user facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. This research also used the Scientific Data and Computing Center, a component of the Computational Science Initiative operated by Brookhaven National Laboratory under Contract No. DE-SC0012704. Notice: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http:// energy.gov/downloads/doe-public-access-plan).
