期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 125, 期 1, 页码 58-73出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.0c08095
关键词
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资金
- Mercedes-Benz Research and Development North America (MBRDNA)
- Center for Mesoscale Transport Properties, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0012673]
- New York State Energy Research and Development Authority (NYSERDA) [75039]
- New York State Department of Economic Development (DED) [76890]
- DOE Office of Science by Brookhaven National Laboratory [DE-SC0012704]
- U.S. DOE Office of Science User Facility, at Brookhaven National Laboratory [DE-SC0012704]
- Brookhaven National Laboratory
- William and Jane Knapp Chair in Energy and the Environment
Ni-rich NMC materials show promise as Li-ion cathodes, but suffer from capacity fade due to structural degradation over extended cycling. Operando XAS studies revealed the structural response and key mechanistic components of Ni-rich NMC materials during cycling, providing insights for future electrode design.
Ni-rich NMC materials are a particularly promising class of Li-ion cathodes for various applications. Li-Ni0.6Mn0.2Co0.2O2 (NMC622) offers a unique balance of thermal stability and energy density, thus attracting attention for electric vehicle implementation. However, upon extended cycling, capacity fade is prevalent due to structural degradation, which is a major drawback for layered oxide cathodes. Therefore, exploring the underlying phenomena that drive detrimental structural response can lead to future improvements. For the first time, operando X-ray absorption spectroscopy (XAS) was performed on NMC622 pouch cells at three different stages. An extensive description of the first cycle (de)lithiation mechanisms was achieved through X-ray absorption near-edge structure analyses and extended X-ray absorption fine structure modeling. Transition metal specific electrochemical participation and structural variation revealed that much of the delivered capacity and distortion is a result of Ni redox behavior, while the local structure of Co and Mn are impacted due to their interdependencies. Key mechanistic components were identified, as the local structural variation from redox processes and Ni3+ Jahn-Teller distortion were decoupled. Further, operando XAS was used to investigate the structural response of NMC622 to extended cycling and was supported by X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy analyses. Reduced capacity was found in the cell after 100 cycles and is attributed to structural degradation and cathode-electrolyte interphase buildup from repeated Li (de)insertion processes, which limit the electrochemical reversibility of Ni and Co through increased polarization. These results expand the understanding of a Ni-rich NMC material under extended cycling, which is vital to the future design of electrode materials.
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