期刊
JOURNAL OF MATERIALS CHEMISTRY A
卷 9, 期 4, 页码 2325-2333出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0ta09609a
关键词
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资金
- National Science and Engineering Research Council of Canada (NSERC)
- University of Waterloo
- National Natural Science Foundation of China [51772219, 51872209, 21471116, 21628102, 61728403]
- Zhejiang Provincial Natural Science Foundation of China [LZ18E030001, LZ17E020002, LZ15E020002]
- NSERC
- National Research Council Canada
- Canadian Institutes of Health Research
- Province of Saskatchewan
- Western Economic Diversification Canada
- University of Saskatchewan
This study successfully reduced the irreversible processes and improved the cycle stability and electrochemical performance by accommodating the cationic redox couple on the surface of Li-rich layered oxides.
The ability to extract/insert more than one Li per formula unit has made Li-rich layered oxides (LLO) one of the most promising cathode materials. However, irreversible transformations triggered by over-delithiation such as phase transitions, oxygen release and Jahn-Teller effects of Mn3+ have limited its practical application. In this work, the irreversible processes during repetitive de/lithiation were found to be diminished by establishing a gradient cationic redox couple of Mn3+/Mn4+ in Li1.2Ni0.2Mn0.6O2. As revealed by STEM, XPS and XAS measurements, the partial substitution of O2- by F- ions promoted nearby Li/transition metal mixing and reduced the valence state of Mn on the surface. Such a configuration shifted the surface redox center towards cationic redox couple (Mn3+/Mn4+), reducing the irreversible oxygen release as well as the ensuing structure and oxidation state changes. As a result of the modification, the product delivered a discharge capacity of 203.4 mA h g(-1) after 80 cycles at 0.2C and achieved capacity retention of 89.6% after 100 cycles at 0.5C. The suppressed irreversible processes during repetitive cycling were investigated through ex situ X-ray absorption energy near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy and DFT calculations, which confirmed the well-preserved oxidation states and atomic configurations in modified Li1.2Ni0.2Mn0.6O2. Overall, this research provided a new avenue to control the irreversible processes in LLO without changing the anion redox behavior of lattice O2- in the bulk area by accommodating the cationic redox couple on the surface.
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