Local and Bulk Probe of Vanadium-Substituted α-Manganese Oxide (α-KxVyMn8–yO16) Lithium Electrochemistry
- 8 July 2021
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 60 (14), 10398-10414
- https://doi.org/10.1021/acs.inorgchem.1c00954
Abstract
A series of V-substituted α-MnO2 (KxMn8–yVyO16·nH2O, y = 0, 0.2, 0.34, 0.75) samples were successfully synthesized without crystalline or amorphous impurities, as evidenced by X-ray diffraction (XRD) and Raman spectroscopy. Transmission electron microscopy (TEM) revealed a morphological evolution from nanorods to nanoplatelets as V-substitution increased, while electron-energy loss spectroscopy (EELS) confirmed uniform distribution of vanadium within the materials. Rietveld refinement of synchrotron XRD showed an increase in bond lengths and a larger range of bond angles with increasing V-substitution. X-ray absorption spectroscopy (XAS) of the as-prepared materials revealed the V valence to be >4+ and the Mn valence to decrease with increasing V content. Upon electrochemical lithiation, increasing amounts of V were found to preserve the Mn–Mnedge relationship at higher depths of discharge, indicating enhanced structural stability. Electrochemical testing showed the y = 0.75 V-substituted sample to deliver the highest capacity and capacity retention after 50 cycles. The experimental findings were consistent with the predictions of density functional theory (DFT), where the V centers impart structural stability to the manganese oxide framework upon lithiation. The enhanced electrochemistry of the y = 0.75 V-substituted sample is also attributed to its smaller crystallite size in the form of a nanoplatelet morphology, which promotes facile ion access via reduced Li-ion diffusion path lengths.Funding Information
- Basic Energy Sciences (DE-SC0012673, DE-SC0012704)
- Division of Graduate Education (1839287)
- U.S. Department of Education
- William and Jane Knapp Chair of Energy and the Environment
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