Characterizing Oxygen Local Environments in Paramagnetic Battery Materials via O-17 NMR and DFT Calculations

• Experimental techniques that probe the local environment around O in paramagnetic Li-ion cathode materials are essential in order to understand the complex phase transformations and O redox processes that can occur during electrochemical delithiation. While Li NMR is a well-established technique for studying the local environment of Li ions in paramagnetic battery materials, the use of O-17 NMR in the same materials has not yet been reported. In this work, we present a combined O-17 NMR and hybrid density functional theory study of the local O environments in Li2MnO3, a model compound for layered Li-ion batteries. After a simple O-17 enrichment procedure, we observed five resonances with large O-17 shifts ascribed to the Fermi contact interaction with directly bonded Mn4+ ions. The five peaks were separated into two groups with shifts at 1600 to 1950 ppm and 2100 to 2450 ppm, which, -with the aid of first principles calculations, were assigned to the O-17 shifts of environments similar to the 4i and 8j sites in pristine Li2MnO3, respectively. The multiple O environments in each region were ascribed to the presence of stacking faults within the Li2MnO3 structure. From the ratio of the intensities of the different O-17 environments, the percentage of stacking faults was found to be ca. 10%. The methodology for studying (17)Oshifts in paramagnetic solids described in this work will be useful for studying the local environments of O in a range of technologically interesting transition metal oxides.

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NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

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