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Size induced structural changes in maricite-NaFePO4: an in-depth study by experiment and simulations

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Abstract

Rechargeable batteries based on the most abundant elements, such as sodium and iron, have a great potential in the development of cost effective sodium ion batteries for large scale energy storage devices. We report, for the first time, crystallite size dependent structural investigations on maricite-NaFePO4 through X-ray diffraction, X-ray absorption spectroscopy and theoretical simulations. Rietveld refinement analysis on the X-ray diffraction data reveals that a decrease in the unit cell parameters leads to volume contraction upon reduction in the crystallite size. Further, the atomic multiplet simulations on X-ray absorption spectra provide unequivocally a change in the site symmetry of transition metal ions. The high resolution oxygen K-edge spectra reveal a substantial change in the bonding character with the reduction of crystallite size, which is the fundamental cause for the change in the unit cell parameters of maricite-NaFePO4. In parallel, we performed first-principles density functional theory (DFT) calculations on maricite-NaFePO4 with different sodium ion vacancy concentrations. The obtained structural parameters are in excellent agreement with the experimental observations on the mesostructured maricite-NaFePO4. The volumetric changes with respect to crystallite size are related to the compressive strain, resulting in the improvement in the electronic diffusivity. The nano-crystalline maricite-NaFePO4 with improved kinetics will open a new avenue for its usage as a cathode material in sodium ion batteries.

Graphical abstract: Size induced structural changes in maricite-NaFePO4: an in-depth study by experiment and simulations

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Publication details

The article was received on 08 Jul 2019, accepted on 21 Oct 2019 and first published on 21 Oct 2019


Article type: Paper
DOI: 10.1039/C9CP03838H
Phys. Chem. Chem. Phys., 2019, Advance Article

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    Size induced structural changes in maricite-NaFePO4: an in-depth study by experiment and simulations

    M. Sharma, M. Gupta, P. Kaghazchi and S. Murugavel, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C9CP03838H

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