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Issue 24, 2020
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Na-Ion storage in iron hydroxide phosphate hydrate through a reversible crystalline-to-amorphous phase transition

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Abstract

Iron(III) hydroxide phosphate hydrate Fe1.13(PO4)(OH)0.39(H2O)0.61 is investigated for the first time as a Na-ion battery cathode, which reveals that the material exhibits similar storage capacities for Na- and Li-ions at relatively low current rates (i.e. C/10). Interestingly, operando X-ray diffraction shows that insertion of Na-ions induces a solid solution transition in the crystalline Fe1.13(PO4)(OH)0.39(H2O)0.61 end-member simultaneously with a major amorphization. This result adds to the series of observations of phosphate-based materials undergoing order-disorder transitions during Na-ion storage. Fe1.13(PO4)(OH)0.39(H2O)0.61 is thus ideal for enhancing our knowledge on such phenomena. To this end, using total X-ray scattering with pair distribution function analysis, we show that the amorphous phase is Na-rich NaxFe1.13(PO4)(OH)0.39(H2O)0.61 with the local [FeO6]-[PO4] motif retained but with coherence lengths of only ca. 0.6 nm. Our investigation also reveals that the crystallinity of Fe1.13(PO4)(OH)0.39(H2O)0.61 is regained upon Na-extraction (battery recharge), i.e. the order-disorder transition is reversible.

Graphical abstract: Na-Ion storage in iron hydroxide phosphate hydrate through a reversible crystalline-to-amorphous phase transition

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Supplementary files

Article information


Submitted
07 Mar 2020
Accepted
26 May 2020
First published
29 May 2020

Nanoscale, 2020,12, 12824-12830
Article type
Paper

Na-Ion storage in iron hydroxide phosphate hydrate through a reversible crystalline-to-amorphous phase transition

C. Henriksen, M. A. Karlsen, C. L. Jakobsen and D. B. Ravnsbæk, Nanoscale, 2020, 12, 12824
DOI: 10.1039/D0NR01922D

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