Polymorphism in Weberite Na2Fe2F7 and its Effects on Electrochemical Properties as a Na-Ion Cathode
© 2023 The Authors. Published by American Chemical Society.
Veröffentlicht in: | Chemistry of materials : a publication of the American Chemical Society. - 1998. - 35(2023), 9 vom: 09. Mai, Seite 3614-3627 |
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1. Verfasser: | |
Weitere Verfasser: | , , , , , |
Format: | Online-Aufsatz |
Sprache: | English |
Veröffentlicht: |
2023
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Zugriff auf das übergeordnete Werk: | Chemistry of materials : a publication of the American Chemical Society |
Schlagworte: | Journal Article |
Zusammenfassung: | © 2023 The Authors. Published by American Chemical Society. Weberite-type sodium transition metal fluorides (Na2M2+M'3+F7) have emerged as potential high-performance sodium intercalation cathodes, with predicted energy densities in the 600-800 W h/kg range and fast Na-ion transport. One of the few weberites that have been electrochemically tested is Na2Fe2F7, yet inconsistencies in its reported structure and electrochemical properties have hampered the establishment of clear structure-property relationships. In this study, we reconcile structural characteristics and electrochemical behavior using a combined experimental-computational approach. First-principles calculations reveal the inherent metastability of weberite-type phases, the close energetics of several Na2Fe2F7 weberite polymorphs, and their predicted (de)intercalation behavior. We find that the as-prepared Na2Fe2F7 samples inevitably contain a mixture of polymorphs, with local probes such as solid-state nuclear magnetic resonance (NMR) and Mössbauer spectroscopy providing unique insights into the distribution of Na and Fe local environments. Polymorphic Na2Fe2F7 exhibits a respectable initial capacity yet steady capacity fade, a consequence of the transformation of the Na2Fe2F7 weberite phases to the more stable perovskite-type NaFeF3 phase upon cycling, as revealed by ex situ synchrotron X-ray diffraction and solid-state NMR. Overall, these findings highlight the need for greater control over weberite polymorphism and phase stability through compositional tuning and synthesis optimization |
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Beschreibung: | Date Revised 16.05.2023 published: Electronic-eCollection Citation Status PubMed-not-MEDLINE |
ISSN: | 0897-4756 |
DOI: | 10.1021/acs.chemmater.3c00233 |