Identifying the Structural Evolution of the Sodium Ion Battery Na2FePO4F Cathode |
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| Authors: | Qi Li Dr. Zigeng Liu Feng Zheng Rui Liu Jeongjae Lee Dr. Gui‐Liang Xu Dr. Guiming Zhong Xu Hou Dr. Riqiang Fu Dr. Zonghai Chen Dr. Khalil Amine Prof. Jinxiao Mi Prof. Shunqing Wu Prof. Clare P. Grey Prof. Yong Yang |
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| Affiliation: | 1. State Key Lab of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials and Department of Chemistry, Xiamen University, Xiamen, China;2. Department of Chemistry, University of Cambridge, Cambridge, UK;3. Current address: Max-Plank-Institut für Chemische Energiekonversion, Mülheim an der Ruhr, Germany;4. Institut für Energie und Klimaforschung (IEK-9), Forschungszentrum Jülich GmbH, Germany;5. Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen University, Xiamen, China;6. Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois, USA;7. Xiamen Institute of Rare Earth Materials, Chinese Academy of Sciences, Xiamen, China;8. National High Magnetic Field Laboratory, Tallahassee, Florida, USA;9. Materials Science and Engineering, Stanford University, Stanford, California, USA;10. Department of Material Science and Engineering, Xiamen University, Xiamen, China |
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| Abstract: | Na2FePO4F is a promising cathode material for Na‐ion batteries owing to its relatively high discharge voltage and excellent cycling performance. Now, the long‐ and short‐range structural evolution of Na2FePO4F during cycling is studied by in situ high‐energy X‐ray diffraction (XRD), ex situ solid‐state nuclear magnetic resonance (NMR), and first‐principles DFT calculations. DFT calculations suggest that the intermediate phase, Na1.5FePO4F, adopts the space group of P21/c, which is a subgroup (P21/b11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na2FePO4F, and this space group provides a good fit to the experimental XRD and NMR results. The two crystallographically unique Na sites in the structure of Na2FePO4F behave differently during cycling, where the Na ions on the Na2 site are electrochemically active while those on the Na1 site are inert. This study determines the structural evolution and the electrochemical reaction mechanisms of Na2FePO4F in a Na‐ion battery. |
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| Keywords: | density functional calculations electrochemistry Na2FePO4F NMR spectroscopy sodium-ion batteries |
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