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Identifying the Structural Evolution of the Sodium Ion Battery Na 2 FePO 4 F Cathode
Author(s) -
Li Qi,
Liu Zigeng,
Zheng Feng,
Liu Rui,
Lee Jeongjae,
Xu GuiLiang,
Zhong Guiming,
Hou Xu,
Fu Riqiang,
Chen Zonghai,
Amine Khalil,
Mi Jinxiao,
Wu Shunqing,
Grey Clare P.,
Yang Yong
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201805555
Subject(s) - electrochemistry , ion , cathode , battery (electricity) , chemistry , phase (matter) , crystallography , materials science , electrode , physics , power (physics) , organic chemistry , quantum mechanics
Na 2 FePO 4 F 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 Na 2 FePO 4 F 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, Na 1.5 FePO 4 F, adopts the space group of P 2 1 / c , which is a subgroup ( P 2 1 / b 11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na 2 FePO 4 F, 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 Na 2 FePO 4 F 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 Na 2 FePO 4 F in a Na‐ion battery.