In Situ XRD Studty on Phase Transitions of NaNi1/3Fe1/3Mn1/3O2 Cathode Materials
Authors: Xie Yingying , Xu Guiliang , Chen Zonghai , Lu Jun , Amine Khalil , Ma Zi-Feng 
Published: February 2020

Sodium is one of the more abundant elements on earth and exhibits similar chemical properties to lithium, which indicating that sodium-based batteries could provide an alternative chemistry to lithium batteries particularly in large scale energy storage. Furthermore, for positive electrode materials sodium intercalation chemistry is very similar to Li, and the electrochemical equivalent and standard potential of sodium, all of these are the most advantageous for sodium ion battery quickly develop and apply to commercialization.  In this paper, the NaNi1/3Fe1/3Mn1/3O2
material was prepared using a large-scale synthesis process and its electrochemical characteristics were measured. In situ synchrotron XRD have been applied to identify phase transformation of NaNi1/3Fe1/3Mn1/3O2 materials during the sodium ions deintercalation.

The morphology, crystal structure and electrochemical characteristics of the prepared NaNi1/3Fe1/3Mn1/3O2
were mesured. It can be found, the sample shows a typical spherical particle size of about 5 μm and composed of many dense and plate-like primary particles. The XRD pattern of the pristine sample confirms the O3-type NaNi1/3Fe1/3Mn1/3O2 could be successfully modeled as the hexagonal layered structure which can be indexed to R-3m space-group with the α-NaFeO2 structure, and the lattice parameters are a = b = 2.9684 Å and c =16.128 Å. The oxygen stacking is ABC and the closest packing arrangement is hexagonally closest-packed. The charge-discharge capacities of NaNi1/3Fe1/3Mn1/3O2
were 131.5 mAh g-1 and 134.7 mAh g-1 in the first cycle, and maintained at 135.3 mAh g-1 and 135.1 mAh g-1 after 10 cycles at 0.1 C rate, and the first cycle charge-discharge capacity reached at 122.3 mAh g-1 and 122.1 mAh g-1at 1C rate, respectively.

In order to understand the metastable structure and phase transformation of NaNi1/3Fe1/3Mn1/3O2 materials during Na ion intercalation, we performed in situ synchrotron XRD on a NaNi1/3Fe1/3Mn1/3O2/C battery during charging process. In situ synchrotron x-ray powder diffraction measurements were carried out in transmission geometry at beamline 17-BM of the Advanced Photon Source at Argonne National Laboratory (wavelength 0.7270 Å, 500-mm-diameter beam).The synchrotron in-situ XRD results demonstrate the phase transformations in nanoparticulate NaNi1/3Fe1/3Mn1/3O2 proceed via a continuous change in structure during cycling,  The structure changed from O3-type NaNi1/3Fe1/3Mn1/3O2 to hexagonal P3 type Na1-
dNi1/3Fe1/3Mn1/3O2 via two layer hexagonal structures coexists with a monoclinic O’3 and P’3.

ACKNOWLEDGMENT

This work was supported by the Natural Science Foundation of China (21336003, 21573147 and 21506123), the 973 Program of China (2014CB239703), the US Department of Energy under contract DE-AC02-06CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy, and the Science and Technology Commission of Shanghai (14DZ2250800).

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