Structural Evolution and Redox Mechanism of O3-NaNi1/3Fe1/3Mn1/3O2 Layered Cathode for Na Rechargeable Batteries

Sodium-ion batteries (SIBs) have great potential to alternate Li-ion batteries (LIBs) for large-scale energy storage systems in view of easy accessibility to Na resources and low cost [1–4]. Since Na ions are similar chemical characteristics of Li ions, the knowledge from research in LIBs can be easily applied to Na-based systems. Derived from the equivalent structures of Li analogue, various electrode materials such as oxides, polyanionic compounds, and sulfates, have been researched in SIBs to date [2,4–8]. One of the cathode candidates for SIBs, layered transition metal oxides (Na x TMO 2 , x ≤ 1, TM = transition metals) are of great interest due to their potential of relatively high capacity, simple structure, and easy synthesis [9,10]. In this study, layered sodium-ion battery cathode, O3-type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , has been systematically investigated by synchrotron-based analyses to characterize the structural behavior during electrochemical reaction. X-ray absorption spectroscopy shows reversible redox process upon cycling and clearly proves that both Ni and Fe are active in Na 1– x Ni 1/3 Fe 1/3 Mn 1/3 O 2 and that redox couples of Ni 2+ /Ni 4+ via Ni 3+ and Fe 3+ /Fe 4+ are responsible for charge compensation. Specifically, the capacity is mainly realized with Ni 2+ /Ni 4+ and slightly from Fe 3+ /Fe 4+ under charging voltage of 4.0 V. At high voltage (> 4.0 V), however, Feredox reaction is dominant and Ni contributes slightly to capacity. In terms of structural evolution, Na 1- x Ni 1/3 Fe 1/3 Mn 1/3 O 2 undergoes phase transformation from O3 to P3 structure below 4.0 V and further reaches OP2 structure above 4.0 V along with a significant contraction of d-spacing. Moreover, quantitative analysis of extended X-ray absorption fine structure suggests that disorder of local structure for Fe is greatly increased in high voltage region. Accordingly, collapse of d -spacing can be considered as being caused by Fe migration in the TM layer into the neighboring Na layer. This study will give a better understanding of phase transformation and clear charge compensation of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 layered cathode during Na + deintercalation/intercalation. Furthermore, we propose the factor to bring the structural distortions under high voltage region by examining the local environment changes of each transition metal. From these experimental results, we will discuss structural evolution behavior and particular redox reaction of layered NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode material. More detailed results and discussion will be presented in the 237 th ECS meeting. References: [1] V. Palomares, M. Casas-Cabanas, E. Castillo-Martínez, M.H. Han, T. Rojo, Update on Na-based battery materials. A growing research path, Energy Environ. Sci. 6 (2013) 2312–2337. [2] B.L. Ellis, L.F. Nazar, Sodium and sodium-ion energy storage batteries, Curr. Opin. Solid State Mater. Sci. 16 (2012) 168–177. [3] D. Larcher, J.-M. Tarascon, Towards greener and more sustainable batteries for electrical energy storage, Nat. Chem. 7 (2015) 19–29. [4] N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Research development on sodium-ion batteries, Chem. Rev. 114 (2014) 11636–11682. [5] S.-W. Kim, D.-H. Seo, X. Ma, G. Ceder, K. Kang, Electrode materials for rechargeable sodium-ion batteries: potential alternatives to current lithium-ion batteries, Adv. Energy Mater. 2 (2012) 710–721. [6] S.Y. Hong, Y. Kim, Y. Park, A. Choi, N.-S. Choi, K.T. Lee, Charge carriers in rechargeable batteries: Na ions vs. Li ions, Energy Environ. Sci. 6 (2013) 2067–2081. [7] X. Xiang, K. Zhang, J. Chen, Recent advances and prospects of cathode materials for sodium-ion batteries, Adv. Mater. 27 (2015) 5343–5364. [8] S. Yuvaraj, W. Oh, W.-S. Yoon, Recent progress on sodium vanadium fluorophosphates for high voltage sodium-ion battery application, J. Electrochem. Sci. Technol. 10 (2019) 1–13. [9] K. Kubota, N. Yabuuchi, H. Yoshida, M. Dahbi, S. Komaba, Layered oxides as positive electrode materials for Na-ion batteries, MRS Bull. 39 (2014) 416–422. [10] M.H. Han, E. Gonzalo, G. Singh, T. Rojo, A comprehensive review of sodium layered oxides: powerful cathodes for Na-ion batteries, Energy Environ. Sci. 8 (2015) 81–102.