A comprehensive picture of the current rate dependence of the structural evolution of P2-Na2/3Fe2/3Mn1/3O2
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Date
2015-09-02
Journal Title
Journal ISSN
Volume Title
Publisher
Royal Society of Chemistry
Abstract
Cathodes that feature a layered structure are attractive reversible sodium hosts for ambient temperature sodium-ion batteries which may meet the demands for large-scale energy storage devices. However, crystallographic data on these electrodes are limited to equilibrium or quasi-equilibrium information. Here we report the current-dependent structural evolution of the P2-Na2/3Fe2/3Mn1/3O2 electrode during charge/discharge at different current rates. The structural evolution is highly dependent on the current rate used, e.g., there is significant disorder in the layered structure near the charged state at slower rates and following the cessation of high-current rate cycling. At moderate and high rates this disordered structure does not appear. In addition, at the slower rates the disordered structure persists during subsequent discharge. In all rates examined, we show the presence of an additional two-phase region that has not been observed before, where both phases maintain P63/mmc symmetry but with varying sodium contents. Notably, most of the charge at each current rate is transferred via P2 (P63/mmc) phases with varying sodium contents. This illustrates that the high-rate performance of these electrodes is in part due to the preservation of the P2 structure and the disordered phases appear predominantly at lower rates. Such current-dependent structural information is critical to understand how electrodes function in batteries which can be used to develop optimised charge/discharge routines and better materials. © 2015 The Royal Society of Chemistry. This article is Open Access.
Description
This article is licenced under a Creative Commons Attribution-Non Commercial 3.0 Unported licence.
Keywords
Cathodes, Electrodes, Electric batteries, Sodium ions, Electric discharges, Crystals
Citation
Sharma, N., Han, M. H., Pramudita, J. C., Gonzalo, E., Brand, H. E. A., & Rojo, T. (2015). A comprehensive picture of the current rate dependence of the structural evolution of P2-Na 2/3 Fe 2/3 Mn 1/3 O 2. Journal of Materials Chemistry A, 3(42), 21023-21038.doi:10.1039/C5TA04976H