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Batteries 2018, 4(4), 68; https://doi.org/10.3390/batteries4040068

Electrochemical Performance and Thermal Stability of Iron Oxyfluoride (FeOF) for Sodium-Ion Batteries

1
Organization for Research Initiatives, Yamaguchi University, Yamaguchi 755-8611, Japan
2
Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 816-8580, Japan
3
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 816-8580, Japan
4
Department of Applied Chemistry, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan
*
Authors to whom correspondence should be addressed.
Received: 18 July 2018 / Revised: 7 November 2018 / Accepted: 27 November 2018 / Published: 7 December 2018
(This article belongs to the Special Issue Sodium-Ion Battery: Materials and Devices)
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Abstract

Self-synthesized rutile iron oxyfluoride (FeOF) was studied as a cathode material for Na-ion batteries. The highly crystalline FeOF provided an initial discharge capacity of 246 mAh g−1 in a voltage range of 1.0–4.0 V, followed by 88% of capacity retention after 20 cycles. This discharge-charge reaction of FeOF between 0.8 and 4.0 V are advanced by the Fe2+/Fe3+ redox reaction. That is, no conversion reaction was involved in the application of FeOF as a cathode material for Na-ion batteries because of the low potential of Na-insertion. In addition, the structure change of FeOF from rutile to cubic during Na ion insertion, which was similar to that in Li-ion batteries. No remarkable HF release was detected even up to 700 °C, indicating a low toxic risk of the FeOF cathode. The thermal properties of sodiated and desodiated FeOF electrodes in the associated electrolyte were investigated by DSC (Differential scanning calorimetry) up to 500 °C. Sodiated FeOF electrodes showed larger exothermic heat generation than desodiated ones, especially at a temperature higher than 380 °C. Finally, the thermal stability of FeOF cathodes in the associated Li- and Na-ion battery electrolytes was quantitatively compared with variations of the electrode/electrolyte ratio. View Full-Text
Keywords: sodium-ion batteries; iron oxyfluoride; thermal stability; X-ray analysis; conversion-type cathode sodium-ion batteries; iron oxyfluoride; thermal stability; X-ray analysis; conversion-type cathode
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Kitajou, A.; Zhao, L.; Nagano, R.; Inoishi, A.; Kobayashi, E.; Okada, S. Electrochemical Performance and Thermal Stability of Iron Oxyfluoride (FeOF) for Sodium-Ion Batteries. Batteries 2018, 4, 68.

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