Synthesis and Reaction Mechanism of Novel Fluorinated Carbon Fiber as a High-Voltage Cathode Material for Rechargeable Na Batteries

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• 作者：Yuanjun Shao ; Hongjun Yue ; Ruimin Qiao ; Jiaqi Hu ; Guiming Zhong ; Shunqing Wu ; Matthew J. McDonald ; Zhengliang Gong ; Zizhong Zhu ; Wanli Yang ; Yong Yang
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：February 23, 2016
• 年：2016
• 卷：28
• 期：4
• 页码：1026-1033
• 全文大小：474K
• ISSN：1520-5002

文摘

While a rechargeable battery based on Na/CF_x has been proposed, its reversible mechanism has remained unclear. Here, a new fluorinated carbon fiber material with the formula CF_0.75 is used as a cathode material for rechargeable sodium batteries, delivering an initial discharge capacity of 705 mA·h g^–1 with a high discharge plateau of 2.75 V and a reversible high discharge capacity of 350 mA·h g^–1 at 20 mA g^–1. The first discharge plateau of 2.75 V is the highest value reported in this family of materials so far, even slightly higher than that of commercial fluorinated graphite tested in a lithium battery (2.7 V). The origins of the observed high voltage of the material are explored by a combination of theoretical calculations and galvanostatic intermittent titration technique data and determined to be related to the disordered structure of the carbon fiber. Soft X-ray absorption spectroscopy and ¹⁹F magic angle spinning nuclear magnetic resonance characterization results disclose a full view of the conversion reaction mechanism involved in the charge and discharge processes, both on the surface and in the bulk, and show evidence of reversible conversion between CF_x and NaF. Although a suitable electrolyte is currently lacking and further research is necessary, the inherent advantages of the compound make it a promising cathode material for future rechargeable sodium batteries.