Synthesis and electrochemical performances of Na(3)V(2)(PO(4))(2)F(3)/C composites as cathode materials for sodium ion batteries.
Synthesis and electrochemical performances of Na(3)V(2)(PO(4))(2)F(3)/C composites as cathode materials for sodium ion batteries.
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钠离子电池正极材料Na3V2(PO4)2F3/C复合材料的合成及电化学性能
作者：
含NaSCION的Na3V2(PO4)2F3(NVPF)具有较高的理论容量，被认为是一种潜在的正极材料。然而，NVPF的电子电导率远低于其离子电导率，严重影响了该材料的性能。碳层可以作为导电介质来提高NVPF的导电性。在本研究中，我们提出了一种以沥青为碳源，基于机械活化的一步固相反应法制备NVPF/C复合材料。用X射线衍射仪、拉曼光谱、比表面积测量、热分析、扫描电子显微镜和透射电子显微镜对样品的晶体结构和形貌进行了研究。并通过循环伏安、恒流充放电和交流阻抗谱等测试手段对其电化学性能和动力学性能进行了分析。试验结果表明，碳含量为12.14wt%的NVPF/C-2复合材料具有优异的倍率性能和循环稳定性。该材料在0.2C和10C下的可逆容量分别为103mA·h·g·−-1和95 mA·h·g-1，在5C下循环500次后的保持率为91.9%。NVPF/C-2复合材料的这些优异性能归功于其高的离子扩散系数和小的电荷转移阻抗。
Na3V2(PO4)2F3 (NVPF) with NASCION (Na superionic conductor) is recognized as a potential cathode material owing to its high theoretical capacity. However, the electronic conductivity of NVPF is much lower than its ionic conductivity, which seriously affects the properties of this material. The carbon layer can be used as the conductive medium to enhance the conductivity of NVPF. In this study, we propose a single-step solid-state reaction method based on mechanical activation with pitch as the carbon source to synthesize NVPF/C composites. The crystallographic structure and morphology of all as-prepared samples were investigated by XRD, Raman spectroscopy, BET measurement, thermal analysis, SEM and TEM. Furthermore, the electrochemical performance and kinetic properties were analyzed by CV, galvanostatic charge–discharge and EIS tests. These tests outcomes demonstrated that the NVPF/C-2 composite with a carbon content of 12.14 wt% showed an excellent rate performance and cycle stability. It presented reversible capacities of 103 and 95 mA h g−1 at 0.2 and 10C, respectively, and an outstanding retention of 91.9% after 500 cycles at 5C. These excellent properties of the NVPF/C-2 composite are attributed to its high ion diffusion coefficient and small charge transfer impedance.
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3.2
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