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A deep eutectic solvent (DES) electrolyte-based vanadium-iron redox flow battery enabling higher specific capacity and improved thermal stability
Electrochimica Acta ( IF 6.6 ) Pub Date : 2018-10-13 , DOI: 10.1016/j.electacta.2018.10.063
Q. Xu , L.Y. Qin , Y.N. Ji , P.K. Leung , H.N. Su , F. Qiao , W.W. Yang , A.A. Shah , H.M. Li

Compared with conventional aqueous electrolyte, due to unique merits of deep eutectic solvents including a wide electrochemical window, ease in preparation, low vapor pressure and low cost, they have been used as electrolyte in the non-aqueous flow battery. This work reports a reline deep eutectic solvent, which is prepared as the anolyte and catholyte of a vanadium-iron redox flow battery. Since the solubility of the vanadium and iron species in deep eutectic solvent has been improved, an increased specific capacity can be obtained, up to 54.6% compared with the aqueous electrolyte one. However, the viscosity of this electrolyte is much larger than that of aqueous electrolyte, which causes more pumping losses. With the increase of operating temperature, the viscosity experiences a huge drop. The open-circuit voltage of such an non-aqueous system begins near 0.9 V with a decrease rate of 0.005 V h−1, suggesting a better capacity retention ability than does the aqueous flow battery. The cycling performance of this redox flow battery is evaluated at a current density of 2.0 mA cm−2 under the temperature of 30 °C. The coulombic efficiency is up to 94.8%, while voltage efficiency and energy efficiency are just 68.3% and 64.7%, respectively. The low voltage efficiency stems from the sluggish redox kinetics of the vanadium ions, and large internal ohmic resistance. With an improved thermal stability, this vanadium-iron redox flow battery is preferred to be operated at elevated temperature, which helps to greatly reduce the ohmic loss and pumping loss, such that to increase the system energy efficiency.



中文翻译:

基于低共熔溶剂(DES)的钒铁氧化还原液流电池,可实现更高的比容量并提高热稳定性

与常规的水性电解质相比,由于具有深的低共熔溶剂的独特优点,包括宽的电化学窗口,易于制备,低蒸汽压和低成本,它们已被用作非水流电池中的电解质。这项工作报告了一种深层共晶溶剂,它被制成钒铁氧化还原液流电池的阳极电解液和阴极电解液。由于提高了钒和铁物种在深共熔溶剂中的溶解度,因此可以获得比容量的增加,与水性电解质相比,其比容量最高可达54.6%。但是,该电解质的粘度比水性电解质的粘度大得多,这导致更多的泵送损失。随着工作温度的升高,粘度急剧下降。-1,这表明其容量保持能力比水性液流电池更好。在30℃的温度下在2.0mA cm -2的电流密度下评估该氧化还原液流电池的循环性能。库仑效率高达94.8%,而电压效率和能源效率分别仅为68.3%和64.7%。较低的电压效率源于钒离子的缓慢氧化还原动力学和较大的内部欧姆电阻。具有改善的热稳定性,该钒-铁氧化还原液流电池优选在高温下运行,这有助于大大降低欧姆损耗和泵浦损耗,从而提高系统能量效率。

更新日期:2018-10-13
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