全钒液流电池关键传输参数的实验确定及全电池数值模拟研究

Nowadays, the performance and system efficiency of the vanadium redox flow battery (VRFB) are far from the initial anticipation. One of the main reasons is that the mass transport polarization is too large during the practical operating. In fact, the mass transport process is closely coupled with the electrochemical reactions within the porous electrode. These coupled behaviors are multi-scale and strongly nonlinear, such that the comprehensive and in-depth research works on them have not appeared until now. Based on this situation, in this project we plan to carry out both experimental and numerical studies. A versatile electrochemical testing platform will be designed and fabricated, by using which some key transport parameters within the porous electrode of a VRFB, i.e. the effective diffusivity of vanadium ions, pore-scale mass transfer coefficient and ion mobility in the electrolyte, will be accurately determined. Compared with the existing correlations, our results include the influences of the realistic factors (e.g. the dispersion effect is included in the effective diffusivity), showing clear physical meanings. With the aid of the measured key transport parameters, we will then develop a comprehensive numerical model to describe the coupled mass transport and electrochemical processes within the porous electrode. The effects of operating condition, electrode material property and flow field in the VRFB on the cell performance and system efficiency will be modeled. By analyzing the modeling results, we can propose the schemes to improve the performance and system efficiency. A lab scale prototype of VRFB will be set up for demonstration. This project is meaningful for enhancing the efficiency of the energy storage system and advancing the utilization of sustainable energy sources.

目前全钒液流电池的性能和系统效率还未达预期目标，一个主要的原因是电池运行过程中的传质极化过大。电池多孔电极内的传质和电化学反应过程紧密耦合，是个多尺度非线性的复杂问题，迄今对其缺乏广泛深入的研究。针对该情况，本项目拟开展实验和数值模拟的研究。设计并建立一个电化学通用实验平台，用电化学的方法精确确定全钒液流电池多孔电极内的关键传质参数，如有效扩散系数，微孔尺度传质系数，离子淌度等。相比现有的结果，本项目测得的参数将包含更多实际影响因素（如考虑弥散效应对有效扩散系数的影响），具有清晰的物理意义。利用测得的关键传质参数，我们将建立一个完整的包含耦合的传质和电化学反应的数值模型，并模拟全钒液流电池的运行条件、电极材料属性及流场板对电池性能和系统效率的影响。通过分析模拟结果，提出提高性能和改进效率的方案并据此建立一个小型的演示电池。该项目对提高储能系统效率，促进可再生能源利用有重要的意义。

目前全钒液流电池的性能和系统效率还未达预期目标，一个主要的原因是电池运行过程中的传质极化过大。电池多孔电极内的传质和电化学反应过程紧密耦合，是个多尺度非线性的复杂问题，迄今对其缺乏广泛深入的研究。针对该问题，本课题通过三年研究，通过设计并组装一个独特的电化学实验装置，用来研究各价钒离子在多孔电极中包含弥散效应的有效扩散率。由该方法得到的有效扩散系数还包含了不同电极材料结构和物性的影响。在前期钒离子应用的基础上，又用铁离子验证了有效扩散系数表述的准确性和有效性。用广义的漂移管与电池结构相结合，用不同电场场强下电池的极限电流之间的差异来间接获得真实的离子淌度，并对一类特定工况范围内的离子淌度拟合其表达公式，该公式能体现离子浓度和离子大小的影响。本部分装置还可适用于研究其它场的影响，具有普遍的意义。结合实验得到的关键传质参数，发展一个全面的数值模型来揭示电池内流动特性和活性物质浓度、过电势和局部电流密度的分布情况，进而为提高全钒液流电池的输出功率和系统效率提供理论依据。根据数值模拟所得优化方案，我们还建立了一个小型的演示电池原型。兼具理论和实验上的研究成果。