离子交换膜厚度对钒电池性能的影响

Effect of membrane thickness on performance of all-vanadium redox flow batteries

电解液穿过离子交换膜的传质现象会导致全钒液流电池性能和寿命降低.作为重要设计参数,膜厚度是影响膜内离子传输的主要因素.本文使用结合了Donnan效应的钒电池一维传质模型,通过数值模拟方法考察离子交换膜厚度对膜内传质控制作用的影响,并得到电池性能的变化规律.结果显示:电池库伦效率随膜厚度变化呈三个阶段.膜厚度较小时,库伦效率恶化严重;膜厚度适中时,库伦效率随膜厚度增加而明显提升;膜厚度较大时,库伦效率随膜厚度增加趋缓.研究发现,随电池运行膜两侧溶液电势差逐渐达到稳定状态,这一过程受初始膜两侧氢离子浓度差和膜厚度控制.此外,膜厚度越小,膜内钒离子流量越大,其作用机制转为扩散主导;随充放电进行,迁移作用受膜两侧浓差平衡电势差影响.

Species crossover through the ion exchange membrane leads to a decrease in the cell performance and lifetime for all-vanadium redox flow batteries（VRFBs）. As an important design parameter, membrane thickness is one of the major factors for ion transport through the membrane. In this paper, a transient electrochemical model incorporating the Donnan effect for VRFBs is utilized to study the effect of membrane thickness on the ion transport in the membrane and on the cell performance. The simulated results show that with an increase in the membrane thickness, the coulombic efficiency is promoted while the extent gradually slows down. When the thickness is small, the coulombic efficiency deteriorates seriously. The study found that the ionic potential through the membrane gradually reaches a steady state, which process is controlled by the H＋ concentration difference across the membrane and the membrane thickness. Moreover, with a decrease in the thickness, the vanadium ion fluxes are enhanced and the diffusion terns into the domination; while the migration is always controlled by the concentration overpotential.