Flow batteries are being increasingly deployed in grid-scale energy storage applications. However, long-term operation of flow batteries still suffers from a different extent of capacity decay. While the effects of ion diffusion and side reactions on capacity degradation have been identified and further minimized by improvement in materials, the mechanism of volumetric transfer and its influence in capacity still receive insufficient attentions that impedes further capacity optimizations for flow batteries. In order to gain an in-depth understanding of volumetric transfer mechanism in flow batteries, six different types of flow batteries are adopted in this study and further classified in accordance with electrolyte viscosities for investigations. Experimental results show that a net volumetric transfer in a conventional flow battery highly depends on viscosity values of the two half-cell electrolytes and is virtually towards the half-cell possessing a smaller electrolyte viscosity. For flow batteries with a mixed electrolyte in both half-cells, moreover, cycling tests further demonstrate a zero net transfer under similar viscosity measurements of both half-cell electrolytes. Unraveling the viscosity impact on volumetric transfer is greatly beneficial to facilitate deeper understandings of transport phenomena in flow batteries, which can contribute to realize long-term flow battery operation with a superior capacity retention.

液流电池正越来越多地部署在电网规模的储能应用中。但是，液流电池的长期运行仍会遭受不同程度的容量衰减。尽管已经确定了离子扩散和副反应对容量降低的影响，并通过材料改进进一步减小了这种影响，但体积转移的机理及其对容量的影响仍未引起足够的重视，这阻碍了液流电池的进一步容量优化。为了深入了解液流电池的体积传递机理，本研究采用了六种不同类型的液流电池，并根据电解质的粘度进行了进一步分类，以进行研究。实验结果表明，常规液流电池中的净体积转移在很大程度上取决于两种半电池电解质的粘度值，实际上朝向具有较小电解质粘度的半电池。此外，对于在两个半电池中都带有混合电解质的液流电池，循环测试进一步表明，在两种半电池电解质的相似粘度测量下，净转移为零。揭开粘度对体积传递的影响，对于促进更深入地了解液流电池中的运输现象非常有利，这可以有助于实现液位电池的长期运行并具有出色的容量保持能力。此外，对于在两个半电池中都带有混合电解质的液流电池，循环测试进一步表明，在两种半电池电解质的相似粘度测量下，净转移为零。揭开粘度对体积传递的影响，对于促进更深入地了解液流电池中的运输现象非常有利，这可以有助于实现液位电池的长期运行并具有出色的容量保持能力。此外，对于在两个半电池中都带有混合电解质的液流电池，循环测试进一步表明，在两种半电池电解质的相似粘度测量下，净转移为零。揭开粘度对体积传递的影响，对于促进更深入地了解液流电池中的运输现象非常有利，这可以有助于实现液位电池的长期运行并具有出色的容量保持能力。