Scaling up flow fields from lab-scale to stack-scale for redox flow batteries

Flow fields are key competent to distribute electrolytes onto electrodes at maximum uniformity while maintaining a minimum pumping loss for redox flow batteries. Previously, efforts are mainly made to develop lab-scale flow fields (<100 cm2) with varying patterns, but due to the lack of reasonable scaling-up methods, a huge gap between lab-scale and stack-scale (>1000 cm2) flow fields exists, limiting the application of designed flow fields for commercialized kW-class battery stacks. In this work, six scaling-up methods, including channel length extension, geometric similarity, multi-parallel channels, splitting subzone, channel multi-parallel length extension and split-area multi-parallel channels, are proposed and evaluated by adopting a rotary serpentine flow field as an example to unravel the flow-related concentration distribution and electrochemical characteristics from lab-scale to stack-scale. Results show that shortening the supply path and enhancing the supply rate by utilizing flow channel structures within the unit area are key factors determining the uniform distribution of active materials at stack-scale flow fields. More remarkably, the flow filed with the multiple-parallel channel scaling-up method shows the lowest charge voltage (1.49 V), the highest discharge voltage (1.32 V), the highest uniformity factor (0.812) and the lowest pressure drop (100.1 kPa) among methods investigated at 100 mA cm−2, leading to a high energy efficiency of 88.4 %, which is almost identical to that of lab-scale counterpart (88.9 %). This work provides an in-depth analysis of flow field scaling-up methods, which is expected to guide the design of kW-class VRFB stacks.