Thermal Effects on the Performance of Stack-Scale Vanadium Redox Flow Batteries

The operating temperature of vanadium redox flow batteries (VRFBs) affects their performance and reliability. However, previous studies focused on evaluating the effects on the performance of lab-scale single cells, in which electrolyte flow rates and current densities are different from those in stack-scale VRFBs, leading to the lack of guidance for the design of stacks. In this work, we investigate thermal effects on the performance of stack-scale VRFBs. It is found that as the operating temperature increases from 25 to 50 °C, the discharge capacity increases by 42%, whereas the energy efficiency increases by 10%, implying that the temperature has greater effects on the discharge capacity than that on the energy efficiency. Additionally, the enhancement effect of temperature on the energy efficiency is gradually weakened with increasing flow rate, while that on the discharge capacity is almost unchanged. Furthermore, the enhancement effect of temperature on energy efficiency increases with the operating current density. Notably, an optimum operating condition of the stack-scale VRFBs is identified with a critical flow rate (2.88 ml min −1 cm −2 ) at 40 °C to achieve a high system efficiency. This work provides guidance for the design of stack-scale VRFBs with high performance and safety.