A Review of Electrolyte Additives in Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) are promising candidates for large-scale energy storage, and the electrolyte plays a critical role in chemical–electrical energy conversion. However, the operating temperature of VRFBs is limited to 10–40 °C because of the stability of the electrolyte. To overcome this, various chemical species are added, but the progress and mechanism have not been summarized and discussed yet. This review summarizes research progress on electrolyte additives that are used for different purposes or systems in the operation of VRFBs, including stabilizing agents (SAs) and electrochemical mass transfer enhancers (EMTEs). Additives in vanadium electrolytes that exhibit microscopic stabilizing mechanisms and electrochemical enhancing mechanisms, including complexation, electrostatic repulsion, growth inhibition, and modifying electrodes, are also discussed, including inorganic, organic, and complex. In the end, the prospects and challenges associated with the side effects of additives in VRFBs are presented, aiming to provide a theoretical and comprehensive reference for researchers to design a higher-performance electrolyte for VRFBs.