A comparative study of all-vanadium and iron-chromium redox flow batteries for large-scale energy storage

• Performance and cost of the VRFB and ICRFB are compared.
• Energy efficiencies of the VRFB and ICRFB are similar at high current densities.
• The ICRFB exhibits a higher capacity decay rate than does the VRFB.
• The ICRFB shows cost advantages at high power densities and large capacities.

The promise of redox flow batteries (RFBs) utilizing soluble redox couples, such as all vanadium ions as well as iron and chromium ions, is becoming increasingly recognized for large-scale energy storage of renewables such as wind and solar, owing to their unique advantages including scalability, intrinsic safety, and long cycle life. An ongoing question associated with these two RFBs is determining whether the vanadium redox flow battery (VRFB) or iron-chromium redox flow battery (ICRFB) is more suitable and competitive for large-scale energy storage. To address this concern, a comparative study has been conducted for the two types of battery based on their charge–discharge performance, cycle performance, and capital cost. It is found that: i) the two batteries have similar energy efficiencies at high current densities; ii) the ICRFB exhibits a higher capacity decay rate than does the VRFB; and iii) the ICRFB is much less expensive in capital costs when operated at high power densities or at large capacities.