Highly stable Mn-Sn flow batteries towards low-temperature energy storage

Abstract

The operating temperature of the reported aqueous redox flow batteries (ARFB) is typically above −20°C, which can be ascribed to the high freezing point of electrolytes, low ionic conductivity, and sluggish redox kinetics in low-temperature environments. Here, an acidic Mn-Sn flow battery system with high cold tolerance was developed to overcome low-temperature limitations, enabling operation at unprecedented −45°C. The cooperative interaction of H+, Mn2+, and Ti4+ ions not only effectively breaks the inherent hydrogen-bond network among water molecules, but also smooths the Mn3+/Mn2+ redox. It depresses the catholyte freezing point beyond −100°C, while a high 1.5 M Mn2+ concentration was obtained, maintaining a high ionic conductivity of 27.9 mS cm⁻1 at −50°C. Furthermore, coupled with Sn2+ anolyte with high reaction kinetics and reversibility at low temperature, the Mn-Sn ARFB with 1 M Mn2+ exerts ~1.5 V at −25°C with 33 Wh L−1 (comparable with all-vanadium redox flow battery) over 4250h (> 177 days, Coulombic efficiency 99.98%). Further decreasing to −45°C, it still shows smooth cycles over 800 h (> 33 days) with high energy efficiency of ~81%, demonstrating considerable application potential towards low-temperature energy storage.