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

Abstract

The operating temperature of the reported aqueous redox flow batteries (ARFBs) is typically above −20 °C, which can be ascribed to the high freezing point of their 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 an unprecedented temperature of −45 °C. The cooperative interaction of H⁺, Mn²⁺, and Ti⁴⁺ ions not only effectively disrupts the inherent hydrogen-bond network among water molecules but also smoothens the Mn³⁺/Mn²⁺ redox process. It depresses the catholyte freezing point below −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 the Sn²⁺ anolyte and 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 an all-vanadium redox flow battery) over 4250 h (>177 days, Coulombic efficiency = 99.98%). Upon further decreasing the temperature to −45 °C, it still shows stable cycling performance over 800 h (>33 days) with a high energy efficiency of ∼81%, demonstrating considerable potential towards low-temperature energy storage applications.