One Stone Two Birds: Enhancing Energy Density and Temperature Adaptability for Vanadium-based Redox Flow Batteries via Dual Active Species Strategy

Abstract

Vanadium-based redox flow batteries, characterized by no cross-contamination issue, are considered as one of the most promising candidates for large-scale energy storage. However, due to vanadium ions show relatively low solubility and are easy to precipitate at extreme temperatures, the battery suffers from the long challenge of low energy density and poor temperature adaptability. In this work, by introducing vanadium and bromine dual active species into the positive electrolyte, a novel V/V-Br redox flow battery (VBrRFB) is developed to boost the energy density and temperature window of vanadium-based flow batteries. The bromine, not only acts as the secondary redox couple to enhance the overall concentration of active species, but also disrupts the hydrogen bond network while optimizing the solvation structure of vanadium. As a result, the VBrRFB achieves an energy density of as high as 152.4 Wh L^-1_catholyte (38.1 Wh L^-1_{catholyte+anolyte}), which is 265.9% higher than traditional all-vanadium redox flow batteries, while maintaining stable cycling over 250 cycles with an energy efficiency of 82.5%. Additionally, the VBrRFB exhibited excellent stability and performance from -10°C to 50°C, with energy densities of 107.6 Wh L^-1_catholyte at 50 °C and 88.8 Wh L^-1_catholyte at -10 °C, demonstrating its strong potential for practical energy storage.