Low‐Cost Titanium–Bromine Flow Battery with Ultrahigh Cycle Stability for Grid‐Scale Energy Storage

Abstract Flow batteries are one of the most promising large‐scale energy‐storage systems. However, the currently used flow batteries have low operation–cost‐effectiveness and exhibit low energy density, which limits their commercialization. Herein, a titanium–bromine flow battery (TBFB) featuring very low operation cost and outstanding stability is reported. In this battery, a novel complexing agent, 3‐chloro‐2‐hydroxypropyltrimethyl ammonium chloride, is employed to stabilize bromine/polybromides and suppress Br diffusion. The results reveal that the complexing agent effectively inhibits Br crossover and reduces Br‐induced corrosivity, which in turn significantly improves the reliability of the TBFB system. The novel TBFB demonstrates 95% coulombic efficiency and 83% energy efficiency at 40 mA cm⁻² current density. Moreover, it can run smoothly for more than 1000 cycles without any capacity decay. Furthermore, an assembled 300 W TBFB stack can be continuously operated for more than 500 cycles, thereby confirming the practical applicability of the proposed TBFB. Because the TBFB utilizes an ultralow‐cost electrolyte (41.29 $ kWh⁻¹) and porous polyolefin membranes, it serves as a reliable and low‐cost energy‐storage device. Therefore, considering its ultrahigh stability and low cost, the TBFB can be used as a large‐scale energy‐storage device.