Tri-chamber Polysulfide/Iodide-Based Redox Flow Batteries with Improved Coulombic Efficiency

The polysulfide/iodide flow battery is a promising candidate for large-scale energy storage systems, but the technology suffers from a notably low Coulombic efficiency. This phenomenon arises because the crossover of hydroxide ions triggers the disproportionation reaction of I3– ions in the posolyte. To mitigate these issues, a middle chamber filled with Na2SO4 solution is created between two cation-exchange membranes to separate the posolyte and negolyte chambers of the PSIFB, thereby constructing a trichamber reactor. This middle chamber can serve as a reservoir for the cross-transportation OH– ions during charge-discharge processes, thereby minimizing their adverse effects on the posolyte. Experimental results reveal that the introduction of the middle chamber leads to a 97.3% reduction in the concentration of OH– ions within the posolyte. Furthermore, finite element analysis demonstrates that the trichamber configuration significantly reduces the flux of OH– ions entering the posolyte, achieving levels even lower than half of those in the dual-chamber structure. This innovative architecture markedly enhances the Coulombic efficiency from approximately 78% in the dual-chamber structure to around 91% in the trichamber structure with a high-concentration electrolyte (4 M NaI and 3 M Na2S2), while concurrently sustaining a highly competitive energy density of 20.05 W h Lposolyte+negolyte–1 at 75% state-of-charge. These findings demonstrate an effective strategy for improving the performance of the polysulfide/iodide flow battery through OH– management, showing potential for developing more efficient flow battery systems for renewable energy storage applications