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

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Polysulfide/iodide flow batteries (PSIFBs) show promise for grid-scale energy storage.
• Low Coulombic efficiency in PSIFBs is caused by hydroxide ion crossover and subsequent I3- disproportionation.
• Effective management of ion transport is crucial for improving PSIFB performance.

Purpose of the Study:

• To develop a novel reactor architecture for PSIFBs to mitigate hydroxide ion crossover.
• To enhance the Coulombic efficiency and overall performance of PSIFBs.
• To investigate the impact of a middle chamber on ion transport and battery performance.

Main Methods:

• Construction of a trichamber reactor with a central Na2SO4 solution chamber between cation-exchange membranes.
• Experimental testing of the trichamber PSIFB under high-concentration electrolyte conditions (4 M NaI and 3 M Na2S2).
• Finite element analysis (FEA) to model and quantify hydroxide ion flux in dual-chamber versus trichamber configurations.

Main Results:

• The trichamber design reduced hydroxide ion concentration in the posolyte by 97.3%.
• FEA confirmed significantly lower hydroxide ion flux into the posolyte in the trichamber configuration compared to dual-chamber systems.
• Coulombic efficiency improved from ~78% in dual-chamber to ~91% in the trichamber structure.
• A competitive energy density of 20.05 Wh L-1 was maintained at 75% state-of-charge.

Conclusions:

• The trichamber reactor effectively manages hydroxide ion crossover, a key limitation in PSIFBs.
• This architectural innovation substantially improves Coulombic efficiency and maintains high energy density.
• The findings present a viable strategy for advancing PSIFB technology for large-scale renewable energy storage.