Engineers develop additive for affordable renewable energy storage

"Bromide-based aqueous flow batteries are a promising solution, but there are many messy electrochemical problems with them. That's why there's no real successful bromide-based products today," said Patrick Sullivan, a UW - Madison PhD graduate in chemistry. "Yet, our one additive can solve so many different problems."

Sullivan, alongside PhD student Gyohun Choi and Assistant Professor Dawei Feng, engineered the additive to enhance battery performance and efficiency. The team's findings were published in 'Nature' on October 23, 2024.

Aqueous Flow Batteries: A Safer Alternative
While lithium-ion batteries are widely used for grid-scale energy storage, their limitations include safety risks, such as fires and explosions, and reliance on a fragile international supply chain. By contrast, aqueous flow batteries, which use water-based electrolytes, offer scalability, sustainability, and improved safety.

The most established flow batteries rely on expensive and scarce vanadium ions. Bromide, a less costly and more abundant alternative, has similar theoretical performance potential. However, bromide-based batteries face practical obstacles. Bromide ions often escape through the membrane, lowering efficiency, or precipitate into an oily residue that disrupts functionality. Worse, the ions can form toxic bromine gas, raising safety concerns.

Solving Challenges with Molecular Engineering
To tackle these issues, Choi and the team developed over 500 molecular candidates, narrowing them to 13 engineered "soft-hard zwitterionic trappers." These multifunctional additives proved highly effective in resolving bromide flow battery problems.

The additive encapsulates bromide ions, preventing them from passing through the membrane while maintaining their water solubility. It also stabilizes the ions, avoiding the formation of residue or harmful gases. The results have been remarkable. "Our devices with the additive functioned without decay for almost two months compared to ones without it, which typically fail within a day," Feng explained.

This improvement significantly extends the operational life of the battery, a key factor for renewable energy storage systems designed for long-term use.

Looking Ahead
Choi plans to delve deeper into the science behind additives for halide flow batteries, while Sullivan, now CEO of renewable energy startup Flux XII, will work on scaling the additive for industrial applications. Early tests indicate the additive is viable for large-scale production.

The innovation marks an important step toward achieving reliable and affordable energy storage solutions, a critical component of the renewable energy future.

Research Report:Soft - hard zwitterionic additives for aqueous halide flow batteries