Reviewed by Lexie CornerNov 25 2024
Engineers from the University of Wisconsin–Madison have developed a water-soluble chemical additive that improves the functionality of a specific type of electrochemical storage, the bromide aqueous flow battery, as part of efforts to address the long-term energy storage problem. The study was published in the journal Nature.
The energy landscape is rapidly evolving with the rise of solar and wind power. However, to fully harness these intermittent renewable energy sources, safe and affordable batteries capable of storing their energy are needed.
Bromide-based aqueous flow batteries are a promising solution, but there are many messy electrochemical problems with them. That is why there is no real successful bromide-based products today. Yet, our one additive can solve so many different problems.
Patrick Sullivan, Department of Materials Science and Engineering, University of Wisconsin–Madison
The additive was created by Sullivan, Ph.D. candidate Gyohun Choi, and Dawei Feng, an Assistant Professor of Materials Science and Engineering at UW–Madison.
Large lithium-ion battery packs, the size of tractor-trailers, are currently used to store energy for the grid. However, they have certain technological drawbacks, including the risk of fires and explosions, as well as safety concerns due to the complex global supply chain associated with lithium batteries.
In contrast, aqueous flow batteries could offer a more affordable and safer solution for grid-scale storage. These batteries use positive and negative liquid electrolytes that flow over electrodes separated by a membrane. Since they use ions dissolved in water, they can be safe, scalable, and sustainable.
The vanadium ions used in the most used flow batteries are costly and difficult to obtain, much like lithium. On paper, though, bromide, a widely accessible and inexpensive ion, functions similarly to vanadium in other types of flow batteries.
However, bromide ions lead to several issues with flow batteries. Their ability to penetrate the membrane separating the electrodes reduces the battery's effectiveness. When the ions precipitate out of the electrolyte, dirty oil that "sinks" to the bottom of the solution is occasionally formed. The ions can also sometimes produce harmful bromine gas. These problems hinder practical performance and reliability.
A complexing agent is an additive that could be useful in this context. Choi set out to find an additive that enhances the performance of bromide aqueous flow batteries. Using molecular design, the researchers developed over 500 potential organic compounds, which they called “soft-hard zwitterionic trappers.” Around 13 of these compounds were produced and tested as possible additions to the bromide battery.
The multifunctional additives created address the primary issues with the flow battery. They encapsulate the bromide ions while keeping them water-soluble, and due to the larger size of the resulting complex, the ions are unable to cross the membrane. The ions are "phase-stable," meaning they do not separate from the water-electrolyte or produce harmful bromine gas.
Crucially, these additives significantly improve the performance of the flow battery, increasing the chemical system's lifespan and efficiency.
Our devices with the additive functioned without decay for almost two months compared to ones without it, which typically fail within a day. This is important because, for green energy storage, you want to use it for 10 or 20 years.
Dawei Feng, Assistant Professor, Materials Science and Engineering, University of Wisconsin–Madison
The group plans to continue advancing this work. While Sullivan, the CEO of Flux XII, a renewable energy spinoff he co-founded with Feng, will explore the commercial viability of the additive—already successfully produced in industrial ton-scale reactions—Choi will focus on researching the basic science behind additives for bromide and iodide flow batteries.
Dawei Feng is an assistant professor of materials science and engineering at Y. Austin Chang. Additional contributors from UW-Madison include Xiu-Liang Lv, Wenjie Li, Kwanpyung Lee, Haoyu Kong, Sam Gessler, and JR Schmidt.
Journal Reference:
Choi, G., et al. (2024) Soft–hard zwitterionic additives for aqueous halide flow batteries. Nature. doi.org/10.1038/s41586-024-08079-4.