Harnessing the full potential of renewable energy sources such as solar and wind calls for effective, safe, and cost-efficient batteries to store the generated power. Engineers from the University of Wisconsin-Madison have taken a giant stride toward solving this energy storage puzzle by inventing a water-soluble chemical additive that greatly enhances the performance of bromide aqueous flow batteries.
Bromide-based aqueous flow batteries hold significant potential for renewable energy storage. Despite this, they are currently underutilized due to several electrochemical challenges. Patrick Sullivan, a PhD chemistry graduate from UW-Madison, points out, “Our novel additive can address these issues and greatly improve the effectiveness of these batteries.”
Sullivan, together with PhD student Gyohun Choi and Dawei Feng, an assistant professor of materials science and engineering at UW-Madison, were the brains behind this game-changing additive. Their groundbreaking research was published in the esteemed journal Nature on October 23, 2024.
At present, massive lithium-ion battery packs, the size of tractor-trailers, are employed for grid energy storage. However, they come with their share of drawbacks, including safety concerns due to the risk of fires and explosions, as well as a complex international supply chain.
Aqueous flow batteries, on the other hand, could provide a safer, more economical solution for grid-scale storage. These batteries employ positive and negative liquid electrolytes that circulate over electrodes, separated by a membrane. Utilizing ions dissolved in water, these batteries are scalable, sustainable, and safe.
While the most commercially advanced flow batteries rely on expensive and hard-to-source vanadium ions, an alternative version utilizes bromide, a cheap and readily available ion. However, its practical application is fraught with challenges. Bromide ions often pass through the membrane separating the electrodes, reducing battery efficiency. They can also precipitate out of the electrolyte, forming an oily residue at the bottom of the solution, or occasionally produce toxic bromine gas.
The solution is found in an additive known as a complexing agent. Choi and his team worked on developing an additive that could bolster the performance of bromide aqueous flow batteries. The team engineered over 500 candidate organic molecules, dubbed “soft-hard zwitterionic trappers,” and tested 13 of these as potential additives.
The resulting multi-functional additives encapsulate the bromide ions, keeping them water-soluble and too large to pass through the membrane. These ions remain “phase-stable,” meaning they don’t separate from the water electrolyte or generate toxic bromine gas.
Notably, these additives significantly boost the battery’s performance, enhancing both efficiency and lifespan. “Batteries with the additive worked flawlessly for nearly two months compared to those without it, which typically fail within a day,” remarks Feng. “This is key because renewable energy storage should ideally last 10 to 20 years.”
The team plans to continue refining their groundbreaking work. Choi will delve deeper into the science behind additives for bromide and iodide flow batteries. Simultaneously, Sullivan, CEO of renewable energy start-up Flux XII, will assess the commercial feasibility of the additive, which has already been successfully produced on an industrial scale.
