Battery scientists at the University of Wisconsin are working on bromide aqueous flow chemistry that's geared to provide a safer, cheaper alternative to lithium-ion packs for grid-level storage, according to a news release from the school.
The research has led to a unique additive meant to contain promising bromide ions, securing the science needed for the packs to cycle.
This type of battery uses positive and negative liquid electrolytes that circulate over electrodes. A membrane separates them. It's a different inner structure compared to common lithium-ion packs, which store and deliver electricity from ion movement between electrodes in an often liquid electrolyte.
Lithium-ion chemistry often involves ingredients that are flammable. As a result, fire risk is a rare, yet serious concern.
Since aqueous batteries "use ions dissolved in a liquid — water — they can be scalable, sustainable, and safe," per the Wisconsin experts.
A key mission for the team is ensuring bromide ions inside the battery cells don't go astray, which has been a problem for past iterations.
"Bromide-based aqueous flow batteries are a promising solution, but there are many messy electrochemical problems with them," Wisconsin chemist Patrick Sullivan said in the release.
Bromide is cheaper and easier to obtain than vanadium ions, which are commonly used in aqueous packs. But wandering bromide forms "a messy oil that 'sinks' to the bottom of the solution." The ions can sometimes create toxic bromine gas, all according to the news release.
In answer, 500 additives tasked with keeping the bromide in place were tested. Finally, 13 "soft-hard zwitterionic trappers" were identified as capable of encapsulating the ions. The bromide remained soluble but no longer passed through the membrane, the Wisconsin experts noted.
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"Our devices with the additive functioned without decay for almost two months compared to ones without it, which typically fail within a day," Assistant Professor Dawei Feng, who helped to develop the additive, said in the release. " … You want to use it for 10 or 20 years."
Improved packs are important as we transition to renewable electricity, which now produces more than 20% of U.S. power, per government data. Tesla has lithium-ion Megapacks that are already deployed. California's B2U Storage is using retired electric vehicle batteries to store energy. While the packs can no longer power a ride, they can still hold electricity.
Energy storage is a concept that can be applied at home with solar panels and smaller batteries that attach to dwellings. Setups from Tesla and other companies should be eligible for a 30% tax credit on installation costs. Homeowners can save on average $700 per year, even after factoring out expenses to put in the panels, a government study found. You can sell some of the electricity back to the grid if you take part in a virtual power plant.
The battery tech is helping to reduce production of heat-trapping air pollution, which the Health Effects Institute linked to 8.1 million deaths worldwide annually. The ailments are largely lung- and heart-related concerns.
Wisconsin's researchers hope to alleviate the pollution burden with better batteries. The team's additive will continue to be tested and refined with the goal of producing it at scale, according to the release.
"Our one additive can solve so many different problems," Sullivan said.
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