A simple chemical “scavenger” is dramatically extending the life and safety of zinc-bromine flow batteries, potentially unlocking a key technology for large-scale renewable energy storage. Researchers have found a way to trap corrosive bromine, a major hurdle in battery performance.
A Breakthrough for Renewable Energy Storage
Flow batteries offer a scalable and safe solution for storing energy from intermittent sources like solar and wind.
- Adding sodium sulfamate (SANa) to the electrolyte traps corrosive bromine.
- The new battery designs lasted over 700 cycles—nearly 1,400 hours—without significant performance loss, compared to 30 cycles for conventional systems.
- The technology boosts energy density and reduces the need for expensive corrosion-resistant materials.
- Findings were published in Nature Energy.
By adding sodium sulfamate (SANa) to the electrolyte, the researchers effectively neutralized the bromine (Br₂) produced during battery operation, converting it into a less harmful brominated amine. This seemingly small change delivers a double benefit: it significantly extends battery lifespan by reducing corrosion and enhances safety for both the environment and maintenance personnel.
Conventional bromine-based flow batteries typically show a sharp decline in performance after just 30 cycles due to corrosion. In contrast, the newly designed batteries operated for over 700 cycles—nearly 1,400 hours—without substantial performance degradation.
Bromine: A Double-Edged Sword
Flow batteries are rechargeable systems that store energy in liquid electrolytes contained in external tanks. This design makes them uniquely scalable and safe for renewable energy applications. Zinc–bromine flow battery variants are gaining traction because of their high energy density and relatively low-cost materials, positioning them as viable alternatives to traditional rechargeable batteries.
These batteries function by pumping liquid solutions through a central reaction unit, where electricity is stored and delivered. During charging, zinc ions solidify on the negative electrode, while bromide ions transform into bromine at the positive electrode. This process reverses during discharge, releasing stored electrical energy as zinc dissolves back into the liquid and bromine reverts to bromide.
However, a significant challenge with current bromine-based flow batteries is their limited lifespan. The bromine released during charging aggressively corrodes critical components like electrodes, pipes, and storage tanks. Furthermore, bromine is a volatile and toxic substance; even minor leaks can pollute the air, irritate skin and eyes, and affect the nervous system.
After extensive research, scientists discovered that sodium sulfamate, or SANa, acts as an effective chemical trap, altering bromine’s behavior within the battery.
SANa initiates a disproportionation reaction—a redox process where a single substance is both oxidized and reduced—splitting the bromine gas and binding it to form N-bromo sodium sulfamate. This reaction reduces the concentration of free-floating bromine to approximately 7 millimoles per liter (mM).
This binding action also triggered a two-electron transfer phenomenon, enabling the battery to store significantly more energy. The flow battery with added SANa achieved an energy density of 152 Wh/l, compared to 90 Wh/l for conventional versions.
To rigorously test the battery’s capabilities, the team constructed a 5 kW stack comprising 30 individual battery cells connected in series. The redesigned flow battery achieved over 700 stable cycles and, crucially, at a lower cost, as it eliminated the need for expensive corrosion-resistant membranes, pumps, and storage tanks.
The researchers express optimism that these findings will pave the way for designing durable, long-lasting, and high-energy-density bromine-based batteries suitable for grid-scale applications.
The findings are published in Nature Energy.
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