This Simple Chemistry Fix Could Revolutionize Flow Batteries

A new twist on bromine-based flow batteries could make large-scale energy storage cheaper, safer, and far longer-lasting.

Bromine-based flow batteries store and release energy through a chemical reaction involving bromide ions and elemental bromine. This approach offers several advantages, including widely available raw materials, strong electrochemical potential, and good solubility in liquid electrolytes.

The challenge comes during charging, when large amounts of bromine are produced. This highly reactive substance can damage internal battery components, reduce how long the battery lasts, and drive up overall costs. Existing bromine-binding additives help limit corrosion, but they often cause the electrolyte to separate into different phases, which disrupts performance and complicates system design.

A New Chemistry Strategy From Nature Energy

In a study published today (December 19) inNature Energya research team led by Prof. Xianfeng Li at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) introduced a new chemical approach for bromine-based flow batteries.

The researchers designed a two-electron transfer reaction involving bromine and successfully integrated it into a zinc-bromine flow battery. The work demonstrates both a working proof of concept and successful scaling toward a long-life battery system.

Turning Free Bromine Into a Stable Compound

To achieve this, the team added amine compounds to the electrolyte, where they act as bromine scavengers. During battery operation, the bromine (Br₂) produced by electrochemical reactions is converted into brominated amine compounds. This process lowers the concentration of free Br₂in the electrolyte to an ultra-low level of about 7 mM.

Unlike the standard reaction in which bromide ions transfer a single electron to form Br₂the new process enables a two-electron transfer from bromide ions to the brominated amine compounds. This change increases the battery’s energy density while sharply reducing corrosive behavior inside the system, helping the battery last longer.

Lower Costs and Long-Term Stability at Larger Scale

The researchers then applied this chemistry to zinc-bromine flow batteries in practical tests. Because the electrolyte contains so little free Br₂the battery can operate stably using a conventional non-fluorinated ion exchange membrane (SPEEK), which helps reduce costs.

In a 5 kW scaled-up system, the battery ran reliably for than 700 charge and discharge cycles at a current density of 40 mA cm^-2and achieved an energy efficiency above 78%. With the Br₂concentration kept extremely low, no corrosion was found in critical components—including current collectors, electrodes, and membranes—either before or after cycling.

A Path Toward Durable Grid-Scale Energy Storage

“Our study provides a novel approach to the design of long-life bromine-based flow batteries and lays the foundation for the further application and promotion of zinc-bromine flow batteries,” said Prof. Li.

Reference: “Grid-scale corrosion-free Zn/Br flow batteries enabled by a multi-electron transfer reaction” 19 December 2025,Nature Energy.
DOI: 10.1038/s41560-025-01907-5

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