Flux XII, a Madison-based energy storage company focused on advancing aqueous flow battery materials, announced it has raised $3.95 million in seed funding. The round was led by The Grantham Foundation for the Protection of the Environment with participation from the Wisconsin Alumni Research Foundation (WARF), Desai Ventures, and gener8tor.
The funding builds on earlier support from Activate Fellowship, Third Derivative, Gigascale Capital, The Collaborative Fund, Safar Partners, and LiquidMetal Ventures, signaling strong investor confidence in the company’s approach to scalable grid storage solutions.
With the new capital, Flux XII has scaled up electrolyte and membrane production in industrial facilities and begun testing multiple kilowatt-scale prototypes. The company plans to validate its minimal viable product module in 2026 under controlled testing conditions and begin designing a fully integrated, containerized Battery Energy Storage System. Flux XII is also establishing a partnership consortium that includes utilities, developers, universities, and research organizations to advance pilot system deployments beginning in 2027.
Flux XII’s platform aims to deliver safe, sustainable, and cost-effective long-duration energy storage by engineering high-performance flow battery materials from widely available chemical feedstocks. The company’s technology approach targets substantially lower system cost and smaller system footprint while maintaining stability and efficiency. And its production methods enable the manufacture of electrolytes and membranes through straightforward industrial processes, allowing them to be integrated into commercial-scale hardware.
At 100 megawatt capacity deployments, Flux XII aims to achieve a 50 percent reduction in capital expenditures for flow battery systems, supporting the growth of grid capacity needs across data centers, electric vehicles, onshoring industrial operations, and broader electrification trends.
Flux XII’s headquarters and research operations are based in Madison, Wisconsin. The company’s mission is to enable renewable power to serve as reliable baseload energy through economically viable long-duration energy storage.
KEY QUOTES:
“Grid power developers need more capacity, and it needs to be cheaper, safer, and cleaner than gas or lithium-ion batteries. Flux is developing a comprehensive product that builds off decades of industry advancements and addresses these key points without the tradeoffs of competing energy storage solutions.”
Dr. Patrick Sullivan, Co-founder and CEO, Flux XII
“We’ve reviewed many new technologies, but Flux XII is a standout with the potential for greatly reducing the cost of energy storage. The chemistry is safe and rapidly scalable. This is what’s needed for renewables to undercut thermal generation, even overnight or when the wind isn’t blowing.”
Josh Agenbroad, Grantham Foundation
