Flux XII, a company developing advanced materials for aqueous flow batteries, has raised $3.95 million in seed funding.
The funding round was led by The Grantham Foundation, with participation from the Wisconsin Alumni Research Foundation (WARF), Desai Ventures, and gener8tor.
With this funding, the company has already increased electrolyte and membrane production in industrial facilities and started testing multiple kilowatt-scale prototypes. In 2026, the company plans to validate its minimal viable product module under controlled testing and design a fully-integrated, containerized battery energy storage system.
The company is also forming a consortium of utilities, developers, universities, and research partners to support system pilot testing in 2027.
“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”, said Dr. Patrick Sullivan, Co-founder and CEO of Flux XII.
The company aims to reduce the CapEx of flow battery systems by 50% at 100 megawatt scales to support load growth from data centers, EVs, onshoring manufacturing, and electrification.
According to Mercom’s 9M and Q3 2025 Funding and M&A for Energy Storage report, VC funding in the sector totaled $2.8 billion in 56 deals, a 4% increase YoY compared to $2.7 billion in 61 deals in 9M 2024. Materials and Components providers received the most VC funding in 9M 2025.
In October, XL Batteries, an Organic Flow Battery solution provider, raised $7.5 million from Merrin Investors, the family office of entrepreneur and philanthropist Seth Merrin. With this funding, the company plans to scale its operations, enhance grid resilience, and support energy independence by reducing reliance on foreign supply chains.
