XL Batteries launches grid-scale organic flow battery project 

A new flow battery start-up has entered the chat.  

Massachusetts-based XL Batteries announced this week the commissioning of its first fully integrated organic flow battery in partnership with global bulk storage provider Stolthaven Terminals. Situated at Stolthaven’s Houston facility, the project marks the commercial debut of XL’s patented water-based batteries and a shift toward safer chemistries.   

Thomas Sisto, the CEO and co-founder of XL Batteries, hadn’t planned on joining the energy storage fray. The key molecule now used in the company’s flow batteries was one Sisto initially developed for use in solar cells during his postdoc at Columbia University.  

But the compound demonstrated remarkable electrochemical stability.  

“It was pure luck,” Sisto told ESS News. He explained that the material never degraded. “That became the lightbulb moment where we realized this could be the foundation for a battery.” 

XL spun out from Columbia in 2019, and Sisto turned from synthetic chemist to clean energy entrepreneur.  

He explained that XL’s systems are true flow batteries, where the charge-storing materials remain dissolved in liquid form and circulate through a central reactor, as opposed to hybrid chemistries that rely on solid-state components. 

Unlike most flow batteries, however, which rely on rare or hazardous materials like vanadium, XL Batteries use proprietary organic molecules in a pH-neutral saltwater solution. The resulting systems are scalable and nonflammable, and face little degradation over their 20-year lifespan. 

“To customers, it’s basically the same product, but everything else on the inside is different,” Sisto said. “Vanadium flow batteries use fluorinated membranes, which are very expensive. We use a desalination membrane instead that lets us be corrosion resistant, and it’s less expensive.”  

And flow batteries get cheaper as energy storage capacity grows.  

“In long-duration applications — 10, 20, even 50 hours — adding capacity is simply a matter of enlarging the tanks,” Sisto said. 

The Stolthaven pilot project will be XL Batteries’ first foray into commercial applications; the batteries are set to support industrial operations for the next two decades and provide data about how the systems perform under real-world conditions.  

As calls to reshore the American battery supply chain rise, Sisto sees the company’s ability to get away from the global mineral trade a valuable resilience plug.  

“Russia and China have 95% of the world’s vanadium,” he explained. XL’s batteries instead rely on an American-made, American-developed molecule that cuts out the need for vanadium.  

Safer, nonflammable batteries are also grabbing the spotlight as recent battery fires around the U.S. have raised concerns around lithium-ion chemistries. Water-based systems like XL’s could help rebuild that public trust in grid-scale storage projects.  

As battery fires at lithium-ion facilities continue to raise concerns, water-based systems like XL’s offer a safer path forward—one that could build public trust in grid-scale storage. “People understand we need storage, but they need to trust that it’s safe,” Sisto said. “That’s why demonstration projects like this one matter.”