In 2019, Tom Sisto was working as a researcher in the laboratories of Columbia University, developing synthetic molecules for solar cells, when his team stumbled upon a “serendipitous” discovery.
“Very much by accident, we found a set of chemistries that never degraded when they were charged or discharged,” Sisto, who is the co-founder and CEO of XL Batteries, told Latitude Media. “We were using them for solar cell applications…and we looked at it and said, ‘Well, that’s a battery molecule, not a solar cell molecule.’”
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That molecule, originally contained in a layer of bright red paint that absorbed light in a solar cell, became the basis for the long-duration energy storage systems developed by his company, XL Batteries, which today announced a $7.5 million seed investment from Merrin Investors, Latitude Media has exclusively learned. This latest round brings the startup’s total funding to date to $28 million.
XL Batteries develops flow batteries, which are rechargeable energy storage systems that generate electricity by circulating liquid electrolytes through a cell stack. Sisto compares them to a car, which functions thanks to an engine, a gas tank, and the fuel in it. In XL Batteries’ flow batteries, cell stacks assembled in an industry-standard shipping container are the equivalent of the engine; a liquid solution containing the startup’s proprietary molecule is the gas; and the industrial storage tanks where the solution is stored are the equivalent of the car’s gas tank.
Electricity goes into the liquid, and then the system charges and discharges as the liquid flows through the cells. Unlike a car, however, it doesn’t need to be refueled. “It’s a closed loop circulating system — you’re able to charge and discharge the tanks again and again and again,” Sisto said.
The system can last for more than 20 years, and the hours of storage it can discharge depends on the amount of liquid in the tanks and the number of stackable containers a company installs. “The duration is whatever size tank the customer may want,” Sisto said. “Let’s pretend the electrodes are lithium: you can add as much lithium as you want, and that’s how much duration you get. If you have a 10-hour battery and you want to make it a 20-hour one, you just double the size of the tank.”
The company recently finished a pilot project with bulk liquid services provider Stolthaven Terminals.
In May, it announced an agreement with data center developer Prometheus Hyperscale. Per the agreement, XL Batteries will deliver and commission a 333-kilowatt demonstration-scale system at Prometheus’ facility in 2027; Prometheus has committed to buy one 125 megawatt-hour commercial-scale system in 2028 and another one in 2029.
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