ESS Tech Inc. (NYSE: GWH) signed a letter of intent for a strategic partnership with Alsym Energy to add 8.5 GWh of sodium-ion cells and modules to its energy storage portfolio, according to a company statement.

The partnership enables ESS to enter the short and medium-duration battery energy storage system segment, expanding beyond its established position in long-duration storage. Alsym's sodium-ion technology is designed to address applications traditionally served by lithium-ion systems without thermal runaway risks.

ESS currently manufactures iron flow energy storage systems for 8-24 hour long-duration applications. The addition of Alsym's sodium-ion technology allows the company to offer solutions for shorter duration storage needs requiring high power and fast cycling capabilities.

"Sodium-ion and iron flow are complementary technologies," said Drew Buckley, Chief Executive Officer of ESS. "Alsym's sodium-ion Na-Series is an ideal solution for ESS's short- and medium-duration applications where high power, fast cycling, and rapid response are paramount."

Alsym's Na-Series batteries use non-flammable sodium-ion chemistry and operate without complex HVAC systems. The technology utilizes materials not subject to foreign entity of concern sourcing restrictions and demonstrates thermal stability that reduces fire suppression infrastructure requirements.

The combined platform positions ESS to serve utilities, independent power producers, data centers, and commercial customers seeking energy storage solutions across multiple duration ranges. ESS was established in 2011 and manufactures long-duration iron flow systems using iron, salt, and water.

Alsym Energy develops sodium-ion batteries using what the company describes as a physics-informed artificial intelligence platform for battery development.