ESS Tech Inc. (NYSE: GWH) announced a letter of intent for a strategic partnership with Alsym Energy to add 8.5 GWh of sodium-ion battery 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 associated with lithium chemistries.

"Sodium-ion and iron flow are complementary technologies," said Drew Buckley, ESS chief executive officer. "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."

The sodium-ion batteries are non-flammable and do not require complex HVAC systems, according to the companies. The technology demonstrates high round trip efficiency and offers fast charge and discharge capabilities.

ESS manufactures long-duration iron flow energy storage systems using iron, salt, and water. The company's Energy Base platform is designed for 8-24 hour long-duration storage applications.

"This partnership represents a major milestone in our strategy to become a full-spectrum, non-lithium solutions provider," said Randall Selesky, ESS chief commercial officer.

Alsym Energy develops sodium-ion batteries using what it describes as a proprietary, physics-informed AI platform for battery development. The Na-Series batteries utilize materials that are not sourced from foreign entities of concern.

The combined platform positions ESS to support utilities, independent power producers, data centers, and commercial customers seeking energy storage solutions across various applications, according to the statement.