A New Sodium-Ion Battery Twist In The Tale Of ESS

US energy storage company ESS Tech has entered a new partnership to manufacture sodium-ion batteries developed by Massachusetts-based startup Alsym Energy. This collaboration marks a significant shift for ESS, which has spent over a decade focusing on iron-based flow battery technology. The agreement includes a letter of intent for ESS to produce 8.5 gigawatt-hours of Alsym’s sodium-ion cells and modules, signalling a major scale-up for the emerging battery chemistry. Sodium-ion batteries, often referred to as “salt batteries,” offer potential advantages over traditional lithium-ion technology, including lower costs, enhanced safety due to reduced fire risk, and the possibility of sourcing materials domestically. Alsym’s sodium-ion cells are designed to be non-flammable and thermally stable, which could eliminate the need for complex cooling and fire suppression systems, thereby lowering total cost of ownership. While sodium-ion technology remains less proven commercially than lithium-ion, Alsym aims to position its batteries as a viable alternative for applications where safety and rapid response are critical. ESS plans to integrate Alsym’s sodium-ion batteries alongside its existing iron flow battery systems, targeting different storage durations to offer a comprehensive solution. CEO Drew Buckley explained that the sodium-ion batteries will serve short- and medium-duration needs requiring fast cycling and high power, while the company’s Energy Base® iron flow batteries will continue to address long-duration storage with deep daily cycling and extended asset life. This complementary approach aims to provide customers with a unified, non-lithium platform covering a broad range of energy storage requirements. ESS’s Chief Commercial Officer Randall Selesky emphasised the strategic value of combining Alsym’s technology with ESS’s expertise, highlighting the safety and economic benefits of moving beyond lithium-ion. The partnership reflects ongoing innovation in the US energy storage sector despite recent policy uncertainties, and positions both companies to compete in a market increasingly focused on decarbonisation and grid resilience. ESS is also exploring further growth opportunities internationally as it navigates this new chapter in its development.