European heatwaves this summer boosted demand for battery storage systems, with San Diego-based startup Unigrid experiencing unexpected orders from Spain, France, Germany and the Netherlands for its home battery systems. This surge highlights the growing market opportunity for sodium-ion batteries, which could help return battery manufacturing to the United States and reduce dependence on China, where the lithium-ion supply chain is dominated.

Unigrid makes nine kilowatt-hour sodium-ion batteries that European homeowners are using to store cheaper off-peak grid power and run air conditioning during peak heat. The company expects to ship 1,000 units before the end of the year after its first 100 units. Sodium-ion batteries are attractive because they are potentially cheaper and safer than lithium-ion alternatives, work in extreme temperatures (down to minus 40C), and could be entirely manufactured in the US using US-sourced materials. However, concerns exist about safety, particularly regarding chromium-3 in Unigrid's cathode potentially forming toxic chromium-6, though the company argues this risk is overblown and has passed European safety certifications.