Ambri is a Boston-area startup that is building molten salt batteries from calcium and antimony. The company recently announced a demonstration project deploying energy storage for Microsoft data centers, and last year raised more than $140 million to expand its manufacturing capacity.
The company says its technology could be 30-50% cheaper over its lifetime than an equivalent lithium-ion system. Molten salt batteries can also be over 80% efficient, meaning that a relatively low amount of energy used to charge the battery is lost to heat.
Ambri was founded in 2010 out of research in Donald Sadoway’s lab at MIT. The goal was to develop a low-cost product for the stationary storage market, says David Bradwell, the company’s founder and CTO.
Inspiration came from an unlikely place: aluminum production. Using chemical reactions similar to those used for aluminum smelting, the team built a low-cost, lab-scale energy storage system. But turning this concept into a real product has not been so simple.
The magnesium-antimony chemistry the company started with proved difficult to manufacture. In 2015, after continuing problems with battery seals, Ambri laid off a quarter of its staff and went back to the drawing board.
In 2017, the company opted for a new approach to its batteries, using calcium and antimony. The new chemistry is based on cheaper materials and should prove simpler to manufacture, Bradwell says. Since the pivot, the company has ironed out technical issues and advanced commercialization, passing third-party security tests and signing its first commercial deals, including with Microsoft.
There are still big challenges ahead for the startup. Batteries operate at high temperatures, over 500°C (about 900°F), which limits the materials that can be used to make them. And going from individual battery cells, which are roughly the size of a lunchbox, to huge container-sized systems can present challenges in system controls and logistics.
That’s not to mention deploying a product in the real world means “dealing with real-world things that happen,” as Bradwell puts it. Everything from lightning to rodents can throw a wrench in a new battery system.