Super hot salt can reach a battery near you

Ambri is a Boston-area startup that builds batteries from molten salt of calcium and antimony. The company recently announced a demonstration project to deploy energy storage for Microsoft data centers, and last year raised more than $140 million to build out its manufacturing capacity.

The company says its technology can be 30-50% cheaper over its lifetime than an equivalent lithium-ion system. Molten salt batteries can also exceed 80% efficiency, meaning that relatively little of the energy used to charge the battery is wasted as heat.

Ambri was founded in 2010 based on research from 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.

The inspiration came from an unlikely place: aluminum production. Using chemical reactions similar to those used to melt aluminum, the team built a low-cost, lab-scale energy storage system. But turning this concept into a real product is not so easy.

The magnesium and antimony-based chemistry the company started with proved difficult to manufacture. In 2015, after ongoing problems with battery seals, Ambri laid off a quarter of its staff and went back to the drawing board.

In 2017, the company took a new approach to its batteries, using calcium and antimony. The new chemistry relies on cheaper materials and should prove easier to manufacture, Bradwell says. Since its inception, the company has ironed out technical issues and made progress in commercialization, passing third-party safety tests and signing its first commercial deals, including one with Microsoft.

Microsoft’s Energy Storage System. Image courtesy of Ambri.

There are still big challenges ahead for the startup. Batteries operate at high temperatures, over 500°C (about 900°F), which limits what materials can be used to make them. And going from single battery cells that are the size of a lunchbox to huge container-sized systems can present challenges in system control and logistics.

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