A Liquid Metal Battery for Grid Storage Nears Production

Photo: Martin LaMonica

Ambri's grid-storage battery uses liquid metals as the anode and cathode.

MIT spin-off Ambri is a step closer to bringing a novel liquid metal battery to the electricity grid.

The company on Thursday cut the ribbon on a new production facility in Marlboro, Mass., where it intends to make shipping-container size batteries. Ambri also said its first two customers will be a military base on Cape Cod, in Massachusetts, and a wind project in Hawaii. The company will be making prototypes and demonstration units in Marlboro for installation next year and intends to have a full-scale manufacturing facility in 2015.

To keep battery prices low, Ambri uses inexpensive materials and a simple design. Each battery cell is a square metal box about 10 centimeters per side. (The image is a beta cell that was larger and circular.) Each cell contains two metals and a salt electrolyte that are all in liquid form when the battery is running. Because the materials have different densities, three distinct layers form. When discharging, metal ions from the top layer, which is the anode, travel through the electrolyte to combine with ions from the bottom layer, which is the cathode. The process works in reverse during charging. The battery operates at hundreds of degrees Celsius, and the heat generated by the charging and discharging keeps the internal cell components liquid.

MIT professor Donald Sadoway and his then-graduate student David Bradwell designed the first proofs of concept using antimony and magnesium with a salt electrolyte. In 2010, they formed a company, which has been funded by Bill Gates, Khosla Ventures, and energy company Total. 

To form a battery pack, 54 cells are stacked together. Sixteen packs, which the company calls an Ambri Core, will provide 200 kWh of energy storage. When several of these storage units are strung together in a full-size unit, Ambri anticipates it can provide 500 kilowatts of power for four hours. The simplicity of the the system means the company can manufacture at low costs, according to company executives

One advantage of the technology, according to Ambri, is that there is little storage capacity loss over time—an important consideration for utilities, which purchase equipment to last for decades. Also, the large cell design means there are fewer wires and connections required, reducing the number of potential points of failure. 

Ambri is among several companies competing to deliver cost-effective energy storage for the grid. Other technologies include flow batteries, compressed air storage machines, and flywheels. With multi-hour storage, wind and solar farms can deliver power on demand and utilities could use batteries to ease bottlenecks in the power distribution network.

Because utilities are very conservative in adopting new technology, Ambri has targeted other types of customers to demonstrate its first working prototypes. The Joint Base Cape Cod will use batteries to provide a steady output from its on-site wind and solar generators at the military base. Such a battery could also potentially provide backup power in the case of an outage. The project is funded by the Massachusetts Clean Energy Center.

Bulk grid storage companies are also targeting island nations, which rely on expensive diesel fuel for electricity generation. Renewable energy developer First Wind will deploy another prototype energy storage system from Ambri in Hawaii next year, using funds from the Department of Energy and the Office of Naval Research.

The key question regarding all emerging grid storage technologies is how well they will perform and at what cost. If a battery can be cheaper than a natural gas "peaking" plant or less than the cost of upgrading distribution equipment to meet growing demand, then utilities could warm to energy storage. That could lead to dramatic changes to how the grid is configured and potentially eliminate the need for power generators only used a few days a year to meet peak demand. But until then, companies like Ambri need to prove their battery is not just a good idea, but also a viable commercial product.

Image: Martin LaMonica

This post was corrected on 12 December 2013.

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