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50 DISRUPTIVE COMPANIES 2013
MIT TECHNOLOGY REVIEW
The ability to bring in stored power when needed would
mean that some of those fossil-fuel power plants could be closed
and new ones wouldn’t have to be built. But so far we have no
good all-purpose way to store energy for the grid. Today, 99 per-
cent of grid storage takes the form of “pumped hydro”—water is
pumped uphill to a reservoir and released to turn a generator
when energy is needed. This low-tech method is efficient, and it’s
cheap over the long term, but it’s limited to places with moun-
tains and readily available water. As a result, it provides less than
1 percent of the power capacity in the United States on a given
day, according to Mark Johnson, director of the grid storage pro-
gram at the Department of Energy’s ARPA-E research agency.
Dozens of companies are developing new energy storage
devices, including various types of giant batteries, large spinning
cylinders called flywheels, and even compressed-air storage tanks.
But so far none of these approaches are cheap enough to be com-
petitive. Depending on its size, a pumped-hydro plant can deliver
power for tens of hours at a cost of about $100 per kilowatt-hour.
Grid-level batteries can cost 10 times that, which is why there are
just a few hundred megawatts of battery power on the grid—less
than the amount contributed by one full-size power plant.
Ambri is betting that by using cheap materials and a simple
battery design with no moving parts, it can deliver reliable bulk
energy storage for well below $500 per kilowatt-hour. That’s still
more expensive than pumped hydro, but since batteries can be
placed nearly anywhere, Ambri thinks its technology can be the
most economical choice for many applications.
“One metric matters more than anything else on the grid,”
says Johnson. “It’s cost, cost, cost.”
hen Sadoway first considered grid storage in 2005,
he looked to aluminum smelters for inspiration.
These massive machines, which can stretch to
more than 200,000 square feet, use huge amounts
of electricity to extract aluminum from molten aluminum oxide
through electrolysis. Sadoway, who is trained as a metallurgist,
realized that smelting could provide a template for a recharge-
able battery that tolerates the current levels needed for the grid.
“I looked at that and said, Wow, that looks like half of a battery!
And it’s big, it’s scalable, and it’s cheap,” he says.
After hitting upon the idea of the liquid-metal battery,
Sadoway searched for the perfect electrodes: he ended up choos-
ing magnesium and antimony because they are cheap and sepa-
rate naturally when in liquid form, the lighter magnesium rising
to the top. A liquid-salt electrolyte rests between the magnesium
and antimony electrodes, creating a cell with three layers.
When the battery is called upon to deliver power to the grid,
magnesium atoms from the top layer—the anode—give off elec-
trons. The resulting magnesium ions travel through the electro-
lyte and react with the antimony, forming an alloy and expanding
the bottom layer of the cell—the cathode. When the battery is
charging, it acts like the smelter, liberating the magnesium from
its alloy and sending it back through the electrolyte to rejoin
the magnesium electrode. The intense flow of current gener-
ates the heat used to keep the metals in a molten state. (Ambri
has switched to cheaper metal alloys and a salt mixture, but the
chemistry works the same way.)
In 2007, when Bradwell was a student in Sadoway’s lab, he
used the magnesium-antimony technology to make an experi-
mental battery with about the diameter of a shot glass. By 2009 it
had attracted nearly $11 million in research funding from ARPA-
E and the French oil company Total. The next year, Sadoway and
Bradwell created a company called Liquid Metal Battery Corpo-
ration; they then secured seed funding from Bill Gates and Total.
The founders expected the technical work to take longer than
the five to seven years that venture capitalists are typically will-
ing to wait before cashing out, so at first they didn’t take money
from such investors as many other clean-tech startups had done.
By the summer of 2011, though, it was time to build a product.
Sadoway recruited a new CEO, Philip Giudice, who helped secure
a $15 million round of investment led by Khosla Ventures. The
company changed its name to Ambri—based on the name of
Cambridge, where the technology was invented.
PRIVATE | FOUNDED: 2012
Restoring the promise of gene
therapy. The Dutch company
has approval to treat a rare
PRIVATE | FOUNDED: 2002
Launching the private space-
flight business. Its rockets are
making new space-based busi-
PUBLIC | FOUNDED: 1909
Pushing autonomous cars
closer to fruition with a laser-
scanning road detector that
fits in a vehicle’s front grille.
PUBLIC | FOUNDED: 1937
Expanding its dominance of
the hybrid-car market with
its new plug-in version of the
Energy Storage Trade-offs
Pumped storage High capacity, low cost Special site requirements
Low energy density
Low energy density
2/6/13 1:12 PM
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