Aluminum batteries increase the range
June 22, 2017
The long range of airborne drones helps them perform critical tasks in
the skies. Now MIT spinout Open Water Power (OWP) aims to greatly
improve the range of unpiloted underwater vehicles (UUVs), helping them
better perform in a range of applications under the sea.
Open Water Power’s battery that
"drinks" in sea water to operate is safer and cheaper, and provides a
tenfold increase in range, over traditional lithium-ion batteries used
for unpiloted underwater vehicles. The power system consists of an
alloyed aluminum anode, an alloyed cathode, and an alkaline electrolyte
positioned between the electrodes. Components are only activated when
flooded with water. Once the aluminum anode corrodes, it can be replaced
at low cost.
Recently acquired by major tech firm
L3 Technologies, OWP has developed a novel aluminum-water power system
that’s safer and more durable, and that gives UUVs a tenfold increase in
range over traditional lithium-ion batteries used for the same
The power systems could find a wide range of uses, including helping
UUVs dive deeper, for longer periods of time, into the ocean’s abyss to
explore ship wreckages, map the ocean floor, and conduct research. They
could also be used for long-range oil prospecting out at sea and various
With the acquisition, OWP now aims to ramp up development of its power
systems, not just for UUVs, but also for various ocean-floor monitoring
systems, sonar buoy systems, and other marine-research devices.
OWP is currently working with the U.S. Navy to replace batteries in
acoustic sensors designed to detect enemy submarines. This summer, the
startup will launch a pilot with Riptide Autonomous Solutions, which
will use the UUVs for underwater surveys. Currently, Riptide’s UUVs
travel roughly 100 nautical miles in one go, but the company hopes OWP
can increase that distance to 1,000 nautical miles.
“Everything people want to do underwater should get a lot easier,” says
co-inventor Ian Salmon McKay ’12, SM ’13, who co-founded OWP with fellow
mechanical engineering graduate Thomas Milnes PhD ’13 and Ruaridh
Macdonald '12, SM '14, who will earn his PhD in nuclear engineering this
year. “We’re off to conquer the oceans.”
“Drinking” sea water for power
Most UUVs use lithium-based batteries, which have several issues.
They’re known to catch fire, for one thing, so UUV-sized batteries are
generally not shippable by air. Also, their energy density is limited,
meaning expensive service ships chaperone UUVs to sea, recharging the
batteries as necessary. And the batteries need to be encased in
expensive metal pressure vessels. In short, they’re rather short-lived
In contrast, OWP’s power system is safer, cheaper, and longer-lasting.
It consists of a alloyed aluminum, a cathode alloyed with a combination
of elements (primarily nickel), and an alkaline electrolyte that’s
positioned between the electrodes.
When a UUV equipped with the power system is placed in the ocean, sea
water is pulled into the battery, and is split at the cathode into
hydroxide anions and hydrogen gas. The hydroxide anions interact with
the aluminum anode, creating aluminum hydroxide and releasing electrons.
Those electrons travel back toward the cathode, donating energy to a
circuit along the way to begin the cycle anew. Both the aluminum
hydroxide and hydrogen gas are jettisoned as harmless waste.
Components are only activated when flooded with water. Once the aluminum
anode corrodes, it can be replaced at low cost.
Think of the power system as type of underwater engine, where water is
the oxidizer feeding the chemical reactions, instead of the air used by
car engines, McKay says. “Our power system can drink sea water and
discard waste products,” he says. “But that exhaust is not harmful,
compared to exhaust of terrestrial engines.”
With the aluminum-based power system, UUVs can launch from shore and
don’t need service ships, opening up new opportunities and dropping
costs. With oil prospecting, for example, UUVs currently used to explore
the Gulf of Mexico need to hug the shores, covering only a few pipeline
assets. OWP-powered UUVs could cover hundreds of miles and return before
needing a new power system, covering all available pipeline assets.
Consider also the Malaysian Airlines crash in 2014, where UUVs were
recruited to search areas that were infeasible for equipment on the
other vessels, McKay says. “In looking for the debris, a sizeable amount
of the power budget for missions like that is used descending to depth
and ascending back to the surface, so their working time on the sea
floor is very limited,” he says. “Our power system will improve on
Nailing the design
The OWP technology started as the co-founders’ side project, which was
modified throughout two MIT classes and a lab. In 2011, McKay joined
2.013/2.014 (Engineering System Design/Development) taught by MIT
professor of mechanical engineering Douglas Hart, a seasoned hardware
entrepreneur who co-founded Brontes Technologies and Lantos
Technologies. Milnes, who was previously a systems engineer at Brontes
and co-founded Viztu Technologies, was Hart’s teaching assistant.
The class was charged with developing an alternate power source for UUVs.
McKay gambled on an energy-dense but challenging element: aluminum. One
major challenge with aluminum batteries is that certain chemical issues
make it difficult to donate electrons to a circuit. Additionally, the
product of the reactions, the aluminum hydroxide, sticks to the
electrode’s surface, inhibiting further reaction. Continuing the work in
10.625 (Electrochemical Energy Conversion and Storage), taught by
materials science Professor Yang Shao-Horn, the W. M. Keck Professor of
Energy, McKay was able to overcome the first challenge by making a
gallium-rich alloyed aluminum anode that successfully donated electrons,
but it corroded very quickly.
Seeing potential in the battery, Milnes joined McKay in further
developing the battery as a side project. The two briefly moved
operations to the lab of Evelyn Wang, the Gail E. Kendall Professor of
Mechanical Engineering. There, they began developing electrolytes and
alloys that inhibit parasitic corrosion processes and prevent that
aluminum hydroxide layer from forming on the anode.
up shop at Greentown Labs in Somerville, Massachusetts, in 2013 — where
the company still operates with about 10 employees — OWP further refined
the power system’s design. Today, that power system uses a pump to
circulate the electrolyte, scooping up unwanted aluminum hydroxide on
the anode and dumping it onto a custom precipitation trap. When
saturated, the traps with the waste are ejected and replaced
automatically. The electrolyte prevents marine organisms from growing
inside the power system.
Now OWP’s chief science officer, McKay says the startup owes much of its
success to MIT’s atmosphere of innovation, where many of his professors
readily offered technical and entrepreneurial advice and allowed him to
work on extracurricular projects.
“It takes a village,” McKay says. “Those classes and that lab are where
the idea took shape. People at MIT were doing strong science for
science’s sake, but everyone was keenly aware of the possibility of
bringing technologies to market. People were always having those great
‘What if?’ conversations — I probably had three to four different
startup ideas in various stages of gestation at any given time, and so
did all my friends. It was an environment that encouraged the playful
exchange of ideas, and encouraged people to take on side projects with
real prizes in mind.”