A sample of ‘Cambridge crude’—a black, gooey substance that can power a highly efficient new type of battery. A prototype of the semi-solid flow battery is seen behind the flask. Photo: Dominick Reuter
radically new approach to the design of batteries, developed by researchers at
MIT, could provide a lightweight and inexpensive alternative to existing
batteries for electric vehicles and the power grid. The technology could even
make “refueling” such batteries as quick and easy as pumping gas into a
new battery relies on an innovative architecture called a semi-solid flow cell,
in which solid particles are suspended in a carrier liquid and pumped through
the system. In this design, the battery’s active components are composed of
particles suspended in a liquid electrolyte. These two different suspensions
are pumped through systems separated by a filter, such as a thin porous
work was carried out by Mihai Duduta ’10 and graduate student Bryan Ho, under
the leadership of professors of materials science W. Craig Carter and Yet-Ming
Chiang. It is described in a paper in Advanced
important characteristic of the new design is that it separates the two
functions of the battery—storing energy until it is needed, and discharging
that energy when it needs to be used—into separate physical structures.
Separating these functions means that batteries can be designed more
efficiently, Chiang says.
new design should make it possible to reduce the size and the cost of a
complete battery system, including all of its structural support and
connectors, to about half the current levels. That reduction could be the key
to making electric vehicles fully competitive with conventional gas- or
diesel-powered vehicles, the researchers say.
potential advantage is that in vehicle applications, such a system would permit
the possibility of simply “refueling” the battery by pumping out the liquid
slurry and pumping in a fresh, fully charged replacement, or by swapping out
the tanks like tires at a pit stop, while still preserving the option of simply
recharging the existing material when time permits.
batteries have existed for some time, but have used liquids with very low
energy density. Because of this, existing flow batteries take up much more
space than fuel cells and require rapid pumping of their fluid, further
reducing their efficiency.
new semi-solid flow batteries pioneered by Chiang and colleagues overcome this
limitation, providing a 10-fold improvement in energy density over present
liquid flow-batteries, and lower-cost manufacturing than conventional
lithium-ion batteries. Because the material has such a high energy density, it
does not need to be pumped rapidly to deliver its power. “It kind of oozes,”
Chiang says. Because the suspensions look and flow like black goo and could end
up used in place of petroleum for transportation, Carter says, “We call it ‘Cambridge crude.'”
key insight by Chiang’s team was that it would be possible to combine the basic
structure of aqueous-flow batteries with the proven chemistry of lithium-ion
batteries by reducing the batteries’ solid materials to tiny particles that
could be carried in a liquid suspension. “We’re using two proven technologies,
and putting them together,” Carter says.
addition to potential applications in vehicles, the new battery system could be
scaled up to very large sizes at low cost. This would make it particularly
well-suited for large-scale electricity storage for utilities, potentially
making intermittent, unpredictable sources such as wind and solar energy
practical for powering the electric grid.
team set out to “reinvent the rechargeable battery,” Chiang says. But the
device they came up with is potentially a whole family of new battery systems,
because it’s a design architecture that “is not linked to any particular chemistry.”
Chiang and his colleagues are now exploring different chemical combinations
that could be used within the semi-solid flow system. “We’ll figure out what
can be practically developed today,” Chiang says, “but as better materials come
along, we can adapt them to this architecture.”
whose earlier insights on lithium-ion battery chemistries led to the 2001
founding of MIT spinoff A123 Systems, says the two technologies are
complementary, and address different potential applications. For example, the
new semi-solid flow batteries will probably never be suitable for smaller
applications such as tools, or where short bursts of very high power are
required—areas where A123’s batteries excel.
new technology is being licensed to a company called 24M Technologies, founded
last summer by Chiang and Carter along with entrepreneur Throop Wilder, who is
the company’s president. The company has already raised more than $16 million
in venture capital and federal research financing.
target of the team’s ongoing work, under a three-year ARPA-E grant awarded in
September 2010, is to have, by the end of the grant period, “a
fully-functioning, reduced-scale prototype system,” Chiang says, ready to be
engineered for production as a replacement for existing electric-car batteries.