New Battery
Design Could Help Solar and Wind Energy Power the Grid
Researchers from the U.S. Department of Energy's (DOE) have designed a low-cost, long-life battery
that could enable solar and wind energy to become major suppliers to the
electrical grid.
For solar and wind power to be used in a significant way, we need
a battery made of economical materials that are easy to scale and still be efficient.
The believe is that the new battery design may be the best yet designed to
regulate the natural fluctuations of these alternative energies.
Currently the electrical grid cannot tolerate large and sudden
power fluctuations caused by wide swings in sunlight and wind. As solar and
wind's combined contributions to an electrical grid approach 20 percent, energy
storage systems must be available to smooth out the peaks and valleys of this
"intermittent" power - storing excess energy and discharging when
input drops.
Among the most promising batteries for intermittent grid storage
today are "flow" batteries, because it's relatively simple to scale
their tanks, pumps and pipes to the sizes needed to handle large capacities of
energy. The new flow battery developed has a simplified, less expensive design that
presents a potentially viable solution for large-scale production.
Today's flow batteries pump two different liquids through an
interaction chamber where dissolved molecules undergo chemical reactions that
store or give up energy. The chamber contains a membrane that only allows ions
not involved in reactions to pass between the liquids while keeping the active
ions physically separated. This battery design has two major drawbacks: the high cost of
liquids containing rare materials such as vanadium - especially in the huge
quantities needed for grid storage - and the membrane, which is also very
expensive and requires frequent maintenance.
The new battery design uses only one stream of molecules and does
not need a membrane at all. Its molecules mostly consist of the relatively
inexpensive elements lithium and sulfur, which interact with a piece of lithium
metal coated with a barrier that permits electrons to pass without degrading
the metal. When discharging, the molecules, called lithium polysulfides,
absorb lithium ions; when charging, they lose them back into the liquid. The
entire molecular stream is dissolved in an organic solvent, which doesn't have
the corrosion issues of water-based flow batteries. In initial lab tests, the new battery also retained excellent
energy-storage performance through more than 2,000 charges and discharges,
equivalent to more than 5.5 years of daily cycles.
To demonstrate the concept, the researchers created a miniature
system using simple glassware. Adding a lithium polysulfide solution to the
flask immediately produces electricity that lights an LED. A utility version of the new battery would be scaled up to store
many megawatt-hours of energy.
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