Scientists on the lookout for utility-scale, high efficiency batteries are developing new “flow”systems that that store energy more effectively than lead-acid or lithium-ion batteries, but there’s a catch. The flow batteries in operation now are about the size of a house and they cost more than the equivalent in lithium-ion batteries. The race is on to find smaller, cheaper alternatives and researchers at Sandia National Laboratories believe that they are on to the solution, which is, in fact, a solution of liquid salts called MetILs.
The limits of lithium-ion for wind and solar
Lithium-ion batteries have been the gold standard of energy storage solutions for a long time, but they fall short when it comes to the utility-scale systems needed to keep up with new high efficiency wind turbines and advanced solar technology. The cost of lithium-ion batteries is one factor. Another is their relatively short lifespan, compared to flow batteries. According to Sandia chemist Travis Anderson, a flow battery can withstand about 14,000 cycles, which adds up to about 20 years of energy storage.
Flow battery basics
Flow batteries work by converting chemical energy into electricity. Stephanie Hobby of Sandia explains it thusly:
“A flow battery pumps a solution of free-floating charged metal ions, dissolved in an electrolyte — substance with free-floating ions that conducts electricity — from an external tank through an electrochemical cell to convert chemical energy into electricity.”
Flow batteries charge and discharge rapidly, and they have a long lifespan, but all is not perfect in flow battery land. The most promising systems so far use zinc bromine and vanadium, both of which are “moderately toxic” according to Hobby. In addition, the price of vanadium can spike wildly on the open market.
The Sandia “American-made energy” solution
In keeping with President Obama’s theme of developing American-made energy, the Sandia team focused on low cost, non-toxic substances that can be dug up out of American soil, including iron, copper and manganese. Working from this foundation the team designed a new family of liquids, the aforementioned MetILs, which stands for Metal-based Ionic Liquids.
By using metal based liquids, the team was able to eliminate the use of water-based solutions that are the foundation of conventional flow batteries (water limits the energy density of the battery, and makes it more susceptible to fluctuations in outside temperatures).
With a few additional tweaks, the result is a flow battery that could be far smaller,
About those tweaks…
As Hobby points out, so far the research has focused primarily on materials for the cathode. There is still the anode to deal with, so the new battery won’t be ready for the market any time soon. In the mean time, the Sandia crew better act fast – researchers at MIT are also working on a new high tech, low cost battery of their own.
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Tina Casey specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. You can also follow her on Twitter @TinaMCasey and Google+.