It goes without saying that in order to move towards a cleaner, greener transportation mix of the future, battery electric vehicles — where electrical power is stored as chemical energy within a traditional battery pack — have an essential part to play.
But while battery cell chemistry is far more advanced today than it was ten or even five years ago, the lithium-ion battery packs found in today’s electric cars still have a couple of big problems facing them: lithium itself is costly and difficult to mine; and even the best lithium-ion cell technology can’t be recharged as quickly as a gasoline car can refuel.
So far, we’ve seen plenty of different solutions to both problems in the form of new exotic battery cell chemistries or the use of composite nanotechnology to dramatically increase the surface area (and therefore the maximum charging current) of an battery electrode. But now a team of researchers at the University of Harvard think they have a solution which could not only eliminate the use of rare earth or difficult-to-mine materials in electric car battery packs, but could change the way we charge our cars, too.
Enter the Alkaline Quinone Flow Battery, a brand new type of flow battery developed by postdoctoral fellow Michael Marshak and graduate student Kaixiang Lin working together with Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science at Harvard.
If you think you’re familiar with the term Flow Battery, it’s because we’ve covered them here on Transport Evolved before while making reference to Swiss automaker Nanoflowcell. If you’ve not heard of the term before, here’s a quick course on how they work.
Unlike traditional electrochemical batteries, in which a flow of electrons is induced between two electrodes made of different metal through a liquid or solid electrolyte when connected in a circuit, flow batteries work by passing two differently charged liquids either side of a permeable catalyst. The liquids, stored in two separate tanks, hold opposite charges to one another just like the two different electrodes in a traditional battery.
The difference? As they are both liquid in nature, flow batteries can be quickly recharged by pumping out the old, discharged electrolytic fluids and replacing them with freshly charged fluid.
So far, so good — but the problem with flow batteries thus far is that they have relied on expensive metals like vanadium, dissolved in acid, as their active electrolytic components.
In addition to being toxic, the resulting solution can be corrosive if spilled, difficult to handle and as the researchers put it, “kinetically sluggish.” All of this makes for a flow battery which is far less appealing in most applications than a conventional lithium-ion cell.
Here’s where the Alkaline Quinone Flow Battery differs from other flow batteries being developed. Instead of using rare earth metals, or acid-dissolved metal compounds, the new flow battery developed by the team at Harvard relies on using organic molecules called quinones. These molecules, which occur naturally in the real world and are essential to processes like photosynthesis in plants and cellular respiration, can be dissolved in water to form the negative electrolytic solution, while the positive electrolytic solution comes courtesy of ferrocyanide mixed with a soluble quinone compound.
As for the ferrocyanide? The chemists are keen to remind us that while cyanide can kill by binding to all of the iron in our body, its that same strong bond between iron and cyanide which makes ferrocyanide non-toxic and relatively harmless. When mixed with the soluble quinone compound, the resulting alkaline solution is about as irritating to the skin as coming into contact with a leaking AA battery.
“It’s not something you want to eat or splash around in, but outside of that it’s really not a problem,” said Marshak.
Because both electrolytic solutions are both easy to make and are made of elements that are easy to source, the new Alkaline Quinone Flow Battery is far cheaper to build than many other flow battery chemistries we’ve see. And a lack of acidic solution means a double-whammy for those working on the technology in terms of construction: not only can cheaper materials like plastics be used to build the flow tanks, but replenishing the tanks with fresh electrolytic solution is less of a challenge.
At the moment, the researchers — whose paper is published in Science Journal — have been focused on small-scale applications in the laboratory as well as potential large-scale projects for use in grid-tied energy backup systems where tank-size isn’t a problem.
But given the right development, we can see flow batteries make their way into automotive applications — provided they have enough power to weight and a robust, safe way of refilling depleted energy tanks on long trips.
We’ll be watching this one with interest.
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