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Batteries MIT hourglass energy storage flow battery

Published on May 26th, 2016 | by Tina Casey


“Hourglass” Coal-Killing Steampunk Energy Storage System Could Pump More Wind, Solar Into Grid

May 26th, 2016 by  

The Intertubes have been buzzing with news of a new “hourglass” flow battery that could provide a durable, low cost energy storage system for the nation’s vast wind and solar resources. The old meme about clean power being unreliable is fast disappearing, and if the new battery pans out, that will seal the deal.

In addition to becoming an area of interest for the Energy Department’s solar and wind grid integration efforts, flow batteries are also edging their way into electric vehicle technology.

MIT hourglass energy storage flow battery

What Is A Flow Battery, Anyways?

A flow battery is a type of energy storage system that deploys liquid instead of solid material. The typical setup enables two different liquids to flow adjacent to each other, separated only by a thin membrane (some newer types eschew the membrane entirely). The nature of the liquids, combined with the flowing action, creates an electrical charge.

As you can probably guess, two main advantages of flow batteries are scalability and reliability. The two liquids can be stored in tanks of practically any size, for practically any length of time, and they can be called quickly into action when needed.

Aside from the technology and expense associated with the membrane (or lack thereof), little else is required aside from pumps to get the liquid flowing.

Like many other forms of new technology, past iterations of flow batteries were large, clunky affairs with low energy density, and their size worked against practical applications. Emerging flow battery technology is moving toward a more energy-dense, compact approach.

The MIT Energy Storage Breakthrough

Some of the cutting edge progress in flow battery technology is taking place in the area of nanotechnology, including membrane improvements and membrane-less systems. The new energy storage breakthrough, from a research team based at the Massachusetts Institute of Technology, focuses on something much more mundane: the pumps.

That’s right. The pumps.

Aside from the holding tanks, pumps are probably the most conventional technology associated with flow battery systems. At first glance there doesn’t seem to be much room for improvement there, but MIT writer David Chandler points out that when you have a pumping system, you also have pipes and valves, all of which adds to complexity and costs while offering numerous opportunities for leakage, breakage, and other mishaps.

Cutting costs through simplification was the goal of the MIT team. Their solution is an unabashedly low tech one, that being to replace the pumps with gravity. About three years ago they began tinkering around with the idea of a gravity fed system, and last month they published the results of their latest flow battery study in the journal Energy & Environmental Science:

Here, we design and demonstrate a proof-of-concept prototype for a “gravity-induced flow cell” (GIFcell), representing one of a family of approaches to simpler, more robust, passively driven, lower-cost flow battery architectures.


Accordingly, we demonstrate the GIFcell using nonaqueous lithium polysulfide solutions containing a nanoscale carbon network in a half-flow-cell configuration and achieve round trip energy efficiency as high as 91%.

Did you get all that? If “lithium polysulfide” reminds you of lithium-ion batteries, you’re on the right track. The liquid in the new MIT flow battery is a slurry containing nanoscale particles of lithium, based on principles similar to that of conventional, solid lithium-ion technology. Don’t get too excited about the slurry, though. The researchers note that it’s a placeholder, and the basic system can be modified to use any number of other chemical compositions.

The demonstration model looks like a steampunk version of a window with two frames. It rests semi-horizontally on a trestle, so the angle of tilt can be easily adjusted.

Instead of having two liquids in the system, the new flow battery deploys a solid sheet of lithium in one frame (the idea was to test the concept in its simplest form before moving on to the next challenge). The slurry flows across the sheet and back again, moving through a narrow “neck” similar to that of an hourglass.

It all sounds simple enough, but one of the main obstacles was to stabilize the rate of flow in the slurry, which has been described as having the consistency of ketchup. Numerous adjustments were made until the team decided that a relatively shallow tilt would do the trick.

While the new system is a hybrid and not 100 percent flow, Chandler points out that it already demonstrates another key advantage of flow batteries compared to conventional, large energy storage systems:

While a conventional, all-solid battery requires electrical connectors for each of the cells that make up a large battery system, in the flow battery only the small region at the center — the “neck” of the hourglass — requires these contacts, greatly simplifying the mechanical assembly of the system…

Manufacturing costs are another key consideration. According to the researchers, low cost fabrication methods like injection molding and 3-D printing could be deployed to produce the components of the system.

Next steps for the research team include ditching the solid sheet in favor of an all-liquid flow battery, so group hug for US taxpayers. The team is funded by the Energy Department’s Joint Center for Energy Storage Research.

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Image: via MIT, courtesy of the research team.

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About the Author

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. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • eveee

    Only a small portion in the center needs to have contacts? Perhaps, but the stack, the area where ion exchange happens must be sized for the maximum current. That determines the stack size.

  • Gerald Katz

    For real compactness and simplicity bladders could be used in some applications. Can be flat or tubular as one is squeezed and emptied the other fills and expands. Polaroid used flat packets of chemicals for its cameras. Bosses carpet shampoo machines have a bladder in side a tank. As Clean water in the bladder is used the bladder emptied and shrinks and dirty water fills in around it it the tank filling the space left by the shrinking bladder. Two bladders on each side of a reaction cell the cell moves between the bladders causing the fluids to move from one bladder to the other. This could work with very viscous electrolytes. Almost as simple as tooth paste tubes.

    • Gerald Katz

      Cylinders could hold two fluids divided by a piston which moves to displace a fluid from one side to the other. Think chalk gun simple. Or two bellows with fixed end and moving center.

  • Steve

    Why not shape it like two inverted triangles with the vertexes meet in the middle?

  • Maybe there’s a way to make big tanks and alter the tilt with electrically driven hydraulics. You’d still have a pump but just a little hydraulic one.

  • JamesWimberley

    You could set it up in rural Africa with a donkey to power the tilting. But it wouldn’t work in the weightless conditions of a spaceflight to Mars, which looks conclusive.

    • Karl the brewer

      Or a huge donkey.

      • Carl Raymond S

        Overhead crane, fork truck, block and tackle, hydraulic ram, worm drive with jack screw, winch with incline plane, lever/ratchet jack, shaduf. Or a huge donkey.

    • Waiting to be bribed

      On a flight to Mars you would have constant acceleration for the fist half of the trip then deceleration for the last half. Artificial gravity. They could also apply rotation to the ship for centrifugal generated gravity.

  • TomK

    Any idea when we might see something like this in a production car, if ever? I mean, just look at that nanoFlowcell scam by Nuncio La Vecchia.

    • A gravity-based design is certainly not suitable for cars. A pump-based one may be but flow batteries tend to have way lower energy and power densities than what is required in cars. Also, round-trip efficiency of flow batteries are in the 60-80% region which compares badly with the 95%+ of Li batteries.

      Now, this chemistry seems to have higher roundtrip eff (91%) but there is no word on densities.

      If they can make the storage material cheap enough and the roundtrip efficiency high, this might prove to be an excellent grid-battery. With sufficiently cheap medium and energy density, this may be even used for seasonal storage.

      • TomK

        Sounds conclusive. Thanks for your thoughts!

  • Marion Meads

    Tilting the battery contraption will occupy even a bigger volume so that it can rotate about, Imagine that!

    • sault

      It’s just a shallow tilt angle, probably a few degrees from level either way. It’s not going to take up much room over and above what’s necessary for passive cooling.

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