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.
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.
Image: via MIT, courtesy of the research team.
Have a tip for CleanTechnica? Want to advertise? Want to suggest a guest for our CleanTech Talk podcast? Contact us here.
Latest CleanTechnica TV Video
CleanTechnica uses affiliate links. See our policy here.