Researchers combine charging and electrolytic flow cells

Researchers combine charging and electrolytic flow cells

Technology News |
By Nick Flaherty

The membrane developed at Ohio State University engineers can be used for both charging a battery and quickly re-filling it with liquid electrolyte so that electric vehicles can travel farther on a single charge. These currently achieve 0.4 miles — less than half a mile of driving — per minute of charging, and the aim is to boost electric car batteries to provide up to tens of miles per minute of charge by refilling the flow cell.

“That’s still an order of magnitude away from the equivalent measure in gasoline, but it’s a place to start,” said Vishnu-Baba Sundaresan, an assistant professor of mechanical and aerospace engineerin gat Ohio State and leader of the study.  “Research over the last 50-plus years has focused on advancing the chemistry of battery electrodes to increase capacity,” he said. “We’ve done that, but the increase in capacity has come at the cost of robustness and the ability to rapidly charge and discharge batteries. Electric vehicle design is mature enough now that we know the limit they’re reaching is because of the chemistry of lithium-ion batteries.”

Sundaresan and doctoral student Travis Hery call their invention an “ionic redox transistor,” and they’re using it to develop a new kind of battery in which energy is stored in a liquid electrolyte—which people can recharge or empty out and refill as they would refill a gas tank. While the researchers have proven that the membrane works with conventional batteries, what Sundaresan and Hery most want to do is use it as the basis of a new type of battery. They are working to combine a flow battery, in which an electrolyte is pumped from the anode to the cathode to generate power, with their smart membrane to create the so-called “redox transistor battery.”

“For everyday commuting, the electrolyte can be simply regenerated by plugging it into a power outlet overnight or while parked at the garage. For long road trips, you could empty out the used electrolyte and refill the battery to get the kind of long driving range we are accustomed to with internal combustion engines,” said Sundaresan. “We believe that this flexibility presents a convincing case for weaning our dependence on internal combustion engines for transportation.”

Sundaresan and Hery believe their membrane, when used with a specially designed electronic control unit, can shut down charge transport and prevent thermal runaway at its onset. They combined an electrically conductive polymer with a polycarbonate filter used for air and water testing. By controlling how they grew the conductive polymer chains on the polycarbonate surface, the researchers found they could control the density of openings in the resulting membrane. When the battery is charging or discharging, the conductive polymer shrinks to open the holes. When the battery isn’t in use, the polymer swells to close the holes.

In laboratory tests, the engineers found that their membrane reliably controlled charging and discharging in batteries powered by ions of lithium, sodium and potassium. They connected batteries to an LED light, programming the holes to open and close in precise patterns. The membrane allowed the batteries to function normally, but reduced charge loss to zero when the batteries were not in use.

The university will license the technology to industry for further development.The same technology could prevent self-discharge in supercapacitors, which give high power and rapid recharge capability to some electric cars, buses and light rail transit systems.


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