Squeezing more mileage out of electric cars with refillable batteries

Prototype membranes developed by engineers at The Ohio State University to keep rechargeable batteries from catching fire, and to help them be more efficient.
Pam Frost Gorder
Prototype membranes developed by engineers at The Ohio State University to keep rechargeable batteries from catching fire, and to help them be more efficient.

Original news release was issued by the Ohio State University.

Maximum distance travelled on a single charge continues to be one of the biggest drawbacks if one should choose to get an electric vehicle (EV), compared to their gas-powered counterparts. Although electric cars were proven ready to satisfy our commuting needs (as we have reported before), they still remain somewhat a long stretch before most of the motorists warm up to them. Recently, engineers from Ohio State University tipped the scales some more in favor of EVs by developing a thin plastic membrane that stops rechargeable batteries from discharging when not in use and allows for rapid recharging.

This invention — called “ionic redox transistor” — is meant as a crucial component upon which the researchers hope to develop a new kind of batteries. Energy of these batteries would be stored in a liquid electrolyte — which people could recharge or empty out and refill as they would refill a gas tank. Should the development be successful, it could boost the performance limit of the eco-cars up to tens of miles per minute of charge. The current best limit appears to be 0.4 miles — less less than half a mile of driving — per minute of charging. To put it in perspective, the maximum distance range of today’s very best EVs is around 200 miles after an 8-hour charge. In comparison, the gas-powered cars can cover the same stretch after only one minute spent at the petrol station.

“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 Vishnu-Baba Sundaresan, an assistant professor of mechanical and aerospace engineering at Ohio State and leader of the study.

Batteries — such as lithium-ion batteries — with membrane separators that conduct charge are nothing new. However, the problem with today’s batteries lies in self-discharge. The phenomenon also known as thermal runaway converts battery’s internal energy into heat. In worst case scenario it causes batteries to even overheat and catch fire.

Researchers demonstrated that their membrane can shut down charge transport and prevent thermal runaway at its onset. The design for the membrane was inspired by cell membranes found in human body, which open and close to let cells perform biological functions. Openings in the cell wall respond to the electrical charge of molecules to expand or contract, and it’s this principle that was applied to the smart membrane. In laboratory tests, the engineers found they could control the density of openings in the membrane. As a result, the batteries fully functioned, but reduced charge loss to zero when the batteries were not in use.

Even though the membrane does work with conventional batteries and might be the only way to push the performance limit at the moment, the team primarily focuses to use it as a basis for a new type of fast-charging batteries. The concept of plugging in a vehicle for long hours just to drive for a few hundred miles might not be generally viewed as appealing. But the development of batteries could prove to be a significant addition to the overnight charging once the drivers find themselves in an urgent need to refill the “juice” on the road.

Michal Madaras

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