EVs to get improved mileage from redox flow batteries

German researchers say a new type of electric vehicle battery that runs on electrolyte fluid can be recharged as easily as refilling a petrol tank. When the redox flow rechargeable batteries are low, the discharged electrolyte fluid can simply be exchanged at the gas station for recharged fluid.

To fulfill the German Government’s ambitious plan of one million electric cars being sold in Germany by the year 2020, many motorists will still need convincing that electric cars won’t leave them “powerless” on the side of the road. The question of adequate on-board energy storage still requires some answers and, while lithium-ion batteries offer a possible solution, it takes hours to charge them – time that an automobile driver doesn’t have when on the road.

Researchers from the Fraunhofer Institute for Chemical Technology ICT in Germany have found an alternative in redox flow batteries. “These batteries are based on fluid electrolytes. They can therefore be recharged at the gas station in a few minutes – the discharged electrolyte is simply pumped out and replaced with recharged fluid,” says engineer Jens Noack from ICT. “The pumped-off electrolyte can be recharged at the gas station, for example, using a wind turbine or solar plant.”

The principle behind redox flow batteries is not something new – two fluid electrolytes containing metal ions flow through porous graphite felt electrodes, separated by a membrane that allows protons to pass through it. During this exchange of charge a current flows over the electrodes, which can be used by a battery-powered device.

While that may sound encouraging, until now redox flow batteries have had the disadvantage of storing much less energy than lithium-ion batteries – around a miserable 25km (15.5 miles) – which means the driver would have to recharge the batteries four times as often.

“We can now increase the mileage four or fivefold, to approximately that of lithium-ion batteries,” Noack says, since the researchers have already produced a prototype of a cell. Their job now is to assemble several cells into a battery and optimize them. This further development is being carried out with colleagues from the University of Applied Sciences, Ostfalia, in Wolfenbüttel and Braunschweig who are testing electric drives and energy storage units on model vehicles that are only a tenth of the size of normal vehicles.

So far, the research team has already built a traditional redox flow battery into a model vehicle. A 1:5 scale vehicle can be seen in action on a test rig set up at the eCarTech in Munich this October. In the coming year the researchers also want to integrate the new battery, with four times greater mileage, into a model vehicle.