The latest auto salons have a message: the future belongs to electric power. Car manufacturers are exploring two nonfossil-fuel technologies, both of which are, in theory, able to replace petrol and diesel – namely electric cars and hydrogen-powered cars.

To keep research on track, the European Investment Bank provides low-cost loans for energy efficiency in transport and the results of research and development are starting to be seen.
A new type of redox flow battery presents a huge advantage for electric cars. If the recharge- able batteries are low, the discharged electrolyte fluid can simply be exchanged at the petrol station for recharged fluid – as easy as refilling the petrol tank.

Electric mobility is becoming increasingly important. The German government’s ambitious plan envisages one-million electric cars being sold in Germany by 2020. Until then, however, researchers still have to overcome some hurdles, such as the question of energy storage.

Lithium-ion batteries offer a possible solution, but it takes hours to charge them.

Researchers from the Fraunhofer Institute for Chemical Technology, in Pfinztal, near Karlsruhe, see an alternative in redox flow batteries. “These batteries are based on fluid electrolytes. They can, therefore, be recharged at the petrol station in a few minutes. The discharged electrolyte is simply pumped out and replaced with recharged fluid,” says the institute’s Jens Noack. “The pumped-off electrolyte can be recharged at the petrol station, for example, using a wind turbine or a solar plant.”

The principle of redox flow batteries is not 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.

Until now, however, redox flow batteries have had the disadvantage of storing significantly less energy than lithium-ion batteries. The vehicles would only be able to cover about a quarter of the normal distance – around 25 km – which means the driver would have to recharge the batteries four times as often.

“We can now increase the mileage four- or fivefold, to about that of lithium-ion batteries,” Noack enthuses.

The researchers have already produced the prototype of a cell. Now they must assemble several cells into a battery and optimise them. This further development is being carried out with colleagues from the University of Applied Sciences, Ostphalia, in Wolfenbüttel and Braunschweig.

They are testing electric drives and energy storage units on model vehicles that are only a tenth of the size of normal vehicles. The research team has already built a traditional redox flow battery into a model vehicle and this vehicle, on a scale of 1 to 5, could be seen in action on a test rig at the eCarTech, in Munich, in mid-October.