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Redox Flow Batteries: a Quickly-Charging Alternative to Li-Ion?


redox-flow-battery-vehicleGermany has an ambitious plan of putting one million electric cars on their roads by 2020, so their scientists are just as interested in discovering better batteries for them. For that, researchers from the Fraunhofer Institute for Chemical Technology (ICT) in Pfintzal, near Karlsruhe, propose an alternative to the lazily-charging Lithium-Ions: the redox flow batteries.

The working principle of redox flow batteries is pretty simple at a first glance: two liquid electrolytes containing metal ions flow through porous graphite felt electrodes. The two electrodes are separated by a membrane that lets protons pass through it. Through this proton exchange, a current flows between the electrodes, creating useful voltage.

The fact that makes redox flow batteries interesting is that they can be recharged by interchanging the liquid electrolyte inside them with a new, ionized one, at a recharging station, for example.

Jens Noack, an engineer working on the redox flow batteries, says: “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. The pumped-off electrolyte can be recharged at the gas station, for example, using a wind turbine or solar plant.”

Redox flow batteries are not new, however, in their original version, they have the big minus of storing little electricity, compared to Li-Ion. The vehicles would only run 25km until they would have to be recharged if it were to use them in their current version. The news is that the Fraunhofer scientists just improved these batteries: “We can now increase the mileage four or fivefold, to approximately that of lithium-ion batteries,” says Jens Noack.

The scientists have already made a prototype of their new redox flow battery, and only have to assemble several cells, and then optimize them. This optimization is made with the help of their colleagues from the University of Applied Sciences, Ostphalia, in Wolfenbi¼ttel and Braunschweig, where the researchers are testing model vehicles with the new improved batteries. You can see one of their scaled vehicles (1:5) at the eCarTech Expo in Munich from 13 to 15 October, so, if you have your road through there, just hurry up!

125km is still insufficient to say we have a reliable battery and car, because we would need all the gas stations modified to have the charged electrolyte around the clock. Considering that there are projects that brag with charging times of just a few minutes, and much higher mileage per charge, the redox flow batteries have, in my opinion, a long way to go. But who knows… they’re worth a serious look, anyway.

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