Researchers from the Fraunhofer Institute for Chemical Technology (ICT) in Pfinztal near Karlsruhe envision a new type of redox flow battery that presents an innovative improvement and perhaps a huge advantage for electric vehicles. If the redox rechargeable batteries are low, the discharged electrolyte fluid can simply be exchanged at the “filling station” for recharged fluid – as easy as refilling the fuel tank.

Electric vehicles for mobility are becoming increasingly important and will accelerate as the costs of vehicles drop and refilling with electron energy exploits its very low cost advantage.  In Germany alone the government plans ambitiously for one million electric cars being sold in Germany by the year 2020.  But the recharge times, hours- even with the best lithium ion technology known to be coming puts a giant barrier before consumer’s acceptance.

Fraunhofer Institute researchers see an alternative in redox flow batteries. Jens Noack, an engineer from the ICT 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.”   Or any other grid source for that matter, and with sufficient inventory the electrolyte recharge can be done at off peak times as well.

The principle of redox flow batteries is not new.  A redox system uses two fluid electrolytes containing metal ions that 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 the battery-powered device.

Currently redox flow batteries have had a serious disadvantage of storing significantly less energy than lithium ion batteries. The Institute’s test vehicles would only be able to cover about a quarter of the normal distance – around 25 kilometers – 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.  That’s a very hopeful signal in a new charging system.

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

Redox Battery Test Vehicle. Click image for more info.

Redox Battery Test Vehicle. Click image for more info.

The group is 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. A vehicle on a scale of 1:5 could have be seen in action on a test rig set up at the eCarTech in Munich from 13 to 15 October. In the coming year the researchers also want to integrate the new battery, with four times greater mileage, into a model vehicle.

The concept of exchanging just the electrolyte fluid is a certain solution if the density can get high enough.  The plan to offer an electrolyte exchange offers stunning simplification and serious opportunity for displacing liquid hydrocarbon fuels.  Moreover, the system could be applied at the extreme – remote areas where wind, solar power or geothermal could be the energy source with only a need for adequate electrolyte inventory to keep things going.  Just the thing for way, way out there.

It’s a marvelous idea, one that will be closely watched.  Keep in mind the redox electrolyte research is just now getting under way and the claim is to meet the lithium ion standards very soon.  There is even room for opportunities in research at the anode and cathode. What remains of great interest is the energy per weight and volume numbers that can really enthuse or befuddle the future.

This is strikingly innovative creativity.  If the weight or density is high and the volume stays low this might be the practical breakthrough so many are seeking.  Let the competition begin, this is a very good idea indeed.


11 Comments so far

  1. jp straley on October 21, 2009 5:24 AM

    Vanadium liquid electrolyte batteries are well-developed, maybe don’t quite have the energy density for automotive use. Here is a good review article on vanadium batteries:

  2. Matt on October 21, 2009 6:56 AM

    This seems way to complex a solution. While technically feasible, it is certainly more expensive to deliver electrolyte than electrons.

  3. Matt on October 21, 2009 6:57 AM

    This seems way too complex a solution. While technically feasible, it is certainly more expensive to deliver electrolyte than electrons.

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