Improved redox flow batteries for electric cars

Improved redox flow batteries for electric cars
This is the test vehicle into which researchers are integrating a redox flow battery. Credit: Hochschule für Angewandte Wissenschaften Ostfalia

A new type of redox flow battery presents a huge advantage for electric cars. If the rechargeable batteries are low, the discharged electrolyte fluid can simply be exchanged at the gas 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 being sold in Germany by the year 2020. Until then, however, researchers still have to overcome some hurdles, such as the question of . Lithium-ion batteries offer a possible solution, but 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 Pfinztal near Karlsruhe see 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 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 of redox flow batteries is not new - two fluid electrolytes containing flow through porous graphite felt electrodes, separated by a membrane which 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 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 enthuses. The researchers have already produced the prototype of a cell. Now they must 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. 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.

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

Source: Fraunhofer-Gesellschaft (news : web)

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Oct 13, 2009
I wonder how toxic the stuff is because it would sure leak after an accident.

Oct 14, 2009
If it's as (or less) toxic than gasoline then there's no real disadvantage here. Batteries are subcompartmetalized into cells. In an accident you'd probably not break all the cells (as opposed to a gasoline tank which is all 'one cell' and therefore has much more of a problem when punctured).

Another advantage is that we wouldn't need (as many) tanker trucks on the roads since the eleoctrolyte can be recharged at the gas station. You'd only need to replace spillage/evaporation and degradation losses.

Given that recharge times and impossibilty to provide guaranteed access to recharge stations over night in urban areas are major Achille's heels for batteries this sounds like a good development.

Oct 14, 2009
Oh sure, I can see right now how it would work: A guy pulls into his local redox fluid filling station, opens the tank, sticks in the nozzle and starts fillin' 'er up. Then he goes to light a cigarette as people in a nearby coffee shop are yelling for him to stop. He flicks his lit match just as the nozzle pops out of the tank and flops on the ground, spewing redox fluid all over. Boom! And then he is attacked by a flock of enraged seagulls, which peck out his eyes.

Why don't you "scientists" learn to anticipate the most obvious flaws in your clever schemes?

Worried in Wisconsin

Oct 14, 2009
I'm surprised this isn't getting more attention. Simply put, it's huge.

The vast majority of automobile usage every day is local. Therefore, the vast majority of gasoline consumption (and the resulting pollution) is done by the millions of local trips performed every day across the world.

Why, then, don't people buy electric cars? Many reasons, but the most important are the miles between charges and the time of recharging. What will you do when you are 10 miles from home and the battery is discharged? Plug it in and roll-out your sleeping bag? Lift out the heavy battery with a fork lift and put in a charged one?

With this increased capacity, the Redox Flow Battery can now travel 75 or more miles before needing a recharge, like lithium batteries. But instead of plugging it in for hours, you simply pull-up to an "electrolyte" station and fill the tank like you would gasoline (exchange, to be exact). The spent electrolyte is completely rechargable. No waste. No pollution. Quick.

Oct 14, 2009
Continuation from above....

The electrolyte is typically vanadium in sulfuric acid, unless this new breakthrough uses something different I'm not aware of. Vanadium, as I understand it, has low toxicity unless in powder microparticulate form. Sulfuric acid is, of course, corrosive. But I'm sure the spillage could be controlled in crashes by good tank design. I would guess it could be limited to about the amount currently held in lead acid batteries today. Either way, it's less dangerous than a tank of gasoline in a collision.

With this technology, you are basically changing the fuel market from expendable, polluting hydrocarbons to a medium (electrolyte) that holds extra protons. You are in essence poring extra protons into your tank when you refill.

To recharge the electrolyte, the gas station can add protons through solar or wind, or there could be solar "refineries" set up to produce mass quantities of charged electrolyte that gets disributed as gasoline is today.

Oct 14, 2009
One more continuation...

The Redox Flow Battery can be completely discharged with no harmful effects. The actual operation of the battery leaves no residue on the electrodes. This translates to a very long life battery. Unlike other batteries that wear out and must be replaced (at a high cost to the consumer), there is no reason why these batteries couldn't last as long as the car itself. And because of the design, flushing the battery with solvent and draining can clean the internal parts, if needed.

OK, sorry for taking so much space. I'm finally done.

Oct 16, 2009
Worried in Wisconsin has never been to a regular gas station.

Oct 17, 2009
Perfect! This is even more useful for trucks and buses. I can envision in some years an electrical airplane for local routes first and intercontinental one night.

Oct 18, 2009
This is great. However, they are saying they can currently travel about 25 KILOMETERS not miles. So even with increased capacity, 75 kilometers is still only about 40 or so miles. Which, IMHO, is still good!
That would mean I'd have to refill/recharge mine only once every two days, and that's assuming I can't just plug it in at the house.

Oct 18, 2009
I think this is not as easy as it sounds... the big problems that flow battery technology have faced have traditionally been storage of highly volatile electrolytic solutions. They eat through stuff over time and especially when you have big vats of them. So, storing and transporting this stuff means we need a wave of sharp design and clever innovations in materials science. By that logic though, we could just as easily create 50 pound cars and solve the problem anyway.

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