Redox flow batteries promise near-instant recharging times
Redox flow battery electric test model - Click above to enlarge
Researchers from the Fraunhofer Institute for Chemical Technology ICT in Pfinztal, Germany, are currently working on improving a new type of battery system that promises recharge times on par with the refilling of a conventional fuel tank using something called redox flow batteries. How do they work? We'll let project engineer Jens Noack explain:
Intriguing, no? The idea of offloading used-up electrolyte and getting a refill of freshly-charged fluids would likely appeal to the public, which is quite familiar with the process of refilling an automobile for more range. Researchers have just recently figured out how to extend the range of these redox flow batteries to that of comparable lithium ion units.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.
Currently, the team from Germany has created a working 1:10 scale model using older redox flow batteries, and future plans call for the assembly of larger-scale battery packs using its refined technology.
[Source: Fraunhofer Institute via The Kneeslider]
Reader Comments (Page 1 of 2)
Jonathan King 1:22PM (10/16/2009)
Lets hope they are cost effective, not made of rare materials, the electrolyte is not harmful to the environment to produce or use, high energy density by volume and weight, high enough power density by volume and weight, and long life cyle. Also hope they can still be charge conventionally to accept energy from regen braking (though the vehicle could also have some conventional batteries or super caps for that.
Lots of questions. Would like to learn more about them. Hope they are on to something here.
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Matt234 1:59PM (10/16/2009)
Looks like it might be harmless materials (from the PDF): "two fluid electrolytes containing metal ions flow through porous graphite felt electrodes, separated by a membrane which allows protons to pass through it"
I wonder what the business model will look like, and how they would deal with partially used up electrolyte (a refund?).
wincros 1:24PM (10/16/2009)
That would, indeed, be a game changer.
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no_one 4:05AM (10/17/2009)
If you look at the Fraunhofer's institute other inventions -- like the MP3, that changed the music industry forever, I would not underestimate these guys.
srue 1:25PM (10/16/2009)
Isn't this essentially how hydrogen fuel cells work?
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LaserBeams 1:35PM (10/16/2009)
No, it's got more in common with your standard cathode/electrolyte/anode battery. With a flow battery, the cathode and anode are smaller (their size determines the current, IIRC), and the electrolyte, which is what actually stores the energy in any battery (by a change in its chemical makeup) is much greater in volume, and circulated between the electrodes. Hence the name "flow" battery.
paulwesterberg 1:41PM (10/16/2009)
Depends on what the battery efficiency is - how much energy is lost charging the electrolyte and how much energy is lost releasing the energy.
Modern batteries are 90-95% efficient for the charge-release cycle. You lose very little energy as waste heat.
Electrolysis to make hydrogen is usually between 50% and 70% efficient(theoretical maximum of 80% to 94%). Hydrogen fuel cells are 50-70% efficient at converting the gas to electricity.
So the overall efficiency of hydrogen from electrolysis is only 25-50%.
It is more efficient to use hydrogen made from reformulated natural gas, but still not as efficient as conventional batteries and then you are still relying on fossil fuels for and the process still releases global warming gases into the atmosphere.
KK 1:49PM (10/16/2009)
Also, hydrogen is not easy to store and transport. It's a gas, and it remains a gas even at high pressure. It also has very low density, which means the tank must be large (physically). An electrolyte solution is easier to handle.
wincros 5:06PM (10/16/2009)
No. The electrolyte would be recharged and reused. Hydrogen is a gaseous high pressure fuel that would need a distribution system just like gasoline or diesel. The cost for on site electrolysis of hydrogen would be stunning.Once a recharge station was stocked with enough electrolyte for its anticipated business, that would be it. Pumping a small amount of electrolyte out and in would be cheap.
Mark Kiernan 1:28PM (10/16/2009)
So it is some sort of liquid chemical battery where you just recharge the liquid. I would be interesting to see how much liquid you need, and does the liquid degrade?
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laserbeams 6:31AM (10/20/2009)
I was looking at this a while back. Zinc-bromine redox flow batteries look like a good solution too, aside from the fact that a system with comparable range to a lithium ion pack would weigh about as much as a lead battery pack. If they found a way to reduce the extra weight that normally has to be carried around in liquid form (most of which is water!), this could be a very good solution. Highly stable too, not terribly toxic, and almost completely recycleable. Also it doesn't self-discharge, has easily replaceable parts, and because it doesn't use an eroding cathode/anode pair, can sustain nearly infinite recharges. Freezing might be a problem... I'd like to see more of this.
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Mark Kiernan 1:44PM (10/16/2009)
In regard to heat, I guess they could carry a warning about restrictions. Or perhaps they could have some insulation that would protect the fluid.
Boyprodigy1 5:56PM (10/16/2009)
In regards to heat they could just have a battery management system like the Tesla roadster has. It keeps optimal temperature on the battery pack from what i understand.
Chris M 2:45AM (10/17/2009)
The salts used as electrolytes in these batteries also act as antifreeze.
Lead acid batteries rely on the sulfuric acid to act as antifreeze, but discharging a lead acid battery causes the sulfuric acid to react with the lead/lead oxide plates, removing sulfuric acid from the electrolyte, so a discharged lead acid battery is vulnerable to freeze damage. Flow batteries, on the other hand, change the ionic state of the electrolyte salts but does not remove them, so freezing shouldn't be a problem.
LaserBeams 1:37PM (10/16/2009)
Here's a good description of one possible chemistry:
http://en.wikipedia.org/wiki/Zinc-bromine_flow_battery
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Chris M 3:00AM (10/17/2009)
Another is the Vanadium Redox battery:
http://en.wikipedia.org/wiki/Vanadium_redox_battery
Energy density is even lower than the Zinc Bromide flow battery.
The advantages of a flow battery is the capacity can be increased simply by using more electrolyte in larger tanks (one for positive, the other for negative) or adding additional tanks. There is virtually no self-discharge, and as the article mentioned, very fast recharge by draining the spent electrolyte and refilling with "charged" electrolyte is possible. It may become an excellent choice for very large stationary power storage for utilities and emergency backup power.
Downsides are low energy density, not much better than lead acid, and low power. Unless the energy density can be dramatically increased, it will remain insufficient for automotive use
wardialer 1:59PM (10/16/2009)
stan ovshinsky came up w/ this almost a decade ago using NiMH (ovonics-->GM-->Texaco-->Chevron-->Cobasys-->samsung bosch limotive [patent licensing still controlled by chevron until 2014]) so its nothing revolutionary besides not violating other patents since Li-ion is so widely used in many different applications. so it could actually be implemented w/o the red tape... but again... nothing new.
Matt Lenart
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Chris M 3:07AM (10/17/2009)
Quite different than the NiMH battery developed by Ovshinsky, he used a standard battery design but with improved electrodes for higher power and higher energy density. This flow battery, on the other hand, stores the energy in the liquid electrolytes (positive and negative) and not in the solid electrodes like regular batteries.
wardialer 3:36PM (10/17/2009)
no.
he ALSO developed a NiMH that could have the depleted electrolyte replaced w/ a charged, energy-rich electrolyte similar to adding gas to your car. this was not of course brought to market as the whole patent control involving texaco/chevron/gm/cobasys cast a dark shadow on that discovery around the same time.
Joeviocoe 5:37AM (10/18/2009)
Do you have a link or a source for that.. because I cannot find anything about it.