Scientists are looking into sustainably powering entire cities, and with liquid-based redox
flow batteries, we’re one step closer to making that happen.
If we’re ever going to replace fossil fuels with renewable sources like solar and wind
power, then we’re going to need a way to store energy for when it’s dark and not
windy, or just for when the demand for power exceeds the output.
If you’re familiar with any sort of electronic device, then there is one pretty obvious answer:
batteries.
Charge them up when demand is low but output it high, then let the juice loose when that
flips.
But there are different battery types, and all have their own strengths and weaknesses.
This best battery for a job like this might be one that uses flowing liquids, called a
redox flow battery.
A redox flow battery is sort of a hybrid between a battery and a fuel cell.
It consists of two tanks of an electrolyte liquid, one positive and one negative.
In between the tanks is a cell stack, where the positive and negative solutions are pumped
to but kept separated by a membrane.
Inside the cell stack the ions in the negatively charged solution give up an electron, a process
called oxidation.
Those electrons are picked up by an electrode in the cell stack, and they travel through
whatever needs to be powered before arriving at another electrode on the other side of
the membrane.
There the ions in the positive solution pick up the electrons, a process called reduction.
This frees up positively charged hydrogen ions, which travel back across the membrane
and maintain the charge balance.
When charging up, the entire process happens in reverse.
But hold up, why go through all this when we have already lithium-ion batteries?
You know, the ones in cell phones, laptops, electric cars, and oh yeah, household battery
packs designed for exactly this purpose?
The problem is that while a big ol’ lithium-ion battery might be suitable for your house,
they don’t scale up well for something as big as an entire city.
Lithium isn’t an abundant material either, so it’s not sustainable to use it for these
huge applications.
And anyone who’s had the same phone for more that a couple years can tell you that
lithium-ion batteries degrade and lose their ability to hold a charge over time.
On the other hand, flow cell batteries have qualities that make them perfect for large-scale
power storage, like scalability.
Need to store more energy?
Get bigger tanks that hold more solution, that’s it.
Worried about degradation?
Some electrolyte solutions used in redox flow batteries can last for about 5,000 charge
cycles, five times longer than lithium-ion batteries.
What about price and sustainability?
Ah, about that…
The most popular metal used in redox flow batteries is vanadium because it charges and
discharges reliably for thousands of cycles.
But the cost of vanadium is rising, and if vanadium redox batteries go mainstream that
price could skyrocket.
Researchers have tried to replace vanadium with organic molecules, but those tend to
degrade and need replacement every few months, or the solution they’re in has to be very
acidic or basic, which can damage pumps or be hazardous in case of a leak.
But scientists are undeterred, and recently researchers from USC announced organic water-based
redox batteries that can last for about 15 years at one tenth the cost of a lithium-ion
battery.
So far the battery they’ve made is enough for the basic electricity demands of a single
house, but their goal is to one day have electricity on tap for entire mega-cities.
The technology is promising enough that China is building a massive vanadium redox flow
battery with a storage capacity of 800 Mega Watt hours.
That’s enough for thousands of homes.
The battery is scheduled to come online by 2020.
China has plenty of vanadium reserves so they’re not too concerned about it’s cost, but if
organic flow cell batteries become comparable, those might not be too far behind.
One day in the near future, they might play a vital role in green energy grids around
the world.
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And then maybe watch this cool video about how we can make batteries..out of DIAMONDS.
And fun fact: While Vanadium may not be the future of redox flow batteries, it is super
cool.
When vanadium gains electrons it changes color, going from yellow, to blue, to green, and
finally purple.
thanks for watching and we’ll see you next time on Seeker.