Long-lasting flow battery could run for more than a decade with minimum upkeep

Long-lasting flow battery could run for more than a decade with minimum upkeep
Credit: Harvard John A. Paulson School of Engineering and Applied Sciences

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new flow battery that stores energy in organic molecules dissolved in neutral pH water. This new chemistry allows for a non-toxic, non-corrosive battery with an exceptionally long lifetime and offers the potential to significantly decrease the costs of production.

The research, published in ACS Energy Letters, was led by Michael Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies and Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science.

Flow batteries store energy in liquid solutions in external tanks—the bigger the tanks, the more energy they store. Flow batteries are a promising storage solution for renewable, intermittent energy like wind and solar but today's flow batteries often suffer degraded energy storage capacity after many charge-discharge cycles, requiring periodic maintenance of the electrolyte to restore the capacity.

By modifying the structures of molecules used in the positive and negative electrolyte solutions, and making them water soluble, the Harvard team was able to engineer a battery that loses only one percent of its capacity per 1000 cycles.

"Lithium ion batteries don't even survive 1000 complete charge/discharge cycles," said Aziz.

"Because we were able to dissolve the electrolytes in neutral water, this is a long-lasting battery that you could put in your basement," said Gordon. "If it spilled on the floor, it wouldn't eat the concrete and since the medium is noncorrosive, you can use cheaper materials to build the components of the batteries, like the tanks and pumps."

This reduction of cost is important. The Department of Energy (DOE) has set a goal of building a battery that can store energy for less than $100 per kilowatt-hour, which would make stored wind and solar energy competitive to produced from traditional power plants.

"If you can get anywhere near this cost target then you change the world," said Aziz. "It becomes cost effective to put batteries in so many places. This research puts us one step closer to reaching that target."

"This work on aqueous soluble organic electrolytes is of high significance in pointing the way towards future batteries with vastly improved cycle life and considerably lower cost," said Imre Gyuk, Director of Energy Storage Research at the Office of Electricity of the DOE. "I expect that efficient, long duration flow batteries will become standard as part of the infrastructure of the electric grid."

The key to designing the battery was to first figure out why previous molecules were degrading so quickly in neutral solutions, said Eugene Beh, a postdoctoral fellow and first author of the paper. By first identifying how the molecule viologen in the negative electrolyte was decomposing, Beh was able to modify its molecular structure to make it more resilient.

Next, the team turned to ferrocene, a molecule well known for its electrochemical properties, for the positive electrolyte.

"Ferrocene is great for storing charge but is completely insoluble in water," said Beh. "It has been used in other batteries with organic solvents, which are flammable and expensive."

But by functionalizing ferrocene molecules in the same way as with the viologen, the team was able to turn an insoluble molecule into a highly soluble one that could also be cycled stably.

"Aqueous soluble ferrocenes represent a whole new class of molecules for flow batteries," said Aziz.

The neutral pH should be especially helpful in lowering the cost of the ion-selective membrane that separates the two sides of the battery. Most flow batteries today use expensive polymers that can withstand the aggressive chemistry inside the battery. They can account for up to one third of the total cost of the device. With essentially salt water on both sides of the membrane, expensive polymers can be replaced by cheap hydrocarbons.

This research was coauthored by Diana De Porcellinis, Rebecca Gracia, and Kay Xia. It was supported by the Office of Electricity Delivery and Energy Reliability of the DOE and by the DOE's Advanced Research Projects Agency-Energy.

With assistance from Harvard's Office of Technology Development (OTD), the researchers are working with several companies to scale up the technology for industrial applications and to optimize the interactions between the membrane and the electrolyte. Harvard OTD has filed a portfolio of pending patents on innovations in flow battery technology.

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More information: Eugene S. Beh et al. A Neutral pH Aqueous Organic/Organometallic Redox Flow Battery with Extremely High Capacity Retention, ACS Energy Letters (2017). DOI: 10.1021/acsenergylett.7b00019
Citation: Long-lasting flow battery could run for more than a decade with minimum upkeep (2017, February 9) retrieved 15 October 2019 from https://techxplore.com/news/2017-02-long-lasting-battery-decade-minimum-upkeep.html
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Feb 10, 2017
Nice. Much preferred battery solution compared to the one about carbon dioxide...

Feb 10, 2017
$100 per kWh but for how many cycles in total?

The paper says the capacity retention is up to 99.967%/day. That is, for 10 years of operation it should lose 70% of capacity.

But if 30% is the maximum daily demand on the battery, so that we can continue to use it for 10 years - in other words we had to initially overbuild the battery by that much - it means we are actually putting only 3650 x 0.3 = 1095 full cycles through the battery before its considered dead and needs to be replaced.

So it's not quite cheap yet. $100/kWh for 1095 cycles = 9.1 cents per kWh cost of storage, and that is in general twice the cost of making the electricity in the first place.

The calendar life of the battery should be 20-25 years before it starts to make sense to use it for grid storage. The cycle life is not so important because the batteries need to be oversized by quite a bit, so that they can store energy one month and release it the next month.

Feb 10, 2017
I remember I checked it out some time ago; even in a sunny state like Arizona, you get 50% less solar energy in the winter, but the energy demand through the winter months drops only by 30%, so you got a 20% gap between supply and demand for several months. Let's say you're running a 20% deficit for 4 months a year - that's in the ballpark of 5% of your total yearly energy demand.

So if you're going to build a lot of batteries to deal with that size of a gap between seasonal production and demand, in the case of Arizona that would be 215,920 MWh * 0.05 = 10 million kWh of energy (source: EIA)

So you take $100/kWh for a start, adjust up by the overprovision margin to account for aging over 10 years and it makes $330/kWh. For the amount of batteries that's 3.3 billion dollars worth of batteries, or 330 million dollars a year. Divide by 10 million kWh per year, and your cost of storage is a whopping $33 per kWh.

It would be cheaper to hire people to pedal treadmills for power.

Feb 10, 2017
Imagine if every house had a backup battery that could keep the lights on during a power outage. That would be great!

Ryan Karl Alldrin

Feb 17, 2017
"Imagine if every house had a backup battery that could keep the lights on during a power outage. That would be great!"

That's assuming power outages are frequent. I haven't had one longer than 30 minutes in a decade.

if power outages were frequent enough to warrant the purchase of a battery system, you'd be living in a 3rd world country. You don't want to design your grid around the idea that you're going to have power cuts on a daily basis because it's a real killer to all the industry that really depends on reliable power.

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