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Published on April 28th, 2015 | by Tina Casey

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Huge Payoff For EV Battery Range — Potentially 3X More Capacity — If Quirky Iron Fluoride Can Be Tamed

April 28th, 2015 by  


The Iron Age has come and gone, but researchers are drooling over the prospect of a super-efficient lithium-ion battery based on iron fluoride, a greenish iron compound used in manufacturing metals. However, there is just one pesky little problem standing between iron fluoride and the leaner, lighter, cheaper EV battery of the future: lithium-ion batteries doped with iron fluoride are great at storing energy, but not so great when it comes to charging and discharging.

Not to worry. A team of researchers from the University of Wisconsin-Madison decided to tackle the problem with the help of some fancy equipment over at the Energy Department’s Brookhaven National Laboratory, so after us taxpayers get done with our group hug, let’s see what they’ve discovered.

EV battery range iron fluoride

Super-Efficient EV Batteries, Now With Iron!

We were just talking about the prospects of graphene and perovskite for improving EV battery range, and iron fluoride is starting to generate similar excitement.

According to the UW-Madison team, when used in a cathode, its potential for lithium storage capacity is “four or five times higher” than cathodes without iron fluoride (the cathode is the part of the battery that collects a charge).

The team calculates that iron fluoride could potentially triple the amount of energy stored in an otherwise conventional lithium-ion battery.

However, that potential has remained tantalizingly out of reach, partly because the chemical changes that iron fluoride undergoes in a battery are poorly understood.



 

According to the team, in a paper just published in Nature.com under the title “Visualization of electrochemically driven solid-state phase transformations using operando hard X-ray spectro-imaging,” it’s not for lack of trying.

Researchers have used a variety of high-tech analytical tools to try to figure out why iron-fluoride batteries don’t charge and discharge efficiently, and the UW-Madison team found shortcomings with all of them.

That’s because analyzing a battery while it’s in operation (that’s the “operando” part of the paper’s title) is a very tricky business. Part of the problem is that other battery components interfere with the imaging process.

In addition, conventional imaging technology provides images that don’t dig down to the nanoscale, and some forms of analysis require “drastically different” special conditions that don’t apply to real-life battery operation.

When In Doubt, Call Brookhaven

That’s where Brookhaven — and we taxpayers — comes in.

The UW-Wisconsin team took a visit to the lab and availed themselves of several different pieces of equipment to assemble large images that resolve down to the nanoscale. The image above is a chemical phase map that shows how the electrochemical discharge proceeds (left to right) from 0% discharge, to 50%, to 95%.

In contrast to other attempts, the team was able to conduct experiments under realistic conditions.

Here’s a rundown from the paper in Nature.com (acronyms deleted for readability):

Taking advantage of the strong and deeply penetrating hard X-rays generated by synchrotron radiation and the chemical and elemental sensitivity with a full-field imaging capability provided by the transmission X-ray microscopy coupled with X-ray absorption near-edge structure spectroscopy, progression of a electrochemical reaction in a realistic battery electrode can be visualized in a large (tens of micrometres) field-of-view with nanoscale spatial resolution.

I know, right?

Edging Closer To Longer EV Battery Range

As described in UW-Madison’s press materials, at least one key finding emerged from the new imaging process, which is that iron fluoride is more effective when it is fabricated with a porous microstructure.

Here’s a bit more detail from Nature.com:

In two specially designed samples with distinctive microstructure and porosity, we observe homogeneous phase transformations during both discharge and charge, faster and more complete Li-storage occurring in porous polycrystalline iron fluoride, and further, incomplete charge reaction following a pathway different from conventional belief.

They’re not giving much else away except to say that the study also “yielded some preliminary insights” into why iron fluoride batteries don’t discharge as much energy as they collect.

The imaging studies were conducted on coin cell batteries, aka button cells. These aren’t exactly big enough to run an EV (a wristwatch would be more like it), but the team is already looking ahead to the day when all of iron fluoride’s problems will be solved, and the technology can be applied to energy storage for microgrids as well as long-range EV batteries.

As you can tell, we’re not exactly holding our breath for the iron fluoride battery of the sparkling green future. Before you cue the Debbie Downer music, though, it’s worth noting that there is a nifty little experiment going on at MIT that involves using a common virus to serve as a template for developing iron-fluoride cathodes.

We first caught wind of that development back in 2010, and last year a graduate student at MIT had applied the virus technique to other materials, namely graphene and manganese oxide.

If you’ve got a line on any other new developments, drop us a note in the comment thread. Thanks to CleanTechnica writer Sandy Dechert for passing this one along.

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Image Credit: Linsen Li 
 
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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



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