The US Army is behind a new research project at the Department of Energy’s Brookhaven National Laboratory that aims to send lithium-ion batteries spinning into a new era of high capacity energy storage. Among other things, that means more wind and solar grid integration, and that’s kind of funny considering that right now DOE is making yet another stab at finding a way to save old coal and nuclear power plants from the dust bin of history. Good luck with that!
Energy storage really is the key to renewable energy grid integration, so let’s take a look at the new Brookhaven research and see what’s up.
High Capacity Energy Storage, With Iron
Earlier this week, CleanTechnica made the case that we are entering the Age of Nickel, but perhaps we spoke too soon. The new Brookhaven lithium-ion battery owes its superior performance thanks to the Age of Iron, or rather iron trifluoride.
Iron trifluoride doesn’t usually pop up when the topic turns to energy storage in general and increasing the capacity of lithium-ion batteries in particular, and for good reason. Here’s the lab with an explainer:
…the compound has not historically worked well in lithium-ion batteries due to three complications with its conversion reaction: poor energy efficiency (hysteresis), a slow reaction rate, and side reactions that can cause poor cycling life.
In other words, the battery is not particularly rechargeable. That sounds like a hopeless case, but on the other hand iron trifluoride is relatively inexpensive and it’s non-toxic, too. Brookhaven chemist and lead researcher Enyuan Hu offers another good reason to pursue the compound for more and better energy storage:
The materials normally used in lithium-ion batteries are based on intercalation chemistry. This type of chemical reaction is very efficient; however, it only transfers a single electron, so the cathode capacity is limited. Some compounds like FeF3 are capable of transferring multiple electrons through a more complex reaction mechanism, called a conversion reaction.
Here’s a more technical breakdown from the study:
…iron trifluoride (FeF3), cheap and environmentally friendly, appears to be unique as a cathode candidate with a total theoretical energy density of 1922 Wh kg−1 and a relatively high working potential due to its ionic nature.
Got all that? Intercalation chemistry refers to the insertion of some things between layers of other things. When that process is reversible, there’s your foundation for a rechargeable lithium-ion battery.
For more details check out the new lithium-ion battery study in the journal Nature, under the title, “High energy-density and reversibility of iron fluoride cathode enabled via an intercalation-extrusion reaction.“
So, How Did They Do It?
Lithium-ion researchers like to focus on applying new materials to the cathode because it is the “bottleneck” for improving energy storage capacity (for those of you new to the subject, a cathode is the part of a battery that collects a positive charge).
Scientists from the University of Maryland provided a modified version of iron trifluoride for the new cathode, by doping it with cobalt and oxygen.
In addition to computer modeling, the research team analyzed the reaction using fancy equipment at Brookhaven’s Center for Functional Nanomaterials, where they were able to identify the mechanism behind part of the sample, and used the lab’s National Synchrotron Light Source II for a more holistic view of the battery.
Combined, the three investigative pathways yielded this result:
This approach revealed that chemical substitution shifted the reaction to a highly reversible state by reducing the particle size of iron and stabilizing the rocksalt phase.
So far, so good. As for tripling the energy storage capacity of lithium-ion batteries, for one thing they’re gonna have to scale up if they mean electric vehicle batteries and renewable energy grid integration. For now they’re still at the coin-type battery stage.
What’s The Story With Iron?
Come to think of it, back in 2015 CleanTechnica took a look at some Li-ion battery research under way at Brookhaven with the University of Madison-Wisconsin that involved iron fluoride, and even farther back — in 2010 — we caught wind of another research pathway involving a virus.
So, this has been going on for quite a while.
Meanwhile, flow battery fans also have something to look forward to in the iron energy storage department.
In 2014 the company Energy Storage Systems received an ARPA-E grant for an all-iron flow battery, and by 2017 it was testing the system with the Army Corps of Engineers and showcasing the technology at the Intersolar trade show.
This past May, the company announced a new partnership for its “Energy Warehouse” system in Brazil, so it looks like things are beginning to take off. The project is designed to store solar power and shave the use of diesel generators during peak use hours.
Speaking of scaling up, the $1.3 million Brazilian project is funded partly through the US Trade and Development Agency. The small scale project is aimed at testing the system, with the goal of applying it to bigger storage jobs.
The USTD mission is to create new jobs in the US by exporting technology overseas, btw. Just saying.
Meanwhile, the US Army is interested in the ESS energy storage system for potential use in forward operating bases. We’ll touch base with them to see how it’s working out, so stay tuned for more on that.
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Photo (cropped): “Brookhaven scientists Enyuan Hu and Sooyeon Hwang are pictured at the Center for Functional Nanomaterial’s TEM facility where the researchers viewed the cathode material at a resolution of 0.1 nanometers,” by Brookhaven National Laboratory via Eurekalert.