Published on September 11th, 2017 | by Tina Casey0
Go Army! US Army Researchers Develop New “Water Battery” For On-The-Go Energy Storage
September 11th, 2017 by Tina Casey
The US Army has been focusing on wearable electronics and advanced lithium-ion batteries to power the fighting force of the future, and they’ve come up with a new approach to energy storage that is tailor-made for your home electronics, too.
The challenge is to combine high performance with a super low risk of fire or explosion, and a research team from the Army Research Laboratory and the University of Maryland has reached a solution.
ARPA-E And The Energy Storage Ripple Effect
In comparison, the world of household electronics may not seem so exciting. However, since the new research is supported by ARPA-E, the Energy Department’s cutting-edge energy technology funding office, it’s probably a good bet that the chemistry behind the new battery research will have a transformative impact on the whole energy storage field.
Reducing Risk For Soldiers
The research team focused on rechargeable lithium-ion energy storage with a water-salt solution for an electrolyte. That type of battery provides sufficient voltage for laptops and other household electronics without the safety risks.
To be clear, safety systems are built into conventional lithium-ion batteries. The issue for soldiers on the go is that these systems add weight. Lighten the load and you get that much more back in endurance and force effectiveness.
In addition, although the risk of fire or explosion from properly designed Li-ion technology is minimal under normal conditions, the extreme conditions of Army activity — in training and in war zones — require that risk to be reduced even further.
Overcoming The “Cathodic Challenge”
Conventional aqueous batteries use electrodes based on a durable material, such as nickel, but the result is an energy storage solution with relatively low power.
The problem is how to boost power without sacrificing safety. The Army – UMD research team made some progress last year with a new aqueous battery reaching the 3.0 volt mark, but then they ran up against something called the cathodic challenge.
That’s what happens when a lithium or graphite electrode is degraded by contact with water in the electrolyte.
UMD’s Chongyin Yang developed a solution for the new, improved battery, in the form of a hydrophobic ceramic/polymer (aka plastic) gel coated onto the anode. That enables the use of lithium or graphite, which are much more efficient than nickel.
Here’s the explainer from the US Army:
This hydrophobic coating expels water molecules from the vicinity of the electrode surface and then, upon charging for the first time, decomposes and forms a stable interphase — a thin mixture of breakdown products that separates the solid anode from the liquid electrolyte. This interphase, inspired by a layer generated within non-aqueous batteries, protects the anode from debilitating side reactions.
Coming up with a formula for the new gel was a challenge all in itself. A balance had to be struck between effectively blocking contact with water, and allowing for a high level of performance.
With the new gel in hand, this year the researchers bumped performance up to the 4-volt level.
For more detail check out the new study in the journal Joule, under the title “4.0 V Aqueous Li-Ion Batteries.” Here’s a taste from the summary:
…we resolved this “cathodic challenge” by adopting an “inhomogeneous additive” approach, in which a fluorinated additive immiscible with aqueous electrolyte can be applied on anode surfaces as an interphase precursor coating. The strong hydrophobicity of the precursor minimizes the competitive water reduction during interphase formation, while its own reductive decomposition forms a unique composite interphase consisting of both organic and inorganic fluorides.
There’s Something In The Water
Since the Army is especially interested in durability under extreme conditions and live fire fights, the safety aspect of the new battery is an especially interesting development.
Although an aqueous electrolyte is generally more safe that the organic solvents typically used in non-aqueous Li-ion batteries, there could still be a fire or explosion risk if the battery is damaged.
The new battery reduces that risk to a minimum:
Unique to this battery…is that even when the interphase layer is damaged (if the battery casing were punctured, for instance), it reacts slowly with the lithium or lithiated graphite anode, preventing the smoking, fire, or explosion that could otherwise occur if a damaged battery brought the metal into direct contact with the electrolyte.
More And Better Energy Storage
There is still a ways to go before the new energy storage solution makes its way over to your laptop. The researchers anticipate that commercialization of the new 4-volt version is about 4-5 years away, assuming that the funding stream holds steady.
Lifecycle, for example, is still a consideration. The new battery can only cycle in the range of 50-100, and the research team figures that a lifespan of at least 500 cycles would be necessary to enable the new battery to compete in the marketplace.
The researchers also need to tweak the chemistry in order to scale up the battery for testing prior to commercial use.
As for the ripple effect, here’s senior co-author Dr. Kang Xu of the Army Research Laboratory enthusing over the possibilities:
“This is the first time that we are able to stabilize really reactive anodes like graphite and lithium in aqueous media…This opens a broad window into many different topics in electrochemistry, including sodium-ion batteries, lithium-sulfur batteries, multiple ion chemistries involving zinc and magnesium, or even electroplating and electrochemical synthesis; we just have not fully explored them yet.”
By the way, happy 25th Anniversary, Army Research Laboratory!
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Photo (cropped): “Dr. Kang Xu, who specializes in electrochemistry and materials science, develops innovative solutions for tomorrow’s Soldiers at the U.S. Army Research Laboratory at Adelphi, Maryland” by Jhi Scott.
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