WaterBattery For On-The-Go Energy Storage
US Army researchers developed New ‘WaterBattery’ for ‘On-The-Go’ Energy Storage.
The announcement was made on Science Direct. The researchers:
In summary, we successfully resolved the “cathodic challenge” of aqueous electrolytes by designing a unique inhomogeneous electrolyte additive approach to minimize competitive water reduction on graphite or Li-metal surfaces during the interphase formation.
Upon reductive decomposition during the first charging process, the highly fluorinated additive forms a protective interphase that enables the reversible cycling of both graphite and Li-metal anodes in aqueous electrolytes.
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 was 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.
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.
…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…
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.
The researchers anticipate that commercialization of the new 4-volt version is about 4-5 years away, assuming that the funding stream holds steady. The lifecycle of the WaterBattery 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.
Co-author Dr. Kang Xu of the Army Research Laboratory is 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.”
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