By growing uniform lithium crystals on a surprising surface, UC San Diego engineers open a new door to fast-charging lithium-metal batteries
In a new paper, engineers report progress toward lithium-metal batteries that charge fast; as fast as one hour.
This fast charging is thanks to lithium metal crystals that can be seeded and grown – quickly and uniformly – on a surprising surface.
The trick is to use a crystal-growing surface that lithium officially doesn’t ‘like’. From these seed crystals grow dense layers of uniform lithium metal.
Uniform layers of lithium metal are of great interest to battery researchers because they lack battery-performance-degrading spikes called dendrites. The formation of these dendrites in battery anodes is a longstanding roadblock to fast-charging ultra-energy-dense lithium-metal batteries.
This new approach, led by University of California San Diego engineers, enables charging of lithium-metal batteries in about an hour, a speed that is competitive against today’s lithium-ion batteries.
dense lithium layers
To grow lithium metal crystals, the researchers replaced the ubiquitous copper surfaces on the negative side (the anode) of lithium-metal batteries with a lithiophobic nanocomposite surface made of lithium fluoride (LiF) and iron (Fe).
Using this lithiophobic surface for lithium deposition, lithium crystal seeds formed, and from these seeds grew dense lithium layers – even at high charging rates. The result was long-cycle-life lithium-metal batteries that can be charged quickly.
UC San Diego nanoengineering professor Ping Liu, the senior author on the new paper, said: “The special nanocomposite surface is the discovery.
“We challenged the traditional notion of what kind of surface is needed to grow lithium crystals. The prevailing wisdom is that lithium grows better on surfaces that it likes, surfaces that are lithiophilic. In this work, we show that is not always true.
“The substrate we use does not like lithium. However, it provides abundant nucleation sites along with fast surface lithium movement. These two factors lead to the growth of these beautiful crystals.
“This is a nice example of a scientific insight solving a technical problem.”
The new advance led by UC San Diego nanoengineers could eliminate a significant roadblock that is holding back widespread use of energy-dense lithium-metal batteries for applications like electric vehicles (EVs) and portable electronics.
While lithium-metal batteries hold great potential for EVs and portable electronics because of their high charge density, today’s lithium-metal batteries must be charged extremely slowly in order to maintain battery performance and avoid safety problems.
The slow charging is necessary to minimise the formation of battery-performance-wrecking lithium dendrites that form as lithium ions join with electrons to form lithium crystals on the anode side of the battery.
Lithium crystals build up as the battery charges, and the lithium crystals dissolve as the battery discharges.
Ping Liu is the director of the Sustainable Power and Energy Center (SPEC) at the UC San Diego Jacobs School of Engineering where he also serves as a professor in the Department of NanoEngineering.
The research is published in Nature Energy.
Image 1: Cryo-TEM image of a single crystal of lithium metal that was seeded on a surprising lithiophobic nanocomposite surface made of lithium fluoride and iron. The lithium crystal has a hexagonal bipyramidal shape. In a paper published in Nature Energy, the UC San Diego and UC Irvine researchers showed that this surprise formation of lithium crystal seeds leads to dense lithium layers even at high charging rates, resulting in long-cycle-life lithium-metal batteries that can also be fast charged. This discovery overcomes a common phenomenon in rechargeable lithium-metal batteries in which high-rate charging always leads to porous lithium and short cycle lives. By replacing the ubiquitous copper surfaces on the negative side (the anode) of lithium-metal batteries with this lithiophobic surface made of lithium fluoride and iron, the researchers have opened a new avenue for creating more reliable, safer, higher performance lithium-metal batteries. © Chunyang Wang and Huolin Xin/ UC Irvine.
Image 2: In this SEM image, large, uniform crystals of lithium metal grow on a surface that is surprising because it doesn’t ‘like’ lithium. UC San Diego battery researchers found that lithium metal crystals can be started (nucleated) and grown, quickly and uniformly, into dense layers of lithium metal that lack performance-degrading dendrites. © Zhaohui Wu and Zeyu Hui/ UC San Diego.