[Image above] Credit: stringy; Flickr CC BY-NC 2.0
We all want our electronic devices to stay charged longer, even though one contributing factor to battery drain can probably be traced back to usage. Between taking selfies, texting, watching videos, and checking Facebook, is it any wonder why we’re burning through our phone batteries in just a few hours?
Scientists are exploring ways to give us longer-lasting and safer lithium-ion batteries. One of the biggest problems researchers attempt to solve in lithium-ion batteries is the dendrite formation that develops after repeated charges, causing batteries to short-circuit and sometimes explode.
And there is no scarcity of research when it comes to combating dendrites in lithium-ion batteries.
To solve the dendrite problem, scientists have explored the use of a glassy interlayer between cathode and electrolyte. Building on that research, others have proven that defect-free smooth surfaces could further prevent dendrite growth. One team of scientists found that nanodiamonds can suppress dendrite formation. And another group of researchers showed that a derivative of asphalt can not only charge lithium batteries faster, but also kill the dendrites.
The latest effort to curb dendrite growth in lithium batteries comes from a collaboration of researchers from Arizona State University and Rice University. Led by Hanqing Jiang, professor at ASU’s School for Engineering of Matter, Transport and Energy, researchers discovered that making a substrate out of a 3-D layer of polydimethylsiloxane (PDMS) for a lithium metal anode can lessen dendrite growth, extend battery life, and reduce safety risk, according to an article on ASU Now.
And the key ingredient? Sugar cubes.
The researchers found that growth of dendrites results from stress in the anode, similar to whiskering that occurs in tin and zinc, reports the Rice University team in a news release.
“People have noticed that dendrites in lithium are similar to the whiskers in tin and zinc, but they haven’t known that compressive stress exists in lithium metal during battery cycling,” Ming Tang, assistant professor of materials science and nanoengineering at Rice, explains. “The experiments by Dr. Jiang’s group provided definitive confirmation of the association between compressive stress and dendrite formation.”
“We already know that tiny tin needles or whiskers can protrude out of tin surfaces under stress, so by analogy we looked at the possibility of stress as a factor in lithium dendrite growth,” Jiang says.
So where do sugar cubes fit in the picture?
The researchers infused sugar cubes with a liquid silicone polymer solution. After solidifying the liquid by increasing temperature and dissolving the sugar, they created a 3-D porous silicone substrate. The final step was to deposit a thin copper layer on top of the substrate to conduct electrons.
“The sugar becomes a sacrificial template,” Tang explains in the release. “When it’s removed, it leaves a substrate with a very large internal surface, like a sponge that can collapse and deform.”
Jiang and his team noticed that when the substrate deformed, it wrinkled—which reduced the stress, and consequently reduced dendrite growth. “The PDMS, which serves as a porous, sponge-like layer, relieves the stress and effectively inhibits dendrite growth,” Jiang adds.
Credit: Arizona State University
The research team’s discovery could be important for lithium-ion batteries, lithium-air batteries, and any batteries containing metal anodes.
“Almost all metals used as battery anodes tend to develop dendrites,” Jiang explains in the article. “For example, these findings have implications for zinc, sodium, and aluminum batteries as well.”
The researchers plan to tweak and test the substrate design to improve battery life. Beyond that, dendrite-free batteries could become a possibility in the near future.
“We have figured out the mechanism that the stress relaxation can suppress lithium dendrite growth,” Jiang writes in an email. “Our next goal is to optimize the design of the 3-D porous substrate, to scale up the manufacturing, and to test the full-cell performance by adopting advanced cathode materials and electrolyte.”
The paper, published in Nature Energy, is “Stress-driven lithium dendrite growth mechanism and dendrite mitigation by electroplating on soft substrates” (DOI: 10.1038/s41560-018-0104-5).
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