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Scientists identify the cause of harmful dendrites and whiskers in lithium batteries



  Scientists pinpoint harmful dendrites and whiskers in lithium batteries
PNNL scientists Chongmin Wang, Wu Xu and Yang He use the specially modified transmission electron microscope to record images and videos of growing whiskers in a lithium battery. Picture credits: Andrea Starr / PNNL

Scientists have discovered a cause for the growth of needle-like structures known as dendrites and whiskers that plague lithium batteries, sometimes causing a short circuit, failure, or even fire.

The team around Chongmin Wang from the Department of Energy's Pacific Northwest National Laboratory has shown that the presence of certain compounds in the electrolyte ̵

1; the liquid material that enables the critical chemistry of a battery – promotes the growth of dendrites and whiskers. The team hopes the discovery will lead to new ways to prevent their growth by manipulating the contents of the battery. The results were published online on October 14 in Nature Nanotechnology .

Dendrites are tiny, rigid tree-like structures that can grow in a lithium battery. Their needle-like protrusions are called whiskers. Both cause enormous damage; In particular, they can pierce a structure known as a separator in a battery, much as weeds can sting through a concrete terrace or a paved road. They also increase undesirable reactions between the electrolyte and the lithium and accelerate battery failure. Dendrites and whiskers inhibit the widespread use of lithium metal batteries that have a higher energy density than their commonly used lithium ion counterparts.

The PNNL team found that the origin of whiskers in a lithium metal battery is in a known structure as "SEI" or solid electrolyte interphase, a film in which the solid lithium surface of the anode strikes the liquid electrolyte. The scientists also found a culprit in the growth process: ethylene carbonate, an indispensable solvent that is added to the electrolyte to improve battery performance.

It has been found that ethylene carbonate makes the battery vulnerable to damage.

Fast Catching Movement in Lithium Batteries

The team's findings include videos showing the gradual growth of a whisker in a nano-sized lithium metal battery developed specifically for this study.






PNNL researchers have seen in the video a growth of a harmful structure known as whiskers in a nanoscale lithium metal battery. Lithium ions began to clump together to form a particle. The structure grows slowly as more and more lithium atoms grow on the bottom of a cave. Then suddenly a beard shoots out. Picture credits: He et. al., Nature Nanotechnology

A dendrite begins when lithium ions begin to clump or "form" on the surface of the anode and form a particle indicating the birth of a dendrite. The structure grows slowly, while more and more lithium atoms grow on the bottom of a cave like a stalagmite. The team found that the energy dynamics on the surface of the SEI push more lithium ions into the slow-growing column. Then suddenly a whisker shoots out.

It was not easy for the team to capture the action. To this end, scientists have integrated an Atomic Force Microscope (AFM) and an Environmental Transmission Electron Microscope (ETEM), a highly regarded instrument that allows scientists to study a powered battery under real-life tiny power of whiskers as it grew. Just as a doctor measures a patient's hand force by asking him to push up against the doctor's outstretched hands, the PNNL team measures the power of the growing whisker by pressing its tip with the AFM's cantilever and pressing the button Power of the dendrite is exercised during its growth.

The Prescription for Electrolyte

The team found that the content of ethylene carbonate correlated directly with the growth of dendrites and whiskers. The more material the team put into the electrolyte, the more the whiskers grew. The scientists experimented with the electrolyte mixture and changed the ingredients to reduce dendrites. Some changes, such as the addition of cyclohexanone, prevented the growth of dendrites and whiskers.

"We do not just want to suppress the growth of dendrites, but get to the root cause and eliminate it," said Wang, a co-author of the work with Wu Xu. "We have recourse to the expertise of our colleagues who have experience in electrochemistry and I hope that our findings will encourage the community to explore this issue in a new way, which will clearly require more research."

Understanding what causes Whisker to start and grow will lead to new ideas to eliminate or at least control them to minimize harm, first author Yang He added. He and the team watched as Whiskers responded to an obstacle, either buckling, giving way, kinking or stopping. Better understanding could help pave the way for the widespread use of lithium metal batteries in electric cars, laptops, cell phones and more.


Testing lithium battery limitations can improve safety and longevity


Further information:
Generation and growth of lithium whiskers under stress, Nature Nanotechnology (2019). DOI: 10.1038 / s41565-019-0558-z, https://nature.com/articles/s41565-019-0558-z

Provided by
Pacific Northwest National Laboratory




Quote :
Scientists locate cause of harmful dendrites and whiskers in lithium batteries (2019, 14 October)
retrieved on October 14, 2019
from https://phys.org/news/2019-10-scientists-dendrites-whiskers-lithium-batteries.html

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