A new approach boosts lithium-ion battery efficiency and puts out fires,
too
Adding polymers and fireproofing to a battery's current collectors makes
it lighter, safer and about 20% more efficient

Date:
October 15, 2020
Source:
DOE/SLAC National Accelerator Laboratory
Summary:
Building new functionality into an overlooked lithium-ion battery
component addresses two major goals of battery research: extending
the driving range of electric vehicles and reducing the danger
that laptops, cell phones and other devices will burst into flames.



FULL STORY ==========================================================================
In an entirely new approach to making lithium-ion batteries lighter, safer
and more efficient, scientists at Stanford University and the Department
of Energy's SLAC National Accelerator Laboratory have reengineered one
of the heaviest battery components - sheets of copper or aluminum foil
known as current collectors - so they weigh 80% less and immediately
quench any fires that flare up.


==========================================================================
If adopted, the researchers said, this technology could address
two major goals of battery research: extending the driving range of
electric vehicles and reducing the danger that laptops, cell phones and
other devices will burst into flames. This is especially important when batteries are charged super-fast, creating more of the types of battery
damage that can lead to fires.

The research team described their work Oct. 15 in Nature Energy.

"The current collector has always been considered dead weight,
and until now it hasn't been successfully exploited to increase
battery performance," said Yi Cui, a professor at SLAC and Stanford and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) who led the research.

"But in our study, making the collector 80% lighter increased the energy density of lithium-ion batteries -- how much energy they can store in a
given weight -- by 16-26%. That's a big jump compared to the average 3% increase achieved in recent years." Desperately seeking weight loss
Whether they come in the form of cylinders or pouches, lithium-ion
batteries have two current collectors, one for each electrode. They
distribute current flowing in or out of the electrode, and account for
15% to as much as 50% of the weight of some high-power or ultrathin
batteries. Shaving a battery's weight is desirable in itself, enabling
lighter devices and reducing the amount of weight electric vehicles have
to lug around; storing more energy per given weight allows both devices
and EVs to go longer between charges.



========================================================================== Reducing battery weight and flammability could also have a big impact
on recycling by making the transportation of recycled batteries less
expensive, Cui said.

Researchers in the battery industry have been trying to reduce the weight
of current collectors by making them thinner or more porous, but these
attempts have had unwanted side effects, such as making batteries more
fragile or chemically unstable or requiring more electrolyte, which
raises the cost, said Yusheng Ye, a postdoctoral researcher in Cui's
lab who carried out the experiments with visiting scholar Lien-Yang Chou.

As far as the safety issue, he said, "People have also tried adding fire retardant to the battery electrolyte, which is the flammable part, but you
can only add so much before it becomes viscous and no longer conducts ions well." Designing a polymer-foil sandwich After brainstorming the problem,
Cui, Ye and graduate student Yayuan Liu designed experiments for making
and testing current collectors based on a lightweight polymer called
polyimide, which resists fire and stands up to the high temperatures
created by fast battery charging. A fire retardant - triphenyl phosphate,
or TPP -- was embedded in the polymer, which was then coated on both
surfaces with an ultrathin layer of copper. The copper would not only
do its usual job of distributing current, but also protect the polymer
and its fire retardant.

Those changes reduced the weight of the current collector by 80%
compared to today's versions, Ye said, which translates to an energy
density increase of 16-26% in various types of batteries, and it conducts current just as well as regular collectors with no degradation.

When exposed to an open flame from a lighter, pouch batteries made with
today's commercial current collectors caught fire and burned vigorously
until all the electrolyte burned away, Ye said. But in batteries with
the new flame-retardant collectors, the fire never really got going,
producing very weak flames that went out within a few seconds, and did
not flare up again even when the scientists tried to relight it.

One of the big advantages of this approach, Cui said, is that the new
collector should be easy to manufacture and also cheaper, because it
replaces some of the copper with an inexpensive polymer. So scaling
it up for commercial production, he said, "should be very doable." The researchers have applied for a patent through Stanford, and Cui said they
will be contacting battery manufacturers to explore the possibilities.


========================================================================== Story Source: Materials provided by
DOE/SLAC_National_Accelerator_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Yusheng Ye, Lien-Yang Chou, Yayuan Liu, Hansen Wang, Hiang Kwee Lee,
Wenxiao Huang, Jiayu Wan, Kai Liu, Guangmin Zhou, Yufei
Yang, Ankun Yang, Xin Xiao, Xin Gao, David Thomas Boyle,
Hao Chen, Wenbo Zhang, Sang Cheol Kim, Yi Cui. Ultralight
and fire-extinguishing current collectors for high-energy and
high-safety lithium-ion batteries. Nature Energy, 2020; 5 (10):
786 DOI: 10.1038/s41560-020-00702-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201015111738.htm

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