Battery & Electrification Technology - November/December 2024 - 20
Researchers Discover a Surprising Way to Jump-Start
Battery Performance
Charging lithium-ion batteries at high currents just before they leave the factory is 30 times faster and
increases battery lifespans by 50 percent, according to a study at the SLAC-Stanford Battery Center.
SLAC National Accelerator Laboratory, Menlo Park, CA
A
lithium-ion battery's very first
charge is more momentous than it
sounds. It determines how well and
how long the battery will work from then
on - in particular, how many cycles of
charging and discharging it can handle
before deteriorating.
In a study published in Joule, researchers
at the SLAC-Stanford Battery Center
report that giving batteries this first
charge at unusually high currents increased
their average lifespan by 50 percent
while decreasing the initial charging
time from 10 hours to just 20 minutes.
Just as important, the researchers were
able to use scientific machine learning to
pinpoint specific changes in the battery
electrodes that account for this increase
in lifespan and performance - invaluable
insights for battery manufacturers looking
to streamline their processes and
improve their products.
The study was carried out by a SLAC/
Stanford team led by Professor
Will
Chueh in collaboration with researchers
from the Toyota Research Institute (TRI),
the Massachusetts Institute of Technology,
and the University of Washington.
The results have practical implications
for manufacturing not just lithium-ion batteries
for electric vehicles and the electric
grid, but for other technologies, too, said
Steven Torrisi, a senior research scientist at
TRI, who collaborated on the research.
" This study is very exciting for us, " he
said. " Battery manufacturing is extremely
capital, energy, and time intensive. It takes
a long time to spin up manufacturing of a
new battery, and it's really difficult to optimize
the manufacturing process because
there are so many factors involved. "
Torrisi said the results of this research
" demonstrate a generalizable approach for
understanding and optimizing this crucial
step in battery manufacturing. Further, we
may be able to transfer what we have
learned to new processes, facilities, equipment,
and battery chemistries in the future. "
20
Giving batteries this first charge at unusually high currents increased their average lifespan by 50
percent while decreasing the initial charging time from 10 hours to just 20 minutes. (Image: SLAC)
To understand what happens during
the battery's initial cycling, Chueh's team
builds pouch cells in which the positive
and negative electrodes are surrounded
by an electrolyte solution where lithium
ions move freely.
When a battery charges, lithium ions
flow into the negative electrode for storage.
When a battery discharges, they flow
back out and travel to the positive electrode;
this triggers a flow of electrons for
powering devices.
The positive electrode of a newly minted
battery is 100 percent full of lithium, said
Xiao Cui, the lead researcher for the battery
informatics team in Chueh's lab. Every time
the battery goes through a charge-discharge
cycle, some of the lithium is deactivated.
Minimizing those losses prolongs
the battery's working lifetime.
Oddly enough, one way to minimize
the overall lithium loss is to deliberately
lose a large percentage of the initial supply
of lithium during the battery's first
charge, Cui said. It's like making a small
investment that yields good returns
down the road.
This first-cycle lithium loss is not in vain.
The lost lithium becomes part of a squishy
layer called the solid electrolyte interphase,
or SEI, that forms on the surface of the
negative electrode during the first charge.
In return, the SEI protects the negative
electrode from side reactions that would
accelerate the lithium loss and degrade the
battery faster over time. Getting the SEI just
right is so important that the first charge is
known as the formation charge.
" Formation is the final step in the manufacturing
process, " Cui said, " so if it fails,
all the value and effort invested in the
battery up to that point are wasted. "
Manufacturers generally give new batteries
their first charge with low currents,
on the theory that this will create the
most robust SEI layer. But there's a downside:
Charging at low currents is time-consuming
and costly and doesn't necessarily
yield optimal results. So, when recent
studies suggested that faster charging
with higher currents does not degrade
battery performance, it was exciting news.
But researchers wanted to dig deeper.
The charging current is just one of dozens
of factors that go into the formation
of SEI during the first charge. Testing all
possible combinations of them in the lab
to see which one worked best is an overwhelming
task.
To whittle the problem down to manageable
size, the research team used scientific
machine learning to identify which factors
Battery & Electrification Technology, November/December 2024
Battery & Electrification Technology - November/December 2024
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