Lithium's narrow paths limit batteries
Date:
April 18, 2022
Source:
Rice University
Summary:
Study suggests that lithium batteries would benefit from more
porous electrodes with better-aligned particles that don't limit
lithium distribution.
FULL STORY ==========================================================================
If you could shrink enough for a fantastic voyage across a lithium battery electrode, you'd see the level of charge at every scale is highly uneven.
==========================================================================
This is not good for the battery's health. Rice University researchers
who recognize the problem worked with the Department of Energy to view
in great detail how the various particles in an electrode interact with
lithium during use.
Specifically, the Rice lab of materials scientist Ming Tang analyzed
nano- and micro-scale interactions within lithium iron phosphate cathodes through modeling and imaging offered by the transmission X-ray microscopy capabilities at Brookhaven National Laboratory and Argonne National
Laboratory.
Their paper in the American Chemical Society journal ACS Energy
Letterssupports theories Tang and his colleagues formed several years
ago that foresaw how lithium travels in the dynamic environment inside
a typical commercial cathode.
Being able to watch sealed cathodes charge and discharge at Brookhaven
offered absolute proof.
"Batteries have a lot of particle aggregates that soak up and give up
lithium, and we wanted to know what happens on their surfaces, how uniform
the reaction is," said Tang, an associate professor of materials science
and nanoengineering. "In general, we always want a more uniform reaction
so we can charge the battery faster." In images taken at Brookhaven's
powerful X-ray synchrotron, the researchers saw some regions inside the
cathode were better at absorption than others. The ability to look at
single or aggregated particles in 3D showed that rather than reacting over their entire surfaces, lithium favored particular regions over others.
========================================================================== "This is very different from conventional wisdom," Tang said. "The most interesting observation is that these reaction regions are shaped like
one- dimensional filaments lying across the surface of these aggregated particles.
It was kind of weird, but it matched what we saw in our models."
Tang said the lithium filaments looked something like thick nanotubes
and were several hundred nanometers wide and several microns long.
He said stress between misaligned crystallites in the particle
agglomerates prevents lithium from being uniformly inserted into or
extracted from the aggregate surface because that will generate too
large an energy penalty.
Instead, lithium is forced to flow into or out of the aggregates at
"hot spots" that develop the filament shape.
What does this mean for battery performance? "This is a bad thing,"
Tang said. "Because the lithium can't go into the cathode uniformly,
it slows down the intercalation mechanics.
========================================================================== "What our study offers is some potential ways to help make lithium
insertion or extraction more uniform on these aggregates or individual particles," he said.
"Introducing some porosity in the particle agglomerates might sacrifice
some energy density, but at the same time would allow lithium to go
in more uniformly. That could allow you to get more energy at a given charge/discharge rate.
"Another thought is if we can somehow align the orientation of these
small particles so their maximum expansion is perpendicular to each other, they'll better accommodate lithium intercalation," he said.
That would be a challenge for battery manufacturers, he admitted.
"We don't have enough experience in synthesis to know how to make that
happen," Tang said. "What we're providing is bait. Let's see if somebody bites." Rice graduate alumni Fan Wang and Kaiqi Yang are co-lead authors
of the paper.
Co-authors are Mingyuan Ge, Jiajun Wang, Jun Wang, Xianghi Xiao and
Wah-Keat Lee, all of Brookhaven National Laboratory, Upton, New York;
and Linsen Li of Shanghai Jiao Tong University.
The Department of Energy, Basic Energy Sciences (DE-SC0019111) and the
National Science Foundation (CMMI-1929949) supported the research.
========================================================================== Story Source: Materials provided by Rice_University. Original written
by Mike Williams. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Fan Wang, Kaiqi Yang, Mingyuan Ge, Jiajun Wang, Jun Wang,
Xianghui Xiao,
Wah-Keat Lee, Linsen Li, Ming Tang. Reaction Heterogeneity in
LiFePO4 Agglomerates and the Role of Intercalation-Induced
Stress. ACS Energy Letters, 2022; 1648 DOI:
10.1021/acsenergylett.2c00226 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220418143845.htm
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