Scientists probe the chemistry of a single battery electrode particle
both inside and out

Date:
September 8, 2020
Source:
DOE/SLAC National Accelerator Laboratory
Summary:
Cracks and chemical reactions on a battery particle's surface can
degrade performance, and the particle's ability to absorb and
release lithium ions also changes over time. Scientists stuck
a single particle the size of a red blood cell to the tip of a
microscopic needle and probed it with X-rays to see how interior
and surface changes influence each other.



FULL STORY ==========================================================================
The particles that make up lithium-ion battery electrodes are microscopic
but mighty: They determine how much charge the battery can store, how
fast it charges and discharges and how it holds up over time -- all
crucial for high performance in an electric vehicle or electronic device.


========================================================================== Cracks and chemical reactions on a particle's surface can degrade
performance, and the whole particle's ability to absorb and release
lithium ions also changes over time. Scientists have studied both, but
until now they had never looked at both the surface and the interior of
an individual particle to see how what happens in one affects the other.

In a new study, a research team led by Yijin Liu at the Department of
Energy's SLAC National Accelerator Laboratory did that. They stuck a
single battery cathode particle, about the size of a red blood cell,
on a needle tip and probed its surface and interior in 3D with two X-ray instruments. They discovered that cracking and chemical changes on the particle's surface varied a lot from place to place and corresponded
with areas of microscopic cracking deep inside the particle that sapped
its capacity for storing energy.

"Our results show that the surface and the interior of a particle talk
to each other, basically," said SLAC lead scientist Yijin Liu, who
led the study at the lab's Stanford Synchrotron Radiation Lightsource
(SSRL). "Understanding this chemical conversation will help us engineer
the whole particle so the battery can cycle faster, for instance."
The scientists describe their findings in Nature Communications today.

Damage both inside and out A lithium-ion battery stores and releases
energy by moving lithium ions through an electrolyte back and forth
between two electrodes, the anode and the cathode. When you charge the
battery, lithium ions rush into the anode for storage. When you use the battery, the ions leave the anode and flow into the cathode, where they generate a flow of electrical current.



==========================================================================
Each electrode consists of many microscopic particles, and each particle contains even smaller grains. Their structure and chemistry are key
to the battery's performance. As the battery charges and discharges,
lithium ions seep in and out of the spaces between the particles' atoms, causing them to swell and shrink. Over time this can crack and break
particles, reducing their ability to absorb and release ions. Particles
also react with the surrounding electrolyte to form a surface layer
that gets in the way of ions entering and leaving. As cracks develop,
the electrolyte penetrates deeper to damage the interior.

This study focused on particles made from a nickel-rich layered
oxide, which can theoretically store more charge than today's battery materials. It also contains less cobalt, making it cheaper and less
ethically problematic, since some cobalt mining involves inhumane
conditions, Liu said.

There's just one problem: The particles' capacity for storing charge
quickly fades during multiple rounds of high-voltage charging - the type
used to fast- charge electric vehicles.

"You have millions of particles in an electrode. Each one is like a rice
ball with many grains," Liu said. "They're the building blocks of the
battery, and each one is unique, just like every person has different characteristics." Taming a next-gen material Liu said scientists
have been working on two basic approaches for minimizing damage and
increasing the performance of particles: Putting a protective coating on
the surface and packing the grains together in different ways to change
the internal structure. "Either approach could be effective," Liu said,
"but combining them would be even more effective, and that's why we have
to address the bigger picture."


========================================================================== Shaofeng Li, a visiting graduate student at SSRL who will be joining
SLAC as a postdoctoral researcher, led X-ray experiments that examined
a single needle- mounted cathode particle from a charged battery with
two instruments -- one scanning the surface, the other probing the
interior. Based on the results, theorists led by Kejie Zhao, an associate professor at Purdue University, developed a computer model showing how
charging would have damaged the particle over a period of 12 minutes
and how that damage pattern reflects interactions between the surface
and interior.

"The picture we are getting is that there are variations everywhere in
the particle," Liu said. "For instance, certain areas on the surface
degrade more than others, and this affects how the interior responds,
which in turn makes the surface degrade in a different manner." Now,
he said, the team plans to apply this technique to other electrode
materials they have studied in the past, with particular attention to how charging speed affects damage patterns. "You want to be able to charge
your electric car in 10 minutes rather than several hours," he said,
"so this is an important direction for follow-up studies."

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


========================================================================== Journal Reference:
1. Shaofeng Li, Zhisen Jiang, Jiaxiu Han, Zhengrui Xu, Chenxu Wang, Hai
Huang, Chang Yu, Sang-Jun Lee, Piero Pianetta, Hendrik Ohldag,
Jieshan Qiu, Jun-Sik Lee, Feng Lin, Kejie Zhao, Yijin Liu. Mutual
modulation between surface chemistry and bulk microstructure
within secondary particles of nickel-rich layered oxides. Nature
Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-18278-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908200511.htm

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