News at Princeton

Thursday, Sept. 18, 2014

Web Stories

Putting the squeeze on batteries


To view the multimedia features on this page, you will need to download the latest version of Flash Player and/or enable JavaScript.


Professor Craig Arnold is working to make lithium-ion batteries last longer and provide more energy. Read more.


Video Closed Captions

[music]

Craig Arnold:
Cars, cell phones, laptops.

Craig Arnold:
We all rely on batteries every day.

Craig Arnold:
My name is Craig Arnold.

Craig Arnold:
And I want to make better batteries.

Craig Arnold:
Lithium-ion batteries are good.

Craig Arnold:
But we all know that they tend
to lose their capacity over

Craig Arnold:
time, and they don't last forever.

Craig Arnold:
Batteries are complex.

Craig Arnold:
They're made up of many layers of different materials.

Craig Arnold:
If we take these layers apart, we could see the dark

Craig Arnold:
electrode material and we could see the

Craig Arnold:
white separator membrane.

Craig Arnold:
This membrane keeps the
electrodes from touching each

Craig Arnold:
other in this tight pack.

Craig Arnold:
In my lab, we try to simulate
what happens to the separator

Craig Arnold:
membrane over its lifetime.

Craig Arnold:
We roll up the material and
expose it to high pressures.

Craig Arnold:
On a microscopic level, this has effects

Craig Arnold:
similar to years of use.

Craig Arnold:
These mechanical stresses can cause

Craig Arnold:
changes to the separator.

Craig Arnold:
But what does that have to do
with your battery failing?

Craig Arnold:
Well, let me explain.

Craig Arnold:
Here's an ordinary sponge.

Craig Arnold:
You'll notice it has a bunch of holes in
it to allow water to pass through.

Craig Arnold:
If I were to press on it, it
would close these holes and

Craig Arnold:
prevent water from passing through the sponge.

Craig Arnold:
This is not unlike the battery separator.

Craig Arnold:
In this material, there is also a lot

Craig Arnold:
of little tiny holes.

Craig Arnold:
If I were to squeeze it, these
holes would also close up,

Craig Arnold:
preventing lithium ions from
passing through the membrane.

[music]

Craig Arnold:
We can see these holes if we
use an electron microscope

Craig Arnold:
with high magnification.

Craig Arnold:
In a new separator, the holes
are all over the membrane,

Craig Arnold:
allowing lithium ions to easily pass.

Craig Arnold:
After simulating long-time use
and storage, we can see the

Craig Arnold:
holes disappearing from the
membrane, making it more

Craig Arnold:
difficult for lithium ions to pass.

Craig Arnold:
So, what can we do about this?

Craig Arnold:
One way to fix this is to prevent
the pores from closing up.

Craig Arnold:
Imagine a battery separator
that's strong enough to resist

Craig Arnold:
mechanical stress.

Craig Arnold:
So in fact, batteries are not
just electrochemical devices.

Craig Arnold:
Their mechanical properties
can also affect their performance.

Craig Arnold:
By better understanding the
science of batteries, we can

Craig Arnold:
begin to engineer ways to keep
the current flowing longer.

Craig Arnold:
Boy, I could really use
that in my smartphone.

Photographer:
Hey, Craig.
That was fun. [laughter]

Back To Top