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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]