Shift Magazine - November 25, 2019 - 15

The Chevy Bolt EV uses
288 lithium ion cells.

THE LAB
physical testing of battery cells, packs
and systems for performance in conditions such as extreme vibration, wild
temperature ranges, human abuse, weird
driving situations - and accidents.
"Basically, the lab is there to confirm
the models produced by simulation,"
said Tim Grewe, GM's head of global
electrification and battery systems. "It's
impossible to test every situation under
every scenario the way that people will
use these cars."
A major emphasis is determining how
performance and safety parameters
change when putting cells into packs,
and packs into vehicles - such as in the
Chevrolet Bolt, which contains 288 cells.
"There are going to be nuances in performance when you use that many cells in
series and parallels," Grewe said.
"When you test an individual cell," he
said, "there's a certain assumption about
its environment. But when you put that
into a battery pack there will be some

temperature differences, some dynamic
impedance" and so on.
Particulars of powertrain performance
must be tested. Cold starts are an obvious one. "Drivers think they'll always
have enough power available to start
their car," Drauch said. "But chemical
reactions in batteries slow down in the
cold, so we need to manage thermally
what's going on."

PACK PRACTICE

The lab also has to figure out how GM
battery systems handle, for instance, the
dynamics of a tire instantly regaining traction on dry pavement after spinning on
ice. With a conventional automatic transmission, the clutch would slip and absorb
the energy.
"But in an electric car, there is no
clutch, and it's a vicious transience, so
all that energy will translate immediately into the battery pack," Grewe said.
"The wheel inertia plus the motor inertia

turns into electrical energy, and the pack
has to be able to surge and suck it up.
So we practice it at the pack level in the
lab to make sure we don't miss it in a
designer simulation. The worst thing in
the world would be to break a half-shaft
in development."
Other key tasks in the lab are to simulate the effects of time on battery durability and safety and to conduct "competitive analysis" of rivals' batteries.
The lab also is trying to optimize recycling of battery systems once their days
powering vehicles are numbered. "We
want to get all the usable value out
of them before recycling," said Peter
Karlson, battery-lifecycle manager.
It's not too much of a stretch to
compare GM's work in its battery lab
to fail-proofing a space flight. "It's an
Apollo-level challenge," Grewe says.
"We actually call some of these projects
moon shots. We just have to avoid the
fate of Apollo 13." n
november 2019 * shift

Shift Magazine - November 25, 2019

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