Despite a compressed, three-year window to develop and test
the lithium-ion battery pack for Chevy's new Volt electric vehicle, experts say
there's a good chance the technology will prove to be durable and dependable
when it hits the streets later this year.
"We don't
know definitively what the failure mechanisms will be for this battery," says
David Swan, CEO and founder of DHS Engineering
and a well-known expert in electric vehicle testing. "But chances are that
General Motors will be right. They can't afford to fail."
Indeed,
GM's reputation is on the line with the Volt. Said to be the biggest program in
the company's 102-year history, the Volt serves as an opportunity for GM to
make up for the media-generated black eye it received after the infamous
shelving of its earlier electric vehicle, the EV1. It also gives the company a
chance to take the lead in the hottest new area of the automotive industry.
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That's why
GM stepped boldly forth in July of this year, announcing that it will offer an
eight-year, 100,000-mile warranty for the Volt's lithium-ion battery pack.
"We offered
that warranty because our confidence (in the battery) has increased
significantly," says Rob Peterson, a spokesman for GM. "What our engineers
accomplished over a short period of time - when you take into account the
batteries, suppliers, electronic controls, manufacturing and dealer training -
is really impressive."
Navigating Parallel
Paths
For engineers, the Volt program has also been a genuine
stomach churner. When General Motors announced the program schedule for its
Chevy Volt electric vehicle early in 2007, the timing appeared to be next to
impossible. In a scant three-and-a-half years, the technical staff faced the
prospect of studying a new material, building prototypes, working with
suppliers, understanding failure modes and then squeezing years of simulated
life into a few months of battery testing - all while the car itself was still
being constructed.
"In the past, innovation and invention was
done before the technology was assigned to a vehicle," Peterson says. "This was
different. Here, we decided to do the innovation and invention on a parallel
path with the vehicle development."
From an engineering perspective,
the short development time raised questions, particularly where the battery was
concerned. Some wondered if two years of testing on the Volt battery would
provide an accurate snapshot of its capabilities under real-world conditions.
Others asked if General Motors' engineering team could feel confident that they
had correctly identified the most likely failure mechanisms for the battery.
"The danger with a new technology
is that maybe you're testing it the old way - the way that mattered for previous
generations of products," says Steven Eppinger, a professor of management
science and innovation at Massachusetts Institute of Technology. "But you're
not always aware of the failure modes for the new technology. It might fail in
a different way. That's always the danger of innovation."
Surprisingly, experts say that the
compressed test period isn't a big issue. The vast majority of engineered
products are subjected to accelerated life tests. "In most products, the kind
of (testing) cycle you want to put it through can be accelerated," Eppinger
says. "If it's charging or discharging, heating or cooling, loading or
unloading, it can be accelerated."
Indeed, accelerated tests for a 10-year
life can be completed quickly, once the failure modes are determined. The key, experts
say, is to determine which tests are right. In batteries, charge/discharge
cycles are often the key, and those can be done relatively quickly. "I can get
the amp-hours in and out, and I can easily simulate 10 years in less than a
year," Swan says. "If I know that the degradation mechanism is associated with
time and temperature, I can choose the right driving cycle and I can do those
tests at elevated temperatures. If nothing else, it will give me the warm,
fuzzy feeling that I'm getting the number of years I want out of the battery."
Experts say that GM has made a mammoth
effort to discover the failure mechanisms and test for them under all possible
conditions. The giant automaker has invested $8 million to double the size of
what already was "the largest and most technically advanced battery lab in the
U.S." Located at the company's Warren, MI, campus, the lab spans 63,000 sq ft
and houses a growing team of approximately 1,000 engineers. It's also equipped
with 176 test channels, 42 thermal chambers, shaker tables for structural
integrity testing, a battery tear-down area and an integrated test automation
system.
GM engineers have also tested outside
the lab. "We've put over a million miles on the real-world vehicles," Peterson
says. "We've taken them to Pikes Peak, Death Valley, the mountains of California, the streets
of LA, and everything in between."
Through countless iterations, the
company's engineers have also made important decisions regarding the battery's
design. As a result of intense scrutiny of the battery's cooling characteristics,
GM engineers chose a 5 x 8-inch prismatic cell configuration, instead of the
wound, cylindrical design employed in mobile electronics (and in the Tesla
Roadster). They also departed from the cobalt oxide cell chemistries commonly
employed in consumer devices, and then added a hot and cold liquid cooling
system to the pack, which consists of 288 cells.
"They busted their butts trying to
get this battery ready," Peterson says.
Learning from Failure
To be sure, all of those efforts aren't assurances. Honda
Motor Co. recently experienced the unexpected when its
Civic
Hybrid batteries started to deteriorate prematurely. The company was forced
to mail more than 100,000 letters to owners of 2006, 2007 and 2008 Civics
warning that their batteries "may deteriorate and eventually fail." Honda now
faces the possibility of replacing thousands of the batteries, which are under
eight- or 10-year warranties and may cost as much as $3,000 apiece, according
to the
Chicago Tribune.
Still,
experts say such problems can't be attributed to lack of test time. "When the
2001 Prius became available, there was no way the engineers had 10 years or
even five years of data on the battery," Swan says. "Yet they went into high
production and, by and large, it's been a very successful battery."
The key is
to understand the physics and failure modes of the battery and then test the
products in every conceivable way, says Eppinger. "That's what you really want
to do," he says. "You want to experience all the failures in the lab, so the
product is robust in the field."
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