NHTSA and lithium ion batteries

[aviators99]

Just read this on CNN, regarding an investigation of the Volt:

Feds open 'formal safety defect' probe into Chevy Volt - CNN.com

There's not much detail, but it has me worried that the gov't may have large lithium ion batteries in its sights. For conspiracy theorists, I'm sure it will add fuel to the fire...

[Robert.Boston]

More info here:
NHTSA opens formal safety defect investigation

[VolkerP]

Conclusion: If you crash your Volt into a pole or a tree, and roll over -- make sure you exit the vehicle within the next 6 hours

[Adm]

Actually, 1 car had no problems, 1 battery fire started after 7 days, 1 battery had sparks and smoke after it was turned over, but no word on open fire.

[VolkerP]

There were some questions back in 2006 why Tesla went with laptop cells, when most other traction battery packs used prismatic cells. Their answer was "safety", especially containing "thermal runaway events" (nice word for a fire sustained by the electric energy stored in the cells). Now there will be Li-Ion bashing, mostly regardless of pack architecture or a look on manufacturers historic log (Tesla: zero events).

Or is there something in the records for Tesla?

[TEG]

Their answer was "safety"...

Umm... I think the reason was energy density and cost per kWh.
Also, the "mass produced commodity item" (due to laptop and other common use) meant that they could chose from multiple suppliers, and little risk that they could get "locked out" or "price gouged" by one supplier.

I think we heard a bunch about the safety aspect, not because they were trying to pick the "most safe" technology, but rather trying to show the world that they could devise a scheme to make the "not so inherently safe" cells "plenty safe" by adding multiple safety systems around them.

[JRP3]

Yes, the basic LiCo chemistry is probably the least safe lithium chemistry. Actually LiPoly is worse but so far no automakers are using those. The problem in the Volt case seems not to be the chemistry or the format but leaking coolant causing a short, possibly leading to a fire.

[Jeff N]

Actually, 1 car had no problems, 1 battery fire started after 7 days, 1 battery had sparks and smoke after it was turned over, but no word on open fire.

There has only been one out of many vehicle crash tests in which the Volt battery caught fire (3 weeks later).

After the fire, NHTSA and GM tried to reproduce the crash test battery fire unsuccessfully. The Euro NCAP test has a similar pole side-impact test, I think, and they have not reported problems during their Volt tests. GM says their own internal Volt crash tests during development have not resulted in battery fires. It seems as if a single side crash test into a 10-inch steel pole at 20 mph caused battery damage that eventually led to the fire. The Volt received a five star occupant safety result from this side pole test as one part of the car's published overall 5 star score.

Recently, NHTSA conducted several tests where they directly replicated the mechanical damage (rather than indirectly via a full pole crash test) seen in the pack that caught fire. After the replicated damage, a rollover was simulated by rotating the car containing the battery. It seems to be the combination of pack damage, broken coolant lines, and 180 degree rotation that triggered a delayed fire in one of the new test cases and a "spark and smoke" event in another test case (the third recent test case had no problems).

The test simulates a post-crash rollover because there is a significant chance of this happening in an SUV or truck after a side impact. The chance of an actual rollover in a Volt is much smaller due to the weight and low center of gravity. This low chance of rollover is one of the many reasons why the Volt received excellent safety scores from NHTSA and EuroNCAP. The website informedforlife.org has rated the 2011 and 2012 Volt among the best 7% of cars and trucks for crash safety with a score of 44.

http://www.informedforlife.org/demos...2riskNov12.pdf

[stopcrazypp]

Umm... I think the reason was energy density and cost per kWh.

I think VolkerP's "their" is referring to the other manufacturers who use prismatic cells questioning the safety of laptop cells.

[VolkerP]

No, I refer to a statement by a Tesla engineer touting the overall safety of Tesla's ESS architecture. On the topic of "better cell safety of prismatic cells vs. laptop cells", he answered to ask the other manufacturers for crash / thermal runaway safety. He sounded pretty sure that the Tesla design would never encounter such a problem.

I'm sorry but I can't find the source for that, neither in my archives, nor in the Tesla blogs, nor in the web. Best cite I found is in Why is the "Tesla Roadster" electric vehicle fitted with commodity lithium-ion batteries? | E2A - ELECTRO-TO-AUTO FORUM. Might have been a youtube interview.

Volker