A CT scan image of a battery cell shows breakdown of layers directly below an indentation. A recent report from Underwriters’ Laboratories Inc. suggests that such dents in the casing are a possible failure mechanism for lithium-ion batteries. “The resulting high stress/strain will lead to a mechanical failure of the separator (with failure of the casing), allowing for direct contact between electrodes at a distance only a few layers below the casing surface,” the report says. (Source: Underwriters Laboratories Inc.)
Chuck, Didn't Tesla get a top safety rating just recently for the S? This is a problem with EVs (and hybrids) that use Lithium Ion batteries. I am not sure that the testing agancies really know how to characterize the failure modes of these batteries. As I have mentioned before, there was an incident in China where an all electric cab of local manufacture caught fire and burned up the driver and passengers completely after a collision with a car that drove away. This is very worrisome.
Since the Tesla Model S batteries can be swapped out in a few seconds at their roadside stations, there must be some sort of quick release that would make it possible in an emergency to drop the battery pack and roll the car away from it, thereby saving the vehicle in case of battery fire.
Perhaps there should be a small, separate battery just for the purpose of driving the vehicle a few feet to get off of and away from the dropped main battery.
You're right on the money, naperlou. Yes, Tesla has "fives" (best rating) across the board in NHTSA's safety ratings. And, yes, the methodology for the ratings is well established. I agree that the ratings agencies don't yet have a handle on how to characterize the relatively new phenomenon of lithium-ion failures.
Ken, my understanding of the battery swap out machine is that it simultaneously unscrews a large number of bolts, drops the battery down, then raises another battery up into place. Reportedly, it is the same piece of equipment they use in the factory. It is not a mobile piece of equipment. In videos of it working, the car is driven up over the device. This is not a quick relesae mechanism. The device reportedly will cost Tesla $500K to intsall.
If the battery is susceptible to being breached the way this one was, any auxiliary battery would be susceptible as well. If it was anywhere near the part tha caught fire, it would also catch fire. Also, the battery weighs over 900 lbs., so I am not sure your idea would work.
I think the idea of having the battery basically cover the bottom of the car is a very bad one. This could prove their undoing. Now they will probably have to put some sort of shielding there. That will increase the weight even more.
"Such occurrences are rare, however. A Tesla spokeswoman told Design News that the Model S has collectively been driven 83 million miles at this point, with dozens of known accidents, and no such battery problems, until now."
Seems to me that this is a misleading statement and is a poor defense for Tesla battery safety. 83 million miles refers to driving distance but does not take into account an impact with an object - and "dozens of known accidents" does not give any quantifiable data regarding this specific issue.
apparently the battery has an armor plate beneath it, 1/4" thick. However,
hit something hard enough, fast enough and it will rip through almost anything.
Lets not forget some minor ice sank the Titanic.
Now that said, Lou's idea of dropping the battery pack isn't neccessarily a bad idea.
if you have a fire, it would seem easiest to have some explosive bolts on the body side, that would cut the structural attachments and let the battery drop off. You would need a small internal battery to drive away, but, it could be done as a future upgrade.
Wow that is scary stuff! It's unfortunate this keeps happening, because it certainly isn't going to do anything to promote the use of hybrid vehicles and EVs. It's especially troubling because of Tesla's high rating, as Lou points out.
So the Pinto, Chevy saddle tanks, and the recent Jeep recalls should all be put aside if we let the Tesla get a pass?
On the otherhand, debris is a part of the road. If consumers expect the cars to be 100% safe, then the only solution is to get rid of the car. At least in this instance, the driver was able to pull over and get out. In fact, I think this was explicitily discussed when many here at DN were critical of the Boeing batteries. Lithium ion chemistry in an airplane, not so good as the option is a plane crash (or crash landing). But in an automobile one could pull over and get out of the car.
The question of whether engineers could have foreseen the shortcut maintenance procedures that led to the crash of American Airlines Flight 191 in 1979 will probably linger for as long as there is an engineering profession.
More than 35 years later, the post-mortem on one of the country’s worst engineering disasters appears to be simple. A contractor asked for a change in an original design. The change was approved by engineers, later resulting in a mammoth structural collapse that killed 114 people and injured 216 more.
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