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Electronics & Test

Lithium-Ion Batteries Overheated in Mitsubishi Vehicles

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Charles Murray
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Re: Definitely not good news
Charles Murray   4/2/2013 8:39:29 PM
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Thank you, Phil_Pearce, for a succint explanation of thermal runaway. It's nice to know we have smart readers at Design News.

dbg
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Re: This actually demonstrates the technology is safe
dbg   4/2/2013 3:53:44 PM
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On the contrary, you probably should worry about gasoline cars "blowing up" given the statistics. See http://www.nfpa.org/assets/files/pdf/vehicleexecsum.pdf - there are an average of 287,000 vehicle fires in the USA every year, causing an average of 480 deaths.  Three quarters of these fires were caused by mechanical problems.

It's precisely because of engineering the battery systems properly that these systems can be made very safe.  Now I don't know if Mitsubishi battery packs are as safe as Tesla's, but you can be sure their engineers did not take a cavalier attitude to safety.

 

Phil Pearce
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Re: Definitely not good news
Phil Pearce   4/2/2013 3:23:58 PM
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Thermal runaway refers to rapid self-heating of a cell derived from the exothermic chemical reaction of the highly oxidizing positive electrode and the highly reducing negative electrode. In a thermal runaway reaction, a cell rapidly releases its stored energy. The more energy a cell has stored, the more energetic a thermal runaway reaction will be. The reasons lithium-ion cell thermal runaway reactions can be very energetic is these cells have very high-energy densities and these cells contain flammable electrolyte, and thus, not only do they store electrical energy in the form of chemical potential energy, they store appreciable chemical energy in the form of combustible materials.

If one cell in a pack undergoes a thermal runaway reaction, typically in the 70 to 90°C (158 to 194°F) range, it is likely to cause thermal runaway in adjacent cells by way of various heat transfer mechanisms: direct cell-to-cell contact, impingement of hot vent gases, or impingement of flaming vent gases.  My work on understanding lithium-ion cell faults has shown that prior to any temperature rise leading to the onset of thermal runaway the cell or cells begin to swell or balloon, by discovering a practical method of detecting this physical deformation at an early stage we have developed a system that is able to respond, before any temperature rise is detected, and prevent thermal runaway or any further reaction or combustion ever taking place.   

phil.pearce@ieee.org

Elizabeth M
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Re: This actually demonstrates the technology is safe
Elizabeth M   4/2/2013 6:11:47 AM
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Well I understand this opinion, dbg, but if this happened on a larger scale, it could be really dangerous. I don't think those who manufactured the products this happened to have such a cavalier attitidue. Of course, gasoline-filled vehicles perhaps are more dangerous in general, but the engineering is such at this point that we don't worry about gas engines just blowing up randomly. I'm sure once these batteries are fine tuned, we will feel the same way about them. For now, there still has to be some effort taken to do this.

naperlou
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Re: Definitely not good news
naperlou   3/31/2013 9:26:20 PM
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jmiller, good point about this not being caught in testing.  These events do not happen often, but they could be catastrophic.  There was an incident in China, with an all electric taxi, where the taxi was hit by a ICE powered car.  The battery in the taxi caused a fire that killed the driver and passengers immediatly.  The other car drove away.  In China they do a lot less testing.  On the other hand, even with the more extensive testing done in the US and Japan, the failure modes with this technology may be hard to stimulate.

jmiller
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Re: Definitely not good news
jmiller   3/31/2013 12:00:21 PM
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It's too bad that not only will the media paint the picture wrong on what the cause was.  But the general public will swallow the story hook line and sinker.  Often I wish there were a design news TV station that could report the facts of what happened and let us determine the truth.  Probabluy not coming any time soon.

jmiller
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Re: Definitely not good news
jmiller   3/31/2013 11:53:58 AM
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Good point.  The statement that the fire had to do with the battery system may be the most accurate.  While the fire wasn't caused by the battery it was in fact caused by the battery system.

jmiller
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Re: Definitely not good news
jmiller   3/31/2013 11:50:10 AM
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I agree there is quite a difference between a fire on the ground or at 40,000 feet.  I guess that's why the design requirements are so stringent for aeronautical components.  However, it would really stink to have ones car catch on fire while doing 70.  Perhaps I missed it or I'm a little confused, is the fire issue contained to accidents or during everyday operation?

jmiller
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Re: Definitely not good news
jmiller   3/31/2013 11:42:55 AM
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I am concerned that a company could get to the point of having to recall something like this.  How was it not caught in testing?

dbg
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This actually demonstrates the technology is safe
dbg   3/30/2013 1:42:15 PM
So a few cells burned, but the fire was contained and did not propagate.  The vehicle was not destroyed.

Compare that to 100,000 gasoline vehicle fires in a typical year in the USA.  Now tell me what kind of car you'd rather be driving... one full of dangerous flammable fluids and vapors, or one with well-protected and contained LiIon batteries?

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