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Coating Stops Exploding Batteries

Thermal breakdown beat at a cost
11/10/2016 11:18 AM EST
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R_Colin_Johnson
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Re: Couple of minor errors
R_Colin_Johnson   11/13/2016 12:23:40 PM
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Thanks for the clarification--of course there is a single eledtrolyte in a dead Li-Ion battery, but when charged the migratin of cations and anion distinguish then plus there are many types of batteries with different types of electrolyte chemistries on each side of the separator. Thanks again for your clarifications regarding the details of thermal breakdown.

gmorita
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Couple of minor errors
gmorita   11/12/2016 2:03:06 PM
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Colin,

There are couple of minor errors in your article.

1) There is only one electrolyte in (almost) any battery.

Older rechargeable battery chemistries such as lead acid or NiMh used aqeous electrolytes like sulfuric acid or potassium hydroxide.  These are high corrosive but not flammable.  In the case of Li-Ion, the electrolyte is a lithium salt dissolved in an organic solvent such as ethylene carbonate or some similar compound since lithium reacts violently with water.  Unfortunately, these organic salts are also highly flammable.

2)  The separator is used to keep the anode and cathode (not electrolytes) from touching, thus preventing internal short circuits.

The separator has to be permeable allow the transport of lithium ions within the battery.  Therefore, the separator has to be very thin (~0.001") and have numerous pores (milions per square inch).  The design of the separator is such that if the battery overheats, the separator melts and seals the pores thus shutting down the battery.  Unfortunately, this process only works to a point.  If the amount of energy dissipated in the battery is high enough AND fast enough, the separator cannot adequately seal the pores fast enough and the battery goes into thermal runaway.

 

The reason why Li-Ion batteries catch fire is that the battery cathode material is a Lithium metal oxide.

These metal oxides, however, are thermally unstable, some moreso than others.  They all decompose at high temperatures to release oxygen.  This is similar to the thermite reaction in whcih a metal oxide such as rust reacts with a powdered metal like aluminum to release molten iron (Mythbusters did a whole show on this).

Once the thermal decomposition temperature in the battery is reached there is no way to stop a thermal runaway since the released oxygen is in intimate contact with a fuel (the electrolyte).  Fire rapidly ensues.  Of course then the battery bursts and the electrolyte is free to burn in the air.

 

This new technology sounds like it mitigates the thermal decomposition of the cathode by trapping or binding the freed oxygen thus preventing a reaction with the electrolyte.  Hopefully we'll see this incorporated into new battery designs in the near future.
 

dt_hayden
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Re: Age of lost derating factors
dt_hayden   11/11/2016 11:19:20 AM
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Colin,  Can you provide some pointers to the root cause of the Samsung battery faliures?  I haven't seen anything anywhere until your post.  Thanks.

R_Colin_Johnson
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Re: Age of lost derating factors
R_Colin_Johnson   11/11/2016 8:43:32 AM
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Samsung just pushed the "cheaper" envelope too agressively. All they would have had to do was make the separator twice as thick as is the case with all successful Li-Ion batteries, but their simulations told them a slightly different formulation could be hallf as thick while providing the same protection. Simulations are one thing, but field testing on consumers costs more than its worth, not only in $, but in brand loyalty.

MWagner_MA
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Age of lost derating factors
MWagner_MA   11/11/2016 7:36:42 AM
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I"m not sure when this happened, but more and more I"m seeing designs and speaking with engineers completely unaware of the concept of derating factors.  I applaud any updates to Li-ion technology that can make it safer, but what about all the millions of other battery applications that got it right?  Were the batteries that Samsung used that inferior?  I doubt it.   If a spec for Max current (charge) is X, it doesn't mean you design the circuit for X continuously!  You must account for items you may not take the time to calculate to the nth degree - you need some margin for error.  Just because engineers are not working on Military contracts, doesn't mean the reliability engineering honed there isn't applicable in the commercial sector.  Pushing a design in blind pursuit of "innovation" and performance will never produce lasting value for the customer.

R_Colin_Johnson
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Re: Lawsuit waiting
R_Colin_Johnson   11/10/2016 6:57:21 PM
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These guys really believe their coating could have prevented the Note 7 from being discontinured, but of course that is pure speculation (of course they would say it is faith in their process).

resistion
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Lawsuit waiting
resistion   11/10/2016 5:29:06 PM
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Never brag hindsight safety before proof, it is a litigation trap.

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