Sunday, October 16, 2016

Finally, we know why the Note 7 exploded.

The answer, according to the New York Times:  Samsung seems to have packed it with so much innovation it became uncontrollable”.  Apparently phone components are like 4-year olds; put 3-4 of them in a room and they are ok, but pack 10 of them in a small place they will destroy the room with all the energy feeding off of each other.  Of all the theories, this one takes the cake. 

As much as I think the community should not be speculating on the underlying case of the explosion, I think we can’t help ourselves.  For battery types, this is the most interesting event that happened since the-last-time-there-was-a-fire, so we are all salivating.  What can I say: we don’t get out much. 

For non-battery types, I can see their need to know if more phones are going to be exploding.  Only way to know is to understand what happened with the Note 7. 

I have been getting this question steadily the past few weeks, so I thought I would collect all the speculation in one single place.  I also provide my views on this.  So here goes:

1. The battery was overcharged (BMS failure, too high an upper cut off voltage, aliens, whatever) and hence the fire.  I think the eager ones among us, who do not believe in waiting for more information, speculatively stated this.  I think Samsung’s revelation that there was a manufacturing flaw negates this theory.

2. Samsung used a 6 um separator in the battery and this lead to defects when assembling with a thin separator. This in turn led to shorts and the explosions.  As I explain below, this may be part of the story.

3. The battery had a manufacturing defect where the anode and cathode did not line up correctly, leading to edge effects, lithium plating and shorting.  This seemed very likely until the New York Times article came out. 

While these three issues are obvious ones that most battery types would guess, the New York Times articles makes the point that after initially concluding that it was the battery, Samsung realized that it was not that simple.  The article claims that Samsung could not pinpoint the reason!  Hence the wacky statement about “uncontrolled innovation”.

Let us be clear: Samsung makes great batteries. ATL makes great batteries.  If this were an obvious issue, they would have caught it after the first few weeks.  There is something to be said about the argument that this is a more complicated problem.

Since the Times article came out, we have had three more, system level, theories that have popped up.

4. The battery was being fast charged due to a chip design flaw.  Faster than it was rated for. This lead to overheating, thermal runaway, ending with you-know-what.  I’m not so sure about this.  The Note 7 phones were exploding even when not fast charged so…

5. There was so much being packed in a small volume that the battery was getting squeezed and the edges pinched, unintentionally, leading to shorts.  This theory does seem possible, but I like the theory below (which is a variant) the most. 

6. Samsung used higher content of silicon in the graphite-silicon blended anode.  The silicon expands on charge and swells the pouch.  Because the pouch was unable to swell in the phone due to the lack of space, it shorted and exploded.  I really like this theory.  There have been problems with battery swelling even before silicon came to the scene, but this has only gotten worse with silicon-graphite anodes.  Many consumer electronics companies have been worried about this and have a spec. for how much the battery can expand.  According to Mashable, the Note 7 had a 750 Wh/l battery; which is PRETTY energy dense.  Much more so than previous generations of batteries, suggesting higher silicon content than before. 

It is possible that higher silicon content combined with a thinner separator and less space in the phone for volume expansion all came together to lead to shorts and fires. 

I’m sure I’ve missed a few other theories (aliens?), but I think I got the majority of the ones I have heard.  

Now that we have that out of the way, let us talk a bit about what this all means. 

I think the initial speculation that this was a battery-level issue appears too simplistic.  Clearly, there is more to the story.  Batteries all over are safe, have been safe, and will continue to be safe.  Assuming you know what you are doing.

But what if you have “uncontrolled innovation” happen again? What is a poor battery to do if the overall system does not want to treat it kindly?  Li-ion batteries are energy storage devices.  Meaning, if you release the energy very very fast it is not going to be pretty.  So, some TLC is in order. 

But even if the system screws up how it handles the battery, shouldn’t the storage device itself be made to withstand any abuse?  As we move toward wearable technology with things attached to every part of our body, we need to ensure that the battery remains robust even if there is a system-level failure.

There has been a narrative going around that Li-ion batteries today are similar to where crystalline silicon solar cells where a decade ago: meaning, the prices are dropping and one can get installers and system integrators to come in and start to make them ubiquitous.  The Note 7 incident shows the perils of this thinking. 

Batteries are not plug and play devices where Jane-solarinstaller is going to buy something off of Alibaba and dump it in your garage and get you city permit folks to sign off as if they are inspecting your plumbing.  We better be buying from someone who knows how to make them well.  And we better know how to design the system correctly, install them well, and control them through the life of the device.

But to get the world where we do treat our batteries like we treat our microwave (bang on it to try to get it working?), we need the batteries to be robust inside out.  This requires a separate blog post, hopefully, in the near future.  

In the meantime, with the Note 7 off the streets, time for the battery folks to crawl back to the cave and focus on achieving a few breakthroughs.  Until the next incident… 


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