back to article Li-ion batteries blow up because they breed nanowire crystals

For the first time a group of scientists has captured close-up images of mysterious finger-like growths known as dendrites that can lead to short circuits and fires in the lithium-ion batteries that power hordes of smartphones, laptops and other gadgetries. By using cryo-electron microscopy (cryo-EM), researchers from Stanford …

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Coat

On the upside. A new way to make Lithium nano wire in various chemistries.

Cryo-EM sounds like a winner that's got lots of directions to go in. It's one of those obvious-when-you-think-about-it-but-no-one-did ideas (then making it work reliably was probably an absolute bu**er to get right).

" By flash-freezing the batteries at different points of its charge and discharge cycle, "

Sadly dunking your overheating cell in a convenient LN2 tanks does not sound like a viable solution.

However. the games not over for Li ion. Obvious strategies are physically stronger separator membranes and some kind of chemically reactive coating to disrupt their formation, or a treatment of the electrode surface to prevent dendrite formation being energetically favourable (which is the usual root cause of this).

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Anonymous Coward

Re: On the upside. A new way to make Lithium nano wire in various chemistries.

... a treatment of the electrode surface to prevent dendrite formation being energetically favourable (which is the usual root cause of this).

This is indeed the root cause of the problem: the bulk-phase lithium is more thermodynamically stable than Li nanoparticles, which have higher surface area. In order to stabilize the nanoparticles, you need to reduce the surface energy by adjusting the electrolyte composition. But, you can't just go all the way and make the surface free-energy negative - this would cause the nanoparticles to dissolve altogether, which is not that you want. So, you can't completely eliminate dendrite formation, but you may be able to slow it down to the point where the lifetime of the cell is determined by other factors.

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Trollface

Re: On the upside. A new way to make Lithium nano wire in various chemistries.

So, uh, a safe, reliable battery is merely ten-twenty years away...?

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Re: On the upside. A new way to make Lithium nano wire in various chemistries.

CryoEM in terms of the preparation of samples has been around for decades. I did thin section EM for my Honours and PhD back in the '80s but others were cutting ultrathin frozen sections but they were not frozen when in the beam. Also those studying synaptic nerve transmission would stimulate nerves then at high speed immerse the whole thing in isopentane slurry.

LN2 is not the best for quick freezing. What happens is a layer of gaseous nitrogen forms around the object and insulates it. So you get a fast frozen outside and an inside that freezes more slowly not good. So you freeze isopentane in the LN2 until it is a slurry and you freeze stuff in that.

But keeping the sample frozen in the EM, that is nice. At least in the vacuum you don't have to worry about condensation.

We used to put our sections on slot grids covered in a thin formvar film. If you went to too high a mag for too long you could burn a hole through your section and the formvar. Then you watched as edges of the hole expanded and ruined your sample. Survey at lower mag, focus down, take a picture, get out again.

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Anonymous Coward

Nominative determinism

Mr Li studies Lithium.

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Die -- lithium crystals!

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Please stop warping words...

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ion Li agree because I'm in a good mood.

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Boffin

How do they know that the crystals are not formed by the Cryo EM experience? I don't mean to be snarky; I'm sure they accounted for it, but just interested.

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Actually this kind of "dendrite" are a well-known cause of short circuits in electronics; similar-ish structures form from solder (especially lead-free solder), for example. The cryo-EM here is just a mean to "fix" the structures at various points of time, since dissassembling the batteries at room temp would probably destroy them.

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Tim whiskers

"Actually this kind of "dendrite" are a well-known cause of short circuits in electronics; similar-ish structures form from solder (especially lead-free solder), "

Tin whiskers, why modern electronics (one of the reasons perhaps) are less reliable.

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Re: Tim whiskers

in early 'pit' training at the world's first wireless factory (Marconi0 where I did my 3 month training course in how to solder, one of the super advanced anti-dendrites ideas required for mil-std radars in those days was to de-gold the electronic component terminal wires; 2N3866 etc were usually CBE leads fully gold plated, and we were required to dip them in a hot solder pot for a second, to 'tin' the gold plate with real Sn/Pb and remove enough gold which was recycled to later buy a racehorse, apparently.

For the generic Li batt dendrites, didn't some other researchers come up with "nano-aspirin" style self-repair mechanisms to counter the various failure modes - I suspect those modes didn't yet include dendrites.

Finally, is this why (insert famous electric car name) limit their batteries with firmware to 80% charge, also just noticed that that other famous sports car manufacturer (Doctor Engineer Ferdinand famous name) wishes to have fully electric supercars to do 200 kilometres range then recharge at a 300kilowatt charging station (in 15 minutes whilst you sip tea)

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finger-like growths known as dendrites

Seems to be an issue with EVERY rechargeable cell except Lead Acid? Not sure about Nickel Iron (obsolete) or Silver Zinc (used 1950s Military in USSR, too expensive.)

With NiCd, a quick pulse from a car battery (very dangerous!) could destroy whiskers.

AF117 transistors suffered from tin dendrites/whiskers growing in the gel and shorting the transistor. They will even grow in air if there is the right conditions and too much tin plating.

So no surprise that Lithium cells recharging suffer from this.

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Re: finger-like growths known as dendrites

Indeed.

We pretty much rely on the fact that metals will gravitate towards a charged pole for things like metal-plating and other uses.

The fact that they do it when we DON'T want them to is also true, and the more power involved, the more they will grow.

I'd be more worried about what this means for those second-hand electric cars with lithium batteries in 10-20 years time if they aren't replaced regularly.

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Anonymous Coward

drones to Dreamliners

"So no surprise that Lithium cells recharging suffer from this."

May not be a surprise to you, and others equally well informed, and now it's pointed out I remember it too from my days working at a mil-spec electronics outfit, but this kind of behaviour seems to have been unknown, or forgotten, or ignored(?) by various people with an interest in using Lithium batteries in various sizes of novel applications, from drones to Dreamliners, and more besides.

I didn't realise a related behaviour affected AF11x geranibum transistors. I used to have some of those in my Philips Electronic Engineer kit.

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Nickel-Iron

Ni-Fe batteries aren't obsolete but they are heckuva expensive for some reason. They have a market niche for static long-term operation (decades or more) and they have good charge and discharge characteristics, they can be discharged repeatedly to zero without taking damage. However they cost ten times as much as Li-ion and they're bulky and heavy so they don't fit the mobile and vehicle markets which is where the money and research is currently going into.

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Re: Nickel-Iron

You get really bad alkaline burns if they leak. Used to be used by some cavers - now superceded by lithium.

Phil.

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Re: finger-like growths known as dendrites

On the plus side, cutting the screen usually got a bit more life out of old radios until a replacement AF117 could be bought.

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Happy

What a promising technique

"Cryo-EM involves freezing the dendrites in liquid nitrogen before thinly slicing them to view under a microscope. By flash-freezing the batteries at different points of its charge and discharge cycle, scientists can see how it changes over time."

This technique has so many possible applications. Think of the things we'll now be able to study in detail by flash-freezing them and then thinly slicing them. Politicians come to mind.

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Joke

Dendrites.... ummm....

Aren't those the things which are inside our brains? Are we sure that Siri, Cortana, etc. really are dumb logic processes in the cloud and aren't really alive in our pockets?

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Re: Dendrites.... ummm....

"Dendrite" simply means anything roughly tree-shaped. And when you think how fundamentally natural such a tree shape is, it's unsurprising they are ubiquitous.

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Pint

A double-whammy of success

"Every time we tried to view lithium metal at high magnification with an electron microscope the electrons would drill holes in the dendrite or even melt it altogether”

So, not only do they now know how to view them, they also know how to prevent dendrite problems occurring.

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Re: A double-whammy of success

So, not only do they now know how to view them, they also know how to prevent dendrite problems occurring.

If you include an electron microscope in every battery, sure. ;)

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With NiCd, a quick pulse from a car battery

Did this a few times, great fun; however suicide was not an option, you we did it in the middle of the carpark with a 25 meter extension lead.

Saw someone do it with a car battery once; took several inches out of the FLOOR in an industrial building; despite the battery starting off sat on a tea trolley.

(Also took out much of the interior and all the windows).

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Re: With NiCd, a quick pulse from a car battery

Yep. People vastly underestimate the stored power of a car battery. And then you look at things like lorry batteries and - yeesh - electric fork-lift power banks.

My dad - before the days of health and fecking safety - once teamed up with a small gaggle of fitters in his job and, from a distance, put a spanner over an old, decrepid fork-lift with lead-acid battery pack. They did it from an improvised bunker further down the warehouse.

I'm told that, after the spanner turned red, then white, then started to bend, the explosion was quite impressive and they were still cleaning battery acid off the ceiling of the industrial aircraft-hangar-sized warehouse for weeks afterwards.

There's a reason my dad told me never to mess with a car battery. And why the fitters kept a large 4x2 wooden post nearby if anyone was working on the underside of the 18-ton lorries with their stupendous batteries. DC electrics make you grab on so you can't let go. You only need the right combination of metal spanner, wet hand, hanging onto the wrong point while in a confined space, etc. and it could go very wrong.

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N2

Re: With NiCd, a quick pulse from a car battery

Agreed, often underestimated the large current a battery as such can deliver

8400 A/Hr @ 250 V DC the biggest battery Ive worked with & you'd only mess up once...

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Unhappy

"They did it from an improvised bunker further down the warehouse."

Which probably explains why they all lived through it.

When you have a sufficiently low resistance path between the two sides of a supply it's amazing how much current can be sent from one side to the other.

And what it can do to anything between.

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Re: When you have a sufficiently low resistance path

IN the battery!

Which is why some cheap toys warn you NOT to fit rechargeable batteries. A short on Zinc Carbon runs it flat. A short on alkaline might melt covering on the wiring. A short on AA NiCd or NiMH sets the plastic case on fire due to the wires going like a toaster element.

Shorting a larger lithium cell or stack of cells can be explosive. Say twenty CR2032 tightly stacked.

I'm not sure how good an idea the single use lithium based cells and batteries are designed to replace Alkaline or Zinc Carbon in consumer electronics.

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Boffin

I think this discussion thread has more materials engineering data than my latest Advanced Materials & Processes journal. Thank you for an enjoyable lunchtime read.

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When I were a lad...

I was fascinated by the results of adding crystals of various types to a jam jar filled with Water Glass to produce a Chemical Garden.

https://en.wikipedia.org/wiki/Chemical_garden

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"Green Prince of Darkness" at FauxScienceSlayer

There are physically limits to photovoltaic and chemical storage 'solutions'

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