back to article Boffins hose down fiery Li-ion batteries with industrial lubricant

As Boeing and Tesla both know, if you mistreat a lithium-ion battery, it can start a fire – which puts a premium on the search for non-flammable components. Now, US researchers say they've found a candidate electrolyte in an unexpected place. When they're overcharged or overheated, the electrolyte in lithium-ion batteries can …

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Anonymous Coward

what about over discharge ?

This also causes thermal runaway and fire. All you need to do is short out a li-on cell in any charge status and wait for the fireworks...

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Re: what about over discharge ?

If you want a device that can provide high current at a reasonable voltage, it's going to capable of fireworks if you short it -- Don't Do That, Then.

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Anonymous Coward

Re: what about over discharge ?

"it's going to capable of fireworks if you short it"

My bad for using the word fireworks - I mean it will catch fire in exactly the same way has when it's overcharged. Obviously not something you do on purpose, but mechanical vibration that causes an internal short on a discharged battery ? Quite a realistic example.

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Re: what about over discharge ?

If a mechanical short can be caused inside a battery purely by vibration, I'd suggest it is not a good design for a battery. Most use cases for batteries are in devices that are either portable (and can be subject to external vibration) or for devices intended to port themselves, like electric cars, which vibrate as part of their normal usage. Don't Design Them Like That.

A external mechanical short across the terminals is a recipe for fire regardless of how hot the battery gets itself; the shorting conductor will heat up as it carries current, and is thus a fire risk itself, independant of the method of providing current. Don't Short Them At All.

12V lead-acid car batteries live in heavy vibration environments, and have a high current capability. They don't internal short despite being inches from internal combustion engines, and are perfectly capable of starting fires with external shorts. These existing cars also contain a lot of rubber and plastic (not to mention diesel or petrol) that once lit continues to burn, and produces noxious fumes, so overall I don't think a rack of (well designed) Li-ion batteries in an electric car is, specifically, more of a fire hazard or health hazard than any other car on the road.

YMMV of course, but I happily drive a car with explosive liquids contained in the fuel tank; changing that for potentially explosive batteries is simply a change of risk, not specifically an increase in risk :)

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Re: what about over discharge ?

No: what over discharge does is cause overheating. Overheating typically causes puffing BUT it wont cause FIRE unless the electrolyte catches, and in this case presumably it wont.

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Re: what about over discharge ?

I have to repeat. Its not just the fact the battery gets HOT its the fact that the electrolyte is highly flammable.

That turns a bad situation into a disaster

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Boffin

Re: what about over discharge ?

What over-discharge does, is it causes the copper electrode to dissolve (Below about 2V for normal Li-Ion tech). If you then recharge the cell, the copper is re-deposited. However the copper is not re-deposited evenly - it tends to grow dendrites because the surface charge is higher at the peak of the dendrite, causing more copper to be deposited there than elsewhere.

Over subsequent charge-discharge cycles, the dendrite(s) tend to puncture the insulation between the positive and negative electrodes and cause a leakage path for current. If the dendrite heats up too much, it may start off a chain reaction. Most Li-Ion cells use a cobalt based chemistry, which enters thermal runaway above about 150°C, or about 100°C if the cell has been abused. IMHO if the electrolyte is inflammable or not doesn’t make much difference if the cell electrodes are thermally degrading at approx. 2000°C

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Joke

Splendid...

...it also stops barnacles accumulating under your laptop.

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Pirate

Re: Splendid...

barnacles accumulating under your laptop.

Aye! That were a painful visit to the sawbones and no mistake.

Shiver me timbers!

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So......

Not Plumbers Tape For Everything but Prevent Fire Protect Everyone

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Facepalm

You sort of wonder why no one looked at this before

It sounds cheaper than the stuff people are using at present.

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Re: You sort of wonder why no one looked at this before

Isn't there always the odd anecdote of how discoveries were made that seem somewhat obvious in hindsight. It's likely a product of unintended cross pollination of different groups working with different materials for different purposes. I can picture one of the researchers popping in to the aerospace department to chat about batteries on some high altitude test rig when they accidentally sit on an open tube of Krytox and ask "what the hell is this shistuff?" - Viola!

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Facepalm

two minutes too late

I have a spelling checker... that obviously doesn't have a French dictionary.

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Trollface

Re: You sort of wonder why no one looked at this before

Two chemists on a train heading to a conference on organic polymers.

One notices the other playing with a lump of flexible material "That looks interesting: may I see?"

"Sure, here you are"

"Hmm flexible, elastic..How did you make it?"

"Oh I just wiped my hand across my nose, and there it was ...."

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Anonymous Coward

Great up to 200 degrees C then what?

The SDS for this stuff (assuming it's similar to the Dupont Krytox used on boats) is nasty.

<http://www.3eonline.com/ImageServer/NewPdf/39630143-0cff-454a-aa0f-d273aafe18c4/396301430cff454aaa0fd273aafe18c4.pdf>

It doesn't burn, yes, but it decomposes into fluorinated compounds around 300 degrees C. Nothing you want to breathe for anything resembling a period of time. Lung injury isn't apparent for several hours, which is going to make emergency rooms all over nuts when dealing with electric car accidents. Never mind the cancer risk from the sodium nitrite. When applying it to ship/boat hulls you're extremely careful.

Don't get me wrong, I'm all in favor of improvements in technology, we just seem to always do it with the nastiest stuff around.

AC since the employer uses this stuff all the time.

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Re: Great up to 200 degrees C then what?

> assuming it's similar to the Dupont Krytox used on boats

That's a big assumption to make.

As far as I know, PFPE (perfluoropolyether) is relatively inert and non-flammable.

Also, sodium nitrite is not carcinogenic, although that fact has no significance to the article.

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Re: Great up to 200 degrees C then what?

While you make some valid points, there is risk in anything. Once something catches fire, all bets are off and I don't care if it's your house/apartment, automobile, laptop, etc. Part of the technology of anything seems to be that when it burns... the output is bad. The only other option is to use wood or rock for everything... but then again, wood burns and discharges some potentially bad things.

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Re: Great up to 200 degrees C then what?

Again the point is whether it makes a bad situation worse with an exothermic reaction. Normal polymer electroilytes do exactly that.

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Anonymous Coward

Re: Great up to 200 degrees C then what?

Most commercial PFPE lubricants, particularly those used to coat seagoing vessels from becoming encrusted with various forms of sealife, as noted in the article, are Krytox variants. By variants I mean they are made and owned by Dupont and are sold under the Krytox name.

Yes, PFPE is relatively inert, and yes it does not burn. It does however decompose at 300 degrees C into various nasty gases, which is the point I was trying to make.

With regards to sodium nitrate; it makes up a chemically significant percentage of Krytox and is marked as having mutagenic effects in fairly low doses. My mistake in calling it out as cancerous, although I fail to see how it being mutagenic is much improved.

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Re: Great up to 200 degrees C then what?

But does it matter for PFPE's use as an electrolyte? There's obviously sodium nitrate in Krytox, but will it be in PFPE mixes used for battery electrolytes? If it doesn't, then what it does is irrelevant because batteries won't contain any.

As for the gases it decomposes into, yes, nasty stuff. But if your battery is 300 degrees celcius your car is probably on fire and if your car is on fire, there are plenty of other materials in the car that emit nasty noxious fumes when they burn. At least with this electrolyte, your battery won't burst into flames at significantly lower temperatures.

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Re: Great up to 200 degrees C then what?

First, you have to heat it to a temperature that causes it to decompose. That happens to be 100 degrees C higher than its maximum rated temperature.

Second, that you think that the common food ingredient, sodium nitrite is a carcinogen shows us all that your knowledge of chemistry is woefully lacking.

Especially since sodium nitrite has no carcinogenic potential, but nitrosamines do. The fix for that? Don't overcook or burn, then eat meat cured in sodium nitrite. Or add vitamin C, vitamin E or a similar antioxidant to the meat when curing it.

As an addendum, there is a big difference between one compound and a paint containing it in terms of toxicity, decomposition due to thermal extremes, etc.

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Re: Great up to 200 degrees C then what?

By the time the electrolyte begins to decompose and release fluorine compounds, the battery case itself has already been decomposing into phosgene and cyanide compounds. Both of which are equally nasty, with phosgenes actually having similar symptoms of lung injury minutes to hours after exposure.

Of course, if your vehicle has a fire under the bonnet, most people tend to rapidly depart the vehicle! If unconscious, most bystanders remove the unconscious person from the potentially soon to be immolated vehicle.

When you add in the paucity of electrolyte in a battery compared to everything else that is flammable, your concerns are unwarranted. Just as a concern about breathing in hydrogen gas from a lead-acid cell decomposition and having it ignited by an electrical fire isn't of concern in a motor vehicle battery malfunction.

The ones to worry about would be workers in a battery plant, maintenance workers and others who may be occupationally exposed to much higher concentrations than someone would be in a casual accident or malfunction of a single device. In an enclosed space or with dozens to hundreds, the exposure that was miniscule suddenly is severe.

But, that is what risk analysis and risk mitigation are for.

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Hardware bloat

Nobody in the process seems to have noticed that PFPE is over twice as dense as typical hydrocarbon polymers. There goes the weight advantage of Li-ion.

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