Stanford boffins snuff out li-ion batt blaze risk The explosive side effects of overheated lithium-ion batteries have long been documented, and have caused everything from groin burns to the suspension of Boeing 787 flights. Now boffins at Stanford think they have the answer. If the electrolyte within a battery reaches 300 degrees Fahrenheit (150 degrees Celsius) then it can …
The user can also suffer serious long term injury or death in severe cases from a Lithium battery in thermal runaway due to the HF generated.
When you have a battery "fire" (ie, the amount of hydrogen being forced out through the hole in the top of the cell at pressure high enough to self ignite) then you also get other nasty stuff coming out of the battery cells such as fluorine. hydrogen + flourine = hydroflouric acid, which melts glass and is otherwise quite dangerous. From the small print in the Material Safety Data Sheet:-
"Hydrofluoric acid is extremely corrosive. Contact with hydrogen fluoride fumes is to be avoided. Permissible exposure limit is 3 parts per million. In case of contact with hydrogen fluoride fumes, immediately leave the area and seek first aid and emergency medical attention. Symptoms may have delayed onset. Fluoride ions penetrate skin readily causing destruction of deep tissue layers and even bone. Fluoride interferes with nerve impulse conduction causing severe pain or absence of sensations."
A cautionary tale is here, which is equally applicable to many of us who deal with things such as laptops that catch fire through battery fires (releasing HF in the smoke):-
http://www.candlepowerforums.com/vb/showthread.php?141137-Inhaled-vapors-from-battery!!!
I'm fully in favour of every possible safety precaution that human ingenuity can devise when dealing with something this nasty!
Might explain why I was sick for weeks after trying to harvest some copper foil from a couple of defunct Lipo's, symptoms: wheezing, nausea, headache, coordination problems, etc
Presumably exposure to fluoride even though the cells were dismantled under water could do that, yet another hazard to e-waste handlers.
"The Register needs a battery invention comment icon, and can finally retire that Paris Hilton one"
Well yes but first they'd have to admit they, uhh, seem to have lost the key to the server room, along with the admin password - in fact all the hardware has just been cruising along unattended for a while now...
Isn't this pretty much how the tried & tested polyswitch fuses work, and I've seen those embedded in battery packs many times.
http://blog.circuitprotection.com/automotive/the-anatomy-of-a-pptc-device-and-why-its-different-than-a-fuse/
They trip with external heat, as well as heat caused by overcurrent.
Maybe the new stuff is cheaper? Still doesn't seem to address within-cell failures, which are the most exciting ones.
Petrol catches fire easily and can explode. Easy to fix: replace petrol with wax cubes containing water. Your car can puncture the cubes one at a time to let out the water, then burn the wax in a steam engine. Perfectly safe. If there is an accident that dumps the contents of the fire box onto the fuel, sufficient water will be released to put out the fire. As an added bonus, the fuel weighs so much that the top speed of a car is unlikely to be much above walking pace and that will reduce the number and severity of accidents. The maximum altitude of aircraft would be reduced to a few centimetres (think hovercraft) so aircraft would no longer be able to fall out of the sky.
The big advantage of petrol is that it contains lots of energy with little weight. Over the years, the energy density of batteries has improved to the point that they can be used in situations that used to require petrol. The down side is that such useful batteries require precautions similar to petrol to avoid fires and explosions.
Battery overloading was solved a long time ago. There's a limiter PCB on battery packs to ensure that voltage, current, and temperature stay within short-term safe operating limits. If that fails, there's a polyfuse (conductor particles in an expanding polymer) to break the connection while the combination of heat and current is too high. The final and non-reversible protection is a porous boundary layer in the battery that is supposed to convert to a solid barrier when heated.
LiPo batteries still catch fire for other reasons. The voltage needed to reach 100% charge becomes fatal after being applied for a few extra hours. Contaminants and physical damage can burn up the battery from the inside. The battery contains enough energy to melt itself free of lightweight protection schemes like aluminum foil wraps and laptop cases.
" The battery contains enough energy to melt itself free of lightweight protection schemes like aluminum foil wraps and laptop cases."
I bought some garden fence solar lights that have a single button Ni-Mh 1.2v battery of probably 40 or 80 mah. One day I noticed one was no longer working. It had a neat hole burned straight through the bottom of the clear plastic cover. It was the same size as the outer case of the button battery that was now lying on the ground.
It appeared a fault had generated enough heat for the battery to disintegrate - and for the falling outer shell to then burn through the lamp's plastic case.
Jury rigging an AAA Ni-Mh battery has worked with no problem - so the fault appeared to have been purely down to the button battery.
does that mean my "hoverboard" won't burn my house down when I charge it, and fall asleep?!
( IDK about the rest of the world, but on this side of the puddle, we where "suggested" not to charge that damn thing over-night/fall asleep during charging. A few house fires where linked to that effect.)
A good article, and an interesting and simple technique to prevent the overheating. Hopefully someone smart will get this into production samples sooner rather than later.
But just one thing... why on earth are we STILL using those bloody fahrenheit things in articles? Honestly, while I appreciate we still have older folks who do still know them, given the fact they're on a tech site you'd think they'd be a little more savvy with the current universal standard.
Right, off to improve my mood with tea and a bacon sarnie.
The problem isn't actually the batteries directly, the charging circuitry is poorly designed and also the batteries get bashed around during shipping due to lack of foam and separator pads.
Its only a matter of time before a sharp edge (typically a badly placed connector strip) pierces a cell.
I had a look at one the other day (expen$ive named brand) and though it does have a balance board only two of the wires are hooked up so in theory the middle cell could overcharge if the one next to it wasn't perfectly matched.
Also they should really have a timer as well so if T> typical 25-100% charge it turns off until user intervention.
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