All Battery Chemistries are dangerous..

[steveo]

Hey Everyone,

I've been testing some lipo battieres at home on my megapower 960-sr charger; and have also been reading up on the bad rep for lipo batteries. I am not a battery expert just fyi for everyone before a blab on more on this topic...

I entirly agree that lipos are dangerous if overcharged.

But i think the same type of theory goes for any battery; I've just seen in another post a set of 7s a123's exploding when they are suppose to be fireproof, what is believed to have happened is they shorted on a charger that was off; Also in the post there was even a set of nickle metal hydrate cells that exploded probably from what i read; was some nimh cells can't be trickle charged while the owner did and the cells exploded.

I'm gone throw a long shot on this, but i think every battery chemestry is completly safe including lipo if:

-Charged properly; according to battery type
-Not discharged past its continious c rating
-battery pack should be secured properly and protected from any shorting
-several fuses should be used built into the battery pack (ex lipo pack) to reduce the likleyness of a short occuring

I'm just upset with the rep lipos get, If you go on youtube and type lipo explosion; every explosion is pertty much garrentted to be by purposly overcharging; shorting; stabing the battery.

I have yet to find and if you do post the link of a perfectly fine lipo cell exploding on a proper discharge or charge cycle (with a proper working charger).

I also quote this from stew007 from anther about battery bike explosion

"by stew007 on Mon Feb 02, 2009 11:33 am

Nasty, all packs should be fused, lipo or otherwise, this looks like a dead short has happened somewhere. A fuse should prevent this sort of thing.

also if this turns into a lipo bashing tread, to keep this in perspective, be aware of the dangers of all batteries, Nimh and Nicad are particularly dangerous when they go wrong, they can explode like a grenade ejecting there casing like red hot razer sharp shrapnel."

http://www.rcuniverse.com/forum/m_6215238/anchors_6219190/mpage_1/key_/anchor/tm.htm#6219190

even LifeP04 can explode, this one could easy have burned the house down.

http://www.rcgroups.com/forums/showthread.php?t=709190

http://www.rcgroups.com/forums/showthread.php?t=772399

-steveo

 

[pwbset]

Been playing with a lot of LiMn 18650s (konions). The "green" sleeve came off of one during a pack dismantle (was "stuck" to the pack casing) and I noticed the cell getting warm to the touch on it's own pretty quickly. I took it outside and put it in a cement block on a cement floor and watched it for a bit. It got to the point where it was extremely hot to the touch, but never 'sploded or vented or anything. The cell was ~2.8v so may not have had the energy to go super nova on me. My theory is that without the green sleeve and little black "washer" on the positive side it simply self-shorted against the outer cell can.

Why does a cell's outside can have to be metal/conductive anyway? That's seems incredibly stupid, but I know nothing of cell construction so would like to hear why this is. Careful out there!

 

[steveo]

Been playing with a lot of LiMn 18650s (konions). The "green" sleeve came off of one during a pack dismantle (was "stuck" to the pack casing) and I noticed the cell getting warm to the touch on it's own pretty quickly. I took it outside and put it in a cement block on a cement floor and watched it for a bit. It got to the point where it was extremely hot to the touch, but never 'sploded or vented or anything. The cell was ~2.8v so may not have had the energy to go super nova on me. My theory is that without the green sleeve and little black "washer" on the positive side it simply self-shorted against the outer cell can.

Why does a cell's outside can have to be metal/conductive anyway? That's seems incredibly stupid, but I know nothing of cell construction so would like to hear why this is. Careful out there!

well

I would think metal would be the best material to hold chemical reaction in it & strongest i think... then i would say the aluminum casing of the a123 would be second place; i don't think any other material would be suitable; keep in mind sla are like in a plastic casing..

also some lifepo4 packs in a plasic casing..

hmm may not be a bad idea maybe ..who knows

-steveo

 

[Doctorbass]

I really think cell can also explode if discharged at high current with a discharged pack that become unbalanced... the case where a cell just overdischarge in the pack and that the current demand is sustained while no protechion of overdischarge is active can ruine a cell and maybe REVERSE it !!.. in this case you force a cell to charge on the negative polarity after it crossed the zero volt... I think that could also make it to overheat and make the inside pressure to cause venting.. and then toxic and flammable gas to ignite due to the short circuit after it explode...

This situation is realistic and can happen to any cell chemistry.

That happened too to one of my 1s 18p li-Mn makita parallel pack while i was in the equalizing procedure after matched them.. I complitly charged a pack in reverse polarity!... at 10A !!

When i came back to see the voltage after 2h... I was attempting to see something like 4.17-4.20V.. but I saw 2.1V !!!!... I was curious because i just attempt that it was charged.. but.. i realized it was in reverse polarity!!.. so the voltage of the cell was -2.1V !!! and the cells was hot but touchable!!.. no fire no explosion!!!

simply INCREDIBLE !!!

Doc

 

[monster]

some cells, if aren't made carefully, they can accumulate an uneven build up of chemicals on the electrode that can puncture the separator and cause an internal short circuit. this can happen spontaneously and without warning. remember the sony laptop battery recalls? some chemistries are more prone to this than others

 

[methods]

If I were going to try to encapsulate a lipo fire I would do it by diverting the heat instead of trying to capture it.

I would build a box with a vent tube pointing away form my ass.
Kind of like a dump tube on a turbo car. Maybe 18" or 24" long venting out by the rear tire.
If the battery went into thermal runaway then the first minute of that fire would vent out the tube (before melting the box)
This would give me time to put a little distance between me and the packs.

One thing that should be pointed out is the very big difference between an explosion (i.e. concussion) and very aggressive spontaneous fire.

Kind of like the difference between lighting off a bowl full of gun powder and lighting off a very tightly wrapped cylinder of gun powder.
Same scary stuff, very different scary outcomes.

-methods

 

[dnmun]

i may be the only person on this thread who actually has had a lipo cell fire actually catch my house on fire, so i speak from a little experience.

in my case, a tenant had left his sony laptop charging, buried in the comforter on his bed, when he went to class. i heard the smoke alarm and knocked on the door and roused one of the guys sleeping upstairs, he was totally oblivious to the smoke alarm, so i had to just take over and went through the house to the bedroom, and when i opened the bedroom door the flames were already 4' high, with the entire bed on fire. i was able to smother the fire almost immediately with the heavy drapes from the sliding glass door, but the battery continued to melt down and when i picked up the laptop, the cells slid out of the end of the laptop because the plastic had all melted off on that end and the cells fell out onto the carpet. they were fully shorted and discharging as rapidly as they could internally, and the external temperature was about 300 degrees, and it immediately melted through the carpet before i scooped it up and carried it outside where it continued to short out for about 10 minutes before it cooled off.

my estimate is that the cell had been shorted for about an hour by the time i threw it out in order to catch the bed on fire to the point i discovered it. that is the best info i can give on what a lipo fire is like. from what i saw at the end of the discharge, i think that the cell itself never caught on fire, and i could not tell if there was any electrolyte left either in the cell, but i assume not.

justin really cooked that big nicad pack in canda, but it wasn't nearly as hot because it did not catch the bag on fire, but it was not insulated so the heat could escape more easily to the air. i really do not think nicads have a real fire or explosion risk since the vent will release before it explodes, and the vents do release hydrogen when the cell is overcharged, which is how they are damaged most. because that dries out the cell too.

there is a chemical difference between lithium cobalt polymer cells and lifepo4 cells. there are 2 regimes under which they each operate, either discharge or charge. the key protection for the lifepo4 when it is overcharged is that the po4 is chemically stable up to about 800 degrees so the overheating doesn't cause it to break down. and there is supposedly all the lithium needed to supply the cathode with lithium ions while charging, but with li co polymer, the amount of lithium available when it is overcharged can be exhausted and that is what causes the rapid temperature rise and breakdown of the organic polymer that supports the lithium ion cobalt matrix, and i don't know how the cobalt is related to that or why the li mn is different, without the similar overcharging sensitivity.

discharging is a little different in that the lithium ion has to be transported through the cathodic structure to the anode where it is plated out onto the anode. supposedly the 'polyanionic' structure of the lifepo4 holds itself open as the lithium ions are being sucked out of all these pores in the cathode on their way over to the anode, and the structural rigidity of this 'polyanionic' crystaline structure prevents it from collapsing so the cell is capable of more discharge cycles without getting so weak that the pore of the crystal get all clogged with broken yuk from the structure breaking down. by contrast supposedly the li co polymer structure kinda collapses because the li ions and cobalt help hold it structurally 'open' and it collapses as they get plated on the anode, so fewer cycles before capacity is dramatically reduced. all to the best of my understanding. dennis

 

[dogman dan]

Nice post! Minimal precautions like putting the laptop on something other than the bed would have made that house fire a lot less dangerous. It's not so unsafe to ride around with lipoly, but common sense says charge em in a place less likely to burn the house down while you sleep! Any chemistry with a dead short can be a big problem, potentially welding your butt to the seat! Simple precautions minimize the risk.