How to kill a Lithium Ion Cell

[aminorjourney]

1) Take your car off the road and remove battery packs.

2) Test cells in pack and replace four worst cells with four brand new cells with no internal resistance issues.

3) Replace fifth worst cell from existing pack with spare 'old stock' cell you got given at the time you purchased the original cells.

4) Make attempts to charge this 'old new' cell and when it appears to be at the correct voltage, integrate it into pack.

5) Refit pack into car. Use BMS to check all voltages and monitor charge cycle.

6) When all twelve cells appear to be fully charged, go out for a nice long test drive.

7) Give the car lots of right foot on hills.

Make sure you're about 8 miles from home....and....

9) Suffer a complete internal short on the 'old new' cell you've been keeping in the garage for the past year.

10) Watch voltage drop across this cell from 3.7V to 0.1V in a matter of seconds as the BMS stops the car from doing anything, just as it's programmed to do.

11) Scream in despair, but realise that, after manually taking voltages on all the other cells that they are all just fine. You know though that the car won't move anywhere with the BMS reading a dead cell.

12) Find the trusty tools in the back. Remove dead cell from the pack entirely, knowing that the car will still drive 4V lower than the intended voltage.

13) Cringe as you disconnect the BMS.

14) Drive home very slowly, cringing at every hill and making sure that no cell drops below 2.9V by attaching your voltmeter to the worst cell.

15) Get home... Cry in anger and despair. (You get the picture) Try desperately to charge dead battery overnight on 4.0V 3A bench supply.

16) Next day, give up. Remove faulty pack. Retrieve the best of the worst five cells you'd replaced a few days earlier. Repackage pack and replace in car. Pray to any deity who will listen, despite being Agnostic.

17) Dismantle dead cell in a well, ventilated area, taking care not to breathe in any nasty organic solvents.



Yeah... So that's been my week...

Anyone else had a cell go this way?

[ChrisB]

Wow these Li-ions seem to be falling over with rather regular abandon Nikki

I presume it didnt go bang just faded away ?

Got any pics of whats inside a Li-ion cell then

ChrisB

[qdos]

maybe I'll stick to good old fashioned PP9s

You're not alone Nikki Peter Perkins lost his in his Solar Van too a while back

[PHEV]

Your way sounds rather longwinded, I found a quicker way this afternoon.. I wanted to test capacity of a large A123 pack, so I connected a meter and a load (bank of big bulbs) and sat back to watch whilst I worked on the next pack. I watched the voltages all the way down...till a customer called and I forgot all about it!
When I came back the pack read 0v (80v pack!).

I trickled it back up to some semblence of charge, and it seems that 2 banks of cells (8 cells in total) are dead. Hell of a job to get them out and replace them, took me all the rest of the day. The dead cells were probably the weak ones I was looking for, but are only dead because they hit 0v first, just as in your case. I suspect they may have had much life left in them if they hadn't been overdischarged/reversed.
Must automate the discharger...I've felt like a right prune all day, glad i'm not the only one

I've had A123 cells apart before, inside looks like a roll of camera film, smells of lemon/acetone, and if you look through a microscope you can clearly see millions of miniture hampsters running around in tiny wheels.
Oh wait, April fools day isn't till Tuesday

[retepsnikrep]

maybe I'll stick to good old fashioned PP9s

You're not alone Nikki Peter Perkins lost his in his Solar Van too a while back

Interestingly 23 of mine still show normal voltage and some capacity (not tested yet) so I'm using those in my home power projects in a huge 12v 1400ah assembly. That suits my two windmills and inverter.

Only 7 out of my orginal cells are now U/S or damaged so it wasn't a complete disaster. Anyone want them for testing playing with?

Nikki it may be you a have a microscopic internal short dendrite, I have heard these can be blown off my a huge high voltage and or current shock charge of short duration. A battery zapper in other words, perhaps worth a try. You could use a 12v car battery (or your combined Li-Ion pack voltage) across your bad cell for a few seconds to see if that can cure it! I'll probably try it on my few 0V cells.

Be careful and only try this outside when all other techniques have failed.

[ChrisB]

Nikki it may be you a have a microscopic internal short dendrite, I have heard these can be blown off my a huge high voltage and or current shock charge of short duration. A battery zapper in other words, perhaps worth a try. You could use a 12v car battery (or your combined Li-Ion pack voltage) across your bad cell for a few seconds to see if that can cure it! I'll probably try it on my few 0V cells.

Be careful and only try this outside when all other techniques have failed.

Use to do this with Nicad dry cells, AA,C,D and F sizes when they wouldnt charge/have any capacity, had varying degrees of sucsess from a battery coming back to normal and being very usable again to them getting VERY VERY hot and me having to lob it down the garden VERY VERY quickly and then after 1/2 hr going to try and find said battery to find it a very odd shape with its guts hanging out never had one actually go pop or catch fire mind you. Dunno how a Li-ion would take it mind you

ChrisB

[aminorjourney]

Yes. Sadly I have tried this and it's a gonner It's a shame, because I could really have made use of five spare cells!

Oh well... I've got four spare ones

[MalcolmB]

So to sum up – three experienced tinkerers have managed to find three different ways of killing lithium cells. Seems like Nicki got off lightest because she has a top-of-the-range BMS that shut down the system when one of the cells failed. I guess the message is that we all need failsafe systems that shut down (or ideally bypass the offending cell/string) whenever an individual voltage goes too high or too low. No matter how smart we are we're going to be distracted some time and forget. Are you planning to fit a BMS to your motorbike pack Steve?

[PHEV]

Its already got a low voltage cutout on the bike (each cell monitored individually), and I have a homebuilt balancer I use every few cycles. I was just testing one part of the pack when this happened (the A123 segment).
I ran a few full discharges on it today (much more carefully), and the rest of the pack seems fine. It could have been alot worse! Its had alot of abuse this a123 pack..it was running at more than 30c in its last bike (300A from an 8AH pack). Top cells for sure..wish they were available by the box

[MalcolmB]

Its already got a low voltage cutout on the bike (each cell monitored individually)

Good to hear the rest of the pack looks OK What sort of LVC have you got on the pack, is that homebuilt as well? Just curious as I want to build a small foolproof A123 pack for my wife's bike.