Weird cell degradation

[pinkpanda3310]

Can anyone explain this -



The pack is a few years old, beaten and abused (by me) it used to be a 6s but one cell got punctured after skidding across the road. So it's been used as a 5s pack for a while. Now it has lost a lot of mah, has poor punch and I could see one of the cells was deformed so I unwrapped it to take a look. The cell at the bottom has general mild puffing but all the others are swollen at the positive end. The swollen bit is rock hard, just back from the swollen ends it feels rather normal. Plus one or more of the cells has a slow leak 'cause I can smell it.

Any theories as to what's going on?

[BrianG]

That doesn't look like your typical puffing from internal gas expansion where it would expand the whole pack and be squishy in a more uniform manner. I wonder if that's from the sudden stops during crashes or front-heavy landings causing the "stuff" inside the cell to bunch up against the front?

[pinkpanda3310]

I think not. Each cell is swolen at the positive end ie- top cell big on left side next cell big on right side.

if you puncture a lipo it will let air in....then it will start to react and oxidize.
if its punctured its as good as dead...and really smelly too
chris

[pinkpanda3310]

So you think they were poorly manufactured? That's why 4 of the cells have puffed in the same way. The pack is as good as dead but I was just curious about the deformation.

i did read up about lipos a few years ago, as a child i was into electronics....im more into mechanics and engineering rather than chemistry, so i didnt understand all of the text.

basically in certain situations like over discharge and over draw, oxygens are created inside the pack....puffing, the oxygene will start to oxydize the internal tabs on the lipo which pickup the voltage and take it out the pack.

this accelerates the degredation of the pack...once it starts there is no stopping it, basically rots the tabs...which creates more heat...

no i dont think they where poorly made...just well used
chris

[Brow]

Remember safety first. Despite the fact that all of us are pyromaniacs at heart, we still do not want to burn ourselves, our toys, our homes or our family and friends.

My friend Mr Google got me a few hits with similar instructions.

From: http://www.chargedrc.com.au/Battery-...your-lipo.html

LiPo battery disposal

In order to properly dispose of a LiPo battery, you must first discharge it as low as possible. Please, if the battery has been damaged DO NOT discharge it, just proceed with the next step
Fill a bucket or some plastic container (NO METAL) with water, and add salt. Add approximately 1/4 cup of salt for every litre of water. The container may have a lid but must not be air tight
Immerse the battery in the salt water fully. Make sure that even the power connectors are submerged. Leave the battery for at least 2 weeks.
After 2 weeks, remove the battery, wrap in newspaper and dispose of in rubbish bin like normal rubbish.

Another one:
http://www.thunderpowerrc.com/PDF/DI...-BATTERIES.pdf

[pinkpanda3310]

Originally Posted by Brow

Leave the battery for at least 2 weeks.

2 WEEKS!

I guess I should hop to and run it down and dunk it. I don't think I'll run the whole 2 weeks, I'll check the voltage now and then and when it gets ~0.5v I will open it.

Thanks cuzi-brow

i wouldnt open it up, read up about lithium, it can burst into flames very voilently when exposed to oxygene ......we learn something new everyday.

i would hate to hear of an accident..i did not open up my 2200 lipo to see what happened (fortunatly) and i would advise you caution too....
chris

[pinkpanda3310]

This weekend I didn't have much energy left after the gym and going for a cycle. This seemed like the perfect potter around job.


This next pic you can just make out the discolouring on the black leaf.

I've cut open lipo's before but never tried 'disassembling' one. Half the leaves are connected to the + and half to - and then spliced together, only a thin plastic sheet separates them. There was one leaf that was not connected, for some reason it had ripped from the + tab.

The + end was the swollen end but it was only the leaves connected to the - that were affected.

[pinkpanda3310]

Here you can see the + leaves are clean and smooth. The - leaves are darker and discoloured.

I also noticed the leaves are made of different metals.



Another thing I noticed while unwrapping it, because it still had a little voltage left the - leaves (buggered ones) were very slightly warm to touch. I thought I can't be feeling it right at first but I compared it to the + leaves and they were stone cold, there was a definite difference.

Anyway it wasn't quite as dramatic as I had hoped with the build up of crap on the leaves but I have a better idea on how they are put together now.

[brainanator]

cool!