Very old Li-Ion batteries

[GeraldTheBonzai]

In another thread I post how I had found an old backpack that had a li-ion battery pack that was charged by a solar panel. I tried to give the battery a charge and it appeared to hold one, but it got very hot whilst charging. As such, I've assumed that its not fit for purpose, as its not been used for over 10 years.

Now, being the sad geek that I am, I was wondering why exactly it had failed. What chemical changes had happened to it? And what I found was quite disturbing. Apologies if this is already known - I did a search to see if I could find any reference relevant to this.

When a li-ion battery is left uncharged for a very long time (in my case 10+ years), it still has a residual chemical charge. Over time, the voltage drops to below 2V. When this happens, copper ions in the anode start to leach into the electrolyte as free ions. Over time the concentration of free ions increases. At the same time, the polyethelene separator starts to break up - it delaminates and becomes porous. The internal resistance of the battery also increases.

If you now try to charge the battery, the ions reform into thin, microscopic "threads". Due to the increases thermal resistance, the battery heats up, which increase the rate at which the ions reform. The immediate effect is that the battery gets hot and can catch fire. However, once formed, these threads persist and continue to grow. Repeated charging will cause them to grow, but so will thermal stress - exposing the battery to heat and cold. If the treads pass through the separator, they can form a short. If there is no charge in the battery then very little happens, but if there is a residual charge, you get a short circuit, which leads to a hot spot which can cause the battery to ignite.

And heres the nasty bit. Even without charging the battery, over a sufficiently long enough time, if the battery is exposed to thermal cycling, it can spontaneous ignite. This is just a side effect of the lithium ion technology uses, and how it degrades over a long time.

Now, if you are anything like me, you probably have a draw full of old mobile phones. Or battery packs from old laptops (sitting in the loft hmmm nice cold/hot cycling)...

So my job this weekend, is to go and rummage round the roof, look through the junk draws, find all the old laptops and mobiles, and get them out the house.

https://www.msn.com/en-us/travel/tips/t ... r-AA1U8ABO

[Winterprep]

Good information thanks for that

WP