How does thermal cycling affect Lithium polymer cells?

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Howdy - I can't seem to find much good information regarding lithium polymer cells. I've had to piece together little bits and pieces from all over the Internets. What I'm curious about is how temperature effects LiPo cells. I did find one nice graph showing discharge curves for LiPo cells - and it's pretty dramatic - they show that you get more than double the discharge capacity when operating at 60 deg C than at -20 deg C. But what about if you cool down a battery, then heat it back up, and then use it? Does that affect capacity? What about for charging - can you charge a cool pack normally? etc etc.

Anybody know a good resource for this sort of information? LiPo datasheets seem to be fairly useless!

Thanks!

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I can only relate experiences in flying model aircraft using LiPo batteries (which are pushing the batteries by dumping about 10C from them). On a colde December morning at maybe -2C the capacity is notably down on that when you fly on a Summer's day at 25C - a previous 8 minute flight duration may have dropped to about 5 minutes. But the batteries have no "memory" of this - when you use them in warm conditions (say an indoor sports hall say) then the capacity is back to where it was. Of course dumping 10C means that the cycle life probably drops to just 200 to 300 cycles anyway.

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Recently I've been researching various batteries' life and capacity, you might want to check my thread over here: https://www.avrfreaks.net/index.p....

To summarise, the higher temperature you use the battery at, the higher the loss of capacity is. Also with storage, when storing at high temperatures the battery ages much faster. It also seems that Lithium based batteries shouldn't be charged at temperatures below 0. Aside from the Wikipedia, one good source of general information is http://www.batteryuniversity.com/, Though the site is quite outdated now.

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cedesit wrote:
Recently I've been researching various batteries' life and capacity, you might want to check my thread over here: https://www.avrfreaks.net/index.p....

To summarise, the higher temperature you use the battery at, the higher the loss of capacity is. Also with storage, when storing at high temperatures the battery ages much faster. It also seems that Lithium based batteries shouldn't be charged at temperatures below 0. Aside from the Wikipedia, one good source of general information is http://www.batteryuniversity.com/, Though the site is quite outdated now.


The datasheet I have goes somewhat against what you're saying. I've included a chart from it. It is showing significantly greater discharge with higher temperatures. I'm sure that is to a limit, of course.

But what I want to know is - if I fully charge two brand new packs at room temperature, then put one in a freezer for a day, then bring it back up to room temperature, then discharge both packs. Will they both show the same discharge capacity? Or will the previously cooled one have lost some charge due to the thermal cycling?

Do you have a source for saying that LiPos shouldn't be charged below zero? That is interesting.

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clawson wrote:
I can only relate experiences in flying model aircraft using LiPo batteries (which are pushing the batteries by dumping about 10C from them). On a colde December morning at maybe -2C the capacity is notably down on that when you fly on a Summer's day at 25C - a previous 8 minute flight duration may have dropped to about 5 minutes. But the batteries have no "memory" of this - when you use them in warm conditions (say an indoor sports hall say) then the capacity is back to where it was. Of course dumping 10C means that the cycle life probably drops to just 200 to 300 cycles anyway.

So the cool temperatures don't do damage - they just temporarily limit the capacity. That's certainly good. Any idea if you lose charge just be cooling then heating them back up?

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Quote:

Any idea if you lose charge just be cooling then heating them back up?

No I'm pretty sure I've had charged batteries that have been cooled/warmed and then flown in a warm environment with no noticeable degradation. So presumably the temperature thing is only relevant while it's actually dumping current.

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AFAIK, the low temperature affects the mobility of the ions inside the polymer, thus 'freezing' the electrical charge in place. So when the battery is heated up, this charge gets free again, thus the electrical charge is usable again. High temperatures seem to have an aging effect more than other things.

Guillem.
"Common sense is the least common of the senses" Anonymous.