Determining cell life

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FireFrog

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Jan 22, 2017
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is it possible to determine how much longer a cell has for lifespan?
Is it based on capacity vs the manufacturer rated capacity?
Im sure that's are many variables to affect a cells life but I'm wondering if certain factors stand out for finding how much longer till a cell gives out.
 

daromer

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I would say no.

But. Some manufacturer have a "capacity vs number of cycle" charts.
How accurate that is for 2nd hand cells is hard to tell since they are very generall but thats how i do it. There is also a degradation on cells based on age.

I think an avg is 1-9% of capacity degradation per year depending on type. 3% is the most common. So basically a 10 year old unused cell can have degraded

0.97^10=0.73. Ie 27%...
 

Elmo

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So much depends on the way the cells are used and the conditions they exist under, keep them between 40-70F, be conservative with your voltage limits and currents during charge and discharge and your cells will last many times longer than if you abuse them electrically and thermally.

I get the impression that degradation slows down somewhat after a certain point but that's purely subjective, I'm not organized enough to have hard data on that. I do know that cells which are inadequate for transportation purposes are still good enough for stationary use where energy density and power density are nowhere near as critical.
 

daromer

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Yeah the degradation over time im not sure of either. I have not actively looked for any numbers either :)

I have had cells that was sitting for 6+ years. They if so should have degraded xxx% but when checking capacity it was only half of that... :)
 

Rerouter

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Jan 1, 2017
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temperature to my knowledge mainly influences rate of degredation, while cycle life influences esr increase.

a li-ion at 3.7V in a freezer (-5C) should last a few decades without any noticible degredation, however if you cycle them at this temperature they will be dead pretty quickly.
 

FireFrog

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Jan 22, 2017
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Awesome I'll take this into consideration for cooling
Most likely I would want to keep in some sort of shack or the like and have a small air conditioner to keep them cool
 

daromer

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Elmo

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I guess my point was missed.. Lithium cells should not be operated or at least charged below freezing, they are like Goldilocks, they want it not too cold and not too hot but just right.

To me at least, thermal management on something like a powerwall seems a given, Tesla does it with liquid cooling.

Something like the chiller portion of an old water cooler maybe... A full blown AC is probably more than even a large pack would need.
 

FireFrog

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Jan 22, 2017
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Oh not a big one
Just to keep ambient temperature around 24c, pretty much room temperature
 

ozz93666

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Feb 22, 2017
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Elmo said:
I guess my point was missed.. Lithium cells should not be operated or at least charged below freezing, they are like Goldilocks, they want it not too cold and not too hot but just right.

To me at least, thermal management on something like a powerwall seems a given, Tesla does it with liquid cooling.

Something like the chiller portion of an old water cooler maybe... A full blown AC is probably more than even a large pack would need.

I can't imagine we need to worry about cooling firewalls ...graph from the link shows cells are happy at 60C ....

age_temperature.gif

Cells should never even get near that .....

Electric cars are another matter ...cells packed togetherin a tight space ... high power demand.... this heat needs to be blown into the car interior to keep occupants warm .
 

Elmo

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In a DIY EV you have natural forced air cooling of the cells, I jammed cells in together when I first started building packs and lost a lot of capacity from heat build up in the inner cells. I rebuilt my packs with bamboo kabob skewers as a spacer/grid and never had any more problems from heat because I channeled a flow of air from the forward motion to the battery compartment.

If you have excess solar capacity when the cells are likely to be hottest it's not "wasteful" to cool them.

At the other extreme you can mostly keep your pack warm in the cold by insulating it heavily.
 
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