A123 M1's- Is capacity a good gauge of cell age

[John in CR]

I've got several hundred good A123 M1 cells. As I wrap up capacity testing it's time to firm up plans to use them. While some will go into typical bike packs, others will be used in ways where changing a dead or dying cell will be a huge pain, so I want those to get the cells with the greatest remaining cycle life.

Is capacity a pretty good gauge of a cells age? If so, does that mean that the nearly 50% of my cells with capacity less than 2.1ah are almost done? Is a fairly wide variance in capacity pretty typical for the toolpack cells...even if new?

 

[liveforphysics]

If they've been sitting for a long time, give'em a big deep cycle or two before judging if they are worn out or not. Those A123 M1 cells can come back from quite a lot after a few cycles to perk-up. Charge to like 3.9-4v, and discharge to 2.5v, charge it back up to 3.6-3.7 and then check capacity. I bet a lot of them come back in a substantial way.

 

[Doctorbass]

Also, Internal resistance is a good way to measure them.. Aged cells will have higher IR

I usually keep cells that can give 2200mAh or more at 4.3C ( 10A)

Like gary also already mentioned, stressed cells can be detected by charging them and let them to sit few hours.. than measure them.. the stressed cells will have the voltage to drop more.. ex charge at 3.700V and good non stressed cells will stay above 3.6V..

There is only the A123 cells that keep the "surface charge" like that.. it's due to their special chemistry. all other lilfepo4 will drop nearly imediatly to 3.3-3.4V after you disconnect them from the charge..

Doc

 

[Doctorbass]

Best fast way would be to charge all them in parallel with two aluminum sheet that make adaptive contact to all the cell tab .. to ensure having all the same charge voltage...
.. with let say.. a BIIIIIG lab PSU for few days of you have hundreds of cells :lol:


and than to connect all them in serie inside many tubes by pushing all them together.. and to discharge them while watching with a thermal camera... the lower capacity will heat up before all others... :lol:

Doc

 

[John in CR]

Thanks guys. I did send everything through at least 3 cycles before measuring capacity, though I only went to a 3.65V cutoff. I'm not looking for a good/bad cutoff, though I certainly hope that not only those above 2.2ah at 10A are good, because I'm just wasting time if so. Instead I'm wondering if there is something measurable that is a reasonable indicator of remaining useful life.

 

[marty]

Are these A123 M1 cells from power tool packs? Look for a date stamp on the plastic case. Makita packs have the year and month stamped into little circles on the plastic. Date of manufacture should give you a pretty good idea of the age of the cells.

 

[scriewy]

how does their lifespan thingy works ?

the cell has a cycle graph ok, initial capacity lets say 2230 mah, after 1000 cycles 1950mah, after 2000 cycles 1700mah.

i get a brand new spunky purky cell, then over discharge it to 1.5v, IR goes to 300 mohm instead of original 30 mohm, i test capacity' it's 1950mah, does it mean i jumped over 1000 cycles in 1 minute ? and from this moment internally all the ions inside in state of 1000 cycles, or only the cathode and anode is messed up ?

like, is there a difference in the materials that actualy went through real 1000 cycles across 1 year and those that were overpowered for a moment but in reality are 1 week old ?

 

[Malcolm]

If you want to learn more about what happens inside the cell and how it affects lifetime, I recommend the video at the top of this thread: http://endless-sphere.com/forums/viewtopic.php?f=14&t=23473