Help reading some Pouch cell discharge results

[DanGT86]

About 4 years ago I bought some 10Ah LiCoNiMnO pouch cells. I have kept them stored in a cool dry environment at about 3.7v. I pulled them out of storage and ran a discharge test with my Hyperion 1420 charger to see what kind of capacity and sag they had under load. Unfortunately the charger doesn't have the capability to produce anymore than a 1C load on these cells. It also only lets me discharge to 3v through the loaded discharge lead rather than the measurement at the cell tab. I was hoping somebody could help me make sense of the results I got from the test.

I used some less than ideal alligator clips on the cell tabs for the main discharge wires to the charger. I also used alligator clips directly on the cell tabs for the balance leads going to the charger. On the graph the Voltage of the main leads is shown in green and the voltage on the balance leads is shown in blue. The charger pulses off about every 30 sec so you have to ignore the spikes and just look at the basic discharge curve shape.

There is an obvious difference between the discharge lead voltage and the balance lead voltage measured at the cell tab. Which of these measurements should I be looking at?

Most cell tests I've seen only have one discharge curve at a specific current. These cells seem to be acceptable if I look at the measurement at the cell tab through the balance lead but they look pretty saggy if I go by the measurement at the main lead under load.

Test was a single pouch at 10A
I got about 7ah before the charger hit its 3v minimum cutoff voltage as measured through the main lead under 10amp load. I got about 2.5ah more by reducing the current to 1amp.

What do you guys think? Do I need to setup a better testing method? Are these worth the trouble of building a pack with or are they compromised from sitting for 4 years? Is this voltage sag acceptable to run 2C avg and 5c peaks?

 

[amberwolf]

I think you'll want to come up with a better connection method, before judging the cells, because clips like that can be kind of high resistance.

So the voltage sag might be just an artifact of the connection.

If not, then it's probably the cells themselves.


Some form of flat clamp, like maybe a regular C-clamp securing a brass or copper plate or bar to the tab, with a wire soldered or crimped to the plate or bar.

 

[Hillhater]

The main power lead voltage, ( green line data) tells you nothing of value. Forget it. !
The blue line , balance lead data is a better indication of cell performancr (sag) but seems to be indicating approx 0.1 volt sag at 10 amps ....
...implying a IR of around 0.010 ohms ?......rather higher than their original spec.
But as AW said make sure you have good contact on those balance lead connections an test a few more cells
You may also want to rig up a dummy load to run the test at 2C.

 

[DanGT86]

Thanks. That's exactly the type of answers I was looking for. I'll try again with better contacts and thicker discharge wire. During the test I was adding more alligator clips in parallel with the main discharge leads to see if the displayed voltage increased and it didn't make much difference.

I really wish the charger would let me discharge to 2.5 volts and or use the balance lead tap to determine the cutoff voltage. Maybe I can lie to it by selecting a different cell chemistry to get it lower than 3v.

As for the IR being .010ohms, the top line that looks like a square wave on the graph is the charger's calculated IR measurement. There is that brief section of .009ohms but seems to stay between 7 and 8 for most of the discharge. Is that a normal looking IR curve?