Cycle life tests of High Energy density cylindrical cells

[From-A-To-B]

Random question. Why test 90% DoD? I daily charge my batteries to 80% or 90% capacity and then charge once in a while to 100% right before a long ride. I think I only discharge down to about 3V per cell. So, I guess I answered my own question.

Which aspect of the 100% DoD test do you think is more damaging to the cells leading to the differences you see between 100% DoD and 90% DoD test results? The charge to 4.2V or the discharge to 2.5V?

I did quite a bit of reading about this in the past, and cannot quickly find the most helpful sources. Some of those threads were here on ES, so it might be worth a search. Previously, I'd read that the top 10% and 10% are about equally as damaging. Thus, I keep my batteries between 90% and 10% SOC whenever I can help it. It does me little good to play around between 3.0 and 2.5 volts per cell, anyway, since I'm worried about getting home at that low level. My battery gets really soft and LVC is just around the corner when I near 3.0V per cell.

On the contrary, this article summarizes some testing that indicates that deep discharges are less impactful than charging to 4.2V per cell. Battery charging: Full versus Partial - PushEVs

At the end of the day, I just take it easy on the battery and know that I don't ride enough to see 1000 full cycles, anyway!

 

[Pajda]

Random question. Why test 90% DoD? I daily charge my batteries to 80% or 90% capacity and then charge once in a while to 100% right before a long ride. I think I only discharge down to about 3V per cell. So, I guess I answered my own question.

The general rule is that synthetic tests are one thing and real-life tests are another. The most difficult thing is just to accept this fact. After that, you just need to choose a standardized test and try to keep the conditions constant. The reason why 4.15-3.00V (about 90% of DoD) is that someone from ES community just asked for it. And the technical reason is that some modern cells can withstand 1000 cycles even at 100% DoD, and as you can see, 90% DoD cycling survived pretty much all samples. So going below 90% means that you won't see significant differences between the cells anymore.

Which aspect of the 100% DoD test do you think is more damaging to the cells leading to the differences you see between 100% DoD and 90% DoD test results? The charge to 4.2V or the discharge to 2.5V?

No general rule here either. I've seen several times a behaviour which does not make a sense. But again, discharging to 2.50V cut-off limit makes practical sense with HP cells at +5C discharge rate or at cold temperatures where the IR ensures that the cell is not fully discharged at this cut-off voltage.

 

[Pajda]

Also, why did you remove the Samsung 50S?

I don't like this cell? The problem I am aware of is the lack of a reasonable online database with graphical interface, where specific cells can be selected for comparison. So it is not only about 50S but many other cells data.

 

[tourist_trapper]

Small update in N38+F40 post. I have added some new informations in the Table. Added temperatures measured without forced air (I just turn off the thermal chamber after conditioning the cells to 25°C, so it acts as isolated box with 100l volume of air. There could be further confusion here , as modern best HE cells handle 3C continuous discharges just fine. No they don't.

Also added results of EVE INR18650 35V which seems to be also a decent cell. Cycle life tests started today.

After switching to the new version of the ES forum, I noticed a limit of 10 images per post. Unfortunately this now restricts me enough to move or add the new results to the first posts of the thread

Any chance you had time to complete the lifecycle tests for the 35v? (considering buying a bunch of reclaimed ones for projects and wondering if they're worth it)