The question centers around how to read the capacity loss graph on page 7
At first glance, the 75-65 cycle seems to be the best for the battery, but you need to normalize it for work done: a 50% depth of discharge cycle does 5 times more work, 1000 cycles of 10% is 100 full cycles. This is labeled as work done in the table below.
SoD / EoD: start and end of discharge.
DoD: depth of discharge, SoD - EoD.
Cap % at 4k: capacity lost at 4000 DST cycles.
Work done: 4000 * DoD / 100%.
Cap loss per 1k work done: capacity loss per 1000 full cycles. 1000 cycles is about the full life time of a phone, about 3 years of 1 full charge a day.
| SoD | EoD | DoD | Cap % at 4k | Cap loss | Work done | Cap loss per 1k work |
| 100 | 25 | 75 | 81.5 | 18.5 | 3000 | 6.2 |
| 100 | 40 | 60 | 83.5 | 16.5 | 2400 | 6.9 |
| 85 | 25 | 60 | 85 | 15 | 2400 | 6.3 |
| 100 | 50 | 50 | 85.5 | 14.5 | 2000 | 7.3 |
| 75 | 25 | 50 | 87 | 13 | 2000 | 6.5 |
| 75 | 45 | 30 | 89.5 | 10.5 | 1200 | 8.8 |
| 75 | 65 | 10 | 93 | 7 | 400 | 17.5 |
As you can see, in this model, the loss is with the 100-25 cycle, or alternatively, the 75-25 cycle. It is unfortunate this information is so hidden in this paper.
Also, note that this test was done with a 3.3V nominal voltage cell, which is not a standard Li-ion cell, that chemistry is 3.7/3.8V, so findings do not always transfer.
References:
Xu, B., Oudalov, A., Ulbig, A., Andersson, G., & Kirschen, D. S. (2018). Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment. IEEE Transactions on Smart Grid, 9(2), 1131-1140. doi:10.1109/tsg.2016.2578950
2 Comments