Re: Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment

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