Lithium Ion LFP cycle degradation data

Greetings,

How the cycle degradation table data was obtained for the Lithium-Ion (LFP)?
Below a partial part for the table which shows the Capacity (%) value sometimes increases as the number of cycles increase and that not realistic, is there any problem with these data or I am missing something?  



10 19282 78.2638
10 22891 78.2956
10 26837 78.7412
10 30819 79.1867
10 34952 79.5686
10 38953 79.8868
10 42829 80.0141
10 46812 80.1414
10 50791 80.2051
10 55205 80.8416
10 59150 80.8416
10 63094 80.9052
10 67040 80.7779
10 71103 80.7143
10 74943 80.6825
10 78957 80.5233
10 82865 80.396




Also for the 10 % DOD as the number of cycles increased, the capacity (%) value has almost a constant value 78%  how I could know when it will reach 70% of the capacity.



Best,

Fahad

Hello Fahad,

That cycling data for LFP is from this paper:

Analysis and modeling of cycle aging of a commercial LiFePO4/graphite cell
Naumann et al. 2020
www.sciencedirect.com/science/article/pii/S0378775319316593#fig6
(screenshot attached)

The differences between this figure and SAM is that SAM is using cycle count at the given DOD whereas the paper uses full-energy cycles; the figure is showing calendar + cycling degradation whereas SAM is showing just cycling.

Given their test data did not reach 70%, I can't say for certain how many cycles are required. Storage condition and calendar degradation also needs to be considered.

Darice

Thank you so much for your response.

So, how did SAM transfer the paper data from full energy cycle format to cycle at given DOD format?


Fahad

Could you please clarify how SAM did transfer the paper data from full energy cycle format to cycle at given DOD format?

And how we can interpret the increase of battery capacity as the number of cycles increases for the data I showed above.



Best,

Fahad

Hi Fahad,

Apologies for delay in response, I didn't receive a notification for some reason. The translation of FEC to cycles of a particular DOD is via energy throughput: cycles = FEC/(DOD*relative_capacity).

The paper does not explain the capacity increase for the cells at DOC=10% and 20%, and says "the capacity loss of test points (TPs) with DOC < 80% shows several trend changes whose underlying mechanisms are unknown at this point".

Best,

Darice