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The effects of 4 years of calendar aging on a large sample of CALB L135F72 cells.

zcskywire2

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There is endless discussion these days here about the effects of calendar aging on cells. Even more so with cell cycle lifes hitting 15000 cycls or more. Unfortunately there is a lack large scale testing as it is both expensive and time consuming. Well through my job I was given a rare opportunity to collect good data on calendar aging over a large sample size of CALB L135F72 (CAM72) cells.

We were tasked to test over 400 cells to see if they were still valid for pack construction. These cells were still in their original shipping crates and had not been touched since they were manufactured 12/21/19. For 3 of the pallets I was able to obtain the original shipping report, containing the original capacity testing. This allows us to directly see the calendar aging after ~4 years of shipping as these were testing between Oct 23 and Feb24. Cells were stored at shipping SoC (~30%) in a heated and cooled warehouse (I believe at least).

For the actual capacity testing the cells were charged and discharged at 0.5C at at temperature ambient of 22c. This is a higher C rate on the charge (0.33C vs 0.5C) but less on the discharge (1C vs 0.5C). Current taper cutoff was kept at the same level (0.05C). Over all not quite the same but comparable enough.

Gear used was a band new B&K9115 power supply for charging and a brand new B&K 8612 electronic load for discharge. Remote sense was used for both.

Actual results are below in a image (I've done enough typing already)
Screenshot_20240419-205644~2.png

Overall we saw a loss of 3.31%- 7.74% with a little less than 5% on average. This means with no cycling there is an average of ~1.25% SoH per year for CALB L135F72 cells. Much lower than many of the smaller studies out there. Giving a ~16year shelf life for cells.

Full results and original shipping documents are attached.
 

Attachments

  • calb_shipping_list-compressed.pdf
    738.4 KB · Views: 8
  • CALB_Cell_SoH.pdf
    25.9 KB · Views: 5
A lot of work and thanks for the data.

Knowing SOH now, will you use these?
 
Great info. Calendar aging may not be linear so initial loss of capacity may be greater than loss when cells age a bit. My 85% SOH Panasonic NCR18650B NCA cells (from ~2013 Tesla model S) seem to be losing 0.6% per year when stored at room temp around 27°C and 50% SOC.
 
Are you concerned about dendrite formation? At 85% SOH
Now I am (again). Forgot about it. My batteries may be closer to 82% SOH. I try to keep them below 50% state of charge and not leave them charging unattended. Will have to move them outside soon.
 
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This came just at the right time for me :)

I've just acquired 32 x 280Ah CATL LiFePO4 cells from an estate clearance. These were manufactured in June 2019 (genuine QR codes) and have been in dry (tropical but not climate controlled) storage in their original packaging since.

I've measured a couple at 273Ah and 270Ah, I'm now confident that they'll all be "good" without testing every single one (I'll do another couple just for my peace of mind).

Since I took a punt and paid 35USD a pop for these I'm on cloud 9 (ok cloud 8.5).
 
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Would be interesting to know 4 year results from stand-by use, ie minimal cycles but hold at 90…100% charge
 
What was the voltage before charging for the first time? Were they kept at 30% soc for the 4 years, or did they self discharge for 4 years?
 
Great info. Calendar aging may not be linear so initial loss of capacity may be greater than loss when cells age a bit.

I hope to be able to come back and test this in the future. While these were outside cells, we also have a crate of L135F72 cells that havent been touched in years. Hopefully it has the original shipping report in it.

I'm also looking at a set of original blue headway cells to test that have been sitting new since ~2006.

Unfortunately any results from these are still way off as they take quite awhile to test, even doing 12+ cells a day. The results for this post took 4 months to compile.
 

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