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MASTER THREAD: 2021 Model 3 - Charge data, battery discussion etc
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Candleflame
Active Member
So it seems from the most recent evidence that sitting/charging to 100% on the nmc/nca batteries is not nearly as bad as people thought. But what it does do is double the cycle intensity.
I. E. Doing one 100 to 0 discharge is as bad as 2x 90 to 0. If you do that everyday thats bad but if you do it just once in a while it probably doesnt matter.
Candleflame
Active Member
Yes ive seen some papers. Iron batteries do initially degrqde less if only i. E. Charged to 50% than 90 or 100% but after around 4 years or so 50% starts overtaking the 100%. The explanation/theory was that at 100% the initial degradation causes a film to form which makes the battery highly resistant to further degradation, which includes degradation from cycling.
For all the research reports i've seen the calendar aging is basically the same for LFP as NCA ands NMC cells, exept for one report from last year.
They did some very very strange test setup and they did draw some conclusions from this by anticipating very much. They use very high temperatures fpr the aging, and had only 2 or three measuring points. From these few points they decided to use exponential functions to calculate the curve. If they are correct you should never leave those LFP at other than 100% as they will hold up for 100 years. Not really probable.
As tesla recommends to charge to 100% once a week(my guess is that is for the BMS to not loose track of the current SOC and NFP), we will have a lot of LFP cars in one year or so that have been standing at high SOC. As we now that you can use a LFP battery when it comes to cycles just about how you like and it still will hold up for thousands of cycles. If we see a clear degradation after on or two years, this isnt due to cycles. Then it will come from calendar aging. My bet is that we will see this.
From research reports:
So, this is the only research report I found that implies that LFP degrade less at very high SOC.
https://www.mdpi.com/1996-1073/14/6/1732/pdf
They took only 6 measurement points, with only three different in the SOC axis: 10, 50 and 90%. For the temperature they only used thee different temperatures: 40, 47.5 and 55C.
Creating a curve from only three points will
mean that you use all three points in the formula and you do not have any extra points to check that the theory fit.
”We” know from other research that using few points can lead to faulty conclusions. There was many calendar aging studies that used four or five points and because of that failed to find the big ”step” in calendar aging around 55-65% SOC(depending on the chemistry). These researchers have only three points and no step at all.
This is the degradation found. In no way close to low at high SOC:
If we put these points ( for 10 months) in the classic NCA/NMC/LFP- degradation graph, it doesnt look different than earlier:
As this test was at 55C, the values do not look different at all. They fit the earlier like a glove.
These researchers did come to this conclusion:
”Keep it at 100%SOC and 25C and it will hold up for 80 years”
No, I dont think so. We see the same pattern as earlier LFP. Perhaps they stay healthy longer than it looks, but the data we have do not point at any revulotionary changes.
https://www.mdpi.com/1996-1073/14/6/1732/pdf
They took only 6 measurement points, with only three different in the SOC axis: 10, 50 and 90%. For the temperature they only used thee different temperatures: 40, 47.5 and 55C.
Creating a curve from only three points will
mean that you use all three points in the formula and you do not have any extra points to check that the theory fit.
”We” know from other research that using few points can lead to faulty conclusions. There was many calendar aging studies that used four or five points and because of that failed to find the big ”step” in calendar aging around 55-65% SOC(depending on the chemistry). These researchers have only three points and no step at all.
This is the degradation found. In no way close to low at high SOC:
If we put these points ( for 10 months) in the classic NCA/NMC/LFP- degradation graph, it doesnt look different than earlier:
As this test was at 55C, the values do not look different at all. They fit the earlier like a glove.
These researchers did come to this conclusion:
”Keep it at 100%SOC and 25C and it will hold up for 80 years”
No, I dont think so. We see the same pattern as earlier LFP. Perhaps they stay healthy longer than it looks, but the data we have do not point at any revulotionary changes.
Last edited:
That film that formes is Solid Electrolyte Interface (SEI).
SEI formes at all types of Li Ions, and they act as a protector for the other types as well. The initial forming of the SEI is good, but the growt of SEI uses up useful lithium and makes the SEI sensitive, which can cause cracks. High SOC is a motor for SEI growth.
We like the SEI to be thin. We keep it thin by keeping the SOC low when the car sleeps.
Very high SOC tends to cause cracks in the SEI, which is bad.
Mrbrock
Active Member
For all you battery geeks out there, is this a normal view when the rear tray is removed showing the back of the battery or is this something different? And can anyone zoom in and clean up the A battery label?
European type certificate - Battery Data:
- LG Chem
- Designator 5L / M50 / E31
- Model 3 + Y
- Long Range + Performance
- Q4/2021 - ???
- NMC according to Tesla (NCMA according to rumours)
As I think we said when the news came; NCMA is supposed to combine the best of NCA and NMC and increase the capacity to a higher level than 2170L( at least according to the news revealing the NCMA).
The capacity in 5L and the calculations I made from the old LG M50 cell implies that this is not a new technology as the 5L do not reach the Panasonic 2170L capacity.
Most probable the ”good old” M50 NMC-cell.
Candleflame
Active Member
I think the general consensus was that NCM is maybe slightly longer lasting/more durable but NCA is a wee bit higher performing especially in cold weather and charges a bit faster. But pretty equal.
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