Ok, scanned thru quickly; basically, I would read from this post onward:
Battery Degradation Scientifically Explained
which links to the paper about cathode cracking, and how staying below 60% SOC, will allow you to avoid cathode cracking that goes all the way from outer to inner, with pictures.
All of the posts afterward are good, then I would also look at this comment:
Battery Degradation Scientifically Explained
That post gets the optimal voltage charge limit to be 3.92V to eliminate all voltage-related stresses, from a Maxim Integrated blog, and believes that voltage is ~60% SOC.
And any post by EV-Tech Exp from the beginning of the thread is excellent. I don't really remember where I got 63% SOC from. Must have been a different thread.
Maybe I just came up with it myself. When you read some of these posts, you get that for every 70mV reduction is 10%, so if 4.1V is 90%, then 3.92V is around 64%, or something like that.
I didnt take the time to read the whole thread, or even the whole test that was refered to. I actually got a little sceptic beacuse they did some very extreme testing and the chosen test setups doesnt even come close to real world use of a Tesla:
The high cycle DOD was run from
4.3V !!! Anyone surprised if they wear out charged to 110-115% ? ( I didnt read so long that I found otut of it was a high voltage lion that was supposed to charge to 4.3V
The other low end, was down to empty battery but we have the low end buffer so we cannot get there, I think.
By the way, as I read the posts about this in this thread, I hope no one mix up DOD (Depth Of Discharge), the depth of the charging/discharging cycle with SOC (as I see a lot of 60% written, but 60% in that test is DOD, not SOC). That test can mayby say a little if it is read with a
lot of other li ion battery tests. Most of the tests have some kind of angle that not really fit, or that the test setup have five different currents, DOD, ans SOC levels and then it can be hard to draw the right conclusions of what actually caused a certain test setup(SOC,DOD, current) to "kill" the battery.
What we know is that we have mainly three different things that wear the batterys: Depth of discharge, current and aging.
Small charging/discharging cycles(DOD) is good for the battery and it isnt very importand to be above or below a certain SOC-number if we stay outside extremes. Low SOC cycles does hurt less then high with the same DOD.
High currents wear, we know that. A lot of supercharging at least increases the internal resistance, but as Its not that high currents for the whole charging cycle it seems to be not too bad. Driving very hard a lot should also affect battery life( both its worth that
)
Aging. For the most cars, the calendar aging is a big part of the battery wear as the car sits(and maybe sleeps) for 20-23hours a day.
This investigation is very well worth the time to read:
Panasonic NCA aging
It'll say that we should stay below the central graphite peak, which is at around 57% SOC. which should be in the ball park around 3.85V.
I have some 15 years experience with lithium batteries in radio controlled aircraft world. (Yes, I play with these, but to my defence I fly real aircrafts for the livin'
)
All lithium battery charger worth the name for R/C batterys have a
Storage charging mode and they charge between 3.8-3.85 v/cell for the same reason as above.
These chargers may be set to as high as safe to store the batteries, to have less charging to do when you need them, and what happens if left in storage with lower SOC then 3.8v is not 100% sience but as I have experienced it, the batterys that have done the winter with perhaps 20 or 30% doesnt keep the punch we need. They may well charge close to the original capacity, but dont perform when you need the power.
For what its worth, I'd like to stress that its important to read much more than one investigation/research report because the most of them doesnt tell the whole truth. When reading two reports, the conclusions might conflict, but if you look carefully at them and find a third you might find that the real reason wasnt high the SOC but maybe the high current that caused the difference. Actually, Id say it takes the reading of a handfull until you are ready to critically explore another battery investigaion/survey etc.
[Edit]: A little teaser from that survey.
[Edit2]The peak at 1.6Ah, central graphite peak is the one we would want to avoid if we like to half the calendar aging.
