Stoaty wrote:From what I have read, calendar life loss does follow the square root of time, so presumably the calendar life loss will slow.
From what I can find in posted literature, that type of degradation is what researchers use when they are fitting calendar life to data measured over the first 10 DAYS of the cell's life. In each case where researchers have actually MEASURED calendar life for many months, the degradation is at least linear and in many cases the degradation accelerates with time.
I have previously posted links to a paper that did measurements back in 2003. Here is a more recent study: 2007 Calendar Li-ion Pouch Cell Calendar Life Study - Zhang and White
. Granted, this is still on a different chemistry, but it shows the same effect. Interestingly, the degradation is linear unless the temperature is above 15C: at 25C and above it rolls off a cliff at some point. The researchers suggest there may be different mechanisms active at the higher temperatures.
I will say that the data we have for the LEAF battery so far does not look very promising, either. Some LEAFs with low miles have been well-pampered and still appear to be degrading quickly.
So I will ask, does anyone have *measured* data for pouch Li-ion cells showing calendar degradation that is linear for many months or years?