Generally for long term storage is better lower temperature as well as lower voltage. Definitely recommend to use voltage bellow 50 % SOC which is bellow 3,7 V for majority of the cell. Good to remind that all producers from BIG FOUR (Panasonic/Sanyo, LG, Samsung, Sony) are sending their products to distribution at 3,5 V. Values in the chart are informative only, not absolute numbers, especially at low SOC end :
I love this forum :)
This very informative study shows a higher degradation of their NCA cathode material at higher voltages, leading to increased internal cell resistance. Don’t have time to look it up now, but it is in the study. Sorry, I read that and then forgot it before my last post.
And thanks for the chart, it is quite helpful. This is real information; I appreciate this forum too.
Yes, excellent information. I’m curious to know what long-term effect is on internal resistance. i.e, are high-discharge cells still good for high-discharge after 15 years, even when the capacity is still good?
Good question. This study utilized Panasonic NCR18650PD cells with the highest discharging current presented in the data sheet of 10 amps (page 16 of the document). There might be differences with other batteries, or maybe not much, I would not know. They did not test high discharge rates in this study. Let us know if you find out.
Concerning the difference in cells from different manufacturers (and the same cell from the same manufacturer produced later) the study sheds light on the changing landscape:
The cells were all of the same type but stemmed from two different production lots. The cells from the first lot were used in the first calendar aging study and in the cycle aging study on driving operation; the cells from the second lot, produced about six months later, were used in the second calendar aging study and in the cycle aging study on charging protocols….
As these cathodic side reactions are not observed in the second study, it is assumed that slight changes in the functional materials, such as modifications of the electrolyte and its additives, have reduced the cathodic side reactions of the cells examined in the second aging study, which were produced several months later.