LiFePO4 Lifespan (not cycle life) question
Does anyone have any data on the lifespan of LiFePO4 batteries, by which I mean the retained capacity over time? Many manufacturers publish cycle life data showing that 2000 cycles, etc. are achieveable, but I'm specifically interested in the effect of time on the capacity.
For example, if I only cycle my battery once a week, a 2000 cycle lifespan to 85% capacity will in theory last until 2046. I wouldn't mind betting though that capacity is lost year by year.
Does anyone have either manufactuer's data, theoretical predictions or real world experience?
The answer is, nobody knows yet. We are all experimenters at this point.
The conservative assumption is that LiFePO4's are similar to other lithium ion chemistries. That is, if stored at 20-25 C and fully charged, they lose at least 20% of their capacity per year even if never cycled. But, if stored at 50% discharged and 0 C, they lose only a couple percent per year.
However, based on the greater "durability" of the phosphate electrode material's crystal structure (which the lithium ions must lodge themselves into, and out of, when charged/discharged), we have good reason to believe that LiFePO4's will have better shelf life, along with their already-demonstrated better cycle life, than the other lithium chemistries.
For now, I am keeping my LiFePO4 motor scooters in an poorly/unheated garage, discharged down to 60% or so, for the winter. I will charge them only as needed for rides during the occasional mild spells.