Storage life and float voltage of lifepo4?

[swbluto]

Hello. It seems to be acknowledged by the battery university that a 40% State Of Charge is one of the best charge states for prolonging the storage lifespan of lithium cobalt, the kind for laptops and cell phones. Instead of declining to 80% of original capacity if held at its highest charge voltage corresponding to 100% charged for a year, it declines to 96% of original capacity if held at 40% charged at room temperature for a year. Source: http://www.batteryuniversity.com/parttwo-34.htm

The explanation for this often goes along the lines that it lasts longer to a lower voltage which produces less stress on the battery. By this logic, it should last even longer at lower charges (like 20%) but I assume they provide some buffer room due to whatever small current the battery protection circuit uses.

So, would the same mechanism be true of lifepo4? If so, wouldn't one have to discharge it to 0-10% to get a noticeable decline in voltage since its voltage curve is pretty flat and thus prolong life? Or would 20% charged be just about as effective as 90% charged since the difference in voltage is so small for lifepo4?

Or is there some other peculiar storage life mechanism behind the scenes kind of like how lead batteries has the sulfation feature/annoyance that prefers 100% floating charge?

 

[Ypedal]

The one thing i know WILL kill a lifepo4 cell is letting it go below 2v, with that in mind i store my packs fully charged minus 2 minutes on the discharge rack to burn off the 3.4v+ charge.. then they sit at 3.2x volts for as long as i leave them sit.

Might be good.. might be bad.. but that's how i do it.

 

[rscamp]

I think the main issue with using a very low SOC for storage is the risk of the cell voltage going too low with the passing of time due to self-discharge. I suspect also that when the cells get below about 50% SOC the advantage of going even lower is rather small. The really big improvement probably comes from dropping the SOC down from 100% (i.e. the SOC vs. life curve is not linear).