I didn’t say zero. I said close to zero. The 0.05 is actually a myth. The real science will tell you that absorption is a phoney phase in Li. If you high C charge , absorption time at CV isn’t needed at all in fact. Much that is written about lithium is salesmen pitches rather then deep technical understandings
Yes, we all know this. Lithium wasn't designed to float, nor absorb - *but people are going to do it anyway*. Get your head out of the lab, and into the real world so we can make the most of it, or limit the degradation if we do.
Float is bad , because ANY voltage impressed on a LI termination will cause Li ion movement. SEI layer growth and lithium plating. The research papers are there to read.
Yes, again I know. However, ALL those papers are assuming a constantly available ac-charge setup, and not solar, where the input source gets turned off each and every day. That alone can limit or skew the degradation. It can also allow for limited applications of simplistic cc/cv routines, but the operator has to know his setup as to what is good or bad - *from a practical standpoint*.
Lab-perfection treatment can also have one running the practical risk of outliving the battery chemically when they don't need to. Usually seen as simple IR aging.
It’s not a sweeping statement it’s simply the truth !
Truth should sometimes take into account the practical side of things for those of us not running systems with lab-perfection. This gets your dander up, I know.
Equally these days with charge control it’s easy to stop chargers and prevent float modes.
Have you ever seen the newcomers who are just starting out with a cheap controller who simply don't have that capability? The system won't blow up or die tomorrow, although we'd prefer that they upgrade. But in the meantime, we don't tell them that they are idiots for not using a controller that may be out of their budget.
And again, you keep narrowing the application focus where it may not apply practically. Like in a vehicle where float is used as a minor load trap to prevent things like parasitic loads from dragging the battery down to the LVD behind the ops back and the road trip is spent solely trying to charge the battery.
There's lab perfection, and there are also different details for those using the system for weekend warrior duty, or those using them for standby UPS type of operations. The details are VASTLY different.
By the way it’s best to avoid any charging < 0.1C as it promotes SEI layer growth and degrades cycle life. The only time you need it is during a pre-qualifying charge phase.
So, instead of 10 years of reasonable life, you have to buy a new one in 9.5 years? Sometimes *industrial lab perfection* may not be practical for some users.
The big kicker here is that again - our application using variable solar conditions, we are QUITE FREQUENTLY charging at <0.1C ! Unless one has a large array, this can happen frequently in winter or during other inclement weather quite often for many hours daily.
But you bring up a good point about SEI layer growth - let's talk about it in regards to float - even though LFP wasn't designed for it. This is probably best for a different category, but I'll bring it up briefly here.
There is a "knife edge" voltage setting where SEI layer growth ISN'T promoted due solely to LFP's chemical structure. At 3.4v CV, or better at slightly under say 3.375v, LFP doesn't allow for so-called absorb to *want to try* to absorb. You'll see this knife-edge confound some who do this type of testing and do capacity tests. At 3.375v - bang - same (reduced) capacity every time. At 3.4v, depending on the vendors LFP mix, you may get slightly varying results in capacity tests due to the knife edge of this phenomenon.
At 3.4v or even slightly higher, chemically LFP *wants* to absorb to full capacity. Whether you actually do so or not is irrelative - the gates are open chemically so to speak. A cv of 3.375v or lower gets you under the knife edge where an absorb to zero or floating forever does no harm - provided you have started out with this, and not charged to full and fallen back to it! This is unlike some other chemistries. We can put this to use!
And this is what has bitten those using LFP for UPS type of duty, where like two-weeks later where they think they won't exceed say 70% capacity have actually reached 100% because even at 3.4v the gates are open and current dribbles in. But it took two weeks to do so - nevermind how harmful that is just getting there from a time perspective.
Stuff like this means one can offer the lab-perfect generalization, or take into account real world differing applications.
And from one engineer to another - since I know you can handle it - the only real world is solely your narrowly focused application, backed up by lab results that don't take in the vagaries of solar from a non-industrial viewpoint.
C'mon - lighten up from the lab. Take a walk on the practical side.
