Historical LFP early-adopter misinformation story (long)

[Substrate]

toms and Gazoo are both right! Huh?

Toms is right that stopping at .05C is recommended *if you are going to do this on a repetetive basis*, where over the course of say 5 years of charging to absolute full, going to zero tail current adds up in time with secondary reactions. Of course this assumes the use of a charger that is higher that is typically at least 0.2C capable to begin with.

Gazoo is right that a one-time shot just to balance the cells at 3.65v even at a very low < 0.05C initial charge rate, especially in a sub-c application, you won't see any issue. A lab might, but for all practical purposes it's irrelevant. Let it go to zero current even. It's a one time shot.

Putting my propeller hat on, since Gazoo is already starting to balance at less than 0.05c, then technically the CV voltage should be dropped to 3.45v if secondary reactions are a keep you up at night issue.

BUT, as hinted at above with the Winston cells getting an initial higher than normal charge just once to make sure that all the active material has an even charge level spread across it, this function of starting out at 0.05C charge current or less, and instead of stopping at 3.45v, but 3.65v for balancing, replicates this initial one time high charge and may actually be beneficial for a one time shot!

So is there degradation? Not that you can measure on a practical level, unless you plan to charge to full this way every single cycle.

 

[toms]

Let me rephrase my question. If parallel top balancing four 280ah cells to 3.65 volts with a 10 amp power supply until the current of the power supply reaches zero how much damage is done to the cells?

Based on what i have seen in decade long tests regarding formation of the SEI, i would say up to 10% loss of lifespan.

The real question is why would you risk any cell damage parallel top balancing when it is simpler to serial balance with a good BMS?

 

[Substrate]

The SEI layer is pretty thin on new cells coming from the factory - just enough to keep the battery from eating itself. It takes 4 or 5 cycles for the SEI layer to develop to it's nominal thickness, so there is a bit of headroom for non-perfection in regards to reasonable time, voltage, or tail current aggravation of secondary reactions building up the SEI on new batts.

Lurkers: This is NOT to be misconstrued as "breaking in an LFP battery". Although maybe if you bought brand-new cells, and did not plan on using them for like 5 years (not a good idea), then a few cycles might be a good idea before normal storage. The very bad analogy for the SEI layer is like the air-filter on your car - it has to be there, but eventually it gets clogged.

toms - I've never seen that much degradation from one-shot balancing, serial or parallel. *Maybe* if you spent a lot of time on an old beater Thundersky Gen1 cell pulled from a circa 2005 electrified Mazda Miata - ok.

 

[Substrate]

To be fair to toms, I am thinking about becoming instantly very unpopular about commenting on Will's Miady 16ah teardown video, and the methods he used to do the test with where he got less than stellar results.

Not sure I want to go there so I don't appear like a disgruntled propeller-head, but yeah, there's a reason why I'd like him to redo the test under my conditions.

 

[Gazoo]

Based on what i have seen in decade long tests regarding formation of the SEI, i would say up to 10% loss of lifespan.

So if that applies to newer prismatic cells, and I am not sure we know if it does yet, maybe a year or two less? But that also would also depend on the usage of the cells and the cells environment. There is much data missing.

The real question is why would you risk any cell damage parallel top balancing when it is simpler to serial balance with a good BMS?

At the time I didn't think about it...was still in the baby stage. I learned a bunch before I ordered my cells and learned a bunch since then, and am still learning. The best part was experiencing the thrill of parallel top balancing and then building the pack in series and connecting the BMS

 

[G8trwood]

Initial charge to 3.65 or 3.6?
Then subsequent at 3.45 or 3.5?

 

[Substrate]

Thing is, absolute textbook values varies depending on actual cell quality, and their designed power vs energy density, and used or unused and application. I brought this up in another danger-thread.

Thing is, we all gotta' work together as a team to pull of stuff like this with A123 LFP. Different application. Do I really have to drag Will to the track?

Leave our generic prismatics at home please.

 

[Gazoo]

Initial charge to 3.65 or 3.6?

Initial parallel top balance yes.

Then subsequent at 3.45 or 3.5?

When connected in series with a BMS it depends on your usage. There is not much capacity between 3.4 volts and 3.65 volts. Or between 3 volts and 2.5 volts. Keeping the cells voltages between the knees will extend cycle life and deliver low deltas (the voltage difference between the cells). Thus the cells will be happy.

 

[toms]

At the time I didn't think about it...was still in the baby stage. I learned a bunch before I ordered my cells and learned a bunch since then, and am still learning. The best part was experiencing the thrill of parallel top balancing and then building the pack in series and connecting the BMS

Everyone is still learning about LiFePO4. One of the most infuriating aspects is that accelerated testing can’t be used to predict low C operation. It is literally a different reaction that occurs at less than approx 0.5C current flow.

 

[Sojourner1]

Everyone is still learning about LiFePO4. One of the most infuriating aspects is that accelerated testing can’t be used to predict low C operation. It is literally a different reaction that occurs at less than approx 0.5C current flow.

True, It's not easy trying to find early adopters that switched to LFP and have been using in a fractional C use day in and day out. Like you said it would take a long time to get some sort of data other than it works well but not knowing what the true time period that a battery bank can be put in to operation and continuously be used.

There was (or is) a forum that I lurked at out of Australia that had folks using LFP off grid. The credentials for the web page stopped working for me and I deleted the link and can't remember the page.

I've been 5 years in an everyday use living off of LFP/ solar with solar charging 99% of the time other than if I need to put a hold over charge on the bank I'll use a small generator. See sig for system. There are others with double the time that I have.

 

[toms]

There was (or is) a forum that I lurked at out of Australia that had folks using LFP off grid. The credentials for the web page stopped working for me and I deleted the link and can't remember the page.

That would have been the energymatters forum. Long gone now.

Many good discussions there, and i have kept in touch with a lot of people that have been using LiFePO4 for well over a decade now.

Dacian (electrodacus) was a very interested forum member as he was developing his BMS.

It’s interesting to me that the introduction of very cheap LiFePO4 has introduced a whole new customer base, many of whom believe LiFePO4 is a new thing.

Things have certainly become a lot simpler now, and yet some people still manage to complicate things at times.

 

[Sojourner1]

Yes, That was it. There was a lot of good info there especially the early adopters that shared it. It's something to read threads from new comers just dipping their toes into LFP asking the questions that were answered many years ago or having revelations that were seen and experienced before, some trying to reinvent the wheel.

 

[grizzzman]

True, It's not easy trying to find early adopters that switched to LFP and have been using in a fractional C use day in and day out. Like you said it would take a long time to get some sort of data other than it works well but not knowing what the true time period that a battery bank can be put in to operation and continuously be used.

There was (or is) a forum that I lurked at out of Australia that had folks using LFP off grid. The credentials for the web page stopped working for me and I deleted the link and can't remember the page.

I've been 5 years in an everyday use living off of LFP/ solar with solar charging 99% of the time other than if I need to put a hold over charge on the bank I'll use a small generator. See sig for system. There are others with double the time that I have.

T1 Terry was a early adopter in LFP in Australia, mostly RVs. They have a real need for A/C though.

 

[Sojourner1]

T1 Terry was a early adopter in LFP in Australia, mostly RVs. They have a real need for A/C though.

He posts at the cruisersforum still. Many folks could learn going back many years and reading/ researching great info form the past that people learned and failed in the process of installing LFP packs. History has away of repeating itself.

What are RVs but just mobile off grid homes at 12v.

 

[grizzzman]

He is a moderator in a forum in Australia. He specializes in all electric solutions "T1 Lithium" is his web site. I read the whole original LFP thread years ago on the cruiserforum. It was a Huge read then.

 

[Substrate]

I remember that forum thread on cruisersforum starting in what - 2011? Followed it religiously until it just got silly.

At the time, when LFP started making consumer inroads, the lead-acid guys went nuts. "You'll never be able to prove the cycle life! -- see, they catch fire! (usually pointing out NON-LFP incidents)" FLA forever! Lotsa' bench-racing followed for both performance and pricing.

I actually outlived my GBS LFP bank, where the calendar life was more of an issue than cycling - even though I did a LOT of that. And I'm the kind of freak that tears it all apart, cleans connectors and busbars, points IR thermometers on it like a nut, test overall and individual cell capacity yearly and so forth.

Eventually, toward the end with great maintenance, but not much cycling, it became apparent that aging, not normal cycling was making me outlive the bank in a sub-c application.

 

[toms]

test overall and individual cell capacity yearly and so forth.

One of our test banks that is approaching 15 years old now has never been outside the 20-80% SOC range since its initial propagation.

As you said, in the early days nobody thought these cells would be good for more than 5 years. Approaching 20 years and it seems less important to squeeze every last bit of calendar life out of them.

Unless you dissect a cell and scan the anode/cathode at a microscopic level you don’t really know what the failure mode is.

Most dendritic failures i’ve seen are from a combination of charging at high temperature, or charging at high current when the cells are close to full.

 

[Substrate]

Right! Stay out of the knees as much as possible. Although most will want to do that at least once if they are top-balancing.

What the simplified lab-charging cycle charts don't tell you is that to achieve that 2000 cycle span, they didn't hit them up at .5 or 1C when down in the discharge knee as they did their cycle test!!

When you get into the discharge knee, to get out of it without causing secondary reactions, you can't hit them up with full-rate charge until you get out of it, typically near 12.8v for a nominal 12v LFP.

Most people don't understand that LFP can't intercalate well enough upon recharge when coming out from the discharge knee.

So what happens? In extreme cases, active material gets blown out into the electrolyte, contaminating it. Dendrites, if not directly shorting as a safety problem upon heavy recharge, are "micro-shorts" and contribute to the apparent IR and higher self-discharge.

Or, if not blowing material into the electrolyte, the huge voltage differential creates ion-storms - they can't intercalate fast enough so they bounce around on each other like gamma rays inside the sun. Creates secondary reactions, and guess where they land? The SEI layer.

Sorry man, I know you know this. That's why way back I was telling people to derate their stated LFP capacity by at least 20% if they wanted to do a long term sub-c application and stay out of the knees. The FLA guys smiled, but that's the way it is.

 

[The New JC777]

What the simplified lab-charging cycle charts don't tell you is that to achieve that 2000 cycle span, they didn't hit them up at .5 or 1C when down in the discharge knee as they did their cycle test!!

Can you provide a source for this statement? Speaking to the EVE LF280 cells, EVE's charts and instructions do not mention this.

 

[Substrate]

Honestly, no I cannot. A trusted old EV'er friend (rip) tipped me off. But that was back in the day when we were told that it was ok to top-balance at 4.2v. Other little things, like graphs copy-n-pasted from others, and lacking important detail was common, so lack of manufacturer details were not questioned, but considered standard-operating procedure. I didn't question it.

Perhaps that's because a lot of us adopted the measure of not hammering cells when down in the knee when you limped your LFP EV into the garage at 0.3v. Which was not ideal, but recoverable if you charged slow. But if hammered in the garage the next morning, without getting somewhat out of the knee before applying full charge current, that cell was never the same.

Solar users may be coming out of a deep knee like this early in the weak morning sun and not know how good that is that it is happening naturally.

For the most part, it is a cross-application concern of motive power which brings demons like this out, whereas with EVE cells and fractional-C use, yeah, no problem.