Lithium adoption strategies for older coach

[Isaac-1]

Keep in mind that Battleborn uses cylindrical cells and the majority of other drop in batteries use pouch cells, I know that there are a number of trait differences between the two, I don't know if storage at high state of charge is one. Either way I would not blindly apply Battleborn suggestions to batteries which use pouch style cells.

[jharrell]

Originally Posted by Isaac-1

Keep in mind that Battleborn uses cylindrical cells and the majority of other drop in batteries use pouch cells, I know that there are a number of trait differences between the two, I don't know if storage at high state of charge is one. Either way I would not blindly apply Battleborn suggestions to batteries which use pouch style cells.

There is no electro-chemical difference its is just form factor they are both LifePo4 cells with exactly the same chemistry. There may be some difference in heat gain and dissipation purely due to the physical form factor but that should have no impact on storage. I have found some research that indicates prismatic cells age slightly faster in EV's due to physical stress factors in movement related again to form factor not SOC.

Floating at 13.6v after absorbing at 14.4v for a short time is 100% SOC on all 4s LFP batteries in the market cylindrical or prismatic (I am not aware of any pouch form factor batteries for consumer use) and the potential driven aging should be identical among them. I am open to any information to contrary.

[Isaac-1]

I was referring to prismatic being a class of pouch, either plastic or Aluminum cased, as cylindrical cells don't tend to suffer from the expansion / swelling issues, or need for compression as plastic case cells, which might have a relation to being kept at 100% charge state. Though of course there are those that claim cells that swell when held at 100% state of charge are inherently defective.

[jharrell]

Originally Posted by Isaac-1

I was referring to prismatic being a class of pouch, either plastic or Aluminum cased, as cylindrical cells don't tend to suffer from the expansion / swelling issues, or need for compression as plastic case cells, which might have a relation to being kept at 100% charge state. Though of course there are those that claim cells that swell when held at 100% state of charge are inherently defective.

There should be basically no swelling at 3.4v per cell if they are in good shape. It is true cylindrical cells provide their own compression due to form factor, with prismatics a case that provides some compression is more important, My SOK's have a metal case with some neoprene between cells and case to provide required compression. Giving proper design in both cylindrical and prismatics batteries they should have nearly the same aging characteristics as far as SOC goes due to identical chemistry.

IMO Battleborn is top notch in physical form factor design and should be able to handle the most physical abuse but their aging characteristic should be no different than my SOC prismatics at the same SOC given my mostly on-road class A RV. Remember Tesla is using CATL prismatics in their LFP versions.

[hclarkx]

Originally Posted by jharrell

There should be basically no swelling at 3.4v per cell if they are in good shape. It is true cylindrical cells provide their own compression due to form factor, with prismatics a case that provides some compression is more important, My SOK's have a metal case with some neoprene between cells and case to provide required compression. Giving proper design in both cylindrical and prismatics batteries they should have nearly the same aging characteristics as far as SOC goes due to identical chemistry.

I've struggled with the compression question. I have Calb cells that seem to have no cell case flexibility and so allow no swelling, at least none that is visible. Yet one of the 280 Ah aluminum case battery makers suggests compression that allows expansion, maintaining a minimum of 6 psi and a maximum of (IIRC) 27 psi with a preferred constant psi of 12-16 psi. They estimate an extra 1000 cycles with a compression system that meets these specs over one that provides little or no compression. This maker's suggestion would rule out a compression system that does not allow expansion; e.g., like the Calb cells. Some builders on DIYSolar build elaborate cases that achieve these specs. I just built three 12V 280 Ah batteries using threaded rods to clamp them. I snugged the rods up for handling then relaxed the rod tension after the batteries were in place in an RV. I left enough rod to add springs, but haven't done so yet.

The sides of the 280 Ah cells are about 50 square inches so 16 psi would mean 800 lbs of compression!!!! The plastic case of my Lifeblue battery couldn't possibly do that. I'm guessing your SOK also doesn't. Credible springs (about $3 each) on the four threaded rods on my 280 Ah batteries would provide about 140 lbs. Better than nothing I guess.

Thoughts?

[jharrell]

Originally Posted by hclarkx

The sides of the 280 Ah cells are about 50 square inches so 16 psi would mean 800 lbs of compression!!!! The plastic case of my Lifeblue battery couldn't possibly do that. I'm guessing your SOK also doesn't. Credible springs (about $3 each) on the four threaded rods on my 280 Ah batteries would provide about 140 lbs. Better than nothing I guess.

Thoughts?

I think you would be surprised what a properly designed plastic case can do its not 800lbs a specific point but across a larger area basically its the case trying to hold the battery together as the cells try to expand.

The info you are reference probably come from this thread on DIYSolar dedicated to this stuff, an amazing resource where one member speaks Chinese and was able to actually talk to the battery engineers for EvE:

https://diysolarforum.com/threads/ev...92/post-161742

What I gather this is new territory for everyone lithium tech is changing and improving very rapidly, these 280ah prismatics are very new and very large, My SOK has 206ah cells, 100ah packs have much smaller 100ah cells while Battleborn uses a bunch of little 3ah cells in parallel to get 100ah.

There is not a lot of solid data on the cycle life difference between compressed and not for various cell sizes and manufacture, the 280 EvE cells seem to have the best documentation and show 2500 cycles at absolutely no compression and 4000 cycles under optimal 12psi compression using a computer controlled hydraulic press apply the pressure perfectly no matter how much the battery expanded or contracts, obviously hard to do with either prismatic or cylindrical:



You can see by the following graph that there is not a lot of difference between 4 psi and 18 psi and according to the EvE engineer over compressing is worse than not compressing:



So for prismatics my conclusion is some compression is ideal and in a mobile environment with lot of shocks and movement you are going to want some sort of compression case just to hold everything together. My SOK's are made of metal and have a pretty well made internal framework to hold the cells under compression with neoprene shock absorbing pads between the case and cells and between the cells themselves. I would say it should provide at least 4psi compression without issue, notice the cells aren't just compressed against the thin outer walls but there is an internal frame that ad significant stiffness:



Battleborns being cylindrical cells provide their own compression but it will never be a perfect 12psi as it will go up and down based on the internal pressures of the cell. Cylindrical cells are physically very robust but waste a lot of space when packing them together compared to prismatics, here is what a Battleborn looks like inside:

[RoadTrip2084]

Originally Posted by jharrell

There is not a lot of solid data on the cycle life difference between compressed and not for various cell sizes and manufacture, the 280 EvE cells seem to have the best documentation and show 2500 cycles at absolutely no compression and 4000 cycles under optimal 12psi compression using a computer controlled hydraulic press apply the pressure perfectly no matter how much the battery expanded or contracts, obviously hard to do with either prismatic or cylindrical:

You can see by the following graph that there is not a lot of difference between 4 psi and 18 psi and according to the EvE engineer over compressing is worse than not compressing:

So for prismatics my conclusion is some compression is ideal and in a mobile environment with lot of shocks and movement you are going to want some sort of compression case just to hold everything together. My SOK's are made of metal and have a pretty well made internal framework to hold the cells under compression with neoprene shock absorbing pads between the case and cells and between the cells themselves. I would say it should provide at least 4psi compression without issue, notice the cells aren't just compressed against the thin outer walls but there is an internal frame that ad significant stiffness...

I too am struggling with determining the right style of box/case for my battery. Realistically, I'm never going to need the additional cycles that compression can provide due to the low utilization of this battery in my coach. That and the fact that applying the "right" amount of compression seems daunting at best, has me leaning toward simply using large zip-ties to hold the cells together, with either thin cutting sheet material between them or maybe some kind of neoprene bumpers. I don't have a lot of space where I want it to go so trying to fit it inside a standard Group 24 battery box.

It's easy to overthink this stuff, which is fun to do of course.

Do the SOK batteries use continuous sheets of neoprene between the cells, or just corner bumpers?

[jharrell]

Originally Posted by RoadTrip2084

Do the SOK batteries use continuous sheets of neoprene between the cells, or just corner bumpers?

Looks to be a couple strips near the center at least in this 100ah teardown:

https://youtu.be/RjpkI8quyzQ?t=383

My 206ah may have more strips but hard to tell as I didn't full teardown the cells, Also mine has strips between every cell vs that tear showing the first tow cells missing neoprene between them, not sure if that was manufacturing goof or intended.

Strips allow some air space for cooling while providing the physical pressure needed toward the center where bulging would occur vs the edges that are strongest.

In the video above it is mentioned they are not under compression, however if they do expand slightly due to high SOC and heat etc. so they should go under compression on their own, how much psi that is would be interesting to know and how much thought was put into that design for compression. Either way the SOK life cycle tests show over 3500 cycles for what thats worth.

[RoadTrip2084]

Originally Posted by jharrell

Looks to be a couple strips near the center at least in this 100ah teardown:

https://youtu.be/RjpkI8quyzQ?t=383

My 206ah may have more strips but hard to tell as I didn't full teardown the cells, Also mine has strips between every cell vs that tear showing the first tow cells missing neoprene between them, not sure if that was manufacturing goof or intended.

Strips allow some air space for cooling while providing the physical pressure needed toward the center where bulging would occur vs the edges that are strongest.

In the video above it is mentioned they are not under compression, however if they do expand slightly due to high SOC and heat etc. so they should go under compression on their own, how much psi that is would be interesting to know and how much thought was put into that design for compression. Either way the SOK life cycle tests show over 3500 cycles for what thats worth.

Thanks for posting that teardown video - very interesting.

I think I will follow the SOK Battery lead and use thin neoprene strips between the cells. Can get a roll of 100' of 5/16" x 1/16" thick neoprene tape for $10 Cdn. I will use 4 or strips between each cell.

Then I will probably use large zip ties to hold the whole thing together. and drop it into a regular plastic battery box, with some kind of padding under it.

[paul65k]

FYI.....here is the interior of the Lion Energy UT1300's.

These batteries use prismatic cells and the unit is constrained within its own powerpack within the case, which seems to be purely cosmetic

[RoadTrip2084]

Originally Posted by paul65k

FYI.....here is the interior of the Lion Energy UT1300's.

These batteries use prismatic cells and the unit is constrained within its own powerpack within the case, which seems to be purely cosmetic

Looks like they used polyurethane or something to seal the battery to the case?

[hclarkx]

Originally Posted by jharrell

There should be basically no swelling at 3.4v per cell if they are in good shape.

I overlooked your mention of this earlier. I exercised the three aluminum case cell 280 Ah 12V batteries that I made and found that swelling occurred mostly under high discharge currents. I discharged them at 60 amps down to about 35% SOC and from there discharged at 129 amps down to just below 20%. That's were I saw the greatest cell expansion. Once charged and sitting for a while they were not flat-sided but had lost nearly all of the expansion.

I only had 60 amps of charge current so could not test at higher charge currents.

FWIW, I used fish paper between my aluminum cased cells. Others have used thin kitchen chopping mats.

[jharrell]

Originally Posted by hclarkx

I overlooked your mention of this earlier. I exercised the three aluminum case cell 280 Ah 12V batteries that I made and found that swelling occurred mostly under high discharge currents.

Yes my understanding is swelling occurs from both heat and high SOC. Both work together to cause aging.

High discharge rates generate heat in the cells through IR however in your case if I am reading right you have 12 280ah cells in a 4s3p config for 840ah at 129a your only at 0.15C discharge which should be very easy on the cells generating minimal heat, I wouldn't normally call that high discharge since the cells are rated a full 1C continuous typically.

[hclarkx]

Originally Posted by jharrell

Yes my understanding is swelling occurs from both heat and high SOC. Both work together to cause aging.

High discharge rates generate heat in the cells through IR however in your case if I am reading right you have 12 280ah cells in a 4s3p config for 840ah at 129a your only at 0.15C discharge which should be very easy on the cells generating minimal heat, I wouldn't normally call that high discharge since the cells are rated a full 1C continuous typically.

Sorry, I wasn't clear. I tested each battery individually at 60 amps and then 129 amps for the last 20 minutes down to a bit under 20% SOC. I used 129 amps as a rigorous test because these batteries are going to see some high loads though hopefully not that high (387 amps total). I was limited to 129 amps because the Overkill BMS are set to trip at 130 amps and actually do. I added load to an inverter until the BMS shut down (I was testing it as well) then backed off a bit. I actually was able to see 129 amps for a while though I think at the end of 20 minutes it was down to 127 amps IIRC.