Best LifePo4 charge controller settings known to man for Maximum Service life and Minimum battery stress!!! 5,000-10,000+ cycles?

[Mr-Sandman]

Actually every piece of literature I have found lumps all Lithium Technology into the same group.
Instead of Ranting about the difference do you actually have some documentation that says it's OK to keep LifePO4 batteries at a constant 100% SOC? I am interested in learning the truth.

It's in THIS THREAD! I will go find the post for you.

Here's the 2 studies I was referring too, posted by Will:

https://www.mdpi.com/1996-1073/14/6/1732/pdf

Starting at page 60:
https://uwspace.uwaterloo.ca/bitstream/handle/10012/12177/Catton_John.pdf

 

[Steve_S]

Actually every piece of literature I have found lumps all Lithium Technology into the same group.
Instead of Ranting about the difference do you actually have some documentation that says it's OK to keep LifePO4 batteries at a constant 100% SOC? I am interested in learning the truth.

Please Review Cell Manufacturer Documents which all say teh same thing more or less pending on translation.

50% SOC of Working Voltage Range = 3.200Vpc
50% of Gross Capacity Range = 3.375Vpc. Which is why Fresh Cells typically arrive above 3.200 and more often closer to 3.300 or a little higher. Depends on how Fresh from Factory they are... LFP will slowly & naturally discharge so an indicator of how fresh they are is teh standing voltage when you receive the cells. The static discharge rates vary a bit between manufacturer formulations and therefore again refer to manufacturer docs & specs.

If you want RANT, go elsewhere. Understand that EVERY company has it's own personal chemistry mix/blend even with general LFP.
Several WhitePapers for you to peruse & learn from: http://liionbms.com/php/white_papers.php

 

[robby]

It's in THIS THREAD! I will go find the post for you.
---SNIP---
Starting at page 60:
https://uwspace.uwaterloo.ca/bitstream/handle/10012/12177/Catton_John.pdf

LOL that's funny because I went to page 60 on my PDF Prg and it was actually page 44 of Document.
The very first thing I read is this:
_______________________________________
4.2 Analyzing cells stored at 100% SOC at different temperatures
The two variables that most affect degradation within Li-ion cells under OCP conditions are
temperature and SOC. [9] The most predominant cause of degradation under OCP is the storage
temperature of the cell. When the storage temperature for the cell is high, secondary reactions
proliferate causing accelerated losses of the cyclable lithium (the main source of losses within
the cell). [6] Testing of various cells at different SOCs but under the same temperature storage

45
conditions has, also, led to the determination that SOC plays a major role in cell degradation.
[14] Cells stored at elevated SOCs experienced increased battery degradation compared to those
stored at lower SOCs [61]. SOC represents the proportion of ions present on either electrode,
thus, for high SOC there is a significant number of lithium-ions available at the graphite
electrode to partake in potential side reactions with the electrolyte.
In addition to the irreversible capacity losses that can occur at high SOC, the degree to which
reversible capacity will occur is also affected. In comparison to the irreversible losses that can
occur within the cell, reversible losses were found by Safari and Delacourt to be more affected
by SOC than by temperature. [14] Li-ion batteries do experience the lowest reversible capacity
losses.
--------------------------------------------------------------------------------
Once again like in every other document I have seen they talk about it as being a Lithium issue and then separate out Lithium Ion as actually having less of a problem than other Lithium chemistries.

I have to leave for a bit but will pick this back up later when I get back home.

 

[Mr-Sandman]

I'll admit some of the wording in the research papers such as highlighted is a bit inverse of what I see and read in the actual testing results. Maybe missing some context, like at elevated temperatures, higher SOC is terrible for batteries, but in general high temps are bad at any SOC based on the studies. That is what prompted my questions, that and a few people stating that 100% SOC is bad for them, which is NOT what I saw in all the testing posted.

From what I understand, 90% to 100% SOC (3.4v or less per cell) and 25c is ideal to maintain LifePo4 batteries at. That's what I'm currently doing in my application and plan to do until someone post something that backs up it is not.

 

[robby]

I'll admit some of the wording in the research papers such as highlighted is a bit inverse of what I see and read in the actual testing results. Maybe missing some context, like at elevated temperatures, higher SOC is terrible for batteries, but in general high temps are bad at any SOC based on the studies. That is what prompted my questions, that and a few people stating that 100% SOC is bad for them, which is NOT what I saw in all the testing posted.

From what I understand, 90% to 100% SOC (3.4v or less per cell) and 25c is ideal to maintain LifePo4 batteries at. That's what I'm currently doing in my application and plan to do until someone post something that backs up it is not.

I have come across documentation that confirms that it is the same for LifePo4 but I don't know how reliable the sources are.

For Example: https://relionbattery.com/blog/charging-lithium-batteries

So Relion Battery states:

What About During Storage?​

Lithium iron phosphate batteries are so much easier to store than lead-acid batteries. For short-term storage of 3-6 months, you don’t have to do a thing. Ideally, leave them at around 50% state of charge before storing. For long-term storage, it is best to store them at a 50% state of charge and then cycle them by discharging them, recharging them and then partially discharging them to approximately 50%, every 6-12 months.

I am still searching for more Info and have also shot off a request to Fortress Battery for Info.

 

[curiouscarbon]

LOL that's funny because I went to page 60 on my PDF Prg and it was actually page 44 of Document.
The very first thing I read is this:
_______________________________________
4.2 Analyzing cells stored at 100% SOC at different temperatures
The two variables that most affect degradation within Li-ion cells under OCP conditions are
temperature and SOC. [9] The most predominant cause of degradation under OCP is the storage
temperature of the cell. When the storage temperature for the cell is high, secondary reactions
proliferate causing accelerated losses of the cyclable lithium (the main source of losses within
the cell). [6] Testing of various cells at different SOCs but under the same temperature storage

45
conditions has, also, led to the determination that SOC plays a major role in cell degradation.
[14] Cells stored at elevated SOCs experienced increased battery degradation compared to those
stored at lower SOCs [61]. SOC represents the proportion of ions present on either electrode,
thus, for high SOC there is a significant number of lithium-ions available at the graphite
electrode to partake in potential side reactions with the electrolyte.
In addition to the irreversible capacity losses that can occur at high SOC, the degree to which
reversible capacity will occur is also affected. In comparison to the irreversible losses that can
occur within the cell, reversible losses were found by Safari and Delacourt to be more affected
by SOC than by temperature. [14] Li-ion batteries do experience the lowest reversible capacity
losses.
--------------------------------------------------------------------------------
Once again like in every other document I have seen they talk about it as being a Lithium issue and then separate out Lithium Ion as actually having less of a problem than other Lithium chemistries.

I have to leave for a bit but will pick this back up later when I get back home.

this resource is also available in the resource section

Calendar Aging and Lifetimes of LiFePO4 Batteries and Considerations for Repurposing

A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Applied Science in Chemical Engineering. by John Catton Abstract In response to rising petroleum prices, the demand for lower...

diysolarforum.com

in the paper, "OCP" stands for Open Circuit Potential

 

[curiouscarbon]

found this fun tidbit in "Calendar aging of commercial graphite/LiFePO4cell – Predicting capacity fade under time dependent storage conditions"

Calendar aging of commercial graphite/LiFePO4 cell – Predicting capacity fade under time dependent storage conditions

In applications such as electrical transportation, most of the battery life is spent under storage. Understanding and estimating aging under storage, …

www.sciencedirect.com

if someone can find the actual full text PDF, please link it here so I may read it.

C/LFP cells were submitted to 11 storage conditions during at least 450 days.

Capacity fade rate is both SoC and temperature dependent

this paper is is reference [8] in John Catton's thesis (Catton_John.pdf)

 

[robby]

this resource is also available in the resource section

Calendar Aging and Lifetimes of LiFePO4 Batteries and Considerations for Repurposing

A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Applied Science in Chemical Engineering. by John Catton Abstract In response to rising petroleum prices, the demand for lower...

diysolarforum.com

in the paper, "OCP" stands for Open Circuit Potential

Y

View attachment 84989
found this fun tidbit in "Calendar aging of commercial graphite/LiFePO4cell – Predicting capacity fade under time dependent storage conditions"

Calendar aging of commercial graphite/LiFePO4 cell – Predicting capacity fade under time dependent storage conditions

In applications such as electrical transportation, most of the battery life is spent under storage. Understanding and estimating aging under storage, …

www.sciencedirect.com

if someone can find the actual full text PDF, please link it here so I may read it.




this paper is is reference [8] in John Catton's thesis (Catton_John.pdf)

Now that lines up perfectly with all the other info I have been reading and hearing. Keep in mind that this is only looking at roughly the first 18 months of hooking up a LiFePo4 pack and keeping them fully charged. I came across another chart that looked at years and projected a number of around 20% capacity loss in less than 3 years if the batteries are kept fully charged. I suspect that is right as Dendrite growth accelerates once it starts. I did not trust the source enough to consider it reliable so I moved on. I am still looking but it's hard to find anything from a major company. I suspect that almost half of all LiFePo4 cells sold for solar use are used in standby mode, so it makes sense that none of the companies wants to kill 50% of their sales by making this widely known. Also it would kill Battery Generator sales if people knew the unit cannot just be thrown in a closet fully charged.

 

[Mr-Sandman]

So this image seems to agree with the charts in the other study that one thing is for sure, lower temps are better for life of the cells. SOC doesn't really show much different when battery is stored at 30c. The other chart actually showed longer life with higher SOC at 25c, this one slightly lower.

Best SOC to hold batteries at for long periods of time might be of some debate still, but one thing seems to be consistent and clear, keeping your batteries as cool as possible, but above freezing is best for them.

 

[robby]

It's in THIS THREAD! I will go find the post for you.

Here's the 2 studies I was referring too, posted by Will:

https://www.mdpi.com/1996-1073/14/6/1732/pdf

My Eyes My Eyes
I just read almost all 21 pages of this Article.
I did not like how the paper focused in on LiFePo4 batteries but would then stray into Lith ion batteries for other things. It would have been nice if they had clarified that both chemistries follow the same rules. As I have said before I suspect they do and for people who would be normally reading this I guess it is a known fact.

Anyway the summary of all of this is that, Yes as we know already temperature is the big killer and SOC is the second killer.
The findings show that batteries that are kept at 90% and above SOC had a shortening effect on battery life and increasing ESR during the life of the battery / until it reached 80% of capacity left. I found it very odd that after that point that a 50% SOC would actually increase the degradation further. So yes, so far everything points to the fact that keeping LiFePo4 batteries fully charged and on standby is going to shorten their life. If someone can find something to the contrary I would love to see it.

A Quote from his conclusion:

On one hand, the low storage temperatures helped reduce the change rate of capacity and resistance,
and the change rate increased exponentially as temperature increased from 25 ◦C to 55 ◦C.
On the other hand, the SOC level had a piecewise effect on the rate of both capacity fade
and resistance increase. Before the capacity fade reached 20%, which could be taken as
the cutoff-point, higher SOC was accompanied by a higher rate of capacity fade. After the
cutoff-point, the influence of mid-SOC increased, which led to the rapid loss of capacity.
Meanwhile, the effect of SOC on the internal resistance was similar, except that the cutoff
point turned out to be a 30% increase in resistance.

 

[Mr-Sandman]

If someone can find something to the contrary I would love to see it.

What does the actual test data and the charts tell you? In all the studies you looked at that I posted and the one posted by @curiouscarbon?

I see higher SOC being better in many cases and not much different in others. One thing I do see is lower temps make a huge positive difference, no matter SOC.

 

[robby]

What does the actual test data and the charts tell you? In all the studies you looked at that I posted and the one posted by @curiouscarbon?

I see higher SOC being better in many cases and not much different in others. One thing I do see is lower temps make a huge positive difference, no matter SOC.

I totally agree that temperature is the number one factor but the charts shown only go out to 450 days with a noticeable increasing trajectory dip at the 380 day mark for 30 DegC. If nothing changes and I was to draw that 100% SOC line going out to lets say the 5 year mark or 1825 Days it looks like it would be a huge drop in capacity.
The fact that the 30% SOC line validates what Fortress Power told me gives me a bit of confidence that their other statement about 100% SOC being kept for long periods of time as being bad is probably correct.

My own experience with Lithium Ion has been that Laptops that are plugged in almost all the time tend to have dead batteries at about the 3 year point while ones that are cycled tend to last for about 5 years.

Based on what I have seen so far I think the solution is pretty simple, just cycle your batteries once every two weeks and mitigate the chances of having a problem later down the road.

I am kind of shocked that one of the big battery manufactures has not published a guideline for this, but then again as I said before, it might not be in their financial interest to do so.

Update: Just Noticed a reply from Fortress Power:
Li batteries all should not be kept at 100%. Keeping them constantly on a charger so the SOC is always at 100% will affect lifetime. By cycling the battery down from 100% then charging back the published aging numbers based on cycles are correct.

 

[Mr-Sandman]

So what about this chart from the other study done @robby? What is it telling us?

 

[robby]

So what about this chart from the other study done @robby? What is it telling us?

View attachment 85028

Your killing me
I read his statement on the graph and I am puzzled. I am not a battery expert, maybe someone else can explain.
-----------------------------------------------------------------------
As shown in Figure 12, the SOC levels at both ends (smaller than 20% SOC or larger
than 80% SOC) and cooler temperatures preserved the Li-ion battery when not in use. The
tested battery cells would be able to withstand approximately 45.1 years if stored at 10%
SOC and 25 ◦C until they reached the EOL criterion. However, the lifetime will decrease
dramatically to 23.8 years if the cells are stored at 50% SOC and 25 ◦C or to 8.7 years if the
storage temperature is 40 ◦C.
----------------------------------------------------------------------------

I get that his is saying that this is without cycling the battery, what I don't get is his numbers for storage. 45.1 YEARS!! and 23.8 YEARS if stored at 50% SOC. And he is talking about Lithium Ion which we know has a much shorter lifespan than LiFePo4. So I would assume his chart would say LiFePo4 has a 150 Year storage life!! Dunno, maybe I am missing something obvious like maybe he is just talking about the electrolyte lifespan and not the Anode, Cathode or Separator. Maybe he meant Months and Not Years! My brain is already spinning from all the reading

This paper from the Government testing center makes more sense for Li-ion batteries.
https://rosap.ntl.bts.gov/view/dot/31257

 

[robby]

Fortresss Power sent me some Links this Morning.

1) https://mospace.umsystem.edu/xmlui/...ng-Shihui-Research.pdf?sequence=1&isAllowed=y (See Page 33- )

2) https://css.umich.edu/sites/default/files/publication/CSS20-08.pdf (Have not looked at it yet)

 

[Mr-Sandman]

Fortresss Power sent me some Links this Morning.

1) https://mospace.umsystem.edu/xmlui/...ng-Shihui-Research.pdf?sequence=1&isAllowed=y (See Page 33- )

2) https://css.umich.edu/sites/default/files/publication/CSS20-08.pdf (Have not looked at it yet)

Nice, except they are not specific to this discussion, but more general on Lithium Ion batteries. LifePo4 chemistry, from what I've read, can't be lumped in with Lithium Ion batteries in general. It's different behaves differently. These studies make note of the LifePo4 chemistry, but were not done on LifePo4 specifically....

 

[Sojourner1]

But the papers all have a L in the battery type so it has to be the same.?

 

[robby]

But the papers all have a L in the battery type so it has to be the same.?

Not following you. All Lithium batteries work on the same principles. The only difference is the energy density, which is greater with Li-Ion and the Amount of cycles which is longer with LiFePo4. If it bothers you it's no sweat off my back if you want to keep your batteries at 100% SOC permanently. Just don't come crying in two years and say your capacity has dropped by 20% and you got ripped off.

 

[Mr-Sandman]

I'm not sold on high SOC "not past 3.4v per cell" being an issue with LifePo4. In fact there is studies with data I keep pointing to that shows in the data it might even be better at high SOC and cool temps. Every study I've read so far that shows negative effects with storing at High SOC was not specific to LifePo4. I have provided a couple that were specific that shows high SOC being OK or even better.

It doesn't really matter, I'm going to keep my between 90% and 100% SOC either way. That's what I bought them for, to be charged and ready for a power outage.

 

[robby]

Nice, except they are not specific to this discussion, but more general on Lithium Ion batteries. LifePo4 chemistry, from what I've read, can't be lumped in with Lithium Ion batteries in general. It's different behaves differently. These studies make note of the LifePo4 chemistry, but were not done on LifePo4 specifically....

Because as I said all Lithium batteries share several properties. The papers you linked to me also went back and forth between Li-Ion.
As stated above the power density of Li-Ion is much greater the LiFePo4. The Tradeoff is that Li-Ion has a shorter Lifespan and less Cycles.
You can do as you want with your batteries, just don't complain when the capacity is dropping off every year.