LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[evm1024]

Originally Posted by Dockhead

I use my boat in cold places, yet I can't imagine this ever being a problem. Charging at -5C? This temperature is not anywhere close to being inside the operating range of the boat itself. As long as the boat is in water (as opposed to being frozen in sea ice or on the hard in very cold weather), it will be at least plus something inside, even if no supplementary heat is being provided. And in normal operating conditions, we will be heating the boat in cold weather and it will be at least +10C.


So for actual practice, I can't imagine anyone would need anything other than a temperature sensor in the battery box and mental note not to charge at high rates on the odd occasion that the batts might be at less than +5C.


Since leaving the batts in low SOC is not a problem I can't imagine you'd ever be in such a big hurry to charge if you are coming onto the boat after leaving it without heating and it gets unusually cold inside. You'd heat it up first, then think about charging. In an emergency, you could do a short heavy discharge first to warm the batteries up, but can't imagine why you would ever need that.


Or am I missing something?

You are quite right. As Denis pointed out there are no "real" issues charging (at typical cruising boat rates) at the temperatures we see in our boats. His batteries are rated to charge at a few degrees below freezing. Ans should my boat get below freezing I've got bigger issues with the fresh water lines and sea water in the heat exchangers.

Layed up for the winter includes setting up the battery for the winter.

On the other end high heat is likely an issue to mitigate - more so for those in the tropics.

My batteries are in the engine room and I've thought of moving them into the living spaces due to temp. Under load in temperate zones I run somewhere between 105 F and 109 F. It was encouraging to hear Denis speak of 140 F as a region where heat induced reduction of life is significant. And that the effect is heat induced increase in the calendar aging rate.

Good stuff in that video that supplants "common wisdom" with real information based on specific testing.

[evm1024]

I took the time to get a copy of the paper from which the degradation mechanisms slide used in the video came from. I found the papers abstract specifically apropos pedantry.

For example:

I know what I know because I know what I know.

vs

I know what I know because I put a few batteries in an oven and measured the effects.

If there is a point to this posting it would be a plea to "cite your sources". That way we can judge the value of the information presented.



Abstract
Degradation in lithium ion (Li-ion) battery cells is the result of a complex interplay of a host of different physical and chemical mechanisms. The measurable, physical effects of these degradation mechanisms on the cell can be summarised in terms of three degradation modes, namely loss of lithium inventory, loss of active positive electrode material and loss of active negative electrode material. The different degradation modes are assumed to have unique and measurable effects on the open circuit voltage (OCV) of Li-ion cells and electrodes. The presumptive nature and extent of these effects has so far been based on logical arguments rather than experimental proof. This work presents, for the first time, experimental evidence supporting the widely reported degradation modes by means of tests conducted on coin cells, engineered to include different, known amounts of lithium inventory and active electrode material. Moreover, the general theory behind the effects of degradation modes on the OCV of cells and electrodes is refined and a diagnostic algorithm is devised, which allows the identification and quantification of the nature and extent of each degradation mode in Li-ion cells at any point in their service lives, by fitting the cells' OCV.

[Dockhead]

Originally Posted by evm1024

I took the time to get a copy of the paper from which the degradation mechanisms slide used in the video came from. I found the papers abstract specifically apropos pedantry.

For example:

I know what I know because I know what I know.

vs

I know what I know because I put a few batteries in an oven and measured the effects.

If there is a point to this posting it would be a plea to "cite your sources". That way we can judge the value of the information presented.



Abstract
Degradation in lithium ion (Li-ion) battery cells is the result of a complex interplay of a host of different physical and chemical mechanisms. The measurable, physical effects of these degradation mechanisms on the cell can be summarised in terms of three degradation modes, namely loss of lithium inventory, loss of active positive electrode material and loss of active negative electrode material. The different degradation modes are assumed to have unique and measurable effects on the open circuit voltage (OCV) of Li-ion cells and electrodes. The presumptive nature and extent of these effects has so far been based on logical arguments rather than experimental proof. This work presents, for the first time, experimental evidence supporting the widely reported degradation modes by means of tests conducted on coin cells, engineered to include different, known amounts of lithium inventory and active electrode material. Moreover, the general theory behind the effects of degradation modes on the OCV of cells and electrodes is refined and a diagnostic algorithm is devised, which allows the identification and quantification of the nature and extent of each degradation mode in Li-ion cells at any point in their service lives, by fitting the cells' OCV.

Sounds reasonable. My battery box is under my raised salon floor so in a place with moderated temperature -- probably between 10C and 20C with very rare excursions above or below that. So for me temperature low and high should be a non-issue, but YMMV in the tropics. I guess it should be eminent good practice to have temperature sensors and instrument panel readout of cell temperature and ambient temperature in the battery box, and probably some kind of alarm for out of range temps.



Just like with different BMS functions, this would seem to be good practice for lead batteries, too.



For really hot climates, I wonder what best practice is. At what temperature do LiFePo4 batts start to significantly degrade?

[evm1024]

Originally Posted by Dockhead

Sounds reasonable. My battery box is under my raised salon floor so in a place with moderated temperature -- probably between 10C and 20C with very rare excursions above or below that. So for me temperature low and high should be a non-issue, but YMMV in the tropics. I guess it should be eminent good practice to have temperature sensors and instrument panel readout of cell temperature and ambient temperature in the battery box, and probably some kind of alarm for out of range temps.



Just like with different BMS functions, this would seem to be good practice for lead batteries, too.



For really hot climates, I wonder what best practice is. At what temperature do LiFePo4 batts start to significantly degrade?

Denis talked about a 30% life reduction when exposed to 140 F (60 C) consistently. Any human occupied space should be under 30 C (TUC spec) and I know that my diesel will not like 60 C intake air temp at all.

You are using Victron as I recall. I switched from the Color Control GX to the Venus GX just because the Venus GX has 2 temperature inputs. I've not looked to set alarms for over temp but it "should" be possible.

[Dockhead]

Originally Posted by evm1024

Denis talked about a 30% life reduction when exposed to 140 F (60 C) consistently. Any human occupied space should be under 30 C (TUC spec) and I know that my diesel will not like 60 C intake air temp at all.

You are using Victron as I recall. I switched from the Color Control GX to the Venus GX just because the Venus GX has 2 temperature inputs. I've not looked to set alarms for over temp but it "should" be possible.

This is just "exposure", whether the battery is being charged or not? This is in terms of so-called "calendar aging", right?



If this reaches 30% only at 60C, then would sound like a non-issue for most boats, even in the tropics. I would think there will be a place on most boats which can be kept at 40C or below almost all the time, even in the tropics.


Here is an actual study of this question: https://uwspace.uwaterloo.ca/bitstre...atton_John.pdf which seems to contradict "only 30%". Storage at 60C kills the battery in a few months, according to this, at least at 0% or 100% SOC.


It's quite detailed and I have only skimmed it so far, but seems to say that calendar aging is drastically accelerated when storage temperature exceeds 50C, but is quite moderate at 35C. It looks to me like they were only testing aging at 0% SOC and 100% SOC; don't know if storage at the recommended range around 50% would make much difference.

[evm1024]

Originally Posted by Dockhead

This is just "exposure", whether the battery is being charged or not? This is in terms of so-called "calendar aging", right?



If this reaches 30% only at 60C, then would sound like a non-issue for most boats, even in the tropics. I would think there will be a place on most boats which can be kept at 40C or below almost all the time, even in the tropics.


Here is an actual study of this question: https://uwspace.uwaterloo.ca/bitstre...atton_John.pdf which seems to contradict "only 30%". Storage at 60C kills the battery in a few months, according to this, at least at 0% or 100% SOC.


It's quite detailed and I have only skimmed it so far, but seems to say that calendar aging is drastically accelerated when storage temperature exceeds 50C, but is quite moderate at 35C. It looks to me like they were only testing aging at 0% SOC and 100% SOC; don't know if storage at the recommended range around 50% would make much difference.

That was my take also.

[newhaul]

Originally Posted by Dockhead

This is just "exposure", whether the battery is being charged or not? This is in terms of so-called "calendar aging", right?



If this reaches 30% only at 60C, then would sound like a non-issue for most boats, even in the tropics. I would think there will be a place on most boats which can be kept at 40C or below almost all the time, even in the tropics.


Here is an actual study of this question: https://uwspace.uwaterloo.ca/bitstre...atton_John.pdf which seems to contradict "only 30%". Storage at 60C kills the battery in a few months, according to this, at least at 0% or 100% SOC.


It's quite detailed and I have only skimmed it so far, but seems to say that calendar aging is drastically accelerated when storage temperature exceeds 50C, but is quite moderate at 35C. It looks to me like they were only testing aging at 0% SOC and 100% SOC; don't know if storage at the recommended range around 50% would make much difference.

IIRC the calendar aging aspect was primarily a consideration untill the day that the cells are placed into service.

[evm1024]

I recall reading that Catton paper.

Here is what was said:

In research performed
by Grolleau et al., 15 Ah Li-ion cells aged at three different storage temperatures resulted in the
following capacity fades: cells stored at 30oC experienced less than 10% capacity loss after 450
days of storage whereas, at 45oC, capacity fade was 20% for fully charged cells [8]. In
comparison, fully charged cells stored at 60oC, reached a 20% capacity loss within only 60 days
[8]

Grolleau's paper was published in 2014 and I may have a copy somewhere. I'll have to see what cells were used. I think that it is safe to say that LiFePO4 materials have changes over the last 6 years that MAY have changes heat intolerance.

More later....

[Dockhead]

Originally Posted by newhaul

IIRC the calendar aging aspect was primarily a consideration untill the day that the cells are placed into service.

Why would that be the case?


The paper anyway contradicts that -- there is computer modelling of the total aging process over 10 years, aggregating cycle aging and calendar aging for EV's. Calendar aging component was about 2% a year in a cool climate at about 4% a year in a hot climate, in typical service. So 40% capacity loss over 10 years just from calendar aging.


I think it's worth taking this into consideration when designing a LiFePo4 bank -- since one of these should last a very long time in typical cruising boat service, but will be gradually losing capacity due to calendar aging. So we should probably oversize them a bit to take account of this effect, especially in a hot climate.

[rvlandlubber]

Originally Posted by Dockhead

Why would that be the case?


Calendar aging component was about 2% a year in a cool climate at about 4% a year in a hot climate, in typical service.

I don’t think I’m seeing this with my cells. My 200Ah Winston prismatics have a date stamp for May 2014. For about 2/3 of their life they have been isolated and stored at around 50% SOC. The rest of the time cycling on solar with max load less than 15 amps. Typical overnight discharge would be 60-100 Ah. Installed in my caravan all this time where ambient temperature would vary between min of 0 deg C to mid 40’s.

At year 4 (DEC 18) I decided to do a discharge test to get an idea of remaining capacity. Top balanced the cells then discharged at 30 amps until the first cell reached 3.00 volts, at which point the BMS disconnected everything. Produced 219Ah.

Year 5 (DEC 19) same deal except just used normal loads to discharge the battery, apart from the last few hours that were at 30 amps. (became impatient). Produced 221 Ah.
Not lab quality testing and I don’t have a baseline from new but the object was to adjust the SOC meter if necessary.

Anyway, one thing I’ve noticed about the care and maintenance advice from drop in LFP vendors and other system integrators is that it is rarely accompanied by their OWN empirical evidence. Just saying..

[CatNewBee]

There is a RV blog and web site in YT from a nomadic cruising couple usind LFP batteries for years (technomadia), that measured the degradation of their battery and empirically came to the conclusion it was the heat. Not Winston cells.

https://www.technomadia.com/lithium/

It's not boating, more land yachting so...

[CatNewBee]

Originally Posted by CatNewBee

There is a RV blog and web site in YT from a nomadic cruising couple usind LFP batteries for years (technomadia), that measured the degradation of their battery and empirically came to the conclusion it was the heat. Not Winston cells.

https://www.technomadia.com/lithium/

It's not boating, more land yachting so...

https://www.technomadia.com/2015/02/...attery-update/

[john61ct]

In cool temps calendar aging of quality LFP cells is nearly non-existent within sub-decade timeframes.

Yes heat changes that, and drastically, true for lead as much as the LIs

but it's a greyscale relationship like avg DoD vs lifetime, no magic B&W boundary or radical hockey stick inflection.

It would not be worth installing aircon just for a bank

but if you have a space that's cooler than others, putting the bank in there would be ideal.

And conversely as everyone knows, sticking it in an engine room comes at a high cost long-term.

If that really can't be avoided, then bite the bullet no point in stressing.

And note we're only talking heat from **ambient** conditions.

Studies based on higher-power density LI chemistries in high-C-rate applications like propulsion will usually be focused on internally generated temp rise from resistance

which at our low House level C-rates should hardly ever be even detectable.

[evm1024]

Originally Posted by evm1024

I recall reading that Catton paper.

Here is what was said:

In research performed
by Grolleau et al., 15 Ah Li-ion cells aged at three different storage temperatures resulted in the
following capacity fades: cells stored at 30oC experienced less than 10% capacity loss after 450
days of storage whereas, at 45oC, capacity fade was 20% for fully charged cells [8]. In
comparison, fully charged cells stored at 60oC, reached a 20% capacity loss within only 60 days
[8]

Grolleau's paper was published in 2014 and I may have a copy somewhere. I'll have to see what cells were used. I think that it is safe to say that LiFePO4 materials have changes over the last 6 years that MAY have changes heat intolerance.

More later....

....More now

The Grolleau paper was based on research done in France. The actual cells are not specified but we may deduce that they were a Saft product and we know that they were 2013 or earlier vintage technology at 15 Ah.

This paper as with many papers attempts to produce a mathematical model that can closely predict real world cell conditions based on some input parameters. Experiments are conducted and the experimental results are used to refine the model to more closely match the experimental results.

The point I am making is that the model does not have to match reality. Back when I was a research systems engineer on a modeling team our chief modeler said he had the best job because his models did not have to be real. Of course we sent ships out to measure the ocean area we were running models on to get real data to make the model better.

Most of the points of the paper are "common knowledge" in LiFePO4 circles but the paper does point out that there and many unaccounted for factors. It is best not be be so sure of our opinions that we ignore reality.

The first point from the paper is that high temps are more detrimental to cell life than any other factor for cells that are being stored. And that the SOC has a lesser effect. With cells stored at lower SOC have reduced loss of life compared to those stored at higher SOC (30% vs 100% SOC).

They also note that cycling based aging is different from storage based aging.

Their capacity testing was done at 1C rate (15 amps) with the capacity done at 25 degrees C.

For those who have access to the paper Figure 3 is the most important. It shows that there is about a 5% capacity loss over the 450 days of the test when cells were stored at 30C (86F) at any SOC (30%, 60% and 100% SOC).

At 45 C (113 F) the SOC 30% cells lost about 11%, 65% SOC lost about 17% and 100% SOC lost about 19%.

At 60 C (140 F) the SOC 30% cells lost about 28%, the 65% SOC lost 46% and the 100% SOC cells lost 50%.

it should be noted that these researchers found outlier cells that died much, much sooner than the other cells. They tossed out those results as is normal. And they also note that the aging processes are many and complex.

They also had a set of cells that they stored where the temperature varied between 30C and 45C each day (9 hours at 45C). These cells showed a reduction in capacity that fell between those cells stored at 30C and 45 C. This indicated that the reduction in capacity was directly related to the time at high temps.

Onto my personal observations and speculations.

These results are based on older technology cells. The changes to all parts of the chemistry over the last 8 years has been profound. Every thing from nano sized graphite, selective orientation of active layer depositions to changes in electrolytes and so on. In short the cells are better today.

I suspect that the outlier cells suffered from defects in materials and construction that (mostly) have been addressed over the years.

Given the advance in technology (and whatever improvements in cells) and given that this paper indicates that cells stored at 30% SOC at 60C have less than a 30% capacity loss I think that we can conclude that what Denis at Battleborn said is very consistent with the papers results.

Lastly I just did a quick google search and this jumped out at me:

Originally Posted by batteryuniversity

The optimum operating temperature for the lead-acid battery is 25*C (77*F). Elevated temperature reduces longevity. As a guideline, every 8°C (15°F) rise in temperature cuts the battery life in half.

[Checkswrecks]

There's a lot of test data out there which shows how storage is reduced by both temp and high SOC. Google lifepo4 aging temperature and then go to Images for examples.

The bit I'll add is that we did a lot of temp testing in accelerating rate calorimeters (ARC) and I know that Sandia has been doing a lot of EV battery testing under a series of NHTSA contracts. Temperature begins to diminish battery life (all types) somewhere just below about 40C (100F) and hotter, so echoing others, as long as you can survive without being too uncomfortable the batteries will have their longest calendar lives. Especially when they are kept somewhere in the mid 30s F to low 40s F.

There is a knee to the degradation at about 60C (140F) and we found that cells could actually begin to go into self heating. (Ref. https://www.ntsb.gov/investigations/...sic_Report.pdf , See Fig 7) They wouldn't go into runaway till much much hotter but enough heat was given off to show the breakdown in the internal chemistry had begun. When teaching classes the analogy I use is baking brownies when discussing temp and time. If the directions say 350 and you use slightly less time or temp you can keep them as batter longer and have the real soft gooey happy version. Put them in the oven for the right length of time at 350F and they come out great. Put them back in the oven either hotter or longer and nobody will want one.

On a related note is the following paper about how batteries are degraded by high charge rates and keeping Lithium cell at high SOC:
https://www.google.com/url?sa=i&rct=...78518935325324

I apply this stuff to my cell phone and battery tools too. Rather than putting the phone on a bed-side charger every night, all night, I use a wireless charger which is a low rate rather than what the phone comes with. When I do charge it, I'll usually take it off when about 80-90%.