LiFePo⁴ battery in extreme cold

[thepartyhound]

It is well known that LFP batteries cannot be charged at temps below 32°F (0°C), but what temps can LFP batteries be discharged at? I know the BMS on my SOK batteries shut off the battery and prevent discharge at a certain temp, but I forget what that temp is exactly. -15°F ballpark seems about right, but it might be slightly lower.
My question is what temp does DISCHARGING LFP begin to cause damage. Is there a low temp that will cause instant damage if the BMS were bypassed and the cells were to to be discharged, and if so, what is that temp? Any info on extreme low temp discharging is welcome! Thank you!

 

[Adam De Lay]

The numbers I’ve always seen are:
- minimum charge temp: 32F
- minimum discharge temp: 0F

 

[RCinFLA]

Depends on what you call acceptable discharge performance. Discharging at low temp is not significantly damaging to LFP cell but the cell's voltage slump under load current gets greater as temp get lower.

Theoretical limit is freezing point of electrolyte which is about -60 degs C (which will likely damage cell) but depending on load current, the terminal voltage may collapse too much at about -10 to -20 degs C temp for reasonable load current demand performance.

Lithium-ion migration through the electrolyte gets more sluggish the colder the electrolyte.

 

[thepartyhound]

I guess I would consider acceptable as being able to discharge at enough current to assist in warming the cells. I was under the impression that damage would be incurred by discharging at cold temps. If this is not the case, why does the BMS on my SOK battery prevent the battery from discharging at cold (sub 0°F) temps? Would there be any negative effects of disabling BMS from preventing discharge in sub 0°F temps?

 

[thepartyhound]

In summary, is discharging at say 200 Watts at -30°F going to cause permenant damage to a 12v 100Ah LiFePo⁴ battery? How about using it to crank the starter on a V8 engine at the same temp up to 170A, or whatever the maximum output of the battery happens to be at that temp.

 

[Wjm1964]

There's a video on YouTube where a guy freezes then discharged a lifepo4 battery from Li-Time. It still worked and was interested to see how the voltage actually increased as the battery warmed up.

 

[thepartyhound]

There's a video on YouTube where a guy freezes then discharged a lifepo4 battery from Li-Time. It still worked and was interested to see how the voltage actually increased as the battery warmed up.

I'll have to keep looking for that video. So far my search results have only pulled up guys using LiFePo⁴ batteries to power their freezers!

 

[wpns]

In summary, is discharging at say 200 Watts at -30°F going to cause permenant damage to a 12v 100Ah LiFePo⁴ battery? How about using it to crank the starter on a V8 engine at the same temp up to 170A, or whatever the maximum output of the battery happens to be at that temp.

Sure, you can discharge it, but don't allow it to charge from the V8 engine till it warms up above freezing.

 

[gotbeans]

Insulating them and heating them causes them to produce more power than they otherwise would when cold. So there's not much of a reason not to.
I tested this winter with 4 inch of rock wool and 20 watt heater

 

[thepartyhound]

Sure, you can discharge it, but don't allow it to charge from the V8 engine till it warms up above freezing.

Yeah, that goes without saying. Any halfway decent quality battery is going to have a BMS in it that prevents it from charging when it is unsafe to do so.

Insulating them and heating them causes them to produce more power than they otherwise would when cold. So there's not much of a reason not to.
I tested this winter with 4 inch of rock wool and 20 watt heater

Yeah, for sure. Mine are insulated and heated as well. All good information and good advice for anyone looking for that. However, what I am trying to determine is if a LiFePo⁴ battery can be damaged by discharging at an extreme cold temp and if so, at what temp and/or discharge rate. So far the answer I seem to have gotten seems kind of like a no, but at some temp the battery will only be able to discharge at a very low rate.
Either way, I am still looking for a definitive yes or no answer. If the answer is in fact "No, a LiFePo⁴ battery will not be damaged by discharging @ 1C down to -40°F", then why is the BMS set to prevent the battery from discharging at low temps?

 

[gotbeans]

Yeah, that goes without saying. Any halfway decent quality battery is going to have a BMS in it that prevents it from charging when it is unsafe to do so.

Yeah, for sure. Mine are insulated and heated as well. All good information and good advice for anyone looking for that. However, what I am trying to determine is if a LiFePo⁴ battery can be damaged by discharging at an extreme cold temp and if so, at what temp and/or discharge rate. So far the answer I seem to have gotten seems kind of like a no, but at some temp the battery will only be able to discharge at a very low rate.
Either way, I am still looking for a definitive yes or no answer. If the answer is in fact "No, a LiFePo⁴ battery will not be damaged by discharging @ 1C down to -40°F", then why is the BMS set to prevent the battery from discharging at low temps?

Pretty much every manufacturer I see says it's fine to discharge down to -20C virtually all of those tests are at 0.5C rating.
No test I see goes down to as low as you say though... and also none that go over 1C which is odd as lifepo4 can handle quite a bit higher discharge rates. I don't see many higher rates even with the temp being room temp though

You see BMS with these settings maybe because of the weird voltage fluctuations lifepo4 has at below 0C temperatures. The voltage curves do weird dips which they don't do otherwise?
Also dealing with the difference between charge/discharge temperatures might be too much for them to deal with lmao. So they just shut it all down at X temp

unrelated but interesting study I found while reading

lithium ion batteries|LiFePO4 battery | Shenzhen A&S Power battery

LiFePO4 Battery and the Zero Voltage Test

www.szaspower.com

 

[thepartyhound]

That was interesting.

 

[thepartyhound]

I have a message in to Current Connected with this question. I look forward to hearing back from them.

 

[thepartyhound]

Hahaha! I simply cannot get a straight answer from currentconnected on this. I get answers including "industry standards" and things like "the manufacturer would not set the discharge cutoff at this limit if it weren't going to damage the battery". I am getting every answer possible besides "Yes, the cells of an SOK battery will be damaged if discharged below -4°F".

 

[wpns]

Hahaha! I simply cannot get a straight answer from currentconnected on this. I get answers including "industry standards" and things like "the manufacturer would not set the discharge cutoff at this limit if it weren't going to damage the battery". I am getting every answer possible besides "Yes, the cells of an SOK battery will be damaged if discharged below -4°F".

Maybe nobody knows for sure?

 

[thepartyhound]

Maybe nobody knows for sure?

You'd sure think there has been SOME kind of documented testing on something so simple as this by now!

 

[S Davis]

EVE states discharge temperature -35c to 65c, probably depends on cell manufacturer though.

 

[thepartyhound]

EVE states discharge temperature -35c to 65c, probably depends on cell manufacturer though.

View attachment 209019

Thank you! That's the first published information that I have seen showing something other than specs for when the BMS cust off!
I am not sure if SOK uses Eve cells, so this may not be 100% applicable. I would think that all batteries of this chemistry should be pretty similar.