Why you cannot charge LiFePO4 below 0 degrees Celsius

Just John

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I believe the only cells capable of below 0C charging are Winston LiFeYPO4 cells the yttrium gives them a wider range.

But they are more expensive
I think you'd better verify that information with Winston before telling people this. Please do share a data sheet that tells us this.
Certainly the specs they post seem to imply this:


But they wouldn't be the first battery manufacturer to publish incorrect temperature data.
I seriously doubt they can be charged at -45 degrees Celsius especially since they say "WATER-BASED lithium yttrium power battery".
Perhaps yttrium is an anti-freeze that also magically does away with the lithium plating at low temperatures?
 
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NobodyOfNaught

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@Just John why so confrontational? I'm not making some wild claim about a battery from some fly by night Alibaba distributor.

Winston was the first manufacturer of prismatic lithium cells and never read about anyone who's had a bad experience with Winston cells.
 

Just John

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@Just John why so confrontational? I'm not making some wild claim about a battery from some fly by night Alibaba distributor.

Winston was the first manufacturer of prismatic lithium cells and never read about anyone who's had a bad experience with Winston cells.

We live in a very litigious society. One manufacturer of batteries just recently started selling batteries they advertised could be charged down to -20 Celsius, guess what? It was discovered the actual cell manufacturer in China had made a mistake in copy/paste cell spec sheet, and it propagated to the battery assembler here in the States that was advertising it heavily, because "it could charge below zero", when in actuality, you'd destroy the battery very quickly by trying. The Winston cells might very well charge at that temperature without self destructing, but no other cell manufacturer makes that claim. This board is aimed primarily at beginner or entry level, and every one likes to come up with this rare edge case exception and tell everyone about it. What happens? Beginners read this, and try to do it with their cells, and destroy a couple of thousand dollars worth of cells, and the first thing they will say is "but so and so said it was OK". You don't want to be that so and so.
 

opticalcarrier

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well i certainly do not want to put lithium batteries in my garage, much less my house. Really, outside it the only way. I guess Ill build a shaded enclosure for them outside. It only rarely gets below freezing here, but does regularly get up into high 90s.

Say, during an outage during freezing temps, the batteries would be used.. then, would the act of discharging the batteries cause them to warm up enough such that solar/genset could charge them w/o damage?
 

Hedges

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Lithium batteries are pretty efficient, and little power is dissipated especially during discharge so little self-heating.
You are better off providing electric heaters. It can take a long time for heat to soak through, so I would apply heat on one side and measure temperature elsewhere (possible a point in the center of the pack, less affected by air temperature.)


Sounds like the "frost line" would not be below ground in your location. So burying the batteries might help. Don't want water getting to the cans (which are apparently electrically connected) so maybe have the batteries elevated and wrapped in a waterproof bag, but with an earthen berm built up around them.
 

DerpsyDoodler

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well i certainly do not want to put lithium batteries in my garage, much less my house. Really, outside it the only way. I guess Ill build a shaded enclosure for them outside. It only rarely gets below freezing here, but does regularly get up into high 90s.

Say, during an outage during freezing temps, the batteries would be used.. then, would the act of discharging the batteries cause them to warm up enough such that solar/genset could charge them w/o damage?

The heat will hurt them before cold will. As I understand it, as long as you don’t charge or discharge below certain temperatures, you’ll see little if any degradation. Not sure the same can be said on the other end of the spectrum.
 

HRTKD

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well i certainly do not want to put lithium batteries in my garage, much less my house. Really, outside it the only way.

Why? LiFePO4 batteries are safer than lead acid batteries because they require no venting in normal situations. Only a catastrophic failure would cause a LiFePO4 battery to vent. These are not like the older Lithium chemistry that made the news when they caught fire.
 

Luthj

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LFP can be discharged at any temperature down to the freezing point of the electrolyte.
 

Sailor77

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My batteries are going in an off grid cabin that is mostly unoccupied in the winter months. I have a diesel generator set up to autostart when the batteries get down to 12v. I installed 2 x 12w 12v bee hive heating pads under each battery. I have a Honeywell aqua-stat in the battery enclosure that is set at 34F with a 5F differential to turn on the heating pads as needed.

What kind of heating pads are you using, and at what wattage?
 

Sailor77

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Substrate

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Say, during an outage during freezing temps, the batteries would be used.. then, would the act of discharging the batteries cause them to warm up enough such that solar/genset could charge them w/o damage?

I'm only remarking on this as an *emergency* procedure, not something you would do on a normal basis. Use other methods to keep your LFP warm if you can.

If you had to do a rapid turnaround during a snap freeze, and had *no other choice*, you could try to lessen the damage by hitting them up with a few heavy discharges, with pauses in between, before trying to recharge.

Now please don't laugh. The Motorcycle LFP starter guys use this "cold start technique" to get going by putting a heavy load to warm up the battery. Thing is, scaled up to our system sizes, would you ever get a heavy enough discharge to warm up? They'll turn on headlights for a little while, turn them off and wait, repeat, and then try to start. The wait period is important not only to allow the starter to cool, but also to allow the cells heat spread out a little bit.

The guy was trying to be helpful, and of course is not our application. He's using an LFP batt, although never specifically mentions it - just a generic "lithium" battery, but LFP is what's there. I thank him for trying to be helpful to members of his community.

So please don't take this as some sort of universal magical solution. It is just an idea to perhaps lessen the damage you would do if you were forced to charge during an emergency in an attempt to get your bank a little warmer lessening (not totally removing) the damage.

If we want to analyze further, after the bike starts, it is recharging at a low temp, but hopefully internally it has warmed up a little to not be quite as damaging. Again - emergency last-ditch effort to possibly save just a little bit of damage - not an operational standard operating procedure.

I was super-hesitant to even post this, because NOBODY should think this is the magic-bullet for our application. It is NOT.
 
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HRTKD

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Given the density of the cells, it takes a long time to warm them up. With the understanding that my battery warmers are designed to provide low, steady heat, it takes over 45 minutes to bring the cells up to 35° F from below say 20° F.

If you know you have a charge source, it may work out better to use the battery power to warm the cells first. That way you can charge.
 

upnorthandpersonal

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If you know you have a charge source, it may work out better to use the battery power to warm the cells first. That way you can charge.

Or use the charge source, i.e. solar, to warm them up to the temperature you need before charging. If you don't have enough solar for that, you don't have enough to charge them anyway so no need to deplete the battery to heat it.
 

HRTKD

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Or use the charge source, i.e. solar, to warm them up to the temperature you need before charging. If you don't have enough solar for that, you don't have enough to charge them anyway so no need to deplete the battery to heat it.

In my case I would have to fool the solar charge controller into thinking the battery was up to temp. Not a huge deal, but does require changing some parameters. I think it could be done in one step on the Victron BMV-712.
 

Just John

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My experience (but consistent and repeatable), is that during discharge, the last 40 to 50 amp hours will raise a cell about 5 degrees Celsius. Everything up to that will raise a cell about 2 degrees maximum. Don't count on discharge to help a lot if you are significantly below zero. Even that little help is right where you should be very nervous.

These are Eve 280AH cells.
 
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