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How critical is low-temp charging protection, really?

BroomJM

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Apr 7, 2021
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I have watched so many videos talking about low-temp charging protection, and I fully understand that you do not want to charge LiFePO4 battery cells when their temperature is at or even near freezing. I get that if you screw up and allow your batteries to charge when they are in a frozen state, you will damage and possibly even completely destroy them. That would be a very expensive mistake, but just how likely is it that we'll forget this important piece of information and charge cells when their temperature is too low? Doesn't it depend a lot on your use case, including when and how you would be charging the batteries back up?

I know there are a great many batteries being sold right now with no low-temp charging protection, but I don't hear very many stories from folks who failed to understand this and ruined their battery. I suspect this is because these batteries are used in locations where they are rarely exposed to freezing temperatures. It also seems like it would be a very simple matter to turn on a 12v seed tray warmer to get the cell temps up before attempting to charge them in extreme conditions.

Is this really a big deal, or is it simply something to be aware of if you buy/build a lithium iron-phosphate battery?
 
What matters is your actual battery location, whether that ever freezes, and if does so for long enough to take the actual cell temperature below freezing. Even then, it's not hard kill the cell, but rather greatly degrades lifespan issue.

Here in the tropics, I care not a whit about whether my BMS has protection. If I lived in a winter climate and had an unheated battery shed I would care quite a bit about it. Whether it matters to you is a question of you looking at your proposed installation.
 
At cold temperatures, lithium-ion migration rate through cell slows down.

During discharge it means you have greater terminal voltage slump for given demanded cell current and less extractable capacity from cell, but other than that, insignificant damage to cell. The extractable capacity will return when cell is warmed up again.

During charging, electrons enter graphite from negative copper anode connection but due to slow lithium-ion migration coming from cathode through electrolyte, the electrons looking for charge balance, immediately jump on the slow-moving lithium-ion population coming into anode, bonding with lithium ions before the lithium ions have a chance to find their parking spot in the graphite lattice structure (called intercalation).

This creates lithium metal plating in anode. It has two permanent damaging effects. It creates lithium metal that creates conductive metal dendrites that will grow and eventually punch their way through separator and short out cell. The more immediate degradation is the created lithium metal permanently ties up lithium that will no longer be free to be used in normal charge/discharge process. It is non-reversible and reduces AH capacity of cell.

Secondary degradation is a larger quantity of the sex starved electrons will jump the anode SEI protective barrier breaking into electrolyte where they bond with electrolyte components causing chemical decomposition of electrolyte. This is gummy tars that clog electrode pores increasing cell impedance and gas bloating. It is similar to overcharging cell.

0 degs C, freezing point, it not an absolute line in the sand. It is just the temp where below which the degradation effects greatly accelerate. The charging damage is reduced the lower the charge current rate. The damage is worse as the cell approaches full charge where there are less graphite parking spots left for lithium-ions. It is much better for charging and discharging if you can keep cell above +10 to +15 degs C.
 
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Leaving batteries unattended for a few days when temperature are near freezing is the reason why you want that option…. It’s not a matter of failing to understand.
 
The most important thing is that everyone has defaulted that LiFePO4 batteries should not be charged below freezing, so not many people will deliberately try and publish related threads. You also know that LiFePO4 batteries are not cheap products. Generally, when LiFePO4 batteries cannot be charged, most of us will select to LiFePO4 battery winterize, and not many people need to charge batteries below freezing point. But if there is such a need, then low-temperature charging protection is very important.
 
The most important thing is that everyone has defaulted that LiFePO4 batteries should not be charged below freezing, so not many people will deliberately try and publish related threads. You also know that LiFePO4 batteries are not cheap products. Generally, when LiFePO4 batteries cannot be charged, most of us will select to LiFePO4 battery winterize, and not many people need to charge batteries below freezing point. But if there is such a need, then low-temperature charging protection is very important.

This. Use case is the primary factor for the low temp protection. There are a few people on here, myself included, that are just unable to use LFP batteries because of environmental issues. Could we buy the fancier more expensive LFP batteries and rig up temperature control systems and heaters and hope they work? Yes. Is it worth the (SIGNIFICANTLY!!) extra expense to do so? No.

Do we WANT to? Oh HELLS yes!
 
I know there are a great many batteries being sold right now with no low-temp charging protection, but I don't hear very many stories from folks who failed to understand this and ruined their battery.

My understanding is that the damage is not readily apparent. It will affect the number of life cycles you can get out of a cell. How significant is that? I don't know, but I'm not going to risk it and that's why I put a warming system on my LiFePO4 cells.
 
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