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I have used LiFePO4 batteries, only in discharge mode, by down to -15 deg C (charging was done 'back to the warmth'), and they worked fine. But from what I read it looks like Li-* batteries do not like to be charged by minus temperatures.

I would like to use large LiFePO4 cells with a solar panel by negative temperatures (typically -15 deg C, may be down to -30 deg C). I will have quite low charging currents, max 1 to 1.5Amps for a 40Ah cell. Do you think it may be OK to charge at such low rates (this guy seems to say no: Solar powered single cell LiFePo4 charger circuit ; but here it sounds like very low charge may be ok http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures)?

Has anybody more specific experience with this? Or has anybody knowledge of a place where I may get military / space grade cells that accept cold if usual LiFePO4 is a no go, or alternative battery chemistry solution? FYI, here are the cells I use as by now:

http://www.batteryspace.com/lifepo4-prismatic-module-3-2v-40-ah-10c-rate-128-wh-----un38-3-passed-dgr.aspx

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  • \$\begingroup\$ I can't give you a real answer. But my understanding, based on conversations with a battery expert, is that the chemical reaction rate inside the battery slows down due to cold temperatures. (Arrhenius equation). If you try to charge at a rate faster than the chemistry can support, you will get some other undesirable reaction (I think metallic lithium may electroplate onto the anode) and rapid destruction of the battery can result. But this does imply that very slow charging may be permissible. \$\endgroup\$ – mkeith Jun 11 '17 at 4:45
  • \$\begingroup\$ Consider insulating battery and using charging input to raise battery temperature. I just did some rough calculations on this and the energy required is more than I'd hoped. eg for a car battery sized unit (say 60 Ah +/- a bit) bringing it up by 20 degrees C with 120 Watts worked out at about an hour. At your 1.5A that's "rather longer :-(. \$\endgroup\$ – Russell McMahon Mar 5 at 11:14
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When working on the fringes of specifications, it is always best to speak with an applications engineer at the manufacturer. They often have access to data that is not part of their published specifications.

With that being said, you should give careful consideration to thermal management within your design. For example, a large insulated thermal mass in contact with the cells will retain heat generated during the exothermic charging cycle. This will help prop up the ambient temperature of the cells during non-charging periods - such as at night.

The choice of enclosure color can also play a role in raising the average ambient temperature of the cells.

You may also go so far as to use your solar power to warm the cells until they reach an acceptable charging temperature. While this is not the most energy efficient approach, it is a pragmatic one that may enable the application.

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