# Real experience on cold temperature charging of lithium cells?



## Siwastaja (Aug 1, 2012)

It is often stated that you may not charge li-ion (incl. LiFePO4) cells at all below temperature of 0 deg C / 32 deg F.

However, AFAIK, this is just a soft limit based on the rate of chemical reactions happening in charging, not a hard temperature point which would suddenly change the battery chemistry (like freezing point). 0 deg C just happens to be the freezing point of water, which would be utterly irrelevant for li-ion batteries.

One reason for the rule is that internal resistance is higher in cold, causing more voltage overshoot given the current normally used. This is however a curve, not a hard point.

Other would be that the intercalation reaction would not work as well in cold. Slowing down the charging, i.e., decreasing current, should compensate. This, also, cannot be a hard point.

My opinion is that you actually may charge a li-ion cell below 0 deg C, you just need to limit the charging current to lower values. And you probably should start the limiting curve even before 0 deg C. It can't be a hard limit.

As many people here have experience on using li-ion (especially LiFePO4) cells in _reality_ and cycling them for maybe years, would you mind sharing your experience? Anyone who dared to charge li-ion cells below 0 deg C? Did the world end?


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## dtbaker (Jan 5, 2008)

well.... my personal experience is that I have been able to garage my Swift at night while charging until a couple weeks ago when I rented it to a friend who has no garage. It doesn't get *very* cold where I live.... so what I am banking on is that I've instructed the renter to plug in and charge the vehicle immediately after returning home for the evening. I'm figuring that from driving around the internal temp of batteries will be above 0C, and that during charging it won't drop much as internal resistance will generate a little heat.... so batteries won't get cold until charge is complete.

other 'friendly' charge thing is that its just a wimpy 1500 watt charger, so not a huge fast charge... only 10 amps or so going in.

then, in am, USE will warm batteries internally and should be 'safe' although a little saggy and probably lower capacity than summer. 

The Swift does NOT have warming pads or cables in battery boxes, but they are fully enclosed, plastic, and 1/2" insulation in bottom so should retain heat for a little while...


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## Ams_AK (Jan 24, 2011)

The Elcon charger I use has a hookup to do temp reading. When below 0C, it limits charging output to 4.5A. when the cells heat up a bit it goes full throttle.
Seems to back up your reasoning.

Still no-one can really say, as you would not know until end of cycle life comes sooner then expected, and even then it is neigh impossible to account for all the other things that might have been ehh, sub-optimal


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## Salty9 (Jul 13, 2009)

From Evtech:

One significant danger with using Lithium cells in cold temperatures is
that if you charge below the minimum temperature, instead of the chemical
reactions happening normally, Li metal will plate the anode, causing
permanent capacity loss. So you need to make sure not to charge when the
cells are too cold!

-Morgan LaMoore


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## Elithion (Oct 6, 2009)

A good digital BMS (such as Orion BMS and others) prevents charging below 0 C, while still allowing discharging below 0 C. The parameters are separately adjustable. 

Unfortunately, analog BMSs do not protect against charging below 0 C

If you don't have a BMS, or your BMS doesn't do thermal management, you can easily implement a circuit to prevent charging below 0 C with a thermal cutoff and little else.


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## dougingraham (Jul 26, 2011)

Siwastaja said:


> As many people here have experience on using li-ion (especially LiFePO4) cells in _reality_ and cycling them for maybe years, would you mind sharing your experience? Anyone who dared to charge li-ion cells below 0 deg C? Did the world end?


My car sits outside and I charge from a 110VAC 15 amp circuit in the garage. To make sure I don't pop the breaker I have limited the charge to about 10 amps. I have charged when the outside temp is about 10F and the batteries might have been at 15F when I started. I've done this a hand full of times and the world is still here. GBS 100AH cells. So basically I am charging cold at a C/10 or less rate. They seem to take a charge just fine at this temp and level. The charge curve does not look any different.

I am not suggesting anyone do this, Just stating that I have done it a handful of times and I can't tell it harmed anything. But then I have not done a cycle test on a cell yet either in the first 1000 EV miles.


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## Salty9 (Jul 13, 2009)

It might be a good idea to have a temp sensor at the center of the pack to insure the entire battery is above freezing before charging.


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## Elithion (Oct 6, 2009)

dougingraham said:


> I am charging cold at a C/10 or less rate.


It turns out that a few cell manufacturers have told us, privately: "well, yes, you can charge at 0.1 C between -20 C and 0 C". Others have told us: " No way Jose."

If you think about it, most of us EVers do charge at below C/10. (My solar Sparrow is charged at a miserly C/160.)
For those who have very small packs, or very fast chargers, then you either don't charge below 0 C, or you use a BMS that has a cold charging function that measures the temperatures of each and every cell, and controls the charger current based on the minimum cell temperature.

(I know of only one that does.)


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## piotrsko (Dec 9, 2007)

Pete, (onegreenev) back when he was Gottdi still, froze a couple of cells and charged them. I don't recall the particulars, but I do recall it was a non-event.


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## Ziggythewiz (May 16, 2010)

One test is not enough to disprove potential damage. Just ask Boeing.


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