I read an article today which points out a little-discussed danger with LiPo batteries: if they are allowed to drop below freezing temperature and attempted to be recharged, they are rendered permanently dangerous and could burst into flame at any time. (Think about this when you buy any device that has these batteries and is shipped to you in winter in colder climates).

The problem is that below freezing (0C) most of the lithium ions fail to intercalate into the graphite.  They instead plate out as metallic lithium on the anode. This blocks access to the lattice of the anode and thus transport of the ions; the result of that is a permanent and severe capacity loss along with much higher internal resistance (inability to deliver the desired current.)

If the bad news ended there it would be bad enough but it doesn't.  What's much worse is that metallic plating is not even. The introduction of lead-free solder saw a new phenomena show up in electronics called "dendrite shorts"; what happens over time is that the metal actually "grows" little spikes and if they grow far enough to reach another connection point you get a short circuit.

Metallic plating inherently forms these dendrites and they are sharp and uneven.

Recall that normal charging causes the anode to expand.  But now, instead of a nice even surface the anode has what amount to thousands of tiny little pins sticking out of it!

If mechanical shock or simply a high enough charge rate causes one or more of those "pins" to puncture the separator between the anode and cathode you get a direct short in the cell, the resulting short circuit causes the cell to heat, the electrolyte boils and bursts the case and the flammable electrolyte ignites.

In other words you get a battery fire.

With lithium-chemistry batteries, however, there is a second problem which is far more-serious: They cannot be recharged below freezing temperatures without being destroyed and, even worse, rendered permanently and immediately dangerous.

Even one charge in a lithium-chemistry cell that takes place below 0C not only will do severe damage to its capacity it also renders the cell permanently unsafe.  There is no way to know how unsafe the event has made it; no cell of this chemistry that has been charged while below 0C is safe to use as it can catch fire at any time without warning.

To Tesla Fans: Don't Live Up North

It is a common made advisory to not charge over-cold LiPo's as in fact all rechargeable batterys should be brought to room temperature ....

Some people put their liPo's in the fridge for storage ... fine ... some even use the freezer ... why freezer I have never understood. Many in fear of storing in house - leave them in the garage.

The above article implies that freezing a lIpo creates the hazard - not the charging of cold cells. Interesting ... never seen that item before. Worth taking note.

Nigel

Is this advisory in the instructions for the DJI Phantoms or their batteries?

I got from the article the main point as that charging COLD LiPo causes the dendrites to form due to failure of the ions to intercalate into the graphite. When this happens, uneven dendrites grow in the opposite direction. These spikey, sharp dendrites can puncture the insulating layer between cells, causing a short circuit, overheating and fire.

Due to the volatile nature of LiPo, I would not advise subjecting it to radical temperatures or pressures.

Yes, keep your batteries warm, for flying. Always.


RedHotPoker