Ebike Lithium Battery use and CHARGING in Winter months - caution !

  • Thread starter Deleted member 4210
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Deleted member 4210

You probably know that its best to store your ebike battery in room temperatures throughout the year.

However, there are those in colder climates who may wish to use their ebike during temperatures that are much colder than the norm. You can probably ride your ebike in weather that is below 32F, but your battery performance will not likely be what you want, and range will decrease considerably.

MORE IMPORTANT however is charging that lithium battery. This applies to cell phones, and Tesla's, and ebike batteries.

The characteristics of the battery chemistry, suggests that you would be very prudent to wait until your ebike battery has sat long enough in room temperature before EVEN attempting to charge it. The BMS may protect it, and prevent charging if it is too cold, but I would not count on that at all, since the OEM's are not likely anticipating anyone riding, let alone charging an ebike battery in temps below 32 F.

This commentary below is from Karl Denninger, who is not necessarily a battery expert, but does a lot of work with technology in general and is one very smart dude.

"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.

Batteries work by using a reversible chemical reaction. When they deliver current the reaction runs one way, and when charged it runs the other. When a lithium battery is charged the lithium ions leave the cathode return to the anode, and when discharged the reverse happens through a chemical reaction in which the electrolyte provides the transport. The anode is a graphite compound and those ions intercalate, meaning they become intertwined into the anode's structure. Because the anode is a layered material this causes the anode to actually expand in size (that's accounted for in the design of the battery and is normal.)

The problem is that below freezing (0C, 32F) 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.

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.

So if you own a battery-powered car with such cells in it the vehicle has to prevent this from happening. It thus must monitor the pack temperature and do whatever it can to prevent the pack from ever going below freezing, because not only will that cause the pack to be unable to deliver its full capacity it is prohibited to charge the pack while any cell in it is below 0C. If the pack is charged in that state it is unsafe and may short internally, burst and catch fire without warning at any point in the future.

If a battery-powered car (e.g. a Tesla) is in your garage and plugged in then it has access to unlimited energy to prevent that from happening. Of course nobody is talking about how stupid it is to have a vehicle that constantly must consume power simply because it gets cold in order to defend itself against becoming a firebomb. That's not very "tree-hugger", right? Well, tough crap because that's exactly what the vehicle has to do due to the inherent reality of the chemistry in its battery system.

What's even worse, however, is if you drive said vehicle somewhere well within its range during below-freezing temperatures and then park it where it will go well below freezing and cannot be plugged in, or if you drive it under conditions that are cold enough that heat lost from the pack and its "cooling system" to the outside air becomes problematic. In either case the car will be forced to consume its available power to keep the pack over 0C -- shortening its return-trip range. If you operate or leave it out there for any material amount of time it will consume enough of that power that it is forced to shut down completely and in that state it cannot be charged until the pack is warmed with some source of external power or the car is towed somewhere warm and given enough time to warm up naturally!

Of course if it gets cold enough the pack will freeze and be destroyed anyway, but that temperature (for lithium cells) is unlikely in the Continental US to be reached on a sustained basis (no such bets are accepted for northern Canada and Alaska, however!)"