You don't even need a heat pump. You can just slightly overvolt the charger, so that some electrical energy is lost as heat rather get than transformed into chemical bonds.
> This is one of those Great New Technology items that smells like a failure simply because it's not competing with the thing the designers think it is.
This technology makes no sense for fast DC charging because there's enough waste heat to keep up the battery temperature, and you can just use some of the power to heat up the battery.
But it can help for slow overnight charging. Keeping battery heated all night is wasteful, but you still want to be able to charge.
That doesn’t work when the problem is the battery is already sub-zero - lithium plating occurs when trying to charge in those conditions, destroying the battery.
You can’t just overvolt out of that - you need an external source of heat until you’re out of the dangerous thermal area.
I'm not sure if that affects all chemistries and compositions. If you look at the spec-sheet for e.g. the LG E63 cells used in some older EVs (notably without TMS), those specify charging down to -20 °C - and the owner's manuals certainly have no warnings in them that the car will implode if you charge in the winter.
At least not in a way that people complain about battery failures or degradation. On the other hand, the battery has to reach that temperature in the first place, which may take a couple days of constant exposure to that temperature.
Actually, it does and will in the right conditions. Look at page 11 of that link.
I did some research, and the plating issue happens when charge currents exceed the ability for the battery to absorb them, which dramatically decreases below freezing.
That is why those battery charts show dramatically reduced charge currents (nearly zero) when around freezing.
That data sheet also doesn’t cover cell life in these conditions conditions.
They have very high normal C ratings (hundreds of amps) which is why it is measurable and not actually zero, but reducing it to a couple amps before failure isn’t much different.
If batteries aren’t failing in these conditions, it’s because of some other protective circuit, not because the battery itself is special. It isn’t.
> You don't even need a heat pump. You can just slightly overvolt the charger
The BMW i3 had inductive heating strips underneath the coolant channels in the battery pack[1]. I know our i3 had a heat pump, I presume both were in play.
We used our i3 down to -25C (-13F) many times, didn't have any issues.
> This is one of those Great New Technology items that smells like a failure simply because it's not competing with the thing the designers think it is.
This technology makes no sense for fast DC charging because there's enough waste heat to keep up the battery temperature, and you can just use some of the power to heat up the battery.
But it can help for slow overnight charging. Keeping battery heated all night is wasteful, but you still want to be able to charge.