Using Lithium-ion Battery at -40 Celsius?
The “coolest” ad for a LiFePO4 battery that I’ve seen comes from a Canadian company that states it “can be “charged down to -35’C. Yet from reading the plots on the engineering spec, it is not included. That implies you can slowly self-heat it up to -20’C, when the ESR is sufficiently low. They don’t dare say how but likely at 0.01C rate based on the rates for -20C (0.05C) and 0’C (0.1C).
This is not due to loss of Ah but due to rapid rise in ESR from which self-heating can imbalance each cell greatly if current is too high, further degrading the lifespan of the battery. If you used the battery power to self heat, you will lose most of your Ah by the time you reach -20’C , I suspect, so for now -20’C with the derated max Ah rating must be followed to avoid damage.
Although I could ask a former colleague who got the 1st Mitsubishi car which I saw in January, which performed quite well after a 30yr anniversary of Unisys closing in Winnipeg. he claimed it was the best “winter car” he ever had for city driving. Lower Motor DCR and thus more starting torque available, instant electric heat and a high power stock BOSE stereo in a very comfortable iMEV compact. The opposing need for cooling to prevent Thermal Runaway and need to insulate for cold weather must take into consideration the thermal time constant and would be a great design challenge. Cool when moving and insulate when parked.