I see here (Battery University) and here (Electrical Engineering StackExchange) some claims that it is indeed possible to charge lithium ion batteries at -30°C if you do so at a 0.02C rate, but I don't see any hard evidence to support these claims. Like research papers, datasheets, whatever. Anyone know?
I'm developing an outdoor solar-powered product that will be charging all year 'round, even in the winter, even in colder climates. The 0.02C rate is acceptable to me but I don't want to proceed unless there is validation that I can indeed do this without either impacting battery life or causing a safety issue.
Best Answer
As an EE that works with lithium-ion, we don't charge our batteries at temperatures that low, typically the software is set to disable charging below -20C to 0C, depending on the application. We make some batteries with resistive heaters in them, which allow operation at temperatures as low as -40C to -60C after a short warming period. I do know that the cells can be charged at a very low rate when they are cold, however it's generally viewed as a bad idea and causes unnecessary stress on the cells.
Bottom line: Is it possible? Yes, you CAN charge them at a very low rate(~0.02C) at -30C. Should it be done? No, I don't recommend charging them cold as it causes unnecessary stress. If you intended to go the route of heating them, you need some "smart" circuitry that only charges them when they are warm enough(I would recommend around ~0C).