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.