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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.

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SlowBro
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2 Answers2

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Yes, you will damage the battery if you charge at low temperatures (beyond the product specification). You can read this if you only believe research papers: https://www.researchgate.net/publication/282407632_Optimal_Low_Temperature_Charging_of_Lithium-ion_Batteries

If you are using solar to charge the battery, then of course you could use solar power to heat the battery. It makes your charging design a little more complex but it would not appear ridiculously so.

Jack Creasey
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  • At the moment a little 1/2W panel is sufficient so adding heating would require (back of the envelope calculation) a 10W panel. Significantly larger. I guess I'll be going with lead-acid instead. – SlowBro Apr 10 '17 at 16:21
  • Found this and estimate it'd take 2 watts. (3cm x 2cm x 2cm uninsulated enclosure.) I'll weigh the cost of that vs. just using a lead acid battery. https://www.oemheaters.com/topic/enclosure-heating – SlowBro Apr 10 '17 at 16:31
  • Battery University (the first link) seems to be a reliable source of information so I would have guessed the claim in the first link to be correct -- but I don't want to risk it without confirmation. The second link seems to be from a knowledgeable commenter here on EE, but they may only be echoing the unsubstantiated claim of BU. – SlowBro Apr 10 '17 at 16:40
  • BU is not a reliable source. – Jamie Hanrahan Apr 10 '17 at 23:02
  • @SlowBro. If your battery size is small then you might try using Aerogel insulation (http://www.buyaerogel.com/product/pyrogel-5-mm-cut-to-size/) around it and a very small heater. I use this insulation in highly stable crystal oscillators with two TO220 power FETs as the heat source. With the heat loss dropped to very small values you dramatically lower the input heat power required. You might even get to the stage that self heating would do most of the task. There is cheaper Aerogel matting available at very reasonable cost on Ebay – Jack Creasey Apr 11 '17 at 00:04
  • @JackCreasey Good. Post that as an answer and I'll upvote it. – SlowBro Apr 12 '17 at 12:56
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    @JamieHanrahan On what do you base your judgment? I'm not doubting, just want to know. – SlowBro Apr 12 '17 at 12:56
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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).

Redja
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