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Explosion-Proof Lithium-Ion Battery Shuts Down At High Temperatures (thestack.com)
An anonymous reader writes: Scientists have designed a lithium-ion battery that self-regulates according to temperature, to prevent itself from overheating. Reaching extreme temperatures, the battery is able to shut itself down, only restarting once it has cooled. The researchers designed the battery to shut down and restart itself over a repeated heating and cooling cycle, without compromising performance. A polyethylene film is applied to one of the electrodes, which expands and shrinks depending on temperature, to create a conductive/non-conductive material.
If you take apart most Li-Ion battery packs from laptops you will find a thermistor. This is to help prevent the battery from overheating while charging/discharging.
More accurately, it is to help the charger not explode the batteries by charging them too quickly. It's usually used for no other purpose although it's not that unusual for a laptop to tap into it to also report the battery temperature. This is also typically done in power packs for cordless tools. Most of them don't have any kind of over-current protection, though. You can overheat them by misusing the tool, and for the same reason, laptop batteries can combust when one cell goes bad. The idea here is to prevent that by simply shutting off the battery when one cell goes tits up. There's a charge controller in the pack, but there's not a discharge controller.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
LiPos have them as well for the same reason.
But this isn't a thermistor that controls a circuit - it's a new cell construction technique that basically has the cell turn itself off when it gets too hot, not externally via a circuit (that may or may not exist, or may be defeated because the Chinese maker of the pack wanted to save a buck).
Yes, counterfeit battery packs exist, and they often are missing the safety circuits as well as using dodgy cells. While there are often very good 3rd party suppliers of battery packs, there are dozens more dodgy sellers of questionable quality 3rd party packs ready and willing to sell you incendiary devices. Probably the reason why those "hoverboards" we see keep catching on fire.
So having the cell be able to protect itself would provide a big increase in safety if you ever find yourself stuck using some crappy quality 3rd party battery packl