I'm no chemist, but I'm a pretty big electronics and EV (electric vehicle) geek. Since lithium batteries are the big boom in the industry today (eh... and yeah, I realize the site I'm on
), it's of particular interest to get a bump and some new information. This topic came up for two separate Google searches regarding lithium battery freezing effects, so it seems to be a popular thread for this subject. Most other results are people asking if it'll hurt their phone/laptop. >.< Not exactly...
So, here's what I've got. I work in PC repair, and the electronics side of computers often ends up in my work - like the Sony VGN-NR240E I inherited after an upgrade to new hardware. The user had *NEVER* used the laptop on battery - it sat on a desk fully charged for its whole life. Terrible for a lithium battery to stay fully charged forever - and it showed. The laptop had about 10 seconds of battery life before crashing off. Under the hood, I'm sure at least one cell pair is super-weak and buckled under the 3.0V level immediately.
So we've got a severe case of capacity lock. The battery is charged, but it's so weak, it could only release it in tiny, tiny amounts. I'd wager a guess that the separator material between anode and cathode (a somewhat hot area of innovation in today's lithium batteries) became clogged with decayed material over the time it's sat at full charge.
After stumbling across this concept of freezing a laptop battery, I tried it out. I put my phone in the freezer with GSAM Battery Monitor showing me instant current and delayed voltage levels. Playing with this setup showed me that low temps dramatically slow the battery, but seems to improve the battery's performance once it warms back up. Voltage at low temps would be very low even with no load - so it seems to affect the resting state of the cell.
The results with the laptop battery have been even more dramatic. I've frozen/thawed that battery about 3 times now, and ran it in a cycle of discharges/recharges - running it until it shut itself off, then immediately plugging it in and watching the wattage (using a Kill-A-Watt) until the charge rate dropped below 10W. Most of the charging was being done in the 5W-2W range. It'd spike to 21W for a few seconds at first, then fall through 18... 14... 12... and when it hit 9.9W, I unplugged it and immediately turned it back on. After roughly 20 of these cycles (each lasting about 1-3 minutes), after a thaw, it jumped by a huge leap - with the computer in a customized low power mode, it ran for almost 20 minutes, with the previous cycle only lasting about 4. The following charge stuck around 21W for almost 5 minutes, then over 20 more minutes above 15 watts.
My guess is that though the electrolyte itself doesn't freeze until -40C, other components in the cell change composition - hence, the significant voltage and performance drop while cold. Like cold syrup becoming thick, the flow of ions through the thickened chemistry probably started "cleaning" the collected gunk off the layers they were being forced through. Whether or not the "cleaning" ended up taking useful parts with it (hence, this "improvement" is only remporary)... that's what I'm still finding out. And like I said, not a chemist, just a good idea of lithium battery construction and performance - though I'm not sure if anything about viscosity and "cleaning" is correct.
At any rate, there's definitely something about freezing these things that they seem to like - at least, as a maintenance routine. Seems like I should drive my LEAF out to the snow some day to give the battery a good chill