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from the had-to-conduct-a-battery-of-tests dept.
Have you ever taken the back off your phone and seen that your battery has swollen up like an inflatable pillow? For the first time, scientists have been able to peer deep inside to see what is happening.
Lithium-ion batteries have become ubiquitous in phones, laptops and hoverboards because they are lightweight and hold a lot of charge. However, a recent spate of explosions has raised safety concerns.
One reason these batteries are damage-prone is because of their structure, says Toby Bond at Canadian Light Source, a synchrotron facility in Saskatoon, Canada. They usually contain electrode sheets wrapped in a spiralling "Swiss roll", or "jelly roll", configuration to fit in as many energy-producing layers as possible, but this causes problems if gas forms inside.
Gas can build up if a battery becomes overheated or overcharged, or is left drained of charge for too long. Under these conditions, the liquid components in the battery can vaporise and produce gas. This causes the external casing to swell up, resulting in the characteristic pillow appearance.
(Score: 2, Informative) by RS3 on Tuesday December 13 2016, @09:22PM
I'm not a chemist but I know some things about batteries and electrochemistry. Gas production in electrochemical things is not new. Large lead-acid batteries (cars, trucks, golf carts, large battery backups, etc.) used to require frequent inspection and replenishment of water due to
https://en.wikipedia.org/wiki/Electrolysis/ [wikipedia.org]. Someone figured out how to reduce this effect (I don't know the details) including some kind of catalytic recombining of O2 and H2 in the tops of the cells and in the caps, and as such many car batteries, "gell-cells", and other "sealed" (they're not really) batteries came about. They all will eventually need some water but far far less than the bad old days. If you overcharge them (too much current during and/or after full charge) they will produce more H2 and O2 than the catalyst can handle and you lose water. Generally batteries getting warm to the touch during charge/discharge is a bad thing.
Since gas production is not new- has been known in battery electrochemistry for well over 100 years, I'm surprised to hear that Li-ion batteries are being produced and used without better gas control / gas mitigation. The battery chemists give good specs (I've looked at many) re: charge/discharge voltages, times, currents, and Li-ion battery packs used to have quite a lot of current control circuitry nestled in the battery pack, including temperature sensors. Perhaps due to "economic refinements" (cheapening) they're not bothering with the proper circuits, current limiting, temp. sensing, etc? And maybe marketing says "we need it to charge faster than the competition- I don't care what the battery manufacturer says"??