18650 fire cases & 18650 vs 21700 comparison

I have tossed individual cells and old packs in water buckets outside to see what happens - I take apart used batteries pretty often, so I often have ones that are accidentally dented from prying the welds off and starting to heat up. The cell had to sit in water a day before it vented and shorted and turned the water black. The pack similarly didn't short immediately and I was able to transfer it to an old ammo can full of dirt. Theoretically that could be better in certain situations than letting it all burn up, one cell reaching thermal runaway, the heat from that triggering another cell, then eventually the whole battery.

Why isn't it just lithium + water = boom? Because we're not dealing with pure elemental lithium here. We're dealing with a lithium salt in a solvent. The lithium salt starts decomposing over 150 degrees:


Then for the solvent in my Samsung cells:


You can see both with and without the presence of water (which admittedly does make it happen earlier), the solvent starts to decompose over 100 degrees as well:


So if water is all you have, there could be some value in using it to help the temperature down, even if the presence of water makes the harmful chemical reactions somewhat worse.

I don't use wet extinguishers with lithium battery fires. That said, I've seen it argued, that the cooling effect of water can be useful despite the harm it otherwise causes. Like if you have a single cell or p-group undergoing thermal runaway, dunking and covering the pack in sand in a metal trash can is what I do. However, dunking in water is still going to keep the temperature down at the boiling point of water, 100 degrees, which is lower than the worst reactions, and will prevent the whole pack from undergoing thermal runaway.I have tossed individual cells and old packs in water buckets outside to see what happens - I take apart used batteries pretty often, so I often have ones that are accidentally dented from prying the welds off and starting to heat up. The cell had to sit in water a day before it vented and shorted and turned the water black. The pack similarly didn't short immediately and I was able to transfer it to an old ammo can full of dirt. Theoretically that could be better in certain situations than letting it all burn up, one cell reaching thermal runaway, the heat from that triggering another cell, then eventually the whole battery.Why isn't it just lithium + water = boom? Because we're not dealing with pure elemental lithium here. We're dealing with a lithium salt in a solvent. The lithium salt starts decomposing over 150 degrees:Then for the solvent in my Samsung cells:You can see both with and without the presence of water (which admittedly does make it happen earlier), the solvent starts to decompose over 100 degrees as well:So if water is all you have, there could be some value in using it to help the temperature down, even if the presence of water makes the harmful chemical reactions somewhat worse.

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