Its metallic sodium. Its about 30 times more volatile than Lithium. We don't use metallic sodium for almost anything industrial because of this volatility. I assumed there would be some mixed Li-Na-ion batteries. A pure Na-ion battery is an explosive waiting to go off. Putting these in a car...seems rather like a poor choice unless you are a personal injury lawyer.

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adrian_b 10 hours ago | parent | next [-]

I doubt that it is metallic sodium, for the same reason why the rechargeable lithium batteries do not use metallic lithium electrodes like the non-rechargeable batteries.

During charge-recharge cycles, a metallic electrode is likely to be degraded quickly.

So it is more likely that the reduced sodium atoms are intercalated in some porous electrode, e.g. of carbon, while at the other electrode the sodium ions are intercalated in some substance similar to Prussian blue.

The volatility of sodium does not matter, because it is not in contact with air or another gas, but only with electrolyte.

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mlsu 10 hours ago | parent | prev [-]

This is incredibly misleading. It's not like there's a bunch of metallic sodium sitting in the battery waiting to react. It's a lot closer to a solid solution. Do you have a personal injury lawyer on speed dial for your table salt?

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chromacity 10 hours ago | parent [-]

Your response is even more misleading than the misconception you're trying to correct. The complexes formed in (charged) lithium batteries are unstable and reactive in ways quite similar to the base metal. The salt molecule, in contrast, is pretty unreactive. Salt shakers don't catch fire if dropped.

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adrian_b 10 hours ago | parent [-]

Which complexes are reactive?

The substances similar with Prussian blue are very stable. During charge and discharge, the ionic charge of iron ions varies between +2 and +3 and the structure of the electrode has spaces that are empty when the charge of the iron ions is +3 and they are filled with sodium ions when the charge of the iron ions is +2.

Both states of the electrode are very stable, being neutral salts. The composition of the electrolyte does not vary depending on the state of charge of the battery and it is also stable.

The only part of the battery that can be unstable is the other electrode, which stores neutral atoms of sodium intercalated in some porous material. If you take a fully charged battery, you cut it and you extract the electrode with sodium atoms, that electrode would react with water, but at a lower speed than pure sodium, so it is not clear how dangerous such an electrode would be in comparison with the similar lithium electrodes.

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hunterpayne 9 hours ago | parent [-]

Fine, now show a video of what happens if you pierce the Na-ion cell with something metallic. Because explosion doesn't even begin to cover what happens next in that situation. And you are suggesting that everyone should be 2 ft from such a cell, traveling at 60 mph, in all weather conditions. These things should be restricted to grid stabilization batteries and nothing else and you know it. Don't mislead people on such things.

	▲	adrian_b 9 hours ago \| parent [-]
		Piercing a Na-ion cell is not good, but the effect is pretty much the same like piercing a Li-ion cell. In both cells the electrode that stores alkaline metal atoms has high reactivity, but in both cases the reactivity is much smaller than for a compact piece of metal, so the reaction with substances like water would proceed much more slowly than in the movies when someone throws an alkaline metal in water. If you pierce the cell, but the electrode does not come in contact with something like water or like your hand, nothing much happens, the air would oxidize the metal, but that cannot lead to explosions or other violent reactions. The electrolyte of lithium-ion batteries is an organic solvent that is very easily flammable if you pierce the battery. The electrolyte of sodium-ion batteries is likely to be water-based, which is safer, because such an electrolyte is not flammable. It would be caustic, but the same is true for any alkaline or acid battery, which have already been used for a couple of centuries without problems. Overall, sodium-ion batteries should be safer than lithium-ion batteries, so safety is certainly something that cannot be hold against them.