It has damped my enthusiasm for perusing it as a potential future home energy storage solution.
I have never heard such a thing and all the articles that I have seen about overcharging concluded that such batteries are much safer during overcharging than other kinds of batteries, the worst case effect being battery swelling.
In normal conditions, even during overcharging there are no obvious chemical reactions that could produce hydrogen cyanide.
For instance, at
https://pubs.acs.org/doi/10.1021/acsenergylett.4c02915
it is said that cyanide release can happen only at temperatures above 300 Celsius degrees. Such temperatures cannot be reached in normal conditions.
Thank you for the reasonable chuckle I got from this understatement of the day.
Burning the battery is something that I define as not normal conditions.
Many plastics produce toxic fumes when burnt and many such plastics may be used in a car. Burning the battery is not the greatest risk of toxic fumes during a fire. If the fire is intense enough, any released cyanide might also be burned.
A battery of any kind can overheat with the output shorted or during excessive overcharging, but normally whenever a battery is used in a device there are protective devices that prevent such events.
If there are no protections, the designer is guilty, not the battery. Moreover, such risks are greater for Li-ion batteries, which have flammable electrolyte.
Na-ion batteries will replace Li-ion only in certain applications, like stationary energy storage, cars for cold climates and cheaper cars, while Li-ion will remain the choice for maximum energy per kilogram.
But it is weird to be concerned about the safety of Na-ion when that is certainly not worse than for Li-ion and most likely it is better.
https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10...
https://www.sciencedirect.com/science/article/pii/S2352152X2...
https://pubs.acs.org/doi/10.1021/acsenergylett.5c02345
Also understand, nothing bad happens under normal conditions. It's when the cell goes awry that bad things happen. 300C is easily obtainable by a runaway cell. I mean, short two ends of the battery together with a thin foil and see how quickly it hits 300C...
Also I'm not trying to fear monger, battery failures are very rare. But SIBs aren't totally free of scary failure modes.
They only warn against the danger of not taking care during fabrication to eliminate the moisture from the electrode.
If such low quality electrodes are made, they are prone to decomposition at lower temperatures than the well made electrodes, which have been dried sufficiently.
Similar risks of bad fabrication exist for any kind of batteries, like there were a few notorious cases of lithium-ion battery models that were prone to catch fire.
Moreover, in most applications of such batteries one must use short-circuit protections, so it should be impossible to overheat a battery by shorting its outputs. If that happens, not the battery is guilty, but whoever has designed a device without protections.
The point is that absolutely any kind of battery presents risks. Without short-circuit protections, any battery could cause a fire when shorted.
There is no reason to believe that sodium-ion batteries are less safe than lithium-ion batteries. On the contrary, it is very likely that sodium-ion batteries are safer, e.g. for not having a flammable electrolyte.
The shorting which causes failure is internal, from manufacturing defects. Yes, it's rare. No, it's not something the end user can detect or short protection can stop. This is pretty basic knowledge...hence my questioning (and you totally wooshing on the foil shorting demonstration I pointed out...batteries internally use foil, the foil is what gets hot).
So you have to decide if you want your possible but very rare event to be a small fire or a hydrogen cyanide gas leak.
Also SIBs are a new tech, so who knows what the failure rate will actually look like. Or if CN will even be a concern, the chemistry for mainstream cells might be different.
I work quite a bit with batteries and the fear of battery fires hunts me in my sleep, especially with lipos.
Also, I think HCN can be scrubbed by adding a special absorptive cap onto the battery.
Cyanide could be released only at high temperatures, e.g. if the battery is opened and burned, not during normal operation, even if overcharging is not prevented, as it should.
The sulfuric acid from the traditional lead-acid car batteries is more dangerous than this.
Very much not an equal comparison.
Cyanide could be released only at high temperatures over 300 Celsius degrees.
During a fire, there are many other things in a car that can release toxic fumes easier than a sealed battery.
It has the same LD50 dose as HCN. It literally _is_ just as bad. It routinely kills people on oil rigs because in lethal concentrations it immediately shuts off your nose.
How often do you hear about people getting poisoned by it from lead-acid batteries?
https://en.wikipedia.org/wiki/Hydrogen_cyanide - 107 ppm (human, 10 min)
https://en.wikipedia.org/wiki/Hydrogen_sulfide - 600 ppm (human, 30 min)
https://en.wikipedia.org/wiki/Carbon_monoxide - 4000 ppm (human, 30 min)
These are "LCLo" values from the databoxes on those pages. More easily comparable numbers may be around somewhere.
Fast charging a car/chemical weapon in your garage isn't terribly appealing.
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.
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.
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.