Will shorting a lithium ion battery cause an explosion?
I've seen batteries get shorted a few times. They heat up, and obviously the battery is not useful after, but I've never seen them explode or catch fire. I've read reports of some batteries catching fire during use (laptops, phones, cars...).
If I take a paper clip and connect it to the contacts of a typical lithium ion battery in 2023, what is the likely outcome? Will it explode or catch fire? How many seconds would I have to escape?
Some notes:
- I am aware that this sort of experiment can be dangerous. I don't plan to actually do it. I am asking out of curiosity, as a thought experiment only.
- Likewise, the paper clip should be read as rhetorical device. In practice I would be more interested with shorts due to failures in the equipment or things like liquid spills, but I don't want to get distracted with the complexities of those here (maybe in another question).
- If it's easier to have an example, here's 1.5 Ah Ryobi battery which is probably not the worst nor best quality on the market. Note that this is an example only. I am asking generally, not about this particular battery.
- Supposedly this battery is not dangerous to short by design. Deliberately shorting is apparently a way to reset it.
- Please avoid generalizing "batteries made in China". There's certainly plenty to criticize about modern outsourcing practices, but China is a big country. iPhones are considered great quality and made in China as well. I think it's not useful here to treat a country with 1 billion+ people and the majority of the planet's industrial capacity as a single homogeneous producer.
- I know that it depends on the type of battery. I am looking for answers that explain how and on what it depends, if there's anything salient. In particular, things that a consumer can easily check when purchasing these batteries. If the truth is that it depends on chaotic, unknowable, utterly unpredictable factors that is a valid (if not very satisfying) answer.
3 answers
It depends on how you define "battery". I guess the definition is different depending on if you are a chemist, an engineer or a consumer. When electrical engineers speak of batteries, they typically mean a battery cell - a component. Then there's the end user application with a cell + electronics embedded in plastics with two metallic poles exposed. That is a more commonly called a battery pack.
If we look at classical alkaline batteries ("AA"/"AAA") which you have in various household equipment, they are actually bought from the local store as nothing but a battery cell. Shorting these won't be as spectacular since they have high internal resistance. They will get hot, but probably not to the point where they catch fire.
Li/ion battery cells often come in the very same mechanical shape. If you would short the poles of such a cell and enable a high current fast discharge, you may get thermal runaway causing a fire or explosion. There is nothing preventing this from happening except the resistance of the paper clip etc, which in case of raw copper won't be high at all.
It is not by any means mandatory that a Li/ion cell has supervisory electronics built-in - this is an option. In case they have it, there will be a current sensing IC included in the mechanics. This seems more common than just having a fuse, because we still want high currents to pass during charging and then a fuse might be too blunt. The supervisory IC will measure current across a resistor, but it might also interract with a thermistor to also check the temperature. Having both makes for "redundancy" - two separate technologies that can be used as backup for each other, if one of them fails.
It is custom that battery chargers for higher currents also use a thermistor, not just to prevent overheating but to prevent charging in too low temperatures. The charger may either interact with the electronics attached to the cell, or in case there is none, place a NTC thermistor physically close to the surface of the batteries.
If more than one cell is used, the supervisory electronics is moved externally to a "BMS" (battery management system IC) which in addition to checking currents also balances the charge/discharge between the multiple cells. A supervisory BMS + multiple cells is what we call a battery pack.
Any combination of all of the above is possible. You can have no supervision, or supervision per cell, or supervision per pack.
Now in case of a battery pack for something like a drill like the one you link, it isn't really a "battery" but rather a whole electric system with a PCB. These need to be extra rugged because of the environment and also because it is expected to sit next to a mean little DC motor drawing all its current from it.
Now if you buy a copy of the Ryobi battery from a fishy site like Aliexpress, they will likely have cheaped out on some or all of this. The manufacturer might not even claim compliance with any particular standard or that the product is suitable for the market in the country where you live. Consumers are supposed to check for markings that verify such compliance: CE, FCC, UL etc.
But all of that is still no guarantee. I stumbled across this report regarding a 4Ah version of these very batteries, original Ryobi. There is nothing a consumer could have done to know that these faulty ones were fire hazards. You'll notice it when it bursts into flames.
Older drills used NiMH or NiCd, which is much more safer and forgiving chemistries, but nowhere near the capacity of Li/ion. They didn't require supervisory circuits.
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Since you seem to be asking about whole batteries, not individual bare cells, dangerous effects should be limited. Consumer batteries made from lithium cells almost always include integrated protection circuits. These prevent over-charging, too deep discharge, and probably also mitigate shorts somewhat. With shorted output, the active circuitry may shut down and retry intermittently, or more likely, just blow a fuse. The result is really more up to what the protection circuit does than what a bare cell would do.
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Will shorting a lithium ion battery cause an explosion?
Chain Reaction: The release of flammable gases can lead to a chain reaction, where the heat generated by the short circuit causes even more heat, which in turn generates more gases. This cycle continues to escalate the temperature and pressure within the battery.
The critical temperature depends on the cell chemistry, and the time to reach this depends on the electrical effective series resistance (ESR) and thus internal power generated V^2/ESR, thermal resistance.
If you see rapid outgassing, it is possible that the critical point has been reached unless there is a protection fuse.
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