lithium explosion

You don't seem to have been paying attention. If you deal with the warning by discharging the battery, and making it safe, it won't explode.

No stored energy means no dramatic heating, no breaking of the seals that protect the contents of the battery from atmospheric oxygen, and no explosion or fire.

Yo do have to get rid of the battery and presumably replace it, but that was implicit in the original purchase. They aren't sold on the basis that they are going to last forever.,

Who it the 'you' in that sentence? Do you mean the average user, in which case this is a hopeless scenario as most users of batteries wouldn't have a clue.

Until recently batteries have been inherently safe: unless you did something stupid they were unlikely to give any trouble. You are now supporting a type of battery that is inherently unsafe and will catch fire or explode unless the user takes some positive action. Even if the user delegates this action to an automated system there is no guarantee that the action will be taken every time it is needed.

'Safety' that depends on taking a positive action to prevent a disaster is not safe at all.

References say that a tiny separator defect spreads radially at centimeters per second. Any somehow-sensed defect will explode in flames in well under a minute, from the bad cell into the whole pack. See Youtube examples... smoke to explosion in seconds.

If I heard an alarm from a lithium battery pack, I wouldn't try to fix it, I'd run in the opposite direction. What automated system could discharge an 80 KWH battery pack in a few seconds? Or even 1 KWH?

And a defect sensor would have to constantly snoop every cell of a pack. A typical Tesla might have 7000 cells.

It is the only thing they can do until the manufacturers create machines that do not catch fire putting the entire metro line out of service. It is not the city transport business or job to mandate what others should do, or what other regulators do to regulate proper battery building. They simply have to protect themselves and their users.

(Oh, no guns around here.)

And yes, of course it is a pain. The combination of a personal transport device and public transportation was working wonderfully for many. You get from home to the station with your wheelie in minutes, cross the city in minutes underground, arrive at job place in minutes from the station using the wheelie again.

Ope, meant per month, not per day! :B

Not entirely. It is still allowed for general aviation.

John

The population mix makes a bigger difference. Bad guys will always find guns.

You personally.

But happens to offer a much higher energy density.

It takes a long time to degrade to the point where it can catch fire or explode, and the degradation is entirely detectable.

And the brakes on your car don't always work, but we do seem to be willing to live with that.

But we live with that, when the advantages are proportionate to the risk.

But you can't provide a link to any such reference.

Google threw up a paper on using airflow to test test battery separators before they were assembled into a battery, so your defect is going to be present in new cells, and detectable before they are into assembled batteries of cells.

Youtube is full of half-baked rubbish, and you are sucker for that.

It doesn't have to discharge it in a few seconds. An increased self-discharge rate is detectable long before a cell gets to the point of thermal runaway - the local temperature has to get up to between

It doesn't. It has to snoop the battery core temperature and compare it with battery surface temperature. A few sensors spread around the core would let you pick up the existence of hot spots - you wouldn't need to work out exactly where they were.

The Telsa battery monitors it own core temperature and has built in resistive heaters to warm it up when outside temperatures are too low to let it deliver full power at start-up.

My van has dual hydraulic systems for the footbrake, a mechanical handbrake and even gears that could slow it down in an emergency. If I park it somewhere, the chance of it crashing into something while I am not there to stop it is very small indeed, I don't need to take any positive action.

I suspect the number of spontaneous fires of vehicles with lithium batteries is far higher in relation to the number on the roads than the number of spontaneous runaways and crashes of diesel and petrol vehicles. In addition there is the same risk of brake failure on an electric vehicle - even more so if it has an electric parking brake which is the driver cannot operate quickly in an emergency.

Most manufacturers produce stuff that doesn't blow up. The rational approach is to ban only the stuff that might.

So ban the cheap junk wheelies that are known to pose a risk of catching fire and exploding.

It isn't - the numbers are quite a bit lower. There have already been some insurance statistics accumulated and some of them have been posted here. Electric cars haven't been around for all that long so to some extent this is comparing relatively new electric cars with a populations of IC cars which includes some antiquated junk, but electric cars do seem to be quite a bit safer.

Newspapers don't emphasise this.

The point was not the efficacy of the brakes but the existence of a risk which we are willing to tolerate.

Guns don't kill people. People kill people.

....

Tesla (and every other EV manufacturer) does monitor the voltage of every individual cell and every cell has its own fusible link in case it becomes shorted.

kw

Tesla uses many small cell in parallel, numbers like 74. I wonder how they could monitor the voltage of each cell.

I assume "becomes shorted" means that the battery terminals are shorted somehow. The bigger hazard is that a cell will short internally, and all its paralleled friends will then dump thousands of amps into it.

Monitoring or fusing won't help a 5-second internal ignition from a separator failure.

I'm certain that few cheap Chinese bike and scooter batteries have any sort of safety systems. As they age, they may get more dangerous.

Not if there was a fuse in series with each cell

The case stated above is "in case it becomes shorted."

If a cell shorts internally, as they tend to do, no monitoring or fusing will help. Running will help.

I once worked with a fire alarm company in Freehold, New Jersey. A sign on the wall said

IN CASE OF FIRE

run, yell FIRE

As you say many are in parallel in a module (the actual number varies with the particular model and revision). The cell voltage of all those cells are the same so can be measured with a single channel of the BMS.

Each cell has its own fusible link so in that case the link for that specific cell will blow. The maximum current for an individual cell is in the region of 40-50A.

In some models Tesla has an overall pyrotechnic fuse to disconnect the pack from the vehicle very rapidly if there is excess current (>1000A or so).

Each cell is in a steel cylinder that can contain a single cell failure and minimize the probability of cascade failure. A fully-charged cell contains about 10-20 Wh of energy.

Some car manufacturers use larger format cells with significantly larger storage per cell.

I believe that some of those use pouch cells (similar to those in cell-phones, tablets and notebook computers). There is less physical protection against cascade failure in that case.

kw

Tesla battery assembly and wiring:

BEV fire risk discussion: