How can the batteries for e-cars burn under water? There was a thread a while ago with videos of e-cars that went under water and started burning. How is that possible? I always thought a fire needed oxygen? Or is there oxygen in the composition of e-car batteries?
Lithium, it burns on contact with water.
They need to use foam to put out an electric car fire.
Is lithium in the same elemental family as sodium?
Yes, yes it does:
Also, lithium polymer batteries are self-sustaining because the electrolyte and cathodes containing oxides or fluorides will break down and provide plenty of oxidizer to completely consume all of the ‘fuel’ (e.g. the lithium salt in a gelled substrate and carbon anode), often burning for many hours.
Stranger
They are both Alkali Metals and are adjacent on the periodic table.
Depending on how pedantic you are, and what definitions you’re using, you might argue that the reaction isn’t technically “burning”. But the important point is that it’s a chemical reaction that rapidly and uncontrolledly releases a lot of energy.
Water is made of oxygen (and hydrogen) , so there is oxygen.
Foam is useless on an EV fire.
Foam works by smothering, and it only works on something that is flat and level. That’s why it’s used on flammable liquid fires, the liquid is flat and level and foam can cover it. Foam doesn’t work on liquids that are moving, we use dry chemicals for that (dry chem knocks out the chemical reaction).
Foam works great on ordinary combustibles, too, like wood, paper, cloth, plastic, etc. But that’s because foam is 97% to 99% water, it’s the water that’s doing its normal water cooling thing.
EV fires are a a heat problem - specifically a thermal runaway problem. The “battery” is actually a collection of small battery cells, close to a AA battery, just lots and lots of them. When one cell gets upset and goes into thermal runaway, it heats up (and eventually bursts while on fire). As the first cell is in runaway, it sends adjacent cells into runaway. Then the cells adjacent to those, etc. Cooling the cells is how you stop the progression of thermal runaway. Water has been our go-to cooling agent for thousands of years.
The problem is that the cells are in a case with all of their siblings. If we put a hole in the case to put water in, we damage a cell and create a new TR focus. If we fill the case with water, we short out cells and send them into TR. There are no chemicals (that I know of) to inject into a case that will stop runaway but not short or damage cells. Foam has a bunch of chlorides in it. If the water wasn’t bad enough for shorting cells, foam is far, far worse.
The most recent guidance on extinguishing EV fires has been to not to. If we put 40,000 gallons of water on the car, it burns into a charred lump in about 8 hours. If we don’t do anything to it, it burns into a charred lump in about 2 hours, but with far less resources and contaminated water. It’s a difficult paradigm to shift to.
About 120 years ago the fire service lost its mind about these crazy horseless carriages and the “inflammable vapors” that were used to power them. We still have laws on the books in Massachusetts on licensing of garages stemming from that era. We adjusted to the new hazard and figured it out. Give it a few years and we’ll have this EV thing solved, too.
Gonna be an exciting next few years, though.
I stand corrected, I was under the impression foam was used like for jet fuel fires
To be more precise, the lithium metal reacts with water to form lithium hydroxide and hydrogen gas in an exothermic reaction. The heat released in the reaction may suffice to ignite the hydrogen gas in the presence of oxygen. A spark in the vicinity will also suffice.
A similar reaction takes place with the other group 1 metals (first column of the periodic table), with the reaction getting more and more energetic as you go from metallic sodium to potassium, etc.
When I taught chemistry, I used to do a demo with all three of these group 1 metals in water to show the progression. Once I cut off a slightly too thick piece of potassium (about the size of a nickel coin)—when I dropped it into the water, it fizzed for a moment, and then the hydrogen detonated, shattering a very large 4-liter beaker full of water in the process. Fortunately I always performed the demo inside of a fume hood with a thick plexiglass “blast shield” you could pull down so there was no harm, just a mess to clean up.
I know it’s marketing material but the fireproof blankets being marketed as a harm minimisation method seem to work very well:
Amazing but true. FTR, there are at least three types of battery cells used in EVs and hybrids, but Tesla and I believe most domestic EV makers use the cylindrical ones that look remarkably like flashlight batteries. The roughly AA size cell is the 18650, which is 18mm in diameter and 65mm long, slightly larger than an AA battery which is 14mm in diameter and 51mm long.
The 2170 standard is slightly bigger, and the newest 4680 type looks roughly like a flashlight “D” cell, and is 46mm in diameter and 80mm long, noticeably larger than a “D” cell which is 33.2mm in diameter and 61.5mm long. The 4680 is used in the Cybertruck, and its larger size means it only needs around 1500 of them. Vehicles that use the roughly AA-sized 2170 typically have multiple thousands.
I’ve wondered why they do that. Intuitively it seems like it would be more efficient in terms of weight and material used to build one or a few big batteries rather than putting together thousands of little ones, with all the casings and connectors that don’t produce any power.
Here is an article I’ve posted before about a fire fighting method that does involve injecting water directly into the battery case. The report makes it sound like much of the research was on the best method to penetrate the battery pack, and determined that penetrating extinguishers, which use a high pressure jet of water to cut, worked the best.
I do not have the expertise to provide any additional evaluation or commentary beyond what is in the article.
It is one big battery. A battery is a bunch of cells. The voltage of any one cell is determined by the chemistry, but most battery chemistries have cell voltages somewhere in the neighborhood of 1.5 V. AAA, AA, C, and D “batteries” are all a single cell each. A 9V battery, if you open it up, contains six cylindrical cells (I think those are called AAAA cells, but they’re not used for much besides the internals of 9V batteries).
To get more power out of cells, you either connect them in series, and get more voltage, or connect them in parallel, to get more current. You could make a single big cell that worked the same as a bunch of cells in parallel, but it wouldn’t save you any on electrode materials, because you’d need the same amount of electrode to get the same current. And making the cells smaller makes mass production easier, and also lets the system intelligently manage discharge and recharge of individual cells.
US airliners (and presumably other nations’ as well) carry several insulated pouches intended to contain runaway battery fires in laptops, tablets, phones, etc.
Grab an oven mitt and a pouch, run to the scene of the occurrence, grab the flaming gizmo, drop it in the pouch, then seal the high temp velcro. Then store the problem in an empty galley oven until the problem burns itself out.
Your cite appears to be the same idea on a larger scale. Keep most of the heat from spreading to surrounding stuff, minimize introducing atmospheric oxygen which reduction may not help much, but can’t hurt. Then just wait until the excitement subsides on its own.
But it’s not free oxygen. To break the water molecule into its components would require a chemical process, such as electrolysis or thermolysis.
A single large cell would be more compact because there isn’t the dead space between cells, but you wouldn’t want to do that because it would be difficult to built a battery of much larger size and maintain the tight quality control required for safe operation, and a thermal runaway with a very large cell would be catastrophic versus individual cells that will pop off one at a time, at least slowing the progress of a fire. There are newer ‘prismatic’ cells that are rectangular and can be packed more closely together and using a chemistry less likely to undergo thermal runaway but the “casings and connectors” are vital parts of a safe and modular battery pack construction.
Stranger
Plus, a giant cell wouldn’t have nearly enough cooling capacity. Batteries are efficient but they aren’t perfectly efficient, and they need to be cooled so as not to damage themselves when charging/discharging. Cylindrical cells play nicely here, since you can have a hex packing, but spread the cells out slightly, and run cooling channels between them.
This is all more difficult with prismatic or pouch cells. The theoretical packing density is slightly better (rectangles can pack 100%, while cylinders only 93%), but in practice cylindrical cells give somewhat better performance.
Cells also have to deal with internal pressure. Cylinders stand up well to pressure. Pouch/prismatic cells need some external force, which means that the pack container needs to be beefier.
Cylindrical cells have been getting bigger; as wolfpup says, from 18650 to 2170 to 4680. Cells have also been getting better, slightly reducing the need for cooling, and the way the cells transmit heat to the case has improved. That has made up for some of the loss in surface area with increasing cylinder size. But not perfectly, and the highest performance cars tend to use the smaller cells (either 18650 or 2170). The Cybertruck may be an exception, but it uses the second-gen 4680 cells, and we don’t know much about what they’ve improved. They’re claiming up to 350 kW charging, but without knowing the overall charge curve, we can’t say if they’ve totally solved the cooling problem with the larger cells.
There are EV’s that use rectangular cells.
Admittedly Robert does tend to concentrate on prototypes and oddities, but off the top of my head I’ve seen him pull apart at least three and maybe more EV’s with rectangular cells.
He’s a hoot, by the way. Well worth watching.