Electrical vehicle fires are not that common, when they do begin, they can be very hard to put out. Scientists still attempting to determine all the information of what actually happens (chemically) when a lithium-ion battery catches fire.
Electric lorries do not capture fire frequently, however when they do, things get spicy. How do these fires start? And why are they so hard to extinguish? There are scientists trying to respond to these concerns, but there are likewise researchers still trying to figure out what really takes place (chemically) when a lithium-ion battery ignites. Can we fix this issue without completely comprehending whats going on?
Video Transcript:
Electric lorries do not capture fire frequently, however when they do, things get spicy.
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( reporter speaking in a foreign language).
This fire took 6,000 gallons of water to put out. And this one took almost 20,000.
How do these fires begin and why are they so hard to put out?
To comprehend that, we can start by looking inside this nine-volt battery.
Turns out a nine-volt isnt one battery. Its actually 6 batteries. These individual batteries are called cells and an EV battery is the same.
Its made of hundreds or countless cells like this one or this one, or even larger ones that I couldnt buy online for some reason.
A battery fire like this one starts in a single cell through a chemical process called thermal runaway. We in fact have x-ray video of this occurring chance at countless frames per second.
This is the top of a cell similar to this one. The brilliant lines are metal oxides and copper.
Okay, a closeup shot of the battery thats shot even slower.
So, gas is developing here, which you cant see directly, however it is moving the internal elements.
This thing right here, this is a pressure release valve, and, right now, it is rupturing, which ought to avoid a surge by alleviating the pressure, however watch this.
Gas accumulation pushes the internal elements of the battery up, blocking the valve.
With no place to vent, a growing number of gas keeps developing and whatever gets hotter and hotter and hotter, which stretches the steel outer case to its breaking point till it stops working and you get a surge.
This is the aftermath. Complete destruction.
These white globs, this is molten copper. Copper melts at 1,085 degrees Celsius, so, inside this battery, youve got temperature levels about as hot as a steel create.
Now, if one cell thermally runs away, it can warm the surrounding cells to the point that they do too, and you got a domino effect and it spreads to even more surrounding cells, and, quite quickly, youve got a huge battery fire.
There are groups of engineers and researchers attempting to fix this issue, however there are also researchers just trying to find out whats actually taking place chemically when a lithium battery ignites. Because even after a couple of years, we dont fully comprehend it yet.
So, what do we understand, and can we resolve this issue without fully understanding whats going on?
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This is called the jelly roll.
This is the anode and it releases electrons.
This is the cathode and it absorbs them.
If you put these two in direct contact with each other, you d get a spark, electrons leaping directly from here to here. If you separate these layers with an electrically insulating layer and supply a path for the electrons via a couple of carrying out layers, you can pull electrons out of the battery and make them do some work for you before they return to the battery once again.
Now, the electrically insulating layer is called the separator, and it is key to understanding thermal runaway.
Its electrically insulating, however chemically conductive, implying electrons can not pass through it, however lithium ions can.
Let that sink in for a 2nd.
Electrons are point-like particles with no volume. We made a whole video about this. You need to definitely examine it out. And a piece of plastic with great deals of holes obstructs them.
However ions are much larger, do have volume, as you can see from this extremely precise diagram I drew, and they can pass right through.
Whats going on?
Well, it actually has absolutely nothing to do with size.
Electrons are way too reactive to travel through products by themselves. They require a course and performing materials like metals have lots of available empty orbitals that form exactly that path.
Plastics do not.
Even though the holes in a piece of plastic are method bigger than an electron, theres no conductive course around or through those holes.
Ions, on the other hand, they do not need a course. They can simply saunter right through.
Anyway, the separator is made of plastic.
Now, lets say that this little cell is humming along in an EV, and, for some reason, the cell starts to overheat.
Once the temperature level in the cell reaches about 130 degrees Celsius, the separator melts, which suggests the anode and the cathode make direct contact and you get a spark.
This is called an internal short circuit or an ISC.
Quick side note here. Great deals of things can trigger an internal short circuit.
If you hammer a nail into the battery, for example, or if a charger breakdowns and overcharges the battery, or if you overheat the battery, or manufacturing flaws.
What? If Im gon na return it, I got ta put this back together.
Okay, so if you wished to design something that produces a total chemical cluster (beep), a battery thats simply experienced an ISC is an exceptional method to do it.
Thats why theyre in the battery to begin with. Youve got high temperature levels, which implies the liquids are prone to alter into gases.
So now we have every phase of matter except plasma.
Youve got a lot of things that begins to decay at higher temperature levels. Metal oxides, when warmed, tend to release oxygen gas.
That oxygen makes it possible for combustion reactions. Now those liquids and gases can burn, which generates more heat and more gases.
By the method, this is why EV fires are so hard to put out. Despite the fact that batteries are way less energy dense than fuel, they generate their own oxygen when they burn.
Gasoline does not.
So, as long as the temperature level is hot enough, the batteries can simply keep reigniting unless you utilize countless gallons of water to bring the temperature level down to the point where that cant occur.
This whole situation is taking place in an electrically-conductive environment, that makes it extra tough to track the electrons and by extension the reactions.
Basically, a total and utter chemical cluster, to the point where there are whole journal short articles that note the chemical reactions that are happening that weve discovered so far.
This is the core of the issue. Its simply really tough to untangle all of the chemistry that drives thermal runaway. So its tough to find out a chemistry-centric method to stop it.
Also, battery tech is altering so quick that, even if you might totally untangle everything thats occurring in, for example, this type of battery, by the time you do, the industrys proceeded to a battery with a different cathode or separator product or whatever.
In spite of all of that, though, we can state some truly intriguing aspects of thermal runaway, things that assist us engineer versus it.
Okay, take a look at this graph, which I have bigger for your benefit, of temperature of a battery versus time.
As you can see, it occurs slowly and after that all at as soon as. Now, this simultaneously bit ideal here, this is the main thermal runaway occasion.
Take a look at how fast that is. The temperature shoots up to its peak in about one second.
Now, the speed here informs us something really crucial about these responses, and to understand what that is, we need to mix baking soda with room-temperature vinegar, and likewise with vinegar at 57 degrees Celsius.
The hot vinegar responded much faster, and if youve ever prepared something, this makes sense. The hotter your pan, the faster the thing cooks.
Svante Arrhenius, a Swedish chemist living in the 1800s, established a model to forecast precisely just how much quicker a response would go at greater temperature levels, and this is it, simply one equation.
The essential things are K, which you can believe of as the speed of the response, and T up here in the exponent, that is temperature in Kelvin.
Now, expect we wished to compare the speed of a reaction at 298 Kelvin, which has to do with the temperature level of a space, with the speed at 330 Kelvin, which has to do with the temperature of the hot vinegar.
What we do is we divide one rate consistent by the other, and when you sub in this equation, you get this mess, and when you clean this up and rearrange some terms, you get this.
Now, lets say the activation energy, which is simply the energy needed to get the response to go, is 150 kilojoules per mole. Toss that in, crunch these numbers, and you get 350.
Simply put, weve just increased the temperature level here by about 30 Kelvin, approximately 10%, however the response happens 350 times faster, and thats because of the temperature in the exponent.
The speed tends to increase greatly when you increase temperature linearly.
Now, here is an insane wrinkle.
What occurs when you have a reaction that produces? Damn it.
What occurs when you have a response that produces?
When you have a response that emits?
Is this just empty?
No.
Plenty.
What occurs when you have a response that releases?
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A lot of heat?
You get what I like to call the Arrhenius ouroboros.
The response produces heat, which increases the temperature level. The boost in temperature means the reaction goes faster, which means it offers off heat quicker, which indicates the temperature increases quicker, which suggests it gets much faster, which indicates it produces heat even faster, which indicates the temperature level increases even much faster. which implies it gets back at much faster.
This is a favorable feedback loop, and, in specific, its a rapid positive feedback loop, which can drive the temperature in the battery from 200 to over a thousand degrees in half a second, and you get …
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( reporter speaking in a foreign language).
By the method, this heat, it does dissipate, and it in fact dissipates faster with increasing temperature, however that relationship is direct.
The exponential increase in response rate greatly overwhelms the linear boost in heat dissipation.
In the early days of lithium-ion, scientists knew a lot less than they know now, and yet they still handle to craft solutions to problems they didnt totally understand.
How?
Well, often, options are apparent, do not depend on the underlying chemistry, and are easy to do.
Batteries are blowing up due to high pressure. Well, lets integrate in a pressure-release valve.
Sometimes services are apparent in theory, however the chemistry is hard.
Separators melting?
Lets engineer one with a greater melting point.
Easier said than done. Changing the melting point without altering other residential or commercial properties needs great deals of experimentation, but we have been making development. Separators today melt at much greater temperatures than they utilized to.
Often the easiest, most apparent solution doesnt solve the problem all the time.
Remember at the beginning when we spoke about this X-ray video footage?
Regardless of this pressure release valve operating exactly as it should, the battery still took off.
Sometimes the solution includes a layer of tech on top of the chemistry.
Software application battery controllers monitor things like charge state and battery temperature, and, for instance, shut down the battery when things are getting a little too hot.
And sometimes the service includes throwing away the entire battery and developing an entire new one with an entirely different ion, state, salt.
One cathode material being tested for sodium-ion batteries is sodium chromite, which releases far less oxygen when warmed than similar cathodes in lithium-ion batteries.
Less oxygen suggests less combustion, which implies less heat, which implies less potential for thermal runaway.
And for reasons we dont really understand, sodium-ion batteries going through thermal runaway tend to release their energy a lot more slowly.
One research study determined the rate of temperature increase for a typical lithium battery versus a sodium battery, and discovered that the lithium battery heated up almost four times faster than the salt one.
That would give other safety features in the battery a lot more time to begin and prevent a surge.
Most of these solutions, pressure release valves, separators, various cathode materials, they do not require full knowledge of every single chemical reaction happening throughout thermal runaway.
Well, we ought to develop one that does not. We need to create one that does not.
We can resolve these issues prior to we complete understanding them, like this video.
I do not actually understand how were gon na end it, but we can solve that issue if I simply keep talking and leave it as much as Andrew to just end the credits whenever he chooses, which could be now, or it might be now, or it could.
There are researchers trying to answer these concerns, however there are also researchers still trying to figure out what actually takes place (chemically) when a lithium-ion battery captures fire. Turns out a nine-volt isnt one battery. Its really six batteries. These specific batteries are called cells and an EV battery is the very same.
Thats why theyre in the battery to start with.