THMG302 – Lithium Car Battery Fires – Part 1

A recent email from a listener sparked a conversation that turned into this double episode. Take a listen and get some intel.

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  1. In recent months the lithium ion battery issue continues to take off. There was an interesting article we would like to share. Then we want to walk through some of the stuff in the tesla manual and add some things that we know.
  2. Let’s first walk a little down the road of why there are so many issues with these batteries.
    1. First off Batteries hold energy. In chemistry energy is used and transferred during a chemical reaction. The more energy that is released in a chemical reaction the more energy potential that reaction has. 
    2. Right so Potential,,,, let’s break this down a bit more. There are 2 types of energy that we are talking about when we deal with batteries. Actual physics of things in general but for this we are going to focus on potential energy and kinetic energy. 
      1. Potential energy is simply just the energy that a system has stored in it. It is not used but it is there. Potential energy can be thought of in the physics world in many different ways. So let’s unpack a few of these ideas.
        1. First let’s remember this first rule of physics. The law of conservation of energy states that energy can neither be created nor destroyed – only converted from one form of energy to another
          1. What does this mean. It means that I can’t just magically create energy. It has to come from somewhere. Like putting gas in my car. Energies can be added to systems and taken away but that energy has to come from somewhere.
        2. Let’s use this classic physics example of potential energy. I have  a ball laying on the ground. The ball is not in motion compared to the ground and therefore has zero potential energy. There is nothing this ball is going to do on its own but sit there.
        3. But now we take that ball and raise it up. As we pick the ball up and bring it away from the ground its potential energy is increased. Just the act of me lifting the ball in the air is me adding energy to the system. By working against gravity I am making it so the ball will end up dropping further in the air and therefore going faster.
        4. By the time I bring the ball up to the highest position before I drop it, I have added as much energy into the system that I can. The potential energy is at its max. 
      2. Now let’s talk about kinetic energy. Kinetic energy which a body possesses by virtue of being in motion. So as that ball starts to drop the motion gets greater and greater, so therefore the kinetic energy gets greater and greater. The more motion the more kinetic energy. The ball will be at its max kinetic energy just before it hits the floor. Then all that energy gets transwed to the floor and the ball again comes to a stop. 
        1. While the kinetic energy is increasing, the potential energy is now decreasing. The two are inverse protioniate to each other. 
        2. Since kinetic energy is the energy of things in motion, it is this energy that can do damage. Replace the ball with a brick, and the ground with a person’s head. The higher i bring the brick, (the more potential energy i put into the system, the more damage that brick can do, the higher its kinetic energy just before impact therefore transferring more energy to the person’s head, doing more damage.
      3. We see this relationship in all systems. Including chemistry. The only difference is the complexity of getting the energy in vs getting the energy out changes.
        1. Let’s start off with the basics. The sharing of electrons within a molecule. This sharing of electrons is known as bonding.
        2. You can think of these bonds like rubber bands. At least for this example. And remember this is a generalization to get a point across, i don’t need angry emails letting me know why electron orbital are nothing like rubber bands. But if we do think of them like rubber bands we can understand how they have different energies. 
          1. Think of all the rubberbands you have played with in your time. Some are thick, some are thin. Some when you snap them on someone make them cry and you smile.
          2. And some don’t and then you are disappointed. This is all a function of energy. The amount of potential energy that a rubber band has when it is stretched out will affect the kinetic energy it has just before it makes contact with someone’s skin.
        3. So different molecules, like rubber bands, have different energies within the system. When a bond is broken or when a chemical reaction takes place this is where the energy that is released comes from. We often see this in the form of heat or light. Take strong acid and mix it with acetone. The container will get super hot really fast. This rapid heating is taking place because the driving force behind the reaction is that the molecules that are formed after the reaction takes place will have lower energy than the acid and the acetone did before they reacted. 
          1. Not much different than the reason the brick falls. From a physics point of view the only reason the brick fell was because it had energy and wanted to get to a lower energy state. So it released its energy to get to that lower energy state. For the brick it was done in the form of dropping, and for the chemical reaction it is done in the form reacting and giving off energy in the form of heat.
        4. Now hear the part that we have to really understand to understand why batteries are reacting the way they are. I used the acid and acetone example because we are all familiar to some degree with an acid base reaction. Take a really strong acid and put it in with a really strong base and what happens?
          1. The two react violently and the acid and base splatter everywhere!
          2. they react violently and splatter everywhere. So what would happen if I were to do that slowly. If I were to add the acid to the base in small droplets.
            1. It wouldn’t be so violent. In Fact you could fully mix the acid and the base drop by drop and not have any violent reaction. 
            2. So does that mean there was less energy released
              1. Nope, the same amount of energy just released over a longer period of time so the energy did not’ bunch up and try to release all at once.
            3. Yes! And we talk about this in the oxidizer lecture. The energy difference between a block of c4 and snickers isn’t much different. The difference between the two of them is that c4 is set up in a way that all that energy is released at once and the snickers bar has to be done over a long long time.
        5. We often think of chemical systems that have a lot of energy to be unstable. They react easily. They tend to want to have their energy lowered to the state of stored energy so they will react with almost anything because anything is better than where they are now.
          1. All this comes into play when we talk about batteries. And the big thing with lithium ion batteries is the amount of stored energy they contain for their size.
            1. And size is really the keyword here. Imagine taking lots of energy and compressing it into a tiny tiny space. When that build up potential energy has the chance to let loose it is going to. And because you have a lot of energy in a small space all trying to react at once you have a very unstable environment.
            2. Now we are not bashing lithium technology. They are great batteries. It’s a great energy storage system…… when it is a working property. I like to compare these to say trust construction on a building. It’s a great system under normal conditions. Strong, lightweight, not labor intensive. But the fail very quickly when things are under fire load
            3. The batteries are the same way. And because they have no much build up energy in them, they have so much potential energy in such a tiny space it doesn’t take alot for these systems to go out of whack. And once they get rolling releasing their energy in an uncontrolled fashion it only gets worse before it get better. And in reality there is almost nothing we can do.

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