A Convenient Response to an Inconvenient Truth - 3

We have two banks of eight of them. And so our system starts at about 108 volts. And it has a very linear discharge curve, whereby 96 volts, as our pack decreases over time, we're pretty much tapped out and have our 80% depth of discharge.

And that's one of the ways that we tell how much we have left in the battery pack is by voltage. Lithium is actually our lightest metal and least dense metal. It is also the most electrochemically active element we have on the planet.

Unfortunately, it's a little bit stable. Lithium is so light, if you put it on water, it'll actually float. It's so unstable that when you do so, it'll actually burst into flames.

And the early efforts at creating lithium metallic batteries were disastrous in most cases. They would catch on fire and often explode. They went from lithium metal batteries to what they call lithium ion batteries.

And that you take lithium in some form of oxide or phosphate, usually mixed with some other rare earth element, and which, being such a reactive metal, it readily combines with almost anything. And you develop, essentially, an ionic battery that works on the flow of cations, or positive ions, from one terminal to the next. This has been a little bit better.

It's had some disadvantages. What you're most familiar with, camera batteries, laptop batteries, have in the past been lithium manganese oxide or lithium cobalt oxide cathodes. And as a result, they are much improved over lithium metal, but they have a couple of drawbacks.

One is, there is an incidence of fires and explosions, which are not something you want in a car. You don't want it in your laptop. You don't want it in your laptop battery or cell phone, either.

But they have had to recall a number of laptops and a number of cell phones that use that chemistry. The current chemistry is much better. One of the things that you couldn't do with the lithium manganese and lithium cobalt batteries is you couldn't charge them at all below freezing.

Well, here in the garage, in the winter in Missouri, it gets below freezing. And so that was a disadvantage. The other disadvantage with lithium ion batteries is they are not very good at dealing with overcharge conditions or overdischarge conditions.

You have to kind of keep them in their voltage range for them to be happy. These cells and most lithium ion cells, if you exceed about 4.2 or 4.25 volts per cell, and that's one of these individual cells, it starts to build up lithium metal plating on the cathode. And that gets you back into the situation where you have a kind of unstable situation.

But before you get to that point too well, the capacity of the battery in these oxide and phosphate batteries deteriorates dramatically. And so we don't want to overcharge them over 4.25 volts. Similarly, if you overdischarge them below two and a half volts, you start to get an oxidation on the anode, the copper carbon terminal of the battery, and that forms cuprous oxide, which reacts fairly dramatically with aluminum.

You do start to build up what they call copper shunts between the aluminum with lithium plates and the copper plates, and that can short out the cell. And so they don't react too well to that. And that gets you to the constant advice to get a good battery management system if you're gonna use lithium ion iron phosphate cells.

Everyone says this, unfortunately there aren't any good battery management systems out there that we can find. We've received several, we've evaluated them. They tend to be battery monitoring systems and not very good at that function.

And so we're always on the lookout for the ultimate battery management system. But in the meantime, we've learned that perhaps that advice is not quite as necessary as we thought if we do a couple of simple things. Let's talk a little bit about the basics of the battery.

I've made kind of a sandwich here. This is a piece of copper plate. This is a piece of aluminum plate, and this is simply a piece of foam.

Actually 90% of the battery is in fact copper foil and aluminum foil. What they do is take the copper foil and on both sides of it smear, they call it a slurry, but a paste of nanocarbon fiber particles and graphite. That's gonna form our anode or negative terminal of the battery.

The aluminum foil is similarly covered with a slurry on both sides, a paste of lithium iron phosphate. And that's the technology currently being used by ThunderSky, and it offers a number of advantages. The foam represents a very thin actually, polymer that is permeable to ions.

And, but non-conductive to current flow. And they take those pieces and they press them together and bake them pretty hard. And then they roll them up into a roll.

Now that's where you see the round cylindrical cells. These are square cells, but they basically just take a plastic form and they still wind it around it several hundred times to get the maximum amount of surface area of the lithium iron phosphate and the graphite. The aluminum foil and the copper foil are simply current collectors and they're tied to the terminals.

And so each cell has a negative terminal and a positive terminal. A positive terminal is aluminum. And in fact, you can look down in it and see that it's aluminum.

And the negative terminal, you can actually see a copper fitting inside the outside and that's the anode material. If you take a charger and hook it up to a battery cell, basically you pull electrons off of the positive terminal and put them into the negative terminal. And what that does is create some cations or lithium ions on the positive terminal.

Those migrate to the negative terminal, the copper anode, and they're held there by the charge. When you disconnect the charger and hook it up to a load, the lithium ions start to migrate toward the cathode and reform on the cathode or positive terminal of the battery. And the electrons have to flow through the external circuit to then recombine with them.

Lithium is a very light metal. When we say it has the greatest potential for electrochemical activity, it actually has a valence band around the orbit of its atom that has a electron that's, you can think of it as like Pluto with our solar system. It's way out there and weakly held by the sun's gravity.

Well, similarly, the single electron in the valence band of the lithium, iron phosphate type situation is very loosely held there, and so it's easy to remove it and it's easy to put it back. And so it leads to very high current flows in a battery situation.