- Most of the batteries we use today are made mostly of solids.

But over a hundred years ago, a new type of battery was invented based almost entirely on liquids.

And these flow batteries might finally revolutionize our energy grid.

The major problem with solar or wind power is that they don't provide enough energy when we need it the most, which is at night and in the winter.

Batteries could help solve this problem, especially grid scale batteries, which are very, very, very large batteries.

Lithium batteries power pretty much everything else that we use.

So why not use 'em for this too?

Four reasons.

One, they are expensive.

Two, they occasionally explode.

Three, they're tough to repair or recycle.

And four, there is a lot of, shall we say, less than environmentally friendly mining involved.

So if you can produce a battery that does better on one or two of those problems, you might have a multi-billion dollar business on your hands.

And right now as I record this, lots of entrepreneurs are betting their inherited wealth on flow batteries because proponents say that these batteries solve three or even all four of lithium's problems.

Now, a flow battery has a liquid anolyte, which you can think of as a liquid anode, and catholyte, which you can think of as a liquid cathode in these big tanks.

The anolyte contains a dissolved metal that gives up electrons, the catholyte contains a dissolved metal that accepts electrons.

The liquids are pumped through the stack, which is the part of the battery that does the charging and discharging.

There's a membrane that lets protons through and metal current collectors connected to wires that allow electrons to leave the anode, go through the device and come back to the cathode.

You can see immediately from this diagram that a leak could cause the anolyte and catholyte solutions to mix and react with each other.

If that reaction is irreversible, your battery would at the very least loose capacity over time, and at the very worst, be broken and unfixable.

So in the 1980s, researchers at the University of New South Wales invented a new type of flow battery based on a single element, vanadium.

Vanadium is capable of four oxidation states.

You can think of an oxidation state as the number of electrons that one atom of an element can lose or share as part of a chemical bond and still be stable.

Vanadium is stable on its own in the two plus or three plus oxidation state and when bonded in the four plus or five plus oxidation state.

So you can have two of these oxidation states cycling at the anode and the other two at the cathode.

And if there's a leak in the stack and everything mixes all together, doesn't matter, you can just regenerate the whole system electrochemically.

Because, it's all vanadium.

Vanadium also happens to be relatively cheap and soluble in aqueous acidic solutions.

Both of those things make it perfect for use in a flow battery.

This container here holds the anolyte, which I've colored blue.

Now, this is a solution of vanadium in the two plus oxidation state dissolved in concentrated sulfuric acid.

So you've got V two plus H plus and SO four two minus.

This container here holds the catholyte, which I've colored yellow.

This is vanadium dioxide, also dissolved in concentrated sulfuric acid.

So you've got VO two plus H plus and SO four two minus.

VO two plus means that the vanadium is in the five plus oxidation state because each oxygen takes two electrons, that's minus four, and then to get the whole compound to a plus one overall charge, vanadium needs to be five plus.

So we've got vanadium in the two plus oxidation state here and vanadium in the five plus oxidation state here.

Let's turn on the pumps and see what happens.

In this chamber, the vanadium two plus is giving up an electron to become vanadium three plus.

This half reaction happens at the surface of this metal rod because metal conducts electricity well.

Those electrons travel up through this wire, up through whatever the battery's connected to, in this case an LED, and down over to here.

In this chamber, the vanadium dioxide reacts with the electron that came over from the first chamber, as well as two protons from sulfuric acid, forming vanadium oxide, VO two plus, as well as water.

And when that happens, the vanadium's oxidation state changes from five plus to four plus.

This half reaction also happens at the surface of the metal rod.

Because electrons are moving from here to here, and because the half reaction at the cathode uses up protons, protons also need to move from here to here.

And they do that through this semi-permeable membrane, which only allows protons through.

This battery can run as long as there is enough unreactive V two plus in the anolyte tank and enough unreactive vanadium dioxide in the catholyte tank.

As you can see over time, this starts going from blue to green, and this starts going from yellow to green, and if we wait long enough, the whole battery will be green and that will be the battery metaphorically running out of juice.

This metaphorical battery is not just a good visual illustration of what is happening in a real flow battery, it also allows me to demonstrate two unique advantages that flow batteries have over say lithium ion.

The first is that this battery is almost entirely aqueous.

It runs on stuff dissolved in water, and that means that I can literally take a blowtorch to this thing and it wouldn't explode.

Now, if I took this blowtorch to a lithium battery, very bad things would ensue.

The short story is it would get hotter than a steel forge.

The long story is we made a whole video about it, you can check it out after watching the rest of this one.

To demonstrate the second advantage, I'm gonna need some more anolyte and canolyte.

There we go.

Okay, here we go, ready?

There, I have just doubled the capacity of this flow battery.

I didn't touch the stack, I just added more anolyte and catholyte.

And if I wanted to go even bigger, oh, I could.

You see where I'm going with this, right?

Compare that to this lithium battery.

To double the capacity of this battery, you would need another battery.

I mean, not quite, but almost.

Double the graphite anode, double the current collectors, double the electrolyte, double the lithium iron phosphate, et cetera.

Whereas to double the capacity of a flow battery, you need more liquids and bigger containers.

This is a lot easier.

You don't need to touch the stack at all, and that's great because the stack is the most complex and expensive part.

All the other parts of the battery are relatively cheap.

This is a graph of how much it costs to build a new battery versus the capacity of that battery.

Now, this straight line right here represents lithium ion.

This curved line represents flow batteries, and you can see that for small batteries, flow batteries are way more expensive than lithium ion.

This is because the stack is expensive.

But eventually this line actually crosses over the lithium line and flow batteries become cheaper.

And you can see from this graph that the whole point of these flow batteries is to be big, to be grid scale, to provide tens of thousands of people with power when the wind isn't blowing or the sun isn't shining.

Now, look, flow batteries are never gonna be as energy dense as lithium ion, but that doesn't matter.

if you're trying to support an electrical grid, it's fine to be massive and fixed in place.

You do not need the portability you need for a laptop or a car battery.

Now the last advantage, recycling, I unfortunately cannot show you with my food coloring flow battery metaphor, but in general, flow batteries are much easier to recycle than lithium because they're easier to dismantle and you can just pump out the anolyte and catholyte, regenerate them, and then reuse 'em.

And there are also lots of possibilities for what liquid you use as a solvent.

Water is the obvious first choice because that helps with flammability.

But the limitation is you can't crank up the voltage past one and a half volts because you'll actually start electrolyzing the water into hydrogen and oxygen.

That's not good.

So there are flow battery designs that use organic solvents to get you a larger voltage window, which means more energy storage.

And there are tens, maybe even hundreds of flow battery companies out there right now.

Some of them are old names like Lockheed Martin and others are very new startups that you probably have never heard of.

Some use all vanadium systems, some use iron, some use other elements.

Just like with solid batteries, you can pretty much throw darts at the periodic table and use whatever element it hits.

So if I were a venture capitalist, would I be putting my money into flow batteries?

The answer is, yeah, sure.

But I'd also be putting it into lithium, pumped hydro, thermal storage, hydrogen, and any other energy storage tech that came down the pipe because we are gonna need a lot of them.

And only the gods of capitalism can decide whether flow batteries will become a viable technology or whether they will die a slow and unprofitable death.

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