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Toothpaste Might Hold The Key To Better, Safer And More Eco-Friendly Batteries
Fluoride solvents could be groundbreaking.
Battery technology is the lynchpin of our climate aspirations. Without them, we can’t turn our backs on planet-wrecking fossil fuels. This utterly sucks because the lithium-ion batteries we use (thanks to their high energy density and fast-charging nature) are terrible for the environment. They have massive carbon footprints, destroy ecosystems and have been linked to humanitarian issues. To make matters worse, these batteries are super hard to recycle, have a tendency to blow up and are damn expensive. Having said that, battery power is still better for the environment than dino-juice; it’s just far from perfect. However, a team of researchers recently found that the same chemical process that makes toothpaste work can unlock a far superior battery type, lithium-metal batteries. But what are lithium-metal batteries, and how can toothpaste bring them to fruition?
Let’s start with lithium-metal batteries. They work in much the same way as lithium-ion batteries, but they are constructed slightly differently.
Lithium-ion batteries consist of layers, a cathode (positive side of the battery), a separator, an electrolyte and an anode (negative side of the battery), all stacked on top of each other. Both the anode and cathode can store lithium within their structure, while the electrolyte can carry lithium ions (atoms with an electron stripped off, giving them a positive charge), and the separator is impervious to electrons.
Lithium-ion batteries store and discharge energy by shuttling lithium-ions to and from the anode and cathode. When fully charged, the lithium atoms are within the anode. The properties of the anode mean that they want to shake off an electron and turn into an ion, but can’t as they are too tightly squeezed into the anode. When the circuit is turned on, this gives these atoms room to split into an electron and a lithium-ion. This pushes the electrons around the circuit (as they can’t go through the battery itself, thanks to the separator) and powers whatever device it’s connected to. The electrons then gather at the cathode, giving it a negative charge. This attracts the lithium ions, which travel through the electrolyte and separator to the cathode, where they reunite with the electrons to form typical lithium. To recharge, simply apply a voltage in the other direction, and this whole process happens in reverse.
All lithium-metal batteries do is change the anode. Rather than having a material that can contain lithium, like graphite or silicon, they just use raw lithium metal itself. Other than that, the way they work is pretty much the same.
So, what makes lithium-metal batteries so good? Well, thanks to this super simple anode, they use far less raw material per kWh than lithium-ion batteries. This makes them incredibly energy dense, at up to 818 Wh/kg or over twice as dense as lithium-ion! Such high energy densities can enable EVs with ranges that would make a top-end Tesla weep, or even practical long-distance electric planes and ships. So, lithium-metal batteries really could enable a fossil-fuel-free world.
But this simple anode also means lithium-metal batteries have the potential to be incredibly eco-friendly. You see, one of the major reasons why lithium-ion batteries have such a considerable ecological impact is how they source and manufacture the anode material, yet you don’t need to do any of that for lithium-metal batteries. This is why researchers have found that lithium metal polymer batteries (a type of lithium-metal battery) are far more kind to Mother Earth than lithium-ion batteries.
So, if lithium metal batteries are so good, why aren’t we using them?
Well, they don’t last long at all. Most can only survive a few charge cycles, maybe a hundred, before they are utterly useless.
This short lifespan comes from how the lithium metal anode reacts to the electrolyte. You see, in theory, during the first few charges, the electrolyte reacts with the raw lithium anode, forming a protective layer that keeps the anode viable and the amount of useable lithium in the cell high. But in practice, this protective layer isn’t formed correctly, causing the anode to degrade and the amount of available lithium to reduce, rapidly lowering the cell’s capacity until, eventually, it is useless.
Despite lithium-metal batteries being around for decades, no one has solved this problem, so this potentially game-changing technology has been overlooked.
That is, until now. Researchers from the US Department of Energy’s Argonne National Laboratory may have found a brilliantly simple solution using fluoride, the same chemical that we use to keep our teeth healthy.
Fluoride is an anion (a negatively charged atom with too many electrons) of fluorine. Fluoride and fluorine are incredibly reactive and form super-strong bonds with many other compounds. This is why fluoride is in toothpaste, as it reacts with your teeth, forming a protective layer. So, when bacteria and acids attack your teeth, it strips off the fluoride layer, not your teeth’s enamel.
These researchers used this property to make a much better protective layer around a lithium-metal battery anode. They swapped the electrolyte of the battery out for one rich in fluorine. This made the electrolyte react with the anode even before the battery started to charge and made that during those first few charge cycles, the reaction between the two was far more substantial. This helped to form a far better protective layer, allowing the battery to live for hundreds of life cycles, giving it a similar life span to a lithium-ion cell.
These genius researchers had cracked it! We can now have long-lasting, high energy density, eco-friendly lithium-metal batteries. But the good news didn’t stop there. It turns out this new electrolyte is cheaper to produce than the old one, potentially making these new cells super affordable. Moreover, this electrolyte can’t catch fire, making these cells far safer than any other lithium-metal or lithium-ion battery. Not only does this mean battery packs can hold more capacity (as less safety shielding is needed), but it also makes it incredibly attractive to the aviation industry for electric planes, as safety is paramount in the skies.
Now, it will still be quite a while before we see EVs or phones with fluorine lithium-metal batteries. This breakthrough technology needs to be refined and developed, then the battery industry needs to be convinced they are a good idea, and then manufacturing has to be scaled. But in time, there is a chance these might become the battery technology that unlocks our net-zero future. So next time you brush your teeth, take a moment to ponder just how potentially impactful the chemical reactions going on in your mouth are.
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