Why Is Gallium Nitride the Next Hot Thing for Batteries?

2022-05-11

Rumors about Tesla entering the lithium-mining business started buzzing around in April after the company hired an exploration geologist from Rio Tinto, the world’s second-largest metals and mining corporation. CEO Elon Musk pretty much confirmed as much in an April 8 tweet:

“Price of lithium has gone to insane levels! Tesla might actually have to get into the mining & refining directly at scale, unless costs improve. There is no shortage of the element itself, as lithium is almost everywhere on Earth, but pace of extraction/refinement is slow,” Musk says.

He has a point: lithium metal costs are soaring. According to a December 2021 S&P Global Commodities Insight report, seaborne lithium carbonate prices climbed 413 percent between January and December 2021; lithium hydroxide prices rose 254 percent over the same period. S&P Global says those costs are expected to continue soaring through 2022, leaving open questions about how to create EV batteries with renewable materials in a cost-effective manner.

The secret, it turns out, may lie in a totally different material, allowing us to use less lithium. Let us introduce you to gallium nitride (GaN), a chemical compound that has been commonly used as a semiconductor in light-emitting diodes since the 1990s.

First Off, How Do Lithium-Ion Batteries Work?

In general, batteries have an anode, a cathode, and an electrolyte. Current flows out through the anode, circulates, and then devices connected to the battery use that current before it flows back in through the cathode. From there, charged ions are pulled through the electrolyte material in order to circulate again.

In a lithium-ion battery of the almost ubiquitous design we see today, the anode material is graphite, the most plentiful naturally occurring form of carbon and a lightweight, highly conductive substance. The electrolyte is a lithium-salt liquid that is highly combustible (a discussion for another day). The cathode is one of various compounds that are made of lithium with select other elements.

Many different parts contribute to the bulk and burden of lithium-ion batteries—which means there are a lot of opportunities to improve performance in a way that reduces our dependence on dwindling lithium. Imagine you had a jar of beautiful saffron threads, and you realized just three were left. What would you do? You’d slow down and think about how to most efficiently use them in your recipes. Our jar of lithium is almost empty.

Why Is Gallium Nitride the Next Hot Thing for Batteries?

There’s a ton of debate within the EV battery industry about what the next great thing will be. It could be solid lithium, which comes with challenges of its own, but offers more stability compared to volatile liquid electrolytes. It could be one of the industry’s dozens of blends of lithium, or something new altogether. But it could also be something as simple as the semiconductors.

Navitas Semiconductor is one of many companies in the space looking to make an impact on the field of EV batteries. It says that by making a simple swap—gallium nitride (GaN) for silicon—EV batteries could shed critical weight and also charge faster. It’s all because of the chemical and physical makeup of GaN compared with silicon, giving GaN larger capacity with less materials.

Gallium is a soft metal in the same family as aluminum. It’s solid at room temperature, but just barely, with a melting point of about 85 degrees Fahrenheit. But when combined with plentiful nitrogen, it becomes GaN, a rock-hard semiconductor material. GaN is no shrinking violet; a 2017 study from Shandong University in China, looking at GaN as an anode material, called it the “most studied III-nitride,” compared with similar conductors AlN (aluminum) and InN (indium), for example.

GaN is already used in light-emitting diode (LED) light bulbs. Where traditional tungsten filament incandescent lightbulbs have an efficiency of just 5 percent, GaN LED bulbs can reach 60 percent efficiency. And it could have a similar, if not quite so dramatic, improvement over commonly used silicon as a semiconductor. That’s because of something called bandgap.

In chemistry, bandgap is the distance between the conduction band and the valence band of the material’s atoms. This refers to the two places where electrons are able to be passed in and out, and it helps scientists calculate how conductive different materials are. The bandgap, as the distance between these two bands, is important to other aspects of semiconductors.

Silicon has a narrow band (1.1 electron volts) and GaN has a much wider one (3.4 electron volts). This ends up meaning that the material can hold more electron-passing particles, which translates to more dense materials that can carry the same amount of current. We’re saving materials by shrinking the semiconductors themselves, saving on weight, and increasing the passthrough of electrons during charging.

Navitas says in its materials that GaN is also, surprisingly, a way that we could improve the traction systems in EVs that literally translate energy into the vehicle’s adhesion to the road. That means more movement with less energy, because less is wasted “spinning the wheels.” Indeed, it seems that GaN could do a lot more with less when it comes to EV semiconductors.

Popular Mechanics, 11 May 2022
; https://popularmechanics.com