- Lithium-ion batteries will dominate the storage industry for years to come, but there hasn’t been a breakthrough in the technology in three decades.
- Now a group of startups that’s raised a total of more than $1 billion is working to bring the next generation of Li-ion batteries to market that are made with silicon anodes.
- Silicon-anode batteries promise a 20% to 40% increase in energy storage, compared to traditional cells, which could revolutionize gadgets, cars, and aircraft.
- Silicon is notoriously difficult to work with. And even if companies can overcome its challenges, there’s another battery in development that might soon make silicon cells obsolete.
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As much as we complain about our dying phones and earbuds and laptops, the lithium-ion cells that power them are nothing short of incredible.
In a typical iPhone XR, for example, the battery weighs just 46 grams and can keep the device alive for up to 25 hours.
So it’s no surprise that experts say Li-ion will be the battery of choice for years to come.
“Nobody’s really close to catching up on it,” Daniel Finn-Foley, the head of energy storage at Wood Mackenzie, told Business Insider.
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But that’s not to say there isn’t a race to develop something better.
A group of startups that’s raised about $1 billion or more, according to PitchBook, is competing to bring to market a new generation of lithium-ion cells that will store significantly more energy.
The secret? Silicon anodes. They’re incredibly challenging to work with, but if done right they could boost the energy storage potential of Li-ion batteries by up to 40%. That means longer-lasting gadgets, more mileage for electric cars, and perhaps even a new industry built around electric aircraft.
Here’s everything you need to know about this promising new technology.
First, some quick battery science: Cells have two electrodes, the cathode and anode, a liquid electrolyte, and a separator that prevents the electrodes from touching.
They release power as ions of some element flow from the anode to the cathode, through the electrolyte. In the case of Li-ion batteries, those ions are of the element lithium.
What’s important to know is that the amount of energy a cell can store is limited by how many ions can squeeze into the anode. Most Li-ion anodes are made of a carbon-based material called graphite, the same stuff found inside pencils.
Graphite has a lot of benefits — for example, you can discharge it repeatedly without much degradation of the battery. But relative to a small number of other elements, graphite can’t store as many ions.
Silicon, on the other hand, is a storage superstar.
One gram of the stuff can store about 1,000 milliamp hours, a measure of electric charge over time, according to Matthew Keyser, a battery expert at the National Renewable Energy Laboratory (NREL). In comparison, graphite can store only about 350 milliamp hours per gram, he says.
That’s why so many battery companies are chasing after silicon, which they say could improve the energy density of batteries by 20% to 40%.
“If you’re not working in silicon, you’re behind,” Alexander Girau, the founder and CEO of one of the many silicon-anode startups, Advano, told Business Insider.
As useful as it is, silicon has a few major drawbacks
Silicon does have a number of drawbacks.
For one, silicon expands in size by a factor of three as it absorbs ions of lithium, Keyser says. That can cause cracking, which can, in turn, disrupt the flow of ions.
Silicon-based materials are also prone to rapid degradation. After a discharge cycle, the amount of energy they can store might drop by half, he says.
It’s pretty complicated, but basically a reaction occurs between silicon and the electrolyte. The reaction eats up electrolyte and lithium to form a thick crust on the surface of the silicon that impedes the flow of ions.
These challenges have laid speed bumps on the road to commercialization of silicon-anode cells. But they’ve also ignited a scientific race, led by a handful of startups.
These include buzzy businesses like Sila Nanotechnologies, one of the few clean-tech unicorns and Advano, which recently emerged from stealth mode with $18.5 million from investors including the iPod designer Tony Fadell.
There are a few different ways to deal with silicon’s shortcomings.
One option is to just limit how much of it you use. If only 10% to 20% of the anode, by weight, is silicon, it won’t expand as much, yet it will still yield an increase in energy storage.
That’s the approach that the Chicago-based startup NanoGraf is taking, which is “expecting a 20% to 30% energy density increase compared to what is currently on the market today,” NanoGraf’s cofounder and CTO Cary Hayner said.
Advano, Sila Nanotechnologies, Enevate, and others are using another approach. Their technologies encase the silicon inside a semi-porous, sponge-like structure. As silicon absorbs the ions, it expands inside the holes while the volume of the sponge stays roughly the same. That way, it doesn’t crack.
“The silicon has to swell and contract,” Gene Berdichevsky, the CEO of Sila Nanotechnologies, said. “When we allow it to do that inside of a macrostructure that has a rigid outer shell, that lets this happen internally.”
Finally, Keyser says some companies including Amprius — one of the world’s most valuable clean-energy startups — are developing what he calls 3D architectures. Essentially, they coat a conductive surface, such as copper, with microscopic columns of graphite, around which they place particles of silicon.
“When it expands and contracts it can expand in the space between the columns,” Keyser said.
Are silicon-anode cells already becoming obsolete?
Silicon-anode cells are a big deal. They’re delivering the first serious battery breakthrough in about three decades, experts say, and a 20% to 40% improvement in energy density will undoubtedly transform our gadgets and cars.
But there are better batteries in the works — namely, solid-state cells with lithium metal anodes.
“Most people view silicon as a good interim step,” said Doug Campbell, the cofounder and CEO of Solid Power, a startup based in Colorado that’s developing solid-state batteries. “Lithium-metal provides that sort of true step change when it comes to enabling very high energies.”
In a solid-state battery, the liquid electrolyte and separator are replaced with a solid, conductive material. That makes them safer, as liquid electrolyte can be prone to explosion.
Plus, anodes made of lithium-metal — which is only really possible using solid state cells, Keyser says — makes them extremely energy-dense.
“If you have a lithium metal sheet, there’s no more energy-dense material than that,” Keyser said. “It basically goes graphite, silicon, and then lithium-metal. That’s really the progression that we’re looking at right now.”
But like silicon-anodes, lithium-metal anodes are difficult to work with, Keyser says. And we’ve only figured out how to make them in small batches — which is one reason why these batteries have been even harder than silicon-anode cells to commercialize.
“If those problems didn’t exist, then we would immediately go to lithium-metal, because why not?” Keyser said.