Solid-state batteries can be a safe alternative to batteries employing liquid electrolytes. Last year, I wrote about Ionic Materials and its pursuit of a solid polymer electrolyte that works at room temperature. Earlier this year, Dr. Lorenzo Grande, a technology analyst at IDTechEx, wrote about several companies working on solid-state electrolytes. In August, Ionic Materials unveiled a solid-state alkaline battery. And now, researchers including Alex Pearse, a doctoral student at the University of Maryland, College Park, and the Nanostructures for Electrical Energy Storage DOE-sponsored Energy Frontier Research Center, have demonstrated a new way to produce more efficient solid-state batteries.
The researchers’ proof-of-principle study may lead to safer and more compact batteries useful for everything from sensor networks to implantable biomedical devices.
To make thin-film solid-state batteries, conventional methods employ line-of-sight physical vapor deposition (PVD). The electrodes and electrolyte are made by directly depositing the material as a film onto a surface.
“You can’t make the films very thick before you get issues with cracking or delamination,” Pearse said. “It takes too long to grow and gets very expensive.”
But a thin battery can’t store much energy in a given area. Just to power your smartphone, Pearse explained, a solid-state battery would need to span one square meter.
One way to increase capacity is to introduce holes, ridges, or other patterns that boosts the surface area. But conventional PVD doesn’t work for these complex, 3D shapes. “You can imagine a can of spray paint and aiming it at some complicated 3D, porous object,” Pearse said. “You won’t be able to cover every nook and cranny with the even coat that’s needed.”
So Pearse and his colleagues tried atomic layer deposition (ALD), which bathes the object in the material—vaporized into a gas—which adheres to the entire surface. The result is a thin film that evenly blankets an object of any shape.
This is the first time ALD has been used to fabricate a full, 3D solid-state battery, Pearse said. To increase surface area, the researchers designed their battery with a series of holes, developing new patterning strategies to create precise coatings. Because the layers are still very thin, the battery can be compact and can also be recharged quickly.
The prototype can’t yet compete with conventional batteries, Pearse said, but it paves the way forward. While solid-state batteries still can’t compete with most conventional ones, they may be suited for certain applications, such as in tiny sensors. Because there are no toxic liquids that can leak, they would also be suitable for biomedical devices implanted in the body.
Pearse presented this work during the AVS 64th International Symposium and Exhibition held last week in Tampa, FL. He has previously coauthored a paper titled “Nanoscale Solid State Batteries Enabled by Thermal Atomic Layer Deposition of a Lithium Polyphosphazene Solid State Electrolyte,” published in Chemistry of Materials.
The Ionic Materials announcement in August focuses on solid-state alkaline battery technology. Bill Joy, the Sun Microsystems cofounder and an investor in the company, said the alkaline implementation would be safer and cheaper than lithium-ion versions. Bloomberg quotes him as saying, “What people didn’t really realize is that alkaline batteries could be made rechargeable. I think people had given up.”
Joy cited three applications for the company’s polymer technology: consumer electronics, automotive, and the power grid. The technology has yet to be commercialized but could be ready for wider use within five years, he said. He told Bloomberg, “We don’t have a factory. We have a revolutionary material.”
Bloomberg further notes that any new battery technology will face strong competition from the entrenched incumbent, with Li-ion battery-pack prices having fallen 73% from 2010 to 2016. “Technology improvements, manufacturing scale, competition between the major battery manufacturers continue to drive costs down,” said Logan Goldie-Scot, a San Francisco-based analyst at Bloomberg New Energy Finance. “This will make it hard for alternative technologies to compete.” Nevertheless, battery demand from electric vehicles alone is projected to grow from 21 GWh in 2016 to 1,300 GWh in 2030, according to Bloomberg New Energy Finance. So there could be room for multiple technologies. As Joy pointed out, even if Ionic Materials grew at 400% every year for a decade, it couldn’t meet the need alone.
