A team at the Florida State University-headquartered National High Magnetic Field Laboratory has discovered how tiny needles of metallic lithium known as dendrites form during solid-state battery use, which can lead to short circuits and battery failure.
The team’s research, which was published in Nature Materials, provides a clearer understanding of dendrite formation and could help develop more reliable and efficient solid-state batteries for various applications, including electric vehicles, energy systems, medical devices and more.
“If you don’t understand the problem, it’s hard to address it,” said Yan-Yan Hu, an FSU chemistry and biochemistry professor who led the research. “We’re trying to understand the mechanisms of dendrite formation in solids.”
The research offers a look at what happens inside a solid-state lithium battery as it’s depleted and recharged repeatedly. Researchers obtained the unprecedented images by developing a custom probe allowing them to see inside the battery during those cycles using the MagLab’s world-record magnetic resonance imaging system.
HOW IT WORKS:
Solid-state batteries, which use a solid electrolyte rather than liquid or gel, are a next-generation technology with the potential to revolutionize energy storage for electric vehicles, consumer electronics and renewable energy systems. They provide more energy density without the safety issues of conventional liquid lithium-ion batteries, which are more likely to overheat or catch fire.
However, developing reliable solid-state lithium batteries faces a challenge of its own: the buildup of dendrites. As the battery is used, these tiny needles of metallic lithium form and branch through the material like growing trees, connecting to each other and short-circuiting the battery.
Now, after more than five years of research using one-of-a-kind magnets and custom techniques, a team at the MagLab has more clearly pinpointed where and how dendrites form.
The research team discharged and recharged batteries inside the nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) probe in the magnetic field and observed dendrite formation inside the batteries to understand how dendrites formed.
“Our high field magnets at the MagLab are ideal for analyzing normally hard to detect elements such as lithium, opening up the periodic table to imaging elements not accessible at lower magnetic fields,” said Sam Grant, an FSU chemical and biomedical engineering professor and director of the MagLab’s MRI program who is a senior author on the study.
The group also developed a unique process to mark the source of dendrite formation chemically — determining whether it was coming from lithium at the edge or middle of the battery. The battery was cycled many times while researchers monitored dendrite buildup.
“One of the unique aspects of this study is high-field MRI coupled with NMR.
MRI provides a picture of the distribution and growth of dendrite formation, while NMR provides insights into the chemistry and origin of the lithium deposited as dendrites,” Grant said.
The test battery consisted of two electrodes made of solid lithium, sandwiching a solid electrolyte compound made of what’s called LLZO: lithium lanthanum and zirconium oxide.
Their work untangled the complex interplay between two mechanisms that cause dendrites. The lithium needles first build up at the interface between the battery’s electrode and electrolyte. The electrode connects the battery terminal to the electrolyte, which moves charged particles through the battery. The researchers also found that, as the battery is used and recharged, other dendrites form in the middle of the solid electrolyte as well. The dendrites at the edge and in the middle then branch out and can link up, leading to short circuits and battery failure.
“We now have a comprehensive understanding of how these dendrites can form, grow, and evolve,” said Florida State University graduate student Yudan Chen, one of the lead authors of the paper.
WHY IT MATTERS:
Solid-state batteries are used in a wide range of applications, including electric vehicles, medical devices, wearable electronics and more. This technology has the potential to improve battery use in various industries by providing a safer, more efficient and longer-lasting power source than existing methods. But there are still challenges with manufacturing, cost and scaling up production that must be addressed before they can replace traditional batteries on a mass scale.
With the new understanding of what causes dendrite buildup and battery breakdown, this research offers a way forward for designing better solid-state batteries.
Scientists are also interested in how this research can help advance alternative and affordable energy from natural sources.
“We have many ways to generate energy,” Chen said. “The key problem is how are we going to store that generated energy to let us use it when needed.”
FUTURE DIRECTIONS:
The next step is to explore ways to prevent dendrite buildup and improve battery design.
The challenge will be tweaking the battery’s ingredients and design to mitigate dendrites. That could include using a different combination of materials, re-engineering the interface where the electrode meets the electrolyte, and adjusting the microstructure of the solid electrolyte.
“We have ideas, or possible methods to engineer, to design, to modify our battery cell,” said Chen, “and after that, we can use our magnetic resonance techniques here to verify whether our engineering methods can work, really mitigate dendrite formation. We can use it as an evaluation toolkit.”