A team of researchers from Brown University has discovered a way of using graphene to double the toughness of a ceramic material used to make solid-state lithium-ion batteries.
The method has the potential to bring the benefits of solid-state batteries, which replace the liquid electrolytes in current batteries, to the mass market.
Solid-state lithium-ion batteries
In recent weeks we've seen news about sodium-ion batteries and a new quantum phase battery for quantum computing. Now, a new strategy for creating a safer and tougher solid-state lithium-ion batteries provides another innovation in the rapidly growing world of electronic devices, vehicles, and battery components.
"There's huge interest in replacing the liquid electrolytes in current batteries with ceramic materials because they're safer and can provide higher energy density," Christos Athanasiou, a postdoctoral researcher in Brown's School of Engineering and lead author of the research, explained in a press release.
"So far, research on solid electrolytes has focused on optimizing their chemical properties. With this work, we're focusing on the mechanical properties, in the hope of making them safer and more practical for widespread use."
The problem with liquid electrolytes
A battery's electrolyte is the barrier between a battery's cathode and anode through which lithium ions flow during charging or discharging. Though liquid electrolytes work pretty well and are found in most batteries today, they do pose a few problems.
At high currents, tiny filaments of lithium metal can form inside the electrolytes, causing batteries to short circuit. The fact that liquid electrolytes are highly flammable also makes them dangerous as short circuits can lead to fires.
One of the main benefits of solid ceramic electrolytes is that they aren't flammable. They can also prevent the formation of lithium filaments, allowing batteries to operate at higher currents.
Working with ceramics
In order to try to overcome the challenge of working with ceramics, which are highly brittle and can fracture during the manufacturing process, the researchers wanted to see if infusing a ceramic with graphene — a super-strong carbon-based nanomaterial — would increase the toughness of the material at the same time as maintaining the electronic properties needed for electrolyte function.
To this end, Athanasiou worked with Brown engineering professors Brian Sheldon and Nitin Padture, who have years of experience of using nanomaterials to toughen ceramics for use in the aerospace industry.
"You want the electrolyte to conduct ions, not electricity," Padture said. "Graphene is a good electrical conductor, so people may think we're shooting ourselves in the foot by putting a conductor in our electrolyte. But if we keep the concentration low enough, we can keep the graphene from conducting, and we still get the structural benefit."
More than double the toughness
Experiments showed that the graphene didn't interfere with the electrical properties of the material and that the composite exhibited a more than two-fold increase in toughness when compared with the ceramic alone.
Overall, the results of the study, which was published in the journal Matter, show that nanocomposites could provide a means for making safer solid electrolytes with mechanical properties that can be used in everyday devices and appliances.
In the future, the group means to test nanomaterials, other than graphene, and different types of ceramic electrolyte.
"To our knowledge, this is the toughest solid electrolyte that anyone has made to date," Sheldon said. "I think what we've shown is that there's a lot of promise in using these composites in battery applications."