New breakthrough in solid-state battery ceramic materials will help bring solid-state batteries to the mass market

A Brown University research team has discovered a way to double the toughness of ceramic materials used to make solid-state lithium-ion batteries , a method that could help bring solid-state batteries to the mass market.

“There’s a lot of interest in replacing electrolytes in existing batteries with ceramic materials because they’re safer and offer higher energy density,” said Christos Athanasiou, a postdoctoral researcher in Brown’s School of Engineering and the study’s lead author. “So far, research on solid electrolytes has focused on optimizing their chemical properties. In this work, we focused on the mechanical properties in hopes of making their use safer, more practical and more widespread.”

The electrolyte is a barrier between the positive and negative electrodes of the battery, through which lithium ions flow when charging or discharging. Liquid electrolytes are currently the most ideal lithium battery material, and most batteries use liquid electrolytes, but they still have some problems. Under high currents, tiny lithium metal filaments will form inside the electrolyte, causing the battery to short-circuit. Since liquid electrolytes are also highly flammable, short circuits can eventually lead to fires.

Solid ceramic electrolytes are nonflammable, and there is evidence that they prevent the formation of lithium filaments, which would allow batteries to operate at higher currents. However, ceramics are highly brittle materials that can break during manufacturing and use.

Image credit: Brown University

In this study, the researchers wondered whether infusing ceramics with graphene could increase the material's fracture toughness while maintaining the electronic properties necessary for electrolyte function.

Athanasiou collaborated with Brown engineering professors Brian Sheldon and Nitin Padture, who for years have been using nanomaterials to strengthen ceramics for the aerospace industry. In this work, the researchers created tiny platelets of graphene oxide, mixed them with a ceramic powder called LATP, and then heated the mixture to form a ceramic-graphene composite.

Mechanical testing of the composite material showed that the toughness of the composite material was more than doubled compared to the ceramic alone. The experiments also showed that the graphene did not affect the electrical properties of the material. The key was to make sure that the right amount of graphene was added to the ceramic. Too little graphene would not achieve the toughening effect. Too much would cause the material to conduct electricity, which is undesirable in an electrolyte.

"You want the electrolyte to conduct ions, not electricity," Padture said. "Graphene conducts electricity well, so people might think they're shooting themselves in the foot by adding a conductor to the electrolyte. But if we keep the concentration low enough, we can stop the graphene from conducting electricity, and we still get the structural benefits."

Taken together, these results suggest that nanocomposites could provide a path toward making mechanically safer solid electrolytes for everyday applications. The team plans to continue improving the material, trying nanomaterials other than graphene and different types of ceramic electrolytes.

The research was published in Matter.