lithium-ion batteries Graphene used to double toughness in solid electrolytes

| Author / Editor: Luke James / Johanna Erbacher

Researchers at Brown University have used graphene to “double” the toughness of a ceramic material that is used to make solid-state lithium-ion batteries. However, there are a few challenges that scientists need to overcome first.

Reduced graphene oxide (rGO) can help prevent cracks from running through ceramic materials
Reduced graphene oxide (rGO) can help prevent cracks from running through ceramic materials
(Source: Brian Sheldon, Brown University)

Solid state batteries where the liquid electrolyte that carries the charge is swapped out for a solid alternative offers a number of improvements in terms of performance and safety when compared to today’s battery technology. Now, Brown University researchers have reported a new design that uses a mix of ceramics and graphene to overcomes some of these key challenges. The result is a solid-state lithium-ion battery which uses an ultra-tough ceramic electrolyte, the strongest one to date.

Doing away with volatile liquid electrolytes

Liquid electrolyte, the solution that carries lithium and ions back and forth between the anode and cathode during charge cycles, plays a vital function in today’s lithium-ion batteries, but it is extremely volatile and carries a fire risk when/if the battery short circuits. And with plenty of recent notable examples involving consumer products from major manufacturers, there is plenty of room for improvement when it comes to battery safety.

Beyond safety concerns, solid and other alternative electrolytes could bring greater energy density and enable other key components to be upgraded. For instance, the anode, which is typically made from copper and graphite, could be replaced with a pure lithium anode if a solid electrolyte is used instead of a liquid one. According to a recent study, switching to a pure lithium anode could break the “energy-density bottleneck.”

Integrating a solid electrolyte is far from easy, however. So far, efforts by researchers the world over have been thwarted by components fracturing and corroding. This includes previous efforts to use ceramic materials whose brittle nature has been problematic.

Using graphene to strengthen ceramic materials

“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,” said Christos Athanasiou, a postdoctoral researcher in Brown’s School of Engineering and lead author of the research. “So far, research on solid electrolytes has focused on optimising 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.

Athanasiou worked with engineering professors Brian Sheldon and Nitin Padture from Brown University who, for several years, have been using nanomaterials to toughen ceramics for use in aerospace applications. They believe that they can overcome the brittleness of ceramic materials by using graphene. As an ultra-strong, highly conductive, and lightweight super material it has, for several years, been the subject of much interest from scientists and engineers worldwide due to its potential applications across many key industries.

In this work, the researchers made tiny platelets of graphene oxide and then mixed them with powder of a ceramic called LAPT. This mixture was then heated to form a ceramic-graphene composite. Initial mechanical testing of the composite is reported to have exhibited more than a two-fold increase in toughness compared to the ceramic alone. Experiments also revealed that the graphene did not interfere with the ceramic’s electrical properties.

“You want the electrolyte to conduct ions, not electricity,” says study author Nitin Padture. “ 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.”