A solid-state battery, where the liquid electrolyte that carries the charge is swapped out for a solid alternative, promises a number of performance benefits over today's solutions, but there are a few problems to solve first. Scientists at Brown University are reporting a new design that overcomes some of the key hurdles, using a delicate mix of ceramics and the wonder material graphene to produce the toughest solid electrolyte to date.
As the solution that carries the lithium ions back and forth between the anode and cathode while the battery is charged and discharged, liquid electrolytes play an important role in the function of today’s lithium-ion batteries. But these highly volatile liquids bring a risk of fire when the battery short circuits, so there is room for improvement in terms of safety.
Beyond that, alternative electrolytes could offer greater energy density and even allow for other components of the battery to be upgraded, too. For example, the anode is typically made out of copper and graphite, but scientists believe a solid electrolyte would enable the battery to function with a pure lithium anode, something that could break the “energy-density bottleneck,” according to one recently published study.
But integrating a solid electrolyte isn’t exactly easy, with efforts so far often plagued by fracturing and corrosion of other parts of the battery. Using ceramic materials has shaped as one option, but their brittle nature has also proved problematic. The Brown University researchers believe they can overcome this drawback by adding a dash of graphene, the strong and lightweight wonder material that also offers high electrical conductivity, an attribute that had to be managed carefully for these purposes.
“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.”
The team found this sweet spot by combining a certain amount of tiny platelets of graphene oxide with a ceramic powder, and then heating the mixture to form a ceramic-graphene composite. Through testing, the team showed the electrolyte material to offer a two-fold increase in toughness on ceramic alone, and that the addition of graphene didn’t interfere with its electrical performance.
“What’s happening is that when crack starts in a material, the graphene platelets essentially hold the broken surfaces together so that more energy is required for the crack to run,” Athanasiou says.
The researchers say that to their knowledge, this is “the toughest solid electrolyte that anyone has made to date,” and hope that with further work it could make its way into devices for everyday applications. From here, the researchers plan to continue experimenting with the material and testing out alternatives to graphene and different types of ceramics to boost its performance even further.
The research was published in the journal Matter.
Source: Brown University
