Lithium-metal batteries can take up to 10 times more charge than conventional lithium-ion batteries. The reason why they haven’t been commercialized so far is that lithium is deposited unevenly on the electrodes while charging and discharging. This buildup cuts the lives of these batteries too short to make them viable, and more importantly can cause the batteries to short-circuit and catch fire.

Now, researchers at the University of Illinois at Chicago have developed a solution to this problem in the form of a graphene-oxide-coated ‘nanosheet’ that, when placed in between the two electrodes of a lithium-metal battery, prevents uneven plating of lithium and allows the battery to safely function for hundreds of charge–discharge cycles.

“Our findings demonstrate that two-dimensional materials—in this case, graphene oxide—can help regulate lithium deposition in such a way that extends the life of lithium-metal batteries,” said Reza Shahbazian-Yassar, associate professor of mechanical and industrial engineering in the UIC College of Engineering.

Lithium-metal batteries are so useful because of their high-energy density and relatively light weights compared with conventional batteries. However, over the course of many charge–discharge cycles, lithium builds up unevenly on the battery’s lithium-metal electrode in a branching or ‘dendritic’ pattern, and ultimately causes the battery to go dead. If the dendrites grow through the electrolyte solution and make contact with the other electrode, then the battery may experience a catastrophic event—in other words, explode or catch fire.

In lithium-ion batteries, a separator, usually made of a porous polymer or glass ceramic fibers, is placed in the electrolyte. The separator allows lithium ions to flow through while keeping the other components blocked, which prevents electrical shorts that can lead to fires.

Reza and colleagues used a modified separator in a lithium-metal battery to modulate the flow of lithium ions and control the rate of lithium deposition, with the aim of preventing dendrites from forming. They spray-coated a fiberglass separator with graphene oxide, producing a nanosheet.

Using various imaging techniques, the researchers showed that when the nanosheet was used in a lithium-metal battery, a uniform film of lithium formed on the lithium electrode’s surface. As noted by graduate student Tara Foroozan, this film was shown to improve battery function and improve the overall safety of the battery.