Graphene doping a step forward for sodium batteries

Concerns surrounding many of the materials found in a typical lithium-ion battery have been well documented of late, and battery suppliers, vehicle manufacturers and other players are working with research institutes the world over to develop storage solutions that rely on more abundant materials.

One option that has already seen limited commercial uptake in the stationary storage segment is sodium-ion technology. Since sodium is far more abundant than lithium, and the risk of fire is much lower with this battery chemistry, there are several advantages. But sodium also has much lower energy density than lithium, which has so far limited uptake, particularly in the electric vehicle and consumer electronics segments, where the physical size of the battery is a deciding factor.

Scientists at EPFL say that their latest research could open up new pathways to boosting the capacity of sodium-ion batteries. “Lithium is becoming a critical material as it is used extensively in cell-phones and car batteries, while, in principle, sodium could be a much cheaper, more abundant alternative,” says Ferenc Simon, a visiting scientist in the group of László Forró at EPFL. “This motivated our quest for a new battery architecture: sodium doped graphene.”

Sodium-doped graphene

One of the challenges to boosting sodium-ion battery capacity is the fact that sodium particles do not intercalate very well into the graphite electrodes commonly used in lithium-ion batteries. By replacing graphite with graphene (both are forms of carbon, graphite has a crystalline structure while graphene is a single layer of atoms), they were able to successfully dope the material with sodium.

The group used a chemical process relying on liquid ammonia as a catalyst to drive the reaction, and were able to produce material consisting of a few layers of graphene with high sodium content. They describe their methods in Ultralong Spin Lifetime in Light Alkali Atom Doped Graphene, published in ACS Nano.

The material also opens up potential new pathways in the field of spintronics, important in transistors and data storage applications. And though a very early-stage discovery, the scientists working with EPFL are confident of its commercial potential. “Our material can be synthesized on industrial scales and still retains its excellent properties,” says Simon, the paper’s lead author.

The group, however, acknowledges that there is still a lot more work to be done to develop an actual device using this technology. “But with the almost exponential growth in demand for batteries, the study opens up very promising possibilities for innovation,” they conclude.