Nanocellular graphene amplifies battery capacity

Nicola Brittain

Mechanically robust nanocellular graphene could help improve the efficiency of sodium-ion batteries.

As the electric vehicle (EV) industry continues to grow, the selection of energy storage solutions is pivotal in driving the transition to a more sustainable future. Lithium-ion batteries have been the leading choice for manufacturers in this space, but demand for these batteries is increasing and the cost of raw materials to make them is high.

The emergence of sodium-ion technologies, however, paves the way for another alternative, with experts touting sodium as being cheaper, more environmentally friendly, and easier to source, with fewer supply chain challenges than that of lithium-ion.

To make sodium-ion batteries a more commercially viable option for EV manufacturers, there is still a look of research and work to be done. So, to improve on the performance and efficiency of these batteries, researchers at Tohoku University in Japan have assessed the use of nanocellular graphene within these applications.

What is graphene?

Ever since its discovery in 2004, graphene has been revolutionising the field of materials science and beyond and comprises two-dimensional sheets of carbon atoms, bonded into a thin hexagonal shape with a thickness of one atom layer. Despite its thinness, graphene is strong, lightweight, flexible, and transparent. It also exhibits extraordinary electrical and thermal conductivity, high surface area, and impermeability to gases. From high-speed transistors to biosensors, it boasts versatility in applications.

Nanocellular graphene (NCG) is a specialised form of graphene that achieves a large specific surface area by stacking multiple layers of graphene and controlling its internal structure with a nanoscale cellular morphology.

NCG is known for its potential to improve the performance of electronic devices, energy devices and sensors, but its development has been stymied by defects that occur during the manufacturing process. Cracks often appear when forming NCG, and scientists are looking for new processing technologies that can fabricate homogeneous, crack-free, and seamless NCGs at appropriate scales.

The research

“We discovered that carbon atoms rapidly self-assemble into crack-free NCG during liquid metal dealloying of an amorphous manganese carbon (Mn-C) precursor in a molten bismuth,” says Won-Young Park, a graduate student at Tohoku University.

Dealloying is a processing technique that exploits the varying miscibility of alloy components in a molten metal bath and selectively corrodes certain components of the alloy while preserving others.

Park and his colleagues demonstrated that NCGs developed by this method exhibited high tensile strength and high conductivity after graphitisation. Moreover, they put the material to the test in a sodium-ion battery (SIB).

“We used the developed NCG as an active material and current collector in a SIB, where it demonstrated a high rate, long life, and excellent deformation resistance. Our method of making crack-free NCG will make it possible to raise the performance and flexibility of SIBs – an alternative technology to lithium-ion batteries for certain applications, particularly in large-scale energy storage and stationary power systems where cost, safety, and sustainability considerations are paramount.”

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