Chalmers University of Technology uses new graphene to increase the capacity of sodium-ion batteries by 10 times

Whether it is formed into special foams used as thermal switches, mixed with ceramics to form ultra-tough electrolytes, or used to wrap fine silicon particles, graphene is shaping the future of battery technology in some interesting ways. According to foreign media reports, Swedish scientists have added a new type of graphene material to sustainable sodium batteries, increasing the battery capacity by 10 times.

(Image source: Chalmers University of Technology)

Scientists are working to find new and better battery designs, hoping to replace expensive and scarce lithium with abundant sodium. Similar to lithium-ion batteries, in sodium-ion batteries, ions move between two electrodes through an electrolyte to generate electricity. However, as of now, its performance is not satisfactory.

Part of the reason is that sodium ions are too large to fit well into graphite electrodes containing stacked graphene layers compared to lithium ions. Normally, ions move freely in and out of graphite electrodes during the intercalation process of battery cycling, but large amounts of sodium ions cannot be stored effectively in this structure. This greatly affects the performance of sodium-ion batteries, which have a capacity of about 35 mAh/g, only one-tenth of that of lithium-ion batteries.

In search of a solution to this problem, researchers at Chalmers University of Technology have focused on a new type of graphene with special properties. This Janus graphene, named after the two-faced god in Roman mythology, is characterized by an asymmetric chemical functionalisation on two opposite faces. At the same time, molecules present only on one side of the material act both as spacers and as active sites for the interaction of sodium ions.

In this case, molecules present only on one side of the graphene material can promote electrostatic interactions between the stacked sheets while creating more space between them. The research team found that this helped to significantly increase capacity. Researcher Jinhua Sun said: "We added molecular spacers on one side of the graphene layer. When the layers are stacked on top of each other, the molecules create more space between the graphene sheets and provide interaction points, resulting in a significant increase in capacity."

By using innovative Janus graphene instead of graphite, the capacity of the experimental sodium-ion battery can reach 332 mAh/g. This is about 10 times higher than conventional designs and close to the lithium capacity in graphite. The researchers said that this research is still in its early stages, but the results are promising. This shows that it is possible to design an ordered structure of graphene layers suitable for sodium ions, making it comparable to graphite.