A Kansas State University engineering team has discovered some of graphene oxide's important properties that can improve sodium- and lithium-ion flexible batteries.

Graphene oxide is an insulating and defective version of graphene that can be converted to a conductor or a semiconductor when it is heated. Singh and his team studied graphene oxide sheets as flexible paper electrodes for sodium- and lithium-ion batteries.

The researchers found that sodium storage capacity of paper electrodes depends on the distance between the individual layers that can be tuned by heating it in argon or ammonia gas. For example, reduced graphene oxide sheets, or rGO, produced at high temperature have near zero sodium capacity, while reduced graphene oxide sheets produced at 500 degrees C have the maximum capacity.

The researchers are the first to show that a flexible paper composed entirely of graphene oxide sheets can charge and discharge with sodium-ions for more than 1,000 cycles. Sodium perchlorate salt dissolved in ethylene carbonate served as the electrolyte in their cells.

Singh and his team also studied the mechanical behavior of the electrodes made of reduced graphene oxide sheets. The researchers measured the strain required to tear apart the electrodes. Through videography, they showed the ability of the crumpled graphene oxide papers to sustain large strains before failing.

Earlier this year, Singh and his team demonstrated large-scale synthesis of few-layer-thick sheets of molybdenum disulfide. They also showed the molybdenum disulfide/graphene composite paper has potential as a high-capacity electrode for sodium-ion battery. In that research, the scientists used graphene as an electron conductor for the molybdenum disulfide sheets and observed graphene to be largely inactive toward sodium.

Their latest research has shown that unlike sodium, the lithium capacity of rGO increases with increasing rGO synthesis temperature reaching maximum value for sample produced at 900 degrees C.

Singh said that research into sodium and nonlithium batteries is important for several reasons. As the focus shifts from vehicles to stationary energy storage systems and large vehicles, stationary batteries need to be cheaper, safe and environmentally benign. Because of its large abundance, sodium is a potential candidate for replacing lithium-ion batteries.

By focusing on nanotechnology, Singh and his team were able to explore and design materials that can store sodium-ions reversibly and without damage. They found their answer in graphene oxide, which can cycle sodium-ions for more than 1,000 cycles.

This story is reprinted from material from Kansas State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.