Gurpreet Singh, assistant professor of mechanical and nuclear engineering at Kansas State University, and his students are the first to demonstrate that a composite paper - made of interleaved molybdenum disulfide and graphene nanosheets - can be both an active material to efficiently store sodium atoms and a flexible current collector.
The newly developed composite paper can be used as a negative electrode in sodium-ion batteries.
"Most negative electrodes for sodium-ion batteries use materials that undergo an 'alloying' reaction with sodium," Singh said.
"These materials can swell as much as 400 to 500 per cent as the battery is charged and discharged, which may result in mechanical damage and loss of electrical contact with the current collector," he said.
"Molybdenum disulfide, the major constituent of the paper electrode, offers a new kind of chemistry with sodium ions, which is a combination of intercalation and a conversion-type reaction," Singh said.
The paper electrode offers stable charge capacity with respect to total electrode weight.
The interleaved and porous structure of the paper electrode offers smooth channels for sodium to diffuse in and out as the cell is charged and discharged quickly.
This design also eliminates the polymeric binders and copper current collector foil used in a traditional battery electrode, researchers said.
The engineers created a large-area composite paper that consisted of acid-treated layered molybdenum disulfide and chemically modified graphene in an interleaved structured.
The research marks the first time that such a flexible paper electrode was used in a sodium-ion battery as an anode that operates at room temperature.
The study appears in the journal ACS Nanoin.