Composite paper leads to breakthrough in rechargeable batteries

A Kansas State University engineer has developed a composite paper that can be used as a negative electrode in sodium-ion batteries.

Gurpreet Singh, assistant professor of mechanical and nuclear engineering, and his student researchers have demonstrated 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.

“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% as the battery is charged and discharged, which may result in mechanical damage and loss of electrical contact with the current collector.

“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 of 230 mAh.g-1, with respect to total electrode weight. Further, 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.”

The research appears in the latest issue of the journal ACS Nano in the article ‘MoS2/graphene composite paper for sodium-ion battery electrodes’.

“For the latest research, 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. Most commercial sodium-sulfur batteries operate close to 300°C, Singh said.

“From the synthesis point of view, we have shown that certain transition metal dichalcogenides can be exfoliated in strong acids,” Singh said. “This method should allow synthesis of gram quantities of few-layer-thick molybdenum disulfide sheets, which is very crucial for applications such as flexible batteries, supercapacitors and polymer composites. For such applications, TMD flakes that are a few atoms thick are sufficient. Very high-quality, single-layer flakes are not a necessity.”

The researchers are working to commercialise the technology, with assistance from the university’s Institute of Commercialization. They are also exploring lithium and sodium storage in other nanomaterials.