Engineer brings new twist to sodium-ion battery technology with discovery of flexible molybdenum disulfide electrodes

Jan 29, 2014
A Kansas State University engineer has made a breakthrough in rechargeable battery applications. The bottom image shows a self-standing molybdenum disulfide/graphene composite paper electrode and the top image highlights its layered structure. Credit: Gurpreet Singh, Kansas State University

(Phys.org) —A Kansas State University engineer has made a breakthrough in rechargeable battery applications.

Gurpreet Singh, assistant professor of mechanical and nuclear engineering, and his student researchers are the first to demonstrate that a composite paper—made of interleaved 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 percent 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 ."

For the last two years the researchers have been developing new methods for quick and cost-effective synthesis of atomically thin two-dimensional materials—graphene, molybdenum and tungsten disulfide—in gram quantities, particularly for rechargeable battery applications.

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 degrees Celsius, Singh said.

Singh said the research is important for two reasons:

1. Synthesis of large quantities of single or few-layer-thick 2-D materials is crucial to understanding the true commercial potential of materials such as transition metal dichalcogenides, or TMD, and graphene.

2. Fundamental understanding of how sodium is stored in a layered material through mechanisms other than the conventional intercalation and alloying reaction. In addition, using graphene as the flexible support and current collector is crucial for eliminating the copper foil and making lighter and bendable . In contrast to lithium, sodium supplies are essentially unlimited and the batteries are expected to be a lot cheaper.

"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 commercialize the technology, with assistance from the university's Institute of Commercialization. They also are exploring lithium and storage in other nanomaterials.

Explore further: Novel exfoliation method paves the way for two-dimensional materials to be used in printable photonics

Related Stories

Komaba Group reports sodium ion battery progress

Sep 28, 2012

(Phys.org)—Scientists with a common goal, to figure out an alternative to the lithium ion battery, the main power source of choice, are not giving up. The quarrel is not with the lithium ion battery's performance ...

New metal alloy electrode designed for plus-sized ions

Apr 04, 2012

(PhysOrg.com) -- Storing energy from wind farms and releasing that electricity on demand requires high-capacity, low-cost batteries; sodium-ion batteries could be part of the answer now, thanks to fundamental ...

Recommended for you

The simplest element: Turning hydrogen into 'graphene'

Dec 16, 2014

New work from Carnegie's Ivan Naumov and Russell Hemley delves into the chemistry underlying some surprising recent observations about hydrogen, and reveals remarkable parallels between hydrogen and graphene ...

Future batteries: Lithium-sulfur with a graphene wrapper

Dec 16, 2014

What do you get when you wrap a thin sheet of the "wonder material" graphene around a novel multifunctional sulfur electrode that combines an energy storage unit and electron/ion transfer networks? An extremely ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.