Sodium-ion batteries offer an attractive alternative to Li-ion batteries not because they outperform Li-ion batteries, but mainly because of lower costs due to the the nearly unlimited supply of sodium. They are also an attractive alternative in part because unlike their sodium-sulfur battery cousins they can be made in similar sizes to Li-ion batteries.
However, the commercial development of sodium-ion batteries has been hampered by the materials used in the negative electrodes. These swell to as much as 400 to 500 percent their original size, leading to mechanical damage and loss of electrical contact.
Now researchers at Kansas State University have developed a composite, paper-like material made from two 2-dimensional materials—molybdenum disulfide and graphene nanosheets—that has been shown to overcome this shortcoming.
In research published in the journal ACS Nano (“MoS2/Graphene Composite Paper for Sodium-Ion Battery Electrodes”), the 2-D composite material developed proved resistant to the “alloying” reaction that electrode materials typically suffer when in contact with sodium.
The research also marks the first time that the flexible paper electrode was used in an anode for sodium-ion battery that operates at room temperature.
The Kansas State researchers began their work by looking for better ways to synthesize 2-D materials for rechargeable battery applications. This led them to create the large-area composite paper that they used for negative electrodes.
The paper is a composite of acid-treated layered molybdenum disulfide and chemically modified graphene in an interleaved structured. “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,” said Gurpreet Singh, an assistant professor at Kansas State and one of the authors of the paper, in a press release. “This design also eliminates the polymeric binders and copper current collector foil used in a traditional battery electrode.”
While the researchers are looking for opportunities to commercialize their technology for rechargeable battery applications, they also feel that they have contributed to the fundamental understanding of how to synthesize 2-D materials.
"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,” Singh said.
Image: Gurpreet Singh
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.