Molybdenum Disulfide Gets a Boost as a Li-ion Electrode Material

While the prospect of aluminum-ion batteries may have received a lift recently, the workhorse battery for both our handheld electronic devices and our electric vehicles remains the ubiquitous lithium-ion (Li-ion) battery.

And now, researchers at Kansas State University (KSU) have taken a fresh look at the venerable Li-ion battery: Using the two-dimensional material molybdenum disulfide (MoS₂) on its electrodes, they say, may dramatically boost its storage capacity. What they have come up with is a hybrid material that combines MoS₂ with silicon carbonitride (SiCN); it can store double the charge of electrodes using MoS₂ on its own.

Last year, KSU researchers, led by Gurpreet Singh, demonstrated the effectiveness of MoS₂ in overcoming some of the key shortcomings of sodium-ion batteries. It appears Singh and his colleagues have turned their attention to addressing the issues of cycling stability and capacity retention as seen with previous research in which bulk MoS₂ was used.

In research published in Nature’s Scientific Reports, the KSU team observed that MoS₂ sheets that had been wrapped in silicon carbonitride could store twice as much lithium as pure MoS₂. The reason may be the same mechanism underlying the issues the researchers faced when studying sulfur-ion batteries: sulfur gets into the electrolyte, reducing its capacity.

"This kind of behavior is similar to a lithium-sulfur type of battery, which uses sulfur as one of its electrodes," Singh said in a press release. "Sulfur is notoriously famous for forming intermediate polysulfides that dissolve in the organic electrolyte of the battery, which leads to capacity fading. We believe that the capacity drop observed in molybdenum disulfide sheets is also due to loss of sulfur into the electrolyte."

By wrapping the MoS₂ in silicon carbonitride, which is a ceramic material capable of withstanding high temperatures, the MoS₂ is prevented from giving off its sulfur atoms and creating the polysulfides that would eventually dissolve in the electrolyte.

"The silicon carbonitride-wrapped molybdenum disulfide sheets show stable cycling of lithium-ions irrespective of whether the battery electrode is on copper foil-traditional method or as a self-supporting flexible paper as in bendable batteries," Singh said in the release.

In a full comparative table provided in the open-access research paper,  you can see the big difference in durability between the SiCN-MoS₂ hybrid versus the MoS₂ on its own. The MoS₂ material on a traditional electrode starts with a charge capacity of 595 milliampere-hour per gram, and after just 20 cycles, falls precipitously to just 16 mAh/g. Meanwhile the SiCN-MoS₂ on a traditional electrode, starts at 572 mAh/g and after 20 cycles is still at 104.8 mAh/g. When a SiCN-MoS₂ paper electrode is used, the new formulation’s numbers are even more impressive, starting at 623.5 mAh/g and registering 417.8 mAh/g after 20 cycles.

In further research, Singh intends to see how this battery design might function in an actual handheld device. The key to this line of research will be testing its ability to store energy over the course of hundreds of charge-discharge cycles.