Nano ‘sandwich’ feeds performance gains for rechargeable lithium-ion batteries
Gurpreet Singh, assistant professor of mechanical and nuclear engineering, and his research team are looking to improve rechargeable lithium-ion battery performance. The team has focused on the lithium cycling of molybdenum disulfide, or MoS2, sheets and the the team has found that silicon carbonitride-wrapped molybdenum disulfide sheets show improved stability as a battery electrode with little capacity fading.
The findings have been published in Nature’s Scientific Reports in the article entitled ‘Polymer-Derived Ceramic Functionalized MoS2Composite Paper as a Stable Lithium-Ion Battery Electrode’. Singh’s team observed that molybdenum disulfide sheets store more than twice as much lithium – or charge – than bulk molybdenum disulfide reported in previous studies. The researchers also found that the high lithium capacity of these sheets does not last long and drops after five charging cycles.
"This kind of behavior is similar to a lithium-sulfur type of battery, which uses sulfur as one of its electrodes," explained Singh. "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."
To reduce the dissolution of sulfur-based products into the electrolyte, the researchers wrapped the molybdenum disulfide sheets with a few layers of the ceramic silicon carbonitride, or SiCN. The ceramic is a high-temperature, glassy material prepared by heating liquid silicon-based polymers and has much higher chemical resistance toward the liquid 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," said Singh.
After the reactions, the research team also dissembled and observed the cells under the electron microscope, which provided evidence that the silicon carbonitride protected against mechanical and chemical degradation with liquid organic electrolyte.
The researchers plan to continue testing the molybdenum disulfide cells during longer recharging cycles to have more data to analyze and to better understand how to improve rechargeable batteries.
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