By Cameron Chai
A team of researchers, led by Linda Nazar from the Waterloo University in Canada and Thomas Bein from the Ludwig-Maximilians-Universitaet Muenchen (LMU) Munich, has synthesized porous carbon nanoparticles that use sulfur molecules to optimize the efficiency of lithium-sulfur batteries, a major breakthrough in the advancement of this next-generation of batteries.
In lithium-sulfur battery prototypes, exchange of lithium ions takes place between sulfur- and lithium-carbon electrodes. Under optimal conditions, two lithium ions can be absorbed by every sulfur atom. Hence sulfur can be used as a superior energy storage material owing to its low weight. However, electron transportation in sulfur is very difficult during charging and discharging due to its poor electrical conductivity.
To optimize the design of the lithium-sulfur battery, the researchers at Nanosystems Initiative Munich (NIM) are working on integrating a nanostructured conductive material to fabricate sulfur phases with largest possible interface area for better electron transportation. As part of this effort, Thomas Bein’s research team at NIM initially synthesized a network of porous carbon nanoparticles with 3-6 nm width pores, which enable homogenous distribution of sulfur. This carbon nanostructure not only makes all sulfur atoms available for absorbing the lithium ions but also places them nearby the conductive carbon.
Thomas Bein explained that the sulfur was highly stabilized and electrically accessible in the porous carbon nanoparticles so that the team was able to attain good cycle stability and a high initial capacity of 1200 mAh/g. The study results emphasize the importance of nano-morphology to improve the performance of innovative energy storage designs. The mesoporous carbon nanoparticles developed by the team have a record surface area of 2445 m2/g and an internal pore volume of 2.32 cm3/g.
The carbon nanostructure minimizes the problem associated with polysulfide, which negatively affects the charging and discharging capability of the battery by forming as intermediate products during the electrochemical processes. The polysulfides are bonded to the carbon network until they have been converted to the desired dilithium sulfide. The researchers applied a thin silicon oxide layer over the carbon material for protecting it from polysulfides without compromising conductivity.