Researchers have discovered that they can come up with longer-lasting lithium-sulfur batteries by wrapping flexible graphene around the sulfur-carbon energy storage unit. This leads to the faster transfer of ions and electrons.
For a paper published in the APL Materials journal, Dr. Vasant Kumar of the University of Cambridge and Professor Renjie Chen of Beijing Institute of Technology led a team of researchers in discussing how they used a metal organic framework (MOF). This acts as a template in creating a conductive porous carbon cage, where sulfur is the host and the sulfur-carbon nanoparticles are the energy storage units where the electrochemical reactions take place.
MOF is a nanomaterial powder that has recently garnered a lot of interest because of its numerous applications, such as carbon dioxide sequestration, gas separation and gas purification.
"Our carbon scaffold acts as a physical barrier to confine the active materials within its porous structure," said researcher Kai Xi of Cambridge. "This leads to improved cycling stability and high efficiency."
Furthermore, the researchers found that by wrapping a thin sheet of graphene around cathodes of lithium-sulfur batteries, they can create a bridge that speeds up the transport of ions and electrons and increases conductivity, thus improving the battery's performance and potentially eliminating performance issues such as low efficiency and battery degradation.
The combination of the graphene wrap and the MOF-derived porous carbon cage creates a composite structure of a porous scaffold that has promising industrial applications.
Xi says the research provides a "basic but flexible approach to both enhance the use of sulfur and improve the cycle stability of batteries." He also says that further modifying the energy storage units, such as doping or coating with a polymer, could still enhance the battery's performance.
The team believes that their novel design, which brings together energy storage and the ion-electron framework, has numerous practical applications, particularly in industries that require high-performance non-topotactic energy storage systems, or systems where chemical reactions do not cause structural changes in the crystalline solids.
Xi says the team is currently working on the development of high-energy density batteries that use hybrid free-standing sulfur cathode systems, which will involve creating novel electrolyte components and lithium "protection layers" to improve batteries' electrochemical performance.
