Researchers from Uppsala University in Sweden have identified the path to commercialising lithium-sulfur battery technology.
Despite the very high theoretical energy density, limited cycle life and energy loss is holding back the application of lithium-sulfur batteries.
The team reported how the cause for the discrepancy between the theoretical and practical discharge capacity of sulfur was the active material of the positive electrode.
The researchers demonstrated that accelerating the transport of lithium-ion inside the porous carbon electrode of a lithium-sulfur battery was the direction for future development of the technology’s positive electrode.
Guest doctoral student at the University told BEST the lithium-sulfur system was distinct from the state-of-the-art lithium-ion systems in several ways, one of which is the reaction intermediates of the positive electrode, which are soluble in the electrolyte while the fully charged state, sulfur, and discharged state, lithium sulfide (Li2S), are insoluble and insulating.
He said: “As the battery discharges, the insulating reaction products can obstruct the process by covering the conductive electrode surface.
“To overcome this problem, researchers have employed highly porous carbon materials, which offer a large conductive surface area. For example, activated carbon. The utilisation of sulfur is indeed enhanced by this method but still around 60% of the theoretical value.
“Some studies still blame the passivation of the electrode area, while other reports have been looking into other possible reasons for the premature termination of the discharge process at the presence of remaining active material, such as the slow reaction kinetics and transport of reactants inside the tortuous porous carbon.
“In our study, with multiple scattering techniques applied on operating lithium-sulfur batteries, a drop in lithium-ion in the electrolyte is observed within the pores of the porous carbon materials as the positive electrode approaches the end of discharge.
“This indicates that the lithium-ion generated by the negative electrode cannot be sufficiently supplied to the location where the electrochemical reaction takes place. This deficiency of lithium-ion therefore terminates the discharge reaction although sulfur is not completely reacted.”
