Enhanced Performance and Safety in Intermediate Temperature Lithium-Sulfur Batteries

Abstract

Due to the high theoretical capacity and energy density, lithium-sulfur is considered one of the most promising battery chemistries. Difficulties with passivation and polysulfide shuttle have traditionally plagued the lithium anode and sulfur cathode, respectively, in conventional liquid electrolyte batteries. Solid-state electrolytes, such as lithium garnets, can largely address these issues as the dense ceramic layer helps block polysulfide shuttle and are stable to metallic lithium. However, poor electron transfer kinetics resulting from high electronic resistance and large volumetric changes of sulfur limit the development of solid-state Li-S batteries. At intermediate temperatures, the diffusivity of sulfur is thermally activated, facilitating electron transfer. Here we mimic encapsulated sulfur through infiltration of sulfur, carbon, and a series of binders into one side of a porous-dense-porous garnet structure. The garnet provides ionic conduction through the cell while helping to entrap sulfur with aid of binder. Cell cycling was performed to determine the effect of binder on specific capacity and capacity fade. Electrochemical impedance spectroscopy was used to elucidate the changes occurring within the cathode. While the pore size is larger than what is used for most encapsulated sulfur cathodes, thermal activation allows certain binder systems enhanced performance. In addition to conductive benefits, this large-scale enclosure of sulfur helps avoid corrosion issues possible with sulfur at elevated temperature.