Confining sulfur particles in clay nanotubes with improved cathode performance of lithium–sulfur batteries

Abstract

Lithium–Sulfur batteries have high energy storage capacity while their sulfur cathode suffers large volume change, polysulfides dissolution and shuttle effect, and capacity fading during long-term cycling. To help lock sulfur and mitigate these problems, we introduce halloysites, a natural clay material with nanotube format, to disperse and confine sulfur nanoparticles as well as to suppress the dissolution and migration of polysulfides. Halloysites are firstly made conductive by covering with a glucose-derived carbon skin. Sulfur nanoparticles are then trapped in both lumen and outside surface of individual nanotubes with a loading dosage up to 80 wt%. In this new halloysite/sulfur composites cathode, the hollow nanostructure of halloysites provides space to allow dimension changes of encapsulated sulfur nanoparticles during repeated lithiation while limit their size up to the diameter of nanotube lumen (i.e., 25 nm or less). The stacked halloysite clusters further create many nanoscale voids to divide the sulfur-electrolyte interface into isolated domains and increase the migration tortuosity in electrolytes to suppress the dissolution and shuttle effect of polysulfides. These features together contribute to improved cycling stability, retaining nearly ~84% of the starting capacity over 250 cycles, though the diffusion of lithium ions into and out of nanotubes show some differences.