Capillary-induced self-crumpled and sulfur-deficient MoS2 nanosheets inhibit polysulfide cycling in lithium–sulfur batteries

Abstract

Stable lithium–sulfur batteries (LSBs) have promise to shape a new generation of stable energy-storage devices. Although the energy densities of LSBs (up to 2500 W h kg⁻¹) are higher than those of conventional Li-ion batteries (LIBs), lithium polysulfides (LiPSs) shuttling remains a pressing issue that leads to irreversible loss of active materials, degraded capacity, and eroded durability of LSBs. To tackle this issue, in this study we modified commercial polypropylene (PP) or pristine separators by laminating them with a layer of crumpled MoS₂ (c-MoS₂) nanosheets; the resulting assembly is referred to herein as MC-separator. We synthesized the c-MoS₂ nanosheets using a special electrohydrodynamic process and laminated them onto the PP separator through simple vacuum filtration. The synthesized c-MoS₂ nanosheets featured a metallic 1T-phase enriched with strained sulfur vacancies and a high surface area, providing additional redox reaction sites for LiPSs during battery operations. The c-MoS₂ thin film could adsorb the LiPSs while providing additional reaction sites to reutilize these LiPSs, ultimately enhancing the specific capacity of the battery. When operated at a rate of 0.5C, a cell comprising a sulfur-expanded graphite cathode, the MC separator, and a Li anode provided a high specific capacity (1242 mA h g⁻¹) with approximately 96% coulombic efficiency over 500 cycles. In contrast, a cell prepared with a PP separator, when operated at 0.5C, provided an initial capacity of only 746 mA h g⁻¹ and could be run for only 296 cycles. The high capacity and good cycling stability of our new cell indicate that the MC separator could suppress the LiPSs shuttle effect, allowing better utilization of the active materials even at high C rates.