High-performance all-solid-state lithium–sulfur batteries with sulfur/carbon nano-hybrids in a composite cathode

Abstract

The shuttle effect poses great challenges to the safety and cycle lifetime of lithium–sulfur (Li–S) batteries. One promising resolution is to substitute liquid electrolytes with solid electrolytes. However, the low intrinsic electrical conductivity of solid electrolytes results in the slow migration of lithium ions and electrons in the composite cathodes and compromises the rate and cycling performance of the all-solid-state Li–S cells. Here, sulfur nanoparticles are fused with carbon species of different dimensions (e.g., 0D carbon nanoparticles, 1D multi-wall carbon nanotubes (MWCNTs) and ultra-long vapor grown carbon fibers (VGCF)) to form nanohybrids by the solvent exchange method, and are then assembled into electrically conducting networks in the composite cathode. The 0D and 1D nanohybrids facilitate the short and long-range migration of electrons, respectively. Fused with sulfur nanoparticles, the conducting networks themselves could act as sulfur-bearing matrixes and shorten the diffusion path of lithium ions. These favorable features give rise to much-enhanced electric/ionic conductivity and high sulfur loading of the composite cathode. The all-solid-state Li–S batteries (ASSLSBs) assembled with these composite cathodes have so far exhibited the highest high-rate cycling capacity and retention at room temperature. A discharge capacity of 1140.9 mA h g⁻¹ at 0.176 mA cm⁻² (about 0.1C) was achieved with a capacity retention of 100% after 400 cycles. After 1000 cycles, the battery still showed a high discharge capacity of 834.3 mA h g⁻¹ at 0.44 mA cm⁻² (about 0.25C).