Fabrication of a sandwich structured electrode for high-performance lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries are receiving intense interest because of their high theoretical energy density. However, rapid capacity fading is a significant problem facing its practical realization. Here we present the fabrication of a sandwich structured electrode by confining elemental sulfur in a TiO₂ nanocrystal (3–5 nm) decorated graphene nanosheet host (graphene/TiO₂). Elemental sulfur occupies the inter-particle mesopores of the TiO₂ nanocrystal layer and is in intimate contact with the graphene. The sandwich structured graphene/TiO₂/S electrode exhibits enhanced cycling stability with high specific capacity and high Coulombic efficiency. The enhanced electrochemical performance is highly related to the well-defined sandwich structure and the in situ formation of a mixed ionic/electronic conductor (Li_xTiO₂). The sandwich structure could favor rapid diffusion of the electrolyte during the charge–discharge process. Pore absorption of the graphene/TiO₂ host and the on-site adsorption of the TiO₂ nanocrystals could alleviate the dissolution and shuttling of the polysulfides. More importantly, the in situ formed Li_xTiO₂ works synergistically with the highly conductive graphene layer to facilitate easier Li⁺/e⁻ transport. The sandwich structure plus the unique functions of the graphene/TiO₂ host conceptually provide new opportunities to achieve the long-term cycling stability of a sulfur electrode.