SnS ₂/TiO ₂ nanohybrids chemically bonded on nitrogen-doped graphene for lithium–sulfur batteries: synergy of vacancy defects and heterostructures

Abstract

Few-layer, sulfur-deficient SnS ₂ sheets and TiO ₂ nanocrystals grown on N-doped graphene serve as an efficient polysulfide mediator.

Abstract

Despite their high-energy density, low cost and environmental friendliness, the commercial application of lithium–sulfur batteries (LSBs) has been plagued by their severe capacity decay during long-term cycling caused by polysulfide shuttling. Herein, we demonstrate a synergetic vacancy and heterostructure engineering strategy using a nitrogen-doped graphene/SnS ₂/TiO ₂ (denoted as NG/SnS ₂/TiO ₂) nanocomposite to enhance the electrochemical performance of LSBs. It is noted that plentiful sulfur vacancy (V _s) defects and nanosized heterojunctions are created on the NG/SnS ₂/TiO ₂ composite as proved using electron paramagnetic resonance, transmission electron microscopy and X-ray photoelectron spectroscopy, which can serve as strong adsorption and activation sites for polar polysulfide intermediates, prevent their dissolution/shuttling, and accelerate their redox reaction. The novel NG/SnS ₂/TiO ₂–S cathode delivers a high initial capacity of 1064 mA h g ⁻¹ at 0.5 C and a high capacity retention rate of 68% after 500 cycles at 0.5 C.