A hierarchical VN/Co3ZnC@NCNT composite as a multifunctional integrated host for lithium–sulfur batteries with enriched adsorption sites and accelerated conversion kinetics

Lithium–sulfur (Li–S) batteries are growing in popularity by virtue of their high energy density, low cost and environmental friendliness. However, the commercialization of Li–S batteries is severely hindered by low sulfur utilization, sluggish sulfur redox chemistry, and the severe shuttle effect of lithium polysulfides (LiPSs). In this work, a hierarchical composite composed of VN and nitrogen-doped carbon nanotubes encapsulated with Co3ZnC nanoparticles (denoted as VN/Co3ZnC@NCNTs) is conceptually designed through a space-confined melamine-assisted nitridation strategy. As a multifunctional integrated sulfur host, the hierarchical VN/Co3ZnC@NCNT composite has a variety of advantages including high electrical conductivity, good physical confinement and chemical adsorption to LiPSs, and superior electrocatalytic activity, which can effectively facilitate the immobilization–diffusion–conversion process of soluble LiPSs. As a result, the Li–S batteries based on the VN/Co3ZnC@NCNT host exhibit a high discharge capacity of 1399.4 mA h g−1 at 0.1C, as well as excellent rate capability (566.4 mA h g−1 at 5C) and long-term cycling stability (557.6 mA h g−1 at 1C after 500 cycles with a low decay rate of 0.064% per cycle). More encouragingly, even at a high sulfur loading of 4.5 mg cm−2, the S@VN/Co3ZnC@NCNT cathode still delivers a high reversible capacity of 639.2 mA h g−1 at 0.2C after 100 cycles. Furthermore, experimental results and theoretical calculations demonstrate that strengthening adsorption is not responsible for the improvement of catalytic activity. This work could provide a novel insight into the rational development of multifunctional integrated sulfur host materials for high-performance Li–S batteries.