A conductive framework embedded with cobalt-doped vanadium nitride as an efficient polysulfide adsorber and convertor for advanced lithium–sulfur batteries

Abstract

The industrialization and commercialization of Li–S batteries are greatly hindered by several defects such as the sluggish reaction kinetics, polysulfide shuttling and large volume expansion. Herein, we propose a heteroatom doping method to optimize the electronic structure for enhancing the adsorption and catalytic activity of VN that is in situ embedded into a spongy N-doped conductive framework, thus obtaining a Co-VN/NC multifunctional catalyst as an ideal sulfur host. The synthesized composite has both the unique structural advantages and the synergistic effect of cobalt, VN, and nitrogen-doped carbon (NC), which not only improve the polysulfide anchoring of the sulfur cathode but also boost the kinetics of polysulfide conversion. The density functional theory (DFT) calculations revealed that Co doping could enrich the d orbit electrons of VN for elevating the d band center, which improves its interaction with lithium polysulfides (LiPSs) and accelerates the interfacial electron transfer, simultaneously. As a result, the batteries present a high initial discharge capacity of 1521 mA h g⁻¹ at 0.1 C, good rate performance, and excellent cycling performances (∼876 mA h g⁻¹ at 0.5 C after 300 cycles and ∼490 mA h g⁻¹ at 2 C after 1000 cycles, respectively), even with a high areal sulfur loading of 4.83 mg cm⁻² (∼4.70 mA h cm⁻² at 0.2 C after 100 cycles). This well-designed work provides a good strategy to develop effective polysulfide catalysis and further obtain high-performance host materials for Li–S batteries.