Selective catalysis of single V atoms and VN1-x nanodots enables fast polysulfides conversion in lithium–sulfur batteries

Abstract

The application of lithium–sulfur (Li–S) batteries are mainly hindered by the shuttle effect of soluble polysulfides and the sluggish kinetics of sulfur redox reaction. Hence, a bidirectional catalyst, in which single vanadium (V) atoms with V-N4 coordination and vanadium nitride nanodots with abundant nitrogen vacancies (VN1-x) are decorated on nitrogen-doped carbon nanosheets (VN1-x@V-NC), was designed to modify the separators for Li–S batteries. Theoretical calculations and experiments show that V-N4 and VN1-x sites display catalytic selectivity for the formation and decomposition of Li2S, respectively. Additionally, nitrogen-deficient VN1-x displays a strong affinity toward soluble polysulfides through V-S and Li-N bonds, and polysulfides are preferentially adsorbed near the nitrogen vacancies. Specially, the strong adsorption ability facilitates the subsequent conversion reaction at the dual-site. Consequently, a Li–S battery with VN1-x@V-NC modified separator based on pure S cathode displays a stable long-term cycling performance over 500 cycles at 2C. Furthermore, the electrochemical performance of pouch cell with 4 mg cm−2 S loading demonstrates the potential of the VN1-x @V-NC modified separator for practical application.