High-density single-atom vanadium catalysts for efficient capture and bidirectional conversion of polysulfides in lithium–sulfur batteries

Abstract

Atomically dispersed metal catalysts have shown substantial potential to mitigate the shuttle effect and accelerate the sluggish redox kinetics of soluble lithium polysulfides (LiPSs) in lithium–sulfur batteries (LSBs), but the low density of active atomic sites in single-atom catalysts (SACs) usually makes the capture and conversion processes of LiPSs inefficient. Herein, we report the synthesis of high-density vanadium SACs (HD-V-SACs) with a vanadium loading of up to 13.0 wt%, which is realized by a simple precursor-assisted in situ anchoring strategy using ultrathin porous nitrogen-doped carbon nanosheets as supports. The HD-V-SACs allow many active V sites to be exposed (6.8 atom nm⁻²) and enable synergy among adjacent metal atoms to expedite the redox of LiPSs. To verify this, we use HD-V-SACs to modify the separator in LSBs and demonstrate that the cell with the HD-V-SAC modification layer exhibits a much higher discharge capacity of 1143.9 mA h g⁻¹ at 0.5C than that without such a layer. Moreover, the HD-V-SAC modified Li–S cell shows stable cycling performance at 1C with 76.3% capacity retention after 500 cycles. Even with a high sulfur loading of 5.1 mg cm⁻², the cell still displays a large areal specific capacity of 5.4 mA h cm⁻² at 0.1C. Through comprehensive experimental characterization and theoretical calculations, we demonstrate that the densely distributed vanadium single-atom sites indeed facilitate the adsorption of LiPS intermediates and show high electrocatalytic performance for their bidirectional conversion. The HD-V-SACs hold substantial promise for boosting electrochemical performance of LSBs with high sulfur loadings.