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 the 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-SACs modification layer exhibits a much higher discharge capacity of 1143.9 mAh g−1 at 0.5 C than that without such a layer. Moreover, the HD-V-SAC modifed Li-S cell shows stable cycling performance at 1 C 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 mAh cm−2 at 0.1 C. Through comprehensive experimental characterization and theoretical calculations, we demonstrate that the densely distributed vanadium single-atom sites indeed facilitate the adsorption of LiPSs intermediates and show high electrocatalytic performance for their bidirectional conversion. The HD-V-SACs hold substantial promise for use to boost electrochemical performance of LSBs with high sulfur loadings.