Synergistic regulation of polysulfides shuttle effect and lithium dendrites from cobalt-molybdenum bimetallic carbides (Co-Mo-C) heterostructure for robust Li-S batteries

Abstract

Lithium-sulfur batteries (LSBs) are considered as the most promising energy storage technologies owing to their large theoretical energy density (2500 Wh/kg) and specific capacity (1675 mAh/g). However, the heavy shuttle effect of polysulfides and the growth of lithium dendrites greatly hinder their further development and commercial application. In this paper, cobalt-molybdenum bimetallic carbides heterostructure (Co₆Mo₆C₂@Co@NC) was successfully prepared through chemical etching procedure of ZIF-67 precursor with sodium molybdate and the subsequent high temperature annealing process. The obtained dodecahedral Co₆Mo₆C₂@Co@NC with hollow and porous structure provides large specific surface area and plentiful active sites, which speeds up the chemisorption and catalytic conversion of polysulfides, thus mitigating the shuttle effect of polysulfides and the generation of lithium dendrites. When applied as the LSBs separator modifier layer, the cell with modified separator present excellent rate capability and durable cycling stability. In particular, the cell with Co₆Mo₆C₂@Co@NC/PP separator can maintain the high capacity of 738 mAh/g at the current density of 2 C and the specific capacity of 782.6 mAh/g after 300 cycles at 0.5 C, with the coulombic efficiency (CE) near to 100%. Moreover, the Co₆Mo₆C₂@Co@NC/PP battery exhibits the impressive capacity of 431 mAh/g in high sulfur loading (4.096 mg/cm²) at 0.5 C after 200 cycles. This work paves the way for the development of bimetallic carbides heterostructure multifunctional catalysts for durable Li-S battery applications and reveals the synergistic regulation of polysulfides and lithium dendrites through the optimization of the structure and composition.