Polysulfides adsorption and catalysis dual-sites on metal-doped molybdenum oxide nanoclusters for Li-S batteries with wide operating temperature

The development of electrocatalysts with high catalytic activity is conducive to enhancing polysulfides adsorption and reducing activation energy of polysulfides conversion, which can effectively reduce polysulfide shuttling in Li-S batteries. Herein, a novel catalyst NiCo-MoO_x/rGO (rGO = reduced graphene oxides) with ultra-nanometer scale and high dispersity is derived from the Anderson-type polyoxometalate precursors, which are electrostatically assembled on the multilayer rGO. The catalyst material possesses dual active sites, in which Ni-doped MoO_x exhibits strong polysulfide anchoring ability, while Co-doped MoO_x facilitates the polysulfides conversion reaction kinetics, thus breaking the Sabatier effect in the conventional electrocatalytic process. In addition, the prepared NiCo-MoO_x/rGO modified PP separator (NiCo-MoO_x/rGO@PP) can serve as a physical barrier to further inhibit the polysulfide shuttling effect and realize the rapid Li⁺ migration. The results demonstrate that Li-S coin cell with NiCo-MoO_x/rGO@PP separator shows excellent cycling performance with the discharge capacity of 680 mAh·g⁻¹ after 600 cycles at 1 C and the capacity fading of 0.064% per cycle. The rate performance is also impressive with the remained capacity of 640 mAh·g⁻¹ after 200 cycles even at 4 C. When the sulfur loading is 4.0 mg·cm⁻² and electrolyte volume/sulfur mass ratio (E/S) ratio is 6.0 μL·mg⁻¹, a specific capacity of 830 mAh·g⁻¹ is achieved after 200 cycles with a capacity decay of 0.049% per cycle. More importantly, the cell with NiCo-MoO_x/rGO@PP separator exhibits cycling performance under wide operating temperature with the reversible capacities of 518, 715, and 915 mAh·g⁻¹ after 100 cycles at −20, 0, and 60 °C, respectively. This study provides a new design approach of highly efficient catalysts for sulfur conversion reaction in Li-S batteries.