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.

MOFs derived ZnSe/N-doped carbon nanosheets as multifunctional interlayers for ultralong-Life lithium-sulfur batteries

The shuttle effect and slow conversion rate of lithium polysulfides(LiPSs)have become the main obstructs to the development of lithium-sulfur(Li-S)batteries.Herein,the low cost metal-organic frameworks derived nitrogen-doped carbon nanosheets embedded with zinc selenide nanoparticles(ZnSe/NC nanosheets)were designed and synthesized for Li-S batteries.As the LiPSs trapping-layer,these nanocomposites provide some key benefits:(1)The nitrogen doping changes local electron distribution in the carbon nanosheets,thus the electrical conductivity is greatly improved for facilitating the transport of electrons/ions.(2)Nitrogen atoms and ZnSe nanoparticles play an important role in anchoring the LiPSs via chemical interactions.(3)The remarkable catalytic activity of ZnSe nanoparticles can accelerate the redox kinetics of LiPSs.As a result,the Li-S battery with the ZnSe/NC nanosheets modified separator exhibits ultralong lifespan over 1500 cycles with a small capacity loss of only 0.046%per cycle at 1 C,which is superior over those reported values.Furthermore,the Li-S battery with a high sulfur loading of 4.71 mg cm^(-2) can still maintain a high areal capacity of 4.28 mAh cm^(-2) after 50 cycles.This work provides a new route to the design of multifunctional low cost and high-performance separators for remarkably stable Li-S batteries.