Cooperative catalytic platinum species accelerating polysulfide redox reactions for Li-S batteries

Abstract

The shuttle effect derived from diffusion of lithium polysulfides (LiPSs) and sluggish redox kinetic bring about poor cycling stability and low utilization of sulfur, which have always been the key challenging issues for the commercial application of lithium-sulfur (Li-S) batteries. Rational design of cathode materials to catalyze Li2S dissociation/nucleation processes is an appealing and valid strategy to develop high-energy practical Li-S batteries. Herein, considering the synergistic effect of bidirectional catalysis on LiPSs conversion and enhanced chemical immobilization for LiPSs by heteroatom doping, Pt nanoparticles loaded on nitrogen-doped carbon spheres (Pt/NCS composites) were constructed as cathode materials. According to the dynamic evolution of Pt catalysts and sulfur species, Pt0 and Pt2+ species were identified as active species for the accelerated dissociation and nucleation of Li2S, respectively. Meanwhile, in-situ Raman results demonstrated the expedited conversion of sulfur species resulted from bidirectional catalysis of active Pt species, corresponding to boosted redox kinetics. Consequently, Pt/NCS cathode exhibited improved long-term cyclability with high initial capacity, along with enhanced rate capability. This work provides a facile approach to construct cathode materials with bidirectional catalysis on Li2S dissociation/nucleation, and sheds light on a more global understanding of the catalytic mechanism of metal catalysts during LiPSs conversion.