Synergistic action of Pt and Nb2O5 ultrafine nanoparticles for bidirectional conversion of polysulfides in high-performance lithium-sulfur cells

Abstract

The shuttling effect in Lithium-sulfur (Li-S) cells can be effectively minimized by increasing the polysulfide redox reaction rate via catalysis. However, previous research has focused on this reaction in a single direction (i.e., either oxidation or reduction of polysulfides), but the acceleration of sulfur species cycling relies on advances in both directions. Herein, a Pt-Nb2O5 mixed catalyst was synthesized by dispersing Pt nanoparticles on the surface of Nb2O5 ultrafine nanoparticles to synergistically enhance bidirectional catalysis. During reduction, Nb2O5 served as a trap while Pt catalytically converted the polysulfides. During oxidation, Nb2O5 and Pt both exhibited enhanced catalytic activity for Li2S dissolution to refresh the catalytic surfaces. Consequently, a sulfur cathode with Pt-Nb2O5 separator achieved an initial discharge capacity as high as 1283 mA h g−1, which was degraded minimally to 979 mA h g−1 after 100 cycles (0.2C). This outstanding cycling stability was further demonstrated, where a discharge capacity of 915 mAh g−1 and average capacity fading rate of 0.093% were achieved after 500 cycles (0.5C). In addition, minimal self-discharge was observed. This work demonstrates the use of two compounds to achieve synergistic action for the bidirectional catalytic transformation of polysulfides for high-efficiency Li-S cells.