Decorating ketjen black with ultra-small Mo2C nanoparticles to enhance polysulfides chemisorption and redox kinetics for lithium-sulfur batteries

Abstract

The low sulfur utilization and fast capacity fading resulting from the sluggish redox reaction and abominable polysulfides shuttle greatly hinder the practical applications of lithium-sulfur (Li-S) batteries. Herein, we develop a facile “ in-situ growth” method to decorate ultra-small Mo 2 C nanoparticles (US-Mo 2 C) on the surface of Ketjen Black (KB) to functionalize the commercial polypropylene (PP) separators, which can accelerate the redox kinetics of lithium polysulfides conversion and effectively increase the utilization of sulfur for Li-S batteries. Importantly, the US-Mo 2 C nanoparticles have abundant sites for chemical adsorption towards polysulfides and the conductive carbon networks of KB have cross-linked pore channels, which can promote electron transport and provide physical barrier and volume expansion space for polysulfides. Due to the combined effects of the US-Mo 2 C and KB, Li-S cells employing the multifunctional PP separators modified with KB/US-Mo 2 C composite (KB/US-Mo 2 C@PP) exhibit a high specific capacity (1212.8 mAh g −1 at 0.2 C), and maintain a reversible capacity of 1053.3 mAh g −1 after 100 cycles. More importantly, the KB/US-Mo 2 C@PP cells with higher sulfur mass loading of 4.9 mg cm −2 have superb areal capacity of 2.3 mAh cm −2 . This work offers a novel and promising perspective for high-performance Li-S batteries from both the shuttle effect and the complex polysulfides conversion. An in-situ growth strategy is developed to construct a multifunctional polypropylene separator by decorating the ultra-small Mo 2 C nanoparticles on the Ketjen Black matrix, thus effectively improving polysulfides chemisorption and redox kinetics for lithium-sulfur batteries.