Bidirectional catalyst design for lithium–sulfur batteries: phase regulation cooperates with N-doping

Abstract

Accelerating the reaction kinetics of S species is considered the key to further improving the performance of lithium–sulfur (Li–S) batteries. However, current research on efficient catalysts for S species is mainly limited to unidirectional catalysis, yet both the oxidation and reduction processes of Li–S electrochemistry are integrated and inseparable. Therefore, developing a suitable bidirectional catalyst is critical for practical applications. Herein, we adopted N-doped ultra-thin MoS₂ nanosheets anchored on multi-walled carbon nanotubes (N-MoS₂@CNTs) as efficient bidirectional catalysts for fast S species conversion by a fast and highly active NH₃ plasma technology under moderate conditions. Reasonable N doping can improve the adsorption ability of soluble lithium polysulfides and effectively inhibit the harmful shuttle effect. In addition, the mild NH₃ plasma N-doping strategy can also regulate the favorable phase transition (2H → 1T phase) of the catalyst and further improve the catalytic activity. Benefiting from the N-doping strategy coupled with phase regulation, N-MoS₂@CNTs reduce the nucleation and decomposition barrier of Li₂S, which greatly improves the conversion reaction kinetics of Li–S batteries. The assembled batteries comprising a S/N-MoS₂@CNT composite cathode exhibit a high capacity of 1313.6 mA h g⁻¹ at 0.1C and deliver excellent cycle stability at 1C for 1000 cycles with an ultra-low capacity decay rate of 0.037% per cycle. More importantly, it can be stably cycled for more than 100 cycles even when increasing the sulfur loading to 5.1 mg cm⁻².