Accelerating the consecutive conversion of polysulfides enabled by heterostructured Ni₃Se₄/FeSe₂ tandem...

Lithium-sulfur (Li-S) batteries are considered as one of the most promising energy storage systems. However, the poor electrical conductivity of sulfur and Li₂S, sluggish sulfur redox kinetics, shuttle effect of soluble lithium polysulfides (LiPSs), and dendrites growth on Li anode severely preclude their practical applications. Herein, a heterostructured Ni₃Se₄/FeSe₂ tandem electrocatalyst directly grown on the electrospun carbon nanofibers (denoted as CNF@Ni₃Se₄/FeSe₂) is demonstrated to efficiently capture soluble LiPSs and catalyzing their consecutive conversion. The designed CNF@Ni₃Se₄/FeSe₂ interlayer possesses various advantages including high electrical conductivity, abundant catalytic active sites, strong chemisorption capability, and superior catalytic activities. Furthermore, theoretical calculations not only confirm that the formation of Ni₃Se₄/FeSe₂ heterostructure is beneficial for fast charge transfer and enhanced LiPSs adsorption capability, but also reveal the FeSe₂ and Ni₃Se₄ are conductive to consecutively catalyze the reduction of long-chain and short-chain polysulfide intermediates, respectively. Consequently, Li-S batteries assembled with the CNF@Ni₃Se₄/FeSe₂ interlayers deliver remarkable electrochemical performance including high reversible discharge capacity (1412.1 mAh g^-1 at 0.1 C), excellent rate performance (588.0 mAh g^-1 at 5 C) and good long-term cycling stability (capacity fading of 0.058 % per cycle at 2 C after 1000 cycles). More encouragingly, a high initial discharge capacity of 1039.3 mAh g^-1 can be obtained even under a high sulfur loading of 4.5 mg cm^-2, indicating the great potential and application prospects. This study provides valuable guidelines for developing advanced tandem catalytic systems in Li-S electrochemistry.