N -Doped Carbon-Anchored Ruthenium Nanoclusters for Enhanced Polysulfide Conversion Kinetics in High-Performance Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) have high energy density and low cost, but their lifespan is shortened by the shuttle effect of sulfur species (lithium polysulfides, LiPSs), restricting their applications. Herein, a novel composite material consisting of Ru nanoclusters with an average diameter of approximately 3.51 nm, embedded in microporous carbon nanospheres (Ru@NC), is facilely synthesized to combat the shuttle effect and improve sulfur’s redox kinetics. Experimental and theoretical studies show that the Ru@NC features a durable spherical structure with abundant exposed active interfaces, high porosity, and a dual lithiophilic and thiophilic Ru–N structure, enabling efficient restriction of LiPSs and facilitating rapid electron and ion transfer. As a result, the battery shows good rate capability and retains a capacity of over 1050 mAh g–1 at 0.5 C after the rate performance test. Moreover, the Ru@NC/S cathode in the LSB exhibits excellent stability, offering a capacity of over 728 mAh g–1 after 800 cycles at a 1 C rate with nearly 100% Coulombic efficiency. Even under an S loading of 5.0 mg cm–2, the Ru@NC/S-based Li–S pouch cell achieves a capacity of 1097 mAh g–1, retaining 536 mAh g–1 after 100 cycles at a current density of 0.5 C.