Giant Molybdenum Clusters Accelerating the Multistep Polysulfide Conversion and Boosting the High-Rate/Low-Temperature Performance of Sodium−Sulfur Batteries

Abstract The shuttle effect, caused by the dissolution of polysulfides and slow sulfur conversion kinetics, has significantly hindered the practical application of rechargeable sodium−sulfur (Na−S) batteries. In response to this challenge, we have meticulously designed a novel series of glass fiber (GF) separators, which are facilely modified with giant molybdenum clusters via robust electrostatic interactions. By integrating a precisely curated giant cluster that encompasses 154 molybdenum cores (abbreviated as {Mo154}), the modified GF separator demonstrates bidirectional electrocatalytic activity toward the reversible sulfur redox process. The unique electron-rich environment of {Mo154}, combined with strong Lewis acid−base interactions, can effectively suppress the diffusion of polysulfides to the anode. Furthermore, the redox-active centers (MoVI/MoV) of {Mo154} have the ability to continuously supply electrons, thereby accelerating the catalysis of polysulfide reduction in the initial discharge phase. Consequently, the innovative application of the GF/Mo154 separator in Na−S batteries facilitates rapid charging and discharging capabilities at an ultrahigh rate of 20 C for more than 4000 cycles, with the capability to achieve a flash charge within merely 50 s. Additionally, it exhibits remarkable cycling stability, delivering a specific capacity of 306.4 mAh g−1 at a rate of 0.5 C under low-temperature conditions of −40 °C. This work has paved a low-cost and highly feasible avenue for the design of new-generation Na−S batteries featuring high-rate capability, long-cycle life, and low-temperature tolerance.