Enhanced Chemical Immobilization and Catalytic Conversion of Polysulfide Intermediates Using Metallic Mo Nanoclusters for High-Performance Li-S Batteries.

Rechargeable lithium-sulfur batteries have attracted tremendous scientific attention owing to their high energy density. However, their practical application is greatly hindered by the notorious shuttling of soluble lithium polysulfide (LPS) intermediates with sluggish redox reactions and uncontrolled precipitation behavior. Herein, we report a semiliquid cathode composed of an active LPS solution/carbon nanofiber (CNF) composite layer, capped with a carbon nanotube (CNT) thin film decorated with metallic Mo nanoclusters that regulate the electrochemical redox reactions of LPS. The trace amount (0.05 mg cm-2) of metallic Mo on the CNT film provides sufficient capturing centers for the chemical immobilization of LPS. Together with physical blocking of LPS by the compact CNT film, free diffusion of LPS is significantly restrained and the self-discharge behavior of the Li-S cell is thus effectively suppressed. Importantly, the metallic Mo nanoclusters enable fast catalytic conversion of LPS and regular deposition of lithium sulfide. As a result, the engineered cathode exhibits a high active sulfur utilization (1401 mAh g-1 at 0.1 C), stable cycling (500 cycles at 1 C with 0.06% decay per cycle), high rate performance (694 mAh g-1 at 5 C), and low self-discharge rate (3% after 72 h of rest). Moreover, a high reversible areal capacity of 4.75 mAh cm-2 is maintained after 100 cycles at 0.2 C for a cathode with a high sulfur loading of 7.64 mg cm-2. This work provides significant insight into the structural and materials design of an advanced sulfur-based cathode that effectively regulates the electrochemical reactions of sulfur species in high-energy Li-S batteries.