Heterovalent Ion Doping in MOFs for Tailoring Lewis Acidity Toward Synergistic Polysulfide Adsorption and Catalytic Conversion in Li–S Batteries

ABSTRACT The sulfur reduction reaction (SRR) involves complex multi‐phase transitions, posing conflicting demands that single‐component catalysts cannot meet. Zr‐based MOFs (e.g., UiO‐66) offer high stability but suffer from orbital mismatch between hard Lewis acidic nodes and soft polysulfides, limiting host–guest interactions and hindering liquid‐to‐solid conversion kinetics. Herein, we bridge this gap through Lewis acidity tailoring. A Co‐doped UiO‐66‐NO 2 modified separator is constructed to establish a synergistic hard–soft acid interface. By incorporating soft Co active sites into the robust hard Zr‐MOF framework, we harmonize the host–guest interaction based on the Hard‐Soft Acid‐Base (HSAB) principle. DFT calculations and kinetic analyses reveal a specific dual‐mechanism where the Co sites utilize optimized d‐p orbital hybridization to strongly anchor soft polysulfides, while concurrently acting as targeted catalytic centers to severely reduce the nucleation barrier of the sluggish Li 2 S 4 → Li 2 S 2 /Li 2 S transformation. Consequently, the cell achieves a high reversible capacity of 902.1 mAh g −1 at 0.5 C and an ultralow decay rate of 0.0238% over 500 cycles. This work not only demonstrates a high‐performance Li–S battery separator but also establishes a molecular‐level HSAB‐guided strategy for designing advanced catalyst materials in multi‐phase conversion electrochemistry.