MoS2/C12A7:e− Electride Heterostructure as a Bifunctional Cathode Host for Polysulfide Immobilization and Accelerated Sulfur Conversion in Na─S Batteries

Abstract

The commercial viability of room-temperature sodium-sulfur (RT-Na/S) batteries remains primarily hindered by the shuttle effect and the sluggish redox kinetics of the sulfur reduction reaction (SRR). The heterostructure materials are promising electrocatalyst candidates that empower advanced RT-Na/S batteries. Herein, we report a cathode design that uses the MoS2/C12A7:e− electride heterostructure as a sulfur cathode host to address these issues. Based on density functional theory (DFT) and molecular dynamics (MD) simulations, we find that coupling MoS2 with highly conductive C12A7:e− significantly enhances the cathode-host functionality beyond that of the pristine MoS2. The presence of C12A7:e− induces atomic rearrangements in MoS2, which consequently modulates the surface polarity of exposed S atoms, thereby strengthening the interaction with the Na atoms in heteropolar sodium polysulfides (Na2Sn; n = 1, 2, 4, 6, 8). The resulting Na─S chemisorption between Na2Sn species and the MoS2/C12A7:e− heterostructure is sufficiently strong to exceed Na2Sn−electrolyte interactions, effectively suppressing polysulfide dissolution and mitigating the shuttle effect. Electronic structure analysis further reveals that the enhanced chemisorption originates from pronounced Na-3s and S-3p orbital interactions. Importantly, this intensified host−polysulfides interaction also promotes the SRR by lowering the Gibbs free-energy changes during Na2Sn conversion. These theoretical findings propose the MoS2/C12A7:e− heterostructure as a potential bifunctional cathode host that simultaneously immobilizes sodium polysulfides and accelerates sulfur redox kinetics in RT-Na/S batteries.