Li₂S Anti-Passivation Deposition Guided by Electrochemically Self-Generated Thiophosphate Molecular Mediators for Lithium-Sulfur Batteries.

Abstract

The practical deployment of high-energy lithium-sulfur (Li-S) batteries is critically impeded by low sulfur utilization, primarily due to the shuttle effect of soluble polysulfides and, less investigated, the passivation of the deposited Li₂S film. To address these challenges, we report an electrochemically in situ self-generated Li₃PS₄ molecules that serve as novel molecular mediators to guide the nucleation of Li₂S preferentially on Li₃PS₄, forming a 3D assembly film composed of Li₃PS₄@Li₂S molecular clusters with an optimized stoichiometry ratio (1:6), thereby effectively suppressing the aggregation and passivation of bulk Li₂S. The Li₃PS₄ mediators were cyclically generated during discharge from a cathode composed of a 3D phosphorus-sulfur covalent inorganic framework (P-S CIF) grown on Ti₃C₂T_x nanosheets (TNS). The P-S CIF features a tetrahedral architecture with phosphorus atoms at vertices interconnected by sulfur chains, spatially confining sulfur species to minimize long-chain polysulfides (Li₂S_n, n≥6) generation. Benefiting from the synergistic effect of Li₃PS₄-mediated Li₂S nucleation plus the spatial confinement provided by the P-S CIF, and the strong polysulfide anchoring capability of TNS, the TNS/P-S CIF cathode achieves exceptional stability and kinetics, delivering an initial capacity of 967 mAh g^-1 at 0.1 A g^-1 and retaining 673 mAh g^-1 after 1000 cycles at 1 A g^-1 (decay rate: 0.022% per cycle). Notably, the electrode maintains an areal capacity of 6.24 mAh cm^-2 under a high loading of 9.8 mg cm^-2, surpassing commercial benchmarks. This work establishes a molecular-level design paradigm for sulfur hosts, integrating structural precision with electrochemical functionality to advance the practical realization of high-performance Li-S batteries.