Breaking Single-Reaction Limits: In Situ Visualization of TiS₂-Driven Conversion-Intercalation Synergy in Lithium-Sulfur Batteries.

Abstract

Conventional cathodes of lithium battery relying on single storage mechanisms-whether intercalation or conversion-face intrinsic limitations in energy density and sluggish electrode kinetics. Hybrid systems combining both mechanisms offer promising pathways to transcend these constraints; yet, their dynamic interfacial synergies remain poorly deciphered at the nanoscale. This study employs multimodal in situ characterization (Electrochemical atomic force microscopy/Raman/Electrochemical impedance spectroscopy) to elucidate the dynamic synergy in TiS₂-S hybrid cathodes, revealing the concurrent interfacial evolution during cycling: nanoscale steps formation via Li-ion intercalation in the TiS₂-LiTiS₂ host and the phase transformation of S-Li₂S/Li₂S₂. Crucially, the TiS₂/LiTiS₂ serves as a bifunctional interface that not only contributes capacity but also mediates sulfide adsorption and catalyzes preferential edge-directed sulfide deposition. The partially delithiated Li_xTiS₂ enhances electronic conductivity, creating rapid electron transport that facilitates subsequent interfacial sulfide conversion reaction. The hybrid storage mechanism retains features characteristic of both S and TiS₂ storage mechanisms, yet manifests synergistic interfacial reconstruction rather than simple superposition, achieving enhanced reversibility, exceptional cycling stability, and superior rate capability.