Lithium concentration and atomic chain bridging induced strength–ductility synergy in amorphous lithiated sulfur cathodes

As an eminent candidate for next-generation cathode materials, sulfur undergoes severe volume changes during electrochemical cycling, resulting in material fractures and performance degradation. Although the electrochemical characteristics of lithiated sulfur have been rigorously studied, their mechanical properties, particularly fracture mechanisms, remain insufficiently understood. To address this gap, we conducted comprehensive atomistic simulations to investigate the fracture behavior of amorphous lithiated sulfur (a-Li_xS). Our findings reveal that as lithium concentration increases, the fracture mechanism transits from brittle governed by nanoscale cavitation instability to ductile dominated by plastic shear bands launched at the crack tip. This transition is contingent upon local hydrostatic stress exceeding the cavitation strength, elucidated through atomic-level bonding dynamics including rupture, reformation and rotation. At low lithium concentrations, atomic chain bridging posterior to the crack tip is simultaneously identified to enhance crack resistance. The lithiation-induced fracture toughness enhancement is further quantified via domain J-integral analysis. Notably, a unique strength–ductility synergy is identified for a-Li_xS, attributed to cooperation between lithiation induced heterogeneous bonding environments and atomic chain bridging. This study provides valuable atomic-scale insights into the fracture mechanisms of sulfur cathodes, thereby informing the design of high-energy and durable electrode materials for future applications.