Enhanced Structure Ductility and Sodium Storage Kinetics of High-Capacity Sulfide Anodes via Medium-Entropy...

Metal sulfide anodes offer high theoretical capacities for sodium-ion batteries but are limited by severe chemo-mechanical degradation from conversion/alloying reactions, poor electronic conductivity, and sluggish ion transport. Here, we present a mechanics-led design strategy, medium-entropy ductility engineering, implemented in a ternary thiospinel, ME-NCUS. Density functional theory shows a high Pugh ratio (2.722), elevated Poisson's ratio (0.336), and a reduced Young's modulus (112.8 GPa), collectively indicating an intrinsically ductile, compliant lattice that accommodates elastic strain and dissipates anisotropic stress. This engineered mechanical response mitigates sodiation/desodiation-induced volume expansion, suppresses crack initiation and propagation, and stabilizes electrode/electrolyte interfaces. Correspondingly, the material exhibits accelerated kinetics, with high Na⁺ diffusivity and markedly lower activation barriers. The result is outstanding durability and power performance, retaining 92% capacity (640 mAh g^-1) after 900 cycles at 5 A g^-1 (7 C) with robust long-term stability. By quantitatively linking elastic constants to ion-transport barriers and failure tolerance, this work elevates ductility as a primary design handle for high-capacity, large volume change anodes. Medium-entropy engineering thus offers a general and scalable route to entropy-stabilized sulfides and other conversion/alloying anodes, enabling mechanically resilient and kinetically fast sodium storage.