Theoretical Screening and Structural Optimization of High-Performing Li₂S/Alkaline-Earth Metal Sulfides Cathodes for...

Anode-fre Li-S batteries can achieve extremely high energy density and excellent intrinsic safety by circumventing the direct use of metallic Li. However, the actual output performance is largely constrained by sluggish reaction kinetics and severe structural deterioration of Li₂S cathode. Here, we report an anchor-encapsulated nanostructure cooperated with alkaline-earth metal sulfides' catalysis to promote Li₂S kinetics and simultaneously stabilize sulfur species. DFT calculations are first implemented to screen out an optimized MgS electrocatalyst, then a synthetic paradigm of metallothermic-sulfidation-carbonization via burning LiMg alloy in CS₂ vapor is proposed to in situ construct Li₂S-MgS@graphene nanocapsules. Systematic studies reveal its integrated anchor-encapsulated structure and synergistic physicochemical interactions among three key components: robust C-S bonding facilitates fast electron/ion transport and stable interface, compact graphene encapsulation alleviates volume change and electrolyte's erosion, and symbiotic MgS bears excellent electrocatalytic effect on Li₂S dissociation, greatly reducing activation barrier. Owing to the improvement on electrical, catalytic and volumetric properties, this cathode design enables promising electrochemical performance. It demonstrates a great potential for anode-free Li-S battery and Li₂S-MgS@graphene//Cu cell exhibits 823 mAh g^-1 initial specific capacity and 73% capacity retention after 100 cycles. Findings in this work are expected to spark a promising direction for designing high-performing anode-free batteries.