Enabling Ultrafast Single Mg 2+ Insertion Kinetics of Magnesium-Ion Batteries via In Situ Dynamic Catalysis and Re-equilibration Effects.

Magnesium-ion batteries (MIBs) have great potential in large-scale energy storage field with high capacity, excellent safety, and low cost. However, the strong solvation effect of Mg ²⁺ will lead to the formation of solvated ions in electrolytes with larger size and sluggish diffusion/reaction kinetics. Here, the concept of interfacial catalytic bond breaking is first introduced into the cathode design of MIBs by hybriding MoS ₂ quantum dots with VS ₄ (VS ₄ @MQDs) as the cathode. The "in situ dynamic catalysis and re-equilibration" effects can catalyze the Cl-Mg bond breaking and trigger single Mg ²⁺ insertion/extraction chemistries, which can significantly accelerate the diffusion and reaction kinetics, as verified by the decreased diffusion energy barriers (0.26 eV for Mg ²⁺ vs 2.47 eV for MgCl ⁺ ) and fast diffusion coefficient. Benefitting from these dynamic catalysis effects, the constructed VS ₄ @MQD-based MIBs deliver a high discharge capacity of ∼120 mA h g ^-1 at 200 mA g ^-1 and a long-term cyclic stability of 1000 cycles at 1 A g ^-1 . The improved performance and detailed characterizations well prove that the active ions in MIBs change from MgCl ⁺ /Mg ₂ Cl ³⁺ to Mg ²⁺ with fast kinetics.