Enabling Ultrafast Single Mg²⁺ Insertion Kinetics of Magnesium-Ion Batteries via In Situ Dynamic Catalysis and Re-equilibration Effects

Abstract

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 Mg2+ 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 MoS2 quantum dots with VS4 (VS4@MQDs) as the cathode. The “in situ dynamic catalysis and re-equilibration” effects can catalyze the Cl–Mg bond breaking and trigger single Mg2+ insertion/extraction chemistries, which can significantly accelerate the diffusion and reaction kinetics, as verified by the decreased diffusion energy barriers (0.26 eV for Mg2+ vs 2.47 eV for MgCl+) and fast diffusion coefficient. Benefitting from these dynamic catalysis effects, the constructed VS4@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+/Mg2Cl3+ to Mg2+ with fast kinetics.

Organic Molecular Intercalation Enabled Anionic Redox Chemistry with Fast Kinetics for High Performance Magnesium Storage

“…Two associated small peaks at 162.5 and 163.5 eV of S 2− are also observed, which can be indexed as 2p 3/2 and 2p 1/2 of S 2− species, respectively. [43] The reason for the presence of S 2− in PAN-VS 4 is that the ─C≡N terminals will be highly cyclized and produce electron-rich species after hydrothermal reaction, and further transfer electrons to VS 4 , finally resulting in the reduction of cations and the generation of S vacancies. [44][45][46] This result can be well confirmed by the high-resolution V 2p XPS peaks, as shown in Figure 2c.…”

“…We fitted the resultant kinetic equations via Equations S1 and S2 (Supporting Information), as shown in Figures 5b and Figure S9 (Supporting Information). [43] The determined b-values can be used to distinguish the contribution of diffusion and capacitance-controlled capacities. As fitted in Figure 5b, the b-values for the three peaks of PAN-VS 4 cathode are 0.8651, 0.9201, and 0.6763, respectively, accompanied by R 2 values above 0.99.…”