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.
Hybrid Mg/Li-ions batteries (MLIBs), combining the fast kinetics of Li and the advantages of magnesium ion batteries (MIBs), are regarded as one of the most prospective electrochemical energy storage systems. Nevertheless, the electrochemical properties of batteries are generally limited by the diffusion kinetics of highly-polarized divalent Mg ions in the cathode materials. Herein, rutile-type molybdenum dioxide (R-MoO 2 ) was synthesized by the hydrothermal treatment and subsequent thermal treatment and used as the cathode materials in MIBs and MLIBs. The initial discharge capacities of R-MoO 2 cathodes in MIBs and MLIBs are 50 and 253 mAh·g − 1 at the current density of 50 mA·g − 1 , respectively. The specific capacities are 17 and 111 mAh·g − 1 after 100 cycles. The R-MoO 2 cathode possesses good Coulombic efficiency and rate capability in MLIBs. Compared with MIBs, the electrochemical performances of MLIBs were greatly enhanced. The energy storage mechanisms were investigated by the experiments results and density functional theory (DFT) calculations. Moreover, the discharge-charge mechanisms were also explored by ex-situ characterizations. The diffusion/migration of Mg 2+ and Mg storage abilities are improved by introducing the Li + , promoting electrochemical performances. The energy storage mechanisms are Mg 2+ intercalation in MIBs and Mg 2+ /Li + co-intercalation in MLIBs. This work further investigates the energy storage mechanism of MLIBs and provides the theoretical groundwork for the follow-up development of high-performance cathode materials.
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