Ultrafast Synthesis of Oxygen Vacancy-Rich MgFeSiO4 Cathode to Boost Diffusion Kinetics for Rechargeable Magnesium-Ion Batteries

Rechargeable magnesium ion batteries (RMBs) have drawn extensive attention due to their high theoretical volumetric capacity and low safety hazards. However, divalent Mg ions suffer sluggish mobility in cathodes owing to the high charge density and slow insertion/extraction kinetics. Herein, it is shown that an ultrafast nonequilibrium high-temperature shock (HTS) method with a high heating/quenching rate can instantly introduce oxygen vacancies into the olivine-structured MgFeSiO₄ cathode (MgFeSiO₄-HTS) in seconds. As a proof of concept, the MgFeSiO₄-HTS exhibits a higher electrochemical property and fast insertion/extraction kinetics in comparison to those prepared from the conventional sintering method. The MgFeSiO₄-HTS displays remarkable long-term cycling lifespan properties with a reversible capacity of 85.65 and 54.43 mAh g^-1 over 500 and 1600 cycles at 2 and 5 C, respectively. Additionally, by combining the electrochemical experiments and density functional theory calculations, oxygen vacancies can weaken the interaction and energy barrier between the Mg²⁺ ions and the cathode, enhancing the Mg²⁺ diffusion kinetics.