Dual-Defect Engineering Strategy Enables High-Durability Rechargeable Magnesium-Metal Batteries

Abstract Rechargeable magnesium-metal batteries (RMMBs) are promising next-generation secondary batteries; however, their development is inhibited by the low capacity and short cycle lifespan of cathodes. Although various strategies have been devised to enhance the Mg 2+ migration kinetics and structural stability of cathodes, they fail to improve electronic conductivity, rendering the cathodes incompatible with magnesium-metal anodes. Herein, we propose a dual-defect engineering strategy, namely, the incorporation of Mg 2+ pre-intercalation defect (P-Mg d ) and oxygen defect (O d ), to simultaneously improve the Mg 2+ migration kinetics, structural stability, and electronic conductivity of the cathodes of RMMBs. Using lamellar V 2 O 5 ·nH 2 O as a demo cathode material, we prepare a cathode comprising Mg 0.07 V 2 O 5 ·1.4H 2 O nanobelts composited with reduced graphene oxide (MVOH/rGO) with P-Mg d and O d . The O d enlarges interlayer spacing, accelerates Mg 2+ migration kinetics, and prevents structural collapse, while the P-Mg d stabilizes the lamellar structure and increases electronic conductivity. Consequently, the MVOH/rGO cathode exhibits a high capacity of 197 mAh g −1 , and the developed Mg foil//MVOH/rGO full cell demonstrates an incredible lifespan of 850 cycles at 0.1 A g −1 , capable of powering a light-emitting diode. The proposed dual-defect engineering strategy provides new insights into developing high-durability, high-capacity cathodes, advancing the practical application of RMMBs, and other new secondary batteries.