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

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 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 pre-intercalation defect (P-Mg) and oxygen defect (O), to simultaneously improve the Mg migration kinetics, structural stability, and electronic conductivity of the cathodes of RMMBs. Using lamellar VO·nHO as a demo cathode material, we prepare a cathode comprising MgVO·1.4HO nanobelts composited with reduced graphene oxide (MVOH/rGO) with P-Mg and O. The O enlarges interlayer spacing, accelerates Mg migration kinetics, and prevents structural collapse, while the P-Mg stabilizes the lamellar structure and increases electronic conductivity. Consequently, the MVOH/rGO cathode exhibits a high capacity of 197 mAh g, and the developed Mg foil//MVOH/rGO full cell demonstrates an incredible lifespan of 850 cycles at 0.1 A g, 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.