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 Mg²⁺ 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 Mg²⁺ pre-intercalation defect (P-Mg_d) and oxygen defect (O_d), to simultaneously improve the Mg²⁺ migration kinetics, structural stability, and electronic conductivity of the cathodes of RMMBs. Using lamellar V₂O₅·nH₂O as a demo cathode material, we prepare a cathode comprising Mg_0.07V₂O₅·1.4H₂O nanobelts composited with reduced graphene oxide (MVOH/rGO) with P-Mg_d and O_d. The O_d enlarges interlayer spacing, accelerates Mg²⁺ 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.