A High-Rate Rechargeable Mg Battery Based on AgCl Conversion Cathode with Fast Solid-State Mg2+ Diffusion Kinetics

Rechargeable Mg batteries are attractive candidates for large-scale energy storage batteries with high safety due to the low-cost and non-dendritic metallic Mg anode. However, exploring high-performance cathode materials is blocking their development. Herein, a high-rate rechargeable Mg battery is established with a AgCl cathode, delivering a high reversible capacity of 70.3 mAh g −1 at 100 mA g −1 , an outstanding rate capability of 32.6 mAh g −1 at 1000 mA g −1 , and a superior long-term cyclability over 500 cycles. Further investigation of the mechanism demonstrates that a conversion reaction takes place between AgCl and metallic Ag 0 for the cathode. The solid-state Mg 2+ diffusion coefficient is as high as 8.1 × 10 −11 cm 2 s −1 , which would be the reason for the high rate capability. The current study reveals significant insights to select promising Mg-storage conversion cathodes by a combination of soft anions and soft transition-metal cations.