Sub-Monolayer Wrapping Stabilizes Magnesium Ion Cathode

Rechargeable magnesium batteries (RMBs) hold promise as next-generation energy storage systems, owing to their high volumetric capacity, high safety, and abundance of Mg. However, their development is hindered by sluggish Mg ion (Mg²⁺) diffusion and cathode instability, especially polysulfide and transition metal dissolution. While ultrathin protection layers offer distinct advantages over conventional bulk coatings, their synthesis remains a significant challenge. Herein, we wrap a sub-monolayer MoS₂ on Cu_1.81S cathode, where MoS₂ layer acts as a functional interface that regulates the local chemical environment and suppresses cathode dissolution. MoS₂ layer also plays an activation role by facilitating Mg adsorption and reducing migration barriers, thereby accelerating storage kinetics. Benefiting from this synergistic design, Cu_1.81S@MoS₂ cathode exhibits enhanced cycling stability and rate performance. It delivers around 246 mAh/g after 200 cycles at 100 mA/g with a low fading rate (0.057% per cycle), maintaining around 107 mAh/g after 600 cycles at 400 mA/g with 99.1% coulombic efficiency (CE). Furthermore, with the MoS₂ layer, the cathode shows excellent rate capability with 106 mAh/g at 1000 mA/g and full recovery at 20 mA/g. This work highlights a feasible nanostructuring strategy to stabilize conversion-type cathodes to advance high-performance RMBs.