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 Cu1.81S 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, Cu1.81S@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.