Nanoconfined Deposition Enables High‐Energy‐Density Mg Metal Batteries

Dendritic growth resulting from inhomogeneous magnesium plating and stripping compromises anode integrity, critically limiting the achievable energy density of magnesium metal batteries. Addressing this challenge requires controlling the spatial uniformity of nucleation site distribution, magnesium ion flux, and interfaces. Herein, a scalable surface architecture is engineered on magnesium foil, forming a conformal nanosheet network that minimizes spatial inconsistencies to ensure uniform nucleation and deposition of magnesium metal. The confinement index is introduced to quantitatively describe the network's stability to regulate magnesium ion deposition. The optimized magnesium anode exhibited exceptional stability, achieving over 500 h of reversible plating/stripping under harsh conditions. After 5 days of air exposure, the optimized magnesium anode maintains cycling performance with no degradation, highlighting its outstanding resistance to atmospheric oxidation. Paired with a high mass loading of 17.4 mg cm^-2 Mo₆S₈, full cells demonstrate remarkable cycling stability throughout 3000 cycles. Moreover, large-sized pouch cells incorporating optimized magnesium anodes demonstrate stable cycling performance over 600 cycles when paired with a high mass loading Mo₆S₈ cathode, while achieving a high energy density of 143.74 Wh kg^-1 in combination with a Cu_2-xSe cathode. These results substantiate the practical applicability and technological promise of an optimized magnesium anode in advanced battery systems.