MXene‐Based Anode‐Free Magnesium Metal Battery

Abstract Rechargeable magnesium batteries (RMBs) are promising next‐generation low‐cost and high‐energy devices. Among all RMBs, anode‐free magnesium metal batteries that use in situ magnesium‐plated current collectors as negative electrodes can afford optimal energy densities. However, anode‐free magnesium metal batteries have remained elusive so far, as their practical application is plagued by low Mg plating/stripping efficiency due to nonuniform Mg deposition on conventional anode current collectors. Herein, for the first time, an anode‐free Mg‐metal battery is developed by employing a 3D MXene (Ti 3 C 2 T x ) film with horizontal Mg electrodeposition. The magnesiophilic oxygen and reactive fluorine terminations in MXene enable an enriched local magnesium‐ion concentration and a durable magnesium fluoride‐rich solid electrolyte interphase on the Ti 3 C 2 T x film surface. Meanwhile, Ti 3 C 2 T x MXene exhibits a high lattice geometrical fit with Mg (≈96%) to guide the horizontal electrodeposition of Mg. Consequently, the developed Ti 3 C 2 T x film achieves reversible Mg plating/stripping with high Coulombic efficiencies (>99.4%) at high‐current‐density (5.0 mA cm −2 ) and high‐Mg‐utilization (50%) conditions. When this Ti 3 C 2 T x film is coupled with a pre‐magnesized Mo 6 S 8 cathode, the anode‐free Mg‐metal full‐cell prototype exhibits a volumetric energy density five times higher than its standard Mg‐metal counterpart. This work provides insights into the rational design of anode current collectors to guide horizontal Mg electrodeposition for anode‐free Mg metal batteries.