MXene-Based Anode-Free Magnesium Metal Battery

摘要

Rechargeable magnesium batteries (RMBs) are promising next-generationlow-cost and high-energy devices. Among all RMBs, anode-free magnesiummetal batteries that use in situ magnesium-plated current collectors asnegative electrodes can afford optimal energy densities. However, anode-freemagnesium metal batteries have remained elusive so far, as their practicalapplication is plagued by low Mg plating/stripping efficiency due tononuniform Mg deposition on conventional anode current collectors. Herein,for the first time, an anode-free Mg-metal battery is developed by employing a3D MXene (Ti_3C_2T_x) film with horizontal Mg electrodeposition. Themagnesiophilic oxygen and reactive fluorine terminations in MXene enable anenriched local magnesium-ion concentration and a durable magnesiumfluoride-rich solid electrolyte interphase on the Ti_3C_2T_x film surface.Meanwhile, Ti_3C_2T_x MXene exhibits a high lattice geometrical fit with Mg(≈96%) to guide the horizontal electrodeposition of Mg. Consequently, thedeveloped Ti_3C_2T_x film achieves reversible Mg plating/stripping with highCoulombic efficiencies (>99.4%) at high-current-density (5.0 mA cm?2) andhigh-Mg-utilization (50%) conditions. When this Ti_3C_2T_x film is coupled witha pre-magnesized Mo_6S_8 cathode, the anode-free Mg-metal full-cell prototypeexhibits a volumetric energy density five times higher than its standardMg-metal counterpart. This work provides insights into the rational design ofanode current collectors to guide horizontal Mg electrodeposition foranode-free Mg metal batteries.