Lithiophilic Three-Dimensional Porous Ti3C2Tx-rGO Membrane as a Stable Scaffold for Safe Alkali Metal (Li or Na) Anodes.

Abstract

Metallic anodes have high theoretical specific capacities and low electrochemical potentials. However, short-circuit problems caused by dendritic deposition and low Coulombic efficiency limit the cyclic life and safety of metallic anode-based batteries. Herein, dendrite-free and flexible three-dimensional (3D) alkali anodes (Li/Na-Ti3C2Tx-rGO) are constructed by infusing molten lithium (Li) or sodium (Na) metal into 3D porous MXene Ti3C2Tx-reduced graphene oxide (Ti3C2Tx-rGO) membranes. First-principles calculations indicate that large fractions of functional groups on the Ti3C2Tx surface lead to the good affinity between the Ti3C2Tx-rGO membrane and molten alkali metal (Li/Na), and the formation of Ti-Li/Na, O-Li/Na, and F-Li/Na mixed covalent/ionic bonds is extremely critical for uniform electrochemical deposition. Furthermore, the porous structure in Li/Na-Ti3C2Tx-rGO composites results in an effective encapsulation, preventing dendritic growth and exhibiting stable stripping/plating behaviors up to 12 mA·cm-2 and a deeper capacity of 10 mA·h·cm-2. Stable cycling performances over 300 h (750 cycles) at 5.0 mA·cm-2 for Li-Ti3C2Tx-rGO and 500 h (750 cycles) at 3.0 mA·cm-2 for Na-Ti3C2Tx-GO are achieved. In a full cell with LiFePO4 cathodes, Li-Ti3C2Tx-rGO electrodes show low polarization and retain 96.6% capacity after 1000 cycles. These findings are based on 2D MXene materials, and the resulting 3D host provides a practical approach for achieving stable and safe alkali metal anodes.