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

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journal contribution
posted on 25.11.2019 by Yongzheng Fang, Ying Zhang, Kai Zhu, Ruqian Lian, Yu Gao, Jinling Yin, Ke Ye, Kui Cheng, Jun Yan, Guiling Wang, Yingjin Wei, Dianxue Cao
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.