1. Article overview

Lithium metal is considered to be one of the most promising lithium-based battery anodes due to its high theoretical weight capacity (3860 mAh g -1) and low potential (-3.04 V vs standard hydrogen electrode (SHE)). Unfortunately, in the repeated plating and stripping process, uncontrollable dendrites generally exist in the lithium anode, which leads to short cycle life and even short circuit of the lithium battery. Here, a single zinc atom is fixed on the MXene (Ti3C2Clx) layer (Zn-MXene) to effectively induce Li nucleation and growth. In the initial plating stage, due to the large amount of Zn atoms, lithium tends to nucleate uniformly on the surface of the Zn-mxene layer, and then due to the strong lightning rod effect at the edge, it grows vertically along the nucleation position to form a bowl-shaped lithium, but there are no lithium branches. crystal. Therefore, the use of Zn-MXene film as the lithium anode has an overpotential of 11.3 mV, a long cycle life (1200 hours), and a deep stripping of up to 40 mAh cm-2.

Two, graphic guide

Figure 1. a) Synthesis process of a single zinc atom fixed on the MXene layer (ZnMXene) for lithium nucleation and growth. b) Typical TEM image of Zn-MXene nanosheets, showing transparent characteristics. c, d) HAADF-STEM image, showing high density of bright spots (zinc atoms) in MXene nanosheets. e) STEM image of the Zn-MXene-Li layer after nitrogen labeling at a plating level of 0.1 μAh cm-2. The distribution of related elements f) Ti and g) N (Li) indicates that Li nucleates uniformly on the ZnMXene layer.

Figure 2.a) Schematic diagram of large-scale preparation of Zn-MXene thin films by rolling and spraying technology. b) Photograph of the prepared Zn-MXene thin film. c) Folding and d) twisting test of Zn-MXene film. SEM image of Zn-mxene film from e) section and top view (upper left corner). f) The contact angles of the electrolyte with the Zn-MXene film, MXene film and Cu foil are respectively low. The contact angle of the Zn-MXene film (4.0 o) g) At 50 μA cm-2, the The voltage-capacity curve of lithium plating on Cu foil shows that the overpotential of the Zn-MXene film is relatively low (11.3 mV). h) Exfoliation and electroplating curves of the first three cycles of Zn-MXene-Li, MXene-Li and Cu-Li anodes.

Figure 3. a) The rate capability of Zn-MXene-Li anodes at different current densities (1 -16 mA cm -2). b) The deep peeling and electroplating behavior of Zn-MXene-Li anodes with different capacities in the range of 5-40 mAh cm-2 (1 mA cm-2). c) SEM images of Zn-MXene-Li anode under 5 d, 10, e) 20 and f) 40mAhcm-2.

Figure 4. a) Selected discharge-charge curves of Zn-MXene-Li/LFP batteries at different rates (0.5-5.0 C). b) The rate capability of Zn-MXene-Li//LFP, MXene-Li//LFP and Cu-Li//LFP batteries shows good rate capability even at 10 C. c) Cycle performance of Zn-MXene-Li //LFP, MXene-Li//LFP and Cu-Li//LFP batteries at 2 C. d) Long-cycle performance of Zn-MXeneLi//LFP battery at 10 C. (C=170 mA g -1)

3. Full text summary

In summary, we prove that metallic lithium initially tends to nucleate and grow on the MXene layer where a single zinc atom is fixed. Subsequently, due to the action of the active zinc sites on the plane and the strong lightning rod effect at the edges, lithium grows vertically along the nucleation sites to provide bowl-shaped lithium. Therefore, the anode has low overpotential, long cycle life and good deep stripping performance. By utilizing the unique electrochemical behavior of Zn-MXene-Li, the complete battery shows a good cycle life of up to 500 times at 10°C. In addition, based on mature rolling and spraying technology, Zn-MXene film and its mixed lithium anode can be easily scaled up, which will greatly benefit the development of lithium batteries in the future.

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