The water-based zinc ion battery has aroused great interest of researchers due to the unique advantages of Zn anode. Although commercial zinc foil has the advantages of low cost and large-scale growth, its inherent surface roughness can cause severe local electric field enhancement. During the discharge process, Zn2+ tends to produce continuous deposition under the enhanced electric field, and then gradually evolve into Zn dendrites. Continuous growth of dendrites will cause internal short-circuit failure after piercing the diaphragm. In addition, in the process of dezincification, the zinc dendrites are easily broken from the inside and converted into "dead zinc", resulting in a decrease in Coulombic efficiency and severe capacity degradation. Using in-situ growth method to prepare highly uniform artificial layer on Zn anode is a way worthy of further exploration. Inspired by this, the team of Professor Niu Zhiqiang from Nankai University published a research paper titled Direct Self-Assembly of MXene on Zn Anodes for Dendrite-Free Aqueous Zinc-Ion Batteries in the top international academic journal Angewandte Chemie International Edition, and proposed a spontaneous research paper. With the reduction/assembly strategy, the ultra-thin and uniform MXene layer can be directly assembled on the surface of the Zn negative electrode, and the thickness of the MXene layer can be well controlled. The ultra-thin thickness will facilitate the rapid transmission of electrolyte ions. In addition, the MXene layer can effectively inhibit the formation of zinc dendrites and side reactions on the negative electrode. Therefore, ZIBs based on Zn anodes with MXene layers exhibit enhanced electrochemical performance.

 Figure 1. Synthetic schematic diagram of stacking MXene nanosheets on the surface of Zn foil.
 

Figure 2. Scanning electron microscope, mapping image, physical image and XPS spectrum of MXene coated Zn anode.

 Figure 3. Electrochemical performance of a symmetrical device composed of pure Zn and MZn-x.
 

Figure 4. In-situ optical visualization of Zn deposition.

Figure 5. Comparison of electrochemical performance of Zn/MnO2 batteries of Zn and MZn-60.
 

In general, in this paper, by uniformly assembling the MXene layer on the Zn anode, a simple in-situ simultaneous reduction/assembly strategy can be adopted. This negative electrode with an MXene layer has some unique advantages, including a ground nucleation barrier and a uniformly distributed electric field, which leads to uniform zinc deposition. Therefore, the MZn anode exhibits long-term cycling stability, lower voltage hysteresis, and smooth dendritic-free surface, indicating its potential as a stable anode for ZIBs. The assembled MZn-60/MnO2 battery can produce outstanding cycle stability, with a capacity retention rate of 81% after 500 cycles. This MXene-improved Zn anode has the advantages of enhanced electrochemical performance and no dendrite generation, which provides a new idea for the research of Zn battery systems.
 Literature link:
https://doi.org/10.1002/anie.202012322
Article source: MXene Frontier
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