CEJ Review: Research Progress of MXenes-Based Materials in Potassium Electrolysis

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As rechargeable secondary batteries, lithium-ion batteries (LIBs) have been widely used in numerous wearable electronic devices and electric vehicles due to their high operating voltage, high energy density, long cycle life and environmental friendliness Sexual advantages. However, the scarcity and uneven distribution of lithium resources increase the cost of LIBs, limiting their further applications. In order to meet the needs of social development, research and development of next-generation secondary batteries with low cost and high performance is continued. Sodium and potassium have become the focus of research because of their similar physical and chemical properties to lithium and their abundance in the earth is much higher than that of lithium. Compared with Na/Na+ (-2.71 V, vs SHE), K/K+ (-2.93 V, vs SHE) standard potential is closer to Li/Li+ (-3.04 V, vs SHE), so PIBs usually have higher operating voltage and energy density.

As a new class of two-dimensional (2D) materials, MXenes have great potential for application in metal-ion batteries due to their unique structural and electronic properties. It is especially worth mentioning that the diffusion barrier of K+ on MXene is very low, which proves that MXene will have outstanding rate capability when applied to PIBs anode material. However, due to its low theoretical potassium storage capacity, pure MXene is not suitable as an anode material for potassium electricity. Recently, Professor Li Hongyan of Jinan University and Professor Niu Li of Guangzhou University published a review article titled: MXenes: Advanced materials in potassium ion batteries in the internationally renowned academic journal Chemical Engineering Journal, summarizing the performance of different improved MXenes-based electrode materials in PIBs Application, the relationship between structure and electrochemical performance was analyzed. The future development direction of MXenes in PIBs is also prospected.






Figure 1. Abundances of lithium, sodium, and potassium in the crust; comparison of lithium, sodium, and potassium in energy density; different MAX phases and their corresponding MXenes; different applications of MXenes.







Figure 2. Possible adsorption sites of monolayer V3C2; adsorption energies and maximum capacities for Li, Na, K, and Ca; adsorption energies and corresponding theoretical capacities for different ions by MXenes containing O-based functional groups.





Figure 3. Electrochemical performance and physical properties of Ti3CNTz electrodes.






Figure 4. Assembly process of PDDA-NPCN/Ti3C2 composite; electrochemical performance of MoSe2/MXene@C electrode.




Figure 5. Synthesis process of a-Ti3C2MNRs and corresponding physical characterization and electrochemical performance testing.





Figure 6. Synthesis process and electrochemical properties of TiOxNy/C; synthesis process, physical characterization, and electrochemical properties of TiO2/RGO composites.


So far, there is not much literature on the application of MXenes in PIBs, mainly due to the immature technology and limited diversity of MXenes. With the gradual maturity of the preparation technology, the application of MXenes in PIBs still has great potential. Mainly reflected in the following aspects:

i) Different MXenes have different potassium storage capacity, electron and ion transport properties. Improving or developing new MXenes preparation methods is the most important factor to improve MXene materials;

ii) Even if MXene can be successfully prepared, the morphologies of macropores and micropores cannot be ignored, which has a great influence on its performance. Among all the improvement methods, compounding MXenes with other materials is the main way to enhance the potassium storage capacity of MXenes and stabilize their structures;

iii) Hetero-atom doping proved to be an effective improvement method to enhance the performance of MXenes, however, the related research is still in the initial stage.

iv) Converting MXene into other anode materials is also an effective way. Similar practices have been applied in Na and Li batteries, and MXene-derived materials prepared in this way can also be used as a potential electrode material.

In addition, despite the excellent energy storage capacity of lithium batteries, it is still difficult to use MXenes in large quantities considering the limited lithium resources. Among other metal ion batteries, divalent or trivalent metal ion batteries have the advantage of high capacity, but Zn2+, Mg2+, Ca2+, Al3+ and other multivalent metal ions are in strong mutual contact with electrode materials, resulting in sluggish kinetics performance. Therefore, PIBs have become a very promising class of secondary batteries due to their close working voltage and price advantage to LIBs. The application of our MXenes to potassium electricity will be more extensive and in-depth research in the near future.

Literature link:

https://doi.org/10.1016/j.cej.2020.126565