【Research Background】
           Structural electrode materials with high mechanical strength and high electrochemical performance have very broad application prospects in the field of lightweight flexible electronics. These materials should be able to withstand extremely high mechanical stresses and deformations while maintaining high charge storage properties, thus The weight and volume that are not electrochemically active are reduced in the limited space. However, most conventional electrode materials cannot meet the above requirements at the same time. Previous reports have mainly involved the use of modified carbon fiber composites or graphene-based materials as structural materials to ensure mechanical strength, but most of these materials cannot compensate for the low electrochemical energy storage capacity. Metal oxides and conductive polymers can be used to increase the capacity of the graphene-based material. Difficulties mainly focus on the weak interaction between different substances, which leads to poor mechanical stability of the final product. Therefore, it is essential for a new generation of structural energy storage nanomaterials with excellent mechanical stability, high electron and ion conductivity, and high charge storage ratio.
 
[Introduction]
      Recently, Professor Mahiar M. Hamedi of the Royal Swedish Academy of Sciences published a news article on Advanced Materials in the International Top Journal of Materials, entitled Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulos. This paper reports a mechanically stable self-assembled 2D MXene composite with 1D cellulose nanofibers with a high aspect ratio (approximately 3.5 nm wide and tens of microns in length), and The special interaction between MXene allows for high mechanical stability without sacrificing electrochemical performance. When the loading of cellulose reaches 20%, it has a mechanical strength of 341 MPa, which is much higher than that of a pure MXene film of 29 MPa, and at the same time has a specific capacitance of 298 F g-1 and a high electrical conductivity of 295 S cm-1.

[Graphic introduction]

Figure 1 Ti3C2Tx MXene/CNF mixed solution a) Synthetic schematic; b) Zeta potential at different times; c) - f) AFM image of MXene and CNF; g)-h) Force/radius and distance between Ti3C2Tx nanosheet and CNF Relationship; i) Relationship between adhesion and ionic strength of Ti3C2Tx nanosheets and CNF.

Figure 2 Characterization of the morphology of different Ti3C2Tx and CNF ratios. Pure MXene, 10%, 20%, 40%, 80% and pure CNF.

Figure 3 Physical characterization: a) Ti3C2Tx/CNF; b) Ti3C2Tx/CNC XRD pattern. c) Ti3C2Tx-20%CNF, Ti3C2Tx/CNC, Ti3C2Tx tensile stress-strain curve; d) tensile strength of Ti3C2Tx/CNF; e) electronic conductivity of Ti3C2Tx/CNF; f) stretching of Ti3C2Tx/CNF and comparative samples Relationship between strength and electrical conductivity: Ashby diagram.

Table 1 Physical properties of Ti3C2Tx MXene, Ti3C2Tx/CNF, CNF.

Figure 4. Characterization of electrochemical performance of Ti3C2Tx/CNF.

Figure 5 shows the preparation process and electrochemical performance characterization of a micro-supercapacitor based on Ti3C2Tx/CNF assembly.
 
[Summary of this article]
       In this study, a multi-functional nanocomposite with three excellent properties was obtained by rational design of a mixed colloidal solution of two-dimensional Ti3C2TxMXene and one-dimensional cellulose nanofiber CNF. (1) The high mechanical strength of 340 MPa is an order of magnitude higher than the pure MXene membrane of 29 MPa due to the interaction between the two substances in the solution and the synergistic effects of different dimensional geometries. (2) Due to the sufficiently small width of CNF (about 3.5 nm), the two-dimensional MXene nanosheets have a higher conductivity of 2.95 × 104 S m-1. (3) Has a high specific capacitance of 298 F g-1 because the presence of CNF promotes ion migration and tantalum capacitor charge storage. The overall performance of this electrode is higher than that of the previously reported supercapacitors. Experiments have further shown that MXene / CNF dispersions can be easily printed into a variety of shapes for use in electronic products and micro-supercapacitors with high power and energy density. The self-assembly method of 1D and 2D composites directly determines the performance of nanocomposites, making it more valuable in the fields of electrochemical energy storage and printed electronics.

Literature link:
Https://doi.org/10.1002/adma.201902977

Source: WeChat public account MXene Frontier