2.3.2 Screen printing
Screen printing is made by placing ink on a template, and then applying a certain pressure to the screen template through a scraper, after which the ink is squeezed on the surface of the substrate (such as paper) through the template during the process. Among them, the pressure exerted in the printing process and the number of printing times will have a certain impact on the product performance. As shown in Figure 11A, Xiong et al. [109] printed conductive ink on the surface of original blank paper (OP) by screen printing technology on the basis of the former research. Then, polyaniline and Vitrimer were introduced into the paper-based electrode by electrochemical polymerization and in-situ polymerization to obtain conductive ink@polyaniline-Vitrimer(IP@PN-V) paper-based electrode. Similarly, the electrode exhibits excellent self-healing and shape memory properties. And at the same time it shows excellent photothermal conversion and electromagnetic shielding performance.
Compared with the method of introducing active materials after building a conductive layer through screen printing, it is very convenient and fast to directly prepare inks with excellent energy storage performance and directly construct paper-based supercapacitors through screen printing. Chen et al. [110] blended two-dimensional graphene with activated carbon nanofiller to prepare a composite ink (Gr/AC-ink) for screen printing. Among them, Gr/AC-ink printed on paper shows excellent energy storage performance. This is mainly due to the presence of AC to effectively prevent the stacking of two-dimensional graphene nanosheets. Figure 11B shows the synergistic effect between graphene nanosheets and AC. Compared to Gr and AC electrodes alone, this electrode exhibits excellent ion storage performance due to the distinct layered structure in the Gr/AC electrode. It can be seen from the paper-based supercapacitor built by this work. The key to the preparation of paper-based supercapacitors by screen printing lies in the design and preparation of energy storage inks. In recent years, Mxene, a two-dimensional material with excellent energy storage performance, has also been used in screen printing to prepare paper-based electrodes. In the traditional Mxene etching process, the products are generally divided into a few layers of Mxene and unetched and unstripped Mxene. The latter are generally discarded as waste, which undoubtedly increases the cost of Mxene-based supercapacitors. Abdolhosseinzadeh et al. [111] prepared paper-based supercapacitors with excellent performance by using unetched and peeled Mxene precipitate and a few layers of Mxene as screen-printed inks (Figure 11C). Among them, a few layers of Mxene nanosheets act as conductive pathways between the precipitates and act as conductive binders in the ink of paper-based electrodes, thereby ensuring the metal conductive network. Finally, the paper-based electrode prepared by screen printing of the ink exhibits a specific capacitance of 158mF cm-2 and an energy density of 1.64μWh cm-2. And the eight paper-based devices connected in series exhibited an electrochemical window of more than 4V and successfully lit the LED lamp (Figure 11D), which is already one of the best performances of Mxene and graphene screen-printed energy storage devices. In conclusion, this work provides a low-cost idea for the preparation of this performance screen-printed paper-based supercapacitor. In particular, the ”turning waste into treasure” of Mxene sediment in this work has a certain reference in the high-value utilization of energy storage.