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.