**4. Technologies for fabricating supercapacitors**

Various structures can be observed supercapacitors, including sandwich structures, interdigitated structures, MXene fiber structures, and core-shell structures. Sandwich structures generally consist of one, composed of two electrodes surrounding a separator at its center, with numerous technologies available to build electrodes, which can be further packaged into sandwich structures. Some supercapacitors, especially micro-supercapacitors, may not require separators, as the electrodes can be fixed without a connection between them. In this section, we list some methods for designing and fabricating electrodes and decorating active materials in sandwich and interdigitated structures.

#### **4.1 Lithography**

Lithography has been used to design and fabricate interdigitated circuit chips with an ultra-nanoscale size, making it extremely easy to fabricate micro-supercapacitors. Using lithography, the supercapacitor can integrate a circuit chip on the silicon wafer. These types of supercapacitors do not require separators, as they do not contain a short circuit with a fixed and hard substrate. Porous silicon and an interdigitated shape are generally used, as they exhibit a large area. Researchers have also designed and fabricated various flexible and transparent supercapacitors on special templates using lithography.

#### **4.2 Electrospinning**

Electrospinning can be used to fabricate a designed nanoscale space pose, making it suitable for the electrodes of supercapacitors. Long nanofibers have been produced into a thin film through electrospinning, and then metals were coated or deposited onto the surfaces of these pre-electrospinning films, where the diameter and thickness of these films could be controlled by the diameters of the nanofibers.

#### **4.3 Inkjet printing**

Dedicated inks consisted of metal nanoparticles, CNTs, and graphene, and after mixing with the gel, these inks could be injected and printed onto the template

surface, forming an active material. They can usually be fabricated in the shapes of interdigitated electrodes to increase the active area.

#### **4.4 Laser scribing**

Various micro- and nanofabrications can be used to build supercapacitors. Direct laser writing also offers the potential to realize a lower cost and largely scalable fabrication [43]. For the preparation of active materials films, which are composed of CNT, metal oxides, and graphene, lasers have generally been used to fabricate interdigitated electrodes, with large capacitors.
