2.1 Vacuum filtration
According to the reported work on cellulose paper based electrode materials for supercapacitors, vacuum filtration is the most widely used and relatively simple method for preparing paper based electrode materials from cellulose [47]. The method is to filter the solvent (mostly water) in the homogenous electrode material slurry by pressure difference, and then form 2D cellulose paper-based electrode material through the interaction between materials. In the vacuum filtration process, the structural design between cellulose and active materials is the key to determine the energy storage performance of cellulose based paper based supercapacitors. In the work related to this preparation process, most of the work is focused on the structural design of cellulose and carbon materials (activated carbon, graphene, carbon nanotubes and graphene quantum dots, etc.) [48-51], polyaniline [52, 53], MXene [54, 55] and other electrically active substances [56-58]. Then, the electrochemical energy storage performance is enhanced by introducing the third component active substance or electropolymerization.
In the application of traditional electrode materials, carbon based electrode materials are prepared by mixing the binder and conductive carbon black. When used as a device, the specific surface area of the active material involved in the electrochemical reaction will be reduced due to the adhesion of the adhesive on the surface of the active material, which severely limits the energy storage performance of the active material. Cellulose, as a good binder, can provide sufficient specific capacitance and good conductivity after being compounded with active materials. Cellulose provides excellent mechanical properties and porous structure. This makes the cellulose paper based supercapacitor have good mechanical and electrochemical properties.