2.4.5 Laser-induced graphene
In 2014, Tour et al.[127] successfully prepared macroporous
laser-induced graphene (LIG) by treating polyimide membranes with
CO2 lasers. Since then, LIGs prepared by various
substrates have been widely used in various fields such as energy
storage and sensing. Among them, paper-based materials have proven to be
excellent precursor substrates for LIG, but because untreated cellulose
paper burns easily when treated at high temperatures in air, it needs to
undergo chemical treatment. Lu et al.[128] soaked the paper in 0.1 M
flame retardant solution sodium tetraborate for pretreatment. This is to
prevent combustion when the laser processes the paper and better produce
LIG. Figure 15E shows SEM images of cellulose paper and LIG. When used
as a supercapacitor, the paper-based LIG exhibits a specific capacitance
of 4.6mF cm-2, and the voltage and energy output of
these devices can be controlled by connecting them in series and
parallel. Although the LIG obtained by the paper-based material treated
with flame retardant has been successfully applied to the field of
supercapacitors, the capacitance performance of the device obtained by
this method is still not very good. Lin et al. [129] The paper-based
device prepared by combining chemical foaming and LIG exhibits a
specific capacitance of 23.8mF cm-2. Figure 15G shows
the preparation process of this paper-based electrode. The paper is
first soaked in the inorganic salt NaHCO3 for
processing. Then, the treated paper is patterned and scanned by a
CO2 laser to obtain a paper-based electrode. Finally,
gel electrolyte is added to obtain a paper-based LIG device. It is worth
mentioning that thanks to the foaming effect of NaHCO3(Figure 15F), the CO2 laser produces a large number of
porous LIG on the paper when processing it. This structure facilitates
the migration of electrons and ions during electrochemical energy
storage.