1. Introduction
With the development of electronic devices and people’s yearning for
electronic devices in the intelligent era [1-6], flexible electronic
devices have shown great application potential in the future portable
consumer electronics and wearable devices [7-12]. Traditional
flexible electronic equipment uses flexible substrates such as metal
[13-15] (copper foil, aluminum foil, etc.) and plastic [16-18]
(such as polyethylene terephthalate, polyethylene, polypropylene, etc.).
Although these flexible substrates can endow flexible energy storage
equipment with excellent mechanical properties, metal and plastic
substrates have their own shortcomings. For example, metal and plastic
are both hard materials with poor bending performance. Moreover, due to
the weak binding force between the substrate and the active material,
the active material will fall off during the use of flexible devices,
resulting in poor cycle stability, which is not friendly to the life of
flexible devices. Therefore, it is very important to develop new
flexible materials with excellent flexibility and strong adhesion with
active materials.
Cellulose is passed by glucose unit β-1,4 glycosidic bond linked natural
polymer [19-21]. Its general molecular formula is
(C6H10O5)n,
which is the most extensive and renewable biomass resource in nature and
can be extracted from trees, algae, bacteria and other substances. Its
structure can be seen from atomic, molecular and macro scales
(Figure1A). Its excellent aspect ratio and porous structure have
important application value in the energy storage field of cellulose
paper based supercapacitors [22-24]. Cellulose has attracted
extensive attention in the field of flexible supercapacitors
[25-27]. On the one hand, it is because cellulose is a kind of
material with rich content, excellent mechanical properties, sustainable
and cheap. On the other hand, the cellulose based paper supercapacitor
electrode has a controllable porous structure and pore size
distribution, which is very important for the rapid transfer of
electrolyte ions during energy storage. For the flexible supercapacitor,
the most important thing is the design and preparation of its electrode
material structure. In recent years, cellulose, including nano
cellulose, bacterial cellulose, cellulose fiber pulp and cellulose
paper, has been used to prepare high-performance cellulose paper based
supercapacitor electrode materials [28-32]. In this field, different
paper based supercapacitors show different emphasis on performance.
Therefore, it is very important to choose an appropriate preparation
method to prepare paper based electrodes. In this paper, the preparation
methods of cellulose based paper based supercapacitors in recent years
are systematically summarized and classified for the first time. As
shown in Figure1B, vacuum filtration [33,34], in-situ polymerization
[35,36] and printing technology [37, 38] based on the division
of multi-component mixing are the main technologies for preparing
cellulose paper-based electrodes at present. In addition, commercially
mature papermaking process [39,40], carbonization [41,42],
impregnation [43,44] and laser induced graphene technology
[45,46] are also used to prepare paper based supercapacitors. In
conclusion, this review is intended to provide convenient reference
materials for researchers in the field of paper-based supercapacitors,
so as to promote the rapid development of paper-based energy storage
devices.