2.3.4 3D printing
3D printing, also known as additive manufacturing, can continuously deposit materials to produce various structures under digital design[117]. This makes it possible to accurately fabricate flexible devices with complex structures in a short time. Aeby et al. [118] prepared a cellulose based ink for one-time 3D printing. Electrode ink is composed of CNF, water, CNC, glycerin, activated carbon and graphite particles. Electrolyte ink is composed of CNC, glycerin and NaCl. As shown in Figure 13A, the design of 3D printing paper based supercapacitor is shown. The two printed devices are folded together to form a paper based supercapacitor. In addition, the author tried to print six paper based supercapacitors in series on curved substrate (Figure 13B). And it realizes the power supply for the alarm clock with the working voltage of 3V. The paper based device also shows excellent biodegradability. After more than half of the weight can be decomposed in 9 weeks, the remaining carbon based materials can be recycled (Figure 13C). In a word, this work has made considerable reference in the field of 3D printing paper-based supercapacitors.