2.4.3 Carbonization
As a renewable biomass material rich in a large amount of carbon, cellulose is activated to prepare carbon-based fibers that also exhibit excellent electric double layer performance. However, the performance of directly using the prepared cellulose-based carbon fiber for energy storage devices is not very good. In recent years, paper-based supercapacitors prepared by compounding cellulose-based carbon fibers with substances with high energy storage activity have also shown excellent performance. Wu et al. [124] loaded carbonized cellulose-based tissue paper (FCP) with NiCO2O4 by hydrothermal method to obtain FCP-NiCO2O4 paper-based electrode (Figure 15B). On the one hand, carbonized FCP provides abundant sites for the loading of highly conductive NiCO2O4. On the other hand, carbonized FCP favors the rapid movement of electrons during electrochemical reactions. Thanks to the synergistic effect of carbonized FCP and NiCO2O4, the FCP-NiCO2O4 paper-based electrode showed excellent area specific capacitance (3115mF cm-2) and excellent energy density (1.2 mWh cm-3) and power density (58.16 mW cm-3). As shown in Figure 15C, Rabani et al. [125] uniformly grow cobalt oxide (Co3O4) nanoparticles on the surface of 1DCNF. Then the resulting composite fiber is molded to obtain CNF/Co3O4 paper matrix composite. Finally, CNF/Co3O4 paper-based electrode was obtained by carbonization treatment at 200°C. Thanks to the excellent performance of CNF fiber and Co3O4 after carbonization treatment. The paper-based energy storage device assembled with this electrode can provide a high specific capacitance of 214F g-1 at 1A g-1.