Layer-by-Layer Self-Assembled TEMPO-Oxidized Cellulose Nanofiber/Reduced Graphene Oxide/Polypyrrole Films for Self-Supporting Flexible Supercapacitor Electrodes

In this study, self-supporting flexible supercapacitor electrodes were prepared by wrapping polypyrrole (PPy) on the surface of the TEMPO-oxidized cellulose nanofiber (TOCN)/reduced graphene oxide (RGO) film using a layer-by-layer self-assembly method under an oil–water separation environment. The obtained film had a three-dimensional-layered structure and exhibited a certain porosity, which is favored for the electrochemical performance. The areal capacitance of the TOCN/RGO/PPy film electrode was as high as 915 mF cm–2, and 96.6% capacitance was retained after 2000 cycles of charge and discharge. Also, it maintained a higher rate retention of 98.4% after undergoing bending 200 times. These capacitance values are significantly better than RGO or PPy single-component films or their mixture with similar constituents. Furthermore, a solid-state symmetric supercapacitor was assembled by combining the TOCN/RGO/PPy electrode and CNF hydrogel films as a separator, which displayed an excellent specific capacitance of 195.8 F g–1 and a volumetric capacitance of 9.8 F cm–3 at the current density of 0.1 mA cm–2. Meanwhile, an outstanding energy density of 13.04 Wh kg–1 with a power density of 200.6 W kg–1 was also obtained. These facts fully suggest that the TOCN/RGO/PPy film with a three-dimensional-layered structure in this study is promising for high-performance flexible energy-storage electrodes.