Recyclable Fe3O4/MWCNT/CNF composite nanopaper as an advanced negative electrode for flexible asymmetric supercapacitors

Asymmetric supercapacitors (ASCs) with flexible performance have considerable potential for applications in wearable and implantable electronics; however, traditional electrodes have low energy intensity and fragility, which makes meeting the increasing requirements of green energy supply devices challenging. In this study, a recyclable Fe3O4/multiwalled carbon nanotube (MWCNT)/cellulose nanofiber (CNF) nanopaper was constructed based on a three-dimensional conductive network between MWCNT@Fe3O4 and CNFs using simple vacuum filtration technology. As the negative electrode, the nanopaper exhibits exceptional flexibility (it can be folded into a small plane without breaking), high electrical conductivity (1016.3 S m(-1)), and extraordinary mass-and volume-specific capacitances of 229.9 F g(-1) and 735.68 mF cm(-2) at 5 mV s(-1), respectively. A flexible ASC comprising Fe3O4/MWCNT/ CNF demonstrated a high specific capacity of 107.0 F g(-1) (2.94 F cm(-2)) at a current density of 0.5 A g(-1). It exhibited an energy density and a power density of 38.0 W h kg(-1) and 405.1 W kg(-1), respectively. Furthermore, the capacitor retained an energy density of 18.8 W h kg(-1) at a high power density (42.2 kW kg(-1)) and >90% of the specific capacitance after 5000 charge-discharge cycles at 5 A g(-1). This research will pave the way for further advances in degradable and recyclable nanopaper electrodes toward building a cutting-edge multifunctional platform for electronic skin, human motion recording, and wearable electronics.