Recyclable FeO/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 Fe 3 O 4 /multiwalled carbon nanotube (MWCNT)/cellulose nanofiber (CNF) nanopaper was constructed based on a three-dimensional conductive network between MWCNT@Fe 3 O 4 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 Fe 3 O 4 /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. This work constructed recyclable Fe 3 O 4 /MWCNT/CNF composite nanopaper, exhibiting exceptional flexibility, high electrical conductivity, and extraordinary mass- and area-specific capacitances as the negative electrode.