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

Abstract

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.