Three-dimensional “skin-framework” hybrid network as electroactive material platform for high-performance solid-state asymmetric supercapacitor

Abstract

Three-dimensional (3D) electrode materials are ideal candidates for use in fabricating high-performance supercapacitors (SCs), owing to their unique network structure and excellent electrochemical properties. In this study, an aerogel film produced by the freeze-drying self-aggregation of multiwall carbon nanotubes (MWCNTs) and cellulose nanofibers (CNFs) served as the “skin”, and an inter-connected 3D network of nickel foam (NF) as the “framework”, for the fabrication of an MWCNT/CNF-NF (called MCN) hybrid material with a distinct “skin-framework” architecture. Considering the metrics of excellent conductivity, high wettability, binder-free and unique 3D “skin-framework” structure, the MCN hybrid material has great potential as an electroactive material platform in constructing state-of-the-art asymmetric supercapacitor (ASC) electrodes. By incorporating MCN with electroactive manganese dioxide (MnO₂) and active carbon (AC), MnO₂-MCN and AC-MCN composite electrodes with respective high areal capacitances of 1784.8 (equal to 469.7 F g⁻¹) and 868.8 mF cm⁻² (equal to 126.3 F g⁻¹) at 5 mA cm⁻² were successfully prepared. Further, both kinds of electrodes exhibited high charge/discharge ability rates and good cycle performance. Moreover, an optimally assembled MnO₂-MCN//AC-MCN solid-state ASC was reversibly charged/discharged at voltages as high as 1.8 V and possessed a remarkable volumetric capacity of 9.83 F cm⁻³ and an energy density of 4.25 mW h cm⁻³, as well as good cycle stability.