Hierarchical aerogels with hollow Co3O4 nanoparticles and graphitized carbon vesicles embedded in multi-channel carbon nanofibers for high-performance asymmetric supercapacitors

Abstract

Low ionic diffusivity, sluggish charge transfer kinetics, and volume shrinkage/expansion during charging/discharging of transition metal oxides and conductive carrier materials seriously reduce capacity and damage cycle stability of electrodes. Herein, we demonstrate an in situ structural transformation strategy for fabricating hierarchical aerogels with hollow Co3O4 (H-Co3O4) nanoparticles embedded in multi-channel carbon nanofibers (MCNFs) by electrospinning polyacrylonitrile/polystyrene/metal organic framework mixtures, freeze-drying, carbonization and oxidation. The positive electrode prepared with MCNF@H-Co3O4 aerogel as the active material exhibits high specific capacity of 244.5 mA h g−1 (1600.6 F g−1) at 1 A g−1, and ultra-long cycle life of retaining 90.5 % of its initial specific capacity after 30,000 cycles at 20 A g−1. Furthermore, N and O co-doped hollow MCNF (NO-HMCNF) aerogels with hollow carbon vesicles embedded in the MCNFs are also prepared by acid-etching. The negative electrode prepared with the NO-HMCNF aerogel as the active material exhibits a high specific capacitance of 362.5 F g−1 at 0.3 A g−1, and retains 95.5 % of its initial specific capacitance after 30,000 cycles at 5 A g−1. The assembled MCNF@H-Co3O4//NO-HMCNF asymmetric supercapacitor provides a high energy density of 51.9 W h kg−1 (750.3 W kg−1) and retains 90.1 % of its initial specific capacity after 5000 cycles at 5 A g−1. The “double-void” structure plays crucial roles in exposing active sites and accommodating volume changes for enhancing capacity and cycling of the electrodes.