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

Low ionic diffusivity, sluggish charge transfer kinetics, and volume shrinkage/expansion during charging/dis-charging 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 hi-erarchical 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 ma-terial 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.