Hierarchical Transition Metal Oxide Arrays Grown on Graphene-Based Fibers with Enhanced Interface by Thin Layer of Carbon toward Solid-State Asymmetric Supercapacitors

Carbon-based asymmetric supercapacitors with high performance hold broad application prospects in wearable devices. Forming a smooth interface between the active transition metal oxides and carbon substrate for providing electron-transfer channels and accommodating the volume contraction for hybrid electrodes is a key issue to be tackled. Herein, both fibrous cathode and anode are designed on the basis of conductive graphene/carbon nanotube hybrid fibers by introducing pseudocapacitive NiCo2O4 nano-grass arrays or forming interconnected pores, respectively. For hierarchical positive fibers, a nitrogen-doped carbon (NC) middle layer is employed to effectively regulate the electronic structural states between NiCo2O4 and fiber substrate. The cycling and rate performance of cathode are significantly improved due to the strong interfacial bonding and abundant electrochemical active sites. Moreover, an interconnected porous structure is also developed to provide both unlimited axial and radial channels to promote electrolyte ion diffusion sufficiently in the porous negative electrode. The assembled solid-state flexible asymmetric supercapacitor delivers a high energy density of 11.2 mu Wh cm(-2) with a power density of 472.1 mu W cm(-2), as well as an excellent long cycling performance with 93 % capacitance retention after 10000 cycles.