Coupled and decoupled hierarchical carbon nanomaterials toward high-energy-density quasi-solid-state Na-Ion hybrid energy storage devices

Sodium-ion (Na-ion) hybrid capacitors as a novel electrochemical energy storage device have triggered considerable attention in recent years. However, the sluggish kinetics at anode and low specific capacity at cathode greatly hinder the overall performance output of Na-ion hybrid capacitors. Herein, we design a high-performance quasi-solid-state Na-ion hybrid capacitor assembled with the Mo2N quantum dots coupled carbon nanotubes as anode, decoupled hierarchical carbon nanotubes as cathode, and a porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane based gel electrolyte. For the anode, the uniformly dispersed Mo2N quantum dots offer abundant ion-accessible active sites and shortened ion diffusion path, which effectively accelerate Na ion storage kinetics. After decoupling and activation, the hierarchical carbon nanotubes with high specific surface area and numerous in-plane nanopores contribute to fast reversible anion adsorption and desorption, greatly boosting the specific capacity. Additionally, the low-tortuosity nanotubular electrode microstructure with open framework is conducive to unimpeded electrolyte ion permeation and thereby can maximize the utilization of active materials. Benefiting from the elaborate electrode architecture engineering and rational device configuration, the assembled quasi-solid-state Na-ion hybrid capacitor can achieve a high energy density of 100.6 Wh kg(-1) at a power density of 117.5 W kg(-1), which is among the best compared with other Na-ion hybrid capacitors. The demonstration of proof-of-concept of the quasi-solid-state Na-ion hybrid capacitors offers new insights into rational design of high-energy-density hybrid energy storage systems.