Ultrafast-charging quasi-solid-state fiber-shaped zinc-ion hybrid supercapacitors with superior flexibility

Fiber-shaped zinc-ion hybrid supercapacitors (FZHSCs) with the combined merits of both SCs and zinc-ion batteries are promising energy storage devices for miniaturized wearable and portable electronics. However, one of their main limitations is developing advanced capacitor-typed fiber electrodes based on high capacitance carbon materials to overcome the wide capacity gap between the positive electrode and negative electrode, thereby achieving high energy and power densities simultaneously, especially when the charging/discharging rate exceeds 1 V s-1. Herein, a 3D nitrogen-doped carbon nanotube architecture@carbon nanotube (N-CNT@CNT) fiber electrode is designed, aiming to improve its capacitance and rate capability by taking advantage of the fast electron transport kinetics of the N-CNT active material and the high specific surface area of the 3D N-CNT network. A quasi-solid-state FZHSC assembled by twisting the N-CNT@CNT fiber and Zn NSs@CNT fiber (electrodeposited Zn nanosheets on a CNT fiber) electrodes exhibits superior electrochemical performance at rates up to 5 V s-1, which is the highest charging/discharging rate reported so far for FZHSCs based on carbon materials, as well as a high areal energy density of 5.18 μW h cm-2. More importantly, thanks to the high stability of the 3D N-CNT nanoarray-based electrode and the twisted architecture, the FZHSC shows outstanding mechanical flexibility and robustness, which is well proved by the finite element (FE) simulation method for the first time.