Joule heating-induced faradaic electrode-decorated graphene fibers for flexible fiber-shaped hybrid supercapacitor with high volumetric energy density

Abstract

The rational design of flexible, portable, and wearable fiber-based electrodes via selective hybridization of materials has motivated researchers to focus on the advancement of miniaturized energy-storage systems with excellent efficacy. Here, we introduce a novel Joule-heating approach for manufacturing hybridized fibers consisting of bark-like NiO as a faradaic shell decorated over electrically treated graphene fibers (EGFs@NiO) as a capacitive core for high-performance hybrid supercapacitors. Each Joule-heating process was conducted for a very short period (∼100 s) to achieve highly restored graphitic structures with a reduced internal resistance of GFs to expedite the electrochemical kinetics and successful hybridization of EGFs with NiO for promoting redox reactions. Moreover, an all-solid-state hybrid supercapacitor was constructed using EGFs@NiO as a positive electrode and chemically reduced GF (CGF) as a negative electrode; the supercapacitor exhibited a volumetric capacitance of 838.3 F cm−3 (volumetric capacity: 139.7 mAh cm−3), wide operating window of 1.5 V, and volumetric energy density of 34.49 mWh cm−3 at a power density of 374.97 mW cm−3. The energy efficiency of the process was evaluated based on the ratio of the volumetric capacitance of the device to the process time, and the proposed supercapacitor outperformed the recently reported asymmetric/hybrid supercapacitors based on the conventional manufacturing process. Thus, this work contributes to the development of fast, scalable, and cost-effective techniques for fabricating wearable electrodes for real-time applications.