Waterproof, Ultrahigh Areal‐Capacitance, Wearable Supercapacitor Fabrics

High-performance supercapacitors (SCs) are promising energy storage devices to meet the pressing demand for future wearable applications. Because the surface area of a human body is limited to 2 m² , the key challenge in this field is how to realize a high areal capacitance for SCs, while achieving rapid charging, good capacitive retention, flexibility, and waterproofing. To address this challenge, low-cost materials are used including multiwall carbon nanotube (MWCNT), reduced graphene oxide (RGO), and metallic textiles to fabricate composite fabric electrodes, in which MWCNT and RGO are alternatively vacuum-filtrated directly onto Ni-coated cotton fabrics. The composite fabric electrodes display typical electrical double layer capacitor behavior, and reach an ultrahigh areal capacitance up to 6.2 F cm^-2 at a high areal current density of 20 mA cm^-2 . All-solid-state fabric-type SC devices made with the composite fabric electrodes and water-repellent treatment can reach record-breaking performance of 2.7 F cm^-2 at 20 mA cm^-2 at the first charge-discharge cycle, 3.2 F cm^-2 after 10 000 charge-discharge cycles, zero capacitive decay after 10 000 bending tests, and 10 h continuous underwater operation. The SC devices are easy to assemble into tandem structures and integrate into garments by simple sewing.