Novel high-performance asymmetric supercapacitors based on nickel-cobalt composite and PPy for flexible and wearable energy storage

Wearable fiber-shaped supercapacitor (SC) is a kind of one-dimensional flexible devices that can be directly knitted or sewn into various kinds of textile soft-substrate for wearable energy storage. Herein, acid-pretreated stainless steel yarn (SSY) has been developed to support electrodeposition of active materials of nickel/cobalt composite and polypyrrole (PPy) as the positive and negative electrodes, respectively. The asymmetric all-solid-state supercapacitors (AASs) showed both high electrochemical properties and excellent mechanical flexibility under various degrees of deformation. The highest volumetric capacitance reached 14.69 F cm⁻³ at the current density of 25 mA cm⁻³, and the maximum energy density was 3.83 mWh·cm⁻³ (0.032 mWh·cm⁻²) at a power density of 18.75 mW cm⁻³ (0.284 mW cm⁻²). The AASs were highly flexible and durable for directly being sewn into textile fabrics, and exhibited a good electrochemical stability under 6000 charging/discharging cycles. This work uses the common materials and facile methods to fabricate the flexible and wearable AASs with enhanced electrochemical properties, showing a decent way in developing flexible SC devices.