Yarn-form electrodes with high capacitance and cycling stability based on hierarchical nanostructured nickel-cobalt mixed oxides for weavable fiber-shaped supercapacitors

Integration of microelectronic devices into traditional clothing for smart wearable electronic textiles attracts increasing attentions in recent years, which will boost the economy in the next few decades. The flexible and weavable micropower units are the key component for smart wearable electronic textiles. Herein, the soft and conductive stainless steel yarn is chosen to serve as both substrate and collector, satisfying the requirements of high flexibility and good electrical conductivity. As expected, the as-obtained yarn-form electrodes based on nickel-cobalt oxide with ultrathin two-dimensional nanosheet hierarchical arrays and grown binder-freely on the conductive stainless steel yarn substrate exhibit a higher specific capacitance (90.82 mF cm⁻¹ or 289.24 mF cm^-2 at the current of 0.33 mA cm⁻¹) and a better cyclic stability (92.4% retention of specific capacitance after 3000 cycles at the current of 1.67 mA cm⁻¹), compared to those based on nickel-cobalt oxide with nanowires in this work. Through the further assembly of the as-prepared yarn-form electrodes into the parallel arrangement, the symmetric all-solid-state fiber-shaped supercapacitor with a high energy density (3.9 μWh·cm⁻¹ or 12.42 μWh·cm⁻²) and good flexibility and weaveability is fabricated, which has great potential to serve as weavable power unit for smart wearable electronic devices.