Self-healable wire-shaped supercapacitors with two twisted NiCo₂O₄ coated polyvinyl alcohol hydrogel fibers

Wire-shaped supercapacitors (SCs) possessing light-weight, good flexibility and weavability have caught much attention, but it is still a challenge to extend the lifespan of the devices with gradual aging due to the rough usage or external factors. Herein, we report a new stretchable and selfhealable wire-shaped SC. In the typical process, two polyvinyl alcohol/potassium hydroxide (PVA/KOH) hydrogel wrapped with urchin-like NiCo₂O₄ nanomaterials were twisted together to form a complete SC devices. It is noted that the as-prepared PVA hydrogel can be easily stretched up to 300% with small tensile stress of 12.51 kPa, superior to nearly 350 kPa at 300% strain of the polyurethane. Moreover, the wire-like SCs exhibit excellent electrochemical performance with areal capacitance of 3.88 mF cm⁻² at the current density of 0.053 mA cm⁻², good cycling stability maintaining 88.23% after 1000 charge/discharge cycles, and 82.19% capacitance retention even after four damaging/healing cycles. These results indicate that wireshaped SCs with two twisted NiCo₂O₄ coated polyvinyl alcohol hydrogel fibers is a promising structure for achieving the goal of high stability and long-life time. This work may provide a new solution for new generation of self-healable and wearable electronic devices.