Thin-walled hollow fibers for flexible high energy density fiber-shaped supercapacitors

Fiber-shaped supercapacitors, which occupy minimal volume and possess remarkable flexibility, are particularly promising candidates for next-generation smart wearable devices. However, the state-of-the-art energy density and mechanical properties of fiber-shaped electrodes are far from satisfactory. Herein, hollow poly(3,4-ethylenedioxythiophene):polystyrene sulfonate thin-walled fibers (HPFs) are continuously prepared by coaxial wet-spinning. These HPFs combine a simple and high continuous preparation with high electrochemical performance and flexibility, owing to their hollow nature, small diameter (125 μm) and thin wall structure (8 μm). As a result, the HPFs display a specific areal capacitance of 115.2 mF cm-2 at a current density of 0.3 mA cm-2 with a high energy density of 9 μWh cm-2 at a power density of 0.112 mW cm-2. Furthermore, the HPFs maintain 81% of the initial capacitance after 10,000 cycles with ~100% Coulombic efficiency. More importantly, the specific capacitance is almost completely maintained after bending 3000 times at 180°.