Knitting Controllable Oxygen-Functionalized Carbon Fiber for Ultrahigh Capacitance Wire-Shaped Supercapacitors

Wire-shaped supercapacitors (WSCs) are promising in wearable electronics but still face critical challenges of limited energy density. Nanostructured materials are dominant in high-performance active materials for improving energy density but are generally limited to wire-shaped electrodes (WSEs) with low mass loading (<0.5 mg cm–1) because of sluggish ionic kinetics in thicker electrodes. To address this problem, we report here the treatment of microstructured carbon fiber (CF) via a surface engineering strategy, which adopts controllable oxygen (O) functional groups on the CF surface with both highly redox-active sites and fast electron/ion transport. By combining a knitting method, we demonstrate that a WSE with high mass loading (∼6.1 mg cm–1) can operate at ultrahigh capacitance (435.1 mF cm–1, 1539.7 mF cm–2, and 68.4 mF cm–3), exceeding that of most of the reported WSEs. An assembled WSC delivers up to 195.3 mF cm–1 and 33 μW h cm–1, surpassing the best carbon symmetric supercapacitor known, and even conducting polymers and metal oxide asymmetric devices. Thus, this work provides a viable method for a high-mass WSE and will stimulate the development of WSCs toward practical applications.