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 (similar to 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 mu W 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.