Interface engineering of triple carbons for binder-free integrated freestanding electrodes derived from coal tar pitch for flexible supercapacitors

The development of flexible electrodes that are cost-effective, possess high mechanical strength and superior electrochemical performance is of significant importance but highly challenging for advancing flexible quasi-solid-state supercapacitors (FSCs). Herein, the integrated, freestanding, and flexible electrodes with excellent electrochemical and mechanical performance were fabricated via a facile and efficient strategy of interface design, with the carbon material precursor of coal tar pitch (CTP) and the flexible substrate of carbon cloth (CC). A polydopamine carbon interface (PA) was first constructed on the CC, and N-doped porous carbon obtained from CTP was grown in situ on the interface to form a triple‑carbon flexible electrode integrating CC, carbon interface, and porous carbon (CC-PA-PC). Ascribing to the structural advantages, the as-prepared electrode presents improved electrochemical performance compared to the electrode fabricated without the carbon interface (CC-PC). The symmetric FSCs assembled using the CC-PA-PC electrode demonstrate a superior areal capacitance of 1303.6 mF cm⁻² at 0.5 mA cm⁻² and an energy density of 0.18 mWh cm⁻², significantly exceeding the corresponding values of 625.4 mF cm⁻² and 0.087 mWh cm⁻² for the CC-PC electrode at the same conditions. Moreover, CC-PA-PC-based FSCs exhibit excellent flexibility and mechanical stability. This design strategy for flexible electrodes provides a pathway for the application of powdery porous carbons in flexible supercapacitors.