[en] Highlights: • A facile one-step nitridation and carbon coating process is introduced for [email protected] nanotube. • The [email protected] based SC shows remarkably enhanced electrochemical and mechanical performance. • The [email protected] based SC can serve as electric cables and store energy devices at the same time. As an emerging energy storage device for wearable electronics, fiber supercapacitors (FSCs) have distinguished themselves from two dimensional SCs. Herein, [email protected] nanotube-based fiber electrodes are designed through a one-step nitridation and complete carbon coating process. They exhibit 260% higher capacitance than the samples obtained by traditional two-step nitridation and carbonization method. The carbon shell and the fabrication method are critical for the performance of the electrodes. The carbon shell remarkably protects the polycrystalline TiN core from mechanical cracking and chemical oxidation. FSCs based on these fiber electrodes demonstrate excellent electrochemical performance and mechanical stability. High capacitance of 2.4 mF cm⁻¹ (19.4 mF cm⁻² and 1.9 F cm⁻³) at a scan rate of 10 mV s⁻¹ with an energy density of 2.69 μW h cm⁻² and a power density of 809 μW cm⁻² can be achieved. Moreover, nearly 80% capacitance retention after 10,000 cycle tests can be realized and the novel FSC can be bent for 2000 times with capacitance decay of 7.2%. Interestingly, our FSCs show almost no decay when cut into two segments due to the adoption of solid state electrolyte, demonstrating excellent tailorability. Finally, they can be also used as electric cables while store energy, demonstrating their bi-functionality.