Rational design of carbon shell endows TiN@C nanotube based fiber supercapacitors with significantly enhanced mechanical stability and electrochemical performance

As an emerging energy storage device for wearable electronics, fiber supercapacitors (FSCs) have distinguished themselves from two dimensional SCs. Herein, TiN@C 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 2.4mFcm−1 (19.4mFcm−2 and 1.9Fcm−3) at a scan rate of 10mVs−1 with an energy density of 2.69μWhcm−2 and a power density of 809μWcm−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.