Rationally designed hierarchical C/TiO₂/Ti multilayer core-sheath wires for high-performance energy storage devices

Fiber-shaped supercapacitors (FSCs) are promising power sources for wearable electronic devices due to their small size, excellent flexibility and deformability. The performance of FSCs has been severely affected by the framework of the fibrous electrodes and the interface between the electrode materials and current collector. Herein, we propose an ingenious strategy that combines anodizing etching and CVD methods to transform the less-active titanium wires into unique hierarchical carbon/TiO₂ nanotube/Ti (CTNT) core-sheath wires, which have high conductivity, good mechanical strength and porous structure on the surface. CTNT wires can be used not only as a high-performance electrode, but also as an ideal substrate for depositing active materials. We have demonstrated the deposition of MnO₂ and MoS₂ on the surface of CTNT to prepare MnO₂@CTNT and MoS₂@CTNT core-sheath composite wires through electrochemical deposition and hydrothermal reaction, respectively. The specific areal capacitance of a single wire (MoS₂@CTNT) can reach up to 557.83 mF cm^-2 in a three-electrode system. Two such wires were further used as electrodes for making an all-solid-state asymmetric fiber-shaped supercapacitor (AFSC). The prepared AFSC has a wide voltage window of 2.7 V, a large areal capacitance of 121.42 mF cm^-2 and an excellent energy density of 74.37 μW h cm^-2. It also shows good rate performance and stability, and even after 10 000 cycles of charging and discharging, a capacitance retention rate of 76.5% can be achieved.