Flexible all-solid-state asymmetric supercapacitors with three-dimensional CoSe₂/carbon cloth electrodes

As electrode materials for energy storage devices, metal chalcogenides have recently attracted great attention due to their unique structure related electrochemical properties. In this paper, hierarchical CoSe₂ nanostructures are successfully grown on conductive carbon fabrics with robust adhesion by a facile two-step method. The electrochemical properties of the as-prepared hierarchical CoSe₂ architectures were investigated in three- and two-electrode systems. In the three-electrode system, the hierarchical CoSe₂ architectures exhibit a large specific capacitance of 332 mF cm^-2 at a current density of 1 mA cm^-2. After charging/discharging for 5000 cycles, the electrode still showed superior stability with the capacity retention of about 95.4%. When assembled into asymmetric supercapacitors (ASCs) based on the hierarchical CoSe₂ negative electrode and MnO₂ nanowire positive electrode, the potential window increased to 1.6 V, larger than that of symmetric supercapacitors (SCs) based on CoSe₂//CoSe₂ electrodes. And a high energy density of 0.588 mW h cm^-3 at a power density of 0.282 W cm^-3 was also reached for the fabricated ASCs. Excitingly, the electrochemical performance of the as-assembled ASCs showed little degradation even under severe bending conditions, demonstrating excellent flexibility and mechanical stability. The as-grown CoSe₂ electrode with a 3D hierarchical structure can be a potential candidate for high-performance ASCs because of its improved electrochemically active sites, electronic conductivity and the reduced ion diffusion path.