Hydrothermal Synthesis and Characterization of Litchi-Like NiCo2Se4@carbon Microspheres for Asymmetric Supercapacitors with High Energy Density

In this paper, litchi-like microspheres structures of NiCo 2 Se 4 @carbon microspheres (NCSC) hybrids were successfully synthesized via a simple two-step hydrothermal method. The effects of the content of NiCo 2 Se 4 on the structure of NCSC composites are investigated. The morphology and nanostructure of the as-obtained NCSC hybrids were examined by XRD, XPS, FESEM and TEM. The results indicate that the carbon microspheres (CM) were uniformly covered with NiCo 2 Se 4 and with the increase of NiCo 2 Se 4 content, the superficies of NCSC also exhibits homogeneous rough nanoparticles and regular spheres connect with each other. Meanwhile, the electrochemical tests indicate a suitable mass ratio of NiCo 2 Se 4 and carbon microspheres (2:3) showed the highest specific capacitance value (1394 F g −1 at the current density of 0.5 A g −1 , 766 F g −1 even at the current density of 50 A g −1 ), excellent rate property and outstanding cycling stability (80.093% of the initial value after 10000 cycles at the current density of 5 A g −1 ). Benefiting from the above integrated advantages, asymmetric supercapacitors (ASC) fabricated with NCSC composites as the positive electrode and porous activated carbon as negative electrode operating at the voltage window of 0–2 V deliver a high energy density of 101 Wh kg −1 at a power density of 0.749 kW kg −1 , with the specific capacitance retention of 81.095% after 10000 cycles at the current density of 10 A g −1 , superior to most of reported supercapacitors.