The multi-structure NiCo_2S_4 prepared by solvothermal method for supercapacitor accompanied with positron annihilation study

摘要

Fluffy spherical structure NiCo2S4 decorated with cubic phase hexagonal nanosheets was successfully synthesized through a two-step solvothermal method for energy storage. The electrochemical measurements reveal its good reversibility together with its high rate ability (1354 F g(-1) at 0.5 A g(-1) and 1128 F g(-1) at 10 A g(-1)). Positron annihilation techniques (positron annihilation lifetime spectra and Doppler broadening spectra) were conducted to investigate the defects and the electronic structure of the two-step synthesized NiCo2S4. The results showed high S/W ratio, which is consistent with the electrochemical results. An asymmetric supercapacitor (ASC) was assembled in a button cell using the two-step synthesized NiCo2S4 as the positive electrode material and commercially activated carbon as the negative electrode material. The ASC presents a high energy density of 30.8 W kg(-1) at a power density of 352.2 W kg(-1) and 15.5 W kg(-1) at a power density of 6860 W kg(-1), with excellent cycling stability (89.3% capacitance retention after 3000 cycles) and nearly 100% Coulombic efficiency. Published under license by AIP Publishing.