Effect of templating agent on Ni, Co, Al-based layered double hydroxides for high-performance asymmetric supercapacitors

Transition metal layered double hydroxides (LDHs) are one of the great potential electrode materials for pseudocapacitors. In this paper, NiCo-LDHs, NiAl-LDHs, CoAl-LDHs, and NiCoAl-LDHs were synthesized by hydrothermal method and these materials directly grew on foamed nickel. The electrochemical performance of these materials was investigated by galvanostatic charge-discharge test (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The morphology and physicochemical properties of the materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The capacity of these materials at 1 A g−1 was 894.4, 942.4, 885, and 1068 F g−1, respectively. The capacity retention rates after 2000 cycles at 10 A g−1 were 80.05%, 76.4%, 81.92%, and 83.7%, respectively. And then, we synthesized NiCoAl-LDHs with 0.002, 0.003, 0.004, and 0.005 mol Tween80 by the same experimental method. The influence on the morphology and electrochemical properties of NiCoAl-LDHs with different dosage of template agents was investigated. The results show that the capacity at 1 A g−1 was 1336.4, 1433.2, 1430, and 1289.2 F g−1, respectively. The capacity retention rates after 2000 cycles at 10 A g−1 were 85%, 92%, 90%, and 88%, respectively. An asymmetric supercapacitor (ASC) was assembled with 0.003 mol Tween80 as positive electrode and activated carbon as negative electrode. The ASC device exhibited an ultra-high energy density of 89.79 Wh kg−1 at power density of 775 W kg−1 as well as long-term stability (86.02% of its initial capacitance retention at 10 A g−1over 2000 cycles), outperforming most of LDH and metal oxides ASCs.