High-stable α-phase NiCo double hydroxide microspheres via microwave synthesis for supercapacitor electrode materials

Fast and low-cost fabrication of high performance electrode materials is of great importance for the application of supercapacitors. Herein, in our research, three-dimensional (3D) flower-like NiCo double hydroxide (NiCo DH) microsphere was successfully synthesized via a rapid, inexpensive and energy saving microwave route without using any template or surfactant under atmospheric pressure. The as obtained NiCo DH microsphere endowed with alpha-phase structure with CNO- ions intercalation in the interlayers (7.3 angstrom) was composed of ultrathin nanosheets with thickness less than 10 nm. Electrochemical test revealed the NiCo DH electrode showed a high specific capacitance of 1120 F g(-1) at 1 A g(-1) and remained 996 F g(-1) at 10 A g(-1) (88.9% retention). Moreover, after 2000 cycles, the capacitance reached 122.5% of its initial value at 10 A g(-1) and still retained 93.8% at 30 A g(-1) after another 1000 cycles, showing superb stability compared with reported alpha-phase hydroxides. The admirable stability could be attributed to the synergistic effect between Ni and Co elements, the ion exchange phenomenon between CNO- and OH- ions in the interlayer of NiCo DH during cycling test, and the coherent 3D superstructure. Besides, the asymmetric supercapacitor, with NiCo DH as positive electrode and activated carbon from coal as negative electrode, delivered a superior energy density of 42.5 Wh kg(-1). Consequently, the pleasant synthesis procedure and excellent integrated performance of NiCo DH enable it to be a promising electrode material for the energy storage devices. (C) 2017 Elsevier B.V. All rights reserved.