Hierarchical core-shell structured CoNi2S4/Ni3S2@Ni(OH)2 nanosheet arrays as electrode for electrochemical energy storage

Abstract

Herein, hierarchical core-shell structured CoNi2S4/Ni3S2@Ni(OH)2 nanosheet arrays are synthesized through a facile method. The electrochemical results show that combining CoNi2S4/Ni3S2 nanosheet arrays (as core) with Ni(OH)2 nanosheets (as shell) is an effective way to improve electrochemical capacitive properties due to the synergetic effect between CoNi2S4/Ni3S2 and Ni(OH)2. The as-prepared CoNi2S4/Ni3S2@Ni(OH)2 exhibits a high capacity of about 772.2 μAh cm−2 at a current density of 1 mA cm−2, with an excellent capacity at very high current densities e.g. 500 μAh cm−2 at 30 mA cm−2 and an outstanding durability (ca. 98% of the capacity retention after 4000 cycles). Moreover, the electrochemical capacitive property of CoNi2S4/Ni3S2@Ni(OH)2 is also evaluated in an asymmetric two-electrode cell assembled by using CoNi2S4/Ni3S2@Ni(OH)2 as the cathode and the active carbon (AC) as the anode. The asymmetric cell shows a high energy density of about 0.432 mWh cm−2 when the power density was 1.646 mW cm−2, making it a promising electrode material for practical energy storage applications.