Facile synthesis of neuronal nickel–cobalt-manganese sulfide for asymmetric supercapacitors with excellent energy density

A neuronal nickel–cobalt–manganese sulfide material with a large surface area and high porosity can be homogeneously grown along a nickel foam via a simple one-step hydrothermal procedure. An optimal molar ratio of Ni, Co, Mn, and thiourea of 3:1:1:5 was obtained by adjusting the molar ratio of thiourea. This binder-free composite material supported by a nickel foam can be directly used as a battery-type electrode for supercapacitors. Under the optimal hydrothermal conditions, the battery-type electrode exhibited excellent electrochemical properties with a favorable specific capacitance (2805.3F/g, 1 A/g) and good rate properties (87.7 %, 10 A/g) because of the synergistic effect of the multiple transition metals. Furthermore, the battery-type electrode exhibited a remarkable capacitance retention rate (82.9 %, 10 A/g) after 10,000 cycles of electric charging and discharging owing to the addition of Mn, which suggests excellent cycle stability. Furthermore, an asymmetric supercapacitor (ASC) device prepared using the battery-type electrode material and activated carbon electrode exhibited a considerable energy density (86.9 W h kg−1) at a high power density (799.1 W kg−1). After charging for 26 s to 3.2 V, two ASC devices in series could light two red-light-emitting diodes for at least 300 s. Thus, a simple and effective synthesis scheme can be designed to prepare high-performing supercapacitors.