Rational Design of Self-Supported Ni3S2 Nanosheets Array for Advanced Asymmetric Supercapacitor with a Superior Energy Density

We report a rationally designed two-step method to fabricate self-supported Ni3S2 nanosheet arrays. We first used 2-methylimidazole (2-MI), an organic molecule commonly served as organic linkers in metal-organic frameworks (MOFs), to synthesize an alpha-Ni(OH)(2) nanosheet array as a precursor, followed by its hydrothermal sulfidization into Ni3S2. The resulting Ni3S2 nanosheet array demonstrated superior supercapacitance properties, with a very high capacitance of about 1,000 F g(-1) being delivered at a high current density of 50 A g(-1) for 20,000 charge discharge cycles. This performance is unparalleled by other reported nickel sulfide-based supercapacitors and is also advantageous compared to other nickel based materials such as NiO and Ni(OH)(2). An asymmetric supercapacitor was then established, exhibiting a very stable capacitance of about 200 F g(-1) at a high current density of 10 A g(-1) for 10,000 cycles and a surprisingly high energy density of 202 W h kg(-1). This value is comparable to that of the lithium-ion batteries, i.e., 180 W h kg(-1). The potential of the material for practical applications was evaluated by building a quasi-solid-state asymmetric supercapacitor which showed good flexibility and power output, and two of these devices connected in series were able to power up 18 green light-emitting diodes.