Tremella-like 2D Nickel-Copper Disulfide with Ultrahigh Capacity and Cyclic Retention for Hybrid Supercapacitors

Two-dimensional (2D) disulfides possess unique physical and chemical properties and are widely used in electronic and photoelectric devices. Tuning the composition and optimizing the structure of the disulfides are feasible approaches to designing target sulfides for hybrid supercapacitors. This work synthesizes the tremella-like nanosheet-connected (CuNi_1-)S₂ via solvothermal and sulfur-vapor vulcanization. The 2D (CuNi_1-)S₂ electrode performs a high reversible capacity (526.0 mA h g^-1 at 1 A g^-1), decent capacity retention (75.6%) at 10 A g^-1, and prolonged cyclic retention (94.4% over 15,000 cycles), which is higher than that of (CuNi_1-)O and monometallic sulfides of NiS₂ and CuS. The elevated electrochemical properties of (CuNi_1-)S₂ are attributed to the optimized composition with increased redox reaction, enlarged lattice distance, abundant active sites, and attractive electronic and ionic conductivity. Also, (CuNi_1-)S₂ and active carbon (AC) are assembled to form a hybrid supercapacitor (HSC). The (CuNi_1-)S₂//AC HSC demonstrates a maximum specific capacitance of 231.0 F g^-1 at 1 A g^-1 and a high energy density of 82.4 W h kg^-1 at a power density of 1.82 kW kg^-1. Outstanding cyclic retentions of 94.9 and 84.5% after 8000 and 10,000 cycles are also obtained. In conclusion, this result suggests a facile routine for preparing a novel 2D layer material of (CuNi_1-)S₂ with outstanding specific capacity and cycling performance for hybrid supercapacitors.