Facile synthesis of high-performance Ni(OH)₂/expanded graphite electrodes for asymmetric supercapacitors

Cost-effective commercial expanded graphite (EG) was used as a raw material, and a facile in-situ electrodeposition method was adopted to synthesize a layered Ni(OH)₂/EG composite electrode in an N,N-dimethylformamide-water system. Scanning electron microscopy images show that expanded graphite sheets, Ni(OH)₂ nanoparticles and carbon nanotubes construct a layered structure, which not only effectively restrains restacking of EG sheets but also prevents aggregation of nickel hydroxide particles. The electrode delivers a satisfactory initial specific capacitance of 1719.5 F/g at 1 A/g with a total mass loading of 5.0 mg/cm². Even at 10 A/g, the capacitance only decreases to 1181.3 F/g, showing a remarkable rate capability. Moreover, an optimized asymmetric supercapacitor (ASC) device was fabricated, in which the Ni(OH)₂/EG electrode was used as a positive electrode and commercial activated carbon (AC) was used as a negative electrode. The ASC device can deliver a prominent energy density of 32.3 Wh/kg at power density 504.7 W/kg, and long cycling life with 79% original capacitance after 1000 cycles at 5 A/g, which can be prospective to be applied in practical devices for energy storage and conversion.