In-situ construction of amorphous–crystalline NiCo bimetallic oxyhydroxide for low-temperature supercapacitor device

Abstract

As rechargeable energy storage device, supercapacitor (SC) cell is facing a new challenge for low-temperature application since the low-temperature environment seriously suppresses the reaction kinetics of the electrode materials. In this work, NiCo bimetallic oxyhydroxides (NixCoyOOH, Ni/Co = x/y) composed of amorphous-crystal structure were in-situ synthesized using electrodeposition, which are capable of operating at temperatures as low as − 4 °C, totally different from the pure Ni or Co oxyhydroxides counterparts. The microstructures of the NixCoyOOH were characterized by XRD, SEM, TEM, and XPS, finding an obviously transit from microparticles (NiOOH) and porous arrays (CoOOH) to flower-like nanospheres and a complicated amorphous-nanocrystalline structure. Electrochemical tests show that the Ni2Co1OOH cathode presents a super-high specific capacitance of 3720 and 2311F g−1 at low and high charging current densities of 1 and 20 A/g at 23 ℃ in aqueous electrolyte, respectively. The assembled device of Ni2Co1OOH//activated carbon (AC) delivers a high energy density of 22.8 Wh kg−1 at 7466 W kg−1 in polyvinyl alcohol (PVA)-KOH hydrogel at 0 ℃, and offers anexceptionalstability of 92.5 % of capacity after 8000 cycles at 10 A/g and 0 ℃. To evaluate the serviceability of the as-prepared electrode materials, the devices in parallel and series connections encapsulated by 3D printing exhibits a stable discharging performance at 0 °C, demonstrating a potential application in cold environment. Heteroatomic intercalating promotes the co-adsorption of hydroxyls on the double active sites of the Ni and Co, resulting in an improved supercapacitance.