Engineered self-standing monolithic Cu-Zn-Ni oxide nanocubes as battery materials for durable all-solid-state hybrid supercapacitor devices

Abstract

The optimum energy storage performance can be attained by combining the advantages of battery and capacitor into one device. This could be fulfilled by the smart design of positive (battery-like) and negative (EDL) electrode materials in a solid-state supercapattery. In this study, a cheap, yet effective, and simple strategy is utilized to synthesize binder-free, ternary metal oxide nanoparticles based on earth-abundant elements, namely Cu, Zn, and Ni. A monolithic sub-100 nm mixed oxide is prepared by anodizing German silver alloy (Cu–Zn–Ni) in an aqueous electrolyte for various time intervals (2,5, and 8 min). Upon analyzing the electrochemical performance of the films as positive electrodes in 1 M KOH, the 5 min anodized film (CZNO-5), with an elemental composition of Cu4Zn2NiOx@Cu-Zn-Ni, depicts remarkable areal and volumetric capacitances of ~27 mF/cm2 and 3150 F/cm3, respectively, at a current density of 1 mA/cm2. The assembled solid-state supercapattery device made of CZNO-5 and bioderived activated carbon (B-AC) exhibits 3.8 mF/cm2 at 1 mA/cm2 with ~35 % rate capability at 5 mA/cm2. The specific energy and specific power of the CZNO-5//B-AC device are found to be 0.97 μW h/cm2 and 0.91 mW/cm2, respectively. Most importantly, unlike many Cu-based devices, CZNO-5//B-AC shows an eminent durability with 100 and 89.6 % retention of the first cycle capacitance after 3800 and 5000 successive charge/discharge cycles.