Sandwich-like NiO/rGO nanoarchitectures for 4 V solid-state asymmetric-supercapacitors with high energy density

Abstract

Hierarchical NiO/reduced graphene oxide (rGO) nanohybrids with tunable microstructures were fabricated via the thermal decomposition of Ni(OH)2/rGO formed by the electrostatic attraction between exfoliated Ni(OH)2 and GO nanosheets. Characterization study revealed that the size of intercalated NiO nanocrystals could be tuned from 2 nm to 10 nm, and the specific surface area of optimized nanohybrids reached to 255 m2/g. Ionogel polymer electrolyte was prepared by entrapping ionic liquid (EMImBF4) and lithium salt (LiTFSI) into copolymer (PVdF-HFP). Effect of NiO particle size on the electrochemical performances was evaluated systemically. Asymmetric supercapacitors with as-prepared nanohybrids as anode and commercial activated carbon as cathode were assembled. Aqueous 6 M KOH solution, organic LiPF6 solution and ionogel polymer were utilized as electrolytes to check their compatibility with nanohybrids. Our study shows that supercapacitors exhibit energy densities of 31.6 Wh/kg, 49 Wh/kg and 146 Wh/kg, respectively, with the above mentioned electrolytes. These results clearly demonstrate that high performance can be actualized by the subtle combination of hybridized electrodes with high voltage formulated ionogel polymer electrolytes.