3D hierarchically porous zinc-nickel-cobalt oxide nanosheets grown on Ni foam as binder-free electrodes for electrochemical energy storage

Three-dimensional (3D) hierarchically porous transition metal oxides, particularly those involving different metal ions of mixed valence states and constructed from interconnected nano-building blocks directly grown on conductive current collectors, are promising electrode candidates for energy storage devices such as Li-ion batteries (LIBs) and supercapacitors (SCs). This study reports a facile and scalable chemical bath deposition process combined with simple calcination for fabricating 3D hierarchically porous Zn-Ni-Co oxide (ZNCO) nanosheet arrays directly grown on Ni foam with robust adhesion. The resulting nanostructures are then evaluated as a binder-free electrode for LIBs and SCs. Given its unique architecture and compositional advantages, the electrode exhibits a reversible capacity of 1131 mA h g(-1) after 50 cycles at a current density of 0.2 A g(-1), an excellent long-term cycling stability at a high current density of 1 A g(-1) for 1000 cycles, and a desirable rate capability when tested as an anode for LIBs. When used for SCs, the electrode demonstrates a high specific capacitance (1728 F g(-1) at 1 A g(-1)), an outstanding rate capability (72% capacitance retention from 1 A g(-1) to 50 A g(-1)), and an excellent cycling stability (capacitance of 1655 F g(-1) after 5000 cycles at a current density of 20 A g(-1) with 108.6% retention). Overall, the unique 3D hierarchically porous ZNCO nanosheets hold a great promise for constructing high-performance energy storage devices.