Three-dimensional ZnFe2O4@MnO2 hierarchical core/shell nanosheet arrays as high-performance battery-type electrode materials

Abstract In this paper, a highly ordered three-dimensional ZnFe2O4@MnO2 core/shell nanosheet arrays (ZnFe2O4@MnO2 NSAs) on three-dimensional (3D) Nickel foam (Ni foam) have been prepared via a facile, stepwise hydrothermal approach and further investigated as a battery-type electrode material. It is found that the honeycomb-like ZnFe2O4@MnO2 NSAs have outstanding electrochemical performances using cyclic voltammetry (CV), galvanostatic charge-discharge (CD), and electrochemical impedance spectroscopy (EIS) in a three-electrode system. Based on the unique nanostructure, the ZnFe2O4@MnO2 NSAs exhibit an exceptional capacity of 1084 C g−1 at current density of 2 A g−1 and long-term capacity retention of 96.1% after 5000 cycles at current density of 4 A g−1. Moreover, the ZnFe2O4 nanosheet arrays (ZnFe2O4 NSAs) also have 714 C g−1 at a current density of 2 A g−1 exhilaratingly and the capacity value is proven to be the highest when compared with other structures of ZnFe2O4 taken from the other literatures. Some synergistic effects are identified to be responsible for the observations: Firstly, high crystalline quality of the ZnFe2O4 NSAs core which is directly grown on 3D Nickel foam (a conductive current collector), allowing fast electron transport; secondly, the unique structure of honeycomb-like MnO2 shell that has an ultralarge surface area for electrochemical reaction; thirdly, smart combination of ZnFe2O4 and MnO2 effectively utilizes their different virtues and also compensate their defects; finally, highly conductive 3D Ni foam substrate, which fully eliminate conductive additives and binders.