Facile Synthesis of MnFe2O4 Hollow Sphere-Reduced Graphene Oxide Nanocomposites as Electrode Materials for All-Solid-State Flexible High-Performance Asymmetric Supercapacitors

In this work, nanocomposites composed of MnFe2O4 hollow spheres and reduced graphene oxide (rGO) were prepared by employing a "one-pot" hydrothermal method. The electrochemical properties of these nanocomposites were studied in detail by assembling a three-electrode setup and two-electrode cell setups (symmetric and asymmetric cells). The nanocomposite having 80 wt % MnFe2O4 and 20 wt % rGO (80MnFe(2)O(4)-20rGO) possessed a high value of specific capacitance of 768 F g(-1) at a current density of 8 A g(-1). The asymmetric cell consisting of 80MnFe(2)O(4)-20rGO as the cathode and rGO as the anode exhibited an energy density of 28.12 Wh kg(-1) at a power density of 750 W kg(-1), with a long cycle life (similar to 95% retention after 4000 cycles). The asymmetric cell, constructed using this nanocomposite as the active electrode material, demonstrated its potential in practical application by lighting 16 red light-emitting diode (LED) lights. An all-solid-state flexible asymmetric supercapacitor device was fabricated, which delivered an energy density of 27.7 Wh kg(-1) and power density of 750 W kg(-1). This device also exhibited consistent electrochemical performance against different bending angles showing its structural robustness. To the best of our knowledge, the performance of the synthesized nanocomposite as an active electrode material was comparable and, in many cases, superior to those of the reported MnFe2O4-based composites as well as commercial supercapacitors. The impressive electrochemical performance makes the synthesized nanocomposite a promising electrode material for high-performance supercapacitor applications.