Anchoring Ultrafine ZnFe₂O₄/C Nanoparticles on 3D ZnFe₂O₄ Nanoflakes for Boosting Cycle Stability and Energy Density of Flexible Asymmetric Supercapacitor

Heterostructure-based metal oxide thin films are recognized as the leading material for new generation, high-performance, stable, and flexible supercapacitors. However, morphologies, like nanoflakes, nanotubes, nanorods, and so forth, have been found to suffer from issues related to poor cycle stability and energy density. Thus, to circumvent these problems, herein, we have developed a low-cost, high surface area, and environmentally benign self-assembled ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructure electrode via anchoring ZnFe₂O₄ and carbon nanoparticles using an in situ biomediated green rotational chemical bath deposition approach for the first time. The synthesized ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructure thin films demonstrate an excellent specific capacitance of 1884 F g^-1 at a current density of 5 mA cm^-2. Additionally, all solid-state flexible asymmetric supercapacitor devices were designed on the basis of ZnFe₂O₄ nanoflake@ZnFe₂O₄/C nanoparticle heterostructures as the negative electrode and reduced graphene oxide and energy density of 81 Wh kg^-1 at a power density of 3.9 kW kg^-1. Similarly, the asymmetric device exhibits ultralong cycle stability of 35 000 cycles by losing only 2% capacitance. The excellent performance of the device is attributed to the self-assembled organization of the heterostructures. Moreover, the in situ biomediated green strategy is also applicable for the synthesis of other metal oxide and carbon-based heterostructure electrodes.