Hierarchical coating of MnO2 nanosheets on ZnCo2O4 nanoflakes for enhanced electrochemical performance of asymmetric supercapacitors

• Published in: Electrochimica acta 2018-05, Vol.271, p.284-296
• Main Authors: Kumbhar, Vijay S., Kim, Do-Heyoung
• Format: Article
• Language: English
• Subjects: Asymmetric supercapacitor; Energy density; MnO2 nanosheets; Specific capacitance; ZnCo2O4 nanoflakes
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2018.03.147

The design of heterostructured pseudo-capacitive materials plays a key role in fabricating asymmetric supercapacitors (ASCs) with high energy density and electrochemical cycle life for the evolution of next-generation energy storage devices. Use of ZnCo2O4 nanoflakes covered with MnO2 nanosheets led to a synergistic effect that produced a larger electroactive surface area for charge storage than that provided by bare ZnCo2O4 nanoflakes or MnO2 nanosheets. The ZnCo2O4 nanoflakes served as the backbone for the growth of the MnO2 nanosheets. The ZnCo2O4-MnO2 heterostructure was synthesized on Ni foam using a combined binder-free electrodeposition and hydrothermal method. The electrode formed using this unique method showed a maximum specific capacitance of 2057 F g−1 at a current density of 1 A g−1 with a rate capability of 65% even after a 15-fold increase in current density. Moreover, the electrode showed a cycling stability of 96.5% after 5000 successive cycles at a current density of 15 A g−1. An ASC formed using ZnCo2O4-MnO2 as the positive electrode and activated carbon as the negative electrode delivered a maximum energy density of 69 W h kg-1 with 93.5% capacity retention after 5000 cycles. Further, an experiment to investigate the commercial application of ASCs was conducted. [Display omitted] •A MnO2 nanosheets were coated on ZnCo2O4 nanoflakes using a simple, eco-friendly, and low cost chemical methods.•The ZnCo2O4-MnO2 heterostructure exhibited a specific capacitance of 2057 F g-1.•The ZnCo2O4-MnO2 heterostructure exhibited a cycling stability of 96.5% after 5000 cycles.•As-fabricated ZnCo2O4//activated carbon asymmetric supercapacitor (ASC) exhibited an energy density of 69 W h kg-1.•Finally the demonstration of the as-prepared ASC confirmed the practical feasibility of the device.