Abstract
A core-shell design for nanostructured electrode materials is introduced for realizing high-performance supercapacitors. In the proposed core-shell design, thin shell-layers of highly electroactive/pseudo-capacitive materials provide the platform for surface or near-surface based faradaic/non-faradaic reactions together with shortened ion-diffusion path facilitating fast-ion intercalation/deintercalation processes, while the highly-conducting core serves as highway for fast electron/ion transfer towards current collector, improving energy and power performance characteristics of the core-shell structure in relation to pristine component materials. Moreover, use of carbon (C)-based materials as shell layer in either electrode not only enhances capacitive performance through double-layer formation but also provides enough mechanical strength to sustain volume changes in the core material during long-cycling of the supercapacitor improving its calendar life. In such an effort, both the negative and positive electrodes, namely ZnO/α-Fe2O3 and ZnO/C core-shell nano-rods of the assembled asymmetric supercapacitor (ASC) exhibit significant improvement in electrochemical performance in terms of the specific capacitance and rate capability as compared to pristine α-Fe2O3, ZnO and C electrodes. Such an ASC exhibits a specific capacitance of ~115 F/g at a scan rate of 10 mV/s in a potential window as high as 1.8V with response time as low as ~ 39 ms and retains more than 80% of its initial capacitance after 4000 cycles. Interestingly, the ASC can deliver an energy density of ~ 41 Wh/kg and a power density of ~ 7 kW/kg that are significantly higher than those reported hitherto for iron-oxide-based ASCs.
Published Version
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