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Fe3O4/carbon nanofibres with necklace architecture for enhanced electrochemical energy storage

Fe3O4 spherulites on carbon nanofibres (CNFs) to form novel necklace structures have been synthesised using a facile and scalable hydrothermal method, and their morphology and structure have been characterized using a range of electron microscopy and other techniques. The formation mechanism for the necklace structure has been proposed. The Fe3O4/CNF necklaces were sprayed onto large area current collectors to form electrodes with no binder and then investigated for their potential in supercapacitor and Li-ion battery applications. Supercapacitor electrodes in an aqueous KOH electrolyte delivered a high capacitance of 225 F g−1 at 1 A g−1 and Li-ion battery electrodes delivered a reversible capacity of over 900 mA h g−1 at 0.05 C, and there was good cycling stability and rate capability in both configurations. When compared with the reduced performance of mixtures of the same materials without the necklace morphology, the enhanced performance can be ascribed to the robust, high mechanical stability and open scaffold structure in the necklace electrode that provides high ion mobility, while the percolating CNFs ensure low resistance electrical connection pathways to every electroactive Fe3O4 spherulite to maximize storage behavior.