Green Bio-template Fabrication of Fe Derivatives@Carbon Composites and Porous Carbon Sheets toward Advanced Li-Ion Capacitors as Low-Cost Electrodes

Li-ion capacitors (LICs), a typical hybrid configuration constructed by combining a capacitive cathode and a battery-type anode with Li-salt based organic electrolytes, are drawing research attention to increase energy densities of the existing state-of-the-art supercapacitors. However, the promising future of hybrid devices is injured by the imbalance of electrochemical kinetics and capacities between the battery-like anodes and capacitive cathodes. Herein, we devise a bio-template strategy to synthesize the highly porous carbon and Fe derivatives@carbon (Fe@C) composite from the same precursor of strawberries. The obtained porous carbon shows a sheet-like morphology with a high specific surface area of 2987 m2/g. Electrochemical evaluation of the 2D porous carbon sheet delivers a high specific capacity of 140.3 mAh/g (202 F/g) and excellent rate capability. The achieved mesoporous Fe@C composite delivers a high specific capacity of 576.3 mAh/g at 0.1 A/g, and even 202.8 mAh/g at 10 A/g. A novel LIC assembled using the porous carbon and Fe@C composite as the positive and negative electrodes yields a high energy density of 97 Wh/kg at 250 W/kg. The scalable methodology here paves the way for widespread commercialization of the advanced yet cost-efficient LICs.