Exploring the effects of carbon meso-structure and macrostructure on the rate performance of porous carbon supercapacitors
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Electrochemical double-layer capacitors are promising energy storage devices with high power density, moderate energy density, rapid charging rates, and high cycle life. In order to maximize energy density, highly porous carbon materials are often incorporated in the electrodes. The structure of the porous carbon network is critical to ensure high power delivery and charging rate. In this study, two types of oil sands petroleum cokes, from either batch or continuous industrial coking, were used to prepare porous carbon samples. The two activated petroleum coke samples have similar chemical compositions, specific surface areas, and pore size distributions, but due to the different industrial coking methods, the two samples have differing macrostructures and porous networks. Using mercury intrusion porosimetry and scanning electron microscopy, the meso-structure, macrostructure, and pore connectivity of the two samples were characterized and compared to the capacitance performance of the activated coke samples. The results show that, in order to ensure high rate performance, especially in ion depleted electrolyte scenarios, the porous carbon samples must have an interconnected network of pores between 10 and 1000 nm in diameter. These pore sizes are shown to improve the rate of ion diffusion, and allow greater capacitance values to be achieved at rapid charging rates.
KeywordsElectrical energy storage Supercapacitors Ion diffusion Porous carbon Charging rate
The authors would like to acknowledge the Natural Science and Engineering Research Council (NSERC), the Consortium on Sustainable Materials (COSM-Japan) and the Chinese–NSF for funding for this project. As well, the authors would like to thank the Canadian Oil Sands industry for supply of raw petroleum coke. The authors would also like to thank Professor Tim Newson and Dr. Nael Yasri from Western University for their help with the Mercury Intrusion Porosimetry analysis. The authors would also like to thank Dr. Rana Sodhi from the University of Toronto for his help with the X-ray photoelectron spectroscopy analysis.
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