关键词: 超级电容器, 老化试验, 碳-铝界面, 离子液体, 泡沫铝

Abstract:

Ionic liquid (IL) electrolyte-based supercapacitors (SCs) have advantages of high operating voltage window, high energy density and nonflammability, as compared to conventional acetonitrile-based organic electrolyte SCs, and are typically suitable for the large-scale energy storage in the era of carbon neutrality full of renewable, but unstable electricity. However, current efforts were concentrated on the study with coin-cell type of IL-SCs, and less has been reported on the pouch type of IL-SCs for a long cycling time yet. To fabricate a reliable SC for the life time test or for the accelerated aging test under high temperature, one should concern the excellent contact in the current collector/electrode interface to minimize the charge transfer resistance. In the present work, the carbon-Al interfacial effect was studied in the new SC system with Al foam as a current collector coated or painted by different carbon layers. Uniform amorphous carbon layer on Al foam was obtained from carbonization of epoxy resin film, giving a strong interaction of Al and carbon phase, as compared to that of the Al foam adhered with graphene by PVDF. In addition, to fully explore the potential of ILs electrolyte with large ion size, mesoporous carbon electrode was adopted here for a rapid ion diffusion across mesopores. Thus, the new structure SCs pouch consisting of mesoporous carbon electrode, ILs electrolyte and carbon coated-3D Al foam current collector was for the first time fabricated in the present work. Based on the as-made different pouches with capacity of 37 F, their time dependent electrochemical properties, including cyclic voltammetric (CV) response, galvanostatic charge and discharge behaviors, capacitance, contact resistance, and electrochemical impedance spectroscopic (EIS) characteristics were studied by accelerating aging test at 65 ^oC for 500 h at 3 V. The former pouch of Al foam coated with amorphous carbon layer exhibited far higher capacitance retention as compared to the pouch of Al foam adhered with graphene layer. Detailed fitting of ESR was made, and the contact resistance, charge transfer resistance, and Warburg resistance were analyzed thoroughly, providing deep insight into the strong C-Al interface effect on the high and stable performance of SCs with high energy density. Characterization of electrode sheet before and after 500 h aging test confirmed the above results. The high temperature and high voltage condition made the graphene-pasted Al foam unreliable. But the in situ coated carbon layer on Al foam exhibited relatively strong interaction and a reliable structure for the stable operation of the SCs pouch during the aging test. These solid data provide sufficient information for the further optimization of the high voltage SCs toward high energy density, high power density and long cycling time.

Key words: supercapacitor, aging test, carbon-aluminum interface, ionic liquid, aluminum foam