Design of polyimide-based separators for effective suppression of self-discharge in non-aqueous electrical double layer capacitors

• Published in: Journal of power sources Vol. 514; p. 230594
• Main Authors: Ku, Hao-Yu, Pai, Jui-Yu, Lu, Yi-Ting, Wang, Li-Qian, Hu, Chi-Chang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2021
• Subjects: Alumina nanoparticles; Electrical double layer capacitors; Polyimide separators; Polyurethane-poly(acrylic acid) copolymer; Self-discharge; Electrical double layer capacitors; Polyimide separators; Alumina nanoparticles; Self-discharge; Polyurethane-poly(acrylic acid) copolymer
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2021.230594

The self-discharge phenomenon is an unavoidable response of electrical double layer capacitors (EDLCs) when the applied voltage is interrupted. How to alleviate this natural behavior is a challenge in the practical usage of EDLCs, especially such a self-discharge phenomenon is demonstrated to be induced by the presence of trace water in the organic electrolyte. This research focuses on the alleviation of the water-induced self-discharge process in non-aqueous EDLCs through the utilization of a polyimide (PI) separator coated with the polyurethane-poly(acrylic acid) (PUPAA) copolymer (denoted as PI@PUPAA). The trace water in the non-aqueous electrolytes is effectively absorbed by the copolymer, leading to the obvious suppression of self-discharge in the EDLC cells. The introduction of Al2O3 nanoparticles into PI to form a composite separator (PI + Al2O3@PUPAA) substantially improves the electrochemical responses of EDLCs though the ionic conductivity of the PI@PUPAA separator is reduced by the PUPAA coating. This PI + Al2O3@PUPAA composite has been demonstrated to be a promising separator significantly decelerating the self-discharge process of an EDLC with a comparable charge/discharge performance in comparison with the same cell utilizing the commercial TF4030 separator. •The higher water content of electrolyte is, the more self-discharge of EDLCs is found.•PUPAA absorbing H2O from electrolytes suppresses water-induced self-discharge of EDLCs.•PI + Al2O3@PUPAA is a cost-effective separator reducing self-discharge of EDLCs.