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Designing a Novel Polymer Electrolyte for Improving the Electrode/Electrolyte Interface in Flexible All-Solid-State Electrical Double-Layer Capacitors

Wang, Jeng-An, Lu, Yi-Ting, Lin, Sheng-Chi, Wang, Yu-Sheng, Ma, Chen-Chi M., Hu, Chi-Chang
ACS applied materials & interfaces 2018 v.10 no.21 pp. 17871-17882
capacitance, carbon, composite polymers, crosslinking, electrical equipment, electrochemistry, electrodes, electrolytes, gels, impedance, moieties, paper, polyacrylic acid, polyurethanes, potassium hydroxide, spectroscopy, stickiness, water content, water uptake
A novel copolymer, polyurethane–poly(acrylic acid) (PAA), is successfully synthesized from poly(acrylic acid) (PAA) backbone cross-linked with waterborne polyurethane (WPU). This sticky polymer, which is neutralized with 1 M KOH and then soaked in 1 M KOH (denoted as WPU-PAAK-K), provides an ionic conductivity greater than 10–² S cm–¹ and acts as a gel electrolyte perfectly improving the electrode/electrolyte interfaces in a flexible all-solid-state electrical double-layer capacitor (EDLC). The PAA backbone chains in the copolymer increase the amount of carboxyl groups and promote the segmental motion. The carboxyl groups enhance the water-uptake capacity, which facilitates the ion transport and promotes the ionic conductivity. The cross-linked agent, WPU chains, effectively maintains the rich water content and provides mechanical stickiness to bind two electrodes together. An acid-treated carbon paper (denoted as ACP) combining with such a gel polymer electrolyte demonstrates excellent capacitive behavior with a high areal capacitance of 211.6 mF cm–² at 10 mV s–¹. A full cell consisting of ACP/WPU-PAAK-K/ACP displays a low equivalent series resistance of 0.44 Ω from the electrochemical impedance spectroscopic results. An all-solid-state ACP/WPU-PAAK-K/ACP EDLC provides an areal specific capacitance of 94.6 mF cm–² at 1 mA cm–². This device under 180° bending shows a capacitance retention over 90%, revealing its remarkable flexibility.