Unveiling the diffusion-controlled operation mechanism of all-in-one type electrochromic supercapacitors: Overcoming slow dynamic response with ternary gel electrolytes

Abstract

All-in-one electrochromic supercapacitors (ECSs) based on a single electrochromic (EC) gel layer are an attractive electronic component owing to their structural simplicity and capacitive and EC dual-function. Understanding the operating mechanism of ECSs is essential to maximize device performance. Particularly, the correlation between EC gel properties and ECS performance has not been properly established. In this study, the diffusion-controlled operating principle of the all-in-one ECSs is elucidated. The charging-discharging behaviors of ECSs based on conventional ion gels consisting of copolymer gelators and ionic liquids are incomplete due to the slow device dynamics arising from the delayed mass transport of redox-active materials through diffusive motion. Therefore, we propose the use of ternary gel electrolytes (TGEs) containing small organic molecules to reduce the overall viscosity and enlarge the free volume in the gel. A sufficient number of redox species can participate in galvanostatic charging-discharging reactions when the all-in-one ECSs are fabricated with highly conductive and elastic TGEs, resulting in a 3.3-times higher capacity (∼6.3 mC cm–2) than those based on typical ion gels (∼1.9 mC cm–2). Moreover, the TGE-based devices overcome the trade-off between transmittance contrast and response time, leading to superb performance. This study improves the overall performance and practical feasibility of all-in-one gel-based ECSs.