An electrochromic supercapacitor and its hybrid derivatives: Quantifiably determining their electrical energy storage by an optical measurement

In this article, an electrochromic supercapacitor was developed with the electrode material active for both electrochromism and energy storage. The detailed measurements of the optical spectra of the device revealed that the normalized optical density, a concept in electrochromic studies, depended linearly on the electrical energy storage (EES) of the supercapacitor. This enabled the precisely quantifiable determination of a solid-state supercapacitor's EES by simple optical transmission measurement, which is demonstrated here for the first time, to the best of our knowledge. One step further, parallel-structured hybrid supercapacitors were designed to integrate the developed smart function with high-performance supercapacitors using polypyrrole (PPy) and manganese oxide (MnO₂) as electrode materials. The developed hybrid supercapacitors exhibited excellent capacitive performance and maintained the ability of electrochromic EES indicators well. Different calibration curves can be produced for different types of hybrid supercapacitors. With these curves, the EES of hybrid supercapacitors can be precisely determined using a simple optical transmission measurement. Our study paves the way for the integration of electrochromic EES indicators in various energy storage devices, as well as the prompt and quantitative determination of the EES of various types of supercapacitors using a simple optical transmission measurement.