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Flexible electrochromic supercapacitors (ECSCs) are currently under considerable investigation as potential smart energy storage components in wearable intelligent electronics. However, the lack of a suitable strategy for precisely judging its real-time energy storage status has hindered its development toward practical application. Herein, an optical-energy feedback strategy based on electrochromic contrast as a quantitative indicator of the state of charge (SOC) in flexible ECSCs has been developed using a polypyrrole (PPy)-based electrochromic electrode: carbon nanotubes (CNTs)/Au/PPy/poly(ethylene terephthalate) (PET). A linear dependence of real-time electrochromic contrast on the SOC is established, enabling a quantitative, accurate, and on-site visualization of the energy level from digitized information. Benefiting from the inherent high color-to-color contrast in PPy during electrochromism, the strategy shows a high detection sensitivity and resolution during charging/discharging. Moreover, the good flexibility, high capacitance of the electrode, and asymmetric device design can synergistically benefit the energy storage performance of the flexible ECSC, resulting in a high energy density of 4.03 μWh cm–2 and high electrochemical stability under deformations. This work largely explores the potential and advantages of PPy for fabricating a high-performance flexible smart supercapacitor and opens up an alternative methodology for realizing a convenient, low-cost, and nondestructive SOC self-monitoring ability in flexible energy storage devices.
Jiao et al. (Wed,) studied this question.