Carbon dots as multifunctional electrolyte additives toward multicolor and low self-discharge electrochromic energy storage devices

Electrochromic energy storage devices (EESDs), integrating energy storage and electrochromism into one cell that can change appearance based on their working states, are presently attracting considerable attention in a wide range of applications. EESDs with long-term stability, multicolor display and slow self-discharge rate are highly desired to broaden their practical applications. However, considering the complexity of integrating various components and multi-layer configurations, obtaining high-performance EESDs with exceptionally aesthetic versatility and excellent anti-self-discharge function via simple approaches is still a big challenge. Herein, a novel concept of EESD with multicolor electrochromic displays and low self-discharge rate was successfully designed and fabricated via employing carbon dots (CDs) as electrolyte additives. The prototype EESD could not only present vivid colors in 2D regional space but also exhibit remarkable electrochromic and electrochemical performances, such as fast switching responses (4.3/5.6 s for the coloration/bleaching processes), high coloration efficiency (similar to 134.8 cm(2) C (-) (1)), high volumetric power/energy density (364 mW cm(-3)/34.7 mWh cm(-3) and 7420 mW cm(-3)/17.4 mWh cm(-3)), along with outstanding cycling stability. Furthermore, the as-fabricated EESD can also demonstrate a reversible and steady electrochromic and electrochemical behavior under harsh temperatures between -25 degrees C and 65 degrees C, presenting enormous potential for consumers to monitor the working status of electronics in full-temperature conditions. Encouragingly, the resultant EESD exhibits slow self-discharge rate (such as 10.2 mVh(-1)at -25 degrees C, 19.4 mVh(-1)at 20 degrees C and 26.5 mVh(-1)at 65 degrees C), which are comparable with some previous researches that based on electrolyte anti-self-discharge modification. It is envisioned that this work may provide a feasible strategy to develop multifunctional EESDs for broad applications in military camouflage and intelligent electronics.