Flexible electrochromic devices have attracted considerable attention in recent years due to their great potential in smart multifunction electrochromic energy storage devices and wearable intelligent electronics. Herein, we present an inorganic flexible Li-based electrochromic energy storage device (EESD) by combining a Prussian white@MnO 2 -composited electrode (PWM) and sputtering-made WO 3 electrode. The synergistic effect of Prussian white and MnO 2 plays a positive role both in energy storage and electrochromic property of the EESD. Its energy level can be quantified by the transmittance spectrum and chrominance difference, and its charging−discharging process can be monitored in real time by optical modulation at special wavelength. Specifically, the EESD can endure a 10,000 times cyclic voltammetry cycle without obvious degradation at wide voltage windows (−2 to 2.5 V) and realize a high coloration efficiency (77.6 cm 2 /C) with 35% optical modulation at 510 nm. In terms of energy storage performance, the EESD demonstrates excellent volumetric energy/power density (1.25 W cm −3 /13.2 mWh cm −3 ) and remarkable stability with close to 98.3% capacitance retention and 99.4% coulombic efficiency after more than 4000 cycles. Its charging and discharging degree can be visualized in different spectral regions. There are 40% transmittance change for charging in the blue light region (450−480 nm) and 45% transmittance change for discharging in the red light region (620−750 nm). Based on its multicolor property, a quantitative indicator of charge state is achieved by the linear dependence of real-time chrominance change as stored or released charge. The ∼11 mC/cm 2 stored charge capacity can cause an ∼11 increase in chrominance difference ΔE value, while ∼7 mC/cm 2 discharge capacity can cause a ΔE value increase of ∼4. This work provides an efficient strategy to develop portable multicolor-integrated EESDs toward high performance and long stability.

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Multicolor display has gradually become a soughtafter trend for electrochromic devices due to its broadened application scope. Meanwhile, the advantages of inorganic electrochromic devices such as stable electrochemical performance and good energy storage ability also have great attraction in practical production applications. However, there are still huge challenges for inorganic electrochromic materials to achieve multicolor transformation due to their single-color hue change. Herein, we design an inorganic and multicolor electrochromic energy storage device (MEESD) exhibiting flexibility and all-solidstate merits. Prussian blue (PB) and MnO 2 , as the asymmetrical electrodes of this MEESD, show good pseudocapacitance property, matching charge capacity, and obvious color change. As a typical electrochromic device, the MEESD shows a fast response of 0.5 s and good coloration efficiency of 144.2 cm 2 /C. As an energy storage device, the MEESD presents excellent rate capability and volumetric energy/power density (84.2 mWh cm −3 /23.3 W cm −3 ). Its energy level can be visually monitored by color contrast and optical modulation. In the charging/discharging process, its color can obviously change to various degrees of yellow, green, and blue along with 40% wide optical modulation at 710 nm. Meanwhile, the stability of the MEESD in a common and humidity environment was analyzed in detail from electrochemical, optical, and energy storage aspects. This work provides feasible thoughts to design multifunctional electrochromic devices integrated with inorganic, flexible, all-solid-state, multicolor, and energy storage properties.

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Depending on adjusting substrate temperature during film depositing, a series of NiOx films has been prepared by magnetron sputtering. The electrochromic (EC) advantage of NiOx films modified by substrate temperature is verified. Moderate heating substrate can improve surface charge transfer (from ≈30 to ≈40 mC cm−2) and energy storage capacity (45% increment) without damaging other performance effectively. Considering the different electrochemical mechanisms in varied electrolytes, the EC performance of NiOx films in two electrolytes is discussed. In KOH electrolyte, NiOx films at 300 °C substrates show prominent optical modulation (≈81%) and high charge capacity (≈40 mC cm−2). 300 °C heating compensates for the shortage of poor stability and tedious activation. In LiClO4‐PC electrolyte, NiOx films can undergo long‐term cycles compared with aqueous conditions, the coloration efficiency keeps high level (≈80 cm2 C−2) which means small charge quantities can drive a wide transmittance range. The cyclic discrepancy in two electrolytes can be ascribed to diverse reacted modes between electrolyte ions and NiOx films. In aqueous KOH electrolyte, EC process and activated state strongly relies on Ni2+ distribution on films surface, while NiOx experiences two phases oxidation to get thorough coloration in PC‐Li based electrolyte.