Coupling of high ion transport efficiency in hydrogel electrolytes and interfacial fusion for performance enhancement in all-solid-state paper-based self-powered electrochromic devices with low-temperature tolerance†

Abstract

Self-powered electrochromic devices (ECDs) have gained considerable attention for applications such as smart labels, displays and rechargeable batteries, thanks to their dynamic balance between color display and energy storage capabilities. The electrochemical performance of existing ECDs, however, is often constrained by the conductivity of electrolytes, the contact interface between electrodes and electrolytes, and the severe intolerance of ECDs to low temperature environments. In this study, we couple two approaches. Firstly, we harness the Hofmeister effect to modulate the concentration of an ionic compound within the hydrogel electrolyte. This modulation enhances ion solvation and ionic conductivity, thereby facilitating internal ion transport within the self-powered ECD and accelerating the device's response time. Secondly, we illustrate how it is possible to capitalize on the designable properties of the substrate. Paper offers a unique controllable substrate structure, which can be readily modified in terms of surface micro-roughness, which, in turn, can be utilized during the forming of the gravure printed electrode. This novel optimization can improve the final surface morphology of the paper-based electrode, enhancing its surface area properties. This enhancement subsequently facilitates improved integration of the electrode interface with the hydrogel electrolyte, reducing interface impedance and increasing ion transport efficiency within the ECD. Combining this morphological effect with the increased ion solvation in the hydrogel electrolyte enables an improved electrochemical performance and cyclic stability, maintaining stability even at temperatures as low as −40 °C.