Ion-Transport Design for High-Performance Na+-Based Electrochromics.

Sodium ion (Na+)-based electrochemical systems have been extensively investigated in batteries and supercapacitors and also can be quality candidates for electrochromic (EC) devices. However, poor diffusion kinetics and severe EC performance degradation occur during the intercalation/deintercalation processes because the ionic radii of Na+ are larger than those of conventional intercalation ions. Here, through intentional design of ion-transport channels in metal-organic frameworks (MOFs), Na+ serves as an efficient intercalation ion for incorporation into a nanostructured electrode with a high diffusion coefficient of approximately 10-8 cm2 s-1. As a result, the well-designed MOF-based EC device demonstrates desirable Na+ EC performance, including fast switching speed, multicolor switching, and high stability. A smart "quick response code" display is fabricated using a mask-free laser writing method for application in the "Internet of Things". In addition, the concept of ion transport pathway design can be widely adopted for fabricating high-performance ion intercalation materials and devices for consumer electronics.