Electrochromic Battery Displays with Energy Retrieval Functions Using Solution‐Processable Colloidal Vanadium Oxide Nanoparticles

Abstract Electrochromic displays have attracted increased attention owing to their reversible switch of multicolors. However, the external voltage requirement for triggering the color switching makes them far from an optimum energy‐efficient technology. The newly developed electrochromic batteries eliminate the energy consumption for coloration while they can retrieve the consumed energy for bleaching. Such features make the electrochromic battery technology the most promising technology for energy‐efficient electrochromic displays. Here, a scalable method to synthesize colloidal V 3 O 7 nanoparticles is presented, which is compatible with solution‐process techniques for aqueous Zn‐V 3 O 7 electrochromic battery displays. The Zn‐V 3 O 7 electrochromic battery display shows an optical transmittance contrast (21%), rapid self‐coloration time (6.6 s), and switching times (10.4/28.6 s for coloration/bleaching processes). Moreover, the electrochromic battery display shows a compelling energy retrieval function. For a proof of concept, a prototype display is constructed, which possesses an open‐circuit potential (OCP) of 1.38 V. The prototype display can reversibly switch between the multicolors (fully yellow, fully grayish‐blue, and half yellow‐half grayish‐blue images) and partially retrieve the consumed energy. This research presents a facile strategy to synthesize colloidal V 3 O 7 nanoparticles, as well as a novel electrochromic battery display having energy retrieval functions, thus facilitating the development of energy‐efficient electrochromic displays.