Progress and prospect of flexible electrochromic devices based on cellulose

Electrochromic technology is a potential applied science, which is gradually attracting the deep attention of academia and industry. In this paper, the working principle, device structure and material application of electrochromic devices (Electrochromic Devices,ECD) are introduced and summarized. The emerging flexible ECD has the advantages of light weight, flexibility and portability, which is more widely used in smart wear and flexible electronic products. However, there are still some defects to be solved in the production and application of flexible ECD: ① The rigid electrochromic devices which prepared on conventional glass substrates are not flexible enough, the raw materials are scarce and non-renewable; ② The traditional liquid electrolytes are easy to leak, corrode and evaporate, which seriously affect the safety and service life of the devices; ③ The electrochemical stability of the electrochromic layer is poor, affecting the service life of the devices.The applications and advantages of cellulose as flexible substrate, electrolyte and electrochromic layer of ECD are discussed in terms of structure and properties. Cellulose material has excellent optical and mechanical properties, which can avoid the defects such as the insufficient flexibility of conventional glass substrate and the scarcity of raw materials when cellulose is used as the substrate of ECD devices, and the three-dimensional network structure and functional groups on the backbone of cellulose can improve the mechanical properties and electrical conductivity of electrolytes by forming ion bonds and hydrogen bonds. With the reasonable introduction of cellulose into the electrochromic layer, the three-dimensional reticular structure of cellulose can provide a larger specific surface area for redox reaction and alleviate the volume expansion caused by electron/ion intercalation and exfoliation process. It is helpful to improve the electrochemical stability of electrochromic materials and prolong the service life of the devices. Cellulose-based flexible ECD have a broad application prospect in the fields of energy-saving buildings, display equipment and energy storage devices. The introduction of cellulose into flexible electronic devices is of great significance to expand its scope of application and enhance its utilization value, and at the same time promote the development of green and environment-friendly intelligent flexible electronic devices.