Functionalized methyl cellulose/LiClO4 composite as an environmentally friendly quasi-solid polymer electrolyte for solid-state electrochromic devices and cellulose-based supercapacitors

Electrochemical devices, including energy storages and modulators, are expected to play key roles in creating a sustainable future. However, to achieve the technological break-through in electrochemical technologies, the development of solid electrolytes applicable in various electrochemical devices seem necessary. In this study, an environmentally friendly fluorine-free quasi-solid polymer electrolyte derived from a functionalized cellulose composited with LiClO4 is synthesized. The synthesized quasi-solid polymer electrolyte, LiClO4–sulfonated methyl cellulose incorporating lithium ion (LiSMC), exhibits a high conductivity exceeding 1 mS/cm with negligible electron leakage. The LiClO4–LiSMC electrolyte also exhibits high optical transparency and mechanical flexibility, thus it can be applied in various solid-state electrochemical systems including electrochromic devices and energy storages. The applicability of the LiClO4-LiSMC electrolyte in quasi-solid-state electrochromic devices and cellulose-based supercapacitor is demonstrated, from which reduction of the operating voltage and enhancement in performances compared with the similar devices with conventional polymer electrolytes are demonstrated. The cellulose-based supercapacitor demonstrates an excellent stability against mechanical bending and charge–discharge cycling (up to 30,000 cycles) as well. Considering the natural abundance and low environmental impacts of cellulose and its derivatives, this work may open a path to the truly sustainable future through the development of an environmentally friendly material for environmentally friendly applications.