Highly-concentrated electrolyte incorporating Li-ion solvation sheath interphase for encapsulation-free organic electrochromic devices

Abstract

Electrolytes play an essential role in boosting the performance of electrochromic devices (ECDs), nevertheless, the detailed impact of highly-concentrated electrolytes (HCEs) on electrochromism remains elusive. In this work, we creatively report an eco-friendly, aqueous HCE based on lithium bis (trifluoromethanesul-phonyl)-imide (TFSILi), and investigate the potential of developed electrolyte for ECD applications through combining experimental and molecular dynamic simulation approaches. The radial distribution function calculations reveal that the primary solvation sheath of Li-ion is greatly alterd by the concentration of electrolyte. The formation of Li-ion solvation sheath containing TFSI− in electrolyte protects the electrochromic (EC) layer from being destroyed by free water. Mean squared displacement shows that the diffusion coefficient of Li-ion in 15 M HCE reaches up to 8.5 × 10−11 m2/s, indicating that high ion mobility enables faster charge transfer and efficient transport of Li-ion promotes interfacial reaction kinetics, which correlates-well with the experimental conductivity results. These findings demonstrate that HCEs can substantially improve the performance of organic ECDs, especially in terms of device stability, optical memory and switching rate. Notably, the solvation sheath nature of the developed HCE enables the development of encapsulation-free devices, which is greatly attractive for the industrialization of EC technology.