Deep eutectic ion-conductive hybrids produced by combining hydroxyl-functionalized silsesquioxane and mono-/difunctional hydrogen bond acceptors

Abstract

The use of ion-conductive organic–inorganic hybrids with high ionic conductivity, suitable flexibility/viscosity, and good thermal and mechanical properties is a promising approach for the development of next-generation, safer solid-state electrolytes. In this study, a series of new deep eutectic silsesquioxane (SQ) hybrids (DESQs) were developed by simply mixing hydroxyl-functionalized SQ acting as a polyol-type hydrogen bond donor (HBD) with imidazolium- and ammonium-based organic salts acting as hydrogen bond acceptors (HBAs) in the presence of a small amount of difunctional HBAs without the use of volatile organic solvents. The use of cross-linkable HBAs results in improved thermal stability and tunable flexibility (glass transition temperature and viscosity). The combination of hydroxyl-functionalized SQs and imidazolium salt-based mono-/difunctional HBAs afforded hybrids with hydrogen bond networks, showing a suitable balance between thermal properties and high ionic conductivity (4.17 × 10⁻⁴ S cm⁻¹ at 25 °C), while maintaining reasonable viscosity (5.62 × 10⁶ mPa S at 25 °C). The ionic conductivity can be improved by adding a lithium salt, allowing for an efficient approach for obtaining safer, greener, and cost-effective electrolytes with good ionic conductivity.