Synthesis and Characterization of Organic/Inorganic Hybrid Ionogel Electrolytes Containing Crosslinkable Polysilsesquioxanes and Ionic Liquids for Lithium Battery Applications

Abstract

This study presents synthesis and characterization of organic/inorganic hybrid ionogel electrolytes containing cross-linkable silsesquioxanes and ionic liquids for lithium battery applications. Firstly, the synthesis of polysilsesquioxanes via a facile, base-catalysed system was used to obtain fully condensed, high molecular weight, ladder-like structured polysilsesquioxanes (LPMASQ) containing over one hundred methacryl moieties in a macromolecule. The fully condensed ladder-like structured LPMASQ provides imperceptible amounts of uncondensed silanol groups that only exist at the chain ends of the polymers. Due to the fully condensed structure, the LPMASQ provided good thermal and electrochemical stability and strong acid-resistance, which is an indispensable requirement for the ionogel electrolyte application. In addition, an abundance of the reactive methacryl pendant groups enhances the possibility that pendant groups meet each other and react to form covalent bonds. As a result, due to the unique structural feature, the fully condensed LPMASQ revealed the good efficiency for the inter-chain crosslinking reaction and achieved very fast gelation. A miniscule 2 wt % of LPMASQ was able to fully solidify the ionic liquid electrolyte solution to yield homogenous, pliant gels with high ionic conductivity and thermal stability. Lithium battery cell test performed with these hybrid gel polymer electrolytes exhibited good Coulombic efficiency and cycling performance. Secondly, a new series of inorganic-organic hybrid ionogel electrolytes consisting of an ionic liquid and synthesized ladder-like structured PEO-functionalized polysilsesquioxane with various PEO-copolymer compositions. By introducing the polyethylene oxide (PEO) groups at the molecular level to the inorganic polysilsesquioxane backbone and a thorough spectroscopic investigation into the ion conduction behavior of the hybrid ionogels as a function of PEO-copolymer composition, we were able to demonstrate how the PEO groups functioned to improve not only ionic conductivity, but their effects on optimal lithium ion battery performance at identical crosslinker concentration. In addition, we demonstrated that these hybrid ionogels revealed excellent thermal, electrochemical, and mechanical stability for improved safety in lithium ion battery cells. Thirdly, a new methodology for fabrication of inorganic–organic hybrid ionogels and scaffolds was developed through facile crosslinking and solution extraction of a newly developed ionic polyhedral oligomeric silsesquioxane with inorganic core. Through design of various cationic tertiary amines as well of crosslinkable functional groups on each arm of the inorganic core, we were able to fabricate high performance ionogels with excellent electrochemical stability. The well-defined, inter-connected, nano-sized pores and the unique ability to increase lithium transference led to exceptional lithium ion battery performance. Moreover, through solvent extraction of the liquid components, hybrid scaffolds with well-defined interconnected mesopores were utilized as heterogeneous catalysts for the CO2-catalyzed cycloaddition of epoxides. Excellent catalytic performances, as well as highly efficient recyclability were observed when compared to other previous literature materials. Finally, a novel ionic mixture of an imidazolium-based room temperature Ionic liquid containing ethylene oxide functionalized phosphite anion and a lithium salt that self-assembles into a smectic-ordered Ionic liquid crystal. The two key features in this study are the unique origin of the smectic order of the ionic mixtures and the facilitated ion transport behavior in the smectic ordered ionic liquid crystal. In fact, the ionic liquid crystals are self-assembled through Coulombic interactions between ion species, not through the hydrophilic-phobic interactions between charged ion heads and hydrophobic long alkyl pendants or the steric interaction between mesogenic moieties. Furthermore, the smectic order in the ionic crystal ionogel facilitates exceptional and remarkable ionic transport. Large ionic conductivity, viscoelastic robustness, and additional electrochemical stability of the Ionic liquid crystal ionogels provide promising opportunities for future electrochemical applications.