Structure and Evolution of Quasi-Solid-State Hybrid Electrolytes Formed Inside Electrochemical Cells

Solid-state electrolytes (SSEs) formed inside an electrochemical cell by polymerization of a liquid precursor provide a promising strategy for overcoming problems with electrolyte wetting in solid-state batteries. Hybrid solid-state polymer electrolytes (HSPEs) created by in situ polymerization of a conventional liquid precursor containing electrochemically inert nanostructures are of particular interest because they offer a mechanism for selectively reinforcing or adding new functionalities to the electrolyte—removing the need for high degrees of polymerization. The synthesis, structure, chemical kinetics, ion-transport properties and electrochemical characteristics of HSPEs created by Al(OTf)₃-initiated polymerization of 1,3-dioxolane (DOL) containing hairy, nano-sized SiO₂ particles are reported. Small-angle X-ray scattering reveals the particles are well-dispersed in liquid DOL. Strong interaction between poly(ethylene glycol) molecules tethered to the SiO₂ particles and poly(DOL) lead to co-crystallization—anchoring the nanoparticles in their host It also enables polymerization–depolymerization processes in DOL to be studied and controlled. The utility of the in-situ-formed HSPE, is demonstrated first in Li|HSPE|Cu half cells, which manifest Coulombic efficiencies (CE) values approaching 99%. HSPEs are also demonstrated in solid-state lithium–sulfur–polyacrylonitrile (SPAN) composite full-cell batteries. The in-situ-formed Li|HSPE|SPAN cells show good cycling stability and thus provide a promising path toward all-solid-state batteries.