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

Abstract 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.