High Ionic Conductivity of Composite Solid Polymer Electrolyte via In Situ Synthesis of Monodispersed SiO₂ Nanospheres in Poly(ethylene oxide)

TLDR

Solid polymer electrolytes with high ionic conductivity are sought for next‑generation lithium batteries, and composite polymer electrolytes with ceramic fillers are promising, but polymer crystallinity, filler agglomeration, and weak polymer–ceramic interactions hinder further conductivity gains. The study introduces an in situ synthesis of ceramic filler particles within the polymer electrolyte to overcome limitations of conventional blending. In situ hydrolysis generates 12‑nm monodispersed SiO₂ nanospheres that form strong chemical and mechanical bonds with PEO chains, suppressing PEO crystallization and enhancing segmental motion for ionic conduction. The resulting composite exhibits a LiClO₄ dissociation degree that improves ionic conductivity to 1.2 × 10⁻³ S cm⁻¹ at 60 °C (4.4 × 10⁻⁵ S cm⁻¹ at 30 °C), an electrochemical stability window up to 5.5 V, and enables all‑solid‑state lithium batteries with excellent rate capability and cycling performance.

Abstract

High ionic conductivity solid polymer electrolyte (SPE) has long been desired for the next generation high energy and safe rechargeable lithium batteries. Among all of the SPEs, composite polymer electrolyte (CPE) with ceramic fillers has garnered great interest due to the enhancement of ionic conductivity. However, the high degree of polymer crystallinity, agglomeration of ceramic fillers, and weak polymer-ceramic interaction limit the further improvement of ionic conductivity. Different from the existing methods of blending preformed ceramic particles with polymers, here we introduce an in situ synthesis of ceramic filler particles in polymer electrolyte. Much stronger chemical/mechanical interactions between monodispersed 12 nm diameter SiO2 nanospheres and poly(ethylene oxide) (PEO) chains were produced by in situ hydrolysis, which significantly suppresses the crystallization of PEO and thus facilitates polymer segmental motion for ionic conduction. In addition, an improved degree of LiClO4 dissociation can also be achieved. All of these lead to good ionic conductivity (1.2 × 10(-3) S cm(-1) at 60 °C, 4.4 × 10(-5) S cm(-1) at 30 °C). At the same time, largely extended electrochemical stability window up to 5.5 V can be observed. We further demonstrated all-solid-state lithium batteries showing excellent rate capability as well as good cycling performance.