# Phase Morphology Dependence of Ionic Conductivity and Oxidative Stability in Fluorinated Ether Solid-State Electrolytes

## TL;DR

This paper shows how adding PEG to fluorinated ether electrolytes improves battery conductivity and stability for safer, high-energy batteries.

## Contribution

A novel approach of blending PEG with PFPE to achieve high ionic conductivity and oxidative stability in solid-state electrolytes.

## Key findings

- Adding PEG to PFPE increases conductivity by 6 orders of magnitude at 60°C.
- Phase separation enhances ion transport in the PEG-rich domain.
- The electrolytes show high-voltage stability beyond 6 V versus Li/Li+.

## Abstract

Solid-state polymer electrolytes can enable the safe
operation
of high energy density lithium metal batteries; unfortunately, they
have low ionic conductivity and poor redox stability at electrode
interfaces. Fluorinated ether polymer electrolytes are a promising
approach because the ether units can solvate and conduct ions, while
the fluorinated moieties can increase oxidative stability. However,
current perfluoropolyether (PFPE) electrolytes exhibit deficient lithium-ion
coordination and ion transport. Here, we incorporate cross-linked
poly(ethylene glycol) (PEG) units within the PFPE matrix and increase
the polymer blend electrolyte conductivity by 6 orders of magnitude
as compared to pure PFPE at 60 °C from 1.55 × 10–11 to 2.26 × 10–5 S/cm. Blending varying ratios
of PEG and PFPE induces microscale phase separation, and we show the
impact of morphology on ion solvation and dynamics in the electrolyte.
Spectroscopy and simulations show weak ion–PFPE interactions,
which promote salt phase segregation into—and ion transport
within—the PEG domain. These polymer electrolytes show promise
for use in high-voltage lithium metal batteries with improved Li|Li
cycling due to enhanced mechanical properties and high-voltage stability
beyond 6 V versus Li/Li+. Our work provides insights into
transport and stability in fluorinated polymer electrolytes for next-generation
batteries.