Cross-linkable Polyester-Based Solid Polymer Electrolytes with Tailored Molecular Design for High-Performance Solid-Sate Li Metal Batteries

With the increasing demand for high-energy-density and safe lithium-ion batteries (LIBs), solid-state electrolytes (SSEs) have emerged as promising alternatives to conventional liquid electrolytes. Among them, solid polymer electrolytes (SPEs) offer excellent flexibility, low density, and scalable fabrication. However, conventional poly(ethylene oxide)-based SPEs suffer from low room-temperature ionic conductivity, narrow electrochemical stability, and low Li⁺ transference numbers. Polyester-based SPEs have attracted attention because carbonyl groups provide higher oxidative stability and more efficient Li⁺ transport, although their mechanical degradation can still induce Li dendrite growth.
Herein, four polyester-based polymer electrolytes with tailored carbonyl oxygen orientations were synthesized to regulate Li⁺ coordination. UV-induced crosslinking enhanced the mechanical, thermal, and electrochemical stability while maintaining high ionic conductivity. In addition, a terminal –CF₃ group was introduced to promote the formation of a uniform LiF-rich interphase on the Li-metal anode. The crosslinked CF₃-capped poly(n-pentylmaleate) electrolyte exhibited a high Li⁺ transference number (~0.77) and stable Li plating/stripping for 1,000 h at 0.1 mA cm^-2 with less than 5 mV polarization. LFP||Li cells achieved 86.6% capacity retention, demonstrating the effectiveness of molecular design and crosslinking for high-performance solid-state lithium-metal batteries.