Low Melting Non-corrosive Asymmetric Thioether-TFSI Li Salts for Solid Polymer Electrolytes

Abstract

High crystallinity in poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) limits ionic transport, electrochemical stability, and the operating temperature range of Li-metal batteries. Herein, two asymmetric, low-melting thioether-TFSI lithium salts were synthesized via a modular thiol–ene strategy and incorporated into PEO-based SPEs. Their pronounced plasticizing effect efficiently suppresses PEO crystallinity while preserving ionic conductivity, Li⁺ transference, and electrochemical stability. In addition, both SPEs mitigate aluminum current-collector corrosion through the formation of a stable passivation layer, addressing a key limitation of conventional LiTFSI systems. As a result, the SPEs show improved compatibility with Li metal and enable stable cycling of Li∥LiFePO₄ cells with high capacity retention and coulombic efficiency. The tunable molecular design and reduced fluorine content further support scalability and regulatory compliance, highlighting these thioether-TFSI salts as promising alternatives for advanced solid-state lithium batteries.