Role of cyclic carbonates in enhancing UV-crosslinked PEO-PEC electrolytes for room-temperature lithium metal batteries

Future Li-based batteries require electrolytes with high safety, thermal stability, and performance, yet poly(ethylene oxide)-based solid polymer electrolytes (SPEs) remain limited by crystallinity-induced low ionic conductivity and stability at room temperature (RT). In this study, a UV-crosslinked poly(ethylene oxide)-poly(ethylene carbonate) (PEO-PEC) salt-in-polymer matrix is developed through dry melt compounding by a mini twin-screw extruder, followed by hot-pressing and UV-induced photopolymerization(crosslinking). The solvent-free manufacturing is designed to mitigate crystallinity and improve mechanical robustness. Resulting SPEs are further modified with cyclic carbonate plasticizers, namely ethylene carbonate (EC), propylene carbonate (PC), and 1,2-butylene carbonate (BC), to enhance ionic mobility and electrochemical stability, thereby addressing the challenge of fabricating next-generation lithium metal batteries (LMBs) with sufficient ion transport at RT. The influence of these additives, individually and in combination, is investigated through a comprehensive set of electrochemical, thermal, and mechanical characterizations. BC-containing SPEs exhibit reduced glass transition temperatures and stable compatibility with lithium metal for over 2300 h at a capacity of 0.2 mAh cm−2. In addition, laboratory-scale solid-state Li metal cells with LFP show remarkable performance, delivering almost full practical specific capacity even at RT, despite the presence of immobilized carbonate plasticizers within the crosslinked polymer matrix. This work presents an effective strategy to tailor SPEs for ambient temperature operation through rational additive design, offering insights into the structure-property relationships critical for practical LMB development.