Synthesis and Characterization of Tethered Polymer for Hybrid Electrolytes in Solid Lithium-Metal Batteries

This study investigates a hybrid polymer-ceramic composite electrolyte for solid-state batteries. The polymer is synthesized through the copolymerization of poly(ethylene glycol) methacrylate and poly(methacrylic acid) via the reversible addition–fragmentation chain transfer (RAFT) method followed by postsynthetic functionalization to add phosphonic acid groups, yielding poly(PEGMA-ran-DEPMMA) that can covalently bind to oxide surfaces (Tpoly). The ceramic phase is porous gadolinium-doped cerium oxide (GDC) with a graded porosity made by a phase inversion method. Both monomers in Tpoly interact with anions synergistically for Li-ion conduction. In addition, the binding of phosphonic acid with GDC improves the interfacial stability. A Li symmetric cell with this hybrid electrolyte demonstrated stable performance for over 2000 h at 0.1 mA cm–2 with a critical current density of up to 0.8 mA cm–2. The interfacial resistance of this hybrid electrolyte/Li electrode is reduced by 50% as compared to nontethered PPEGMA. The findings highlight the potential of hybrid polymer-ceramic composites in overcoming interfacial challenges of solid-state lithium-metal battery technology.