In situ-polymerized polyether electrolytes for high-voltage lithium-metal batteries: Failure mechanisms and molecular stabilization strategies

In situ-polymerized polyether electrolytes (IPPEs) combine the wettability of liquid precursors with intimate electrode-electrolyte contact and Li-ion transport pathways, making them promising electrolytes for high-voltage lithium-metal batteries (LMBs). However, their practical application is limited by coupled bulk and interfacial degradation. Oxidation-prone ether-oxygen sites and reactive terminal groups reduce the intrinsic stability of polyether chains, while strong Li + –O coordination can hinder ion migration and alter interfacial reaction pathways. Catalytic cathode surfaces, unstable reactions at lithium metal, and residual monomers or initiators can further accelerate electrolyte decomposition, dendrite growth, and cycling decay. To address these challenges, molecular stabilization strategies have been developed, including cross-linked network construction, local charge homogenization, terminal-group passivation, halogenation or fluorination, cyclic ether monomer redesign, and regulation of the polymerization microenvironment. This review systematically analyzes the chemical origins and coupled evolution of high-voltage failure in IPPEs, and summarizes how these strategies regulate backbone oxidation resistance, Li-ion coordination and transport, interphase chemistry, and full-cell durability. Particular emphasis is placed on the relationships among molecular electronic structure, solvation environment, polymerization behavior, and cathode/anode interphase formation. Finally, future directions are proposed for stable polyether design, precise in situ polymerization, coordinated interface stabilization, and validation under practical conditions.