Sang-Young Lee

Presentation Beyond PEO: Redesigning Polymer Electrolytes for Scalable Solid-State Batteries

All-solid-state batteries (ASSBs) have long been recognized as a promising route toward high-energy-density and safer electrochemical energy storage. Among the electrolyte platforms explored to date, polymer electrolytes have attracted enduring interest owing to their synthetic versatility, favorable interfacial contact, and compatibility with scalable cell manufacturing. Yet their practical development has remained largely constrained by polyethylene oxide (PEO) chemistry, whose ion-transport characteristics impose fundamental limitations. In particular, insufficient salt dissociation, crystallinity-induced chain immobilization, segmental-motion-dependent Li⁺ transport, and a low Li⁺ transference number collectively define a performance ceiling that cannot be overcome through incremental modification alone. In this presentation, we revisit the limitations of PEO-based electrolytes from a fundamental perspective and introduce a “Beyond PEO” framework for the design of next-generation polymer electrolytes for solid-state batteries. Rather than treating polymer electrolytes as passive ion-solvating matrices, this framework reconceives them as engineered ion-transport architectures in which entropy, supramolecular ordering, and dynamic bonding topology are deliberately controlled to regulate ionic conduction, mechanical resilience, and electrochemical integration. Three distinct PEO-free materials chemistries exemplify this design philosophy. First, conflicting-entropy-driven zwitterionic polymer electrolytes harness entropy modulation to promote salt dissociation and establish directionally organized Li⁺-transport pathways that are decoupled from conventional segmental relaxation, enabling high-energy pouch-type ASSBs under ambient conditions. Second, ionic dimer elastomers introduce dynamic ionic crosslinking motifs that reconcile ion-conductive functionality with mechanical robustness, thereby addressing a long-standing trade-off in polymer electrolyte design. Third, monomer-in-salt polymer catholytes extend the same conceptual principles to electrode manufacturing by enabling solvent-free, compositionally homogeneous, and ionically percolated catholyte frameworks through in situ polymerization, thereby offering a low-cost, manufacturing-compatible route to dry-processed Ah-class pouch ASSBs. Although differing in molecular construction, these systems share a common principle: they decouple Li⁺ transport from the classical PEO paradigm, replace stochastic ion migration with programmed ionic pathways, and incorporate manufacturability as an intrinsic design parameter. Importantly, this approach offers strong compatibility with established lithium-ion battery fabrication processes and enables stable operation under practically relevant low-stack-pressure conditions. These studies establish “Beyond PEO” not as an alternative polymer-electrolyte concept, but as a materials-chemistry foundation for positioning polymer-based ASSBs as a scientifically robust and technologically scalable platform within a solid-state battery landscape that has been predominantly shaped by inorganic electrolytes. 1. S. Y. Lee et al. Advanced Materials e08670 (2025). 2. S. Y. Lee et al. Nature Communications 17, 330 (2026). 3. S. Y. Lee et al. Manuscript submitted.