Phenyl-Reinforced Uniform Chains: Triblock Copolyether Plasticizer Refining the Strength and Conductivity of PEO Electrolyte

Triblock copolymers consisting of poly(ethylene oxide) (PEO) and poly(styrene oxide) (PSO), i.e., PSO-b-PEO-b-PSO (EGES), are synthesized by a one-pot organocatalytic approach and used as plasticizers to refine PEO-based solid polymer electrolytes. The high similarity of C–C–O-type polyether backbones of PEO and PSO moderated microphase separation of EGES and ensured its good compatibility with the PEO matrix. These effects, coupled with the weak coordinative interaction between Li+ ions and oxygen atoms in the PSO segments, enhance Li+ conductivity and lower ion transport activation energy, thus alleviating the “dead zone” issue of conventional PEO–polystyrene block copolymers. With optimal plasticizer composition and blend ratio, a nearly 100-fold increase in ionic conductivity is achieved at 30 °C (3.60 × 10–5 S cm–1). At 50 °C, the conductivity remains substantially higher than that of neat PEO, and an expanded electrochemical stability window of 4.42 V and a higher Li+ transference number of 0.35 are also allowed. XPS characterization confirms the formation of a stable organic/inorganic bilayer solid electrolyte interphase on the Li metal surface, enabling excellent interfacial stability. Puncture resistance tests demonstrate improved plasticity of the electrolytes, which is considered effective in preventing lithium dendrite penetration. This study shows that the rationally designable and easily accessible copolyether plasticizers may open up a wide avenue for advancing all-solid-state lithium metal batteries.