Star-Shaped Polymer Electrolyte with Microphase Separation Structure for All-Solid-State Lithium Batteries

A star-shaped copolymer, poly(styrene)-block-poly[poly(ethylene glycol) methyl ethyl methacrylate (PS-block-PPEGMA 2 ) 8 , was synthesized by the combination of living anionic polymerization of styrene and ruthenium-catalyzed living radical polymerization of poly(ethylene glycol) methyl ether methacrylate. The prepared star-shaped copolymer was characterized to evaluate its use as a solid polymer electrolyte (SPE) in lithium-ion batteries. The star polymer comprised a hard, condensed poly(styrene) part at the center, which enhanced the mechanical properties of the solid-state polymer, and a soft, mobile poly[poly(ethylene glycol) methyl ethyl methacrylate] (PPEGMA) outer part that was responsible for the high ionic conductivity of the SPE. The design of this star polymer resulted in a well-ordered spherical microphase separation structure, in which the individual star polymers were systematically ordered to form the PPEGMA continuous phase distinctly observed in transmission electron microscopy and atomic force microscopy images. The SPE containing the lithium bis(pentafluoroethanesulfonyl) imide salt exhibited high ionic conductivities due to the unique morphology of the polymer; the ionic conductivity of this salt was 10 ―4 S cm ―1 at 30°C and 10 ―5 S cm ―1 at 5°C at [Li]/[EO] = 0.03.