Block Copolymer Electrolytes with Excellent Properties in a Wide Temperature Range

Abstract

A series of block copolymers (BCPs) with a polynorbornene backbone containing short poly­(ethylene oxide) (PEO) side chains and rigid side chains were synthesized by tandem ring-opening metathesis polymerization (ROMP). The contents of PEO in the BCPs are regulated by the degrees of polymerization (DPs) of main chains. The crystallization of the PEO side chains is suppressed. Confirmed by small-angle X-ray scattering (SAXS) results, the BCPs doped with lithium salt and ionic liquid self-assemble into lamellar (LAM) or hexagonally packed cylindrical (HEX) nanostructures that remain stable up to 200 °C. The ionic conductivity (σ) values of the complexes with an optimized doping ratio are above the order of 1 × 10–4 S/cm over the temperature range of −25 to 200 °C, and the highest is 6.41 × 10–3 S/cm at 200 °C, reaching the top level for PEO-based polymer electrolytes at high temperatures. In addition, the results of shear rheological experiments indicate that the thermally stable electrolyte membranes can maintain the solid state up to 200 °C. These BCP electrolytes with high σ values and excellent thermal stability in a wide temperature range may be applied in high-temperature lithium-ion batteries.