Ionic Conductivities of Broad Dispersity Lithium Salt-Doped Polystyrene/Poly(ethylene oxide) Triblock Polymers

We describe the impact of center polyether segment dispersity (Đ = M_w/M_n ∼ 1.45) on the ionic conductivities of lithium salt-doped polystyrene-block-poly­(oligo­(ethylene oxide) carbonate)-block-polystyrene (bSOS) electrolytes with narrow dispersity end blocks. Three bSOS samples with M_n,total = 11.7–23.9 kg/mol were doped with lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) with r = [Li⁺]/[EO units] = 0.09. Small-angle X-ray scattering (SAXS) analyses reveal that these samples with f_O/salt = 0.55–0.60 self-assemble into lamellar morphologies, with ionic conductivities as high as σ = 0.19 mS/cm at 90 °C measured by electrochemical impedance spectroscopy (EIS). The ionic conductivities of LiTFSI-doped bSOS are comparable to those of salt-doped, narrow dispersity nSOS triblocks with M_n ≳ 20 kg/mol, and they are 2–3 times greater than those of the narrow dispersity nSO diblock control samples. These findings are rationalized in terms of decreases in the lamellar grain sizes induced by molecular architecture and segment dispersity, which enhance intergrain connectivity and ion transport.