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 withM n,total= 11.7-23.9 kg/mol were doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) withr= [Li +]/[EO units] = 0.09. Small-angle X-ray scattering (SAXS) analyses reveal that these samples withf 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 withM 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.
Bibliographical noteFunding Information:
This work was funded by National Science Foundation grants DMR-1307606 and DMR-1708874. Synchrotron SAXS patterns were collected at the 12-ID-B beamline of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The authors thank Frank S. Bates, Grayson L. Jackson, and Shuyi Xie for helpful discussions, and the authors thank Matthew T. Irwin and Robert J. Hickey for providing nSO diblock polymers.
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