Li NMR Splitting*

Mixtures of block copolymers and salts have been studied for use as safe electrolytes for batteries with energy-dense lithium metal anodes. Locating the order-to-disorder transition (ODT) in these systems is important, because microscopic morphology has a profound impact on bulk properties including ionic conductivity and mechanical rigidity. In this study, the ordered morphologies in a series of mixtures of polystyrene-b-poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are shown to be aligned due to exposure to the magnetic field in an NMR instrument, which is confirmed using small-angle X-ray scattering (SAXS). This alignment results in quadrupolar triplet peak splitting in ⁷Li NMR, which disappears above the T_ODT. The T_ODT identified using this novel NMR method is consistent with that determined using SAXS.