Dependence of Morphology, Shear Modulus, and Conductivity on the Composition of Lithiated and Magnesiated Single-Ion-Conducting Block Copolymer Electrolytes

Single-ion-conducting block copolymers are of considerable interest as electrolytes for battery systems, as they eliminate overpotentials due to concentration gradients. In this study, we characterize a library of poly(ethylene oxide) (PEO)-based diblock copolymers where the second block is poly(styrene-4-sulfonyltrifluoromethylsulfonyl)imide with either cation: univalent lithium or divalent magnesium counterions (PEO–PSLiTFSI or PEO–P[(STFSI)2Mg]). The PEO chain length is held fixed in this study. Polymers were synthesized in matched pairs that were identical in all aspects except for the identity of the counterion. Using rheology, SAXS, DSC, and AC impedance spectroscopy, we show that the dependence of morphology, modulus, and conductivity on composition in these charged copolymer systems is fundamentally different from uncharged block copolymers. At a given frequency and temperature, the shear moduli of the magnesiated copolymer systems were approximately 3–4 orders of magnitude higher than those of th...