Divalent ion identity tunes nanoscale ordering in single-ion conducting polymer blends

Controlling the nanostructure of single-ion-conducting polymer blends is crucial for designing advanced solid-state battery electrolytes. Though electrostatic interactions in charged polymer blends can theoretically stabilize ordered nanostructures, direct experimental evidence remains limited. Here, we investigate the effects of divalent cation identity on the nanoscale morphology of single-ion conducting polymer blends composed of poly(ethylene oxide) (PEO) and magnesiated or calciated ion-containing polymers, poly[3-(methylacryloxy)propylsulfonyl-1-(trifluoromethanesulfonylimide)] (P(Mg(MTFSI)₂) or P(Ca(MTFSI)₂). Differential scanning calorimetry as well as small- and wide-angle X-ray scattering measurements reveal that Mg²⁺ and Ca²⁺ induce distinct structural behavior. The magnesiated blends exhibit well-defined lamellar nanostructures with tunable domain spacing and long-range order and these nanostructures become more pronounced at higher charged polymer content. In contrast, calcium, with weaker interaction strength, is more readily decoupled from the polymer backbone by PEO, producing more homogeneous blends. In contrast, the calciated blends display homogeneous, amorphous morphologies characterized by a single glass-transition temperature and featureless SAXS data.