Ion Conductivity–Shear Modulus Relationship of Single-Ion Solid Polymer Electrolytes Composed of Polyanionic Miktoarm Star Copolymers

Single-ion electrolytes are of considerable interest as electrolytes for battery systems, as they hold the key for the realization of safe, long-lasting, high-energy batteries. Here, we study the relationship between the ion conductivity and mechanical modulus of single-ion-conducting polyanion miktoarm star copolymers composed of poly(styrene-4-sulfonyltrifluoromethylsulfonyl) imide lithium (PSTFSILi) arms that are a complement to longer ion-conducting poly(ethylene oxide) (PEO) arms, (PSTFSILi)n(PEO)n, where n ≈ 22, attached to a poly(divinylbenzene) (PDVB) cross-linked core. The degree of polymerization of the PEO arms was kept fixed at 105, while that of PSTFSILi was systematically varied from 5 to 18 approximately, resulting in molar ratios, r = [Li+]/[EO], from 0.048 to 0.171, respectively. We show that, due to the fact that these macromolecular systems may be envisioned as core/shell nanoparticles (with the core region composed of PSTFSILi and PEO segments while the shell is composed of the longer PEO arms), their ion conductivity may be simply rationalized in terms of their differences in volume fractions of PSTFSI and PEO and corresponding changes in segmental dynamics due to the degree and strength of the Li+/EO complexation. Notably, due to the macromolecular architecture, the rheological measurements reveal a solid-like behavior of the single-ion electrolytes with a shear modulus G′ ≈ 1 GPa for the (PSTFSILi)n(PEO)n with the largest volume fraction of PSTFSILi (0.42). Our data reveal that these systems possess a significantly better trade-off between mechanical response and ion conductivity compared to the linear polyanionic block copolymer analogues. Our macromolecular design approach offers a tremendous potential for the design of high-performance single-ion solid polymer electrolytes.