Tapered block polymer electrolytes for lithium-ion batteries: enhancement of ion transport through the tuning of intra-domain structure*

Tapered block polymers (TBPs) contain modified (e.g., gradient) monomer segment composition profiles at the chemical junction between two homogeneous blocks. In this work, we studied how the tuning of monomer segment and ion distributions (i.e., intra-domain structure) imparted enhanced ion transport in nanostructured polystyrene‑block‑poly(oligo-oxyethylene methacrylate) (PS-b-POEM) TBP electrolytes through a combination of X-ray reflectometry experiments and coarse-grained molecular dynamics simulations that included strong ion solvation effects. This combined experimental-computational approach revealed that in normal‑tapered electrolytes, the significant S/OEM covalent bonding and global stretching of chains across a domain (rather than the back-and-forth folding of chains across an interface) reduced local stretching throughout the domain and reduced the confinement of OEM/ions. Both of these effects improved ion transport. However, these factors were competing constraints in non- and inverse‑tapered electrolytes. The above-mentioned results provide important design parameters and synthesis/formulation avenues toward next‑generation nanostructured electrolytes.