The increasing demand for portable electronics and electric vehicles has necessitated improved electrochemical energy storage devices, and lithium-based batteries will be a critical component of this growing energy storage market. More energy dense batteries could be made possible by the use of Li metal anodes, though solid electrolytes are likely necessary to inhibit dendrite growth and enable safe battery cycling. Solid polymer electrolytes (SPEs), and microphase separating block copolymer electrolytes (BCEs) in particular, are one interesting set of candidate materials for this application. Developing SPEs that meet the stringent material property requirements for use in a Li battery, however, requires further improvement to their ionic conductivity, among other properties. Greater understanding of the ion transport behavior of these materials is necessary to make these improvements. Developing molecular-level structure-function relationships for nanostructured BCEs has been limited by the inability to precisely control or quantify the ion transport pathways through the material. This remains a challenge due to fundamental limitations of the experimental approach taken to studying these materials that results in hierarchical assembly of randomly ordered grains with tortuous, defect-filled transport pathways. In this dissertation, a different approach consisting of coplanar interdigitated electrodes (IDEs) and polymer electrolyte thin films is developed. In Chapter 3, the microfabrication procedure and a derivation of the cell constant for these devices are presented. In Chapter 4, this theoretical cell constant is validated experimentally, and a robust framework for the use of IDEs for electrochemical impedance spectroscopy (EIS) measurements of thin SPE films is developed. In Chapter 5, thin BCE films are assembled into single-grain structures on top of IDEs in order to probe the intrinsic ion transport behavior of the material. In Chapter 6, thin films of cylinder-forming materials are self-assembled on the IDEs, and complexities related to different wetting-behaviors are discussed. The results from these studies clarify the importance of monomeric mixing and dilution of the ion solvation site network at the BCE domain interface. In the final section of the dissertation, the role of solvation site formation and connectivity is explored for a series of side-chain SPEs synthesized by controlled radical polymerization. In Chapter 7, the role of side-chain length in determining ion solvation and transport behavior is elucidated through a combined experimental and computational study. In contrast to linear polymer electrolytes, the ionic conductivity is poorly predicted by differences in glass transition temperature. Instead, conductivity is determined by the local relaxation rate of specific solvation sites. In Chapter 8, these side-chain materials are copolymerized with a highly polar cyclic carbonate monomer to explore the role of polarity in ion solvation and transport. Surprisingly, lithium ions are solvated exclusively by the low polarity polyether segments, and ionic conductivity was adversely affected by the addition of the high polarity component. These findings are in contrast with analogous small molecule electrolyte systems. In Chapter 9, these results are summarized, and some interesting future research directions are discussed.