Role of Defects in Ion Transport in Block Copolymer Electrolytes

Abstract

Ion conducting block copolymers can overcome traditional limitations of homopolymer electrolytes by phase separating into nanoarchitectures that can be simultaneously optimized for two or more orthogonal material properties such as high ionic conductivity and mechanical stability. A key challenge in understanding the ion transport properties of these materials is the difficulty of extracting structure−function relationships without having complete knowledge of all nanoscale transport pathways in bulk samples. Here we demonstrate a method for deriving structure-transport relationships for ion conducting block copolymers using thin films and interdigitated electrodes. Well-defined and directly imaged structure in films of poly(styrene)-block-poly(2-vinylpyridine) is controlled using techniques of directed self-assembly then the poly(2-vinylpyridine) is selectively converted into an ion conductor. The ion conductivity is found to be directly proportional to the total number of connected paths between electrodes and the path length. A single defect such as a dislocation anywhere in the path of an ion conducting route disconnects and precludes that pathway from contributing to the conductivity and results in an increase in the dielectric parameter of the film. When all the ion conduction pathways are blocked between electrodes, the conductivity is negligible, 4 orders of magnitude lower compared to a completely connected morphology and the dielectric parameter increases by a factor of 50. These results have profound implications for the interpretation, design, and processing of block copolymer electrolytes for applications as ion conducting membranes.

Understanding the ionic activity and conductivity value differences between random copolymer electrolytes and block copolymer electrolytes of the same chemistry

“…To corroborate the MD simulation ndings, ionic conductivity measurements were performed on interdigitated electrodes (IDEs) as described in our previous works. 12,31 These measurements were performed under 100% relative humidity (RH) at 27 C. The conductivity values obtained under the specied conditions for the RCE and the PSbP2VP 40-44k BCE are provided in Fig. 4.…”

“…These membranes oen physically separate two liquid compartments in electrodialysis 3 and electrodeionization 9,10 or electrodes when used in membrane capacitive deionization. 4 A subset of polymeric materials that has received signicant attention includes block copolymer electrolytes (BCEs) 11,12 as their percolated pathways of ionic domains ameliorate ionic conductivity and the non-ionic domains foster mechanical properties and curtail excess swelling. Although several studies 1,11,13,14 exist comparing the ionic conductivity of random/ amorphous polymer electrolytes (RCEs) and microphase separated BCEs (as well as aligned and anti-aligned ionic domains), 12 there is a lack of studies dedicated to the ionic activity differences within these materials with systematically varied macromolecular architecturesespecially when the repeat unit chemistries are the same.…”

Structure Code for Advanced Polymer Electrolyte in Lithium‐Ion Batteries

“…[ 83 ] Recently, Nealey's group developed a method for seeking the structure–transport relationship in poly(styrene)‐ b ‐poly(2‐vinylpyridine) (PS‐ b ‐P2VP) via thin films and interdigitated electrode, as shown in Figure 2d, and ultimately proved that even a single defect can preclude the ionic conductive pathway, thus leading to a decreased ion conductivity. [ 85 ] Therefore, this study on the relationship of phase behavior of BCP and its electrical properties could contribute to the design of novel highly‐conductive materials.…”

Electrolysis on a Chip with Tunable Thin Film Nanostructured PGM Electrocatalysts Generated from Self‐Assembled Block Copolymer Templates

“…Directed self-assembly of block copolymers (BCPs) is a bottom-up nanomanufacturing platform that realizes dense, periodic nanoscale structures with simple architectures and long-range order. [11][12][13] Such nanostructures can be systematically tuned to obtain various morphologies and periodic feature sizes (3-50 nm). [11,14,15] For instance, varying the volume fraction (f) of one polymer block in relation to its other block for A-B canonical diblocks and A-B-A triblocks can systematically generate lamellar, gyroid, cylindrical, and spherical morphologies.…”